111111111111111111111111111111111111111111111141114111114141111111 - [ERAS 3 1293 104539 Michigan 962-3? ”IL University ' mwfi‘“ v.31». A This is to certify that the thesis entitled I. INVESTIGATIONS INTO THE CAUSES OF BIEXPONENTIAL PRESSURE DECAYS FOLLOWING THE INTERRUPTION OF GAS FLOW INTO A COLLATERALLY VENTILATING LUNG SEGMENT II. INTERACTION OF ALVEOLAR 1 CARBON DIOXIDE LEVELS AND THE VAGUS NERVE ON COLLATERAL VENTILATION IN DOG LUNGS presented by Lynne E. Olson has been accepted towards fulfillment of the requirements for Ph .D . degree in PhYSIOIOE‘I /\. I , f 4 WM Major professor Date May 20, 1981 0-7639 . ll.‘ ‘4“ $&;n \\\‘ L 4 V ‘4“ «3.1.1!!! 4 v I!” - OVERDUE FINES: 25¢ per du per item RETURNING LIQRARY MATERIALS: Place in book return to move rge from circulation records - ‘ . ‘i -‘1.~"..nful 1‘ ' 7' ‘ . . :1: 1L ' 1;. 3. K 7-“ ‘ ‘ - -.—‘7~!‘:: ‘ - I ' ' '1 I}. I. . .- ‘ ' ~ "5 ‘ « 'ZE‘qu-“t - ‘Hzcm 34m Suita- :.- in partial (u: Hoard“ ~ "a. 41‘5““..4, for him {sfr ~~ .‘ m "k" 53‘. f: --::4 31.9.“: 1 3 . sis ‘il'.’:44_,~ ‘ I A‘u- r. n'. .’ ‘L‘S'. ‘ f em)" we'— 0 v. i"4-r V e I. INVESTIGATIONS INTO THE CAUSES OF BIEXPONENTIAL PRESSURE DECAYS FOLLOWING THE INTERRUPTION OF GAS FLOW INTO A COLLATERALLY VENTILATING LUNG SEGMENT. II. INTERACTION 0F ALVEOLAR CARBON DIOXIDE LEVELS AND THE VAGUS NERVE ON COLLATERAL VENTILATION IN DOG LUNGS By Lynne E. Olson A DISSERTATION Submitted to ‘ Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Physiology 1981 1:! 7L” . ..' .4’L154Fr4 44 44 ’5 @9375. o 5 ABSTRACT I. INVESTIGATIONS INTO THE CAUSES OF BIEXPONENTIAL PRESSURE DECAYS FOLLOWING THE INTERRUPTION OF GAS FLOW INTO A COLLATERALLY VENTILATING LUNG SEGMENT. II. INTERACTION 0F ALVEOLAR CARBON DIOXIDE LEVELS AND THE VAGUS NERVE ON COLLATERAL VENTILATION IN DOG LUNGS By Lynne E. Olson Steady state resistance (Rss) of airways in a collaterally ventilating lung segment was studied using a double—lumen catheter wedged in a subsegmental bronchus. Gas flow (V) entered the segment of lung distal to the catheter through the outer lumen and left through collateral pathways. Steady state resistance was calculated as: Rss = (PS-Pa°)/V where PS is pressure at the catheter tip and Pao is tracheal pressure. When flow was discontinued. Ps-Pao decayed to zero as gas flowed from the segment into the remainder of the lung. Pressure decays following flow interruption were biexponential. I. By measuring RSS and recording pressure decays using He, N2. or SF 6 dogs. this study confirmed that flow through the segment was not at three transpulmonary pressures (Ftp) in intact, anesthetized laminar. RSS increased as transpulmonary pressure decreased or as gas density increased. Both the rapid portion and the slower portion of the pressure decays were prolonged when Ptp decreased or gas density increased. w v—vv—vvw Lynne E. Olson Collateral pathways were artificially created in a segment of excised calf lung distal to a wedged catheter by inserting needles into the segment. This model was used to determine the shape of pressure decays after flow interruption when "collateral airway resistance" was decreased by inserting additional subpleural needles. Increasing the number of subpleural needles shortened the duration of both phases of the pressure decays suggesting that the biphasic pressure decays were not due to two anatomically distinct compartments, one being peripheral airways between the catheter and collateral pathways the other being lung parenchyma and collateral pathways. II. The wedged catheter technique was used to determine if vagal stimulation and segment alveolar CO2 tensions interact to affect the efficiency of collateral ventilation in anesthetized, paralyzed, intact dogs artificially ventilated with room air. RSS and the time for 90% pressure equilibration (T90) were determined in dogs with the vagi intact, after sectioning the cervical vagus nerve on the same side as the catheter was wedged (ipsilateral-IL). and during electrical stimulation of the ipsilateral vagus nerve when 1001 02 01 C02. 95% O2 5% 002, or 881 02 121 CO2 was flowing into the segment. During ipsilateral vagal stimulation in 9 dogs which did not receive the beta adrenergic antagonist propranolol, Rss and T90 were least when 51 C02 was flowing into the segment. During ipsilateral vagal stimulation in 9 dogs pretreated with propranolol, Rss and T90 decreased as 1C02 was increased from O to 5 to 12%. In both groups. ipsilateral vagal sectioning had no effect, and R33 and T90 did not change when 1C02 was changed with the vagi intact or after ipsilateral vagal sectioning. f"). o——. Lynne E. Olson Ripsilateral vagal stimulation was greater after propranolol. Jigs less suggesting that propranolol decreased segment «“. None of the three levels of 002 tested prevented increases 7 ,5 L )- fl; "1 4 ~44 , iv -’-"_ q u “it" a: i, A .5 .:_ H . q, ”R; ..\_'_.1 .- .1: .. 4-1.. I.-r ACKNOWLEDGMENTS The successful completion of the Ph.D. reaffirms my belief that the ‘;Ehest way to learn is to observe the "pros". The "pros" in this case 0 linere my Guidance Committee. Drs. N.E. Robinson. R. Roth. J.B. Scott, . m 4 fellow graduate students. Bill Jackson, Sam Rhodes, and Paul Sorenson. Very special thanks to Dr. Ed Robinson for being an outstanding t .hizardry of Paul Sorenson. I acknowledge the assistance of Dr. Charles Cress in the TABLE OF CONTENTS LIST OF TABLES ..... 4........ ..... . ...... .... ........ .......... v LIST OF FIGURES........................ ............ ... ...... . Vi LIST OF ABBREVIATIONS................ ..... ................... viii INTRODUCTION.......................... ....... . .............. . 1 LITERATURE REVIEW............................................ 4 Anatomy............. ..... ................................ 5 Mechanical Properties of Lungs.... ...... ................. 7 Compliance.... ...... . ...... .... ....... .............. 8 Resistance. .......... ....... ........... ...... ....... 8 Inertance...... ............. .................. 9 Methods of Measuring Lung Mechanical Properties.......... 9 Pulmonary Innervation.................................... 1H Collateral Ventilation............. . ................. 19 Methods of Measuring Collateral Ventilation. ........ 20 Factors Affecting Collateral Ventilation. ........... 23 Pathways for Collateral Ventilation.......... ..... 28 What does the Wedged Catheter Technique Really Measure?..... ........... ........................ 31 Purpose of this Dissertation. ............................ 36 MATERIALS AND METHODS AND RESULTS ...... ..................... ”3 Protocol 1............................................... ”3 Purpose................. ..... ....................... N3 Methods............................................. M3 Protocol 2............................................... 52 Data Analysis............................................ 53 General............................................. 53 Protocols 1 and 2................................... 53 Results: Protocols 1 and 2.............................. 5” Protocol 3............................................... 60 Purpose............................................. 60 Methods............................................. 60 Data Analysis....................................... 62 Results............................................. 65 Protocol u............................................... 75 Purpose............................................. 75 Methods............................................. 75 Data Analysis....................................... 78 Results............................................. 83 iii i\CONTENTS-continued HI.‘................I......C......I....'...'......... 97 -: :0 44jfi§nlaminar Plow as a Cause for Double Exponential l . 'fiPpesSure Decays.......................................... 98 . 'ifliféripheral Airway Resistance and Compliance as -u‘8 Cause of Double Exponential Pressure Decays............ 10A ,‘.The Interaction of Alveolar CO and the Vagus Nerves in TV Determining the'Efficiency of Collateral Ventilation..... 117 - '45 3 1L ft,T-sunrcss 'b. THO conpnarurur MODEL or OLSON AND ROBINSON.......... 125 ANOVA TABLES AND RESULTS OF Racazssron ANALYSES...... 128 CALCULATION OF REYNOLD'S NUMBER...................... 136 REFERENCES.......Io0......OIso.Doctoollooooo-oooooooo 137 iv LIST OF TABLES Physical Properties of Re. N2, and SF6............. Average Flow in ml/min of He. N 2. and SF Necessary to Create a 3 cm H 0 Difference2 Between ghe Lung Segment and the Airway Opening at Three Transpulmonary Pressures........................... Average Flow in ml/min of He. N 2, and SF Necessary to Create a 3 cm H 0 Difference2 Between ghe Lung Segment and the Airway Opening After Bilateral Vagotomy and During Stimulation of the Ipsilateral (IL) Vagus Nerve. at Functional Residual Capacity.. Compliance of Excised Calf Lungs Computed from the Static Pressure-Volume Curve of the Segment, (C1o C2 0' o), and the Lungs (C ). and from the ' Pressure 2oDecgys After Flow into tRe Segment was Interrupted (csing'c f, C 3)........................ Parameters of the Hyperbolic Curve Fit (Equation 27) of Steady State Resistance (Rs Resistance of the Fast Compartment (R ) and Resistance of the Slow Compartment (R ) as a Function of the Number of Needles in She Segment of Excised Calf Lung............................... E,4). Calculation of Reynold's Number at fledged catheter Tip...0......-ICIIIIOIOIIOIIIIOOIOOOOIIOOI Page 61 6A 65 88 96 136 FIGURE 1. LIST OF FIGURES Schematic representation of equipment used to determine the mechanical properties of a collaterally ventilating segment of dog lung....... Schematic representation of equipment used to determine the mechanical properties of a collaterally ventilating segment of dog lung..... Steady state resistance (Rss) of airways in a collaterally ventilating segment of dog lung as a function of $C02 flowing into the segment.......... ............. ..... ........... ..... Time for 901 pressure equilibration (T ) between the collaterally ventilating segment aggth remainder of the lung as a function of $CO:e flowing into the segment ..... ...... ...... .......... The effect of gas viscosity (u ) in micropoise on the steady state resistance (RSS ) of airways in a collaterally ventilating segment of dog lung at three transpulmonary pressures (P tp)... ......... The effect of the product of flow (V) in ml/min and gas density (p) in gm/l on the steady state resistance (R ) of airways in a collaterally ventilating segment of dog lung (Panel A) and the ratio of the coefficients of the double exponential equation describing the pressure decay after flow interruption (Panel B) at three transpulmonary pressures (Ftp).................................... The effect of transpulmonary pressure in cm H20 on the steady state resistance (R ) of airways in a collaterally ventilating segment of dog lung when helium (He). nitrogen (N ) or sulfur hexaflouride (SF ) was flowing through the segment after biIateral vagotomy................... The effect of the product of flow (V) in ml/min and gas density (p) in gm/l on the steady state resistance (R ) of airways in a collaterally ventilating segment of dog lung (Panel A) and the ratio of the coefficients of the double exponential equation describing the pressure decay after flow interruption (Panel B)........................ vi Page H5 “9 57 59 67 7O 72 7M LIST OF FIGURES—-continued FIGURE 9. 16. A1. Page Schematic representation of the equipment used to record the pressure-volume curve and volume of a segment of excised calf lung distal to a wedged double lumen catheter using a 30 ml syringe................................... 80 Individual pressure—volume curves for four excised calf lungs and two peripheral lung segments in each lung............................. 85 Compliance (C) in ml/cm H O of a segment of excised calf lung distal go a wedged catheter as a function of the number of needles in the segment (N)........................ ..... .......... 90 The effect of increasing the number of needles (N) in a segment of excised calf lung on the time constant of the fast compartment (TCf) in seconds and the time constant of the slow compartment (TC ) in Seconds at three different segment pressures (PS).................................... 92 Resistance (R) of airways and needles in cm H O/ml/sec in a segment of excised calf lung distal to a wedged catheter as a function of the number of needles in the segment (N).............. 95 Flow (V) in ml/min as a function of the difference between pressure in cm H O at the tip of a wedged catheter (Ps) and pressure at the airway opening (Pao) in an excised dog lung...................... 102 Schematic representation of a segment of excised calf lung distal to a wedged catheter 0.5 cm in diameter.......................................... 108 Electrical model of a segment of excised calf lung distal to a wedged catheter.................. 11” Model proposed to explain double exponential pressure decays following the interruption of steady state gas flow into a collaterally ventilating segment of dog lung................... 125 LIST OF ABBREVIATIONS Resistance Steady state resistance of airways in lobe segment Resistance of fast compartment Resistance of slow compartment 3.1-? v - _¢I’j" _'dn:4§s. ‘éit '1 ‘ ‘ . ‘ cw: ‘ ‘ 44“}... 4 .' J4 "- Compliance. capacitance .9 .... Dynamic compliance .‘4 -'.| "I .'_ ,3“ 4‘.‘ '34. n 1?? 1 as 1 Ha». Compliance of fast compartment at" o 1 Compliance of slow compartment 15; ARR-F. 1’ Time constant; time for 631 pressure equilibration between lung segment and remainder of lung 7‘ . "J . Ii“ «if- ' a Time constant of fast compartment J Time constant of slow compartment Time for 90% pressure equilibration between lung segment and remainder of lung Pressure at the tip of the wedged catheter or bronchoscope Airway opening pressure Transpulmonary pressure Atmospheric pressure Viscosity Density Number of needles in calf lung segment Compliance of lung segment from single exponential curve fit Compliance from segment pressure-volume curve from 0 to 10 cm R20 Ptp viii Compliance from segment pressure-volume curve from 0 to 20 cm R20 Ptp Compliance from segment pressure-volume curve from 0 to 30 cm H20 Ptp Volume Flow . Acceleration Inertance Subscript referring to "airway" Subscript referring to "lung" Subscript referring to ”tissue" .3...” “A... n '3'- INTRODUCTION In 1931 Van Allen and coworkers demonstrated that air can be transferred across peripheral lung units in animal species with unlobulated or semilobulated lungs and termed the phenomenon "collateral respiration". It has since been observed that species with unlobulated lungs are less prone to develop hypoxemia when peripheral airways are obstructed. This finding had been attributed to the efficiency of collateral ventilation in these species. Numerous researchers have attempted to define the anatomical structures through which collateral gas transfer occurs and to determine physiological factors which influence the efficiency of collateral ventilation. Anastomosing peripheral airways and interalveolar pores have been proposed as pathways for collateral ventilation. A simple technique for quantifying the efficiency of collateral ventilation using a wedged double lumen catheter was developed by Hilpert in 1970. Gas enters the segment of lung distal to the catheter through the outer lumen and leaves through collateral pathways. The inner lumen measures pressure at the catheter tip (Ps)' Airway opening pressure (P30) is measured at the trachea. Steady state resistance of airways in the segment is calculated as: Rss = (Ps"Pao)/v When flow (V) is discontinued. Ps-Pao decays to zero as gas flows from the segment into the remainder of the lung. As originally proposed, this method assumes that the segment behaves as a capacitor discharging through a fixed resistor and that the time constant (TC) is calculated 1 as the time for 63% pressure equilibration. Because TC = Rssc' segment compliance (C) can be calculated. For this method of data analysis to be valid, the pressure decays following flow interruption must be monoexponential. Several investigators have noted that pressure decays are biexponential and have analyzed data recovered using the technique in a variety of ways. The following hypotheses have been proposed to explain biphasic pressure decays: 1. non-laminar flow through the segment resulting in segment resistance being flow dependent 2. significant peripheral airway resistance and compliance between the catheter and collateral pathways 3. variable segment resistance and/or compliance during the decay due to changes in segment volume 1. multiple segment units having a bimodal or broad frequency distribution of time constants. The studies outlined in Protocols 3 and A were designed to test whether double exponential pressure decays are due to nonlaminar flow in the segment or to significant peripheral airway resistance and compliance between the catheter and collateral pathways. In a previous study I showed that vagal stimulation increases the resistance (Rss) of airways in a collaterally ventilating segment of dog lung and prolongs the time (T90) for pressure equilibration between the lung segment and the remainder of the lung. This suggests that collateral ventilation is impaired during vagal stimulation. Numerous investigators have demonstrated that increasing alveolar CO2 tensions in a collaterally ventilating segment of dog lung reduces the resistance of airways in the segment and decreases the time for segment-lung pressure equilibration. When ventilation to a segment of lung is reduced relative to segment blood flow. segment alveolar CO2 tensions increase. The study outlined in Protocols 1 and 2 were designed to investigate whether this increase in alveolar 002 tensions could prevent increases r" 1?“ and T90 caused by vagal stimulation. If so. this would suggest iniqualities in regional ventilation are minimized by changes in 602 tensions. 7 “374The review of the literature is presented in three parts. The ;.falperipheral lung segment. Next the theoretical basis of the mechanical yproperties of the respiratory system and methods of measuring those properties are reviewed to provide background for an understanding of j-ie‘the remainder of the literature review and the discussion. Studies J i 5 gesigned to elucidate the innervation of the lungs are then reviewed to 1,4 I} fdémonstrate that the interpretation of results is Justified. The final ‘41 . ‘ section of the literature review presents background information on ;50 3mfllateral ventilation and poses the questions investigated by this 14. , 4;jifiatomy of the lung is briefly reviewed to define clearly the anatomy of ”wow“ LITERATURE REVIEW Given our present understanding of the lungs, it is difficult to imagine a time when lungs were thought to dissipate "innate heat" produced by the heart. Yet even after Malpighi observed that the lung was composed of membranes and that the blood was contained in vessels, the function of the lungs was unclear (Perkins, 1964). It is now recognized that the respiratory system is essential in defense mechanisms. lipid and protein synthesis. and the chemical modification of pharmacologically active substances, as well as the important function of gas exchange (Lenfant. 1977). Complex physiological mechanisms must exist to regulate the delivery of blood and air to the more than no different cell types performing these functions. As the study of lung physiology becomes more sophisticated. the question regarding these regulatory mechanisms becomes how they interact to maintain homeostasis rather than simply what is the single mechanism regulating blood flow and/or ventilation. Gas exchange in the lung depends on the delivery of oxygen to the alveoli and subsequent diffusion into the pulmonary capillary blood. together with diffusion of C02 from the capillary blood to the alveoli. The efficiency of this process is characterized by the ratio of ventilation (V) to perfusion (Q). Perfusion is determined by the rate and force of contraction of the heart and resistance (R). compliance (C). and inertance (I) of the pulmonary blood and vessels. Ventilation occurs when a pressure difference is created between the alveoli and atmosphere. When alveolar pressure is lowered relative to atmospheric 4 aa- 5. P . 61v a .3 «v. a a n o P . .P." .. F m 5 i _ . A01 Ilia AP. In .hwb pressure by expansion of the ribcage. air flows through the mouth or nose to the alveoli. The amount of energy required to cause volume transfer of air depends on the compliance. resistance and inertance of the airways. parenchyma and chest wall. The compliance and resistance of the lung are determined by the structure of the tracheobronchial tree and lung parenchyma. Anatomy The tracheobronchial tree consists of irregularly branching, epithelium lined airways. The distribution of cartilage. smooth muscle. nerve endings, glandular tissue and epithelial cell types changes as the airways bifurcate and decrease in diameter from trachea to alveoli. Airways are classified as conducting or nonconducting. Conducting airways are those through which no gas exchange occurs. and include the trachea, bronchi and bronchioles; the last generation of conducting bronchioles being designated "terminal". The volume of gas contained in these structures represents the anatomical dead space. C-shaped cartilage lined by glandular epithelium provides structural support from the trachea to the primary bronchi. At the level of the primary bronchi, the cartilage rings are replaced by cartilagenous plates and ultimately by small islands of cartilage. No cartilage is present in the bronchioles. As the amount of cartilage decreases. the amount of smooth muscle increases. being greatest relative to airway diameter in the terminal bronchioles (0.5 mm diameter). Mucus secreting glands and cells also decrease in number from trachea to bronchioles. Ciliated cells which propel mucus from the airways to the pharynx persist into the respiratory bronchioles. Nonconducting airways begin at the respiratory bronchioles which are distinquished from terminal bronchioles by the alveoli opening into the bronchiolar lumen. The epithelium contains secretory cells referred to as Clara cells. No mucus glands are present in the nonconducting airways of normal lungs. Respiratory bronchioles contain large amounts of smooth muscle and elastic tissue but no cartilage. The number of alveoli opening into the lumen of the respiratory bronchioles increases toward the periphery. When the entire wall is composed of alveoli. the structure is known as an alveolar duct. Smooth muscle is concentrated at the opening of the duct. The ducts terminate in variable numbers of alveOli which are perforated by holes 3—13 microns in diameter referred to as Pores of Kohn. When examining histological sectiOns of lung it is apparent that bronchi are separated from surrounding parenchyma by a connective tissue sheath through which pulmonary blood vessels travel. The more peripheral bronchioles lack this sheath and are in direct contact with parenchyma. Although lung architecture is similar in all mammals, species differ in the amount of interlobular fibrous tissue. In ruminant and porcine lungs the interlobular septa are complete so that when a bronchus becomes obstructed, the segment of lung distal to the obstruction does not ventilate. Dog lungs, in contrast. are unlobulated. When a bronchus is obstructed in a dog lung. the distal lung segment receives ventilation from adjacent lung segments through collateral airways. Human and horse lungs are less lobulated than cow lungs but more lobulated than dog lungs. ..v- Mechanical Properties of Lungs In 1925. Rohrer (per Mead and Whittenberger. 