CONTROL OF SKIN AND DURING HEMORRHAGE ' SKELETAL MUSCLE BLDDD vsssaLs E73": Dissertation for the-"Degreeof FILED. if__ 7 ' Ml’CHEGAN STATE UNIVERSITY ' JOHN. EDWARD HALL ” K1974 ’ » This is to certify that the thesis entitled Control of Skin and Skeletal Muscle _~.n-‘ Blood Vessles During Hemorrhage presented by John Edward Hall has been accepted towards fulfillment of the requirements for Ph.D. degree in Physiology I 64%.! AQLa/w‘AJ—mm Major professor(J 07639 H0 DHH & SUHS .3”? ‘-' TRY 'HC .- ‘ " L. ~~ i'iDERS 1.. gated-r312: HCNI‘IN ABSTRACT CONTROL OF SKIN AND SKELETAL MUSCLE BLOOD VESSELS DURING HEMORRHAGE BY John Edward Hall A combined gravimetric and segmental resistance technique was used to study the contributions of passive vascular collapse. sympathetic nerve activity, and circu- lating hormones to hemorrhage-induced changes in net trans— capillary fluid movement, vascular capacitance, and large and small vessel resistance in the forelegs of 55 dogs anesthetized with sodium pentobarbital. In one series of experiments (Series I; n=16), the forelimb nerves were left intact and arterial perfusion pressure was reduced in steps to 100, 75, 50, and 35 mm Hg by compression of the brachial artery with a screw clamp. The local hypotension produced by clamping elicited slight increases in vascular resistances which were significant (PL=0.05) only at brachial artery pressures (PEA) of 75 mm Hg and below in skeletal muscle and at 50 mm Hg and below in skin. Local hypotension caused a slow phase limb weight loss (attributed to a net reabsorption of extravascular fluid) which reached a maximum of 0.15 :_0.02 g/min at a John Edward Hall :PBA.°f 50 mm Hg. The clamp was removed and after forelimb arterial and venous pressures and blood flows had returned to pre-clamp control values, P was reduced in steps to BA 100, 75, 50, and 35 mm Hg by rapid bleeding from a carotid artery into a pressurized reservoir. Hemorrhagic hypoten- sion caused marked and progressive increases in forelimb total and segmental vascular resistances along with slow phase decreases in limb weight. At each of the pressure reductions produced by hemorrhage, increases in total and all segmental resistances in skin and skeletal muscle, as well as the slow phase decreases in forelimb weight, were significantly greater (P‘<0.0S) than those observed at corre- sponding P ‘5 during local hypotension. Fast phase changes BA in forelimb weight, attributed primarily to reductions in intravascular volume, were consistently greater during hemorrhagic hypotension than during corresponding amounts of local hypotension. The forelimb resistance and weight data indicate that the decreased vascular capacity and extra- vascular fluid reabsorption observed during hemorrhage are not primarily the result of passive vessel collapse, but are largely due to active constriction of forelimb vessels. The resistance data indicate that most of the hemorrhage-induced constriction in all forelimb vascular segments, including the large veins, can also be attributed to active smooth John Edward Hall muscle contraction rather than to passive vascular collapse subsequent to reductions in transmural pressure. In Series II (17 dogs), the forelimb nerves were severed, and arterial perfusion pressure was reduced by clamping the brachial artery and by hemorrhage according to the protocol described for Series I. Clamping the brachial artery produced slight increases in forelimb vascular resistances, whereas hemorrhage produced a much more pro- nounced constriction in all skin and muscle vascular segments. Except in the large skin arteries, the hemorrhage-induced constriction of denervated forelimb vascular segments was not substantially less than that of innervated segments. Slow phase limb weight losses during hemorrhage were not significantly different in innervated and denervated fore- limbs. These data suggest that circulating vasoconstrictors, rather than sympathetic nerves, mediate most of the in- creased vascular resistance and extravascular fluid reab- sorption in skin and skeletal muscle during rapid, severe hemorrhage. In Series III, the forelimbs of 5 recipient dogs were pump-perfused with carotid arterial blood from 5 donor dogs. Forelimb perfusion pressure was controlled by a servosystem whicfl1 continuously adjusted the pump flow rate. After a 20-30 min control period, the recipient dog was rapidly John Edward Hall bled so that its mean systemic arterial pressure was re- duced in steps to 100, 75, 50, and 35 mm Hg. After each hemorrhage, the set-point of the servosystem was altered so that brachial artery pressure matched the recipient dog's systemic arterial pressure. Bleeding the recipient dog elicited relatively small but significant increases (P<:0.05) in skin and skeletal muscle vascular resistances. At a brachial artery pressure of 35 mm Hg, skin and muscle total resistance increased only 4.2 and 3.4 fold, respec- tively. The shed blood was reinfused, the forelimb nerves were severed, and intravascular pressures and venous outflows allowed to stabilize. The donor dog was then rapidly bled and forelimb perfusion pressure of the recipient dog reduced according to the protocol described for bleeding the recipient dog. Bleeding the donor dog elicited large increases in vascular resistances in the forelimbs of the recipient dogs. Total vascular resistance in skin and skeletal muscle increased 12.0 and 10.6 fold respectively at a brachial artery pressure of 35 mm Hg. These data sup- port the findings in Series I and II; i.e., that most of the increased skin and muscle vascular resistance observed during rapid, severe hemorrhage is mediated by circulating vasoconstrictors rather than by sympathetic nerves. John Edward Hall To determine whether the relative importance of neural and humoral control of the forelimb vasculature is influ- enced by the bleeding rate, 17 dogs (8 with innervated and 9 with denervated forelimbs; Series IV) were bled 0.41 ml/kg body weight per minute for 60 minutes, and changes in forelimb vascular resistances determined every 2 minutes during the bleeding period. After 60 minutes of bleeding, total skin vascular resistance increased 7.6 i 2.8 fold in innervated limbs, but only 1.9 i 0.3 fold in denervated limbs. In the muscle vasculature, denervation attenuated the constrictor response to hemorrhage; but, total muscle vascular resistance in denervated forelimbs still increased 3.0 i_0.6 fold after 60 minutes of bleeding. These data indicate that during slow, sustained hemorrhage, the resistance response of the skin vasculature is almost en- tirely neurogenically mediated, whereas in skeletal muscle, both circulating vasoconstrictors and sympathetic nerves contribute to the increased vascular resistance. CONTROL OF SKIN AND SKELETAL MUSCLE BLOOD VESSELS DURING HEMORRHAGE BY John Edward Hall A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Physiology 1974 To Becky and My Parents ACKNOWLEDGEMENTS I am indebted to my advisor, Dr. J. M. Schwinghamer for assistance in the preparation of this dissertation and for support and guidance throughout my graduate pro— gram. I would also like to acknowledge Drs. S. R. Heisey, T. Adams, D. L. Gilliland, L. F. Wolterink, and R. J. Sauer for serving on my guidance committee and for provid- ing many helpful suggestions in the preparation of this manuscript. Mr. B. LaLone assisted with many of the experiments and Miss Nancy Turner typed the preliminary drafts of this dissertation. A special thanks is due to my wife, Becky who helped with the editing and typing of this dissertation and sacrificed in many ways for me to complete my graduate training. iii LIST OF LIST OF TABLE OF CONTENTS TABLES O I O O O O O O O O O O FIGURES. O O O O O O O O O O O INTRODUCTION 0 O C O I O O O O C O O 0 LITERATURE REVIEW. . . . . . . . . . . I. II. III. METHODS. Control of Vascular Resistance rhage . . . . . . . . . . . A. General Considerations. . . B. Neural Control. . . . . . . C. Humoral Control . . . . . . l. Catecholamines . . . . . 2. Angiotensin. . . . . . . 3. Vasopressin. . . . . . . D. Passive Responses . . . . . During Hemor- Control of Vascular Capacitance During Hemorrhage. . . . . . . . . A. General Considerations. . . B. Neural Control. . . . . . . C. Humoral Control . . . . . . D. Passive Responses . . . . . Transcapillary Fluid Movement During Hemor- rhage . . . . . . . . . . . A. General Considerations. . . B. Neural Control. . . . . . . C. Humoral Control . . . . . . D. Passive Responses; Indirect Neuro-humoral Control. . DATA ANALYS I S O O O O O O O O O O O O 0 iv Effects of Page vii ix 11 11 l6 l8 19 21 21 22 25 28 30 30 34 37 41 44 60 TABLE OF CONTENTS--Continued RESULTS. I. II. III. IV. Series I: Naturally Perfused, Innervated Forelimbs; Effects of Local Hypotension and Rapid Arterial Hemorrhage . . . . . Forelimb Weight . . . . . . . . . . . . Intraluminal Pressures. . . . . . . . . ances. I O O O O O O O O O O O O O O . Muscle Total an Segmental Vascular Resistances. . . . . . . . . . . . . U om» Series II: Naturally Perfused, Denervated Forelimbs; Effects of Local Hypotension and Rapid Arterial Hemorrhage . . . . . A. Forelimb Weight . . . . . . . . . . . . B. Mean Intraluminal Pressures . . . . . . C. Skin Total and Segmental Vascular Resistances. . . . . . . . . . . . . D. Muscle Total and Segmental Vascular Resistances. . . . . . . . . . . . . Series III: Cross-perfused Forelimbs; Effects of Rapid Arterial Hemorrhage of the Recipient and Donor Dogs. . . . . . A. Skin Total and Segmental Vascular Resistances. . . . . . . . . . . . . B. Muscle Total and Segmental Vascular Resistances. . . . . . . . . . . . . Series IV: Naturally Perfused, Innervated or Denervated Forelimbs; Effects of Slow, Continuous Hemorrhage . . . . . . . . . A. Mean Arterial Pressure, Pulse Pressure, and Central Venous Pressure. . . . . B. Skin Total and Segmental Vascular Resistances. . . . . . . . . . . . . C. Muscle Total and Segmental Vascular Resistances. . . . . . . . . . . . . DISCUSSION 0 O O O O O O O O O O O O O O O O O O O I. Series I: Naturally Perfused, Innervated Forelimbs; Local Hypotension and Rapid Arterial Hemorrhage . . . . . . . . . . A. Forelimb Weight . . . . . . . . . . . . Skin Total and Segmental Vascular Resist- Page 61 61 61 66 69 72 77 77 80 84 91 98 98 102 106 106 109 114 120 120 120 TABLE OF CONTENTSFFContinued Page B. Forelimb Vascular Resistances. . . . . . 125 II. Series II: Naturally Perfused, Denervated Forelimbs; Local Hypotension and Rapid Arterial Hemorrhage. . . . . . . . . . . 127 A. Forelimb weight. 0 O O I O O O O O O O O 127 B. Forelimb Vascular Resistances. . . . . . 129 III. Series III: Cross-perfused Forelimbs; Rapid, Arterial Hemorrhage of Recipient and Donor Dogs . . . . . . . . . . . . . 131 IV. Series IV: Naturally Perfused, Innervated or Denervated Forelimbs; Slow, Continu— cus Hemorrhage . . . . . . . . . . . . . 134 A. Mean Systemic Arterial, Arterial Pulse, and Central Venous Pressures. . . . . 134 B. Forelimb Resistances . . . . . . . . . . 134 SUMMARY AND CONCLUSIONS . . . . . . . . . . . . . . 138 APPENDICES. . . . . . . . . . . . . . . . . . . . . 140 A. List of Abbreviations and Forelimb Vascular Resistance Calculations. . . . . . . . . 140 B. Pressure, Flow, and Resistance Data . . . . 143 C. Statistical Methods . . . . . . . . . . . . 161 BIBLIOGRAPHY. . . . . . . . . . . . . . . . . . . . 170 vi TABLE 1. LIST OF TABLES Effects of local hypotension and rapid arterial hemorrhage on mean intraluminal pressure in innervated skin arteries, small vessels, and veins . . . . . . . . . . . . . . . . . . . . . Effects of local hypotension and rapid arterial hemorrhage on mean intraluminal pressure in innervated muscle arteries, small vessels, and veins 0 O O O O O O O O O O O O O O O O I I O 0 Effects of local hypotension and rapid arterial hemorrhage on skin total, arterial, small vessel,and venous resistances (expressed as per- cent of control) in innervated forelimbs. . . . Effects of local hypotension and rapid arterial hemorrhage on muscle total, arterial, small vessel, and venous resistances (expressed as percent of control) in innervated forelimbs . . Effects of local hypotension and rapid arterial hemorrhage on slow, sustained changes in weight of innervated or denervated forelimbs . . . . . Effects of denervation, local hypotension, and rapid arterial hemorrhage on mean intraluminal pressure in skin arteries, small vessels, and veins 0 O O O O O O O O O O O O O O I O O O O 0 Effects of denervation, local hypotension, and rapid arterial hemorrhage on mean intraluminal pressure in muscle arteries, small vessels, and veins 0 O O O O O O O O O O O O O C O O O O I 0 Effects of local hypotension and rapid arterial hemorrhage on skin total, arterial, small vessel, and venous resistances (expressed as percent of control) in denervated forelimbs . . Effects of local hypotension and rapid arterial hemorrhage on muscle total, arterial, small vessel, and venous resistances (expressed as percent of control) in denervated forelimbs . . vii Page 67 68 73 76 81 82 83 88 95 LIST OF TABLES-“Continued TABLE 10. 11. 12. 13. 14. 15. Effects of rapid arterial hemorrhage on skin total, arterial, small vessel, and venous resistances (expressed as percent of control) in crOSSvperfused forelimbs. . . . . . . . . . Effects of rapid arterial hemorrhage on muscle total, arterial, small vessel, and venous resistances (expressed as percent of control) in cross—perfused forelimbs. . . . . . . . . . Effects of slow, continuous hemorrhage on skin total, arterial, small vessel, and venous resistances (expressed as percent of control) in innervated forelimbs. . . . . . . . . . . . Effects of slow, continuous hemorrhage on skin total, arterial, small vessel, and venous resistances (expressed as percent of control) in denervated forelimbs. . . . . . . . . . . . Effects of slow, continuous hemorrhage on mus— cle total, arterial, small vessel, and venous resistances (expressed as percent of control) in innervated forelimbs. . . . . . . . . . . . Effects of slow, continuous hemorrhage on mus- cle total, arterial, small vessel, and venous resistances (expressed as percent of control) in denervated forelimbs. . . . . . . . . . . . Effects of local hypotension and rapid arterial hemorrhage on systemic arterial pres- sure and arterial pressures in innervated forelimbs. . . . . . . . . . . . . . . . . . . Effects of local hypotension and rapid arteri- al hemorrhage on venous pressures and blood flows in innervated forelimbs. . . . . . . . . Effects of local hypotension and rapid arteri- al hemorrhage on the percent of total skin or skeletal muscle resistance residing in inner- vated large arteries, small vessels, and large veins. . . . . . . . . . . . . . . . . . . . . viii Page 101 105 112 113 117 118 144 145 146 LIST OF TABLES~-Continued TABLE B-4o B'7o B“10 o B'll o 3’12 0 Effects of denervation, local hypotension, and rapid arterial hemorrhage on systemic arterial and forelimb arterial pressures . . . Effects of denervation, local hypotension, and rapid arterial hemorrhage on forelimb venous pressures and blood flows. . . . . . . . . . . Effects of denervation, local hypotension, and rapid arterial hemorrhage on the percent of total skin or skeletal muscle resistance resid- ing in large arteries, small vessels, and large veins. . . . . . . . . . . . . . . . . . Effects of rapid arterial hemorrhage on sys- temic arterial pressure in donor and recipient dogs and on arterial pressures in cross-per- fused forelimbs. . . . . . . . . . . . . . . . Effects of rapid arterial hemorrhage on venous pressures and blood flows in cross-perfused forelimbs. O O O O O O O I O O O O I O O O O 0 Effects of rapid arterial hemorrhage on mean intraluminal pressure of skin arteries, small vessels, and veins in cross-perfused forelimbs Effects of rapid arterial hemorrhage on mean intraluminal pressure of muscle arteries, small vessels, and veins in cross-perfused _ forelimbs. . . . . . . . . . . . . . . . . . . Effects of rapid arterial hemorrhage on the percent of total skin or skeletal muscle resistance residing in large arteries, small vessels, and large veins in cross-perfused forelimbs. . . . . . . . . . . . . . . . . . . Effects of slow, continuous hemorrhage on systemic arterial pressure and arterial pres- sures in innervated forelimbs. . . . . . . . . Effects of slow, continuous hemorrhage on venous pressures and blood flows in innervated forelimbs. . O O O O O O O I O O O O O O O O 0 ix Page 147 148 149 150 151 152 153 154 155 156 LIST OF TABLES--Continued TABLE B-l4 a B-15 O B-l7 0 Effects of slow, continuous hemorrhage on systemic arterial pressure and arterial pres- sures in denervated forelimbs . . . . . . . . Effects of slow, continuous hemorrhage on venous pressures and blood flows in dener- vated forelimbs . . . . . . . . . . . . . . . Effects of slow, continuous hemorrhage on the percent of total skin or skeletal muscle re- sistance residing in innervated large arter- ies, small vessels, and large veins . . . . . Effects of slow, continuous hemorrhage on the percent of total skin or skeletal muscle re- sistance residing in denervated large arter- ies, small vessels, and large veins . . . . . Page 157 158 159 160 nu- L.- FIGURE 1. 2. 10. 11. LIST OF FIGURES Schematic of the canine forelimb preparation. Peak brachial and cephalic venous flow rates (expressed as percent of control) in 3 dogs after the release of l and 3 minute brachial artery occlusions . . . . . . . . . . . . . . Schematic of the servosystem used to control brachial artery pressure. . . . . . . . . . . Changes in forelimb weight during local hyva tension and rapid arterial hemorrhage . . . . Slow, sustained changes in weight of inner- vated forelimbs during local hypotension and rapid arterial hemorrhage . . . . . . . . . . Effects of local hypotension and rapid arter- ial hemorrhage on skin total, arterial, small vessel, and venous resistances in innervated forelimbs . . . . . . . . . . . . . . . . . . Effects of local hypotension and rapid arter— ial hemorrhage on muscle total, arterial, small vessel, and venous resistances in inner- vated forelimbs . . . . . . . . . . . . . . . Slow, sustained changes in weight of dener— vated forelimbs during local hypotension and rapid arterial hemorrhage . . . . . . . . . . Effects of denervation, local hypotension, and rapid arterial hemorrhage on skin total, arterial, small vessel, and venous resistances Effects of rapid arterial hemorrhage on skin vascular resistances in innervated or dener- vated forelimbs . . . . . . . . . . . . . . . Effects of denervation, local hypotension, and rapid arterial hemorrhage on muscle total, arterial, small vessel, and venous resist- ances . . . . . . . . . . . . . . . . . . . . xi Page 47 51 57 63 65 71 75 79 86 90 93 LIST OF FIGURESv-Continued FIGURE 12. 13. 14. 15. 16. 17. Effects of rapid arterial hemorrhage on muscle vascular resistances in innervated or dener— vated forelimbs. . . . . . . . . . . . . . . . Effects of rapid arterial hemorrhage of recip- ient and donor dogs on skin total, arterial, small vessel, and venous resistances in cross— perfused forelimbs . . . . . . . . . . . . . . Effects of rapid arterial hemorrhage of recip- ient and donor dogs on muscle total, arterial, small vessel, and venous resistances in cross- perfused forelimbs . . . . . . . . . . . . . . Effects of slow, continuous hemorrhage on mean systemic arterial, arterial pulse, and central venous pressures in dogs with innervated or denervated forelimbs . . . . . . . . . . . . . Effects of slow, continuous hemorrhage on skin total, arterial, small vessel, and venous re- sistances in innervated or denervated fore- limbs. O O O O O O O O O O O O O I O O O O O 0 Effects of slow, continuous hemorrhage on muscle total, arterial, small vessel, and venous resistances in innervated or denervated forelimbs. . . . . . . . . . . . . . . . . . . xii Page 97 100 104 108 111 116 INTRODUCTION Hemorrhage initiates direct and reflexly mediated changes in the cardiovascular system. Some of these changes tend to restore blood volume while others redistribute cardiac output helping to maintain perfusion in the corOv nary and cerebral circulations at the expense of that in tissues more capable of withstanding temporary oxygen and nutrient deficits. Restoration of the effective blood volume (ratio of blood volume to vascular capacity) follOWv ing hemorrhage is accomplished partly by absorption of extravascular fluid into the circulation (6,16,31,75,90,98), by decreased renal excretion of salt and water (53,59,60, 119,120), and by reduction of the intravascular capacity (31,41,69,89). Cardiac output is redistributed as a result of vasoconstriction in some tissues, especially skin, skeletal muscle, adipose, splanchnic, and renal, while in myocardial and cerebral tissues, little or no constriction occurs (31,48,55). The increase in total vascular resist- ance resulting from systemic vasoconstriction helps to maintain arterial pressure and perfusion of the myocardium and brain, which are not capable of withstanding prolonged oxygen and nutrient deficits. Because hemorrhagevinduced constriction is most in- tense in precapillary vessels (31,75,89,98), the pre- to postcapillary resistance ratio increases, tending to lower capillary hydrostatic pressure, to promote absorption of extravascular fluid, and to help restore plasma volume. The venous constriction observed during hemorrhage de- creases intravascular capacity and thereby helps to main- tain venous return and cardiac output despite the reduced blood volume (53,69). I Skin and skeletal muscle are important sites for some of the initial compensatory responses to bleeding because of their large vasoconstrictor response (21,22,66,89,115), and because they comprise a large proportion of the total body mass. In man, skeletal muscle and skin make up approximately 50 and 6 percent, respectively, of the total body mass (121) and together, during resting conditions, receive approximately 25 percent of the total cardiac out- put (53). Because of their potential compensatory impor- tance, responses of the skin and skeletal muscle vasculature to hemorrhage have been studied by many investigators (21, 22,66,75,89,98,115). Although the initial vasoconstriction, reduction in intravascular capacity, and reabsorption of extravascular fluid in skin and skeletal muscle during hemorrhage are well documented (21,22,31,89,115), there is considerable disagree- ment about the mechanisms by which these changes occur. Some investigators (41,75,87,108) suggest that the venous constriction, and the consequent reduction in intravascu- lar volume observed during hemorrhage, is due primarily to passive collapse of veins subsequent to a fall in trans- mural pressure. Others (76,89,98) suggest that venous constriction and intravascular fluid mobilization are due largely to active smooth muscle contraction. There are also conflicting reports about the relative importance of sympathetic nerves and circulating vasocon- strictors in mediating the active portion of the increased vascular resistance in skin and skeletal muscle during hypovolemia. According to Bond 92.21' (21,22), circulat- ing catecholamines are the primary mediators of the hemorrhage-induced vasoconstriction in skin, whereas both sympathetic nerves and circulating catecholamines mediate the increased vascular resistance in skeletal muscle. However, several other investigators (89,93,95,96,98) have reported that sympathetic nerves are the primary mediators of the resistance response to hemorrhage in both skin and skeletal muscle. These disparate findings may be related to differences in experimental design. Most investigators have standardized hemorrhages either according to the amount of hypotension produced (21,22,75), or the total volume of blood removed (89,115). In some cases (87) the rate of blood loss has been controlled, but few investigators have examined the effect of different bleeding rates on skin and muscle vascular control. The present study was designed to examine systematically the relative contributions of neural, humoral, and passive factors to the compensatory vasoconstriction, reduction in intravascular capacity, and reabsorption of extravascular fluid which occur in skin and skeletal muscle during hemorrhage. \. n LITERATURE REVIEW 1. Control of Vascular Resistance During Hemorrhage A. General Considerations According to the law of Pouiseuille, the determinants of resistance to fluid flow in cylindrical tubes are: R = 4 eq. 1 where: R = resistance to fluid flow n = fluid viscosity = tube length = constant of proportionality Hdlml-J = tube radius Although this relationship applies to Newtonian fluids (in which the ratio of shear stress to shear strain is constant) flowing in cylindrical tubes, it has been used extensively in modeling the circulation and analyzing the factors which contribute to the control of vascular resistance during hemorrhage. Physiologically, the most important factor in equation 1 influencing vascular resistance is blood vessel radius. The radii of blood vessels can be altered by con- tzraction and relaxation of circularly arranged vascular smnooth muscle, which in turn is influenced by autonomic c'v - II- («~- 0" up. ~o. - u.