,fiTfii-Z'” - ‘ HEMODIALYS Ls STUDIES 0F THE EFFECTS OF- LOW BLOOD POTASSIUM AND Low BLOOD MAGNESIUM"-- 0N SKELETAL MUSCLE VASCULAR RESISTANCE ' , T0 BLOOD FLOW ’ Thesis To: the Degree 0T M S MICHIGAN STATE UNIVERSITY , ROBERT A BRACE 1971 ‘ ............... ........ CCCCC UNNER H ALTA LLLWLLLILLI LIB “”3““ Michigan Sate v University TTY LGA F'LGFATE UNNERS NW LTBRARY —5 ‘ fl 6“ J3 . .12». Tit -L- 1 = 4 ‘ ‘ g ( 1‘ J‘ \J MICHIGAN STA LIBT-TARY UNIVERSIW ABSTRACT HEMODIALYSIS STUDIES OF THE EFFECTS OF LOW BLOOD POTASSIUM AND LOW BLOOD MAGNESIUM ON SKELETAL MUSCLE VASCULAR RESISTANCE TO BLOOD FLOW By Robert A. Brace The ionic composition of plasma directly effects vascular resistance to blood flow. Arterioles. the major resistance to blood flow. respond to changes in the plasma concentration of the potassium ion. hydrogen ion, and calcium ion by actively changing their diameter. and thereby altering resistance to flow. Many diseases that are associated with hypertension or hypotension are characterized by chronic abnormalities in plasma ionic composition. The purposes of these studies were to determine the effect produced upon vascular resistance to blood flow through skeletal muscle by low plasma magnesium ion concentration (hypomagnesemia), both singly and in com- bination with low plasma potassium ion concentration (hypokalemia). The collateral-free. gracilis muscle of the dog was utilized in this study. Plasma concentrations of potassium and/hr magnesium were lowered by interposing a small hemodialyzer in the blood supply to the gracilis muscle. Flow was held constant in any given experiment. Initially. blood flowing to the muscle was dialyzed against Robert A. Brace a Ringer's solution which contained all the major ions of the plasma in approximately equal concentrations. Response to low plasma ion concentration was determined by switching to another isoosmolal dialysate lacking the A meg/liter of K+ and/or the 2 meq/liter of Mg++ and observing changes in pressure required to pump the constant volume of blood through the muscle. The gracilis muscle was electrically stimulated via the gracilis nerve for 3 minutes before switching from the control dialysate to the dialysate lacking the potassium ion. After one hour of hypokalemic perfusion. the muscle was again electrically stimulated for 3 minutes to determine the effect of K+ depletion upon change in response during active hyperemia. Our findings from this study show reduction in plasma magnesium ion concentration by up to 85% causes no immediate change in vascular resistance in the dog gracilis muscle. Reduction of plasma magnesium ion concentration in combination with low plasma potassium ion concentration appears to produce a response not different from low potassium ion concentration alone. Furthermore, removal of 10% of the potassium in the gracilis muscle does not appreciably change the active hyperemia response. In addition. it was shown that the absolute level of plasma potassium ion concentration is not alone responsible for the changes in vascular resis- tance during active hyperemia. HEMODIALYSIS STUDIES OF THE EFFECTS OF LOW BLOOD POTASSIUM AND LOW BLOOD MAGNESIUM ON SKELETAL MUSCLE VASCULAR RESISTANCE TO BLOOD FLOW By Robert A. Brace A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Chemical Engineering 1971 To my loving wife Catherine ii ACKNOWLEDGMENTS The author would like to express his appreciation to his academic advisor. Dr. D. K. Anderson. for his guidance, encouragement and assistance. Appreciation is also given to Dr. J. S. Scott, D. P. Radowski. and B. T. Swindall for their assistance during the experiments and thanks to Mrs. J. Johnston for the necessary chemical analysis. The author also wishes to acknowledge the work of S. A. Roth, who designed and did initial work with the hemodialyzers used in the experiments. The financial support of the Michigan Heart Association is gratefully acknowledged. iii TABLE OF CONTENTS LIST OF FIGURES ...................................... LIST OF TABLES ....................................... INTRODUCTION ............................o............ BACKGROUND ........................................... Vascular Effects of Potassium and Magnesium Ions. Experimental Technique ooooo00.000000000000000... Hemodialysis oooooocooooooooooooooooooooooooooooo APPARATUS OOOOOOOOOOOOOOOIOOOOOOOOOOOOOOOOOOOOOOOOCOOO Dialyzers ooooooooooocoo-0000000000000ooooooooooo Dialyzer Membranes 00.000000000000000...ooooooooo Dialysate supply System onooooooooooooooooooooooo Blood Supply System cocoonooooooooooooooooooooooo EXPERIMENTAL PROCEDURE 00.0.00...OOOOOOOOOOOOOOOOOOOO. Experimental Vascular Bed Preparation ........... Dialysate SOlUtionS nooooooooo00000000000000.0000 Testing for Change in Resistance to Blood Flow .. RESULTS AND DISCUSSION ............................... Short Term Response to Hypokalemia .............. Long Term Response to Hypokalemia ............... Effect of Potassium Depletion on Response to Levarterenol ................ Response to Hypomagnesemia ...................... Response to Combination of Hypokalemia and Hypomagnesemia ............. Effect of Potassium Depletion On Response to ACtive Hyperemia oooooooooooo SUMMARY AND CONCLUSIONS ooooooooooo00000000060000.0000 Prolonged Hypokalemia ooooooooooooooooooooooooooo Hypomagnesemia 00000000000000.0000.-0000090000000 Potassium's Role in Active Hyperemia ............ iv Page RECOMMENDATIONS ...................................... 35 APPENDIX: TABULATED EXPERIMENTAL DATA ............... 36 NOMENCLATURE ......................................... #8 LITERATURE CITED ..................................... 49 1. 2. 3. 7. 8. 9. LIST OF FIGURES Schematic Representation of Arteriolar Structure .. EXPIOded View Of HemOdialyzer cocoon-00000000000000 a) Dialysate Flow CifCUit 00000000000000.0000oooooo b) BlOOd Flow CirCUIL coo0000000000.000000000000000 Typical Response of Gracilis Muscle to Hypokalemia. Percent Change in Perfusion Pressure as a Function of Change in Potassium and Magnesium Ion Concentrations coooooooooooooooooooooooooo Change in Response to Hypokalemia upon Repeated Exposures to Hypokalemia ............ Perfusion Pressure Responses to Levarterenol Injection During Normal and Hypokalemic BlOOd PerfUSion 0000000000000...0000000000000u Typical Perfusion Pressure Response of Gracilis Muscle to Electrical Stimulation .... Average Changes in K+ Concentration and Perfusion Pressure During Stimulation ........ vi Page 11 11 18 19 22 2C 28 30 1. 3. u. 5. 6. 7. 8. 9. LIST OF TABLES Page A Comparison of Blood Plasma Composition and Control Dialysate Compostion 00000000000000 1# Average Effects of Prolonged Hypokalemia on Perfusion Pressure at Constant Flow ........... 23 Average Perfusion Pressure Responses to Levarterenol Injections During Normal and Hypokalemic B100d Perfusion coco-cooooooooooooooooooooooooo 26 Effect of One Hour of Hypokalemic Perfusion on Active Dilation During Electrical Stimulation.. 31 Tabulated Results for the Short Term Vascular Response to Hypokalemia .............. 37 Tabulated Results Showing Change in Response to Hypokalemia with Repeated Exposures to Hypokalemia 00.0000000000000000000000000000. 38 Tabulated Perfusion Pressures Showing Effect of Hypokalemic Perfusion for One Hour upon Perfusion Pressure During Hypokalemic and Post Control Perfusion Pressure ............... 39 Tabulated Results for Vascular Response to Levarterenol Injected During Normal and Hypokalemic Perfusion for One Hour ............ 40 a) Control Perfusion 0.000000000000000cocoon... 40 b) After 5 Minutes of Hypokalemic Perfusion ... #1 c) After 30 Minutes of Hypokalemic Perfusion .. 41 d) After 45 Minutes of Hypokalemic Perfusion .. 42 e) Control After 1 Hour of Hypokalemic Perfusion nocoooooooo00.000000000000000... “2 Tabulated Data Showing Change in Perfusion Pressure When Arterial Magnesium Concentration is Lowered ooooooooooooooooooooooo0000000000000 “3 vii Page 10. Tabulated Results for Vascular Response to Simultaneous Perfusion With Hypokalemic and Hypomagnesemic BlOOd ....0.............000. 