1953) proposed that the mechanical properties of the lungs could be described by an equation of motion relating pulmonary pressures, respired volume and volume flow rate. He concluded that the pressure difference causing ventilation. the difference between airway opening pressure (P80) and pleural pressure (Ppl), can be separated into three components: 1. pressure required to overcome the elastic force of the lungs (Pel) 2. pressure required to overcome the resistance to air and tissue movement (Pres) and 3. pressure required to accelerate the gas and lung tissue (Pin)' Pe is related to the volume of the lung (V). Pr is related to the 1 es rate of change of volume i.e. flow (V). and P1“ is related to the rate of change of flow. i.e. acceleration (V). In symbolic form this equation is represented as: (Pao—Ppl) = Pel + Pres + Pin (1) where: Pel = V/C (2) Pres : VR (3) and Pin = VI (4) By recording transpulmonary pressure (Ftp = Pao'Ppl) under static conditions or the portion of transpulmonary pressure in phase with lung volume during tidal breathing. lung compliance (C) can be calculated. Likewise by recording the portion of transpulmonary pressure in phase with flow. lung resistance (R) can be calculated or recording the pressure in phase with acceleration. lung inertia (I) can be calculated. Because the lungs are contained within the chest. if transthoracic pressure. the difference between airway opening pressure and atmospheric pressure (Patm)' is measured. C. R. and I include the mechanical properties of the chest wall. Compliance As can be seen from Equation 2. Pe1 represents the elastic recoil pressure generated by the lung tissue at a given lung volume. Compliance is calculated as the change in static recoil pressure produced by a change in lung volume. The simplest method of determining compliance is to introduce known volumes of air into the lungs until total lung capacity (TLC) is reached. then withdraw known volumes of air. Transpulmonary pressure is recorded when flow is zero. The slope of a plot of cumulative volume added and withdrawn against transpulmonary pressure is static lung compliance. The units of compliance are typically ml/cm H20. Examining a pressure-volume curve (see Figure 10) reveals that compliance is not constant, but gradually decreases as TLC is reached. For this reason the volume range over which compliance is calculated must be specified. Because compliance varies with lung size. being larger in larger lungs. it is necessary to normalize compliance to lung size if meaningful comparisons are to be made among different sized lungs. Such a value is known as specific compliance and has units of 1/cm H20. Resistance Equation 3 shows that resistance is a dynamic property in that it is the portion of transpulmonary pressure required to overcome friction in a system in constant motion. In the lung there are two sources of friction. that caused by gas flow in the airways (Raw) . and that caused by tissues sliding against one another (R ). Airway resistance (Raw) tiss (I! . o. f) K‘) {1:1 r or it! n; 51“ V. \vV diam: my H1“ than .ung . GAI GV [H is calculated as the pressure required to maintain a constant volume flow rate. i.e. (P -Pao)/V and depends on whether air flow is laminar alv or turbulent. Because the type of flow is determined by the physical characteristics of the gas being breathed. i.e. density (p) and viscosity (u). gas velocity. and the geometry of the airways i.e. diameter. length and branching pattern. altering any of these parameters will change airway resistance. Because the geometry of the airways changes with lung volume. airway resistance is different at different lung volumes. For these reasons it is important to know the flow rate. geometry and gas being breathed when interpreting airway resistance. Lung tissue resistance (Rtiss) is calculated as the pressure required to overcome friction between tissues in constant motion. i.e. (Ppl-P )/V. Total lung resistance is the sum of airway resistance and alv tissue resistance. i.e. (Pao'Ppl)/v' Inertance In addition to overcoming elastic and resistive forces. a portion of transpulmonary pressure is required to overcome the inertia (I) of the lungs. Pin is the pressure required to accelerate and decelerate the gas in the airways and the lung tissues. Like airway resistance. airway inertance is affected by the physical properties of the gas being breathed. Methods of Measuring Lung Mechanical Properties All methods of determining the mechanical properties of the lungs are based on Equation 1. Furthermore. most assume that resistance and compliance are constants and that inertia is negligible. The first assumption is valid only over small volume changes because the 10 pressure-volume and pressure-flow curves are curvilinear. The second assumption has been validated for human respiratory rates less than 100/min when air is being breathed. In 1927 two German investigators devised several methods of measuring lung resistance and compliance based on Rohrer's equation of motion (Equation 1) (von Neergaard and Wirz per Mead and Whittenberger. 1953). In these methods lung resistance and compliance are derived from the simultaneous recording of transpulmonary pressure. tidal volume and flow. It is known that over a tidal breath: 4194p = AV/C + VR + VI (5) and that I is negligible. Therefore at points of zero flow (V = 0): AP = AV/C (6) tp Because volume and pressure are known. compliance can be calculated. Resistance is then computed as: R = (APtp - AV/C)/V (7) Resistance can be computed at any point in the respiratory cycle or averaged over inspiration or expiration or both. An assumption implicit in this method of computing compliance is that flow in the lung has ceased when zero flow is recorded at the airway opening. While this assumption may be valid for normal lungs which ventilate synchronously. it may not be valid for diseased lungs which do not. For this reason compliance computed using the method of von Neergaard and Wirz is termed dynamic compliance (C ). dyn The rate at which volume enters a lung region and therefore the change in regional lung volume over a given time is determined by the regional time constant (TC) which is the product of regional resistance and regional compliance. If a region of lung has a long time constant relative to breathing frequency. tidal volume will preferentially 11 distribute to lung regions with shorter time constants. If a significant portion of the lung units have time constants greater than breathing frequency. compliance appears to be decreased because the tidal volume which would distribute to the entire lung given sufficient time. only reaches those units with short time constants. Dynamic compliance falls as frequency increases if there are time constant inequalities in the lung. In constrast. static compliance is not altered by time constant inequalities if they are due to differences in regional resistance. In 1923. Rohrer studied the relationship of pressure and flow to airway geometry in excised human lungs. He empirically described the relationship of pressure to flow by the following quadratic equation: V Pres = k1V + k2 v2 (8) He estimated the Reynold's number using airway geometry. air viscosity and density and estimates of flow velocity to determine the probability of fully developed turbulent flow in the airways. A miscalculation. which went unnoticed until 1953 (Gaensler per Mead and Whittenberger). led Rohrer to conclude incorrectly that gas flow in the airways was never fully turbulent. He reasoned that k1V represented the pressure required to maintain laminar flow. Because laminar flow in a rigid. smooth cylindrical tube can be described by Poiseuille's equation: p = (8u1)/«r“ (9) R1 was presumed to depend on the geometry of the airways and the viscosity (u) of the gas being breathed. Recognizing that even though fully turbulent flow did not exist. eddying turbulence probably ocurred at airway bifurcations. he presumed k2V2 to be the pressure required to maintain nonlaminar flow. ...... 12 Because the probability of turbulence is determined by airway geometry. flow velocity and gas kinematic viscosity (viscosity/density). he concluded that sz2 would depend on airway geometry and gas density and viscosity. When using engineering principles to analyze a physiological system such as the lungs it is important to realize both the power and the limitations of the analysis. Obviously a rigorous treatment of the pressure-flow relationships in the lungs is exceedingly difficult because of the nonuniform branching pattern and distensibility of the airways and the compressibility of gases. Although this was well recognized by the early investigators. they chose to utilize the concepts and recognize the limitations. While this may seem nonrigorous. it does provide some insight into the working of the lung. which is the objective of physiological research. Recently engineers have examined the mechanical properties of lungs during pressure oscillations up to 10000 kHz (Fredburg, 1980). Although still in the formative stage. models of the lung based on the results take into account the mechanical properties and geometry of individual lung structures and the compressibility of gases. In 1959. Dubois et a1. developed a method for measuring airway resistance directly. This method is based on the principal that there is no change in total gas volume if a person breathes while seated in a closed chamber. Because the airways constitute a significant resistance. alveolar pressure exceeds chamber pressure during expiration and chamber pressure exceeds alveolar pressure during inspiration. Because the system is closed. the magnitude of the two pressures is proportional and opposite. Chamber pressure therefore reflects alveolar pressure over the respiratory cycle. Calibrating the system to absolute peas-v-v-—v-- 13 alveolar pressure requires knowing initial alveolar pressure and volume. Alternately the system can be calibrated by recording chamber pressure and flow during breathing both before and during airway opening occlusion. When inspiratory efforts are made against a closed airway. alveolar volume does not change. Under this condition. airway opening pressure equals alveolar pressure and chamber pressure reflects absolute alveolar pressure. Because total gas volume of the system is constant. this ratio can be used to calibrate the pressure changes occurring when the airway is unoccluded. Presently one of the most common methods of determining lung resistance is that of forced oscillation. This method evolved from a study designed to investigate the frequency response characteristics of the respiratory system (Dubois et al.. 19568). From an analysis of pressures and flows at different frequencies. an estimate could be made of the inertial term of Equation 1 which until now has been assumed negligible. Because a sine wave is easily manipulated mathematically. a variable speed. volume pump was designed to apply a sinusoidal wave of pressure to the mouth. By modeling the chest as an electrical circuit composed of resistors. capacitors and inductors. estimates of pulmonary resistance. compliance and inertance were obtained. When a sinusoidal wave of pressure is applied to a system composed of resistors. capacitors. and inductors. pressure is related to flow by the impedance of the system. Impedance is the vector sum of the resistance and reactance (X): P = (VRE + x2)v (11) Reactance is the sum of components related to inertance (Xi) and compliance (Xe). Assuming a simple system. Xi = 2n(f)I and X0 = -1/2«(f)C. As frequency increases compliance becomes smaller and i .ne" . h leno‘ a?» :Ye Va‘ 14 inertia becomes larger. At the resonant frequency (fr)’ Xi = X0 and impedance reflects only resistance (Fisher et4al. 1968). Therefore when the lungs are oscillated at their resonant frequency. resistance equals the inverse slope of a plot of flow against transpulmonary pressure. Because phase lags introduced by the pressure catheters affect the magnitude of the pressure perceived to be in phase with flow. the frequency response of the recording system is important when using this method. Recent studies using this technique apply a sinusiodal pressure at the mouth with a loudspeaker driven by an amplifier connected to a variable frequency sine wave generator. Pulmonary Innervation Factors affecting the mechanical properties of lungs fall into two broad classifications. active and passive. Because the lung and chest wall are normally interconnected via the pleural space. expanding the chest expands the lungs. Increasing lung volume passively reduces airway resistance by increased traction on the bronchi and bronchioles - a phenomenon known as interdependence (Macklem et a1” 1969. Hoppin et al.. 1978). Lung compliance is reduced at higher lung volumes as the elastic limit of the tissues is reached. Contraction of tracheobronchial smooth muscle results in active alterations in lung resistance and compliance. Smooth muscle contraction can be elicited by intrinsic or extrinsic mechanisms. Intrinsic factors do not involve neural pathways but rather act directly on the smooth muscle. Examples are histamine (which also has extrinsic effects). and exogenous parasympathomimetic agents. Contracted airways can be relaxed by sympathomimetics and possibly high alveolar C02 (Widdicombe. 1963). Because extrinsic mechanisms act in smooth muscle through neural 15 pathways. their effect on the lung is regional and dependent on the distribution of efferent nerves. It has long been known that pulmonary parasympathetic innervation is via the vagus nerve. Widdicombe (1963) cites a 1819 paper in which lung contraction was observed when the vagus nerves were galvanized. In contrast, the first demonstration of adrenalin induced bronchodilation occurred in 1909 (cited by Daly and Hebb. 1966). More recent histochemical investigations have established the presence of parasympathetic nerve endings. Additionally. researchers have attempted to determine the distribution of sympathetic bronchodilator fibers and parasympathetic bronchoconstrictor fibers using radiographic and physiological techniques. The distributiOn of cholinergic nerve endings is investigated histochemically by applying acetylthiocholine and butyrylthiocholine in combination with diisopropylphosphofluoridate. a butyrylcholinesterase inhibitor. to tissues to localize the site of acetylcholinesterase. Large amounts of acetylcholinesterase are found in canine ganglia and nerves in the conducting airways suggesting that these structures are parasympathetically innervated (Daly and Hebb. 1966). The distribution of vagal efferent nerves has been studied physiologically by measuring large and small airway resistance during vagal stimulation. Airway resistance is partitioned by introducing a piano wire attached to a polyethylene catheter with a flared tip into the trachea and advancing it down the tracheobronchial tree. By puncturing the pleura with the wire and pulling the wire through the pleura. the flared tip of the catheter wedges in a peripheral airway. Assuming that the pressure recorded with the retrograde catheter represents airway pressure in all bronchi of comparable size. resistance 16 is partioned into a central and peripheral component. Because the retrograde catheter wedges about one cm subpleurally. the catheter is short and the frequency response is good. Total resistance is calculated by oscillating the lungs with a loudspeaker and relating pressure and flow. Peripheral resistance is calculated by measuring the pressure difference between the retrogade catheter and the pleural space. subtracting elastic recoil pressure. and dividing the result by flow measured at the trachea with a pneumotachygraph. Central airway resistance is computed by subtracting peripheral resistance from total resistance (Macklem and Mead. 1967). Macklem et a1. (1969) utilized this technique to evaluate the effect of lung volume on airway resistance. They found that large airway resistance decreased as lung volume increased but small airway resistance did not change if the vagi were intact. The retrograde catheter technique of Macklem and Mead was used by Woolcock et a1. (1969A) to evaluate the effect of vagal stimulation on central and peripheral airways. The size of the airway in which the catheter wedged was found by excising and air drying the lungs and dissecting down to the catheter. Airway size ranged between 0.8 and 3.2 mm. The 21 dogs studied could be divided into two groups on the basis of the response of their peripheral and central airways to vagal stimulation. While total resistance. central resistance and peripheral resistance increased with vagal stimulation in all dogs. in one group (n=13) the increase in central resistance was greatest and in the other (n=7) the increase in peripheral resistance was greatest. Significantly. the increase in total resistance in 6 of the 7 peripheral responders was smaller than that of the central responders. This finding supports the hypothesis that large changes in peripheral airway l7 resistance must occur before total lung resistance changes, making the early detection of small airway disease clinically difficult. Static and dynamic compliance decreased with vagal stimulation. suggesting an increase in elastic recoil pressure. Using the same techniques. Woolcock et a1. (1969B) extended the study to include 9 dogs before and after beta adrenergic blockade with propranolol. Propranolol increased peripheral resistance in all dogs and markedly potentiated the effect of vagal stimulation on peripheral resistance and dynamic and static compliance. The effect of propranolol and vagal stimulation on central resistance was less consistent and not significant. Surprisingly. in one dog. propranolol alone decreased vital capacity and increased elastic recoil. Additionally. of the 6 dogs studied. propranolol reduced vital capacity by between 0 and 17% (mean 81). The authors conclude that beta adrenergic bronchodilator fibers innervate the peripheral airways. masking the bronchoconstrictor effect of vagal stimulation. They speculate that sympathetic nerve activity may be important in animals with normal vagal bronchomotor tone in maintaining a high lung compliance and reducing the work of breathing. Using a modification of the retrograde technique in which alveolar pressure is measured with subpleural needles and the pleural surface oscillated. Hoppin et a1. (1978) found that peripheral airway resistance decreased as lung volume increased. Hoppin et al. suggest that the original technique of Macklem and Mead introduced errors by estimating the tissue resistance and applying positive pressure oscillations at the airway opening which prevented their measuring a change in peripheral resistance. 