‘ PI. ‘5. nerves, circulating vasoactive chemicals, local vasodilator metabolites, and physical factors such as transmural pres- sure (intraluminal pressure-tissue pressure). An "active" change in vascular radius is mediated through an alteration in the contractile state of vascular smooth muscle; a "passive" change in radius is any change not mediated through alterations in the contractile state of vascular smooth muscle (72). During hemorrhage, both active and passive constriction contribute to the increased vascular resistance in skin and skeletal muscle (72). Since resist- ance is inversely proportional to the fourth power of the radius (equation 1), small decreases in blood vessel radius will produce marked increases in vascular resistance. Changes in blood viscosity (equation 1) may also con- tribute slightly to elevations in skin and skeletal muscle vascular resistance during hemorrhage. Early in hemorrhage, blood viscosity may increase slightly since flow velocity is decreased, and in some species, splenic contraction releases blood rich in red cells into the circulation result— ing in a transient increase in hematocrit (31,72,110). The increase in hematocrit is not prolonged since reabsorption of extravascular fluid into the circulation returns the red blood cell concentration toward normal (72,75). Consequently, Linoreases in blood viscosity are probably of minor importance ix: increasing vascular resistance during hemorrhage (31,72). -, The other variable in equation 1 which could influence vascular resistance during hemorrhage is blood vessel length. Since the length of blood vessels is normally con- stant, increases in skin and muscle vascular resistance during hemorrhage are due primarily to reductions in blood vessel radius (72). Hemorrhage could reduce vessel radius by eliciting constriction mediated through sympathetic nerves or through the release of hormones such as catechol- amines, angiotensin, and vasopressin. When blood loss is severe enough to reduce transmural pressure, passive vascu- lar constriction may also contribute to the increased resistance to blood flow, especially in veins. B. Neural Control Sympathetic adrenergic nerve fibers are considered by many investigators to play the dominant role in adjusting skin and muscle vascular resistance during hemorrhage (89, 93,95,96,98). Adjustments of blood flow by sympathetic constrictor fibers depends on regional nerve fiber distribu- tion density, effector sensitivity. and variations in vaso- constrictor fiber discharge frequency (53). Several investigators have studied the distribution of adrenergic nerve terminals in the vasculature of skin and skeletal muscle. Fuxe and Sedvall (58) found that lairge arteries and veins in the cat gastrocnemius and tibialis anterior muscles had sparse adrenergic innervation, but that intramuscular small arteries, arterioles, and metarterioles were richly supplied with adrenergic nerve terminals. Angelakos gt 21- (ll), using fluorescence histochemical techniques, found extensive adrenergic inner- vation in all skeletal muscle vessels. In skin, arteries, small vessels, and veins, all have an abundant adrenergic innervation (53,46). Effector sensitivity to sympathetic nerve stimulation has been studied in several skin and muscle vascular beds. In the dog forelimb (a combined skin and skeletal muscle preparation), stimulation of nerve fibers within "physiological" frequencies (1-16 impulses/sec) produced increases in total forelimb vascular resistance due primar- ily to increases in skin large artery resistance, but partly due to constriction of muscle large arteries and veins, and skin large veins (3,5). However, in the skin and muscle small vessels, which provided the greatest percentage of total forelimb vascular resistance, nerve stimulation produced no consistent changes in resistance (3,5). Hammond, Davis, and Dow (78) studied resistance changes of the arterial, small vessel, and venous segments of the dog hind paw (primarily skin) during stimulation of the sciatic nerve and three of its branches (tibial, deep and superficial fibular nerves). They observed increased resistance in all xrascular segments during sciatic nerve stimulation with the greatest percent increases occurring in the large artery segment. Small vessel resistance increased only 16 percent above control values even during supermaximal voltage and frequency stimulations. Zimmerman (130) also observed large increases in skin arterial resistance but relatively minor small vessel constrictor responses during sympathetic nerve stimulation. These studies demonstrate that stimula- tion of sympathetic nerves elicits increases in skin and skeletal muscle vascular resistance mainly by constricting large arteries. The small vessels, which offer the largest percent of total vascular resistance, are relatively unre- sponsive to sympathetic nerve stimulation. Variation of sympathetic nerve fiber discharge fre- quency during hemorrhagic hypotension has also been examined (18,34,61,62). Gernadt g£_§l, (61), reported that hemorrhage increased efferent impulses in the splanchnic nerve of the cat. Corazza (34) recorded action potentials in the cer- vical sympathetic nerve of rats and reported an increase in frequency after hemorrhage. Beck and Dontos (18) reported increases in electrical activity of splanchnic nerves in both dogs and cats hemorrhaged to mean arterial pressures of 55 and 45 mm Hg. Other investigators have attempted to determine indi- rectly changes in sympathetic impulse traffic during hemor— :rhage by comparing the hemodynamic responses in the skin and skeletal muscle vasculature observed during graded sympathetic nerve stimulation to those found in hemorrhage. 10 Lungren §E_al. (89) using cat hindlimb muscles cross- perfused at constant flow with blood from normovolemic donor cats, concluded that various levels of hemorrhage were associated with increases in sympathetic impulse fre- quency from a control value of less than 1 impulse per second to as high as 7 impulses per second. Evaluation of changes in sympathetic activity was based on comparison of reflexly mediated resistance changes during hemorrhage with those obtained by graded stimulation of hindlimb vasocon- strictor nerve fibers. Neural control of vascular resistance during hemor— rhage has also been studied by comparing the hemodynamic responses of innervated and denervated skin and skeletal muscle vascular beds. Green (63), observed that hemorrhage produced an increase in cutaneous vascular resistance which could be partially blocked by acute denervation. Rothe gt $1. (109), perfusing the dog gracilis muscle at constant arterial pressure, reported a rise in vascular resistance after hemorrhage which was abolished by cooling the gracilis nerve. Bond 33 31. (21), using a dog hindpaw preparation (primarily skin), reported that acute denervation did not attenuate the resistance response to severe bleeding, and concluded that cutaneous vasoconstriction during hemorrhage teas not mediated by sympathetic nerves. In another study, tising a dog hindlimb preparation (primarily muscle), Bond (31: 31. (22) reported that denervation reduced but did not 11 abolish the resistance response of the muscle vasculature to hemorrhage, suggesting that both sympathetic nerves and circulating hormones mediated the vasoconstriction in muscle. Although the resistance vessels of skin and skeletal muscle are innervated by sympathetic adrenergic fibers, most of the available data suggest that hemorrhage-induced constriction, especially in small vessels, is not mediated entirely by nerves. The small vessels, which offer the largest percentage of resting resistance and the greatest capacity to increase resistance during hemorrhage, show little response to nerve stimulation. Therefore, the large increases (10 fold) in vascular resistance during severe hemorrhage are mediated partly by circulating vasocon- strictors. C. Humoral Control 1. Catecholamines Activation of the sympathetic nervous system by blood loss increases release of epinephrine and norepinephrine from the adrenal medulla (45). Investigators using bioassay or fluorometric techniques demonstrated that hemorrhage resulted in elevated catecholamine concentrations in sys- temic (19,77) or adrenal venous blood (56,124,126). In reviewing the data from several studies on hemorrhage in anesthetized dogs, Watts (125) reported that severe blood loss may result in a 50 fold increase in systemic venous 12 plasma concentration of epinephrine and a 10 fold increase in norepinephrine concentration. Similar results were found in unanesthetized dogs (125). Hall and Hodge (77) observed no increase in circulating catecholamine levels in the dog during slow hemorrhage which was not severe enough to lower mean arterial pressure. However, rapid hemorrhage which significantly reduced mean arterial pres- sure, resulted in marked increases in blood catecholamine concentrations. Carey (28) measured the adrenal secretory rate of epinephrine and norepinephrine in unanesthetized pigs and reported that slow, continuous hemorrhage (10 per- cent reduction in blood volume in 30 minutes or 30 percent reduction in 90 minutes) elicited no significant increases in adrenal vein epinephrine and norepinephrine concentra- tions even if bleeding was continued until mean arterial pressure was reduced to 50-60 mm Hg. However, he reported that rapid blood losses (10 percent of the total blood volume in 10 minutes or 30 percent in 30 minutes) elicited large increases in both epinephrine and norepinephrine concentrations in adrenal venous blood. He concluded that the rate of release of catecholamines from the adrenal medulla during hemorrhage depended on the rate of blood loss more than the magnitude of the blood pressure reduction produced. These data indicate that large increases in blood catecholamine concentrations can occur during rapid, severe henmmrhage, but during slow hemorrhage blood catecholamine 13 levels may not be significantly increased. Several investigators have demonstrated that catechol- amines are potent cutaneous and skeletal muscle vasocon- strictors (2,5,37,92,129). Abboud and Eckstein (5) reported that l and 2 pg injections of norepinephrine into the arterial supply of the dog forelimb produced marked .increases in total skin vascular resistance due primarily to constriction of small vessels and large veins. In the muscle vasculature, norepinephrine injection increased small vessel and venous resistances, but much less so than in the skin vasculature. In another study, Abboud (2) in- fused norepinephrine into the dog gracilis muscle and hind- paw and confirmed his findings in the forelimb. Mellander (92) found similarities between the responses to norepine- phrine and sympathetic nerve stimulation in the hindlimbs of cats (primarily skin and muscle). In Mellander's studies, the arterial and venous pressures were held con- stant and changes in hindlimb weight, rate of venous outflow, and protein content of the drained venous plasma were measured. Since arterial and venous pressures were held constant, and plasma protein concentrations were not measure- ably altered by nerve stimulation or norepinephrine infusion, changes in limb weight after flow had stabilized were as- sumed to be due to alterations in the pre— to postcapillary resistance ratio. He concluded from these studies that norepinephrine, as well as nerve stimulation, constricted 14 precapillary vessels relatively more than postcapillary vessels. These studies (2,5,92,129) indicate that cate- cholamines produce marked increases in skin and skeletal muscle vascular resistance in normovolemic animals. However, some investigators suggest that during hemorrhage, vascular constriction due to increased release of catechol- amines from the adrenal medulla is relatively minor compared to that produced by sympathetic nerve stimulation. Celander (29) estimated that the maximal secretion rate of catecholamines (both norepinephrine and epinephrine) from the adrenal medulla was not greater than 5 ug/kg body weight per minute. The vasoconstriction induced by intra- venous infusions of norepinephrine and epinephrine at doses ranging from 0.1 to 5 ug/kg body weight per minute in these studies was always much less than that produced by sympa- thetic nerve stimulation within "physiological" ranges (i.e., 1-16 impulses/sec.). Celander also noted that stimulation of the nerve supply to the adrenal gland, which releases catecholamines into the systemic circulation, was much less effective in producing vasoconstriction than was stimulation, at comparable frequencies, of nerve fibers to the leg mus- cles. He concluded from these studies that blood vessels of skin and skeletal muscles are dominated by activity of sympathetic adrenergic fibers and that any constriction by cuatecholamines from the adrenal medulla is relatively insig— nificant. 15 Several investigators (53,95,98) have extrapolated Celander's observations to suggest that circulating cate- cholamines are not important mediators of vasoconstriction in skin and skeletal muscle during hemorrhage. However, Celander's findings may not be applicable to hypovolemic animals for the following reasons: a) Celander assumed that splanchnic nerve stimulation (up to 10 impulses/sec) produced maximum release of epinephrine and norepinephrine from the adrenal medulla. However, several studies suggest that during hemorrhage other factors such as hypoxia of the adrenal medulla, and elevated concentrations of angio- tensin, vasopressin, and adrenal corticoids also contribute to an increased release of catecholamines from the adrenal medulla (31,47,77,79); b) Celander attempted to determine the effects of maximum "physiological" doses of catechol- amines on skin and skeletal muscle vascular resistance by infusing the catecholamines intravenously in normovolemic animals. However, vasopressin, angiotensin, and adrenal corticoids which are all released during hypovolemia (36,77, 107,119), not only stimulate the release of catecholamines, but also potentiate their effects on vascular smooth muscle contraction (4,8,113,ll4,131). Consequently, during hemor- rhage, when vasopressin, angiotensin, and adrenal corticoid blood concentrations are elevated, the effects of catechol- anunes on vascular smooth muscle contraction may be greater tfllan in a normovolemic, normotensive animal; 0) Intravenous 16 infusion of catecholamines in normovolemic animals may have produced reflex effects (i.e., an increased blood pressure causing reductions in the release of circulating vasocon- strictors such as angiotensin or vasopressin) which may have partially masked the direct effects of the infused catecholamines on the skin and muscle vasculature. Because the concentrations of circulating catechol- amines in hypovolemic animals may not be the same as those produced by splanchnic nerve stimulation, and because the effects of catecholamines on vascular smooth muscle contrac- tions may differ in normovolemic and hypovolemic animals, it is hazardous to conclude from Celander's study that circulating catecholamines do not affect vascular resistance during hemorrhage. The studies of Bond gt ii- (21) suggest that during hemorrhage, circulating catecholamines are the primary mediators of the resistance response in skin vessels, and contribute significantly to the vasoconstriction in skeletal muscle. 2. Angiotensin Elevated plasma concentrations of angiotensin may also contribute to increased vascular resistance in skin and skeletal muscle during hemorrhage. Several investigators have shown that the blood concentration of angiotensin rises during hemorrhage (24,32,77). The data of Claybaugh and Share (32) and Brown (24) indicate that renin release, and presumably angiotensin formation, is related to the rate of 9” ‘ In..- ~nay am. ”5'4- '. I”. a... §_‘ 1“. a 17 blood loss; slow rates of hemorrhage did not increase plasma renin concentrations significantly, but rapid blood losses increased plasma renin concentrations markedly. Increased plasma concentrations of angiotensin exert a direct vasoconstrictor effect on skin and skeletal muscle blood vessels (2,51,70,129). Experiments on cat hindlimbs (51) and dog forelimbs (2,70) indicated that angiotensin infusion produces a marked constriction in precapillary resistance vessels. Zimmerman (129) and Abboud (2) reported that angiotensin's vasoconstrictor action was augmented at high sympathetic tone. In addition to its direct effects on skin and muscle vascular resistance, angiotensin exerts indirect effects on vascular tone through adrenergic mechanisms. Feldberg and Lewis (47) demonstrated that angiotensin stimulates release of catecholamines from the adrenal medulla. Angio- tensin also increases release of norepinephrine from peri- pheral nerve endings, stimulates discharge of central vaso- motor neurons, and interacts with catecholamines at alpha receptors to augment contraction of vascular smooth muscle (131). The significance of angiotensin in mediating increases in vascular resistance in skin and skeletal muscle during immorrhage has not been thoroughly evaluated. Although lkMeill at 31. (91) reported that angiotensin is an important nmdiator of intestinal vasoconstriction during hemorrhage, 18 some investigators (72,73,95) conclude that the rising concentrations of angiotensin are not sufficient to cause important direct effects on vascular resistance. However, angiotensin's indirect effects on vascular resistance through adrenergic mechanisms may contribute significantly to the vasoconstriction observed during hemorrhage. 3. Vasopressin Vasopressin, a potent skin and skeletal muscle vaso- constrictor (73,95), is released from the posterior pitui- tary during hemorrhage (119). Because vasopressin exerts antidiuretic effects at plasma concentrations well below those required for vascular changes, some investigators suggest that vasopressin is most important as a regulator of water reabsorption in the renal tubules and does not contribute significantly to the regulation of vascular resistance (53,95). However, Rocha e Silva and Rosenberg (107) reported that infusions of vasopressin, which repro- duced plasma concentrations observed during hemorrhage, caused pressor responses. In a recent study, Schmid gt 31. (112) reported that intravenous infusions of 1-2 uU vasopressin/kg per minute, which produced plasma concentra— tions below those reported during hemorrhage, elicited a significant vasoconstriction in dog skeletal muscle. The increased vascular resistance was attributed to a direct effect of vaSOpressin on vascular smooth muscle since hexa- umthonium bromide, which blocks transmission in autonomic 19 ganglia, was administered. Other investigators (2,71) have demonstrated that intravarterial infusions of vaso— pressin constrict precapillary resistance vessels in skin and skeletal muscle. The role of vasopressin in the regulation of skin and skeletal muscle vascular resistance during hemorrhage has not been investigated extensively. In a study using the dog forelimb, Haddy e£_al, (75) reported that the constrin tor response to hemorrhage was abolished by a combination of carotid sinus procainization, vagotomy, adrenalectomy, and bilateral nephrectomy. The investigators assumed that these four procedures blocked adrenergic and angiotensin constrictor mechanisms but did not reduce the release of vasopressin during hemorrhage. Therefore, they concluded that the vasopressin released during hemorrhage was not sufficient to constrict forelimb vessels. However, Rocha e Silva and Rosenberg (107) reported that arterial barorecep— tors play a very important role in the hemorrhagevinduced release of vasopressin. Consequently, in Haddy gt_§lfs. study carotid sinus procainization and vagotomy may have inhibited vasopressin secretion during hemorrhage. D. Passive Responses Sympathetic nerve stimulation, catecholamines, angio- tensin, and vasopressin all constrict the skin and skeletal numcle vasculature through active changes in blood vessel radius (changes due to contraction of vascular smooth muscle). ':A_D our. 9'- 'Q» I... u v :3 - p.'