44 11. Tabulated Results Showing Vascular Response to Electrical Stimulation of Normal and Hypokalemic Perfused Gracilis Muscle .......... #5 12. Tabulated Data Showing K+ Removal from and Weight Change of Gracilis Muscle During a 3 Minute Stimulation and Following 1 Hour Of Hypokalemic Perfusion 0..................0.. #7 viii INTRODUCTION The effect of ions upon resistnace to blood flow has been the subject of a great deal of research, both when ion concentrations are above and below their normal values. Data from that research have increased our knowledge and understanding of specific ion importance in blood flow regulation, mechanism of blood flow regulation. nature of diseases characterized by abnormal plasma ionic compositions. and also the ion's role in life's processes. Under normal conditions. the arterioles are primarily responsible for local blood flow regulation. Their structure is illustrated in Figure 1. (Note that arteri- oles are distinguished from other blood vessels by their relatively thick muscular wall in relation to the small inner diameter.) The smooth muscle walls of arterioles respond to three different types of stimuli that regulate blood flow. First. they respond to the chemical compo- sition of the blood and surrounding interstitial fluid, decreasing flow when a vasoconstrictor is introduced and increasing flow in the presence of a vasodilator. Second. they respond to the local needs of the tissues. increasing blood flow when the supply of nutrients to the tissues falls too low and decreasing the flow when the nutrient supply becomes too great. Third. autonomic nerve impulses have a profound effect on the degree of contraction of arterioles. 1. Inner layer of endothelium cells. 2. Wavy internal elastic layer. 3. Thick layer of smooth muscle. h. External elastic layer. 5. Fibrous tissue. Outer diameter of arterioles is typically 70 to 100 microns. Figure 1. Schematic Representation of Arteriole Structure 3 Decreased plasma concentrations of hydrogen ion and potassium ion and increased concentration of calcium ion cause active decreases in arteriole inner diameter. Changes in arteriole diameter result in altered resistance to flow as shown by the Hagen-Pouseville equation for laminar flow through a tube: 128 v L Q AP = 1; ° (1) gen D Since pressure drop across a vascular bed and blood viscosity are normally relatively constant. blood flow rate through that vascular bed will vary directly as a function of diameter to the fourth power. The very strong muscular wall of the arteriole is constructed in such a manner that the diameter can change as much as 3- to 5-fold (1). With resistance inversely proportional to the fourth power of vessel diameter. it becomes obvious that the resistance to blood flow through arterioles can be changed as much as several hundred fold by simply relaxing or constricting the smooth muscle walls. This ability to make such drastic changes in resistance is an effective means of controlling local blood flow. BACKGROUND Vascular Effects of Potassium and Magnesium Ions Tremendous amounts of research have been done in the medical and physiological fields with the potassium ion and a somewhat lesser amount with the magnesium ion. Data pertinent to this study was given in a report by Haddy et al.(2). They indicate that, over a time period of a few minutes. low plasma potassium ion concentration results in active constriction in canine forelimb and kidney while low plasma magnesium ion concentration has no observeable effect. except possibly in combination with other abnormalities. Experimental Technigues In order to determine the effect an ion has on resistance to blood flow. the ion must be either removed from or added to the blood so that its plasma concentration changes. If this blood and normal blood are alternately passed through a vascular bed. a change in resistance may be observed. In in vivo experiments. increasing the blood concentration of most ions is conveniently accomplished by infusion of the ion in an isoosmolal solution. Decreasing the blood concentration of a single ion while producing no other change is very difficult. Researchers have resorted to the dilutional technique(2) and in vitro studies(3) in an attempt to determine the u 5 local effect of low blood ion concentration on resistance and vascular smooth muscle activity, respectively. However. the dilutional technique used to produce concentration changes presents some disadvantages. Dilution produces secondary changes in other variables such as hematocrit, viscosity. protein binding. nonelec- trolyte concentrations, etc. Local responses are inter- preted by comparison with infusion of a control solution that produces all of the changes, except that under study. The technique used in this study, hemodialysis. allows transfer of selected ions to and from plasma with little or no change in hematocrit. viscosity. and plasma protein concentrations. With all variables except the one under consideration approximately