18 Hensley et a1. (1978) found that sympathetic bronchodilator fibers predominantly innervate peripheral airways in awake humans by comparing closing volume and dead space after pharmacologically stimulating beta sympathetic receptors with isoetharine or by blocking muscarinic receptors with atropine. Changes in deadspace reflect changes in large airway volume. Closing volume indicates the lung volume at which peripheral airways collapse. Total airway resistance was determined plethysmographically and the drug dose calculated to produce identical changes in specific airway conductance (1/(Raw X vol)). Anatomical deadspace increased 6% following isoetharine and 171 following atropine suggesting preferential dilation of large airways after parasympathetic blockade. Closing volume was significantly increased following isoetharine but unaffected by atropine. Because closing volume represents the volume at which the expirate comes primarily from nondependent lung regions and because dilated airways are more compliant. the authors conclude that sympathetic fibers mainly innervate peripheral airways and parasympathetic fibers mainly innervate central airways. Cabezas et al. (1971) used a radiographic technique to examine the distribution of autonomic fibers in dog lungs. Powdered tantalum was insufflated into the lungs and roentgenograms taken. Airway diameters were measured at equivalent sites with a graduated hand lens or calipers. Electrical stimulation of the right sympathetic nerves (stellate ganglion and ventral limb of the ansa subclavia) inhibited moderate bronchoconstriction produced by electrical stimulation of the cervical vagi and reflex bronchoconstriction induced by apneic asphyxia. Sympathetic dilation was attenuated by the beta adrenergic antagonists. l9 propranolol or dichloroisoproterenol. Maximum bronchoconstriction induced by high voltage electrical stimulation could not be completely reversed by sympathetic stimulation. Vagal stimulation reduced airway diameter from the trachea to bronchioles 0.5 mm in diameter and had the greatest effect on airways 1-5 mm in diameter. Sympathetic stimulation dilated constricted airways from 0.5 - 5 mm in diameter with the greatest effect on airways with diameters of 1-5 mm. These findings were recently confirmed by Russell (1980) who studied airways (5-1.5 mm diameter) in vitro. Epinephrine relaxed airways pretreated with histamine and the effect was antagonized by propranolol. These latter findings are difficult to reconcile with the preferential sympathetic innervation of peripheral airways found by Woolcock et a1. (1969B). A possible explanation offered by Russell is that central mechanisms preferentially excite peripheral airway sympathetic fibers. An alternate explanation is that the inconsistent effect of vagal stimulation and propranolol on central airway resistance would have revealed sympathetic innervation of central airways. had more dogs been studied. It is also possible that propranolol affected tissue resistance which is included in the measurement of peripheral airway resistance. Collateral Ventilation The observation by Van Allen et al. (1931) that atelectasis did not always occur in human lungs distal to an obstructed airway was difficult to reconcile with the then current notion that peripheral lobar units were independent of one another. A cannula with a dilatable tip was used to study the phenomenon of peripheral transfer of air in human. dog. cat. rabbit. calf and pig lungs. In one experiment the cannula was 20 tied into a bronchial branch of an isolated. degassed dog lobe. Serial roentgenograms confirmed that the entire lobe could be inflated by infusing air through the cannula. In a second experiment the cannula was inserted into a peripheral bronchus of an anesthetized dog. A valve was attached to the proximal end of the cannula to permit exhalation only and held under water. Because air bubbled through the cannula when the remainder of the lung was ventilated normally. it was concluded that peripheral transfer of gas occurred during quiet breathing and was not an artifact of ruptured airways. Studies on calf and pig lungs indicated that peripheral transfer of gas does not occur across lung lobules completely separated by fibrous septa. Van Allen et al. termed the transfer of air between adjacent lung lobules "collateral respiration". The remarkable finding that lung lobules were not airtight at the periphery was largely ignored until 1948. Baarsma observed clinically that occlusion of the lower lobar bronchus caused atelectasis of the lobe whereas occlusion of the first dorsal branch of the bronchus did not. He confirmed his clinical findings by selectively wedging a valved cannula in different bronchi of patients undergoing differential spirometry and measuring the volume of collaterally respired air. Methods of Measuring Collateral Ventilation The methods used to study collateral ventilation are grouped into two major classes; qualitative and quantitative. Qualitative methods such as serial radiographs or a wedged cannula bubbling into a water 21 glass (Van Allen et al.. 1931) can only indicate whether collateral ventilation occurs. To estimate factors affecting collateral ventilation. quantitative methods must be used. Until 1970. the effectiveness of collateral ventilation was assessed quantitatively by wedging a cannula in the lung. The cannula was connected to a spirometer by a one-way valve so that the segment received ventilation from adjacent lung segments and exhaled into the spirometer. Timed collections of collaterally respired air were used to estimate the volume and flow rate of collaterally transferred air. Collateral flow may be underestimated however. because gas entering the collaterally ventilating segment by collateral airways can leave by the same route. Hogg et a1. (1969) modified this method and calculated the resistance of collateral airways in excised human lungs. A cannula was tied into a basal segmental bronchus. catheters were inserted through the pleura above and below the fissure and a cannula was tied into an apical segmental bronchus. A pneumotachygraph in the outflow line estimated collateral airflow. Air flowing into the basal cannula passed through lower lobe airways. cOllateral airways across the fissure and upper lobe airways. finally leaving the lung through the apical cannula. Collateral resistance was calculated as the pressure drop across the fissure divided by flow measured with the pneumotachygraph. Airway resistance was calculated from the pressure difference between the cannulae and the appropriate pleural catheter and collateral flow. Collateral resistance was greater than airway resistance in normal lungs but less than airway resistance in emphysematous lungs. Hogg et al. proposed that the ventilation of lung units by collateral airways 22 accounts in part for the frequency dependence of compliance seen in emphysema. They noted. however. that until the mechanical properties of small lung units could be determined. the proposal would remain speculative. In a comprehensive review article on collateral ventilation and airway obstruction. Macklem (1971) credits two laboratories with independently developing techniques to assess the resistance and compliance of small segments of lung. Hilpert's method (per Macklem. 1971) consists of obstructing a segmental bronchus with a double lumen catheter. Air is infused into the segment of lung distal to the obstructed bronchus through one lumen and pressure recorded with the other. Airflow into the segment is adjusted until a steady pressure difference exists between the obstructed segment and the remainder of the lobe. When the airflow is discontinued. the pressure difference dissipates as air leaves the segment through collateral airways. Collateral resistance is calculated as the steady state pressure difference divided by flow rate. Because the pressure decay resulting when inflow stops approximates a single exponential. Hilpert likened the segment to a capacitor discharging through a resistor. He therefore computed the time constant (TC) of the segment as the time for the pressure difference to decay by 63%. Because the time constant in this simple system is the product of segment resistance and compliance. segment compliance is calculated by dividing the time constant by segment resistance. Alternate methods for determining the time constant of small segments of lung were devised by Woolcock and Macklem (1971). The first method involved securely wedging a double lumen catheter into a peripheral bronchus. One lumen was for bolus injections of air and the 23 other for recording pressure at the catheter tip. The volume of air necessary to cause a 30-90 cm water pressure difference between the catheter and the pleural space (or atmosphere in excised lungs) was established by trial and error. Pressure was recorded against time during the rapid injection of air and subsequent decay in pressure recorded as the air passed through collateral airways into the remainder of the lung. The segment time constant was calculated as the time for 63% pressure decay. Effective compliance was calculated as the volume injected divided by peak pressure difference and segment resistance calculated as the quotient of TC and segment compliance. Rarely was the decay monoexponential so a back extrapolation technique was used to recover multiple time constants. The second method used a loudspeaker to oscillate the lungs by positive pressure at the trachea. When Ps-P was recorded against lung pl volume during sinusoidal oscillation. the phase lag between pressure changes at the airway opening and pressure changes in the lung segment distal to the catheter could be determined. Because the lag was due to the time constant of the collaterally ventilating space being greater than the time constant of the lungs. knowing the phase angle of the lag permitted the calculation of the segment time constant. Factors Affecting Collateral Ventilation Because collateral airways were postulated to serve a "backup" function in providing ventilation to lung segments in which the normal route of ventilation was obstructed. factors affecting the efficacy of collateral ventilation were investigated. Clearly if the cause of airway obstruction also inhibited collateral ventilation. this postulate could not hold. 24 Since 1998. many investigators have experimented with factors 4affecting collateral ventilation. When examined in perspective. the striking observation is that collaterally ventilated segments respond to physiological interventions exactly like the remainder of the lungs. Pulmonary edema caused by sodium amytal (Van Allen et al.. 1931) or ANTU (Alley and Lindskog. 1998) inhibits collateral ventilation as determined by collecting collaterally transferred gas through a wedged catheter. Segment resistance varies inversely with lung volume in human and canine lungs when either Hilpert's method (Inners et al.. 1979. Kaplan et al.. 1980) or Woolcock and Macklem's phase lag method is used (Woolcock and Macklem. 1971). Hypocapnia. in either the collaterally ventilating segment or the remainder of the lobe decreases the efficiency of collateral ventilation by increasing segment resistance (Traystman et al.. 1976. 1978. Smith et al.. 1979). Studies measuring the volume and flow rate of collaterally transferred gas have also indicated that the efficiency of collateral ventilation is impaired by decreasing alveolar 602 levels either by changing the concentration of C02 in the inspired gas or clamping the pulmonary artery (Johnson and Lindskog. 1971). In contrast. hypercapnia induced by increasing inspired CO2 to 5.6. or 15% increases the collateral flow of gas (Johnson and Lindskog. 1971, Sealy and Seaber. 1975) and reduces segment resistance (Traystman et al.. 1976). Changing the alveolar oxygen level does not appear to alter the volume of collaterally transferred air (Chen et al.. 1970. Johnson and Lindskog. 1971) but using 5% 02 in N2 as the inflow gas in Hilpert's method reportedly increases the resistance and time constant of a collaterally ventilating lung segment (Traystman et al.. 1976). 25 Evidence that airways through which gas is transferred collaterally possess smooth muscle has been demonstrated by several methods. Electrical vagal stimulation decreases collateral ventilation by increasing segment resistance (Woolcock and Macklem. 1971. Olson and Robinson. 1980). Infusing methacholine into a lung segment through a wedged catheter increases segment resistance (Smith et al.. 1979. Kaplan et al.. 1980) and intravenous methachOline decreases the volume of collaterally transferred gas (Chen et al.. 1970). Because dog lungs have good collateral ventilation and pig lungs do not (Van Allen et al.. 1931. Woolcock and Macklem. 1971) several investigators compared the effect of airway obstruction with beads on the mechanical and gas exchange properties of the lungs of the two species. Brown et'al. (1969) measured lung resistance. dynamic compliance and vital capacity in excised dog and pig lobes before and after obstructing some airways with plastic beads. Small airways were obstructed by impacting 2 mm beads with a central hole into the lungs and large airways obstructed by impacting 5-11 mm beads with and without central holes into the lungs. Beads with central holes were used to simulate partial airway obstruction. They reasoned that if the segment of lung distal to the bead had no collateral ventilation. vital capacity should decrease. Random obstruction or partial obstruction should cause inequalities of time constants within the lung resulting in frequency dependance of compliance. Large airway obstruction should increase resistance while small airway obstruction should not. due to the large number of small airways in parallel. One of the three pig lobes showed a clear decrease in vital capacity with small beads and one of two showed a decrease with large beads. In only one dog lobe did vital capacity decrease and then only after 36 26 large beads were impacted. As hypothesized. lung resistance was not much altered by small bead impaction in either species but increased with large bead impaction. The species differences became apparent when the frequency dependence of compliance was tested. Dog lungs had to be severely obstructed before a change in compliance with frequency was observed whereas the compliance of pig lungs was always frequency dependent. This indicated that the average time constant of pig lungs but not dog lungs was long relative to the ventilatory rate resulting in unequal distribution of volume. The authors postulated that species differences in collateral ventilation accounted for the results. Flenly. et a1. (1972A) examined the relationship of ventilation (V) to perfusion (Q) in dog and pig lungs after airway obstruction with 2 mm beads. The distribution of blood flow was measured by radiolabelled isotOpes and the three compartment model of Riley and Permutt used to calculate V/Q. Control measurements in normal upper lobes were compared to measurements made in lower lobes into which beads had been placed. Careful anaIysis of the results revealed that airway obstruction in dogs did not alter the arterial-alveolar oxygen gradient. shunt fraction of pulmonary blood or ventilation to perfusion ratio. In pig lungs. however. similar obstruction caused hypoxemia and increased the arterial-alveolar oxygen difference. The ratio of ventilation to perfusion did not change. suggesting that blood was shunted from poorly ventilated alveoli. Again extensive collateral ventilation in dog lungs was postulated to explain the results. Airway resistance increases during an allergic asthma attack. This can be simulated in experimental animals by sensitizing them to a particular protein then challenging them with an aerosol of the antigen. 27 In 1978. Rubinfeld et al.. investigated the effect of inhaled antigen challenge on the ventilation/perfusion relationship of sensitized dog lungs. Multiple inert gases were used to assess the ventilation/perfusion ratio. No units were found which had a V/Q of zero indicating that all regions of the lungs received some ventilation. Because histological examination of the lungs revealed extensive mucus plugging of peripheral airways. presumably. ventilation reached lung units distal to a severly constricted airway through collateral airways. Because Gold et a1. (1972) demonstrated that the pulmonary effects of inhaled antigen challenge can be prevented by vagal sectioning or atropine. Rubinfeld's results are difficult to reconcile with the fact that vagal stimulation decreases collateral ventilation (Woolcock and Macklem. 1971. Olsen and Robinson. 1980). The present study was designed to determine. in part. if increased alveolar CO2 levels could override the decrease in collateral ventilation caused by electrical vagal stimulation. If airway resistance were increased by a vagally mediated mechanism presumably collateral ventilation would be impaired also. The time constant of the afflicted segment of lung would then be longer than that of the remainder of the lungs. The distribution of ventilation to the segment would then be impaired. resulting in the alveolar gas concentrations approaching that of the pulmonary arterial (mixed venous) blood. If the resultant rise in alveolar CO2 levels increased the efficiency of collateral ventilation. a more normal distribution of ventilation would result. 28 Pathways For Collateral Ventilation When Van Allen et a1. (1931) published their remarkable paper on collateral ventilation they were aware that the alveoli were perforated by tiny holes known as the Pores of Kohn. They speculated that collateral ventilation might occur through the Pores but also believed diffusion to be involved. Analysis of helium washouts from collaterally ventilating lung segments and completely obstructed lung segments suggests that collateral ventilation is too rapid to be accounted for by diffusion (Hilpert per Menkes and Traystman. 1977). In addition to the Pores of Kohn, two other structures have been proposed as collateral airways. The first are the bronchiole-alveolar communications first described by Lambert (1955). Nonmuscular. epithelium lined tubules. up to 30 microns in diameter in the uninflated lung. were found to connect terminal and respiratory bronchioles to alveoli. These structures were found in human lungs of all ages and in cat and rabbit lungs. A study of coal miners lungs revealed that dust cell accumulation was particularly heavy in the tubules and in the alveoli to which the tubules were connected. The second possible route for collateral ventilation other than alveolar pores was first described by Martin (1966). Because he was able to pass polystyrene spheres of up to 120 microns in diameter collaterally with only 9 cm H 0 pressure. he concluded that either the 2 bronchiole—alveolar tubules of Lambert had to be extremely compliant or that some other pathway existed. By reconstructing 1600 serial sections of a lung segment dusted with India ink powder. he found respiratory bronchioles which connected two terminal bronchioles from adjacent lung segments. He concluded that such muscular walled anastomosing bronchioles (100-200 microns diameter) could serve as collateral airways 29 in the dog. Henderson et a1. (1968/1969) were able to pass spheres of 69 microns in human lungs suggesting that collateral pathways bigger than alveolar pores exist in human lungs also. At the present time there is no agreement as to which pulmonary structure provides the major route for collateral ventilation. Physiological experiments designed to elucidate which structure is the major route of collateral ventilation have been inconclusive. Menkes et al. (1971) reasoned that because increasing surface tension by instilling kerosene into the segment of lung distal to a wedged catheter decreased segment resistance and increased segment compliance. alveolar pores had to be the major route for collateral ventilation. Because pressure is proportional to the ratio of surface tension to radius. a decrease in surface tension in a tubular structure. such as a collateral airway. should have increased segment resistance. This study has been cricitized on the basis that the kerosene may not have been evenly distributed and that a decrease in the surface tension of the tissue surrounding a collateral airway would reduce segment resistance by interdependence (Mead per Menkes and Traystman. 1977). In 1972. Flenly et a1. determined the ventilation/perfusion ratio of a collaterally ventilating lung segment by analyzing alveolar gas tensions in samples drawn from the lung segment and measuring arterial and mixed venous blood gas tensions. The ventilation/perfusion ratio of the whole lung was calculated from an analysis of alveolar gas tensions at the trachea and determinations of cardiac output. While the V/Q ratio of the collaterally ventilating segment was always less than the V/Q ratio of the entire lung. the alveolar oxygen tension of the segment was always greater than the mixed venous oxygen tension and was between the arterial and alveolar oxygen tensions. The authors conclude that 30 the segment received significant ventilation through collateral pathways. Further calculations using their data. the values of segment time constants measured by Woolcock and Macklem (1971) and an estimate of the shunt fraction. revealed that the collaterally ventilating lung segment had a large dead space. The authors conclude that the large dead space was the result of collaterally transferred air coming from gas exchanging structures. thereby suggesting that the Pores of Kohn are the major collateral pathway in the dog. Most recently. Sasaki et a1. (1980) estimated collateral resistance in excised dog lungs using a new technique. Hemispherical plastic capsules (3 mm diameter) were glued onto the pleural surface of excised dog lobes into which numerous micropunctures had been made. Two capsules were glued over a segment of lung which ventilated through collateral airways only. the normal route of ventilation being obstructed by a wedged catheter. A third capsule was glued over an adjacent portion of normally ventilating lung. Silicone rubber was instilled into the trachea so that bronchioles. except those within the lung segment distal to the catheter. were obstructed. Presumably. air could only pass collaterally through the Pores of Kohn. Measurements of the resistance between the capsules on the segment and the capsule outside the segment indicated the Pore resistance to be 10 to 100 times igreater than the resistance between the same capsules when air was flowing down the catheter and the bronchioles were unobstructed. The lung was at held at a transpulmonary pressure of 30 cm H20 during both measurements. The conclusion is that Hilpert's method measures the resistance of collateral airways. but not interalveolar pores. The authors conclude that alveolar pores would be the major route in 31 obstructive lung disease however. reasoning that if peripheral airways are obstructed. collateral airways will likewise be obstructed. What Does the Wedged Catheter Technique Really Measure? Evaluation of the experiments determining factors affecting the efficiency of collateral ventilation and those designed to estimate which structure is the major route through which interlobular airflow occurs. leads to some interesting speculations. If the resistance of the structures estimated with the wedged catheter technique responds to physiological perturbation in the same manner as the whole lung resistance. what is the technique measuring? The logical deduction is that either collateral airways are anastomosing peripheral airways or that the technique is not measuring the mechanical properties of collateral airways- be they pores or bronchioles. Because the lung can be thought of as being composed of multiple segments. it has been argued that the segment time constant should equal the time constant of the lung. Such a calculation was presented by Woolcock and Macklem (1971). For human lungs the product of lung O/l/sec x 0.2 l/cm H O = 0.2 resistance and compliance equals 1.0 cm H2 2 sec. The average segment time constant recovered during lung deflation was 0.3 sec indicating that obstructed lung segments ventilate as easily as unobstructed lung segments. Similar results were found in dog lungs. In both species however. segment resistance was considerably greater that airway resistance for the same lung volume. Because TC = RC. the logical deduction is that the specific compliance of the segment is less than the specific compliance of the lung. This is explained by the fact that the lung parenchyma surrounding the collaterally ventilating lung segment inhibits segment expansion when segment volume is increased. 