¥ u. kl. u." ‘- ‘Ud ‘ 20 However, when blood loss is severe enough to lower arterial and venous pressures, passive constriction (due to elastic recoil of blood vessels subsequent to a decreased transmural pressure) may also contribute to the increased vascular resistance in skin and skeletal muscle. Precapillary vessels, which provide most of the total skin and skeletal muscle vascular resistance, show only small changes in resistance when perfusion pressure is reduced (54,94,95). This response is due in part to local vasodilatory mechanisms which relax arterioles when perfu- sion pressure is reduced (74,95), but occurs partly because precapillary resistance vessels have a relatively large wall thickness to lumen diameter ratio (27), and therefore can withstand reductions in transmural pressure without col- lapsing. The large veins have a relatively low wall thickness to lumen diameter ratio and some investigators have proposed that the venous constriction observed during hemorrhage results primarily from passive vascular collapse subsequent to a reduced transmural pressure (75,87). Other investiga- tors (76,89) have concluded that active constriction, rather than passive vascular collapse, accounts for most of the increased venous resistance during hemorrhage (see section II-D for a discussion of active vs. passive changes in venous resistance during hemorrhage). Regardless of the relative importance of active and passive venous constriction 21 during hemorrhage, passive collapse probably contributes only slightly to the increased total skin and skeletal muscle vascular resistance which accompanies hemorrhage, since large veins offer a small fraction of the total resistance (1). II. Control of Vascular Capacitance Durinngemorrhage A. General Considerations Decreased vascular capacitance helps to compensate for hemorrhage by transiently displacing blood from vessels and thereby providing a momentarily increased venous return. The new steady state decrease in capacitance results in a smaller vascular volume and a shorter mean transit time for blood flow from the left to the right heart. This de- creased transit time helps to maintain venous return and cardiac output despite a decreased blood volume. Veins are especially important in changing vascular capacitance because they contain most (60-80 percent) of the total blood volume (7,128). Reductions in venous capa- citance during hemorrhage could result from passive collapse of veins subsequent to decreases in venous transmural pres- sure or from active contraction of venous smooth muscle. Active venoconstriction during hemorrhage could be mediated kw increased sympathetic adrenergic nerve stimulation and/or increased concentrations of blood-borne vasoconstrictors 22 such as catecholamines, angiotensin, or vasopressin. While there is general agreement that vascular capacitance in skin and skeletal muscle is reduced during hemorrhage, there is disagreement about the relative importance of neural, humoral, and passive venoconstriction in mediating these capacitance changes. B. Neural Control Large veins in skin and skeletal muscle are innervated by sympathetic adrenergic fibers (3,46,58), and stimulation of these fibers elicits active venoconstriction (3,50,78, 130). Mellander (92), using graded sympathetic nerve stimulation, observed marked increases in resistance and decreases in capacitance of skin and skeletal muscle veins. When sympathetic nerves were stimulated during a period of complete arterial occlusion, a decrease in tissue volume was observed. Since arterial inflow was stopped, the reduction in tissue volume could not have been due to passive collapse of veins subsequent to arteriolar constriction (which would decrease venous inflow), but was attributed to active con- Striction of capacitance vessels. Mellander estimated that at "basal vascular tone" (resting contractile state of Vascular smooth muscle when all known extrinsic excitatory influences are removed) up to one-third of the blood in a Skin and skeletal muscle preparation could be mobilized as éi.result of sympathetically mediated venous constriction. 23 Other investigators have studied venomotor reactions to nerve stimulation by monitoring pressure changes in occluded veins. After the vein has been occluded and the venous pressure has stabilized, any change in venous pres- sure is presumed to be due to active changes in venous tone as long as extravascular compression due to skeletal muscle contraction is eliminated by a neuromuscular block- ing agent. Browse et_al. (26), using the venous occlusion technique, found that sympathetic nerve stimulation pro- duced active constriction of veins in the dog hindlimb (primarily skin and skeletal muscle). Browse gt_al. (25), using this same technique, also reported that carotid sinus hypotension produced reflexly mediated decreases in venous capacitance. Although most investigators agree that sympathetic nerve stimulation can elicit significant increases in venous resistance and decreases in capacitance, there is disagree- ment about the importance of neurogenically mediated capa- citance changes during hemorrhage. Lesh and Rothe (87) studied reflex venoconstrictor responses in dog gracilis muscle during hemorrhage and during local hypotension pro- duced by mechanically reducing arterial inflow. Since the initial rapid phase of muscle weight loss (attributed prim— arily to reduction in intravascular capacity) was not sig— nificantly greater during hemorrhage than during local hypotension, they concluded that active venous constriction 24 accounts for a negligible fraction of the reduced venous capacitance observed during hemorrhage. Instead, Lesh and Rothe attributed most of the decreased venous capacitance to elastic recoil of veins subsequent to a reduced trans? mural pressure. However, they noted that when blood flow was held constant, sympathetic nerve stimulation produced a decrease in mean transit time (T) of a tracer dye (indo— Cyanine green). The relationship between T} blood flow (F), and blood volume (V) in a vascular bed is expressed as: V = F x T. eq. 2 In Lesh and Rothe's study, the observation that nerve stimulation decreased T with F held constant implies that vascular volume was reduced. They suggested that T may have been reduced because nerve stimulation contracted pre- capillary sphincters causing "functional shunting" of blood (i.e., a high proportion of blood flowing through relatively short, direct channels from the arterial to the venous side). Although non-exchange shunt vessels have not been observed in skeletal muscle (17), the concept of "functional shunt- ing“ is supported by Renkin and Rosell's (105) observation that nerve stimulation decreased the extraction of 86Rb dur« ing constant flow perfusion. But even if short, non-exchange shunt vessels do exist, there is no evidence in Lesh and Rothe's study that the reduced mean transit time which they 25 observed during nerve stimulation was due to shunting of blood rather than to decreased vascular capacity. C. Humoral Control Active constriction of veins due to increased concen- trations of circulating vasoconstrictors such as norepine- phrine, epinephrine, angiotensin, and vasopressin may con- tribute to decreases in vascular capacitance during hemor- rhage. Norepinephrine and epinephrine have been shown to constrict veins in the human forearm (17), dog forelimb (5), dog hindpaw (130) and dog gracilis muscle (87). Tissue volume changes, measured with plethysmographic (92) or gravimetric techniques (118) indicate that catecholamine infusions or injections produced decreases in venous volume. Shadle 25 31. (118) using a dog hindlimb preparation placed in a plethysmograph and perfused at constant arterial inflow, observed an increased perfusion pressure (indicating in- creased resistance to blood flow), a transient decrease in venous outflow, and a transient increase in limb weight dur- ing norepinephrine infusion. They attributed the initial increase in weight to distention of arteries proximal to the site of constriction. Eventually as the rising perfusion pressure overcame the increased resistance to flow, venous outflow increased above arterial inflow and limb weight decreased rapidly. They concluded that the rapid decrease in limb weight was due to translocation of blood centrally 26 by active constriction of veins. Because only small changes in blood concentrations of plasma-tag T—1824 and erythrocyte— tag 32P occurred as limb weight was reduced, only a small part of the change in limb weight was attributed to net reabsorption of interstitial fluid. Mellander (92) noted decreases in flow and vascular volume in the cat hindleg dur- ing norepinephrine infusion and concluded that both resist- ance and capacitance vessels were actively constricted. Intra-arterial infusions of epinephrine resulted in transient increases in venous outflow, simultaneously with a decreased limb volume, suggesting a reduction in vascular capacitance. Although a potent constrictor of precapillary vessels, angiotensin is reported to exert minimal influence on post- capillary vessels (1,2,51,70). Folkow gt 21. (51) compared the effects of angiotensin and norepinephrine on the cat hindlimb when infused intra—arterially in concentrations that produced equal increases in vascular resistance, and noted that norepinephrine produced a marked decrease in tissue volume but angiotensin produced only a small decrease in tissue volume. These observations suggested that angio- tensin elicited only small increases in venous resistance and hence only small decreases in vascular capacity. Abboud (2), using dog forelimb and hindpaw preparations, also noted that angiotensin produced increases in total skin and muscle vascular resistance, but did not appreciably constrict venous vessels. 27 Although many investigators have concluded that angiOv tensin does not exert significant direct effects on venous capacitance, it is possible that indirect effects of angio- tensin on venous capacitance and resistance may be important during hemorrhage. Angiotensin not only stimulates the release of norepinephrine from the adrenal medulla and adrenergic nerve terminal, but is also reported to interact with catecholamines at a receptors to augment contraction of vascular smooth muscle (130). Consequently, the contribution of angiotensin to active changes in vascular capacitance during hemorrhage can not be determined simply by perfusing vascular beds of normovolemic animals with concentrations of angiotensin known to occur during hemorrhage. Vasopressin, like angiotensin, constricts precapillary resistance vessels but exerts minimal effects on postcapil- lary capacitance vessels (2,20,73,95). Haddy gt_gl. (70,71) reported that vasopressin infusions produced an increased total forelimb vascular resistance, but did not increase venous resistance. Abboud (2) found similar results in the dog forelimb and hindpaw. However, injections of vasopres- sin into a small digital vein caused a marked increase in digital vein pressure, suggesting that vasopressin in high concentrations will constrict veins (39). Although these studies suggest that the direct effects of vasopressin on vascular capacitance during hemorrhage are minimal, vasopressin's indirect effects through its 28 interaction with other vasoconstrictors at smooth muscle receptor sites have not been investigated thoroughly. Vasopressin may contribute to decreases in vascular capacity during hemorrhage via a potentiation of the venoconstriction produced by catecholamines. Powell and Du Charme (103) recently presented evidence that a non-angiotensin pressor material released from the kidney contributed significantly to the decreased total vascular capacity which accompanied hemorrhagic hypotension. In an earlier study, Du Charme and Beck (42) studied capa— citance responses of the whole circulatory system by observ- ing translocations of blood between the vascular system and an extracoporeal reservoir and found that the potential of the renal pressor system to reduce total vascular capa- city was approximately 60 percent of the potential of the sympathetic nervous system. Although these investigators did not identify the pressor agent or the specific site(s) of decreased vascular capacity, it is possible that this pressor agent decreases vascular capacity in skin and skeletal muscle during hemorrhage. D. Passive Responses Active constriction of veins during hemorrhage may also be accompanied by passive expulsion of blood whenever venous transmural pressure is reduced. Venous transmural pressure could be reduced during hemorrhage by a fall in arterial 29 blood pressure and consequently a reduced venous inflow even if no vasomotor adjustments occurred. Active precapil- lary constriction further reduces venous inflow and hence venous transmural pressure. The magnitude of passive adjustments of venous volume apparently varies considerably depending on the prevailing venous transmural pressure (99), since the distensibility of veins varies greatly with the venous pressure (7,27). At low pressures, even a small decrease in pressure is followed by a marked decrease in volume, as indicated by the convexity of the venous pressure-volume curve towards the volume axis (i.e., the distensibility of large veins is very high at low venous pressures). At high venous pres- sures, the veins contain a large blood volume and are dis- tended (7,27). Oberg (99) reports that the volume of dis- tended veins is little affected by moderate changes in transmural pressure (i.e., the distensibility of veins is low when transmural pressures are high). Consequently, during hemorrhage, the relative importance of active and passive changes in venous capacitance should vary depending upon the prevailing venous transmural pressure. Lungren gt a1. (89) measured changes in regional blood volume in cat hindlimbs with a plethysmograph during hemor- rhage and when blood flow was mechanically reduced to the levels observed during hemorrhage. They deduced that only 5-10 percent of the total regional blood volume was passively 30 expelled during moderate hemorrhage (15-20 percent of the total blood volume) while active constriction mobilized 20-25 percent of the regional blood volume. Although these data differ from those reported by Lesh and Rothe (see section II-B), who suggested that passive collapse accounted for most of the reduced vascular capacity during hemorrhage, they indicate that a small but significant reduction in vascular capacity occurs due to passive vascular collapse. III. Transcapillary Fluid Movement During Hemorrhage A. General Considerations Many investigators have demonstrated that hemorrhage is accompanied by a redistribution of the extracellular fluid, leading to a compensatory increase in plasma volume at the expense of the interstitial fluid volume (6,15,16, 40). The fluid which enters the microcirculation from the tissue is largely protein free (30,38,122), and the degree and rate of entry appears to depend on the severity of the blood loss (31). Adolph at al. (6) found that dogs sub- jected to a 20-35 ml/kg body weight blood loss replaced 35 percent of the plasma volume deficit within 20 minutes. Hemorrhage has also been observed to cause hemodilution in man (88), cats (68), and rats (102). These studies (6,16, 30,40) indicate that a considerable amount of fluid can be mobilized rapidly from extravascular sites to aid in the .‘ ,o. on; a. In". I 31 restoration of plasma volume following hemorrhage. However, the complete restoration of plasma volume requires several days, and involves reduction of renal salt and water excrev tion concurrently with an increased salt and water intake (59,60,119,120). The principle factors which alter the distribution of fluid between the intra« and extravascular compartments dur: ing hemorrhage were proposed by Starling (123) as follows: the direction and rate of fluid transfer between plasma and the tissue spaces depends on the hydrostatic Pressure on each side of the capillary wall, on the protein osmotic pressures of plasma and tissue fluid, and on the filtering properties of the capillary membrane. Experimental support for this hypothesis was obtained by Landis (84) for frog mesenteric capillaries and by Pappenheimer and Soto—Rivera (101) for capillaries in dog skeletal muscle. The follow- ing equation has been used to express Starling's hypothesis (85): F = K [(Pc - Pt) - (up - nt)] eq. 3 where: F = rate of transcapillary fluid movement (ml/min per 100 gm tissue weight; a positive number indicates fluid filtration out of the capillaries, whereas a negative number indicates fluid reabsorption into the capillaries. K = a coefficient for capillary filtration which represents the product of total surface area and permeability per unit surface area to the fil- tered flTid (ml/min per 100 gm tissue weight) x (mm Hg)’ ) 32 PC = capillary hydrostatic pressure (mm Hg) Pt = tissue hydrostatic pressure (mm Hg) Hp = plasma colloid osmotic pressure (mm Hg) “t = tissue fluid colloid osmotic pressure (mm Hg) In skin and skeletal muscle, there is normally a slight net outward movement of fluid, which is returned to the circulation via the lymphatic system (53). During hemor- rhage, this balance is upset, and a net reabsorption of fluid from the tissues into the microcirculation occurs. This net reabsorption could occur through several mechan- isms. Reflex vasomotor adjustments could affect directly or indirectly all of the variables in equation 3, but the most direct effects are probably on capillary hydrostatic pressure (PC), which according to Pappenheimer and Soto- Rivera (101), can be expressed as: Pc — (R;7Ra) + 1 eq‘ 4 where: Ra = precapillary vascular resistance RV = postcapillary vascular resistance Pa = arterial pressure Pv = venous pressure Hemorrhage tends to lower Pa and PV and hence Pc' facilitating fluid transfer from the tissues into the micro- circulation. Reflex alterations in the distribution of pre— and postcapillary resistance also occur during hemorrhage 33 due to differential effects of adrenergic nerve stimulation, circulating vasoconstrictors, and changes in transmural pressure on pre- and postcapillary vessels (73,96,98). For example, an increase in the pre- to postcapillary re- sistance ratio would favor a net movement of fluid into the circulation. The rate of fluid movement across the capillaries is affected not only by the hydrostatic and colloid osmotic pressure gradients, but also by the properties of the capil- lary membrane (expressed by coefficient K in equation 3). Both the permeability and the surface area of the vessels available for exchange will influence the rate of fluid movement produced by a given hydrostatic or osmotic pressure gradient across the capillaries. Since capillary permeabil- ity is not altered during hemorrhage (31) or even severe hypoxia (116), changes in K depend on changes in the func- tional capillary surface area due to opening or closure of precapillary sphincters (31,95). For example, contractions of precapillary sphincters will exclude some capillaries from participating in fluid exchange between intra- and extravascular compartments, thus reducing the functional capillary surface area. Two different methods have been used to evaluate rela- tive changes in capillary surface area. One involves calcu- lating a permeability surface area (PS) product from the arteriovenous extraction fraction of radioactive potassium or 34 rubidium (104,105,106), or from rate of tissue washout of hydrophilic radioactive tracers (i.e., iodide or sodium) (12,13,14,86) at known flow rates. These tracers move rapidly across the capillary membrane and backflux is usual- ly negligible, but can be corrected for if necessary. This method cannot separate the permeability or surface area terms from the PS product. The other method is based on hydrodynamic conductivity of the exchange vessels in terms of a capillary filtration coefficient (CFC). The CFC is determined by volumetric or gravimetric recording of the amount of fluid filtration into the tissues produced by an estimated increase in Pc' assuming that P and np re- t' 1Tt' main reasonably constant (52,92,98). The capillary filtra- tion coefficient is assumed to be largely independent of blood flow rate (94) whereas PS is recognized to vary with flow rate (105). CFC like PS, reflects the product of capillary surface area and permeability and is presumed to be proportional to PS under most conditions (94,95). Since capillary permeability is unaltered in most physiological conditions, changes in PS or CFC in a given vascular bed will reflect alterations in the functional capillary surface area (94,95). B. Neural Control There is general agreement that stimulation of sympa- thetic adrenergic nerves can alter the distribution of 35 intra- and extravascular fluid (31,33,92,95). Adrenergic fibers innervate pre- and postcapillary vessels, and pre- capillary sphincters, and stimulation of these fibers has been demonstrated to alter the rate of fluid movement across the capillaries by changing both the pre- to postcapillary resistance ratio and the capillary surface area (33,92). Mellander (92) used cat hindlimb preparations to esti- mate changes in pre- and postcapillary resistance and tissue volume during sympathetic nerve stimulation. The inflow and outflow pressures were held constant while changes in tissue volume and blood flow were measured continuously. Nerve stimulation produced a rapid, transient volume reduc- tion, attributed to a decreased vascular capacitance, followed by a slower more sustained volume reduction attri— buted to a net reabsorption of extravascular fluid. The movement of extravascular fluid into the capillaries was attributed primarily to a fall in capillary hydrostatic pressure subsequent to an increased pre- to postcapillary resistance ratio. Mellander also measured changes in CFC and found that initially, nerve stimulation produced a re- duction in CFC; with continued stimulation, CFC increased above control, presumably because precapillary sphincters relaxed. These changes could be graded by increasing the frequency of stimulation. Oberg (98) and Cobbold §E_§l. (33) observed similar results in cat hindlimb preparations. . .. (I) «-, a.