constant. there is a quantitative response that should provide insight into the mechanisms that control resistance to blood flow. Hemodialysis Hemodialysis may be defined as the removal from blood of substances by means of diffusion through a semi- permeable membrane. The membrane is semipermeable in the sense that it is permeable to small particles such as the metal cations and impermeable to large particles such as red blood cells and plasma proteins. In a hemodialyzer. blood flows through a membrane envelope. A water solution which contains all the major 6 ions that are in blood, in approximately equal concentra- tions. flows on the membrane side opposite to blood. This is called the dialysate fluid. The substance being removed from the blood diffuses to and permeates the membrane according to its concentra- tion gradient. In clinical hemodialysis, such substances as urea and creatinine are dialyzed from the blood. In experimental hemodialysis, an ion of interest or other permeable substance is added to or deleted from a second dialysate solution while keeping all other concentrations the same as in the first solution. Osmolality is kept constant by adjusting sodium chloride concentration. The ionic concentration of blood is changed by switching the fluid bathing the membrane from the first to the second dialysate fluid. The feature of hemodialysis is that an ion can be selectively removed from blood while keeping variables such as other electrolyte concentrations. hematocrit, viscosity, protein binding. etc.. essentially constant. In a parallel-plate hemodialyzer. blood flows between two membranes in a thin film. Thickness of the film is adjusted by using spacers of appropriate thickness. The dialysate fluid flows on the outside of the membrane through the structure of the membrane support. Perfor- mance of a parallel-plate hemodialyzer can be adequately predicted from theory. Detailed theory of design and 7 performance of parallel-plate dialyzers. as well as dis- cussion of membrane support can be found in L. Grimsrud's thesis(h). In a coiled tube dialyzer. blood flows through a coil of tubular cellulose membrane which is bathed in a dialysate fluid. Since blood flows via the path of least resistance through the collapsed membrane tube. consider- able channeling results and the dialyzer has a low efficiency. APPARATUS Dialyzers Two parallel-plate dialyzers similar in design to that developed by Babb and Grimsrud(#.5.6.7) as an artificial kidney were used. The design is illustrated in Figure 2. In this design. the unique feature is the foam nickel metal* used to support the membrane. The porous metal (nominal density of 3% of solid nickel) allows the dialysate fluid to flow through its structure while maintaining rigid support for the membrane. Rigid support is necessary in order for the dialyzer to attain a high efficiency and have the desireable low blood volume holdup. With sagging membranes. blood volume holdup increases and efficiency decreases. If the membrane has rigid support. dialyzer performance can be adequately predicted from theory (See references h.5.6.7). Dialysis Membranes Cuprophane PT 150 membranes of regenerated cellulose were used in this study. They have a dry thickness of 0.5 x 10"3 inch and swell when submersed in water to a wet thickness of 1.0 x 10"3 inch. Molecules and ions permeate the membrane if their sizes and shapes are {- Available commercially from Metallurgical Products Department. General Electric Company. Detroit. Michigan. 8 PRESSURE TAP NICKEL FOAM SUPPORT MEMBRANE SPACER \ HEMODIALYZER EXPLODED VIEW OF HEMODIALYZER I HALYSATE PORT FIGURE 2 . 10 sufficiently small to allow their passage through the membrane's pores. Dialysate Supply System The dialysate solutions were held at 37°C by placing the dialysate containers in a constant temperature bath. With the dialysate at 37°. the blood remains isothermal as it enters the experimental vascular bed. A pump was used to circulate the dialysate fluid through the dialyzer. Dialysate solution supply to the pump and return to the container was rapidly changeable by means of a valving arrangement. The dialysate flow circuit is shown in N Figure 3a. Blood Supply System A blood pump which outputs a constant volume at varying pressures was used to supply the dialyzer. Blood flows into the dialyzer header channel and distributes itself in a thin film (thickness normally controlled at 0.01 inch) across the dialyzer. As the flow procedes. the blood encounters the section of the membrane in contact with the foam metal support and transfer of material from blood to dialysate occurs. The blood then flows from the dialyzer into the experimental vascular bed. This blood flow circuit is shown in Figure 3b. 11 Tl:_—?