32 The segment and the surrounding parenchyma are therefore considered to be interdependent (Mead et al.. 1970). However. because of collateral airways. there is no good way to measure the static compliance of a segment of dog lung to compare with static lung compliance or with compliance calculated using Hilpert's method. A recent study by Robinson and Milar (1980) emphasizes that segment resistance may not be a function of volume of the segment per se. but rather a function of the geometry of the segment within the lobe. If collateral airways traverse the interface between the segment and the remainder of the lobe. then segment resistance should vary directly with interface area which should depend on the shape of the lobe. A systematic study of segment pleural surface area to volume ratios and the segment resistance. compliance and time constant in different lobes of excised dog lungs confirmed this theory. Lobar differences in segment resistance could not be explained on the basis of differences in segment volume. but rather correlated inversely with the segment area to volume ratios suggesting a direct correlation with segment/lobar parenchymal interface area. When the lungs were held at a transpulmonary pressure of 5 cm H 0 (approximately FRC). specific 2 segment compliance was half that of estimated specific lung compliance. This finding confirmed previous reports that inhomogenous expansion during inflation of the segment by flow results in the lung segment appearing stiffer (Woolcock and Macklem. 1971, Menkes et al.. 1972). When interpreting the results of the studies discussed above. the authors have assumed that the data can be analyzed as originally proposed by Hilpert. Specifically. they assume that segment resistance represents the resistance of collateral airways only. and is independent of flow rate, and that the segment time constant is the product of 33 segment resistance and segment compliance. Recent observations suggest that these assumptions are not valid. Levy and Wood (Abstract. 1976) examined the pressure-flow characteristics of a collaterally ventilating segment of dog lung in vivo. Flow measurements were made at segment pressures of 1 and 2 cm H20 using 15% 02 and 5% C02 in He. N2. and SF6. The finding that segment resistance increased with increased gas density suggested that flow in the segment was nonlaminer i.e. segment resistance was not constant but depended on flow rate and gas density. The same conclusion was reached by Robinson and Sorenson (1978) in a study of excised dog and horse lungs. Using a wedged catheter. the segment resistance and time constant were determined at PS-Pao = 2.5. and 10 cm H20 at three different transpulmonary pressures. In dog lungs. segment resistance increased as flow increased at all transpulmonary pressures. In horse lungs segment resistance increased as flow increased at higher transpulmonary pressures only. The authors conclude that turbulence at higher flow rates causes segment resistance to increase. Because the pressure decay curves following flow interruption were seldom monoexponential. these investigators did not calculate a segment compliance. When Hilpert's method is used. air is infused down the wedged catheter at a constant rate and the steady state pressure difference between the catheter tip and the trachea is used to calculate segment resistance. Clearly this pressure drop occurs not only across collateral airways but also across airways between the catheter tip and the collateral airways and airways between the external boundary of the segment and the trachea. Robinson and Mukhtar (Abstract. 1977) partitioned segment resistance by inserting subpleural catheters into a 34 lung segment distal to a wedged catheter in excised dog lungs. A second subpleural catheter was inserted into the parenchyma external to the segment boundary. Because there was no measurable pressure difference between the external catheter and the airway opening. they concluded that extrasegmental airway resistance was a negligible portion of segment resistance. Because the double lumen catheter is wedged in a subsegmental bronchus and collateral airways begin at the level of terminal and respiratory bronchioles. intrasegmental peripheral airway resistance may contribute significantly to segment resistance measured with Hilpert's method. The finding of a significant pressure difference between the catheter tip and the subpleural catheter within the segment (Robinson and Muhktar. Abstract 1977) suggested that segment resistance included a significant intrasegmental peripheral airway component. A similar finding was reported by Sasaki et al. (1980) using pleural capsules in excised dog lungs. Menkes and Traystman (1977) concluded that intrasegmental peripheral airway resistance was significant in emphysematous lungs by comparing the pressure decays after flow was stopped in emphysematous human lungs and in dog lungs in which methacholine. a potent bronchoconstrictor. was instilled through the wedged catheter. A rapid pressure drop followed by a slower monoexponential pressure decay was seen in both cases. The authors conclude that the rapid pressure drop represented pressure equilibration across the peripheral airways between the wedged catheter and collateral airways. To calculate peripheral airway resistance. Smith et a1. (1979) analyzed the pressure decay by a semilogarithmic plot of Pb at 0.25. -Pao 0.5. 0.75. and 1.0 see after flow was stopped. Pb being the pressure measured at the catheter tip. The line of best fit through the four 35‘ points was back extrapolated to time zero and the resulting pressure designated segment pressure. P . The difference between P at time s b'Pao zero and P3 was presumed to represent the pressure drop across intrasegmental peripheral airways. The remaining pressure drop was presumed to be the pressure driving flow across collateral airways. By dividing (Pb-Pao)-Ps by flow. peripheral airway resistance was computed. Collateral resistance was computed by dividing Ps by flow. Adding 10% C02 to the air flowing down the catheter decreased collateral and small airway resistance. Instilling methacholine down the catheter increased collateral resistance when air or 10% CO was used but did not affect 2 small airway resistance. The figure presented indicates that at 1 see. some decays were only 50% complete. It is likely that significant information was lost by only choosing four points during the first second of the decay. Olson and Robinson (1980) investigated the effect of vagal stimulation and sectioning on the mechanical properties of a lung segment distal to a wedged catheter in open chested dogs. During electrical stimulation of the vagus nerve. the pressure decay following interruption of flow could not be described well by a single exponential equation. The curve was found to approximate a double exponential equation by using a nonlinear curve fitting routine performed by digital computer. Based on the anatomical arrangement of the segment within the lung and airways within the segment. the segment was modelled as two fixed resistance. series RC circuits (see Appendix A). The RC circuit with the most rapid time constant was presumed to represent the resistance and compliance of peripheral airways between the catheter and collateral airways. The RC circuit with the slowest time constant was presumed to represent the resistance of collateral airways and the 36 compliance of segment parenchyma. The double exponential decay was explained by the two compartments having different time constants and therefore different rates of decay. This interpretation is similar to that of Menkes and Traystman. (1977) and Smith et al.. (1979). Olson and Robinson (1980) acknowledge that while the simple compartmental model may explain double exponential pressure decays. there are other possible explanations. Alternate hypotheses suggested were that resistance and compliance change during the decay or that a broad or bimodal frequency distribution of time constants exists within the segment. Purpose of this Dissertation From the background information presented above. I am selecting two questions to be answered. First. what is being measured with the wedged catheter technique? Second. can alveolar CO2 tensions modify the effect of vagal stimulation on collateral ventilation? Regarding the first question. there is no doubt that when a constant flow of air is passed through a collaterally ventilating lung segment and the driving pressure for flow recorded that a resistance can be computed. If the flow is laminar the resistance can be attributed to the geometry of airways in the segment. Airway geometry includes both the diameters and lengths of individual airways and the arrangement of those airways in the segment. The resistance is therefore a weighted average of the resistance of all airways in the segment. If flow in the segment is not laminar. resistance is influenced by airway geometry AND the flow rate and the physical properties of the gas. If this measure of resistance is to be used to quantify factors presumably affecting airway geometry. the flow pattern must be known. 37 Because this resistance is a weighted average of individual intersegmental airway resistance and because the segment is composed of peripheral and collateral airways. any change in segment resistance can not be presumed to represent a change in collateral airway resistance only. The problem is further complicated by the fact that there is no agreement as to which intrasegmental structure represents the main pathway for collateral ventilation. When the flow of gas into the segment is stopped. pressure in the segment equilibrates with pressure in the remainder of the lung. The time for pressure equilibration can be interpreted to indicate the ease with which the peripheral lung segment could ventilate if the airway was obstructed. The time for equilibration compared to breathing frequency is a measure of the efficiency of collateral ventilation. Yet the equilibration time depends not only on the resistance of collateral pathways at the segment boundary. but the resistance of airways or alveolar pores between the alveoli and the segment boundary and the elastic recoil properties of the segment. So while the time for equilibration can be used to determine if a treatment affects collateral ventilation. it does not indicate where the effect occurred. Even if the peripheral airway resistance or the arrangement of airways were known. additional pressure measurements would be necessary to localize the treatment effect. The shape of the pressure decay provides additional information regarding the mechanical properties of a collaterally ventilating lung segment. Inferences regarding the arrangement of resistive and capacitive elements within the segment can be made by analyzing the shape of the curve. A monoexponential pressure decay signifies that the 38 natural logarithm of the rate of change of pressure is constant. That is: ln dP/dt = k (12) If the decays are always monoexponential it is reasonable to assume that the segment behaves as a homogenous unit. The model of a capacitor discharging through a fixed resistor is then appropriate providing that peripheral airway resistance is negligible. The time for 63¢ pressure equilibration (TC) is then the product of segment resistance and compliance and because TC and segment resistance are measured. segment compliance can be calculated. When the driving pressure for collateral airflow (Ps'Pao) during a decay is plotted against time (t) on semilogarithmic paper. the points appear to fall on two straight lines. Likewise when analytical methods are used to determine the shape of the decay curve. the decays empirically fit the following double exponential equation: —k1t -k2t (PS-Pao)t/(Ps-Pao)t=o = Ae + (1-A)e K1 and R2 are constants which describe the rate of pressure decay and (13) must have units of 1/sec. A and (1-A) are coefficients which indicate the percentage of the total pressure drop ((Ps'Pao)t=O) attributable to each rate constant and must be unitless. The only irrefutable deduction from this is that the segment is nonhomogeneous. The following hypotheses are proposed to explain why the pressure decays are double exponential. Each hypothesis predicts that the coefficients and rate constants represent different physical aspects of the system. There are several ways to determine if a hypothesis is correct. First. the hypothesis must be theoretically sound. Second. the physical values predicted by the rate constants and/or coefficients must agree with 39 independent measurements of the values. Finally. the actual response of the system to a perturbation must agree with the response predicted by the hypothesis. 1. Variable RC due to changes in segment volume If the effective resistance and/or compliance of the segment is not constant but changes during the decay. the rate of decay will not be constant unless they change in equal and opposite directions. Because the volume of the segment changes during the pressure decay. it is likely that the resistance and compliance change because both parameters are volume dependent. The likelihood that compliance varies during the decay is minimized by making measurements over small pressure ranges (3 cm H20) and making measurements at FRC. Around FRC. the lung pressure-volume curve is quite linear. When segment resistance is calculated at different lung volumes. the greatest change in segment resistance occurs at transpulmonary pressures less than 5 cm H20. (Woolcock and Macklem. 1971. Olson. 1978). Double exponential pressure decays are recorded when Ps-Pao decays from 8 to S cm 820. Because changes in segment resistance are minimal over this pressure range. it is unlikely that passive changes in resistance due to changes in segment volume can account for the double exponential behavior. 2. Nonlaminar flow If flow through the segment is laminar. resistance can be calculated using Poiseulle's equation (Equation 9). From this equation it is obvious that resistance is independent of flow rate. If flow through the segment is not laminar. resistance will vary with flow rate. Because flow decreases as driving pressure decreases. resistance would change resulting in multiphasic pressure decays. Alternately. if flow in the airways just distal to the catheter is turbulent and laminar in 40 the more peripheral airways due to the increase in cross sectional area. transition from turbulent to laminar flow following flow interruption could cause biexponential pressure decays. The reasoning is as follows. If flow is turbulent. when gas is flowing through the segment. a portion of the.pressure is dissipated in random movement of the gas molecules. When flow is interrupted. the velocity of the molecules falls and flow becomes laminar. resulting in a rapid decrease in pressure. The coefficient of the larger k indicates the magnitude of the pressure dissipated as turbulence. Decreasing the kinematic viscosity of the gas would increase this coefficient because more turbulence would result at the same velocity. 3. Significant peripheral airway resistance If the peripheral airways just distal to the catheter have a significant resistance and capacitance. and their time constant is significantly different than the time constant of the segment parenchyma and collateral airways. pressure decays will be biphasic and the segment can be modelled as two series RC circuits. The coefficients will then equal the resistances of the two compartments and k1 and k2 will equal the inverse of the time constants (TC) of the two compartments. The time constants will equal the product of the resistance and compliance of each compartment (Olson and Robinson, 1980). u. Nonhomogeneity of RC units An alternative way of characterizing the segment is to regard it as a collection of fixed resistive and capacitive units. A monoexponential pressure decay indicates that the time constants of the units are identical. Double exponential pressure decays will result if there are two populations of units. one with an average rate constant equal to k1 and one with an average rate constant equal to k2. The coefficients. A 41 and (1-A). indicate the relative size of each population. In this case the rate constants will not necessarily equal 1/RC. but will be some function of the unit resistances and compliances. Experiments reported to date do not differentiate among these hypotheses. The following experiments were designed to test several of the hypotheses. It is postulated that if double exponential behavior is the result of flow dependent resistance. using gases with different physical properties would accentuate the effect. If flow is laminar segment resistance should increase with increases in gas viscosity (Equation 9). If flow is nonlaminar. segment resistance should increase with decreases in gas kinematic viscosity. If biphasic pressure decays are due to a transition from nonlaminar to laminar flow. using a gas with a low kinematic should accentuate the nonlaminar portion of the decay. If double exponential pressure decays are due to the resistance and compliance of peripheral airways between the catheter and collateral airways. the two compartment model of Olson and Robinson (1980) will describe the decay. There are two ways to test this model. The first is to measure pressure at the level where collateral airways begin O 1 _ - 1 _ - (Ps ). (Ps P A should equal P8 P8 and (P8 P (1 A) should ao)t=0 ao)t=O equal Ps'-P . Because this is impractical in intact lungs. the second ao method was devised. If the model is correct. the values for compliance recovered from the model should approximate the static compliance of the lung segment. Furthermore, if the model is correct. decreasing the resistance only of collateral airways should affect the time constant of the slow compartment only. Experiments described in this thesis were performed in bovine lungs in which a static segment pressure volume curve could be recorded and artificial collateral airways created 42 by inserting subpleural needles into the segment. If the model is correct. and there is a significant peripheral airway resistance and compliance between the catheter and the needles. increasing the number of needles in the segment should decrease the time constant of the compartment composed of parenchyma and needles and not affect the time constant of the compartment composed of peripheral airways. Furthermore. if one time constant truly represents parenchymal compliance and needle resistance. increasing the number of needles in parallel should decrease the resistance of this compartment only. Finally. experiments were designed to test the hypothesis that high alveolar CO2 concentrations can prevent the decrease in collateral Ventilation caused by vagal stimulation. These data are analyzed based On the conclusions of the first two experiments. MATERIALS AND METHODS AND RESULTS Protocol 1 Purpose The following experiments were designed to_investigate whether altering alveolar CO2 concentrations in a collaterally ventilating lung Segment changes the response of the segment to vagal stimulation. EXperiments were also performed to determine if beta adrenergic blockade altered the response. Of the 18 dogs studied. 9 were pretreated with DPOpranolol (Group II), and 9 were not (Group 1). Methods &gical Preparation Nine mongrel dogs of both sexes were anesthetized with alpha Chloralose (100 mg/kg iv. ICN Pharamaceutical. Cleveland. OH) and urethan (500 mg/kg iv. Sigma Chemical Co.. St. Louis. MO) and paralyzed With ‘succinylcholine (20 mg iv, Sucostrin. E.R. Squibb Sons. Inc.. Princeton. NJ) to prevent spontaneous ventilation during data collection. A femoral artery catheter filled with heparinized saline and connected to a pressure transducer (P23Db. Statham Instruments. Hato 39?. PR) monitored arterial blood pressure and a femoral vein catheter pet"mitted the infusion of supplemental anesthetic and relaxant. Figure 1 18 a schematic drawing of the experimental set-up. An esophageal balloon was placed in the middle to distal third of the esophagus and connected to the negative side of a differential 43 44 .Loumassaum nmmcu m no“: coumflsewum mm: o>coc mamm> HmoH>Loo one .Lowzamcm moo nocumcmcw no sea: nocouficoe aflmsoscwpcoo mm: moo ucoocoa can Loumafiuco> nem>cmm m no“: woumHHuco> ocoz mmcsa one .Louosonh a no“: commaswoc mm: Sesame» on» one“ oncomonocoen on» smsocnu 30am nmo .Loamm omfiuamcom usmfifl co voueoooe new memosoncmep oesmmoca ammucwmoemfio new: vocouacoe was: A m1 mv pcoemom on» mmocom oo:ocommfio oesmmoca on» new A m1 av ocsmmoea hechEHSchmca .wcza woo Lo accewom mcflumaflpco> xaamLOpmHHoo a mo moflucoaoeq Hmowcmnooe on» ceaseouoo on com: pcoeafiaao mo scapmpconoeaoe ofiumsonom .P oezmfim 45 a shaman zooxzfioxeal 209%: zoxsq 20 VoOO|1 mm< mo...<.:._.zw> maoomozozomm . ¢H>._scillating pressures of variable frequencies applied to the flask. The :frequency response of the system was adequate to 1 Hz. The 90% response time of the system was computed by placing an air filled balloon over ‘bhe bronchoscope tip. Pressure was recorded as the balloon was burst twith a lighted match. Ninety percent response time was 70 msec. .Second. the bronchoscope was connected to a piece of polyethylene tubing 10f sufficient length so that a 3 cm 820 difference could be generated between Ps and atmospheric pressure (Pat ). Flow through the bronchoscope and tubing was adjusted until Ps-Patm = 3 cm H20. Flow was abruptly discontinued by turning the stopcock and the Ps'Patm pressure decay recorded on light sensitive paper. Ninety percent response time was 80 msec. Qperimental Protocol The mechanical properties of a collaterally ventilating lung segment E'Qre determined by a modification of Hilpert's method. Figure 2 is a .