“ on I! ,. I (I 36 Renkin and Rosell (105) measured the PS product in isolated skeletal muscles of dogs and cats perfused at con— stant blood flow and observed that sympathetic nerve stimu- lation at frequencies between 1 and 20 impulses per second produced sustained reductions in the PS product and marked increases in vascular resistance. The reductions in the PS product were attributed to a reduction in the exchange sur- face area presumably due to closure of precapillary sphinc- ters. Some investigators (66,89,98,115) have observed changes in transcapillary fluid movement during hemorrhage similar to those produced by sympathetic nerve stimulation; initially the pre- to postcapillary resistance ratio increased and some investigators report that CFC also increased (89,99) producing a substantial flux of fluid into the circulation of skin and skeletal muscle. This fluid reabsorption was abolished when the vessels were acutely denervated (96), but could be demonstrated in preparations which were completely isolated from the hemorrhaged cat except through neural connections (89). Therefore, these investigators (89,96) attributed the fluid reabsorption primarily to an increased pre- to postcapillary resistance ratio which was mediated through activation of sympathetic adrenergic nerves. When hemorrhage was severe and prolonged, a reduction in the rate of fluid reabsorption, and eventually a net filtration of fluid into skin and muscle tissues has been 0' ll. covx ‘flhv A HUI. Q.”- ,- V..- n ,. V a II- . , O :4 .,._ .AI‘ '4... vy...‘ mu.“ ‘u N- .“~ 37 reported (89,96). These results were attributed to a redqu tion in the pre— to postcapillary resistance ratio due to accumulation of vasodilator metabolites which allegedly caused selective dilation of precapillary vessels while postcapillary vessels remained constricted. However, Schwinghamer\§£_al. (115) and Grega et a1, (66) noted in the dog forelimb that fluid continued to move from the tissues into the blood stream during prolonged, severe hypovolemia. They concluded that if the pre- to postcapillary resistance ratio was reduced during prolonged hemorrhage, the reduction failed to increase capillary hydrostatic pressure above control because of the large reductions in arterial and venous pressures which occurred during bleeding. Most investigators agree that sympathetic nerve stimu- lation of pre- and postcapillary vessels, and precapillary sphincters initially favors the reabsorption of fluid into the microcirculation of skin and skeletal muscle during hemorrhage. However, the effect of the sympathetic nervous system on the distribution of intra— and extravascular fluid during prolonged hypovolemia is controversial. C. Humoral Control Since catecholamines, angiotensin, vasopressin, and possibly other constrictors are released during hemorrhage and cause vascular constriction in skin and skeletal muscle, they may also produce changes in the direction and rate of 38 transcapillary fluid movement by altering the pre- to post- capillary resistance ratio and/or functional capillary sur- face area. The effect of norepinephrine and epinephrine on trans- capillary fluid movement in normovolemic animals has been studied by several investigators (64,65,92). In skin and skeletal muscle of denervated cat hindlimbs, short-term, intravenous infusions of norepinephrine produced greater resistance increases in precapillary than postcapillary vessels causing a reduction in capillary hydrostatic pres- sure and a net fluid movement from the tissues into the microcirculation (92). In the dog forelimb, a net trans- capillary fluid reabsorption occurs during short- and long- term intra-arterial infusion of norepinephrine (64,65). Epinephrine, when infused intra-arterially into the dener— vated cat hindlimb also constricted precapillary more than postcapillary vessels, causing a net reabsorption of extra- vascular fluid (92). Intra-arterial infusions of epine- phrine in dog forelimbs produced increases in total and segmental resistances in skin and skeletal muscle along with decreases in forelimb weight which were sustained for 180 minutes of infusion (64,65). Catecholamines, in addition to altering the pre— to postcapillary resistance ratio, can alter the rate of trans? capillary fluid movement via their effects on functional capillary surface area (51,92,95). Topical applications of u...- wt v¢ n ivv .- .‘o l l . av. 5‘.- 'FOV one. . '~' on}. .“R v.» I'-. ”s:\. . - ~ 4" .‘.. ‘Q. -.'.- ‘h 'Q All Lg; 39 both norepinephrine and epinephrine constricted precapil- lary sphincter vessels and presumably decreased the total surface area available for exchange (9). However, prolonged intravenous infusion of norepinephrine has been reported to increase functional capillary surface area as reflected by CFC measurements (92). The increased CFC was attributed to precapillary sphincter relaxation subsequent to the accumu- lation of vasodilator metabolites. Although catecholamines can cause substantial changes in intra— and extravascular fluid distribution in skin and skeletal muscle, some investigators conclude that the in- fluence of catecholamines on transcapillary fluid reabsorp- tion during hemorrhage is minimal, since in cat skeletal muscle, fluid reabsorption during hemorrhage was not af- fected by adrenalectomy (96), or by isolating the prepara— tion from the hemorrhaged cat except for neural connections (89). In addition, fluid reabsorption was not maintained during hemorrhage when the cat hindlimb was acutely dener— vated (96). Angiotensin's role in regulating transcapillary fluid movement during hemorrhage has not been investigated thoroughly. Intravarterial angiotensin infusion constricted precapillary more than postcapillary vessels in dog fore- limbs (2,3,70) and hindpaws (2,3), and in cat hindlimbs (51). However, angiotensin caused a much smaller reabsorption of extravascular fluid than norepinephrine when administered in 40 equipressor doses (51). Mellander and Johanssen (95) have suggested that the relatively weak effects of angiotensin on transcapillary fluid reabsorption may be related to its strong constriction of precapillary sphincters which de- creases capillary surface area available for exchange. VaSOpressin, like angiotensin, is reported to constrict precapillary more than postcapillary vessels in dog fore- limbs (70,71) and hindlimbs (1,2), thereby reducing capil- lary hydrostatic pressure. However, vasopressin has been reported to produce much less fluid reabsorption than equipressor doses of norepinephrine (95). One explanation for the minimal effects of both vasopressin and angiotensin on transcapillary fluid reabsorption, is that both agents may have produced a marked constriction of small venules but not large veins. In dog forelimb studies (70,71), evidence that vasopressin and angiotensin increased the pre- to postcapillary resistance ratio were based primarily on measurements of large artery and large vein resistances. Resistances in the small vessel segment could not be separated into pre-aumipostcapillary components. Consequent- ly, if the small venular resistance increased proportionately to arteriolar resistance, the prev to postcapillary re- sistance ratio would remain relatively constant and little fluid reabsorption would occur. This hypothesis is sup- ported by studies of the mesenteric microcirculation, which indicate that vasopressin caused strong contraction of venules (10). 0%!“ .1 h Ivno . t a .1 g ‘4 uni“ bu- a. you. l tan-p ~ysn “'9 ‘ "o... ’ a P_« a I." I ."‘)~ On... I ¢ .2- 'r y o In (I) Q. h- I“~ ’ . I"! ‘1 41 Even though several studies of the effects of angio- tensin and vasopressin on transcapillary fluid movement in skin and muscle have been conducted on normovolemic animals, tzhe effects of these agents in hypovolemic animals have not been thoroughly evaluated. I).. Passive Responses; Indirect Effects of Neuro-humoral Control In addition to neuro-humoral mechanisms which influence primarily the pre- and postcapillary resistance vessels and E>Jreecapillary sphincters to alter capillary pressure and iftaructional surface area, there are other factors that may k> 4.32m mqomnz 44% m40m:2 26d z_m>\ a 43555 .W. WWW EmE< . 2.12% "mm o ‘ , » $5.szle w a, \K.‘ K, 39... z_u> . - 03:88 mmsmmmmn. mmammmma z_m> 2.258 z_m> ._<_Iomm._.m< 444.55 22m ’\\ mmzwmmmm Z_m> .3455 22m 48 fraction of the total cross sectional area of the arterial or venous bed, and there are abundant artery to artery and vein to vein anastomoses (70,71,97). All cannulae used for pressure measurements were filled with saline and connected to Statham low volume displacement transducers (Model No. P23Gb, Statham Laboratories, Hato Rey, Puerto Rico) which were coupled to a Hewlett Packard direct writing oscillograph (Model No. 7784A, Hewlett Packard Co., Waltham, Massachusetts). The brachial and cephalic veins were partially transected and cannulated with 6—8" sections of P.E. 320 tubing (o.d. = 0.138"), downstream from the sites of large vein pressure measurements. Flow from both veins was directed into an open reservoir maintained at constant volume by a variable speed, roller pump (Lange Model RE 161, Extracorporeal Medical Specialties Inc., Mt. Laurel Township, New Jersey) which returned blood to the animal via a large vein. Forelimb blood flow was determined by timed collection of brachial and cephalic venous outflows. When the forelimb was prepared as described above, the median cubital vein was the major remaining anastomotic channel between the brachial and cephalic veins. The median cubital vein was ligated in all experiments so that brachial venous flow was predominantly from muscle and cephalic flow gmedominantly from skin. Evidence from several sources (35, 37,97) indicates that blood flow separation in the parallel skhland muscle circulations is nearly complete with this fix Tulle: h H.» I?! : _ 49 preparation. According to Miller (98), the cephalic vein drains skin of the forepaw and antebrachium whereas muscles of the antebrachium are drained by branches of the median vein which becomes the brachial vein near the elbow. Daugherty gt 2l° (37) report that serotonin, which is a potent constrictor in the cutaneous vasculature, but exerts little effect on skeletal muscle blood vessels (35), produces large reductions in cephalic vein flow and no consistent changes in brachial vein flow when infused into the brachial artery of the dog forelimb. Finally, the locally mediated vasodilator response which follows release of an arterial occlusion (reactive hyperemia), is well developed in skeletal muscle but poorly developed or absent in skin (27). In the dog forelimb, reactive hyperemia is pronounced in the vascu- lature drained by the brachial vein and minimal in vessels drained by the cephalic vein as illustrated in Figure 2. In all experiments, total, arterial, small vessel, and venous resistances in muscle were calculated by dividing the appropriate pressure gradient by brachial vein flow. Total and segmental vascular resistances in skin were calculated by dividing cutaneous pressure gradients by cephalic vein flow. A more complete description of vascular resistance calculations for the forelimb is contained in Appendix B. Mean intraluminal pressure in each vascular segment of skin and skeletal muscle was calculated as: 50 Figure 2. Peak brachial (cross-hatched bars) and cephalic venous (white bars) flow rates (expressed as percent of control) in 3 dogs after the release of l and 3 minute brachial artery occlusions (indicated by the numbers 1 and 3 above the bars). 51 brachial. [:1 cephalic . I . 1.x. .....u..\...\. . ..\. 1 flow (percent of control) 340 300 60 2 20 2 80 1 Figure 2 52 P+§P 5:1 2 2 where: P = mean intraluminal pressure P1 = inflow pressure P2 = outflow pressure. Since transmural pressure equals intraluminal pressure minus tissue hydrostatic pressure, mean intraluminal pressure can be used to approximate mean transmural pressure if the tis- sue pressure is assumed to remain nearly constant at about 0 mm Hg. In some experiments, changes in forelimb weight were recorded by placing the limb on a plastic grid platform attached to a calibrated strain gauge balance which was coupled to a direct writing oscillograph. A 2 g weight usual- ly produced a 10-15 mm pen deflection on the oscillograph. Observations of forelimb weight and vascular resistances were used to estimate changes in intravascular volume and net transcapillary fluid movement. A rapid weight loss associated with large increases in vascular resistance was attributed largely to decreased intravascular volume. However, slower, prolonged weight loss associated with steady or decreasing vascular resistance was attributed to net transcapillary fluid reabsorption. Mean systemic arterial pressure was measured in all experiments from a P.E. 240 catheter inserted into the lower abdominal aorta via the right femoral artery. In some experi— :ments, arterial systolic and diastolic pressures were recorded 53 and pulse pressure calculated as the difference between systolic and diastolic pressures. Central venous pressure was measured in some experiments from a P.E. 320 catheter inserted into the left jugular vein and advanced to within 2—3 cm of the right atrium. Series I: Naturally perfused, innervated forelimbs; local hypotension and rapid arterial hemor- rhage In 16 dogs, the forelimb nerves were left intact. .After a 30 minute control period, mean forelimb perfusion pressure was reduced to 100 mm Hg by compression of the brachial artery with a screw clamp. Changes in limb weight were recorded continuously and pressure—flow determinations were obtained 1, 3, and 5 minutes after mean brachial artery pressure had stabilized at 100 mm Hg. This procedure for pressure, flow, and weight measurements was repeated after forelimb perfusion pressure had been reduced to 75, 50, and 35 mm Hg by further tightening of the screw clamp. In some experiments, pressure-flow determinations were made every 2 minutes for a total of 20 minutes at each of these fore- limb perfusion pressures (100, 75, 50, and 35 mm Hg). The clamp was then released so that brachial artery pressure and venous outflows returned to their prevclamp control levels. After a recovery period, which was terminated when pres- sures, flows, and forelimb weight had stabilized, brachial artery pressure was reduced in steps to 100, 75, 50, and 35 54 mm Hg by rapid bleeding from a carotid artery into a preSv surized reservoir. The protocol for measuring changes in forelimb weight, intravascular pressures, and venous out- flows was identical to that described for the preceding clamp period. Series II: Naturally perfused, denervated forelimbs; local hypotension and rapid arterial hemorrhage In 17 dogs, the forelimb nerves were coated with a local anesthetic (Cetacaine, Cetylite Industries., Long Island City, New York) and severed 3-5 cm above the elbow. Pressure-flow determinations were made immediately before and at 5, 10, 15, and 20 minutes after denervation. Twenty-five minutes after the nerves had been cut, fore- limb perfusion pressure was reduced in steps to 100, 75, 50, and 35 mm Hg by clamping the brachial artery. PresSure- flow determinations were obtained 1, 3, and 5 minutes after mean brachial artery pressure had stabilized at each of these pressures (100, 75, 50, and 35 mm Hg). The clamp was released, and after a recovery period, brachial artery pres- sure was reduced in steps to 100, 75, 50, and 35 mm Hg by rapid bleeding from a carotid artery into a pressurized reservoir, and intravascular pressures and venous outflows determined according to the protocol described for Series I. 55 Series III: Cross-perfused forelimbs; rapid arterial hemorrhage of recipient and donor dogs The right forelimbs of 5 recipient dogs (16-20 kg) were prepared as described above, leaving the nerves intact, and perfused with blood from the carotid arteries of 5 donor dogs (25-30 kg) by using a variable speed roller pump (Lange Model RE 161, Extracorporeal Medical Specialties Inc., Mt. Laurel Township, New Jersey). Blood samples from the donor and recipient dogs were cross—matched and CIOSS*typed to minimize transfusion reactions. During the control period, forelimb perfusion pressure was set at 100—125 mm Hg with a servosystem (Figure 3) which continuously adjusted the flow rate of the perfusion pump to maintain brachial artery pressure constant. After a 20-30 minute control period, the recipient dog was rapidly bled from a carotid artery into a pressurized reservoir so that its mean systemic arterial pressure was reduced in steps to 100, 75, 50, and 35 mm Hg. At each step reduction in systemic arterial pressure, the set-point of the servo- system was altered so that brachial artery pressure matched the recipient dog's systemic arterial pressure, and forelimb intravascular pressures and venous outflows were then determined every 3 minutes for 15 minutes. As long as the donor dog remained normotensive and normovolemic, this cross- circulation technique eliminated the hemorrhaged-induced accumulation of circulating vasoconstrictors in the arterial 56 .pmsflmuswmfi ma moansmumm 30H“ uqmumaoo .mpofi Humane nufl3 “usmumcoo.madmmmumchHmsmn m :Hmucflmfi on cmaaouucoo ma pmmmm.m§5¢,coflmdmumm gmcoatoflfimaounm nuflz...mpoa Hmssma map ca soauflmom undamam Honpsoo;amaam mnu Mo unmaumsflpw Hmssma muHEHmm cam .mmUoE Hodqdfi snazpmumsoufid-nmmsnmn xammmamsbn EmpmMm Houucoo on» mummmsmuusLmuflsoHHo mcflnoufl3m Azlmv Hmssmzloflumfiousm .m .Hmcmflm usmuso HmHMHHmEm man mo mUSpHHmEm paw unflumaom ou msflcuooom ucmHHdo-usmudo map mmflum> “nmflwflamam map Scum mmmuao> m mo mocmmnm map CH Hm>ma.mCHumummo-pdmumdoo.m um usmuso uanHso m mcfimusflmfi cam mmcfl>onmnlaouusoo usmuso Ammme.mswumsho< pcmuunov .B.<.U .v .mmmuao> mocmumMMHc may on HMGOHHHOQOHQ mmmuao> usmuso so mocfl>oum cam mommuao> Mownpmmm paw Houum.pmwMHcofi Gnu mmnmmfioollumHMflHmmd Honucoo .m .Hmaaouucoo may mo usmuuso usmpso on» EOHM pm>flump ma coopao> xomnpmmw one .mmmmuao> xomnpmmw was Hound msu.ou:mc0fluuddm mMH.Ho .muwu cam uwmmu .cflmm Hmcoflunomoum magnumsnpm mpUMIlmucmfiumsflwm Hmsmm Houucoo .m .cmmoam>wp ma mmmuao> uonuw so .ucflom umm Eouw mmuMH>mp manmflum> pwaaouusoo may smsz .Hmfluflamfim 04 may Eoum mmmuao> may on cmhmmeoo ma SUHQB mmmuao> wocmummmu m mmnmfianmummlluflsouflo ucfiom pom .H .musmmmum mumuum Amanomun Houucoo ow com: Empm>m0>uwm map mo oamewcom :I‘ '|.'-.' .m ousmflm 57 m OHSGH .m {4:00.533 98-..." h I — I08¢hn_uflt 0 I :05 05.2000. ‘ s I x , H 5.....n.u.=_ — L C(J30fl(> II.JII°& Jumscfl cm mcflm: ucmEHmexm Umuomamm m Eoum ma mama .pmcflaumump mumz momsmno ucmflm3 £0H£3 um Amm EEV mmusmmmum wumunm Hmflsomun mumum mommum on wamu Amm cam .om .mn .ooav mumaess pmaouflu .Ammuscfla oavmpoflumm aouucoo n U .Ammaouflov mmmnhnoawn assumpum UHQMH can AmDOU pHHomv coflmsmuommn HmooH msflusp Ampmsflpuo.nmamumv Davao? nEflHwHow CH mmmcmso .v musmflm 63 v wusmflm AEEV 9):... 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Since these weight losses con- tinued after vascular resistances and arterial and venous pressures had stabilized, they were attributed to extra- vascular fluid reabsorption, rather than to a reduction in intravascular blood volume. There was a significant, sus- tained weight loss at all levels of hypotension produced either by clamping the brachial artery or by arterial hemorrhage. However, the weight losses during hemorrhage were always significantly greater than those observed at corresponding pressures during clamping. Local hypotension induced by clamping the brachial artery produced a maximum rate of weight loss of 0.15\: 0.02 g/min at a forelimb per- fusion pressure of 50 mm Hg, whereas at this same pressure, hemorrhagic hypotension produced a 0.34 :_0.03 g/min weight loss. B. Intraluminal Pressures Data in Tables 1 and 2 are mean intraluminal pressures in all forelimb vascular segments when forelimb perfusion pressure was reduced by clamping the brachial artery or by arterial hemorrhage. Mean intraluminal pressure decreased significantly in all forelimb vascular segments during clamping and during bleeding. Except in the large skin veins, the reductions in intraluminal pressure in skin and muscle vascular segments produced by hemorrhage were not signifi— cantly different than those produced by clamping the brachial 67 Table 1. Effects of local hypotension and rapid arterial hemorrhage on mean intraluminal pressure (P) in innervated skin arteries (SA), small vessels (SSV), and veins (SV). PEA = brachial artery pressure. Values in mm Hg are means : standard errors from 16 experiments. PEA PSA PSSV PSV Control 122.3:2.8 110.9:?.8 56.0:l.6 9.9:p.5 Clamp 100.0:p.S 91.3:p.8 46.010.8 7.910.? 76.1:0.6 69.2:0.6 35.0:p.6 5.5:p.4 51.9:0.5 46.9:0.5 23.9:0.5 3.7:p.4 34.8:p.6 31.2:0.6 16.0:0.4 2.7:0.4 Control 123.3:2.9 110.5:3.0 55.7:l.7 10.5:0.6 Bleed 98.9:p.6 9l.l:p.7 45.6:p.6 5.4:0.4 74.2:p.6 67.3:0.8 33.1:0.7 3.6:0.3 50.5:p.7 45.6:0.7 22.6:p.5 2.2:p.4 35.9:0.5 32.4:p.6 l6.6:0.4 2.0:0.4 68 Table 2. Effects of local hypotension_§nd rapid arterial hemorrhage on mean intraluminal pressure (P) in innervated muscle arteries (MA), small vessels (MSV), and veins(MV). PBA = brachial artery pressure. Values in mm Hg are means i_standard errors from 16 experiments. ' PEA PSA PSSV PSV Control 122.3:2.8 112.9:?.8 53.2:l.6 5.8:0.3 Clamp 100.0:0.5 93.2:p.7 45.8:0.8 4.0:0.3 76.1:0.6 70.3:0.7 35.0:0.4 3.2:0.3 51.9:p.5 47.5:0.6 23.3ip.5 2.4:9 3 34.8:p.6 3l.4:0.5 15.5:0.4 l.9:0.3 Control 123.3:2.9 ll4.4:g.9 55.5:l.7 6.2:p.4 Bleed 98.9:p.6 93.8:p.7 46.4:0.5 3.2:p.3 74.2:0.6 69.8:0.5 34.7:0.4 2.8:0.3 50.5:0.7 46.4:0.6 22.5:0.4 2.5:p.3 35.9:p.5 32.2:0.6 15.9:p.5 2.2+0.3 69 artery to corresponding pressures. In the large skin veins, hemorrhage produced slightly greater reductions in intra- luminal pressure at brachial artery pressures of 100 and 75 mm Hg, but not at 50 and 35 mm Hg. C. Skin Total and Segmental Vascular Resistances Data in Figure 6 report total and segmental resistances in the skin vasculature as functions of brachial artery pressure when forelimb perfusion pressure was reduced by clamping the brachial artery or by hemorrhage. When forelimb perfusion pressure was reduced by clamping the brachial artery, resistance in all cutaneous vascular segments did not change significantly until brachial artery pressure fell to 50 and 35 mm Hg. Skin venous resistance increased from a control value of 0.09 i 0.01 to 0.1%: 0.02 and 0.30 i 0.04 at brachial artery pressures 50 and 35 mm Hg respectively. Clamping the brachial artery did not produce any significant changes in skin arterial and small vessel resistances. When forelimb perfusion pressure was lowered by hemor- rhage, total and segmental vascular resistances in skin increased significantly at all brachial artery pressures of 100 mm Hg and below. Total skin resistance increased pro- gressively from a control value of 2.13 :_0.16 to 19.04 i 3.81 at a brachial artery pressure of 35 mm Hg. Most of this increase was due to constriction of the small vessel segment, where resistance increased from a control value of 1.61 i Figure 6. 