__é_1_<:iEMODIALYZER r' " "1 I Two Dialysate I Solutions L ______ Constant Temperature Bath (37" C) (o) Dialysate Circuit Blood -~ Frqm LottI saggy” emora Artery? [ .____,, j j -——-.-1. lésclgtifig . B'°°a pump] 1’fflsmoomurzezri M”‘°'° Gracilis Vein and Side Branch for Venous Samples (b) Blood Circuit Figure 3. EXPERIMENTAL PROCEDURE Experimental Vascular Bed Preparation Dogs ranging in weight from 20 to #0 kg were anes- thetized by intravenous injection of sodium pentobarbitol (33mg/kg) and ventilated with a mechanical positive pressure respirator via an intratracheal tube. The right hindlimb gracilis muscle was surgically exposed (For detailed procedure see reference 8). The muscle was isolated. except for the main gracilis artery. vein and nerve. from trunk and leg attachments with ligatures. This was followed by an intravenous injection of sodium heparin(5mg/kg). A cannula was placed in a side branch of the gracilis vein to allow for sampling of venous blood. The left femoral artery was ligated and a constant displacement blood pump was interposed between the proximal segment of the femoral artery and the hemodialyzer. Initially the dialyzer was flushed with saline and then filled with arterial blood. Blood leaving the dialyzer entered the gracilis muscle (as shown in Figure 3b) and blood flow rate was adjusted so that the perfusion pressure was at or slightly above systemic pressure. Flow rate ranged from 5 to 25 ml/min in different experi- ments. depending on muscle size and initial resistance. but was maintained constant in any given experiment. Inlet dialyzer pressure as well as perfusion pressure and systemic pressure were monitored continuously on a 12 13 direct writing oscillograph. Three pressure transducers were used and all tubes and needles were flushed period- ically with heparinized saline. Dialysate Solutions Blood concentration changes were achieved by using different dialysate solutions.“ Table 1 compares the ionic concentrations of the modified Ringer's solution used as control with blood. In the hypokalemia experiments. the dialysates were the control solution and another in which the h meq/liter of K+ were replaced with Na+. Similarly for the hypomagnesemia experiments. Mg++ was replaced with Na+. For the combination of hypokalemia and hypomagnesemia. both K+ and Mg++ in the dialysate were replaced with Na+. The dialysate solution volume (6 liters) was suf- ficiently large so that at no time did the K+ concentration (dialyzed from blood) in the K+ free dialysate reach 10% of the blood concentration. All solutions were maintained at 37°C. keeping the blood isothermal. Testigg for Chapge in Resistance to Blood Flow The gracilis muscle was perfused with blood dialyzed against the control solution until pressure was steady and then. by means of a valving arrangement. the control solution was changed to the dialysate solution lacking the ion(s) of interest. After a new steady state perfusion l. 2. 3. ’4. Blood Plasma Composition Blood Cells Plasma Proteins g Organic Substances '§ Inorganic Substances: g H20 Na+ 150 -———— K+ L1 —— Mg++ 2 -—- Ca++ 5 ______ Cl' 103 --—— H003' 29 --_—. Others 19 7-— 1h Control Dialysate Composition H20 — 1116 Na+ — Ll K+ __ 2 Mg++ F_ 5 Ca++ — 131 01' -- 21 HCO3 - 5 Others Concentrations in meq/liter Table 1. A Comparison Of Blood Plasma Composition and Control Dialysate Composition 15 pressure had been reached. samples were drawn from blood entering the dialyzer. as well as arterial blood entering and venous blood leaving the gracilis muscle. These samples were analyzed for plasma potassium concentration with the Beckman flame photometer and/or magnesium concentration with the Perkin-Elmer atomic absorption. Osmolality. determined with the Advanced osmometer. pH and hematocrit were checked periodically and found to be unchanged by the dialyzer. The experimental program consisted of dialyzing the blood alternately against the control dialysate and the zero potassium