>\Aomm1mmv mm commasoamo no: ucoewom mesa on» :HspH3 mzmzmmm mo Am may oocmpmwmoc woman annoum .oeou o» cosmoou monocomufio mesmwMLa on» ma coucoooe mm: mm m can xoooqoum m mcflccsu hp oopazeeoucfl mm: 30am .m ucfioa »< .A av 18 mcficoqo zmzcfim on» new A my oncomonocoen on» no am» on» coozuon cocosommao o I 50 m m :Hmucfims .4 on ooumsnum no: A>v 30am .n was m mucfioa p< .LOpoeonm m mH> same now m scam oaoononocoen on» smsoenp newsman on» cue“ oozoah mmo .wc3H moo no acoemom mcwumafipco> maamcopmaaoo O CO moHaLoqoLa HmoHcmnooe on» ocfiscouoo on com: acoeafisao on» mo cofiumpcomoeaos ofiumsosom .m oesmfim 49 O\OO_ Noosxmos finkngodm N GHDWHK mmoowoxozomm 50 schematic representation of the method. The bronchoscope was wedged wi th gas flowing down the suction port at a low flow rate. I attempted to wedge the bronchoscope in the right upper lobe because of the long time constant and minimal cardiac oscillations in that lobe. When this was not possible. due to variations in the size of the lobar bronchus. Other lobes were studied. The bronchoscope was determined to be securely wedged when PS-Pao rapidly exceeded 3 cm H20 and the pressure difference between Ps and Ptp was out of phase when the dog was Ventilated. The mechanical properties of the lung segment were determined by shutting the ventilator off. permitting the lungs to deflate passively to functional residual capacity (FRC) and infusing gas down the bronchoscope at a flow rate sufficient to create a steady 3 cm H20 difference between'the lung segment and the remainder of the lung. The flow rate was recorded and the stopcock at the suction port turned manually to interrupt the flow of gas into the segment. The Ps-Pao difference was recorded as it decayed to zero as gas left the segment t:hrough collateral airways. Steady state resistance (Rss) of airways between the bronchoscope 131p and the trachea was calculated as: RSS = (PS-Pao)/V (13) lBecause of the large cross sectional area of airways between the trachea sand the external boundary of the collaterally ventilating lung segment Eind the low flow rate through them. Rss predominantly reflects the resistance of airways between the bronchoscope tip and the external bOundary of the segment (Robinson and Mukhtar. (Abstract) 1977). Measurements of R88 and pressure decays were made in triplicate with each gas mixture. The order in which the gas mixtures were tested was Var‘ied. Between each gas mixture. 200 m1 of the test gas was infused 51 into the segment while the animal was ventilated. Estimating the average segment size to be about 50 ml (Woolcock and Macklem. 1971. Menkes et al.. 1973. Robinson and Milar, 1980). this procedure flushed the segment with about four times it's volume. After control measurements were taken. the vagus nerve on the same side (ipsilateral-IL) as the lobe containing the bronchoscope was sectioned and the distal end placed over silver electrodes in a plexiglass chamber containing warmed mineral oil. The nerve was stimulated (SD-9, Grass Medical Instruments, Quincy, MA) electrically and voltage was adjusted so that stimulation stopped the heart (5-7 Volts, 30 Hz, 3 msec). The contralateral (CL) nerve was left intact so tzhat the bronchoscope could be placed in the opposite lobe and the study r‘epeated if necessary. Measurements were made with each gas mixture in 1:riplicate alternating between a measurement with the nerve cut and with the nerve stimulated. The order in which the gas mixtures were tested was varied . The decay in Ps-Pao following the interruption of gas flow into the segment was analyzed by a generalized nonlinear curve fitting procedure. Between 8 and 90 points were sampled from each curve by a digitizer (Graf Pen, Science Accessories Corp.. Southport, CN) interfaced to a digital computer (PD? "/3“, Digital Equipment Corporation, Maynard. NA). The frequency with which points were sampled was determined by the dog's heart rate. Points were sampled during the same phase of each heart beat . This time was determined by noting where Ps'Pa was zero 0 during heartbeats after the decay was complete. A similar sampling frequency was used during vagal stimulation when the heart was stopped. The computer transformed and scaled the points for subsequent analysis by the curve fitting routine (DATFT2 - P. Sorenson, 1980) Curves were fit as declining double exponentials to the following equation: 52 -kx -kx y=Ae1+(1-A)e 2 The specific form of the equation is: (15) -k1t -k2t (P —P ) =(P -P ) A6 + (1-A)e (16) s ao t 3 ac t=0 : The time for pressure to decay by 901 (t = 0.9) was computed by a computerized iterative procedure using the parameters of the double eXponential curve fit. This improved the precision of the measurement by making extrapolations by eye between heartbeats unnecessary and improving resolution when the rate of decay was slow. P rotocol 2 Protocol 1 was repeated in an additional 9 dogs which had been pretreated with propranolol (Group II). The efficacy of beta blockade was determined as follows. The anesthetized dogs were injected with a bolus of isoproterenol HCl (Isuprel, 0.2 microg/kg iv, Sterling Drug Inc.. New York, NY). Heart rate was monitored from standard ECG leads (Foregger Forescope, Space Labs, Inc.. Chatsworth, CA). Peak changes in heart rate and blood pressure were recorded. Of 9 dogs tested, heart r‘ate increased 821 and mean blood pressure fell 50%. A bolus of Propranolol was injected (dl-propranolol HCl, 2.0 mg/kg iv. Sigma Chemical Co.. St. Louis, MO) and the isoproterenol test repeated. Heart I"ate now increased only 1:: and blood pressure fell 3% indicating effective beta adrenergic blockade. A half dose of propranolol was adulinstered every half hour during data collection. At the end of the experiment the isoproterenol test was repeated. Heart rate increased 6% and blood pressure increased 11 confirming beta adrenergic blockade. 53 D ata Analysi 3 General The analysis of variance (ANOVA) tables and the results of the r-eegression analyses for all protocols are presented in Appendix B. Significance was determined at P<0.05 in all cases. grotocols 1 and 2 Steady state resistance and T90 from the 18 dogs were each analyzed using a completely random, split plot, three factorial ANOVA with Sampling. This design permitted the evaluation of vagal effects, CO2 effects, and interaction between vagus and 002, vagus and propranolol, and C02 and propranolol. Because $002 is a continuous variable the effect of 602 on R33 and T90 for all vagal states (intact, cut, Stimulated) was determined by regression analysis using the method of Orthogonal polynomials. Because three levels of 002 were tested, linear and quadratic regressions were performed and the variance of each tested against random error. A significant 1" statistic indicates which regression, linear or quadratic, best fits the data. If neither regression is significant, it is concluded that changing CO2 Concentration did not affect Rss or T90. Because the three vagal states represent three discrete variables, 1~”J"eatment differences were determined by the least significant difference (LSD) procedure. Within each group of 9 dogs, for a given 1eVel of 002, the effect of vagal sectioning and stimulation was determined using a least significant difference (LSDW) computed from the 8leplot error mean square of the ANOVA. 54 The effect of propranolol for a given vagal state and C02 level was determined by computing an LSD using a weighted average of the whole plot and subplot error mean square (LSDa). For a given level of C02 and vagal state, if the difference between the value for Group I and Group II was greater than or equal to the LSDa, the effect of propranolol was considered significant. Results: Protocols 1 and 2 The results of the ANOVA's (see Appendix B) indicate that the main treatments, vagus and C02, significantly affected T and Rss' This 90 means that when the variance of all 002 concentrations both before and after propranolol is compared with the random variance, i.e. error, the difference is significant. This significant difference is presumably due to vagal sectioning or stimulation. Likewise when the variance of all vagal states both before and after propranolol is tested against random error variance, the difference is significant - due to C02. The significant second order terms suggest that there is a significant interaction between the effect of the vagus and CO2 and the vagus and propranolol on both T and R33“ This indicates that the 90 response of the parameter to one variable is altered by a change in the second variable. For example, changing vagal tone alters the effect that changing alveolar CO2 concentrations has on the resistance of airways within the collaterally ventilating lung segment. The significant interaction between dog and vagus when the data from both groups are combined indicates that a variable response to vagal sectioning and stimulation occurs among dogs. Because this was anticipated, based on previous experiments, this term was removed from the error term. 55 For both groups of dogs at each level of C02, ipsilateral vagal stimulation increased R88 and prolonged T when compared to control 90 (vagi intact). Vagal sectioning had no effect. This is shown in Figures 3 and u by the asterisks. With the vagus nerves intact or after ipsilateral vagal sectioning, in both Group I and II, changing the concentration of CO2 in the segment did not alter Rss' This was indicated by nonsignificant regressions. During ipsilateral vagal stimulation, in dogs which did not receive propranolol (Group I), changing the concentration of C02 in the segment from 51 to either 0% or 12% increased R33. This was indicated by a significant quadratic regression of R88 against C02 and is depicted with a "Q" in Figure 3. In contrast, in dogs pretreated with propranolol (Group II). increasing C02 concentration in the segment from OS to 5% and to 12% decreased Rss‘ This was indicated by a significant linear regression of Rss against CO and is depicted with an "L" in Figure 3. 2 When Rss was compared between groups at each of the 9 treatments, the only significant difference was during vagal stimulation with 0% C02 flowing into the segment. This suggests that propranolol had no effect on the effect of vagal stimulation when 51 and 121 C02 was flowing into the segment. This difference is indicated with a star in Figure 3. Comparing the curves of RSS against C02 with the vagi intact, after ipsilateral sectioning and during ipsilateral vagal stimulation for Group I indicates that they are similar in shape. It is only at high levels of vagal tone that the CO effect becomes pronounced enough to be 2 significant by regression analysis. There was no significant linear or quadratic regression of T90 against CO with the vagi intact or after ipsilateral vagal sectioning. 2 This suggests that changing CO2 concentration in the collaterally Figure 3. 56 Steady state resistance (Rs ) of airways in a collaterally ventilating segment of dog fung as a function of ICC flowing into the segment. Closed symbols represent {he average of 9 dogs which did not receive propranolol (Group I). Open symbols represent the average of 9 dogs pretreated with propranolol (Group II). Squares represent R8 with the vagi intact, circles represent Rs with the ipsilateral (IL) vagus nerve sectioned, and triangles represent RS during electrical stimulation of the IL vagus nerve. Asterisks indicate the R 3 during IL stimulation differed significantly from R8 with the vagi intact in both groups of dogs. The star inaicates that R 3 during IL vagal stimulation in dogs which did not receive propranolol was significantly greater than R during IL stimulation in dogs which were pretreated with propranolol when 01 CO was flowing into the segment. The "Q" signifies that the regression of R during vagal stimulation against 1C02 was significantly quadratic in dogs which did not receive propranolol. The "L" signifies that the regression of R during vagal stimulation against 100 was significantly linear in dogs which were pretreated with propranolol. LSD indicates the least significant difference to be used when comparing values of R within a group for a given level of CO . LSD indicates {fie least significant difference to be used when comparing values of R between groups for a given level of CO2 and vagal state. Significance was determined at P<0.05. Rss (cm HZO/mI/sec) 57 ' intact ° IL sectioned Group I ‘ IL stimulated 0 intact 0 IL sectioned : Group It A IL stimulated 3.0-“ " ’5 2.0- \ *L LO" \//Q 00 I I 1 LISDw L300 0 5 I2 °/o CO2 Figure 3 Figure u. 58 Time for 90% pressure equilibration (T 0) between the collaterally ventilating lung segment and the remainder of the lung as a function of $00 flowing into the segment. Closed symbols represent the average of 9 dogs which did not receive propranolol (Group I). Open symbols represent the average of 9 dogs which were pretreated with propranolol (Group II). Squares represent T O with the vagi intact, circles represent T with the ipsilateral vagus nerve (IL) sectioned and triangles represent T during electrical stimulation of the IL vagus nerve. sterisks indicate that T 0 during IL vagal stimulation was significantly greater t an T with the vagi intact in both groups of dogs. The star iggicates that T during 11 stimulation in dogs which did not receive propranolol than T during vagal stimulation in dogs which were pre reated with propranolol when 121 CO was flowing into the segment. The "Q" signifies that the regression of T 0 during IL stimulation against $C02 was significantly quaaratic in dogs which did not receive propranolol. The "L" indicates that the regression of T 0 during IL stimulation against 1C0 was significantly linear in dogs which were pretreated with propranolol. LSDw indicates the least significant difference to be used when comparing T within a group of dogs for a given level of CO . LSD iggicates the least significant difference to be used when comparing T90 between groups for a given level of CO and vagal state. Significance was determined at P<0.05. 59 IIintact ( 'IL sectioned ' Group I ‘ IL stimulated ) ° intact ’ ( 0 IL sectioned AIL stimulated ) Group III T90 (sec) 45 9 * ,. 20- \fi 4 LSD LSD o.o . I . " ° 0 5 :2 %c02 Figure 4 60 ventilating lung segment had no effect on T90 in either group for these vagal states. The regression of T90 against CO2 in Group I was significantly quadratic and is indicated with a "Q" in Figure ll. In Group II the regression of T90 against 002 was significantly linear and is indicated with an "L". When each of the 9 treatments was compared between Groups I and II, the only significant difference was during vagal stimulation with 12% CO2 flowing into the segment and is indicated by a star in Figure ll. This suggests that propranolol only affected T90 when 12% was flowing into the segment. Protocol 3 Purpose This experiment was designed to determine if flow through the segment is laminar or nonlaminar and to determine whether the biphasic pressure decays are the result of transition from nonlaminar to laminar flow. Measurements were made at three transpulmonary pressures and during vagal stimulation using gases with different physical Properties to determine if these factors potentially altered the relative distribution of laminar to nonlaminar flow. Methods Five mongrel dogs were surgically prepared as in Protocol 1. The bronchoscope was wedged in a peripheral bronchus and both cervical vagi Were sectioned. The flowmeter was connected by a stopcock manifold to 61 gas tanks containing 100% N2, 100% He, and 100% SF6. The density, viscosity and kinematic viscosity of these gases are presented in Table 1. Table 1. Physical Properties of He, N2, and SF6 .112. fig _S_F6 Viscosity 19N.1 178.1 133.0 (micropoise) Density 0.18 1.25 6.60 (gm/1) Kinematic viscosity 1078.3 192.5 20.2 (centistoke) The position and volume of the esophageal balloon were adjusted so that P = 0 cm H20 at FRC. The transpulmonary pressures recorded are tP therefore not absolute but relative to transpulmonary pressure at FRC. They are misleading because at FRC transpulmonary pressure is usually about 5 cm H20. For this reason, transpulmonary pressure is referred to as FRC, FRC + 2 cm H20, and FRC + u cm H20. Steady state resistance of the lung segment was determined and Ps-Pao pressure decays recorded for each gas when Ptp = FRC, FRC + 2 cm H20 and FRC + u cm H20. The steady state resistance of airways within the segment was computed as (PS-Pao)/V. All pressure decays were digitized, transformed, normalized and scaled as in Protocol 1. The resulting points were fit as declining ciouble exponential functions (see Equation 16). The ratio of the <>oefficients, (A)/(1-A). was calculated. A is the coefficient of the exponent with the largest k and (1-A) is the coefficient of the exponent "1fith.the smallest k. This ratio was calculated to determine if 62 decreasing the kinematic viscosity of the gas flowing through the segment increased A only, as hypothesized. The three gases and three transpulmonary pressures were tested in a double Latin Square design. Additionally segment resistance and pressure decays were determined for each gas at FRC during ipsilateral vagal stimulation. Most measurements were made in triplicate and the results averaged. Data Analysis This experiment yielded two results which were analyzed separately. When this experiment was designed, I intended to use a complete randomized block, two factorial, ANOVA to analyze the results. One factor was to be transpulmonary pressure at three levels, FRC, FRC + 2 cm H20, and FRC + u cm H20. The second factor was to be gas density at three levels, 0.18 micropoise for He, 1.25 micropoise for N2, and 6.6 Inicropoise for SF6. I reasoned that it was important for geometric considerations to keep the distending pressure across the collaterally ventilating lung segment constant and so flow rate was adjusted for each gas such that Ps-Pao = 3 cm 820. When analyzing the data, it became clear that flow rate WAS a critical factor. The logic is as follows: The different density gases were used to determine the pattern of flow through the segment. It was anticipated that the pressure-flow l"elationship in the segment would be quadratic like Rohrer had predicted for the whole lung. The quadratic equation is: _ 2 (PS-Pao) - k1V + k2V (17) Dividing through by V yields: R + kzv (18) as = R1 This equation can be further reduced to: 63 where k3 and ku are dependent on airway geometry. If flow is laminar, changing density (p) or flow (V) should not alter R but decreasing ss’ viscosity (u) should decrease Rss' Conversely, if flow has any nonlaminar component, altering the product of gas density and flow rate should alter segment resistance. Because flow was not constant for a given gas at each transpulmonary pressure tested, the factorial analysis could not be used. Rather, the results of the effect of gas density and transpulmonary pressure were analyzed as a complete randomized block, one-way ANOVA with 9 treatments (see Appendix B). Because the pressure decays at FRC + 2 cm H20 and FRC + u cm H20 were too rapid to be analyzed in one dog, the results are based on four dogs only. It was still legitimate to partition the treatment effects using regression analysis. The regression of A/(I-A) and R88 against the product of gas density and flow was calculated for each transpulmonary pressure. Because the flow rate required to create a 3 cm H20 Ps-Pao difference changed with gas density and transpulmonary pressure, flow rate was averaged over all dogs for each gas at each transpulmonary pressure. The average values are presented in Table 2. These flow rates were multiplied by the density of the gas and orthogonal polynomials for linear and quadratic regression computed from the results. The regression of A/(1-A) and R88 against transpulmonary pressure was calculated for each gas. Significance was determined at P<0.05 in all cases. 64 Table 2. Average Flow in ml/min of He, N , and SF Necessary to Create a 3 cm H 0 Difference Between the Lung Segment and the Airway Opening At Three Transpulmonary Pressures -£tp '53 '52 §E6 FRC + u cm H20 #66 (“02) 521 (53“) 330 (332) FRC + 2 cm H20 399 (396) 918 ("28) 290 (331) FRC 353 (399) 315 (352) 239 (287) mean (SD) [1:11 Because the levels of transpulmonary pressure tested were equally spaced, i.e. FRC, FRC + 2 cm H20 and FRC + u cm H20, the orthogonal polynomials for the linear and quadratic regressions of A/(1-A) and RSS against transpulmonary pressure were looked up in standard tables (Steel and Torie, 1960). The variance of the linear and quadratic regressions were tested against random error, i.e. error mean square. A significant F indicated the best curve fit and indicated that the parameter changed predictably with transpulmonary pressure or the product of gas density and flow. If there was no significant linear or quadratic regression, it was concluded that altering the product of gas density and flow or transpulmononary pressure did not affect A/(1-A) or 833' The second part of the experiment was designed to investigate the effect of vagal tone and gas density on steady state resistance and A/(l-A) at FRC. Data for all five dogs are included and analyzed with a complete block, one-way ANOVA with 6 treatments (see Appendix B). Because the variable response to changes in vagal tone among dogs was anticipated, this component was not included in the error term. 65 Because vagal stimulation is a qualitative, discrete variable, an LSD was computed and used to determine the vagal effect. For a given gas, if Rss stim - R33 cut was greater than or equal to the LSD, the difference was considered significant. The effect of the product of gas density and flow on RSS and A/(1-A) for each vagal state was assessed by regression using the method of orthogonal polynomials. The average flow rates were computed and multiplied by gas density. Average flow rates are presented in Table 3. Orthogonal polynomials for linear and quadratic regression were computed from these results. Table 3. Average Flow in ml/min of He, N , and SF Necessary to Create a 3 cm H 0 Difference Between the Lung Segment and the Airway Opening After Bilateral Vagotomy and During Stimulation of the Ipsilateral (IL) Vagus Nerve, at Functional Residual Capacity. .QEE Bilateral Vagotomy IL Vagal Stimulation He 299 (366) 119 (128) N2 271 (320) 111 (121) SF6 203 (262) 99 (121) mean (SD) n=5 The results of the regression of steady state resistance against the product of gas density and flow with the vagi sectioned and during ipsilateral vagal stimulation were assessed as stated above. Results The results of this study are most clearly understood by examining Figure 5 which shows that steady state resistance decreased as viscosity Figure 5. 