70 Effects of local hypotension (solid dots) and rapid arterial hemorrhage (circles) on skin total, arterial, small vessel, and venous resistances in innervated forelimbs. Ordinates represent resistance in mm Hg (ml/min)"1 and abscissas represent brachial artery pressure (PBA) in mm Hg. (2: pre-clamp and pre-hemorrhage control values. Data represent means 1 standard errors from 16 experiments. (__J 71 HC M SKIN RESISTANCE HBLéEg r TOTAL 5F ARTERIAL 25 25 20r 5r SMALL VESSEL VENOUS I6~ 4» I2» 3~ 8- 2» 4- c I- ‘ C I m L . . . I 0_ . 25 I25 IOO 75 50 25 I25 I00 75 50 25 PBA PBA Figure 6 72 0.14 to 13.23 i 2.92 at a brachial artery pressure of 35 mm Hg. However, as shown in Table 3 the large veins con- stricted proportionately more than the small vessels during hemorrhage. At a brachial artery pressure of 35 mm Hg, skin venous resistance was more than 24 times greater than con- trol. Total and all segmental resistances during hemorrhage were significantly greater than those observed at corre- sponding pressures during clamping. D. Muscle Total and Segmental Vascular \BeSistances Changes in total and segmental resistances in the muscle vasculature during local hypotension produced by clamping the brachial artery, and during hemorrhagic hypotension are illustrated in Figure 7. Local hypotension elicited sig- nificant increases in muscle total, small vessel, and venous resistances at brachial artery pressures of 75, 50, and 35 mm Hg. Arterial resistance in muscle increased significantly only at brachial artery pressures of 50 and 35 mm Hg. Muscle total, arterial, small vessel,and venous resistances in- creased from control values of 3.02 i 0.24, 0.49 :_0.05, 2.37 i 0.24, 0.10 :_0.02 to 6.49 i 0.45, 1.35 i 0.14, 4.19 i 0.21, and 0.38 i 0.03 respectively at a brachial artery pres— sure of 35 mm Hg. When forelimb perfusion pressure was reduced by hemor- :rhage, total and all segmental vascular resistances in muscle :anreased progressively above control values as brachial 73 Table 3. Effects of local hypotension and rapid arterial hemorrhage on skin total (ST), arterial (SA), small vessel (SSV), and venous (SV) resistances (R) (expressed as percent of control) in innervated forelimbs. PEA = brachial artery pressure in mm Hg. Values are means from 16 experiments. PEA RST RSA Rssv Rsv % 8 Control 122.3 100 100 100 100 Clamp 100.0 104 95 105 114 76.1 95 97 93 126 51.9 100 114 92 195 34.8 117 154 98 306 Control 123.3 100 100 100 100 Bleed 98.9 258 170 282 233 74.2 345 263 358 455 50.5 702 597 696 1160 35.9 893 732 822 2475 Figure 7. 74 Effects of local hypotension (solid dots) and rapid arterial hemorrhage (circles) on muscle total, arterial, small vessel, and venous resistances in innervated forelimbs. Ordinates represent resistance in mm Hg (ml/min)‘1 and abscissas represent brachial artery pressure (PEA) in mm Hg. C = pre-clamp and pre-hemorrhage control values. Data represent means i_standard errors from 16 experiments. 75 o—oCLAMP MUSCLE RESISTANCE o—oBLEED 50? TOTAL 'OT ARTERIAL 40 8- 30r 6- 20» 4- IO* 2 C C l l 011, O_., |25 IOO 75 5O 25 l25 IOO 75 50 25 PBA P8A 401 SMALL VESSEL 5' VENOUS 327 4* 24* 3- l6* 2* 8- c I L C ‘ I O E, . . . 1. O. . . .1 I25 I00 75 50 25 |25 I00 75 5O 25 P8A PBA Figure 7 76 Table 4. Effects of local hypotension and rapid arterial hemorrhage on muscle total (MT), arterial (MA), small vessel (MSV), and venous (MV) resistances (R) (expressed as percent of control) in innervated forelimbs. PEA = brachial artery pressure in mm Hg. ’Values are means from 16 experiments. PEA RMT RNA RMSV RMV % % % % Control 122.3 100 100 100 100 Clamp 100.0 122 105 121 124 76.1 138 132 126 150 51.9 176 191 156 223 34.8 215 274 176 362 Control 123.3 100 100 100 100 Bleed 98.9 336 248 337 318 74.2 539 444 506 650 50.5 906 974 680 1377 35.9 1207 1670 870 2703 77 artery pressure was reduced to 35 mm Hg. At a brachial artery pressure of 35 mm Hg, total muscle vascular resist- ance was increased more than 12 times above the control value. As in the skin, most of this increase in total muscle vascular resistance was due to constriction of the small vessel segment. However, the large artery and venous segments constricted proportionately more than the small vessel segment as illustrated in Table 4. At each brachial artery pressure reduction during hemorrhage, total and all segmental vascular resistances in muscle were significantly greater than those observed at corresponding pressures during clamping. II. Series II: Naturally Perfused, Denervated Forelimbs; Effects of Local Hypotension and Rapid Arterial Hemorrhage A. Forelimb Weight Mean values and standard errors from 17 experiments for the slow sustained weight losses observed during local hypo- tension and during rapid arterial hemorrhage are reported in Figure 8. During the clamp and hemorrhage control periods, the forelimbs were gaining weight at rates of 0.15 i 0.03 and 0.14 :_0.02 g/min respectively. There was a significant, sustained weight loss below control values at all levels of .hYFNDtension produced either by clamping the brachial artery .01‘ kxy arterial hemorrhage. The weight losses at brachial 78 .o 23 H Soon u 2303 883088 .mm 8E cH Admmv musmmmnm hnouum Hmflsomnn mudmmmummn mmmflomnd .mucoeflnwmxw 5H EOHH=mHOHHmfoumocoum H momma mucmmmumou mama .Amnmn omnoumnrmmOHOVImddfiHHOEmanmfluouHm Canon Ho Amman muflb3v coflmcmuomhn amooa-mcfiud©:mQEHH®H0w.omum>nmsmo mo AmuscHE mom madam “mundflouov unmam3 ow woodman omcwmumsm .Bon .m musmwm 79 mm 'YYY vvv Iv \. it - YYYYVVvvvvvvvvvvvvtvuvvvvvvv- m 095685 cm o 00.. me -\ iliV5Iror- 80 artery pressures of 100 and 75 mm Hg during hemorrhage were significantly greater than those observed at corresponding pressures during clamping. However, at brachial artery pressures of 50 and 35 mm Hg, the weight losses during clamping and bleeding were not statistically different. Comparisons of weight changes of innervated and denervated forelimbs during local hypotension and during rapid arterial hemorrhage are shown in Table 5. Since the denervated limbs were gaining weight during the control periods, the weight changes in both innervated and denervated forelimbs were normalized as experimental weight change minus weight change during the control period. During clamping, the rate of weight loss in denervated forelimbs was significantly greater than in innervated limbs at brachial artery pressures of 50 and 35 mm Hg. However, during hemorrhage, weight losses were not statistically different in innervated and denerv- ated limbs. B. Mean Intraluminal Pressures Mean intraluminal pressures in all forelimb vascular segments before and after denervation, during local hypo- tension produced by clamping the brachial artery, and during systemic hypotension induced by arterial hemorrhage are reported in Tables 6 and 7. Denervation significantly re— duced mean intraluminal pressure in skin and muscle arterial and small vessel segments, and increased mean intraluminal 81 Table 5. Effects of local hypotension and rapid arterial hemorrhage on slow, sustained changes in weight (grams per minute; A wt.) of innervated (N=l6) or denervated (N=l7) forelimbs. Weight changes were expressed as experimental weight change minus weight change during the control period. Values are means :_ standard errors. PEA = brachial artery pressure. Innervated Forelimb weight = 529.1 :_29.6 g; Denervated Forelimb weight = 508.8 :_l8.9 g. Innervated Denervated A , 7A , PBA wt PEA wt Control 122.3:?.8 0.00 ll4.7:?.l 0.00 Clamp 100.0:0.5 -0.11:0.02 99.3:0.5 -0.l9:0.04 76.110.6 -0.1510.03 76.4:p.4 -0.24:0.05 51.9:0.5 -0.l7:0.03 51.0:0.4 -0.30:0.05 34.8:0.6 -0.l3ip.03 34.4:0.4 -0.32:0.06 Control 123.3:2.9 0.00 116.6:l.9 0.00 Bleed 98.9:0.6 -0.34:p.05 100.0:p.9 -0.32:p.04 74.2:0.6 -0.48:0.05 76.7:0.3 -0.36ip.05 50.5:0.7 -0.41:0.03 52.9:p.3 -O.34:p.05 35.9:p.5 -0.39:0.05 35.7:0.3 -0.33:0.05 82 Table 6. Effects of denervation, local hypotension, and rapid_ arterial hemorrhage on mean intraluminal pressure (P) in skin arteries (SA), small vessels (SSV), and veins (SV). PBA = brachial artery pressure. Values in mm Hg are means 1 standard errors from 17 experiments. PEA PSA PSSV PSV BEFORE DENERVATION Control 122.7:l.7 109.011.? 54.41}.1 9.9:0.4 AFTER DENERVATION Control ll4.7:2.1 92.6:l.7 45.1il.0 l4.9:0.6 ' Clamp 99.3:0.5 80.2:l.3 38.0:l.l ll.l:p.5 76.4:0.4 62.9:0.8 30.4:0.6 8.3:0.3 51.0:p.4 41.8:0.4 19.9:p.4 4.8ip.3 34.4:p.4 27.8:p.4 13.3:0.3 2.8:p.2 Control 116.6:l.9 92.8:l.7 45.4:}.0 l6.8:p.9 Bleed 100.0:p.9 84.3:l.5 40.3:l.l 8.7:0.6 76.7:0.3 67.7:p.8 33.4:0.7 4.9:0.4 52.9:0.3 48.1:0.7 24.4:0.7 2.3:p.3 35.7:0.3 33.4:0.4 l7.8:p.4 l.3:0.3 83 Table 7. Effects of denervation, local hypotension,_and rapid arterial hemorrhage on mean intraluminal pressure (P) in muscle arteries (MA), small vessels (MSV), and veins (MV). PBA = brachial artery pressure. Values in mm Hg are means :_ standard errors from 17 experiments. PBA PMA PMSV PMV BEFORE DENERVA‘I‘ION Control 122.711.? ll4.2:}.8 56.7:l.0 6.9:0.4 AFTER DENERVATION Control 114.7:2.l 104.8:2.l 52.5:l.2 8.8:p.4 Clamp 99.3:p.5 89.5:0.9 44.1:p.7 7.5:p.5 76.4ip.4 69.7:p.6 34.8:0.5 5.3:p.3 51.0:0.4 45.2:p.6 22.6:p.4 3.7:p.3 34.410.11 29.6105 14.7:O.4 2.810 3 Control ll6.6:l.9 105.2:l.9 52.4:l.3 10.3:0.7 Bleed 100.0:0.9 91.2:l.2 44.9:l.0 5.9:0.6 76.7:p.3 70.7:0.6 34.5:0.5 3.5:0 3 52.9:0.3 48.3:0.6 24.3:0.4 2 9:0.3 35.7:0.3 31.9:0.5 l6.3:0.4 2 8+0.3 '8. 84 pressure in skin and muscle venous segments. .Mean intra~ luminal pressure was significantly reduced below postv denervation control values in all forelimb vascular segments during clamping and during bleeding. Clamping the brachial artery to 75, 50, and 35 mm Hg produced greater reductions of mean intraluminal pressures in the skin arteries and small vessels than did bleeding to the same brachial artery pressures. At brachial artery pressures of 75, 50, and 35 mm Hg, hemorrhage produced greater reductions in skin venous intraluminal pressure than did clamping to corresponding brachial artery pressures. In skeletal muscle, at brachial artery pressures of 50 and 35 mm Hg, local hypotension pro- duced greater reductions in arterial and small vessel intra— luminal pressures than did hemorrhage. However, muscle venous mean intraluminal pressure was not significantly dif— ferent during hemorrhage and local hypotension at any of the brachial artery pressures studied. C- Skin Total and Segmental Vascular Resistances Total and segmental resistances in the cutaneous vas—. culature of 17 forelimbs before and after denervation, and during hypotension produced either by clamping the brachial artery or by arterial hemorrhage are shown in Figure 9. When the forelimb nerves were sectioned (indicated by the first arrow on each graph), total skin resistance decreased from 1.41 i 0.07 immediately before denervation to Figure 9. 85 Effects of denervation (first arrow on each graph), local hypotension (solid dots), and rapid arterial hemorrhage (circles) on skin total, arterial, small vessel, and venous resistances. Ordinates represent resistance in mm Hg (ml/min)‘ and abscissas represent brachial artery pressure (PEA) in mm Hg and time in minutes (MIN) after denervation. C = pre-clamp and pre-hemorrhage control values. Data represent means :_standard errors from 17 experiments. 86 SKIN RESISTANCE .... CLAMP °—° BLEED 25" 4r TOTAL ARTERIAL 20~ 3.- I5~ 2.— I0- I»- 5' C O S 54L‘**°. O 0 IO 20I25 I00 75 50 25 O 0 I0 20I25 I00 75 50 25 MIN PBA MIN RBA 20, 5 SMALL VESSEL VENOUS 4,. Isr 3h I0- ZI- 5... II- ' (v: 0 S 0 IO 20I25 IOO 75 50 25 0 I0 20I25 IOO 75 50 25 MIN PBA MIN P8A Figure 9 87 0.94 :t 0.07 20 minutes after denervation. This response, which represents a 33 percent reduction from control resistance, is due primarily to dilation of the small vessel segment in which resistance decreased from 1.01 i 0.06 before denervation to 0.47 :_0.03 20 minutes after denerva- tion. Denervation increased skin arterial resistance but did not alter skin venous resistance significantly. Local hypotension in the forelimb vasculature, produced by clamping the brachial artery, did not elicit significant changes in skin total, arterial, or small vessel resistance. Skin venous resistance was significantly elevated only at a brachial artery pressure of 35 mm Hg, where resistance increased from a control value of 0.09 i 0.01 to 0.17 i 0.01. When forelimb perfusion pressure was lowered by hemor- rhage, skin total, small vessel, and venous resistances increased significantly above control at all brachial artery pressures of 100 mm Hg and below. Skin total vascular re— sistance increased progressively from a control value of 0.88 i 0.04 to 20.96 : 2°14 at a brachial artery pressure of 35 mm Hg. Although most of the increase in total skin vascular resistance resulted from constriction of the small vessel segment, the percent increase in resistance was greatest in the skin veins as shown in Table 8. Skin arteri- al resistance was not significantly increased above control until brachial artery pressure was reduced to 50 mm Hg and below. 88 Table 8. Effects of local hypotension and rapid arterial hemorrhage on skin total (ST), arterial (SA), small vessel (SSV), and venous (SV) resistances (R) (expressed as percent of control) in denervated forelimbs. PBA = brachial artery pressure in mm Hg. Values are means from 17 experiments. PBA RST RSA RSSV RSV Control 114.7 100 100 100 100 Clamp 99.3 107 105 111 97 76.4 99 89 107 92 51.0 102 94 106 117 34.4 120 116 109 197 Control 116.6 100 100 100 100 Bleed 100.0 214 120 317 158 76.7 663 143 1191 552 52.9 1423 265 2455 1901 35.7 2387 465 3824 4533 89 Figure 10. Effects of rapid arterial hemorrhage on skin vascular resistances in innervated (solid lines; N = 16) or denervated (dashed lines; N = 17) forelimbs. Ordinates represent resistance in mm Hg (ml/min)’ and abscissas represent brachial artery pressure (PB ) in mm Hg. C = pre-hemorrhage control values. Data represent mean values : standard errors. 90 o—oINNERVATED SKIN RESISTANCE .--. DENERVATED 25' TOTAL SI ARTERIAL 20 ' VENOUS I6- I 4- PBA Figure 10 91 A comparison of the responses to bleeding in innervated and denervated skin vascular segments is presented in Figure 10. Data are the same as those reported in Figure 6 (innervated) and 9 (denervated). Resistance was signifiv cantly lower in the denervated skin arteries at all brachial artery pressures below control, indicating that denervation attenuates the hemorrhage—induced constrictor response in this vascular segment. Resistance in denervated skin small vessels was significantly lower than in innervated small vessels only at a brachial artery pressure of 100 mm Hg, indicating a slight attenuation of the constrictor response of this vascular segment during moderate hemorrhage. The response of the skin venous segment to bleeding was not significantly reduced by denervation. D. Muscle Total and Segmental Vascular Resistances Total and segmental resistances in the muscle vascular ture of 17 forelimbs before and after denervation and during hypotension produced by clamping the brachial artery or by arterial hemorrhage are shown in Figure 11. When the fore? limb nerves were sectioned (indicated by the first arrow on each graph), total muscle vascular resistance decreased from 2.42 i 0.16 before denervation to 1.68 :_0.14 20 minutes after denervation. This response, which represents a 31 per- cent reduction in resting resistance, is due largely to dilation of the small vessel segment, in which resistance Figure 11. 92 Effects of denervation (first arrow on each graph), local hypotension (solid dots), and rapid arterial hemorrhage (circles) on muscle total, arterial, small vessel, and venous resistances. Ordinates represent resistance in mm Hg(m1/min)"'1 and abscissas represent brachial artery pressure (PEA) in mm Hg and time in minutes (MIN) after denervation. C = pre-clamp and pre-hemorrhage control values. Data represent means 1 standard errors from 17 experiments. MUSCLE RESISTANCE 40' TOTAL 30” . ‘5 ”*u-a-u 93 OLI_L 0 l0 20I25 IOO 75 PBA MIN 3°I SMALL VESSEL 24. ' 9’ M 0be I0 20l25 I00 MIN 75 P8A 5O 50 25 25 .... CLAMP o—o BLEED PARTERIAL C 9 V 0 IO 20I25 I00 75 5O 25 MIN PBA PVENOUS C V V .2211: 1 . 0 IO 20|25 IOO 75 50 25 MIN PBA Figure 11 94 decreased from 2.03 i 0.13 before denervation to 1.34 i 0.12 20 minutes after denervation. Denervation produced no significant decreases in muscle arterial or venous resistances. When forelimb perfusion pressure was lowered by clamp— ing the brachial artery, small but significant increases in muscle arterial and small vessel resistances occurred at brachial artery pressures of 75, 50, and 35 mm Hg. Muscle arterial and small vessel resistance increased from control values of 0.31 i 0.03 and 1.34 i 0.12, to 1.34 i 0.16 and 2.74 :_0.26 respectively at a brachial artery pressure of 35 mm Hg. Muscle total and venous resistances increased significantly only at brachial artery pressures of 50 and 35 mm Hg. Arterial hemorrhage elicited significant increases in muscle total and all segmental vascular resistances at brachial artery pressures of 100, 75, 50, and 35 mm Hg. Muscle total resistance increased progressively from a con- trol value of 1.57 i 0.10 to 30.07 i.3-62 at brachial artery pressure 35 mm Hg. Although constriction in the small vessel segment accounted for most of the increase in total muscle resistance, the muscle arterial and venous segments constricted proportionately more than the small vessel seg— ment during hemorrhage as shown in Table 9. A comparison of the results in series I and II (Figure 12) reveals that denervation did not significantly reduce 95 Table 9. Effects of local hypotension and rapid arterial hemorrhage on muscle total (MT), arterial (MA), small vessel (MSV), and venous (MV) resistances (R) (expressed as percent of control) in denervated forelimbs. PBA = brachial artery pressure in mm Hg. Values are means from 17 experiments. PBA RMT RMA RMSV RMV % % % % Control 114.7 100 100 100 100 Clamp 99.3 127 138 127 112 76.4 136 135 137 132 51.0 210 276 193 273 34.4 255 432 204 442 Control 116.6 100 100 100 100 Bleed 100.0 545 230 683 286 76.7 1300 848 1500 819 52.9 1899 1565 2024 2420 35.5 1915 2036 1775 4130 Figure 12. 96 Effects of rapid arterial hemorrhage on muscle vascular resistances in innervated (solid lines; N = 16) or denervated (dashed lines; N = 17) forelimbs. Ordinat s repre- sent resistance in mm Hg (ml/min)' and abscissas represent brachial artery pressure (P A) in mm Hg. C = pre-hemorrhage control va ues. Data represent mean values : standard errors. 97 H INNERVATED MUSCLE RESISTANCE ..-. DENERVATED 5°I TOTAL '0' ARTERIAL 40" 8" 30r 6- 20* 4* IO"c 2* I, , o_ n: . . . . O. |25 I00 75 50 25 P8A “I SMALL VESSEL SI VENOUS 32’ 4 Figure 12 98 the resistance response to hemorrhage in the muscle small vessels or veins. Resistance in the denervated muscle large arteries was significantly lower than in the innerv- ated large arteries at a brachial artery pressure of 100 mm Hg; at brachial artery pressures of 75, 50, and 35 mm Hg, resistances in innervated and denervated muscle large arteries were not significantly different. III. Series III: Crossjperfused Forelimbs; Effects of Rapid Arterial Hemorrhage of the Recipient and Donor DogST’ A. Skin Total and Segmental Vascular ReSIStances Bleeding the recipient or donor dogs produced signifi- cant increases in skin total and segmental vascular resist- ances in the forelimbs of the recipient dogs (Figure 13). . However, at brachial artery pressures of 75, 50, and 35 mm Hg, hemorrhagic hypotension in the donor dogs elicited a significantly greater increase in skin total and small vessel resistance than did a corresponding degree of hypotension in the recipient dogs. Bleeding the donor dogs to a mean systemic arterial pressure of 35 mm Hg produced a 12.0 fold increase in skin total resistance whereas, hemorrhaging the recipient dogs to a corresponding brachial artery pressure elicited only a 4.2 fold increase in total skin vascular resistance (Table 10). Increases in skin venous resistance at brachial artery pressures of 50 and 35 mm Hg were Figure 13. 99 Effects of rapid arterial hemorrhage of recipient (solid dots) and donor (circles) dogs on skin total, arterial, small vessel, and venous resistances in cross-perfused forelimbs. Ordinates represent resistance in mm Hg (ml/min)"1 and abscissas represent brachial artery pressure (PBA) in mm Hg. C = pre-hemorrhage control.values- Data represents means : standard errors from 5 experiments. 