and/or zero magnesium dialysate for 5 to 10 minutes and calculating changes in vascular resistance from the steady state perfusion pressures. In addition. the experimental procedure included challenging the muscle for an extended period. one hour. with blood dialyzed against the zero potassium dialysate to determine if the acute response to hypokalemia was altered with time. Also. the effect of potassium depletion upon gracilis muscle response to levarterenol was examined by injecting 0.1 ml of levarterenol (cone. 1 ug/ml) into the blood perfusing the muscle when dialyzed against normal Ringer's and comparing this response to that due to levarterenol injection at 5. 30. and #5 minutes into a one hour potassium depletion. In a second series of experiments (nalo). the gracilis nerve was electrically stimulated (6 volts - 1.6 msec - 16 6 cps) for three minutes to induce active hyperemia. At 2.5 to 3.0 minutes into the stimulation period. the dialysate was switched from the control to K+ free Ringer's and the muscle was perfused with hypokalemic blood for one hour. The muscle was stimulated again for 3 minutes. examining the effects of K+ depletion on response to active hyperemia. Arterial and venous samples were taken before. during and after stimulation. These were analyzed for K+ concentration and osmolality. RESULTS AND DISCUSSION Short Term Response to Hypokalemia The amount of potassium removed from the blood depends mainly on the blood flow rate and the transfer area available in the dialyzer. Blood flow rates to the gracilis varied from about 5 to 25 ml/min and the two dialyzers had transfer areas of approzimately 200 and 1000 cm2. The combination of the low flow rate with the larger dialyzer makes it possible to remove in excess of 95% of the normal potassium from the perfusing blood in a single pass through the dialyzer. Figure 4 is a tracing from a typical hypokalemia experiment. The arrow indicates the point at which the dialysate solution was switched from normal Ringer's to zero potassium. Note the time lag. about one minute. before the muscle is perfused with hypokalemic blood and the vascular resistance increases. Initially there is no rise in perfusion pressure after switching dialysate sources since the gracilis muscle continues to be perfused with blood from the connecting tubing and outlet header of the hemodialyzer which contained normal KT. After this period. hypokalemic blood entered the gracilis and the perfusion pressure rose rapidly to a new level. Figure 5 summarizes the results of short term hypokalemia including that reported by Roth(9.10). Each point represents one gracilis muscle preparation and 17 5H UJUJ ‘emsseld Switch Dialysate Ime, min T Typical Response of Gracilis Muscle to Hypokalemia. Figure 4. 19 . x .m> m as coppoaa .33. ms was a :owvngSoo .0 moaonao uoaaflnmmono «spec mm .x mommono «same x Pathofi . O mowouwo 3.3”: “memo x .O moaouwo .mcofipmnpcommoo coH sawmocmmz use aswmmMpom cw owssno Mo cowpocsm a mm unammoum sowmshuom cw owcwno psoouom .m ouswfim coakupcoosoo :oH CH owsmno psoonom 00a om ow o: om 0 Ti 3 p P n v n r . - 1m: .0 .m Aw . 1m“ rom O 5 H eanssead uotsngaeg u; eSueuo iueoaed .W rom 20 is an average value relative to control of several alter- nate responses to control and hypokalemic blood. For the range of plasma potassium concentrations considered. approximately 0.2 to 4.0 meq/liter. Roth fit his data to the straight line P - P K - K ( _2____2 ) = -0.25 ( _2____2 ) (2) Pc Kc with a coefficient of correlation of 0.90. P and K refer to the perfusion pressure and plasma potassium concentration entering the muscle. respectively. Sub- scripts e and c refer to the experimental and control values of the perfusion pressure and plasma potassium concentration entering the muscle. Each point represents an increase in vascular resistance or perfusion pressure when switching from control to hypokalemic blood and a decrease in vascular resistance or perfusion pressure when switching from hypokalemic blood to control. No significant difference is obtained when these responses are plotted separately. When change in resistance is compared to plasma potassium concentration.leaving the muscle. there is less correlation (correlation coefficient = 0.20). Data for individual experiments are included in the Appendix. It was common during these experiments for