66 The effect of gas viscosity (u) in micropoise on the steady state resistance (R ) of airways in a collaterally ventilating segment of dog lung at three transpulmonary pressures (Pt ). Each point represents the average of u dogs. The quares represent results at functional residual capacity (FRC) after bilateral vagotomy, the triangles represent results at P = FRC + 2 cm H 0 after bilateral vagotomy. and the circlgs represent results at FRC + u cm H 0 after bilateral vagotomy. The diamonds represent results at FRC during stimulation of the ipsilateral vagus nerve. R 33 (cm HZO/mI/sec) 3.0 -' 2.0 -‘ 1.0- 0.0 -' 67 I; - FRC - IL stimulated p F) tp lip! FRC '1' 2 cm H20 VOOOIOITIY P I FRC +4301“ H 0 tp 2 . FRC ) l r. 1 IOO 150 200 p (micrOpoise) Figure 5 68 increased. Because Poiseuille's equation (Equation 9) predicts that resistance increases as viscosity increases, it is clear that flow through the segment is nonlaminar. The results of the ANOVA comparing the effect of altering transpulmonary pressure and gas density and flow on steady state resistance indicate the treatment effect to be significant. The regression of R88 against the product of gas density and flow is linear when transpulmonary pressure equaled FRC. This is represented by an "L" in Figure 6A. Because the F ratio progressively increased from FRC + u cm H O to FRC, I conclude that decreasing segment volume by altering 2 transpulmonary pressure increased the effect of density and flow on steady state resistance. Increasing gas density and flow increased the dependency of steady state resistance on transpulmonary pressure as evidenced by the linear regression of RSS against transpulmonary pressure with N2 and SF6. This is represented by HL'" in Figure 7. The ANOVA examining the effect of the product of gas density and flow and transpulmonary pressure on A/(1-A) indicates that there is no significant treatment effect, suggesting that the treatments affected both coefficients equally (see Figure 6B). The results of the regression of steady state resistance against the product of gas density and flow with the vagi sectioned and during ipsilateral vagal stimulation are presented in Figure 8A. At all gas densities and flow rates, vagal stimulation increased steady state resistance. Additionally, increasing vagal tone potentiated the effect of the product of gas density and flow on Rss' Comparing Figure 8A to Figure 6A, it appears that Rss during vagal stimulation was the high end of a family of curves. At a high transpulmonary pressure, steady state resistance was small and not density dependent. As transpulmonary 69 .mo.ovm um confisgouoc no: oocoofiuwcwfim .omm um Loocfia hflpcmofiuwcwuo no: pa awesomm a no :onooLmoL on» own» moauacmfim :4: one .mmoo a no owmmo>m on» mucooocmwu ucaoa comm .zsouomm> Hmcouoaan . 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(OOSAUI/OZH um) "a Figure 7. 71 The effect of transpulmonary pressure in cm H O on the steady state resistance (Rs ) of airways in a collaterally ventilating segment of dog lung when helium (He). nitrogen (N ) or sulfur hexaflouride (SF ) was flowing through the segment after bilateral vagotomy. Each point represents the average of u dogs. Squares represent results when He was used, triangles represent results when N was used and circles represent results when SF was used. The "L"s signify that the regression of R against transpulmonary pressure was significantly linear when SF or N was flowing into the segment. Transpulmonary pressure is represented as being zero at FRC, 2 cm H O at FRC + 2 cm H O, and u cm H20 at FRC + u cm H20. Significance was determined at P<0.05. IHe A N 0 Sfi; 1.5- ‘3 L0- L 1’ S E 3 f” L g 0.5- a 0 m 0.0 l I l O 2 4 TRANSPULMONARY PRESSURE (cm H O) 2 Figure 7 73 .mo.ovm ow nonsenouon omm oocwofiuacmam .Aamqv oocogoumwn unwowhacmflm unwoa on» so nocssaopon mw ssouomw> Loumw m on nocwaeoo m nowwogocs saucwofiwacmfim coapwassfium 4H awn» ouonn:« oxosgoumw one .wmon m so owwco>w on» nucomogaog pesos nowm .sosowawo sznflmog choHuocsm aw o>Loc oamw> AAHV ngouwasmnu on» so casuwasssuw weapon new seapomw> Hweouwawn Lopmw noncowogq oLw ouaswom .swoon on» so cosucoa :on on» weapon nouwawmwfln ogswooca on» nucomocqoc <1~ ncw swoon on» so coaueoa nfiqwn on» wcagan nopwawwnwn ogswwoca on» nucowocaoa < .sm Hocwmv coHuascgoucs 30am Louhw swoon ousmmoeq on» wcflnsuowon coupwsco Hwapcoconxo oHnson on» so nucoaoahmomw on» so oHqu on» new s< Hocwmv mesa won mo acoEmom wcduwflfiuco> sHHwLouwaHoo w :H mswxgsw mo A m0 oocwunfimog oawum snwoum oz» no H\Ew ca A00 suflwcon mww new :fie\Hs :H Ape 30am so uosnogq on» no uoommo och M” .w ossmam 74 000. £535.53 000. b i 000 w ouswwm 0 0.0 0.0 (v-I)/v E55553 >00 000. 000. 000 p - r em; I \.\ 8.835... ... 4 2.3302. c 0.0 C) “I (”SAW/02141113) "a 75 pressure decreased, R88 increased and became density dependent. Vagal stimulation increased RSS and the effect of gas density on Rss' The results of the ANOVA indicate that vagal tone and the product of gas density and flow did not alter A/(l-A). This is represented in Figure 8B. Because there was no significant treatment effect, regressions were not done. Protocol u Purpose The purpose of this study was to determine if biphasic pressure decays were due to significant peripheral airway resistance and compliance between the wedged catheter and the collateral pathways. Methods Surgical Preparation Four one week-old Holstein bull calves (approximately 95 kg) were anesthetized with intravenous thiamylal sodium (500 mg, iv, Surital, Parke Davis, Inc., Detroit, MI) and paralyzed with succinylcholine (22 mg/kg, iv). The trachea was exposed and cannulated with a three way connector. Because it is difficult to reinflate bovine lungs if they remain collapsed for even short periods of time, the lungs were ventilated and positive end expiratory pressure maintained during the surgery. One side of the connector was clamped and the other side connected to a fixed-volume ventilator set to deliver a tidal volume of 750 ml. A vacuum cleaner controlled by a rheostat was connected to the exhaust port of the ventilator so that variable positive pressure could be applied to the lungs. 76 The animals were exsanguinated by severing the carotid arteries and the heart and lungs were carefully removed. The heart and lungs were floated in a large water-filled basin and covered with moistened gauze to prevent drying. Lung Volume and Pressure-Volume Curve Transpulmonary pressure was measured by connecting the positive side of a differential pressure transducer to a needle tipped catheter in the trachea and leaving the negative side open to atmosphere. Pressure transducers were calibrated daily against a water manometer and pressures recorded on light sensitive paper. After three consecutive inflations to Ptp = 30 and deflation to = 5 cm H O a 1500 ml syringe filled with 60 ml helium and 700 ml air Ptp 2 was connected to one port of the tracheal connector and the other port was clamped. The lungs were ventilated 20 times with the syringe which was then removed. The concentration of helium in the syringe was determined with a helium analyzer (Warren E. Collins, Inc., Braintree, MA). Lung volume (V1) at Ptp 5 cm H20 was calculated by the following formula: = (VSCHe - CHe )/CHe (20) 1 2 2 is the concentration of helium in the syringe before 1 where CHe1 ventilating the lungs (60/760) and C is the concentration of helium He2 in the syringe after ventilating the lungs. V8 is the volume of the syringe. No correction was made for connector volume. After three consecutive inflations to Ptp = 30 and deflation to Ftp = 0 cm H20, a static pressure-volume curve of the lungs was obtained. Because the lungs were excised, 0 cm H20 represents minimal volume. The 1500 ml syringe was connected to one port of the tracheal connector and the other part clamped. 1N00 ml air was added to the lungs in 200 ml 77 steps and then withdrawn in 200 m1 steps. Transpulmonary pressure was recorded during inflation and deflation. A pressure-volume curve was constructed by plotting cumulative volume added and withdrawn against tranpulmonary pressure at zero flow. A double lumen polyethylene catheter (flared tip = 0.5 cm) was advanced via a sidearm of the tracheal connector down the trachea until it became securely wedged in a peripheral airway, isolating the segment of lung distal to it. Transsegment pressure (PS-P80) was measured by connecting the inner catheter to the positive side of a differential pressure transducer and a needle tipped catheter in the trachea to the negative side of the transducer. The outer lumen of the catheter was connected to a stopcock through which known volumes of air could be injected with a 30 ml syringe. The catheter was assumed to be securely wedged when a transsegment pressure of 25 cm H20 could be maintained. Additionally when the segment volume was reduced and the remainder of the lungs ventilated, no air appeared to enter the segment confirming it to be isolated from the remainder of the lung. For data collection P8 was measured relative to atmospheric pressure (Patm) because air from the segment entered the room, not the remainder of the lung. A pressure-volume curve of the segment was recorded in the same manner as that of the lung using a 30 ml syringe. 25 ml was injected in increments of 5 ml and then withdrawn in increments of 5 ml and Ps-Pa0 recorded. Segment volume was determined, like lung volume, by equilibrating a 30 m1 syringe containing 5 m1 helium and 25 ml air with the segment. Segment volume was corrected by subtracting the dead space of the catheter (Vd = u ml). Catheter dead space volume was determined by filling the catheter with a measured volume of water. 78 Segment Resistance To evaluate the effect of decreasing a resistance in series with segmental airway resistance the following protocol was followed. The outer lumen of the catheter was connected to a rotameter which was connected to a gas tank containing 5% CO2 95% 02. A 7 mm length of 21 g needle was inserted through the pleura of the segment and affixed with cyanoacrylic glue (Elmer's WonderBond). The flow of gas down the catheter (V) was adjusted until a 30 cm H20 difference existed between the segment and atmosphere. The gas entering the segment left through the subpleural needle (see Figure 9). Gas flow was abruptly interrupted by turning a stopcock and the subsequent decay in PS-P recorded. The atm combined resistance of the airways and the needle was computed as: R = (P -P )/V (21) The same procedure was repeated for Ps-Pa m = 20 and Ps—Pa - 10 cm t tm ’ H20. A second needle was inserted and glued into the segment and the protocol repeated. The entire sequence was repeated after up to 14 needles had been sequentially inserted into the segment. Transpulmonary pressure was maintained at 5 cm H20 (approximately FRC) throughout the experiment. Data Analysis Segment pressure-volume curves were constructed by plotting cumulative volume added and withdrawn against pressure. Points were digitized from the deflation limb of the pressure-volume curves and used to compute an average compliance (AV/AP) from Ps-Patm = 0 to 10 cm H20 (C10), 0 to 20 cm H20 (C20) and 0 to 30 cm H20 (C30). Specific compliance was calculated as C10/segment volume. 79 .wueoeoeswwoe Haw N so ooe on» ewsoee» ueoewom meaeen o I so m pw noefiwpemmm mm: wmv oeswmoea weseoeo swzes< .moaww m on» uuoa wwm mw noneoooe m1 s new noeefiueoomfin eon» ow: 30am .A my oeoeemospw new s as as» eouoeuwo on» eoozuoe nouwfixo ooeoeouefln oeemmoee uewumeoo w HHuee eouoezoflm w ea“: nonmennw ow: 30am .peosmow on» one“ Loaoeuwo on» no eoEeH Lopeo on» emeoeeu sew» mwm w sons nozoam moo am mo «ma .noesseouon ooewumfimoe neoemoo new ueoEmom one cues nopeowes eon» oeo: moanooz .omeaesw as om w wean: eouoepwo eossa oaneon nownoz w on kumfln mesa meo nomaoxo so ueoEwoo w mo oeeao> new o>eeo oeeHo>Ioeewwoee on» neoooe on now: neoeefieao on» so eofipwpeowoeeoe ofipwsoeom .m oeswfim 80 9 30 °/. gej 203 °/. “=‘L m02.¢>m mwkm 2301.“.— m ouewam 81 The pressure-volume curve of the whole lung was constructed by plotting volume against transpulmonary pressure and compliance (C) computed as the slope of a line drawn tangent to the deflation limb at Ptp = 5 cm H2 compliance by lung volume. 0. Specific lung compliance was computed by dividing . The pressure decays following flow interruption were digitized and the resulting points were transformed, scaled. normalized by dividing (Ps'Patm)t by (Pa-Patm)t=0’ and analyzed by a generalized curve fitting routine. The curves were fit to the following single exponential equation y = e‘kx (22) Assuming Hilpert's single fixed RC model this equation may be rewritten as: _ -(1/TC)t (Ps-Patm)t ' (Ps Patm)t= 0e (23) The normalized form of this equation is: (PS -9 ) /(ps 9 > - MW“)t (24) atm t atm t=0 ' Compliance (Csing) was computed as TC/Rss’ Secondly, the points were fit to the following double exponential equation: -k1x -k2x y = Ae + (1-A)e (25) Assuming the two series fixed RC compartment model of Olson and Robinson (1980). this equation may be rewritten as: (Ps atm)t/(Ps ”Patm t=0 z -(1/TCf)t -(1/TC8)t + (R /R )e (26) 3 ss ) (Rf/Rss)e The time constants and resistances of the two compartments were derived from this equation (see Appendix A). 82 The compliance (Cf) of the compartment with the faster time constant was computed as TCf/Rf and the compliance (C8) of the compartment with the slower time constant computed as TCs/Rs’ From the methods outlined above, compliance was calculated in three ways: ;. €10, C l9(,mcég‘; :::m the static P-V curves of the segment . sin gle exponential curve fit 3. C8 afid Cf from the double exponential curve fit. Because variable numbers of needles were placed in each segment, Csing’ Cs and Cf were analyzed as follows: the compliance values for all 8 segments studied with 1,2,3,u,6,8,10, and 12 needles in the segment were averaged. Because compliance indicates lung elasticity, it was antipicated that inserting subpleural needles would not alter compliance. To test this hypothesis, a linear regression of average compliance against number of needles (N) was performed and an analysis of variance used to determine if the slope was significantly different from zero. A significant F test indicated that compliance varied with the number of needles in the segment (Steel and Torie, 1960). The ANOVA tables are in Appendix B. From the double exponential curve fit of the pressure decays from P P = 30, 20 and 10 cm H20, R88 was partitioned into two components, atm and Rs' Steady state resistance, Rf and R3 for N = 1,2,3,u,6.8,10, 3- Rf and 12 were analyzed by a generalized curve fitting routine. Because resistance was infinite at N = 0, and because at N = a, RSS should approximate airway resistance, the following hyperbolic equation was fit: y = yasympt + A/X (27) For example, specifically the equation for RSS may be written as: (ass)n = (“33)n=. + A/N (28) 83 Values for (R ) . (R ) . (R A A were recovered 88 11:0 8 n=cn ' and A f)n=o' Rf’ Rs Rss from the fit of the curves to the above equation. The parameter "A" indicates the shape of the rectangular hyperbola. Results Compliance The individual segment and lung pressure-volume curves are presented in Figure 10. The results of the analysis of the static pressure—volume curves of the segment and the lung are presented in Table n. For comparison, lung volume and segment volume at Ptp = 5 cm H20, and C Cf and C8 at N = 12 are also presented. sing' C C and C8 are plotted against N in Figure 11. Panel A sing’ f represents results when Ps-Patm = 30 cm H20, Panel B when PS-Patm : 20 cm H20, and Panel C when Ps'Patm : 10 cm H20. An asterisk indicates that the slope of the regression was significantly different than zero at P<0.05. Regressions were significant for Cs at Ps-Patm : 30 cm H20 and Cf and Csing at Ps-Pa m at 20 cm H O. For comparison, C averaged t 2 10 over all segments is represented as a star. Time Constants The time constants derived from the model of Olson and Robinson are presented in Figure 12. Panel A represents the time constant of the fast compartment and Panel B represents the time constant of the slow compartment. 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( l I I. l. O O s l°._l’ Iowan an 9 l a .. w. m. 1 O In F 0 N ... QM on: .5 o. «5...... m a ow: :5 ow “Ev- M. . ow: so on «.5. v . 93 Resistance Steady state resistance, Rf and Rs are plotted against N in Figure 13. Panel A represents results when Ps-Pa = 30 cm H 0, Panel B when tm 8-Patm = 20 cm H20, and Panel 0 when Ps-Pa 2 tm = 10 cm H20. The resistance of a single needle computed using Poiseuille's equation is P indicated with a star for comparison. The parameters and estimates of error for the hyperbolic curve fit of R against N, yasympt and A are presented in Table 5. As predicted, Rs approached zero as N approaches infinity and Rf approached Rss as N approaches infinity. This suggests that R8 is the effective resistance of the needles and Rf is the resistance of the peripheral airways. 4 9 .ow: so op eo oeemmoeo eeosmow w ow noefiseooon oeo: oooewowamom . .om: so om no oeemwoee oeosmow w ow noesseooon oeo: mooewuwamom . .om: so om eo oeemwoee oeosmom w ow noeuseooon oeo: nooewomfimo . no mueoswom o unwoa ow so omweo>w on» woeomoeooe oeaoo oowm .o = so m ow: m .eooaewesoo emu ewom w so nooeonoeooe we oHnooe oamefiw w mo ooewuwhmoe ooh .moewsao so nooeoooeeoe ma A :0 oeosoewasoo 30am on» so ooewomwmoe one new monewHeo so nooeomoeooe as Aemv oeosoewosoo owwm on» no ooewowswoe on» .moHoeHo so nooeowoeooe ms Aowmv ooewowwwoe oowow snwoom .sz oeoswoo one es onnooe no eomsee ooo mo eoflpoeeu w ow eooooowo nomno: w on Hwowsn mesa «Hwo nowfioxo so peoswow w es oow\Hs\o a so eh moHnooe new wswzeww so Ame ooewomsnom v :oHs .es oeewee 102 Ind e. ouewhm 00 a em: as a-.. on ow ow n_ ow m o . . .. ..m o a. a. «a q q a on o . .. .0 o . Iooc . m 0. O O .. -ooo O .0 new Z 88. ”:4 .. o: .. Aux-BOmuLO& (“NU/19‘) AI 103 resistance—density-flow curve increased as transpulmonary pressure, and therefore lung volume, decreased. Vagal stimulation magnified this effect as shown in Figure 8A. For a given transpulmonary pressure it is unlikely that the geometry of the airways changed as the product of gas density and flow increased yet, as shown in Figure 6A, Rss increased. The increase in steady state resistance with the product of gas density and flow became more pronounced as transpulmonary pressure decreased. Therefore, the geometry of the segment changed with transpulmonary pressure to promote eddying turbulence as transpulmonary pressure decreased. Vagal stimulation further accentuated this change. The question still unanswered is how the shape of the pressure decay curve after flow is interrupted is altered by nonlaminar flow through the segment. I hypothesized that if a significant portion of Ps-Pao were due to turbulent airflow in the airways proximal to the collateral pathways, when flow was interrupted and flow rate (and therefore velocity) decreased, Ps-Pao would drop rapidly. If this hypothesis were true, decreasing the kinematic viscosity of the gas should have increased the rapid pressure drop if the flow rate and geometry were the same. Tables 2 and 3 indicate the magnitude of the change in flow rate as transpulmonary pressure, vagal tone, and inflow gas were changed. ANOVA's presented in Appendix B, indicate that flow rate changed significantly with changes in gas density or during vagal stimulation. Examination of Tables 2 and 3 indicates that flow changed by 1001 at most. Table 1 shows that gas viscosity differed by a negligible amount among gases. Table 1 also shows that gas density differed by two orders of magnitude. I conclude that the change in the product of gas flow and 104 density is primarily due to differences in gas density. Based on this conclusion, decreasing the kinematic viscosity of the inflow gas should have increased the rapid portion of the pressure decay, A. Figures 68 and 8B show that the rapid pressure drap, A, did not change relative to the slow pressure drop (l-A), suggesting that double exponential pressure decays are not due to a rapid transition from nonlaminar to laminar flow. Furthermore, examining Figure 14 shows that as flow decreased, resistance decreased. If resistance changed with flow rate only, and compliance was constant, the rate of pressure decay should have increased as Ps-Pao decreased, due to the decrease in flow. The conclusions from these data can be summarized as follows. Flow through a collaterally ventilating lung segment at flow rates at which resistance measurements were made was not laminar nor fully turbulent. Resistance was flow rate dependent but this did not explain the double exponential pressure decays observed when inflow was discontinued because increasing the density of the inflow gas did not increase the magnitude of the rapid portion of the pressure drop. Decreasing transpulmonary pressure altered the geometry of the airways to increase the flow rate and density dependence of steady state resistance. Vagal stimulation also increased the flow-density dependence of Rss' Peripheral Airway Resistance and Compliance as a Case of Double ExponentiagPressure Decays The calf lung experiment was designed to determine the effect of reducing a resistance in series with the resistance of intrasegmental airways. The needles were used to simulate collateral airways. I presumed that the resistance and compliance of the intrasegmental 105 airways was significant. The segment was then analyzed as an analogy of the two series RC circuit model of a collaterally ventilating segment of dog lung proposed by Olson and Robinson (see Appendix A). Three parameters were analyzed using this system, compliance, resistance and time constant. Segment compliance was determined in three ways: 1. from the segment static pressure—volume curve 2. from analysis of the pressure decays assuming the segment behaved as a single fixed RC unit ‘ 3. from analysis of the decays assuming the segment behaved as two series fixed RC units. Pressure decays were obtained in calf lungs by allowing air to leak through needles of known resistance inserted into the segment. The closest approximation to decays in dog lungs would have been to maintain transpulmonary pressure at 5 cm H20 (about FRC). create a 3 cm H20 difference between the segment and atmosphere and record the decay when flow was interrupted. This ideal situation was not possible because isolated segments consistently trapped air. This was probably due to small airway closure, which occurs readily in excised bovine lungs. Pressure decays were therefore measured at a transpulmonary pressure of 5 cm H 0 from P -P = 30, 20, and 10 cm H 2 8 atm 0. Pressure decays were 2 recorded as segment pressure relative to atmospheric pressure because air passed from the segment into the room not into the remainder of the lung. While segment compliance was not constant when the decays spanned C . such large pressure ranges (see Figure 10), I expected that Csing’ s and Cf would represent some weighted average of the segment compliance over each range of pressure studied, comparable to compliance values computed from the segment pressure-volume curve. A cursory examination of the results of this study reveals that the magnitudes of csing' Cf, C8, and C10 are very different (see Table 4). C In addition, C and Cs change with the number of needles in the sing' f 106 segment (N) as shown in Figure 11. To interpret these data correctly however, the assumptions necessary for the calculation of these compliances must be reviewed. Csing is computed by assuming the segment behaves as a capacitor discharging through a resistor. The segment time constant is recorded from the pressure decay and divided by R38 to calculate C The subgross anatomy of the segment must be considered sing' to determine the validity of this assumption. Figure 15 is a schematic diagram of the segment. The unit of lung distal to the last respiratory bronchiole is referred to as a primary lung lobule. A secondary lung lobule is the portion of lung surrounded by fibrous connective tissue. Dog lungs do not have secondary lung lobules. Secondary lung lobules of calf lungs are clearly visible on the lung surface and have a surface area of about 3 sq am. There were roughly 20 secondary lobules visible on the pleural surface of each segment studied. The double lumen catheter was wedged in a subsegmental bronchus. The subpleural needle was inserted into the center of a secondary lobule. The steady state resistance is, therefore, the resistance of only those airways directly between the catheter tip and the needle, including bronchioles and alveolar ducts. Yet when flow was interrupted, all secondary lobules discharged through the single needle as shown in Figure 158. To do so air must have passed from the alveoli back up the airways to the airways in direct line with the needle. The rate at which segment pressure equilibrates with atmospheric pressure clearly depends on the resistance of all airways between the alveoli and the needle. Because the steady state resistance is only a portion of many series and parallel resistances, dividing the segment time constant Figure 15. 