100 9—9 BLEED RECIPIENT °—° BLEED DONOR SKIN RESISTANCE 'ZI TOTAL 4 I ARTERIAL 9- 3_ Gt 2_ 3— I _ C C I I 0' E3 I00 715 510 2‘5 0' I25 I00 75 50 2'5 P8A P8A 'OF SMALL VESSEL Z'OI VENOUS 8- I6t 6* I2- 4- O.8~ 2- 04- C 0' IE I00 75 510 2'5 0‘ P8A Figure 13 101 Table 10. Effects of rapid arterial hemorrhage on skin total (ST), arterial (SA), small vessel (SSV), and Venous (SV) resist- ances (R) (expressed as percent of control) in cross- perfused forelimbs. PBA = brachial artery pressure in mm Hg. Values are means from 5 experiments. PBA RST RSA RSSV RSV % % % Control 106.3 100 100 100 100 Bleed Recipient 100.0 104 111 98 120 75.0 132 150 122 140 50.0 255 368 176 280 35.4 419 650 229 660 Control 104.7 100 100 100 100 Bleed Donor 100.0 116 124 111 117 74.8 266 179 360 200 49.1 635 321 894 833 34.2 1199 536 1600 2500 102 significantly greater during hemorrhage of the donor dogs than during bleeding of the recipient dogs. Hemorrhaging the donor or recipient dogs produced no significant differ- ences in the resistance reSponse of the skin arteries. B. Muscle Total and Segmental Vascular Resistances Muscle total and all segmental vascular resistances in the forelimbs of the recipient dogs were increased by bleeding the donor or recipient dogs (Figure 14). At brat chial artery pressures of 75, 50, and 35 mm Hg, signifi- cantly greater increases in muscle total, small vessel, and venous resistances occurred when the donor dogs were bled than when the recipient dogs were bled to corresponding systemic arterial pressures. At a brachial artery pressure of 35 mm Hg, muscle total resistance increased 10.6 fold when the donor dogs were bled, but only 3.4 fold when the recipient dogs were hemorrhaged to a corresponding pressure (Table 11). In muscle arteries, bleeding the donor dogs to arterial pressures of 50 and 35 mm Hg elicited significantly greater increases in resistance than did hemorrhaging the recipient dogs to the same systemic arterial pressures. Figure 14. 103 Effects of rapid arterial hemorrhage of recipient (solid dots) and donor (circles) dogs on muscle total, arterial, small vessel, and venous resistances in cross-perfused forelimbs. Ordinates represent resistance in mm Hg (ml/min)‘ and abscissas represent brachial artery pressure (PEA) in mm Hg. C = pre-hemorrhage control values. Data represents means : standard errors from 5 experiments. 104 MUSCLE RESISTANCE 20' TOTAL I2- 0 L . I25 P75 50 215 8A I SMALL VESSEL IOO 20 I O [— O . l I 1 I25 I00 P 75 50 25 BA 2!) (18 04» H BLEED RECIPIENT °—° BLEED DONOR [ARTERIAL r r C LI2TS I00 75 50 25 8A TVENOUS I I “I25 I00 P75 50 25 8A Figure 14 105 Table 11. Effects of rapid arterial hemorrhage on muscle total (MT), arterial (MA), small vessel (MSV), and venous (MV) resist- ances (R) (expressed as percent of control) in cross- perfused forelimbs. PBA = brachial artery pressure in mm Hg. Values are means from 5 experiments. PEA RMT RMA RMSV RMV % % % % Control 106.3 100 100 100 100 Bleed Recipient 100.0 106 97 105 100 75.0 152 158 141 175 50.0 248 252 223 325 35.4 340 418 261 525 Control 104.7 100 100 100 100 Bleed Donor 100.0 103 80 108 125 74.8 392 317 422 288 49.1 693 733 670 838 34.2 1057 747 1065 2113 106 IV. Series IV: Naturally Perfused, Innervated or Denervated ForeITmbs; Effects of T” ' Slow, Continuousgflemorrhage' A. Mean Arterial Pressure, Pulse Pressure, and Central Venous Pressure Mean systemic arterial pressure, pulse pressure, and central venous pressures are shown as functions of the total blood loss in ml/kg body weight in Figure 15. The responses of 8 dogs with innervated forelimbs are compared to the responses of 9 dogs with acutely denervated limbs during the removal of 0.41 ml blood/kg body weight per minute. Hemorrhage did not produce a significant change in mean arterial pressure until the cumulative blood loss reached approximately 14.7 mg/kg (after 36 minutes of bleeding) in the dogs with innervated or denervated forelimbs. At the end of the 60 minute bleeding period, when approximately 24.4 ml of blood/kg body weight had been removed, mean arterial pressure was reduced from a control value of 114.7 : 2.0 and 115.2 : 2.8 to 63.5 :_6.5 and 73.4 i.5°6 mm Hg in the innervated and denervated groups respectively. Arterial pulse pressure was significantly reduced after removal of approximately 4.9 ml/kg body weight in the innervated and denErvated groups, and continued to decrease progressively in both groups throughout the bleeding period. Central ven- ous pressure decreased significantly after a total blood loss of 4.9 ml/kg body weight in the innervated and denerv- ated groups and continued to decrease during hemorrhage. Figure 15. .107 Effects of slow, continuous hemorrhage on mean systemic arterial, arterial pulse, and central venous pressures in dogs with innervated (solid dots; N = 8) or denervated (circles; N = 9) forelimbs. Ordinates represent pressure in mm Hg and abscissas represent accumulated blood loss in ml/kg body weight. Data represent means 1 standard errors. 108 PRESSURE o—o INNERVATED O-—ODENERVATED '3OT MEAN SYSTEMK: IN)- 9C)~ 70- 50} Oi 1 1 l I l l O 4 8 l2 I6 20 24 I007 PULSE 8C>~ 60" 4O- 00f CENTRAL VENOUS -21)~ -4.0J: I I; I I I I I I 0 4 8 I2 I6 20 24 Figure 15 109 There were no significant differences in mean systemic arterial pressure, arterial pulse pressure, or central venous pressure between the innervated and denervated groups during the control period or during the hemorrhage period, suggesting that both groups were subjected to similar bleeding stresses. B. Skin Total and Segmental Vascular Resistances Data in Figure 16 illustrate the resistance response in the skin vasculature of 8 innervated and 9 denervated forelimbs in animals subjected to a blood loss of 0.41 ml/kg body weight per minute. Hemorrhage produced significant increases in skin total, arterial, small vessel, and venous resistances in both innervated and denervated forelimbs. A marked and progressive constriction was observed in all innervated skin segments, and total skin resistance increased from a control value of 1.38 i 0.12 to 9.25 i 2.85 after 60 minutes of bleeding (or after approximately 24.4 ml blood loss per kg body weight). However, the constriction in all denervated skin vascular segments was small, with total skin resistance increasing from a control value of 0.81 i 0.05 to 1.49 i 0.19 after 60 minutes of hemorrhage. The increases in skin total and small vessel resistances were significantly greater in innervated than denervated fore- limbs after removal of approximately 5 ml blood/kg body weight (12 minutes of bleeding). The increase in skin Figure 16. 110 Effects of slow, continuous hemorrhage on skin total, arterial, small vessel, and venous resistances in innervated (solid dots; N = 8) or denervated (circles; N = 9) forelimbs. Ordinates represent resistance in.mm Hg (ml/min)'1 and abscissas represent aCcumulated blood loss in ml/kg body weight. Data represent means : standard errors. I20 I00 80 60 40 20 00 0 I20 I00 80 SO 40 20 00 111 SKIN RESISTANCE ' TOTAL r 7 SMALL VESSEL Figure 16 08 06 O4 02 OO 08 06 04 02 00 o—aINNERVATED O—ODENERVATED _ ARTERML BL l 1 J J J_ 42 0 4 8 I2 IS 20 24 r VENOUS T- L- I To 4 8 I2 I6 20 24 112 Table 12. Effects of slow, continuous hemorrhage on skin total (ST), arterial (SA), small vessel (SSV), and venous (SV) resist- ances (R) (expressed as percent of control) in innervated forelimbs. MIN = time in minutes after onset of bleeding. Blood Loss = accumulated blood loss in ml/kg body weight. Values are means 3 standard errors from 8 experiments. Blood MIN RST RSA RSSV RSV Loss 0 100 100 100 100 0.00 2 1063 2 10734 1063 3 1053 2 0.81 4 1073 3 10435 1083 4 1103 5 1.63 6 1103 4 10334 1123 5 1133 6 2.44 8 1143 4 10332 1163 5 1193 7 3.20 10 1193_ 5 1073 3 1233_ 7 1193. 8 4.07 12 1233 6 10136 1293 8 125311 4.88 14 1273 6 11038 1323 7 133315 5.70 16 1343_ 7 125312 1373_ 8 l493_17 6.51 H18 1393_ 8 126310 1413_ 9 1573 21 7.33 20 1443. 8 132315 1473 10 1623 25 8.14 22 1443 9 1243 9 1483 11 1643 23 8.95 24 1473 9 12635 150311 1733 24 9.77 26 1523 11 1283 9 1573 14 1833_29 10.58 28 1633 15 135313 1693 19 2013 36 11.40 30 1753 18 141312 1813 23 2133 39 12.21 32 1793 21 157318 1833 24 2183 38 13.02 34 2093 37 162317 2193 46 2723_58 13.84 36 23b3 53 16032? 2483 66 3013 76 14.65 38 2453 57 174321 2623 71 3183 84 15.47 40 2873 81 153325 3213106 3863121 16.28 42 3523142 153325 4013182 4863186 17.09 44 3823153 203334 4253193 5223193 17.91 46 3893152 216336 4313192 5403193 18.72 48 4243180 211328 4763226 5923231 19.54 50 4693184 24934? 5193231 6993246 20.35 52 5263202 238339 5923249 8523310 21.16 54 5883208 326378 6413258 9853347 21.98 56 6533239 344364 7173291 11563411 22.79 58 6993253 3643]? 7683316 12703448 23.61 60 7633277 393369 8413340 14583511 24.42 113 Table 13. Effects of slow, continuous hemorrhage on skin total (ST), arterial (SA), small vessel (SSV), and venous (SV) resist- ances TR) (expressed as percent of control) in denervated forelimbs. MIN = time in minutes after onset of bleeding. Blood Loss = accumulated blood loss in.ml/kg body weight. Values are means 3 standard errors from 9 experiments. Blood MIN RST RSA RSSV RSV Loss 0 100 100 100 100 0.00 2 1003 1 1013 1 1003 2 1033 2 0.81 4 1003 1 1003 1 1013 2 1023 2 1.03 6 103+ 2 1023 l 1043 3 1053 l 2.44 8 105+ 2 1043 1 1073 3 1053 1 3.20 10 105+ 2 1043 l 1073 3 1053_2 4.07 12 1063 3 1053 1 1083 4 1033 2 4.88 14 105+ 3 1063 2 1093 4 1053 l 5.70 16 1093 3 106+ 2 1143 5 1053 2 6.51 18 1113 3 109+ 2 1153 6 1113 4 7.33 20 113+ 3 1123 2 1173 7 1113 3 8.14 22 113+ 4 111+ 4 1203 8 1083 3 8.95 24 ll63_4 116+ 5 1193_7 1093 3 9.77 26 1163 4 117+ 6 1203 8 1133 4 10.58 28 118+ 4 1163 7 1243 9 1143 4 11.40 30 120+ 4 1173 7 1283 9 1113 4 12.21 32 1223 4 1183 8 1323 9 1103 6 13.02 34 123+ 5 ll93_7 134310 1123 5 13.84 36 1273 4 1193 8 142311 1153 6 14.65 38 1313 4 1233 8 146311 1163 ? 15.47 40 1343 5 1253 9 150311 1193 8 16.28 42 1393 5 127310 158312 1183 8 17.09 44 1423 6 129310 163313 120310 17.91 46 1473 8 1313 9 170313 138312 18.72 48 1493 9 1273 6 178315 136314 19.54 50 155310 1263 6 193321 142316 20.35 52 158312 1363 7 189322 148319 21.16 54 164314 139312 198329 148321 21.98 56 15?315 134312 210334 159324 22.79 58 180321 143312 228343 172334 23.61 60 193331 152312 244353 196352 24.42 114 arterial resistance was significantly greater in the in- nervated limbs only after the cumulative blood loss had reached about 20 ml/kg body weight (48 minutes of bleeding). Resistance in innervated skin veins exceeded that in de- nervated skin veins after the accumulated blood loss was approximately 10 ml/kg body weight (24 minutes of bleed- ing). In the innervated skin vasculature, although small vessel constriction produced most of the rise in total skin resistance, the skin veins constricted proportionately more than the small vessels as shown in Table 12. In the de- nervated forelimbs, small vessels constricted proportionately more than any other skin vascular segment during hemorrhage as shown in Table 13. C. Muscle Total and Segmental Vascular Resistances Total and segmental resistances in the muscle vascula- ture of 8 innervated and 9 denervated forelimbs during slow hemorrhage are presented in Figure 17. Muscle total and all segmental vascular resistances in both innervated and denervated forelimbs increased significantly during hemor- rhage. However, a more pronounced increase in muscle total, small vessel, and venous resistance occurred in innervated than in denervated forelimbs. In the innervated limbs, muscle total resistance increased from 2.20 3 0.13 during the control period to 11.01 3 1.85 after 60 minutes of bleeding. Total muscle vascular resistance in the denervated Figure 1?. 115 Effects of slow, continuous hemorrhage on muscle total, arterial, small vessel, and venous resistances in innervated (solid dots; N = 8) or denervated (circles; N = 9) fore- limbs. Ordinates represent resistance in mm Hg (ml/min)’ and abscissas represent accumu- 1ated blood loss in ml/kg body weight. Data represent means 3 standard errors. I20 I00 8.0 6.0 4.0 2.0 00 I20 I00 8.0 6.0 4.0 2.0 0.0 P p CI- OI’ MUSCLE RESISTANCE TOTAL #- SMALL VESSEL 116 2.4 H 2.0 0.8 0.4 0.0 0.8 0.6 0.2 0.0 Figure l? o—o INNERVATED 0—0 DENERVATED ' ARTEmAL I. TO 4 8 I2 I6 20 24 ' VENOUS _I 4 I I I I I O 4 8 I2 I6 20 24 117 Table 14. Effects of slow, continuous hemorrhage on muscle total (MT), arterial (MA), small vessel (MSV), and venous (MV) resist- ances (R) (expressed as percent of control) in innervated forelimbs. MIN = time in minutes after onset of bleeding. Blood Loss = accumulated blood loss in ml/kg body weight. Values are means 3 standard errors from 8 experiments. Blood MIN RMT RMA RMSV RMV Loss 0 100 100 100 100 0.00 2 1063_l ll?3_10 1053 2 1043_ 4 0.81 4 1063 2 1083 10 1063 2 1083_ 6 1.63 6 11034 1173 7 10934 1123 8 2.44 8 11434 1043 8 11636 1173 8 3.20 10 1223 6 1133 4 1243 6 1253 10 4.07 12 1273_8 1153_ 6 1303 9 1323 13 4.88 14 1313 7 1063 8 1363 8 1373 14 5.70 16 141310 1453 20 143311 1473 15 6.51 18 147312 1413 14 150313 1563 18 7.33 20 149312 1403 19 154314 1553 21 8.14 22 157315 1333_ 5 162317 1593 23 8.95 24 162315 1433. 8 166316 1663 24 9.77 26 169315 1513_ 9 174317 1783 23 10.58 28 187319 1583 11 194322 1933 30 11.40 30 190322 1543 10 200326 2013 34 12.21 32 198326 1703 22 204327 2123 48 13.02 34 212331 1973 24 217333 2473 66 13.84 36 231334 1833 28 243328 2643 62 14.65 38 240330 2113_27 248332 2753 65 15.47 40 264336 1983 30 277335 3093 72 16.28 42 303354 2473 50 317357 3693_97 17.09 44 318351 2613 41 332357 3713100 17.91 46 330368 2723 38 339353 4073 94 18.72 48 344353 2593 37 359357 4303102 19.54 50 384362 3033 46 398366 4853107 20.35 52 410363 2943 82 424364 5263115 21.16 54 442368 3803 78 423371 6043128 21.98 56 48b381 4203 99 483364 6553137 22.79 58 511391 4443112 508+93 7443171 23.61 60 528389 466_+_l36 518390 8023181 24 .42 118 Table 15. Effects of slow, continuous hemorrhage on muscle total (MT), arterial (MA), small vessel (MSV), and venous (MV) resist- ances (R) (expressed as percent of control) in denervated forelimbs. MIN = time in minutes after onset of bleeding. Blood Loss = accumulated blood loss in ml/kg body weight. Values are means 3 standard errors from 9 experiments. Blood MIN Pm Rm Pm Rm L... 0 100 100 100 100 0.00 2 1013 l 963 4 1023 l 1053 4 0.81 4 1023 1 943 5 1033 2 1073 5 1.63 6 1063 2 101314 1073 3 1073 7 2.44 8 1093 3 1013 5 1123 4 1063 4 3.20 10 1123 5 1033 6 1153 5 1063 4 4.07 12 1153_4 1053 6 1183 5 1103_ 5 4.88 14 1203 5 1093 8 1233 6 1243 6 5.70 16 1233_6 108311 1283_6 1183 10 6.51 18 1233 7 106311 1313 7 1213_ 9 7.33 20 132310 109314 138311 1323 11 8.14 22 136311 115313 143311 1313 11 8.95 24 1393 9 122311 144310 1333 13 9.77 26 142310 119313 148310 1363_14 10.58 28 149310 124315 156310 1373 16 11.40 30 159315 123322 169314 1473 16 12.21 32 16Q314 123318 169314 1533 21 13.02 34 161313 138319 167312 1753 35 13.84 36 173316 140320 181315 1873 35 14.65 38 178316 146321 185314 1963 38 15.47 40 187317 152322 194316 2103 38 16.28 42 196322 160326 203321 2263 47 17.09 44 213327 166332 223326 2473 52 17.91 46 219330 191336 223329 2463 51 18.72 48 231337 196339 237336 2673 62 19.54 50 245343 207344 252342 2883 68 20.35 52 256349 219345 262349 3013 85 21.16 54 259347 255353 257344 3253 91 21.98 56 269346 231354 274344 3533 91 22.79 58 287354 284370 283348 4003117 23.61 60 304359 296378 300352 4283132 24.42 119 limbs increased from a control value of 1.66 3 0.10 to 5.48 3 1.47 after 60 minutes of bleeding. The increases in muscle total and small vessel resistance were signifi- cantly greater in the innervated than in the denervated limbs after a cumulative blood loss of 15 ml/kg body weight (36 minutes of bleeding). The increases in muscle venous resistance were significantly greater in the innervated limbs after removal of 20 ml blood/kg body weight (48 min- utes of bleeding). However, the increases in muscle arterial resistance were not statistically different in the_ innervated and denervated limbs. The resistance responses of the muscle vasculature in innervated and denervated fore- limbs during hemorrhage are shown in Tables 14 and 15 as percent of control resistance. In the innervated forelimbs, the veins constricted proportionately more than any other muscle vascular segment. However, in the denervated fore- limbs, vascular resistance in arteries, small vessels, and veins increased almost proportionately. DISCUSSION I. Series I: Naturally Perfused, Innervated Forelimbs; Local Hypotension and Rap1d Arterial Hemorrhage A. Forelimb Weight In the present study, slow, sustained changes in fore- limb weight were attributed to net transcapillary fluid movement. Since intravascular pressures, venous outflows, and vascular resistances had stabilized before the slow phases of weight loss were measured, it was assumed that changes in vascular capacity did not contribute to this portion of the weight loss. The rate of extravascular fluid reabsorption during hemorrhage varied between 0.30 3 0.03 g/min (at a brachial artery pressure of 100 mm Hg) and 0.42 3 0.03 g/min (at a brachial artery pressure of 75 mm Hg) (Figure 5). Since total forelimb weight averaged 529.1 3 29.6, with bone com- prising approximately 38 percent (82), the combined weight of forelimb skin and skeletal muscle averaged about 325 g. Therefore, the reabsorption rate in soft tissues (primarily skin and skeletal muscle) during hemorrhage averaged between 0.09 and 0.13 g/min per 100 9. Because skin and skeletal muscle comprise about 55 percent of the total body weight 120 121 (121), a 15 kg dog subjected to severe hemorrhage might be expected to reabsorb 8-12 g of fluid per minute from these tissues alone. However, quantifications of this type are somewhat hazardous since skin and muscle vascular responses in other parts of the dog may not mimic those in the fore- limb. Estimates of the total volume of plasma replaced over several minutes by reabsorption of extravascular fluid in skin and skeletal muscle are further complicated because the amount of extravascular fluid which can be mobilized is limited. In addition, continuous dilution of plasma pro- teins along with a gradual increase in tissue colloid osmotic pressure will progressively decrease the rate of fluid reabsorption. Estimates of the total contribution made by skin and muscle to the restoration of plasma volume are therefore difficult. However, data reported in this thesis demonstrate that the rate of fluid reabsorption in skin and skeletal muscle is large enough to cause a significant replacement of plasma volume following hemorrhage. Our findings support those of other investigators (66, 89,98,115) who reported that reabsorption of extravascular fluid in skin and skeletal muscle is important in restoring plasma volume during the early stages of hemorrhagic hypoten- sion. The rate of fluid reabsorption in the present study closely approximates that reported for cat skeletal muscle during the early stages (first 10-15 minutes) of "moderate" or "severe" hemorrhage (rapid removal of 15-40 percent of 122 the total blood volume) (89). However, some investigators (89,93,96) have reported that fluid reabsorption is not maintained during prolonged hemorrhage. According to Lungren gg_§3, (89), after 20-25 minutes of hypotension, fluid reabsorption in cat skeletal muscle is replaced by net filtration. They attributed the gradual decrease in the rate of fluid reabsorption to a fall in the pre- to post- capillary resistance ratio which allegedly occurred because local regulatory mechanisms selectively dilated precapillary vessels while postcapillary vessels remained constricted. However, Schwinghamer EE.El' (115) and Grega 33.23. (66) reported that fluid reabsorption and constriction of pre- capillary vessels are sustained for at least 4 hours during severe hemorrhage (removal of 25360 percent of the total blood volume). In the present study, the rate of fluid reabsorption was well maintained throughout each of the 20- 30 minute periods of hypovolemia (a total of about 80-120 minutes of bleeding) and resistance in all vascular segments of skin and skeletal muscle increased progressively as blood losses increased. Differences between the observations of Lungren 33'33. and those in the present study, as well as those of Schwinghamer 33.33. and Grega 33:23,, may be re- lated to differences in species (cats vs. dogs), anesthetic (chloralose-urethane vs. sodium pentobarbital), or experi— mental design. It is important to note that Lungren 33.33. held venous pressure constant during hemorrhage. Perhaps 123 when venous pressure is permitted to fall, as it normally does during hemorrhage, transcapillary fluid absorption is maintained because of a greater, more sustained fall in capillary hydrostatic pressure. The hemorrhage-induced reabsorption of extravascular fluid could be due to a reduced transcapillary hydrostatic gradient or to an increased transcapillary osmotic gradient (see equation 3). Jarhult (80,81) reported that an increased arteriovenous plasma osmolarity gradient (and pnesumably an increased transcapillary osmolarity gradient) mediates a small but significant portion of the extravascular fluid reabsorption in skeletal muscle during hemorrhage. Plasma osmolarity was not measured in the present study but other investigators (66,115) have reported only small changes in plasma osmolarity in the dog during severe hemorrhage. Therefore, it is unlikely that the rapid rates of fluid re— absorption observed in the present study were due primarily to increases in the transcapillary osmotic gradient. Instead, most of the net transcapillary fluid reabsorption probably resulted from reductions in the net transcapillary hydrostatic gradient due to a fall in capillary pressure. Capillary hydrostatic pressure could fall because of increases in the pre— to postcapillary resistance ratio and/or decreases in arterial and venous pressures (see equa- tion 4). The slow, sustained weight losses observed when the brachial artery was clamped indicate that reducing 124 arterial and venous pressures produces significant fluid reabsorption. However, the rate of fluid reabsorption dur- ing local hypotension (produced by clamping the brachial artery) was always much less than that observed during hemorrhage even though arterial and venous pressures were reduced to corresponding levels (Figure 5). Therefore, the net fluid reabsorption elicited by hemorrhage is not due primarily to reductions in arterial and venous pressures, but is due largely to a greater pre- to postcapillary resistance ratio and/0r an increased capillary filtration coefficient (CFC). Since adrenergic nerves and circulating vasoconstrictors (i.e., catecholamines, angiotensin, vaso- pressin) which are activated or released during hemorrhage constrict precapillary sphincters and reduce the capillary surface area available for exchange (9,33,98), it is unlikely that CFC is actually higher during hemorrhage than during local hypotension. Therefore, differences in the rate of fluid reabsorption during clamping and bleeding are probably due to differences in the pre- to postcapillary resistance ratio. The initial, rapid phase of forelimb weight loss, associated with reductions in intravascular capacity, was consistently greater during hemorrhage than during local hypotension (Figure 4). Since bleeding and clamping to corre8ponding brachial artery pressures did not produce appreciably different mean intraluminal pressures, the larger 125 reductions in vascular capacity during hemorrhage resulted from active venous constriction. This conclusion is sup- ported by the resistance data (Figures 6 and 7) which indi- cate that hemorrhage elicits a much larger increase in venous resistance than does a corresponding degree of local hypotension. Data from the present study do not permit accurate quantification of the amount of blood mobilized from the skin and muscle vasculature due to active and passive venous constriction. However, these data do support those of Lungren 33.33, (89) and aberg (98) who concluded that most of the vascular volume reduction in skin and skeletal muscle during hemorrhage could be attributed to active constriction of capacitance vessels. B. Forelimb Vascular Resistances Local hypotension elicited slight increases in forelimb. vascular resistances. In skin, significant passive constric- tion occurred only in the large veins. In skeletal muscle, total and segmental resistances increase significantly, but these changes were small and occurred only at brachial artery pressures of 75, 50, and 35 mm Hg. These data suggest that local reductions in arterial and venous pressures do not elicit large decreases in the radii of forelimb vessels. During hemorrhage, resistance in forelimb vascular segments increased progressively as brachial artery pressure 126 was reduced to 100 mm Hg and below. The resistance increases observed during hemorrhage were always significantly greater than those produced by clamping to corresponding perfusion pressures. At a brachial artery pressure of 35 mm Hg, total vascular resistances in skin and skeletal muscle in- creased 9 and 12 fold, respectively, during hemorrhage, whereas, during local hypotension total vascular resistance in skeletal muscle increased only 2 fold and total skin vas- cular resistance did not increase significantly. These data clearly indicate that the hemorrhage-induced constriction of all vascular segments in skin and skeletal muscle, including the large veins, results primarily from active smooth muscle contraction rather than from passive vascular collapse. The resistance data for arteries and small vessels agree with those of several other investigators (89,66,115). However, hemorrhage-induced increases in venous resistance have been reported by Lesh and Rothe (87) and Haddy 33 33. (75) to occur primarily because of passive vascular collapse subse- quent to a reduced venous transmural pressure. Lesh and Rothe did not calculate large vein resistance, but based their conclusions on observations of changes in muscle weight (see Section II-B of Literature Review). Haddy\g£.