107 Schematic representation of a segment of excised calf lung distal to a wedged catheter 0.5 cm in diameter. A. Schematic representation when gas is flowing into the segment and pressure at the catheter tip (P ) is constant. B. Schematic representation when inflow is interrupted. P decays as gas flows from the secondary lung lobules to the atmosphere through a subpleural needle. C. Schematic representation of the segment when segment pressure has equilibrated with atmospheric pressure (Patm)' D. Schematic representation of n secondary lung lobules in parallel in a segment of excised calf lung distal to a wedged catheter assuming that every secondary lung lobules has a subpleural needle and that the resistance and compliance of each lobule is identical. 8 109 by segment resistance to compute the segment compliance overestimates segment compliance. As shown in Figure 11 and Table 4, C is always sing greater than C10. The influence of N on RSS was determined from pressure decays recorded at N = 1.2,3,4.6,8,10. and 12. Figure 13 shows steady state resistance plotted against N for pressure decays from PS-P = 30, 20. atm and 10 cm H20. The curves are clearly hyperbolic. This is reasonable for the following reasons. When N is zero, Rss is infinite because no air can leave the segment. The theoretical condition where steady state resistance equals airway resistance is met at N = o, because the resistance of an infinite number of needles in parallel is zero. At N between one and infinity, steady state resistance decreases as I additional resistances are added in parallel. Until the theoretical limit of each lobule having a needle, (N = k). is reached, steady state resistance will always underestimate the resistance determining the rate of decay. If it is assumed that airway resistance is equal in all compartments, and compliance is equal in all compartments, the limit of N = k can be represented as in Figure 15D. Pressure decays would then be monoexponential. At this limit, the rate of decay will depend on segment compliance and needle resistance. If peripheral airway resistance is very small relative to needle resistance (Rn), then steady state resistance equals needle resistance and segment compliance can be computed by dividing the segment time constant by steady state resistance. If peripheral airway resistance is large relative to needle resistance, steady state resistance will overestimate the resistance determining the decay and saegment compliance will be underestimated. Table 5 shows that at N = m (asymptote), the resistance of the slow compartment (Rs) approached zero and the resistance of the fast compartr that the res resistance c represents ' istherefor compliance state resi could have not monoea The c. the slow segment I this 335' DIOposed °°mpliar reasonal number the ca: airway lobule and tc 110 fast compartment (Rf) approached steady state resistance, suggesting that the resistance of the slow compartment represents the effective resistance of the needles and the resistance of the fast compartment represents the effective resistance of the airways. Airway resistance is therefore not negligible relative to needle resistance and therefore compliance computed by dividing the segment time constant by steady state resistance will not approximate segment compliance. This model could have been more simply rejected by the fact that the decays were not monoexponential. The compliance of the fast compartment (Cf) and the compliance of the slow compartment (Cs) were therefore computed assuming that the segment behaved as two series RC circuits. As in the case for Csing' this assumption must be validated. The two series RC circuits model was proposed assuming significant peripheral airway resistance and compliance between the catheter tip and collateral airways. This is a reasonable assumption for the bovine lung segment also considering the number of airways between the catheter and the subpleural needle. For the case of N = 1, steady state resistance would again be the sum of airway resistance and needle resistance for a single secondary lung lobule. The rate of decay would depend on both total airway resistance and total needle resistance as shown for the single exponential case. At the limit where each secondary lung lobule has a needle, (N = k). Rf and Cf should describe the peripheral airway compartment and R808 the alveoli and needle. The pressure decays would be double exponential if the time constant of the fast compartment (Rfcf) did not equal the time constant of the slow compartment (Rscs)' As stated previously, the pressure decays following flow interruption were double exponential indicating that the natural lagarlthm directly 1 leasareme however, from the segment ' and rest did. A: needles should infinit lndlcal As. and th the 3] coast; that, Panel decre 800d inap doul 38g] QVe 111 logarithm of the rate of decay was not constant., There is no way to directly validate the two series RC model without an additional pressure measurement at the junction of the two compartments, which is unknown. However, the model can be validated by comparing the compliances derived from the model with the static segment compliance derived from the segment pressure-volme curve, and by predicting what the time constants and resistance should do as N increased and comparing what they actually did. As stated earlier, if R3 is the effective resistance of the needles and R1. is the effective resistance of the peripheral airways, R 8 should approach zero and R should approach RSS as N approaches f infinity. The results of the hyperbolic curve fit presented in Table 5 indicate that this is so suggesting that the model holds. Assuming that R8 is needle resistance and R is airway resistance f and that increasing N does not affect compliance, the time constant of the slow compartment should decrease as N increases and the time constant of the fast compartment should be unchanged. Figure 12B shows that, as expected the slow time constant decreased as N increased. Panel A shows that contrary to expectations, the fast time constant decreased also, suggesting that either the bovine lung segment is not a good analogy of the 2RC compartment model or that the model is inappropriate for bovine or canine lungs. Finally, if the model is correct, the compliance recovered from the double exponential fit of the decay curves should approximate static segment compliance. Because the model is valid only as the limit of every lobule having a needle is reached, C8 and Cr at N = 12 are compared to static compliance (C10) in Table 4. The finding that the compliance of the slow compartment is an order of magnitude larger than g0 confi' anatonlca bovine 11 omen nodel is lungs. 1 m< explain ls pres conside each 1 The re broncl conne total const conpi (J. Np] eat all Hit 31 de 9C 112 C10 confirms that the model or the analogy is inappropriate. Based an anatomical considerations of the bovine lung segment, I believe that the bovine lung segment with needles is a reasonable physical representation of the two series RC model of Olson and Robinson. I conclude that the model is an inappropriate description of collateral ventilation in dog lungs. A more reasonable interpretation of Figure 15 was formulated to explain the double exponential pressure decays. This electrical network is presented in Figure 16. For simplicity airway resistance was considered equal in each lobule and compliance was considered equal in each lobule. Each series RC circuit represents a secondary lung lobule. The resistance leading to these circuits represents bronchi and bronchioles proximal to the secondary lung lobule. The resistance connecting the RC circuit to ground represents a single needle. The total number of secondary lobules in the peripheral segment remains constant (k). There are then J compartments without needles and N compartments with needles and J + N = k. When a needle is inserted, k = (J - 1) + (N + 1). Consider that prior to flow interruption, steady state resistance represents the effective resistance of airways directly between the catheter tip and the needles plus needle resistance. At constant flow all capacitors are charged. When flow is interrupted, the capacitors discharge along a pathway toward the segment with a needle. The units with a needle discharge most rapidly, those without discharge more slowly due to the longer path length. A double exponential pressure decay would result. In this case, the rate constants do not simply equal 1/TC. 113 .oAnooe Hweeoaooem w «o ooewomflwoe ooo woeomoeooe em new oaeooH mesa sewneooow w so ooewHAosoo ooo woeoooeooe u .erooH mesa sewneooow w mo ooewoosmoe oou woeowoeooe m .onnooe Hweeoaeoeo ops: noflsooa sewneooow 2 new onnooe Hwteoaooen oeoooaz woasooa sewneoooo e no nowoesoo we ueosmom ooh .eooooowo nomno: w on Hwowsn mesa meo nowfioxo no oeosmoo w mo Honos Hwoaeoooam .oe onemee 114 115 Obviously this model could equally explain the double exponential pressure decays seen in dog lungs. The only airspaces that can discharge directly into the remainder of the lung are those at the segment boundary. Airspaces within the segment must discharge back through adjacent units to reach the segment boundary. Airspaces at the boundary are analogous to secondary lung lobules with needles. The remainder of the airspaces are analogous to lung lobules without needles. As attractive as this model seems, it is still an oversimplification of a collaterally ventilating lung segment for the following reasons. In this model resistance and capacitance (compliance) must be constant. Because of the known effect of lung volume on airway resistance and lung compliance this is obviously not true in the real lung even though the effect is small. Secondly, it does not take into account the distance an airspace is from the segment boundary. A better model might be concentric shells of airspaces. Airspaces in a given shell might be expected to have similar time constants. The resistance through which the inner most shell must decay is greatest, that through which the outermost shell decays least. The shape of the decay curve would depend on the relative size and average time constant of the shells. The second simplifying assumption is that all units have identical resistances and compliances. A frequency distribution of time constants within the segment would produce nonuniform rates of emptying and further complicate the coefficients and rate constants of the solution. Finally, this model assumes that the volume of the peripheral airways distal to the catheter is neglible compared to the volume of the secondary lung lobule, which may be an incorrect assumption. The resu smarized: properties is simple n resistance assuming t series fir flow inte factors p iIhat ventilat for qnar Physioll whether s‘3Emenl can be Steady dissip 116 The results of the experiments with calf lungs may be simply summarized: An adequate mathematical description of the mechanical properties of a collaterally ventilating lung segment is NOT simple. It is simple minded and misleading to assume that compliance, collateral resistance, and peripheral airway resistance can be recovered by assuming that the segment behaves as a simple fixed RC unit or two series fixed RC units. The double exponential pressure decays following flow interruption are most likely due to a combination of all four (f factors presented earlier. What is the best way, then, to quantify the efficiency of collateral ventilation? These studies have convinced me that the best criterion for quantitating collateral ventilation is the intuitive and physiological one A time for ventilation. What matters to the animal is whether sufficient volume can enter the collaterally ventilating lung segment during a tidal breath. The efficiency of collateral ventilation can be estimated from the duration of the Ps-Pao pressure decay after steady flow is discontinued. The longer it takes this pressure to dissipate the longer it would take the segment to ventilate. The time for pressure equlibration depends on the effective resistance and compliance of the segment. The effective resistance can be estimated by measuring Rss' Steady state resistance however, is a weighted average of the resistance of all airways within the segment and is flow rate dependent. There is no way to calculate segment compliance from the pressure decay curve. The best way to calculate segment compliance is probably that of Woolcock and Macklem (1971), in which a step change in volume is applied to the segment and peak pressure recorded. Provided the injection time is short relative to the time constant of the segment, dynamic compliance will be estimated. 117 Inferences about segment compliance can be made by noting the relative change in steady state resistance and the time for pressure equilibration. For these reasons, the efficiency of collateral ventilation when vagal tone and alveolar 002 were changed was quantified by determining Rss and the time for 901 Ps-Pao equilibration (T90). The Interaction of Alveolar COa and the Vagus Nerve in Determining the Efficiency of Collateral Ventilation I The experiments described in Protocols 1 and 2 demonstrate that electrical stimulation of the vagus nerve increased the resistance (Rss) of airways in a collaterally ventilating lung segment and increased the time for pressure equilibration between the segment and the remainder of 9 the lung (T O) in dogs which received propranolol and in dogs which did 9 not when segment alveolar CO was 0. 5 or 12%. These results confirm 2 the finding of previous investigators that the ability of a peripheral lung segment to ventilate through collateral airways is impaired by parasympathetic excitation (Woolcock and Macklem, 1971, Smith et al.. 1979. Olson and Robinson, 1980). Because 12% CO2 represented a partial pressure of about 85 mm Hg, and because vagal stimulation increased Rss with 12% CO2 flowing into the segment, it is unlikely that increases in alveolar CO could prevent vagal increases in segment resistance even 2 with extreme hypoventilation. Because the wedged catheter method involves infusing known gas flows into a sublobar segment of lung, it is difficult to assess the composition of alveolar gas within the segment. Flow rate through the segment and segment volume must be considered when using this technique to determine the effect of CO on collateral ventilation. Although the 2 volume of the segment of lung distal to the wedged bronchoscope was not 118 measured, several studies using catheters of about the same size report segment volume to be about 50 ml (Woolcock and Macklem, 1971, Menkes at al.. 1973. Robinson and Milar, 1980). Furthermore, the volume of the calf lung segments averaged 55 ml (see Table 4). I presume, therefore, that the volume of the lung segment distal to the bronchoscope was about 50 ml. The average flow necessary to create a 3 cm H20 difference between the segment and the remainder of the lung is about 7 ml/sec. It takes about 7 sec to achieve a stable pressure difference using 5% or 12% C02, slightly longer when using 0% CO because of the delayed 2 bronchoconstrictor effect of hypocapnia. During equilibration, at least 49 ml of gas entered the segment. Additionally, prior to making measurements with a different test gas, 200 ml of the gas to be tested was flushed into the segment while the dog was ventilated to assure that segment alveolar CO2 approached that of the test gas. Considering that there is very little anatomic dead space in the segment, it is reasonable to conclude that 0% CO resulted in segment hypocapnia, SS 2 C02 resulted in isocapnia, and 12% CO2 resulted in hypercapnia. Based on this conclusion, the results of the present study indicate that during vagal stimulation, alveolar hypocapnia increased the resistance of airways in the collaterally ventilating lung segment and increased the time for segment-lung pressure equilibration when the sympathetic efferent nerves are functioning (Group I) or when they are blocked (Group II). The regression of R88 against $002 in both groups of dogs with the vagi intact or after ipsilateral vagal sectioning were not significant indicating that CO had no effect on RSS in these cases. 2 However, steady state resistance with 51 C02 flowing into the segment was 251 less than with 0% CO2 flowing into the segment in both cases. This agrees with a previous study using the wedged catheter technique in 119 which a 43% decrease in collateral resistance is reported when the inflow gas was switched from air to 51 CO in air (Traystman et al.. 2 1976). The results of the present study indicate that at high levels of vagal tone, the effect of increasing inflow CO from 51 to 12$ depended 2 on whether the the beta sympathetic efferent fibers were functional. Twelve percent carbon dioxide increased R88 and T in dogs which did 90 not receive propranolol and decreased R88 and T90 in dogs which were pretreated with propranolol when compared to values using 5% C02. The significant vagus-CO2 interaction does not indicate whether changing segment alveolar CO concentration changed the magnitude of 2 bronchoconstriction induced by electrical vagal stimulation or whether the effects of CO were only measurable at high levels of vagal tone. 2 The finding that ipsilateral vagal sectioning did not alter Rss or T 90 suggests that there is no vagal tone in collaterally ventilating lung segments of dogs anesthetized with alpha chloralose-urethan and paralyzed with succinylcholine. These results confirm a previous study by Olson and Robinson (1980) in which bilateral vagotomy did not alter RSS in propranolol treated dogs. Because bronchodilation can only occur in constricted airways, and because there was no vagal tone, R88 did not change with 12% CO with the vagi intact or after ipsilateral vagal 2 sectioning in dogs pretreated with propranolol. Steady state resistance was significantly greater in propranolol-treated dogs during vagal stimulation and 01 C02. I suspect that the cardiac arrest and subsequent fall in blood pressure caused by vagal stimulation increased central sympathetic outflow. The resulting sympathetic bronchodilation mitigated the constrictor effect of electrical vagal stimulation. After beta blockade, vagal 120 bronchoconstriction was unopposed, resulting in increased steady state resistance. Studies of isolated canine bronchial rings stimulated to contract by electrical parasympathetic excitation, indicate that norepinephrine and isoproterenol inhibit bronchoconstriction. These same pharmacologic agents are ineffective against contraction induced with exogenous acetylcholine suggesting that they interfere with neurotransmitter release (Vermeire and Vanhoutte, 1979). Verbeuren et al. (1978) demonstrated that moderate metabolic acidosis (pH 7.1) induced by lowering bicarbonate at constant carbon dioxide tensions reduced sympathetically induced smooth muscle contraction in isolated dog veins. Studies using veins incubated with radiolabelled norepinephrine indicate that acidosis inhibits alpha adrenergic neurotransmitter release. I propose that a similar interaction occurs at airway beta adrenergic nerve endings. In propranolol-untreated dogs, smooth muscle acidosis induced by increasing segment alveolar CO inhibited sympathetic bronchodilation. This would 2 explain why steady state resistance during vagal stimulation was identical in propranolol-treated and propranolol-untreated dogs when 12% CO2 was flowing into the collaterally ventilating lung segment. Comparing Figures 3 and 4, it is evident that with the vagi intact and after ipsilateral sectioning, steady state resistance was identical in propranolol-treated and propranolol-untreated dogs, yet the 90% eqilibration time appeared shorter in propranolol treated dogs. Because T90 depends on the resistance and compliance of the lung segment, this suggests that propranolol reduced lung compliance. Although I do not have estimates of segment compliance, a similar finding was reported by Woolcock et al. (19698). In that study, a retrograde catheter was used to partition total lung resistance into a central (large airway) and peripi const nerve curve lung syn; keep prc di? C0 121 peripheral (smaller airway) component. After propranolol, the constrictor effect of electrical stimulation of the cervical vagus nerves was increased. Propranolol also shifted the lung pressure-volume curve downward and to the right indicating that beta blockade decreased lung compliance. The authors suggest that the function of normal sympathetic input to the lung is to decrease the work of breathing by keeping lung compliance high. The results of the present study must be considered with the E probable mechanisms for hypocapnic bronchoconstriction and hypercapnia - dilation or constriction. In studies elucidating these mechanisms, the CO2 tensions in the whole lung have been changed, either by voluntary 1! hyperventilati or by changing the fraction of inspired 002. Although not always documented, it is likely that such maneuvers change arterial CO2 tensions. This adds an additional level of complexity in that the effect of arterial CO and pH on chemoreceptors and the central nervous 2 system must be considered. In contrast, in the present study when the CO2 tension of the gas flowing into the collaterally ventilating lung segment was changed, is unlikely that arterial gas tensions changed because of the small volume of the segment and short duration of the measurements. In 1964, Newhouse et al. studied the effect of voluntary hyperventilation with air and 7: C02 in air on five seated normal humans. Dynamic compliance (Cdyn) and total lung resistance were computed from simultaneous recordings of tidal volume, flow rate and transpulmonary pressure. End tidal CO2 was sampled at the mouth. Voluntary hyperventilation with air which reduced end tidal CO2 to between 14 and 25 mm Hg increased inspiratory and expiratory resistance when compared to voluntary hyperventilation with 75 C02 to maintain 122 alveolar CO2 levels between 38 and 50 mm Hg. Dynamic compliance was unchanged. Intravenous atropine or isoproterenol reduced the increase in lung resistance with CO2 and when given together abolished the response. Because both cholinergic blockade and beta adrenergic stimulation prevented hypocapnic bronchoconstriction, the authors believe the effect to be mediated locally - not reflexly. They suggest that both pharmacological agents abolish normal vagal tone; atropine by blocking vagal constriction, isOproterenol by relaxing airway smooth muscle. When airways are maximally dilated by either mechanism the reduction in diameter induced by hypocapnia causes less increase in resistance. This argument does not rule out a reflex effect, however. Sterling (1968) repeated the study in normal humans using a body plethysmograph to obtain airway resistance and measure lung volume. Hyperventilating with air reduced specific airway conductance (SGaw = 1/(Raw X vol)); hyperventilating with 51 C02 in air abolished the response. After intravenous atropine hyperventilating with air reduced specific conductance significantly although the magnitude of the effect was only 7.4% compared to a 35% change before atropine. Sterling concluded that hypocapnic bronchoconstriction is largely mediated reflexly by the vagi, but small increases in airway resistance can be mediated locally. Sterling (1969) also studied the effect of hypercapnia induced by inhaling 7% CO2 in 30% 02 on specific airway conductance determined plethysmographically in seated humans. Measurements were made before and after intravenous atropine, aerosol orciprenaline, a selective beta two agonist, and intravenous propranolol. Before and after all drugs, hypercapnia decreased specific airway conductance. When the magnitude of the response was compared across drug treatment groups, treatment 123 with atropine and orciprenaline significantly increased the hypercapnic constriction. The author concluded that because blocking the vagi with atropine or relaxing airway smooth muscle with orciprenaline did not abolish the response, the decrease in specific airway conductance was not due to bronchoconstriction but rather to laryngeal constriction. An earlier study in dogs, however, indicates that ventilation with 4 or 81 CO2 in air decreases dead space, lung compliance, and tracheal volume and increases total lung resistance (Green and Widdicombe, 1966). After bilateral sympathectomy, the results were about the same. It must be reiterated that the results cited above and the results wI-‘cr-w ..- of the present study may not be directly comparable because of differences in the likelihood of changes in arterial blood gases and resulting central nervous system effects. A recent study by Scarpelli and Agasso (1979) emphasizes the importance of this difference. In awake dogs, chronically instrumented with a mercury strain gauge around the extrathoracic trachea, hypercapnia induced by 40-50 minutes of breathing 12% CO2 exaggerated the tracheal constrictor effect of intravenous acetylcholine. In contrast, the tracheal dilator effect of epinephrine or isoproterenol infusion were attenuated by hypercapnic acidosis. When arterial pH was returned to normal by sodium bicarbonate infusion, the magnitude of acetylcholine induced constriction returned to control. Measurement of cerebrospinal fluid pH indicated that cisternal acidosis had not been corrected by the bicarbonate infusion. 124 Although the results of Scarpelli and Agasso can not be compared with the results of the present study, the suggestion that the response characteristics of airway smooth muscle receptors are altered by acidosis is consistant with the hypothesis presented to explain the effect of 12% CO2 on propranolol-treated and propranolol—untreated dogs. In summary, the results of this study indicate that vagal stimulation reduced the ability of a peripheral lung segment to ventilate through collateral airways at alveolar C02 levels between approximately 0 and 12%, as evidenced by increased steady state resistance and increased segment—lung equilibration time. During vagal stimulation, lowering the concentration of C02 in the segment further reduced collateral ventilation in propranolol-treated and propranolol-untreated dogs. Raising the concentration of CO2 in the segment during vagal stimulation reduced collateral ventilation in dogs which were not pretreated with propranolol and promoted collateral ventilation in dogs which were pretreated with propranolol. There is no evidence that increasing the concentration of 002 in the segment to 12% prevented the decrease in collateral ventilation caused by vagal stimulation in anesthetized dogs. This is not to suggest that the demonstration of Rubinfeld et al. (1978) that induced canine allergic asthma does not produce lung units with ventilation/perfusion ratios equal to zero cannot be attributed to good collateral ventilation. It does suggest that perfusion must be regulated in proportion to the amount of ventilation a peripheral lung unit receives through collateral airways. 1?; "I e. APPENDICES APPENDIX A TWO COMPARTMENT MODEL OF OLSON AND ROBINSON E K a .‘U as Figure A1. Model proposed to explain double exponential pressure decays following the interruption of steady state gas flow into a collaterally ventilating segment of dog lung. A. schematic representation of the segment within a lung lobe B. electrical analog of A. When the two node equations describing B are solved simultaneously, the equation describing the decay at the first node (PS) becomes: (PS-Pao)t/(Ps'Pao)t:0 = -(1/TCf)t —(1/TCs)t (Rs/(Rf+Rs))e + (Rs/(R8+Rf))e The general double exponential form of this equation is: —k1t —k2t (PS-Pao)t = Ae + Be A, 8, k1 and k2 are recovered from the generalized nonlinear curve fitting routine and used to calculate Rf and Rs as: RSS = Rf + RS A/B = Rf/Rs BY Co 126 By substitution: R8 = Rss/(1+A/B) Rfo - 1/k1 Because Rf is known: Cf = (1/k1)(1/Rf) Knowing Rs: C8 = (1/k2)(1/RS) This model is supported by several independent observations. First, collateral airways begin at the level of respiratory bronchioles. Respiratory bronchioles begin at about generation 17, the trachea being considered generation 0, the mainstem bronchi 1 etc. A catheter 0.5 cm in diameter wedged in a subsegmental bronchus. Subsegmental bronchi begin at about generation 4 and continue to about generation 7. Thus, there may be up to 13 generations of airways between the catheter tip and collateral airways. When the lungs are collapsed and the segment is distended, the segment always inflates up the catheter tip. The segment might, therefore, functionally behave as two compartments, one within the other. When flow is interrupted, pressure in the two compartments rapidly equilibrates as gas in the segmental airways is discharged into the alveoli and out of the segment through collateral airways at the segment boundary. The pressure difference between the segmental alveoli and extrasegmental alveoli dissipates more slowly as gas leaves the segment. COHS‘ slow biph cons stri airt pre ins 127 We therefore consider the compartment with the most rapid time <3onstant to represent segmental airways, and the compartment with the :slower time constant to represent parenchyma and collateral airways. Smith et al. (1979) propose the same interpretation to explain the taiphasic pressure decay observed after methacholine, a potent airway <3onstrictor, is blown into the segment. Using a graphical curve stripping technique, Smith and colleagues recover values of segmental airway resistance similar in magnitude to Rf. Finally, when Robinson and Mukhtar (Abstract 1977) measured the pressure difference between the catheter tip and a subpleural catheter inserted in the segment in excised dog lungs, and computed the I~esistance between the two catheters, the value was similar to Rf. ANOVA TABLES 1ND RESULTS OF REGRESSION ANALYSES APPENDIX B significant at P<0.05 128 Source of variance df SS F 1138 Propranolol 1 2.57 0.42 Error 1 16 98.10 Vagus 2 76.10 109.82 * C02 2 12.09 17.44 * Vagus-C02 4 6.46 4.66 * Dog-vagus + dog-propranolol-vagus 32 63.26 5.70 * Propranolol—vagus 2 8.17 11.79 Propranolol-CO2 2 2.44 3.52 Propranolol-vagus—CO2 4 2.53 1.82 Error 2 96 33.26 Sampling 324 15.74 0.05 Total 485 320.72 129 Source of Variation df SS F 390 Propranolol 1 991.59 1.30 Error 1 16 12215.53 Vagus 2 2755.53 110.26 C02 2 223.92 8.96 Vagus-C02 4 132.55 2.65 Dog-vagus + Dog-prop-vagus 32 5655.43 14.14 Propranolol-vagus 2 154.31 6.17 Propranolol-C02 2 22.08 0.88 Propranolol-vagus-CO2 4 78.19 1.56 Error 2 96 1199.57 Sampling 324 628.06 Total . 483 24056.77 4 = significant at P<0.05 130 Results of Regression Analyses -ss 2&0 df MS MS Group I - no propranolol vagi intact linear 0.2273 13.5850 quadratic 0.1859 2t5304 IL sectioned linear 0.0552 9.4757 quadratic 0.1490 0.4905 IL stimulated linear 0.9018 13.1836 quadratic 2.1615 75.3781 Group II - propranolol vagi intact linear 0.4631 3.1536 quadratic 0.2243 0.5256 IL sectioned linear 0.5719 4.9863 quadratic 0.2199 0.9231 IL stimulated linear 1 16.3901 * 299.8259 quadratic 1 1.9723 * 32.6648 EMS=0.3465 EMS=12.50 ‘ significant at P<0.05 EMS = error mean square 131 'Source of Variation ' df SS F Rasfor Flow-Density:Volume Studies Dog 3 21.30 52.27 * Treatment 8 4.30 3.98 * ' Error 24 3.26 Total 35 28.86 A/(l-A) for Flow-Density-Volume Studies Dog 3 3.04 4.39 Treatment 8 2.54 1.39 Error 24 5.60 Total 35 11.18 Results of Regression Analysis er. us -fiss—Etp = FRC + 4 cm H29 linear 1 0.3251 quadratic 1 0.0122 -§ss-Etp = FRC + 2 cm H29 linear 1 0.4233 quadratic 1 0.0278 £85 Ftp = FRC linear 1 0.8992 quadratic 1 0.0381 EMS=0.1356 * significant at P<0.05 EMS : error mean square 132 Source of Variation df SS F fiss_for Vagal Stimulation-Density Studies Dog 4 76.46 39.31 * Treatment 5 29.13 11.98 * Dog-vagus 4 11.93 6.13 ' Error 16 7.78 Total 29 125.30 A/(1-A) for Vagal Stimulation-Density Studies Dog 4 4.05 7.92 * Treatment 5 0.50 0.78 Dog-vagus 4 1.91 3.76 * Error 16 2.04 Total 29 8.50 Results of Regression Analysis :3 M_S. RSS - vagi sectioned linear 1 2.0789 quadratic 1 0.0069 RSS — IL stimulated linear 1 4.1050 * quadratic 1 0.3030 EMS=0.4864 ' = significant at P<0.05 EMS = error mean square 133 Source of Variation df SS F 12f for Decays from P8 = 30 cm H90 N 1 0.004 0.53 Residual 6 0-00“5 Total 7 0.0049 .gf for Decays from P8 = 20 cm H19 N 1 0.07 14.00 9 Residual 6 0.03 Total 7 0.10 .Qf for Decays from P8: 10 cm H99 N 1 0.05 2.74 9 Residual 6 0-11 Esing for Decays from Ps=30 cm H29 N 1 0.06 5.14 Residual 6 0.07 0.01 Total 7 0.13 -Esing for Decays from P8 = 20 cm Hag N 1 0.44 22.00 9 Residual 6 0.12 Total 7 0-56 Esing for Decays from P3: 10 cm H29 N 1 0.10 2.00 Residual 6 0.30 Total 7 0-"0 9 = significant at P<0.05 N = number of needles in segment 134 Source of Variation df SS F 98 for Decays from P8 = 30 cm Hag N 1 238.31 17.16 9 Residual 6 83.31 Total 7 321.62 -Es for decays from P8 = 20 cm H39 n 1 30.75 1-81 Residual 6 101-86 I Total 7 132.61 "“ 9 = significant at P<0.05 135 Source of Variation df SS F Flow for Volume-Density Studies D08 3 3.97E06 211.20 9 Density 2 1.28E05 10.22 9 Volume 2 1.12E05 8.94 9 Density-volume 4 1.54E04 0.62 Error 24 1.50E05 Total 35 4.51E06 Flow for Vagal Stimulation—Density Studies Dog 4 1.15E06 180.00 9 Density 2 1.78E04 5.56 9 Vagus 1 1.64E05 102.50 9 Density-vagus 2 7.91E03 2.50 Dog-vagus 4 2.26E05 35.31 9 Error 16 2.55E04 Total 35 1.59E06 9 = significant at P<0.05 APPENDIX C CALCULATION OF REYNOLD'S NUMBER Reynold's number is a unitless number used to predict the probability of turbulent flow. Turbulence is high likely to occur at Re greater than 2000. The following equation was used to calculate Re at the catheter tip for flows in 4 dogs after bilateral vagotomy: Re = (dvp)/u = (de)/(Au) where d = diameter in cm A = area in cm2 V = flow in l/sec density in gm/l p u = viscosity in poise = gm/(cm—sec). At the catheter tip d = 0.5 cm therefore A = «(0.25 em)2 = 0.1963 cm2. Table C1. Calculation of Reynold's Number at Wedged Catheter Tip 2,, s l2 s, FRC 18.42 155.53 695.19 FRC + 2 cm H20 15.83 125.14 606.71 FRC + 4 cm H20 13.94 94.75 505.59 . 136 LI ST OF REFERENCES LIST OF REFERENCES Alley, R.D. and G.E. Lindskog. Pharmacologic factors influencing collateral respiration: possible relation to the etiology of pulmonary complication. Ann. Surg. 128:497-508, 1948. Baarsma, P.R., M.N.J. Dirkin and E. Huizinga. Collateral ventilation in man. J. Thorac. Surg. 17:252-263. 1948. Brown, R., A.J. Woolcock, N.J. Vincent and P.T. Macklem. Physiological effects of experimental airway obstruction with beads. J. Appl. Physiol. 27:328-335. 1969. Cabezas, G.A., P.D. Graf and J.A. Nadel. Sympathetic versus parasympathetic nervous regulation of airways in dogs. J. Appl. Physiol. 5:651—644, 1971. Chen, C., W.C. Sealy and A.V. Seaber. The dynamic nature of collateral ventilation. J. Thorac. Cardiovasc. Surg. 59:518-529. 1970. Daly, I. deB. and C. Hebb. Pulmonary and Bronchial Vascular Systems. Williams and Wilkins Co. Baltimore, MD. 1966. Dubois, A.B.. S.Y. Botelho and J.H. Comroe, Jr. A new method for measuring airway resistance in man using a body plethysmograph: values in normal subjects and in patients with respiratory disease. J. Clin. Invest. 35:327-335. 1956A. Dubois, A.B., A.W. Brody, D.H. Lewis and B.F. Burgess, Jr. Oscillation mechanics of lungs and chest in man. J. Appl. Physiol. 8:587—594, 1956B. Fisher, A.B., A.B. DuBois and R.W. Hyde. Evaluation of the forced oscillation technique for the determination of resistance to breathing. J. Clin. Invest. 47:2045-2057, 1968. Flenley, 0.0., J. Picken, L. Welchel, F. Ruff, P.M. Corry and P.T. Macklem. Blood gas transfer after small airway obstruction in the dog and minipig. Resp. Physiol. 15:39-51, 1972A. Flenley, D.C., L. Welchel and P.T. Macklem. Factors affecting gas exchange by collateral ventilation in the dog. Resp. Physiol. Fredberg, J.J. Spatial considerations in oscillation mechanics of the lung. Fed. Proc. 39:2747-2754, 1980. 137 138 Gold, W.M., G.-F. Kessler and D.Y.C. Yu. Role of vagus nerves in experimental asthma in allergic dogs. J. Appl. Physiol. 33:719-725. 1972. Green, M. and J.G. Widdicombe. The effects of ventilation of dogs with different gas mixtures on airway calibre and lung mechanics. J. Physiol. 186:363-381, 1966. Henderson, R., K. Horsefield and G. Cumming. Intersegmental collateral ventilation in the human lung. Resp. Physiol. 6:128-134, 1968/1969. Hensley, M.J., C.F. O'Cain, E.R. McFadden, Jr. and R.H. Ingram, Jr. Distribution of bronchodilation in normal subjects: beta agonist versus atropine. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 45:778-782. 1978. Hogg, J.C., P.T. Macklem and W.M. Thurlbeck. The resistance of collateral channels in excised human lungs. J. Clin. Invest. 48:421—431, 1969. Hoppin Jr., F.G.. M. Green and M.S. Morgan. Relationship of central and peripheral airway resistance to lung volume in dogs. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 44:728-737. 1978. Inners, C.R., P.B. Terry, R.J. Traystman and H.A. Menkes. Effect of lung volume on collateral and airways resistance in man. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 46:67-73. 1979. Johnson, R.M. and G.E. Lindskog. Further studies on factors influencing collateral ventilation. J. Thorac. Cardiovasc. Surg. 62:321-329, 1971. Kaplan,.J.. R.C. Koehler, P.B. Terry, H.A. Menkes and R.J. Traystman. Effect of lung volume on collateral ventilation in the dog. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 49:9-15. 1980. Lambert, M.W. Accessory bronchiole-alveolar communications. J. Path. Bacterial. 70:311-314, 1955. Lenfant, C. Nonrespiratory aspects of lung physiology. Fed. Proc. 36:2651-2652, 1977. Levy, H.L. and L.D.H. Wood. Effect of gas physical properties on resistance to collateral ventilation (Abstract). Fed. Proc. 35:134, 1976. Macklem, P.T. Airway obstruction and collateral ventilation. Physiol. Rev. 51:368-436, 1971. Macklem, P.T. and J. Mead. Resistance of central and peripheral airways measured by a retrograde catheter. J. Appl. Physiol. 22:395-401, 1967. 139 Macklem, P.T., A.J. Woolcock, J.G. Hogg, J.A. Nadel and N.J. Wilson. Partitioning of pulmonary resistance in the dog. J. Appl. Physiol. 26:798-805. 1969. Martin, H.B. Respiratory bronchioles as the pathway for collateral ventilation. .J. Appl. Physiol. 21:1443-1447, 1966. Mead, J. and J.L. Whittenberger. Physical properties of human lungs measured during spontaneous respiration. J. Appl. Physiol. 5:779-796. 1953. Mead, J., T. Takishima and D. Leith. Stress distribution in lungs, a model of pulmonary elasticity. J. Appl. Physiol. 28:596-608. 1970. Menkes, H.A. and R.J. Traystman. Collateral ventilation. Am. Rev. Resp. Dis. 116:287-309. 1977. Menkes, H., A. Gardiner, G. Gamsu, J. Lempert and P.T. Macklem. Influence of surface forces on collateral ventilation. J. Appl. Physiol. 31:544—549. 1971. Menkes, H.. G. Gamsu, R. Schroter and P.T. Macklem. Interdependence of lung units in isolated dog lungs. J. Appl. Physiol. 32:675-680, 1972. Menkes, H.. D. Lindsay, G. Gamsu, L. Wood, A. Muir and P.T. Macklem. Measurement of sublobar lung volume and collateral flow resistance in dogs. J. Appl. Physiol. 35:917-921. 1973. Newhouse, M.T., M.R. Becklake, P.T. Macklem and M. McGregor. Effect of alterations in end-tidal C02 tension on flow resistance. J. Appl. Physiol. 19:745-749. 1964. Olson, L.E. Vagal effects on collateral flow resistance in the dog. M.S. Thesis, Michigan State University, 1978. Olson, L.E. and N.E. Robinson. Effect of vagal stimulation on collateral flow resistance in dog lungs. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 49:287-293. 1980. Perkins, Jr., J.F. Chapter 1. Historical development of respiratory physiology. In Fenn, W.0. and H. Rahn, eds. Handbook of Physiology — Respiration Vol. 1, American Physiological Society, pp.1-63, Wahington D.C., 1964. Robinson, N.E. and M.R. Mukhtar. Partitioning of collateral resistance in dogs (Abstract). Physiologist 20:80, 1977. Robinson, N.E. and R. Milar. Lobar variations in collateral ventilation in excised dog lungs. Am. Rev. Resp. Dis. 121:827-834, 1980. Robinson, N.E. and P.R. Sorenson. Collateral flow resistance and time constants in dog and horse lungs. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 44:63-68. 1978. 140 Rubinfeld, A.R., P.D. Wagner and J.B. West. Gas exchange during acute experimental canine asthma. Am. Rev. Resp. Dis. 118:525-536. 1978. Russell, J.A. Noradrenergic inhibitory innervation of canine airways. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 48:16-22, 1980. Sasaki, H., T. Takishima and M. Nakamura. Collateral resistance at alveolar level in excised dog lungs. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 48:982-990, 1980. Scarpelli, E.M. and E.J. Agasso. Arterial pH, airway calibre and response to acetylcholine and catecholamines in vivo. Resp. Physiol. 38:235-242, 1979. Sealy, W.C. and A.V. Seaber. The action of carbon dioxide on the collateral pathways of pulmonary ventilation. J. Thorac. Cardiovasc. Surg. 69:533-538. 1975. Smith, L.J., C.R. Inners, H.A. Menkes and R.J. Traystman. Effects of methacholine and hypocapnia on airways and collateral ventilation in dogs. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 45:966-972. 1979. Steel, R.G.D. and J.H. Torrie. Principles and Procedures of Statistics, McGraw-Hill, NY, 1960. Sterling, G.M. The mechanism of bronchoconstriction due to hypocapnia in man. Clin. Sci. 34:277-285, 1968. Sterling, G.M. The mechanism of decreased specific airway conductance in man during hypercapnia caused by inhalation of 7% CO2. Clin. 8C1. 37:539‘5n89 19690 Traystman, R.J., G.K. Batra and H.A. Menkes. Local regulation of collateral ventilation. J. Appl. Physiol. 40:819-823, 1976. Traystman, R.J., P.B.Terry and H.A. Menkes. Carbon dioxide - a major determinant of collateral ventilation. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 45:69-74, 1978. Van Allen, C.M., G.E. Lindskog and H.G. Richter. Collateral respiration. Transfer of air collaterally between pulmonary lobules. J. Clin. Invest. 10:559-590. 1931. Verbeuren, T.J., W.J. Janssens, and P.M. Vanhoutte. Effects of moderate acidosis on adrenergic neurotransmission in canine saphenous veins. J. Pharmacol. Exp. Ther. 206:105-114, 1978. Vermiere, P.A. and P.M. Vanhoutte. Inhibitory effects of catecholamines in isolated canine bronchial smooth muscle. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 46:737-791, 1979. Widdicombe, J.G. Regulation of tracheobronchial smooth muscle. Physiol. Rev. 43:1-37. 1963. 141 Woolcock. A.J.. P.T. Macklem, J.C. Hogg, N.J. Wilson, J.A. Nadel. N.R. Frank and J. Brain. Effect of vagal stimulation on central and peripheral airways in dogs. J. Appl. Physiol. 26:806-813, 1969A. Woolcock, A.J., P.T. Macklem, J.C. Hogg and N.J. Wilson. Influence of autonomic nervous sytem on airway resistance and elastic recoil. J. Appl. Physiol. 26:814-818. 1969B. Woolcock. A.J. and P.T..Macklem. Mechanical factors influencing collateral ventilation in human, dog. and pig lungs. J. Appl. Physiol. 30:99-115. 1971. General References Copenhaver, W.M.. D.E. Kelly and R.L. Wood. Bailey's Textbook of 'w_ Histology. Chapter 17. 17th ed. pp.552-576. Williams and Wilkins , a Ca. Baltimore. MD. 1978. Getty. R. Sisson and Grossman's The Anatomy of the Domestic Animals. 5th , ed.. Vol. 1. W.B. Saunders Co. Philadelphia, PA. 1975. E} [lg/111211ILIIII/III!Ill/1111111111III/111111III