§3., using a dog forelimb preparation perfused at constant flow, failed to observe an increase in large vein resistance when the dogs were hemorrhaged approximately 21 percent of their total blood volume. In the present study, large vein resistances 127 were calculated during natural flow conditions, thus avoidr ing the use of a pump (required for constant flow studies)' which may alter vascular reactivity (49). Differences be- tween Haddy 33 33.'s observations and those in the present study may therefore be related to differences in the method of forelimb perfusion. Other investigators (76,89,98) using natural flow preparations have reported that venous constric- tion during hemorrhage results partly from active smooth muscle contraction. II. Series II: Naturally PerfusedL3Denervated Forelimbs; Local Hypotension and Rapid Arterial Hemorrhage A. Forelimb Weight In the denervated forelimbs, both local and hemorrhagic hypotension caused a substantial reabsorption of extravascu- lar fluid as evidenced by the slow, sustained limb weight losses observed during clamping and bleeding (Figure 8). At forelimb perfusion pressures of 100 and 75 mm Hg, hemor- rhage elicited a significantly greater rate of fluid reab- sorption than did local hypotension, suggesting that the pre- to postcapillary resistance ratio was higher in the skin and muscle vasculature during hemorrhage. This conclusion is based on an analysis of equations 3 and 4 and the assumption that the capillary filtration coefficient during local'hypo- tension was at least as great as during hemorrhage (see Discussion I-A). 128 The observation that clamping or bleeding to brachial artery pressures of 50 and 35 mm Hg elicited the same rates of weight loss in denervated forelimbs could be explained by either of the following hypotheses: 1) Pre- to post- capillary resistance ratios and CFC's in the denervated fore— limbs were not different during local hypotension and hemor- rhage. 2) Forelimb pre- to postcapillary resistance ratio is greater during hemorrhage, but CFC is higher during local hypotension. Hypothesis 2 is more plausible since circulat- ing vasoconstrictors, which are released during hemorrhage (i.e., catecholamines, angiotensin, vasopressin), contract precapillary sphincters and thereby decrease the functional capillary surface area (9,51,92,95). This conclusion is sup- ported by the finding that in skeletal muscle, CFC is higher during local hypotension than during hemorrhage (98). There were no significant differences between the rates of slow, sustained limb weight loss in innervated (Series I) and denervated (Series II) forelimbs during hemorrhage to corresponding brachial artery pressures (Table 5). These data suggest that circulating vasoconstrictors, as well as reductions in arterial and venous pressures, are responsible for most of the extravascular fluid reabsorption in skin and skeletal muscle during rapid arterial hemorrhage, with sympa- thetic nerves apparently contributing little to this response. These observations differ from those of 0berg (98) who reported that denervation abolished the hemorrhage'induced 129 reabsorption of extravascular fluid in cat skin and skelev tal muscle. An explanation for the differences between 0berg's findings and those in the present study is not appar- ent, but may be related to differences in animal species (cats vs. dogs) or anesthesia used (chloralose vs. sodium pentobarbital). Critical analysis of Oberg's report is complicated by the fact that all data presented were from single "typical" experiments. B. Forelimb Vascular Resistances Local hypotension, produced by clamping the brachial artery, elicited increases in skin and skeletal muscle vascular resistances which were always much less than those observed at corresponding brachial artery pressures during hemorrhage (Figures 9 and 11). These data agree with those in Series I, which indicated that hemorrhage-induced con- striction in all skin and muscle vascular segments, includ- ing the large veins, results primarily from active smooth muscle contraction rather than from passive vascular col- lapse. A comparison of the resistance data in Series I and II (Figures 10 and 12) reveals that the resistance response to hemorrhage in all forelimb vascular segments, except the large skin arteries, was not substantially attenuated by denervation. These data suggest that when the bleeding rate is rapid, and the blood loss severe enough to lower arterial blood pressure markedly (i.e., from a control value of 125 130 mm Hg to 100 mm Hg or below), blood-borne agents are the primary mediators of the vascular constriction in skin and skeletal muscle. Bond EE.§£- (21) also observed that con- striction of cutaneous vessels during large, rapid blood losses was not attenuated by denervation and therefore con- cluded that circulating hormones, rather than sympathetic nerves, are the primary mediators of hemorrhage-induced vasoconstriction in skin. In Bond 23_§3,'s study, cutaneous vasoconstriction was also unaffected by bilateral nephrec- tomy, but was abolished by a adrenergic blockade, suggesting to them that circulating catecholamines mediated this re- sponse. In another study, Bond gg_§3, (22) reported that circulating hormones and sympathetic nerves both mediate the vasoconstriction in skeletal muscle during rapid, severe hemorrhage. They observed that the resistance response to hemorrhage did not differ in innervated and denervated skeletal muscle vessels at perfusion pressures above 80 mm Hg. However, at perfusion pressures between 70 and 40 mm Hg, denervation reduced the resistance response to hemorrhage. Bond 23_§3.'s data differ from those in the present study only at perfusion pressures of 70 mm Hg and below; our data indicate that denervation does not reduce hemorrhage-induced constriction in skeletal muscle vessels at pressures between 35 and 100 mm Hg. Differences between Bond gg_33,'s observ- ations and those in the present study may be related to dif- ferences in the method of bleeding (5 ml/kg step hemorrhages 131 vs. 25 mm Hg step reductions in arterial pressure by rapid bleeding) or the preparation used (dog hindlimb muscle vs. dog forelimb muscle). In the present study, the sympathetic nerves contribu- ted significantly to the control of resting vascular resistv ance in skin and muscle, as evidenced by the reductions in resistance after denervation: but during rapid, severe hemorv rhage, the nerves did not contribute appreciably to the increased vascular resistance, except in the large skin arteries. III. Series III: Crosseperfused Forelimbs; Rapid, Arterial Hemorrhage39f 1.-- Recipient and Donor Dog; This series of experiments was conducted to test the hypothesis that during rapid, severe hemorrhage, circulat- ing vasoconstrictors and sympathetic nerves may be acting as simultaneous and overlapping mediators of skin and skele- tal muscle vasoconstriction. That is, sympathetic nerves alone, or circulating vasoconstrictors alone, may cause forelimb resistance responses of similar magnitude to those observed when both factors act together. The results from Series I and II indicated that circulating vasoconstrictors can elicit increases in forelimb vascular resistance of similar magnitude to those observed when both neural and blood-borne factors are present: however, these studies did 132 not rule out the possibility that increased sympathetic nerve activity is also an important mediator of vasoconstric- tion in the forelimb during rapid, severe hemorrhage. The cross-circulation technique used in the present study eliminated the hemorrhage—induced accumulation of vasoconstrictors in the arterial supply to the recipient dog's forelimb as long as the donor dog remained normoten- sive and normovolemic. The vasoconstriction which occurred in the forelimb when the recipient dog was bled can be attributed to a combination of the effects of increased sympathetic nerve activity and reduced forelimb perfusion pressure. Bleeding the recipient dog elicited relatively small increases in forelimb vascular resistances (Figures 13 and 14). Total vascular resistance in skin and skeletal muscle increased only 4.2 and 3.4 fold respectively at the most severe level of hemorrhage. A significant part of these in- creased resistances was undoubtedly due to passive vascular collapse subsequent to reducing forelimb perfusion pressure, since the results of Series I and II indicate that reducing brachial artery pressure to 35 mm Hg alone results in a 1.2—2.5 fold increase in total skin or skeletal muscle vascular resistance. Therefore, when the recipient dog was hemorrhaged, increased sympathetic nerve activity elicited, at most, only a 3.0 and 2.2 fold increase in total skin and skeletal muscle vascular resistance respectively. These data 133 support the results of Series I and II which suggested that the contribution of sympathetic nerve activity to the in- creased forelimb vascular resistance during rapid, severe hemorrhage is modest relative to that due to circulating vasoconstrictors. The data in Series III do not support the hypothesis that circulating vasoconstrictors and sympa— thetic nerves are acting as simultaneous and overlapping mechanisms in eliciting skin and skeletal muscle vasocon- striction during rapid, severe hemorrhage. After the shed blood was reinfused into the recipient dog and the forelimb nerves were severed, the forelimb vasculature was no longer reflexly controlled by the recip- ient dog. Therefore, vasoconstriction which accompanied hemorrhage of the donor dog can be attributed to passive vascular collapse due to reduced forelimb perfusion pressure, and to the effects of blood-borne vasoconstrictors released in the donor dog. Bleeding the donor dog to 35 mm Hg systemic arterial pressure elicited a 12.0 and 10.6 fold increase in total skin and skeletal muscle vascular resist- ance as compared to the 4.2 and 3.4 fold increase observed when the recipient dog was hemorrhaged to the same systemic arterial pressure. These data further support the hypothe- sis that circulating vasoconstrictors rather than sympathetic nerves, are the most important controllers of skin and skele- tal muscle vessels during rapid, severe hemorrhage. 134 IV. Series IV: NaturallyPerfusgg, Innervated or Denervated Forelimbs; Slow, Continuous Hemorrhage A. Mean Systemic Arterial, Arterial Pulse, and Central Venous Pressures A comparison of mean systemic arterial, arterial pulse, and central venous pressures between dogs with innervated and denervated forelimbs reveals that hemorrhage of 0.41 ml/kg body weight per minute produced the same pressure re- sponses in both groups (Figure 15). These data indicate that both groups of dogs were subjected to similar bleeding stresses, a prerequisite for comparing resistance responses of innervated and denervated forelimbs. B. Forelimb Resistances In skin, slow, sustained hemorrhage (0.41 ml/kg body weight per minute) produced significant increases in total and all segmental vascular resistances of innervated and denervated forelimbs (Figure 16). In denervated forelimbs, the resistance increases were small; total skin resistance increased only 1.9 times above prevhemorrhage control values. However, innervated forelimbs demonstrated a marked and pro- gressive constriction in all skin vascular segments; total skin resistance increased more than 7.6 times above the control value. These data indicate that when the bleeding rate is slow, constriction of the skin vasculature is almost entirely neurogenically mediated. 135 Slow, sustained, hemorrhage produced significant in- creases in skeletal muscle total and segmental vascular resistances in innervated as well as denervated forelimbs, with the constriction being less pronounced in the dener- vated muscle vasculature (total resistance increased to 5.2 and 3.0 times above control in innervated and denervated forelimbs, respectively, after 60 minutes of bleeding) (Figure 17). These data demonstrate that denervation atten- uates constriction of the muscle vasculature during slow hemorrhage. Since the denervated muscle vasculature still shows appreciable constriction during slow hemorrhage, circulating vasoconstrictors must mediate part of this re- sponse. A comparison of the forelimb resistance responses to rapid and slow hemorrhage indicates that the relative importance of sympathetic nerves and blood-borne agents in mediating vasoconstriction depends on the rate of blood loss. When the bleeding rate is rapid, constriction in all fore- limb vascular segments, except the large skin arteries, is not reduced by denervation. When the bleeding rate is much slower, denervation almost abolishes the hemorrhage-induced vasoconstriction in skin, and greatly attenuates it in skele- tal muscle. These observations suggest that sympathetic nerves play a minor role in controlling vascular resistance during rapid, severe hemorrhage, but are much more important during slow, gradual blood losses. 136 These differences in the mediation of vasoconstriction do not appear to be related to differences in arterial baroreceptor stimulation during rapid and slow hemorrhage. For example, when mean arterial pressure was rapidly reduced to 75 mm Hg, increases in total skin and muscle vascular resistances were not significantly different in innervated and denervated forelimbs. In contrast, when mean arterial pressure is reduced to 75 mm Hg by slow hemorrhage, denerva- tion almost abolishes the constriction in skin and greatly reduces it in muscle. Furthermore, several investigators (23,100,111) have reported that baroreceptor feedback is proportional not only to mean arterial pressure, but also to the derivative of the pressure. Therefore, rapid reduction of mean arterial pressure should produce a greater sympathet- ic nerve activity than should much slower reduction of mean arterial pressure to corresponding levels. These considera- tions suggest that differences in the relative importance of neurally mediated control of the skin and muscle vasculature during rapid and slow hemorrhage are not due to an arterial baroreceptor—mediated mechanism. One explanation for the differences in vascular control during rapid and slow hemorrhage is that the release of circulating vasoconstrictors may depend on the rate of blood loss more than on the magnitude of the blood pressure reduc- tion, with rapid hemorrhage eliciting a much greater release of circulating vasoconstrictors than slow hemorrhage even if 137 arterial blood pressure is equally reduced by both types of bleeding. This hypothesis is supported by Carey (28), who reported that slow, continuous hemorrhage (10% of the total blood volume in 30 min., or 30% in 90 min.) elicits no significant increase in adrenal epinephrine or norepine- phrine secretion. Rapid hemorrhage (10% of the total blood volume in 10 min., or 30% in 30 min.) produced large in- creases in adrenal secretion of epinephrine and norepine- phrine. Assuming that total blood volume in the dog is approximately 8 percent of body weight, the rate of blood loss in Series IV of the present study was about 15 percent of the total blood volume in 30 minutes (a rate somewhat higher than Carey's slow hemorrhage, but only one—half as great as his rapid hemorrhage rate). Therefore, the bleed— ing rate in Series IV may not have been great enough to elicit large increases in adrenal catecholamine secretion. In Series I and II, in which the bleeding rate was much more rapid, adrenal secretion of catecholamines would be expected to increase markedly and elicit a substantial con- striction in the forelimb vasculature. It is also possible that the release of other circulating vasoconstrictors (i.e., angiotensin, vasopressin, and unidentified agents) is sensi- tive to the rate of blood loss. SUMMARY AND CONCLUS IONS l. A substantial reabsorption of extravascular fluid, which is not reduced by denervation, occurs in skin and skeletal muscle during rapid, severe hemorrhage. 2. The extravascular fluid reabsorption which accom- panies hemorrhage results from a fall in capillary hydro- static pressure, which in turn, results primarily from active changes in the pre— to postcapillary resistance ratio, and to a lesser extent, from a fall in arterial and venous pressures. 3. Hemorrhage-induced reductions in vascular capaciw tance are due primarily to active smooth.muscle contraction rather than to passive vascular collapse subsequent to re- duced transmural pressures. During rapid, severe hemorrhage, circulating vasoconstrictors mediate most of the active com- ponent of the decreased vascular capacitance. 4. Hemorrhage elicits a marked constriction in all skin and skeletal muscle vascular segments of the dog forelimb, whereas local hypotension produces relatively small increases in skin and skeletal muscle vascular resistances. These observations indicate that hemorrhage-induced constriction of all forelimb vascular segments, including the large veins, results largely from active smooth muscle contraction rather than from passive vascular collapse. 138 139 5. During rapid, severe hemorrhage, the increased resistance in all skin and muscle vascular segments, except the large skin arteries, is not substantially reduced by denervation. When hemorrhagevinduced circulating vasocon- strictors are prevented from accumulating in the forelimb by using a cross-circulation technique, increases in skin and skeletal muscle vascular resistances during rapid, severe hemorrhage are modest. These observations suggest that circulating vasoconstrictors, rather than sympathetic nerves, are the primary mediators of active constriction in the skin and muscle vasculature during rapid, severe hemor« rhage. 6. During slow, sustained hemorrhage (0.41 ml blood loss/kg body weight per minute) denervation almost abolishes the constrictor response in the skin vasculature and greatly attenuates it in skeletal muscle, indicating that sympathetic nerves are much more important in mediating vasoconstriction during slow hemorrhage than during rapid, severe hemorrhage. However, circulating vasoconstrictors mediate part of the forelimb resistance response to slow hemorrhage as evidenced by the constriction which occurred in skeletal muscle even after denervation. APPENDICES APPENDIX A LIST OF ABBREVIATIONS AND FORELIMB VASCULAR RESISTANCE CALCULATIONS 140. APPENDIX A LIST OF ABBREVIATIONS AND FORELIMB VASCULAR RESISTANCE CALCULATIONS Vascular Resistances = R in mm Hg x (ml/min)‘l ST SA SSV SV MT MSV MV Pressures SYS BA CV SSA SSVE BV MSA MSVE Blood skin total skin large artery skin small vessel skin large vein muscle total muscle large artery muscle small vessel muscle large vein = P in mm Hg mean systemic arterial brachial artery cephalic vein skin small artery skin small vein brachial vein muscle small artery muscle small vein Flows = F in ml/min cephalic brachial 141 142 4. Forelimb Vascular Resistance Calculations RST = (PEA ’ Pcv) / Fc RSA = (PBA ' PSSA) / Fc Rssv = (PSSA ’ PSSVE) / Fc Rsv = (PSSVE ’ Pcv) / Fc RMT = (PEA ' PB v) / FB RMA = (PBA ' PMSA) / FB RMSV = (PMSA ’ PMSVE) / FB RMv = (PMSVE- PBV) / FB APPENDIX B PRESSURE, FLOW, AND RESISTANCE DATA 143 144 m.omm.m~ Tommdm m.omo.mm m.omm.mm >.pHn.~v m.th.ov m.£Hv.vm n.0Hm.om b.0Hv.mm m.flHv.oo m.th.mb 0.9Hm.vb m.o+m.wm m.a+m.mm N.A+m.¢oa m.o+m.mm comam m.mHv.moa m.mHh.nm m.mHm.oma m.mHm.mNH Houusou 9&me 9&me Sawfmma fommém m.pHH.m¢ 0.9Ho.m¢ o.NHm.Hma m.on.Hm m.pHm.vm m.pHv.mm m.flHh.oma b.0HH.mh 374.31 918% m.m+m.¢2 90.6.03 9:30 m. «no.2: H .mHm .mm m.m.....m.m2 m.mHm .8: H9986 «mZm «mmm mwmm «mm .musmfiwuwmxm ma Scum muouuo chopcmum.fl momma mum mm 58 ca mosam> .mnfiaaouom paum>uocsw cw mousmmmum Hawuouum was mudmmoum Hafiumuum oaswumhm so ommsunosmn Hmwumunm Gamma new :oflmcmuomhn Hmooa mo muoommm .Hlm magma 145 m.owm.H m.om6.m m.pHo.a v.6Hs.m v.oMm.ou quDWmuv. m.pHm.~ e.HHn.oa ~.pwm.a v.pHo.v 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H.fiwm.¢m m.mwa.5a s.pHa.m m.on.m o.pHa.v 8.65m.m m.v+w.mo o.m+~.mmH m.o+o.v m.o+v.s ~.H+m.m o.H+5.mH pamHmHomm cmmam 0.nH0.ms 8.0Hm.mma s.qum.e o.dHo.m o.mua.m o.dua.ma Houucoo m o a m >mm m>mzm >om m>mmm .muawsauomxo m scum muouuw pumpcmum.fi momma mum mosam> AcflE\HSV m3on vocab 0cm Rom EEV wwusmmoum msocm> co mmmnuuosmn Hmflumuum pflmmu Mo muommmm .mlm manna .mnsflaouom pomsmuomnmmouo ca 152 Table B-9. Effects of_rapid arterial hemorrhage on mean intraluminal pressure (P) of skin arteries (SA), small vessels (SSV), and veins (SV) in crosstperfused forelimbs. P = brachial artery pressure. Values in mm Hg are means 3_s ndard errors from 5 experiments. PBA PSA PSSV PSV Control 106.332.8 87.533.5 42.632.0 12.73110 Bleed Recipient 100.030.0 80.531.7 38.331.3 12.131.0 75.030.0 59.431.0 26.830.8 7.330.5 50.030.0 37.23p.9 15.030.9 3.830.2 35.430.2 25.330.7 10.03p.6 3.030.1 Control 104.732.5 83.332.8 40.131.6 14.431.4 Bleed Donor 100.03p.0 78.832.l 38.732.2 12.13p.6 74.830.2 62.730.7 30.130.7 7.03p.9 49.130.5 42.830.6 21.83p.9 4.83p.6 34.23p.4 30.530.4 l7.03p.5 4.3+0.5 153 Table B-lO. Effects of rapid arterial hemorrhage on mean intraluminal pressure (P') of muscle arteries (MA), small vessels (MSV), and veins (MV) in cross-perfused forelimbs. P = brachial artery pressure. Values in mm Hg are means 3 s andard errors from 5 experiments. WI PBA PMA MSV PMV Control 106.332.8 94-519-1 45.2:g.2 5.83p.5 Bleed-Recipient 100.0:p.o 89.331.6 41.5:1.4 5.03p.8 7s.q:p.o 65.931.l 30.03p.8 3.2ip.s 50.0:p.o 43.930.8 20.43p.6 1.9:p.4 3s.4:p.2 30.13p.6 l3.63p.4 1.2ip.3 Control 104.732.5 94.032.6 46.731.4 7.0:p.9 Bleed Donor 100.030.0 92.5:p.7 47.5:p.9 6.730.5 74.83p.2 68.730.4 33.2:p.s 1.9:p.3 49.1:p.s 43.7ip.5 20.3ip.4 0 630.2 34.2:p.4 31.53p.6 15.539.5 o.2+o.2 154 N.HH o.V5 m.vH m.0H H.m0 0.0m m.vm 0.0 o.H5 ~.~N 5.0a 5.00 0.~N H.mv H.v o.m5 m.0H H.0 o.v0 m.mm m.¢5 0.0 m.05 m.0H H.m 0.vv H.5w o.ooa Hoson cmoam 5.0 v.M5 m.om H.m m.5¢ 0.ve 5.voa Houuooo m.m 5.H0 ¢.mm 5.0a v.0m m.mm «.mm ¢.5 m.m0 m.mm 0.5 H.mm v.vm 0.00 m.0 «.05 m.mm a.5 0.00 ¢.mv 0.05 H.m m.v5 w.o~ m.5 m.am ~.ov o.ooa ucmfimflomm woman m.m o.m5 5.Hm 0.0 v.00 0.5m m.0oa Houucoo mcfim> mammmm> moflumuud , mcwo> maommo> ,mofluouud mmumq Hamsm manna mound Hamam omnmg mam qumDZ Adfimqum ZHMm .mucofiwuomxo m scum momma mum mosam> .mm Efi.cw musmmmum 5uouum Huanomnn H 0mm .mgswaouom pomsmumgsmmono ca mqwm> mmHmH 0am «madmwo>ndamem .mofluwuum mound cw mswpflmmu mosmumflmmu odomsfi Hmuoamxm Ho nflxm Hmuou mo uzmoumm on» :0 ommnuuoamn amaumuum comm“ mo muoowmm .HHIm magma 155 Table B-12. Effects of slow, continuous hemorrhage on systemic arterial pressure and arterial pressures in innervated forelimbs. Values in mm Hg are means 3 standard errors from 8 experi- ments. MIN - time in minutes after the onset of bleeding. Blood Loss = accumulated blood loss in ml/kg body weight. MIN PBA PSYS PSSA PMSA Blood Loss 0 110.331.9 114.732.0 89.332.0 95.531.8 0.00 2 109.133.1 113.433.1 88.033.5 93.633.1 0.81 4 108.433.2 112.633.2 87.933.8 93.933.2 1.63 6 107.234.1 112.033.? 870333.? 91.933.1 2.44 8 105.634.4 110.134.0 86.634.0 9l.933.0 3.20 10 105.434.6 110.134.4 86.834.4 91.933.4 4.07 12 103.635.5 108.934.3 86.134.7 90.734.2 4.88 14 102.236.0 106.635.8 84.935.7 90.434.8 5.70 16 101.136.2 105.236.2 82.935.7 88.035.1 6.51 18 97.836.9 104.036.? 82.036.2 87.135.7 7.33 20 98.537.3 102.937.3 81.436.6 86.736.2 8.14 22 97.637.8 101.937.5 80.937.0 85.636.3 8.95 24 96.437.7 100.737.5 79.636.8 84.036.2 9.77 26 94.537.7 98.837.4 78.636.9 82.936.4 10.58 28 92.937.8 97.137.5 77.537.2 81.936.6 11.40 30 91.337.7 95.437.5 76.036.9 81.036.5 12.21 32 89.937.7 94.037.7 74.036.8 78.936.4 13.02 34 87.737.7 91.637.8 73.437.0 76.736.7 13.84 36 85.337.5 89.533.4 72.437.1 76.436.9 14.65 38 83.837.7 88.037.5 70.537.1 73.836.8 15.47 40 81.437.6 85.037.5 70.037.1 73.036.7 16.28 42 80.037.4 83.937.3 69.437.0 71.537.0 17.09 44 78.237.l 82.037.l 66.436.8 69.436.5 17.91 46 76.736.9 81.036.8 65.136.8 67.536.6 18.72 48 75.036.9 79.136.7 64.236.8 67.136.5 19.54 50 73.036.5 77.036.5 62.136.7 65.136.4 20.35 52 70.436.2 74.236.2 61.136.3 63.436.2 21.16 54 68.136.5 72.036.5 58.036.9 59.636.7 21.98 56 65.636.4 69.436.6 56.536.8 57.536.7 22.79 58 62.436.2 65.736.4 53.636.6 54.736.8 23.61 60 60.036.5 63.536.5 51.736.3 52.436.7 24.42 156 Table B-l3. Effects of slow, continuous hemorrhage on venous pressures (mm Hg) and blood flows (ml/min) in innervated forelimbs. Values are means 3 standard errors from 8 experiments. MIN = time in minutes after the onset of bleeding. Blood Loss = accumulated blood loss in ml/kg body weight. MIN PSSVE PCV PMSVE PBv FC FB Blood Loss 0 13.23p.7 7.330.7 9.330.6 4.73p.4 94.63 6.8 56.434.3 0.00 2 13.131.3 7.131.4 9.531.2 4.43p.7 90.1312.4 52.137.3 0.82 4 12.931.3 6.831.4 9.431.1 4.330.7 88.8312.5 51.537.0 1.63 6 12.631.3 6.531.3 9.231.1 4.13p.7 86.3312.8 49.236.6 2.44 8 12.43l.3 6.331.3 9.031 1 3.930.7 83.2313.l 47.637.2 3.20 10 12.131.3 6.331.3 8.931.2 3.83p.7 79.4312.9 44.336.6 4.07 12 ll.831.3 6.031.3 8.631.l 3.730.7 76.2312.9 41.936.1 4.88 14 11.631.2 5.831.3 8.431.2 3.539.73 73.4312.7 40.436.2 5.70 16 ll.331.2 5.431.3 8.231.2 3.330.7 70.2313.2 38.136.7 6.51 18 ll.431.3 5.33l.3 8.131.3 3.230.7 67.3313.2 36.136.3 7.33 20 ll.l31.3 5.331.2 7.831.2 3.230.7 64.4312.8 35.336.4 8.14 22 11.031.2 5 231.3 7.531.2 3.030.8 63.3312.8 33.436.2 8.95 24 10.931.2 4.831 3 7.331.l 2.830.7 61.4312.6 31.735.8 9.77 26 10.731.2 4.831.3 7.331.2 2.73p.7 58.7312.8 29.234.6 10.58 28 10.531.2 4.631.3 7.131.1 2.730.7 55.5313.2 26.033.8 11.40 30 10.131.1 4 531.3 7.031.2 2 530.7 51.3312.2 26.034.9 12.21 32 9.931.2 4.331.3 6.831.2 2.430.7 50.4312.8 25.235.2 13.02 34 9.931.2 4.131.3 6.931.3 2.330.7 45.4312.7 23.534.8 13.84 36 9.631.2 3.931.3 6.631.2 2.230.7 42.4312.1 20.833.8 14.65 38 9.131.0 3.631.2 6.331.1 2.030.7 40.0312.0 l9.l33.3 15.47 40 8.931.0 3.531.l 6.231.1 1.93p.7 35.2310.8 17.233.l 16.28 42 8.931.0 3.231.1 6.131.l l.73p.7 33.5310.6 15.532.8 17.09 44 8.731.0 3.131.0 5.831.1 1.730.7 30.7310.4 14.232.3 17.91 46 8.430.9 2.831.0 5.831.0 1.530.6. 28.83 9.4 13.132.0 18.72 48 8.230.8 2.73p.9 5.731.0 1.430.6 27.63 9.5 12.532.0 19.54 50 8.03p.8 2.330.9 5.631.0 l.330.6 24.33 8.7 10.931.6 20.35 52 7.930.8 2.130.8 5.431.0 1.330.6 21.23 7.9 9.731.3 21.16 54 7.530.8 1.93p.7 5.431.0 1.230.6 18.53 7.3 8.731.2 21.98 56 7.330.8 1.53p.6 5.231.0 1.130.6 15.93;5.9 7.931;l 22.79 58 7.030.8 1.230.6 5.231.0 l.030.6 13.83 4.7 7.231.1 23.61 60 6.83p.7 1.130.5 5.131.0 1.0+0.5 12.33 4.3 6.631.0 24.42 157 Table B-14. Effects of slow, continuous hemorrhage on systemic arterial pressure and arterial pressures in denervated forelimbs. Values in mm Hg are means 3 standard errors from 9 experi- ments. MIN = time in minutes after the onset of bleeding. Blood Loss = accumulated blood loss in ml/kg body weight. MIN PBA PSYS Pssn PMSA Blood LOSS 0 104.631.9 115.232.8 61.731.3 85.931.2 0.00 2 103.933.7 114.635.4 61.232.4 86.032.6 1.81 4 103.033.6 114.335.5 61.132.3 85.932.9 1.63 6 102.633.6 113.235.2 61.032.2 85.032.9 2.44 8 102.133.6 112.635.4 60.832.2 85.332.9 3.27 10 101.633.5 111.935.4 60.432.4 84.932.8 4.07 12 100.933.7 111.435.4 59.832.3 84.633.1 4.88 14 101.033.8 110.935.2 59.932.3 84.833.3 5.70 16 100.133.8 110.335.2 60.132.4 84.733.3 6.51 18 98.833.8 109.435.3 58.932.4 83.933.3 7.33 20 97.833.8 107.634.9 58.032.6 83.633.4 8.14 22 97.133.9 106.735.l 58.132.6 82.733.4 8.95 24 97.033.9 106.635.1 57.132.8 81.933.2 9.77 26 95.034.0 104.935.0 55.832.9 80.733.3 10.58 28 92.833.9 102.834.9 55.439.0 79.133.7 11.40 30 90.634.2 100.635.1 53.333.2 78.133.6 12.21 32 89.734.0 99.134.8 53.935.0 77.333.5 13.02 34 88.334.0 97.934.7 53.433.1 75.334.1 13.84 36 85.834.6 95.035.2 52.833.2 73.734.2 15.47 38 83.934.7 92.735.l 51.433.3 71.834.2 15.47 40 82.834.9 91.735.4 51.033.4 70.734.2 16.28 42 81.234.9 89.435.0 50.433.4 69.434.5 17.09 44 80.234.8 88.634.9 50.033.3 69.234.2 17.91 46 79.434.5 87.934.6 49.832.8 67.134.5 18.72 48 76.234.9 85.034.7 48.933.0 64.934.5 19.54 50 74.835.3 82.735.2 48.833.1 63.434.6 20.35 52 72.935.4 80.835.2 46.733.8 61.634.7 21.16 54 71.835.5 79.835.4 46.134.l 59.635.1 21.98 56 69.035.3 77.335.4 45.334.l 58.734.7 22.79 58 67.935.1 76.235.1 44.633.8 56.734.7 23.61 60 65.435.3 73.435.6 42.933.7 54.734.7 24.42 158 Table B-15. Effects of slow, continuous hemorrhage on venous pressures (mm Hg) and blood flows (ml/min) in denervated.forelimbs. Values are means 3 standard errors from 9 experiments. MIN - time in minutes after the onset of bleeding. Blbod Loss = accumulated blood loss in ml/kg body weight. MIN PSSVE PCV PMSVE PBv FC FB Blood Loss 0 l9.530.6 12.130.6 10.830.5 6.?30.5 126.93 8.7 65.13 5.0 0.00 2 19.431.1 11.331.1 10.830.9 6.730 9 126.2316.5 64.4310.8 1.81 4 19.131.1 11.731.1 10.831.0 6.630.9 124.6316.0 63.33 9.4 1.63 6 18.631.l ll.53_1.l 10.531.0 6.630.9 121.2315.l 60.83 9.0 2.44 8 18.531.1 11.331.l 10.331.0 6.430.9 118.3314.5 58.93 8.5 3.2? 10 l8.431.2 11.231.1 10.131.0 6.430.8 117.9314.7 57.93 9.0 4.0? 12 18.131.2 11.231.1 10.231.0 6.330.9 115.9314.3 56.33 9.1 4.88 14 l8.l31.2 11.031.1 10.130.9 6.230.8 115.6314.4 54.43 9.2 5.70 16 l?.631.2 10.83l.1 9.?30.9 6.130 8 lll.73_13.2 52.63 8.4 6.51 18 17.431.1 10.431.1 9.530.8 5.830 6 109.0312.7 51.33 8.0 7.33 20 17.031.l 10.231.l 9.330.8 5.630.6 105.8312.3 49.53 8.0 8.14 22 16.?31.0 10.131.1 9.030.? 5.530 6 105.2312.8 48.23_8.7 8.95 24 16.631.1 10.031.1 9.030.? 5.530.? 102.7312.5 46.73 8.2 9.7? 26 16.331.l 9.731.l 8.830.7 5.430.? 100.4312.5 44.93_8.2 10.58 28 15.831.0 9.431.1 8.330.8 5.230.? 96.83ll.8 42.03 8.1 11.40 30 15.03l.1 9.131.2 8.130.7 5.030.? 93.9312.6 40.03 8.4 12.21 32 l4.731.0 8.931.1 8.030.? 4.930.? 91.3312.l 39.43 8.3 13.02 34 14.531.0 8.831.1 8.030.? 4.730.8 89.1312.1 38.43 8.3 13.84 36 14.131.1 8.531.2 7.830.? 4.630.8 84.5312.4 35.53 8.4 14.65 38 13.531.l 8.231.l ?.630.7 4.430.9 81.9313.0 33.83 8.4 15.47 40 13.731.l 8.031.2 7.530.7 4.330.9 78.8312.8 32.03 8.0 16.28 42 12.331.1 7.731.2 7.330.? 4.130.8 75.0312.5 31.43 8.3 17.09 44 12.631.1 7.631.2 ?.330.7 4.130.8 72.8312.3 29.53_8.4 17.91 46 12.331.0 7.130.9 7.130.? 4.030 8 70.3312.0 28.43 7.9 18.72 48 ll.830.9 6.830.9 6.930.? 3.930.8 67.5312.3 27.23 8.1 19.54 50 11.430.8 6.430.8 6.730.? 3.630.8 64.0311.9 25.73 7.7 20.35 52 11.230.8 6.330.8 6.430.6 3.630.8 61.8312.1 24.63 7.8 21.16 54 10.830.8 6.030.? 6.530.6 3.330.8 59.231l.? 23.83_?.6 21.98 56 10.530.8 5.730.? 6.530.6 3.430.? 56.031l.0 22.03 6.9 22.79 58 10.130.? 5.430.? 6.430.6 3.230 7 52.1310.1 20.13 6.0 23.61 60 9.830.6 . 5.130.?, 6.130.6 3.0+O.6 48.6310.2 l9.l+ 6.1 24.42 159 Table B-l6. Effects of slow, continuous hemorrhage on the percent of total skin or skeletal muscle resistance residing in innervated large arteries, small vessels, and large veins. MIN = time in minutes after onset of bleeding. Blood Loss = accumulated blood loss in ml/kg body weight. Values are means from 8 experiments. SKIN SKELETAL MUSCLE Large Small Large Large Small Large Blood MIN Arteries Vessels Veins Arteries Vessels Veins Loss 0 17.8 76.3 6.0 13.8 81.0 5.1 0.00 2 17.9 76.4 5.7 13.6 81.4 5.0 0.81 4 18.5 75.6 5.9 14.8 80.4 4.8 1.63 6 1?.7 76.3 6.0 14.0 81.0 5.0 2.44 8 17.0 77,0 6.0 14.7 80.3 5.0 3.20 10 16.5 77.3 6.2 13.0 81.9 5.1 4.07 12 16.4 77.? 6.0 13.0 82.1 5.0 4.88 14 15.0 78.9 6.1 12.7 82.3 5.0 5.70 16 15.6 78.0 6.3 11.7 83.1 5.1 6.51 18 16.8 76.6 6.6 13.4 81.5 5.1 7.33 20 16.2 77.0 6.8 13.0 81.8 5.2 8.14 22 16.4 76.8 6.8 12.1 82.8 5.1 8.95 24 15.8 77.7 6.8 11.9 83.1 5.0 9.77 26 15.4 77.5 7.1 12.? 82.3 5.0 10.58 28 15.3 77.4 7.3 12.5 82.4 5.1 11.40 30 14.9 77.5 7.6 12.3 82.8 4.9 12.21 32 14.6 77.9 7.5 10.9 84.1 5.0 13.02 34 16.0 76.7 7.3 12.9 82.2 4.9 13.84 36 14.1 78.1 7.7 13.2 81.6 5.2 14.65 38 12.5 79.6 7.9 11.1 83.8 5.1 15.47 40 12.9 79.2 7.8 12.3 82.5 5.1 16.28 42 9.? 82.2 8.0 10.7 84.1 5.3 17.09 44 8.0 83.8 8.2 11.9 82.? 5.4 17.91 46 10.0 81.9 8.0 11.5 83.2 5.3 18.72 48 10.5 81.4 8.1 12.6 81.8 5.5 19.54 50 9.3 82.5 8.2 11.3 83.1 5.6 20.35 52 10.2 81.4 8.4 11.5 82.8 5.7 21.16 54 8.6 82.5 8.9 12.3 81.9 5.8 21.98 56 10.8 80.4 8.9 14.3 79.5 6.2 22.79 58 10.2 80.6 9.2 14.6 79.1 6.2 23.61 60 10.2 80.6 9.2 14.? 78.8 6.5 24.42 160 Table B-l7. Effects of slow, continuous hemorrhage on the percent of total skin or skeletal muscle resistance residing in denervated large arteries, small vessels, and large veins. MIN = time in minutes after onset of bleeding. Blood Loss = accumulated blood loss in ml/kg body weight. Values are means from 9 experiments. SKIN SKELETAL MUSCLE Large Small Large Large Small Large Blood MIN Arteries Vessels .Veins Arteries Vessels Veins Loss 0 44.4 47.9 7.? 18.8 76.8 4.4 0.00 2 44.9 47.3 7.9 18.2 77.5 4.4 0.81 4 44.7 47.5 7.8 17.8 77.8 4.5 1.63 6 44.2 47.9 7.9 18.2 77.4 4.3 2.44 8 44.1 48.2 7.8 17.8 78.1 4.1 3.20 10 44.4 48.0 7.? 17.7 78.3 4.0 4.07 12 44.4 48.0 7.6 17.4 78.5 4.1 4.88 14 44.4 47.9 7.6 17.4 78.4 4.2 5.70 16 43.7 48.8 7.5 17.0 79.0 3.9 6.51 18 44.1 48.1 7.8 16.6 79.4 3.9 7.33 20 44.5 47.8 7.7 16.1 79.9 3.9 8.14 22 43.9 48.5 7.6 16.2 80.0 3.8 8.95 24 44.8 47.7 7.5 17.0 79.2 3.8 9.77 26 44.9 47.4 7.7 16.5 79.7 3.8 10.58 28 44.1 48.3 7.7 16.5 79.7 3.8 11.40 30 43.5 49.2 7.3 15.5 80.? 3.9 12.21 32 43.2 49.6 7.2 15.1 80.9 4.0 13.02 34 42.8 49.9 7.2 16.5 79.2 4.2 13.89 36 41.5 51.3 7.2 15.? 79.9 4.4 14.65 38 41.2 51.9 6.9 16.2 79.3 4.5 15.47 40 41.1 51.9 7.0 16.1 79.2 4.? 16.28 42 40.4 52.9 6.7 16.1 79.1 4.8 17.09 44 40.1 53.3 6.7 15.5 79.6 4.9 17.91 46 39.6 53.3 7.1 17.7 77.5 4.8 18.72 48 37.9 55.0 7.0 16.7 78.6 4.7 19.54 50 36.0 56.9 7.1 16.6 78.5 4.8 20.35 52 38.4 54.5 7.1 16.7 78.4 4.9 21.16 54 38.3 54.7 6.9 19.4 75.4 5.2 21.98 56 36.4 56.4 7.2 17.0 77.5 5.5 22.79 58 36.3 56.5 7.2 19.7 74.5 5.7 23.61 60 35.9 56.5 7.6 19.3 74.9 5.8 24.42 APPENDIX C STATISTICAL METHODS 161 APPENDIX C STATISTICAL METHODS I. Series I and II Intravascular pressures, blood flows, rate of forelimb weight change, and vascular resistances were determined for control periods and during four experimental periods (P = 100, 75, 50, and 35 mm Hg) during local hypotension BA or rapid arterial hemorrhage. For each period, individual means (i) were calculated for each parameter from three values obtained 1, 3, and 5 minutes after brachial artery pressure stabilized. The individual means were used to cal- culate a grand mean (i), variance (82), standard deviation (S), and standard error of the mean (SE?) for each period during clamping or bleeding as follows: X. x = >3 i=1n 11 2 ( 2 x.) giz-Eli- 2 i=11 n SE— 162 163 A. Comparisons of Control Means with Four Experimental Means During Local Hypo- tension or Hemorrhage Since a control period preceded the experimental maneuvers (reducing forelimb perfusion pressure by clamping or bleeding), each animal served as its own control and comparisons were made between the control mean and each of the four experimental means (P = 100, 75, 50, and 35 mm BA Hg). If c independent comparisons among means are made, the probability of obtaining at least one significant comparison by chance is 1 - (1 - a)c (where a = error rate for each comparison) (83). Therefore, as the number of comparisons increases, the probability of finding at least one spuriously significant result also increases. Dunnett (43,44) has described a procedure for comparing a control mean with several experimental means in which the probability of mak- ing a type I error (a) for the collection of comparisons can be set at a desired level. Dunnett's procedure was used in the present study to determine whether clamping or bleeding to brachial artery pressures of 100, 75, 50, or 35 mm Hg produced significant changes in vascular resistances, mean intraluminal pressures, and rate of forelimb weight change. To eliminate extraneous variance existing among animals, variances of the differences between control and experimental means were used in the test statistic. The test statistic (ts) for each comparison was: 164 t = d 3 3d // n where: d = mean difference between the control and experi- mental values (i.e., mean clamp control resist- ance minus mean resistance at P = 100 mm Hg) BA Sd a standard deviation of the difference between the control and experimental mean n = (number of observations The test statistic was compared with critical values (tD, 0.05, k, v) from a Dunnett's t distribution table for 2 sided comparisons based on k experimental periods and v de- grees of freedom (n-l). When variances of the control and experimental means were markedly different, the critical values were modified as: MCV = tD,0.05, k,V (fl where: MCV = modified critical value f0 05, k, v = adjustment factor from a Dunnett's t ' distribution table Sc2 = variance of control mean Se2 = variance of experimental mean If tS exceeded MCV, the null hypothesis (pa = 0) was re- jected and the alternative hypothesis (pa + 0) was accepted. In this study, a significance level of 0.05 was used for all comparisons. 165 B. gomparisons ongarameters During Clamping and Bleeding A standard paired difference test was used to determine whether clamping and bleeding produced significantly difv ferent resistances, rate of forelimb weight changes, and mean intraluminal pressures at corresponding brachial artery pressures. The test statistic (ts) for each comparison was: t = ha - S Sd / M n where: d = difference between clamp mean and hemorrhage mean at corresponding brachial artery pressures Sd = standard deviation of the difference between the clamp and hemorrhage means at a correspond- ing brachial artery pressure The test statistic was compared with critical values (t0 05,v) obtained from a Student's t distribution table. If t8 exceeded t 5,v, the null hypothesis (pa = 0) was 0.0 rejected and the alternative hypothesis (pa + 0) was accepted. C. Comparison of the Resistance Responses of Innervated and Denervated Limbs During Rapid Hemorrhage To determine whether vascular resistances during rapid hemorrhage were significantly different in innervated (Series I) and denervated (Series II) forelimbs at correspond- ing brachial artery pressures, a t' statistical test described by Welch (127) for unpaired comparisons was used. 166 The t' statistic is very accurate in maintaining the desired probability of a type I error over a wide range of sample sizes and does not require that variances of the compared populations be equal (83). The test statistic (ts) for each comparison was: where: i and X' -= mean resistance in corresponding vascular I D . segments of innervated and denervated forelimbs at corresponding brachial artery pressures. SI2 and SD2= variances of mean resistances in inner- vated and denervated forelimbs at corre- sponding brachial artery pressures. nI and nD = number of observations. The test statistic was compared with critical values A t'0 05, v obtained from a standard Student's t distribution table based on v degrees of freedom obtained by Welch's procedure: A V (1 + 932 / [92 / (nI-l) + 1 / (nD-l)] where: 2 ' 2 A . For non-integer values of v, the critical values were ob- tained by interpolation in a Student's t distribution table. If tS exceeded t'0.05' v, the null hypothesis (HI = uD) 167 was rejected and the alternative hypothesis (01 + 0D) was accepted. 11. Series III A Mann-Whitney U test was used to determine whether forelimb vascular resistances were significantly different at corresponding brachial artery pressures when the recip- ient and donor dogs were bled. Since only a small number of experiments (N = 5) were conducted, a non-parametric test was chosen in order to avoid assumptions (required when using parametric methods) about the form of the population distributions. The Mann-Whitney statistic (U or U'), is obtained by ranking the observations from populations A and B, letting the smallest observation have a rank of l, and using the formulae: U = nA nB + nA (n; + l? - TA or ' U. = nA nB + n3 (3% f i1"- TB where: TA = .rank sum of population A TE = rank sum of population B nA = number of observations in population A nB = number of observations in population B Ties in the observations are handled by averaging the ranks that would have been assigned to the tied observations and 168 assigning the average to each. The test statistic (U or U', whichever is smaller) was used to test the hypothesis that populations A and B are equally distributed. For example, if nA = nB A and B are equally distributed would be rejected since the = 5, and U = 2, the hypothesis that populations probability that U 3 2 is 0.016 (83). III. Series IV A. Comparisons Between Control and Experimental Means To determine whether hemorrhage produced significant changes in vascular resistances, mean systemic arterial pressure, arterial pulse pressure, and central venous pres- sures in dogs with innervated or denervated forelimbs, Dunnett's t test was used (see Section I-A). Since the probability of rejecting the null hypothesis when it is false (power of a statistical test) decreases as the number of comparisons increases (83), control means were compared with experimental means only at 12, 24, 36, 48, and 60 minutes of bleeding. B. Comparisons Between Responses of Dogs w1th Innervated or Denervated Fore- limbs Welch's t' test (see Section I-C) was used to determine whether slow hemorrhage produced significantly different vascular resistance and pressure responses in dogs with innervated or denervated forelimbs. Since vascular 169 resistances were significantly lower in denervated than innervated forelimbs, resistances were normalized as percent of control before statistical comparison. Means from animals with innervated or denervated forelimbs were comv pared at 12, 24, 36, 48, and 60 minutes of bleeding. BIBLIOGRAPHY 10. BIBLIOGRAPHY Abdel-Sayed, W. A., F. M. Abboud, and D. R. Ballard. Contribution of venous resistance to total vascular resistance in skeletal muscle. Am. J. Physiol. 218:1291-1295, 1970. Abboud, F. M. Vascular responses to norepinephrine, angiotensin, vasopressin, and serotonin. Fed. Proc. 27:1391-1395, 1967. Abboud, F. M. Control of various components of the peripheral vasculature. Fed. Proc. 31:1226-1239, 1969. Abboud, F. M. Effects of sodium, angiotensin, and steroids on vascular reactivity in man. Fed. Proc. 33:143-149, 1974. Abboud, F. M. and J. W. Eckstein. Comparative changes in segmental vascular resistances in response to nerve stimulation and to norepinephrine. 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