the gracilis muscle to respond more strongly to its second exposure to hypokalemia than to the first. Further 21 exposures to hypokalemia usually produced only small changes from the second exposure. Average percent change in perfusion pressure (n=7) for 3 exposures to hypokalemia are shown in Figure 6. Note that the amount of K+ removed from the blood varied from one experiment to the next. but remained constant during any given experiment. Lppg Term Response to Hypokalemia One hour of hypokalemic perfusion produced an increase in perfusion pressure above the short term (5 to 10 minutes) response to hypokalemia in all but one experiment (n=10). At the end of one hour. perfusion pressure after switching from K+ free to control Ringer's was above control in all experiments. averaging 38% higher as shown in Table 2. After one hour of hypokalemic perfusion. the response of the muscle to short term hypokalemia was examined. When change in resistance is correlated with change in K+ concentration in the perfusing arterial blood. correlation is poor (correlation coefficient = 0.20 for the best straight line). Effect of Potassium Depletion orlResponse to Levarterenol Figure 7 is a typical tracing showing gracilis perfusion pressure response to levarterenol. Injection of levarterenol during perfusion with normal blood produced the usual increase in vascular resistance. I I‘ll. I I'll II I. I'll. (Ill: . 1| 22 15.9 16. 14-1 12. 10* 8. 4. 2. Percent Change In Perfusion Pressure nd rd 2 3 Exposure to Hypokalemia Figure 6. 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I... 000.... 00.0..0.0.0.0000...0.00.00.09.0‘0‘000. m $2 H on eoapeaasapm Heoaoeooam wcaaao :oaeeaaa o>aeo< co scamsmpom oHEonxonm: mo nsoz one mo Poommm .a oases ousmwopm cowmsmnon zommvm u m hpmeHoEmo mso:o> u >smo Anopaa\moHoEmoHHHHsv hpwamaosmo Hmwnoppm u msmo cofipmupcoocoo +a m:o:o> u >+M Aumpwa\dosv soflpmnvCoocoo +x Hmflpopum u m+x up e.o~ Hao.o mm- we own Ne.m +x god a: a mcaaao :.om ”Ho.o moa mom Hon mm.“ :m.o +m SoH n: a whomon e.om 0 an. as man sm.m Hooecoo mcaaao e.om 0 sea mom . son mm.m mm.m Hopscoo oaomon afi£\as odomse em you > m > a mafia soak co>oson +x woe m4m m Emo Emo +x +x opsmhamwc cowvmasefipm 32 hypokalemic). Since this perfusion pressure response to stimulation was identical with the initial response while K+ concentrations differed significantly. it was concluded that the absolute level of K+ is not responsible for the response to active hyperemia. The osmolality of the blood increased during stim- ulation as shown in Table 4. These are large increases in osmolality and their effect on perfusion pressure has to be examined. It is estimated that perfusion pressure change in response to such osmolality changes would be larger than the pressure change due to the changes in K+ concentration alone(11). Using the blood flow and the arterio-venous difference in K+ concentrations as an indicator. an average of approximately 1.0 meq of potassium was removed from the muscle during the one hour of low potassium perfusion. The muscle was weighed at the conclusion of the experiment and it is estimated that an average of 11% of the cellular potassium was removed. Since perfusion pressure response to stimulation after 1 hour of hypokalemic perfusion was identical with that before the potassium depletion. it was concluded that K+ depletion of up to 11% has no effect on response to active hyperemia. SUMMARY AND CONCLUSTIONS Prolonged Hypokalemia Depleting a muscle of potassium by dialyzing the perfusing blood against a potassium-free Ringer's solution elevates vascular resistance to blood flow. As shown in Table 2. at the end of one hour of hypokalemic perfusion. vascular resistance is greater than the resistance of the nondepleted muscle when first exposed to hypokalemia. When the muscle is again perfused with normal blood. resistance remains above the control resistance before potassium depletion. Response of the gracilis muscle to levarterenol injection decreases as potassium is depleted. As was shown in Table 3. the area under the perfusion pressure curve produced by levarterenol injection was progressively reduced as the time of hypokalemic perfusion increased. After one hour of hypokalemic perfusion. response to levarterenol injection was only 4% of the initial control response. Hypomggnesemia The results of this study show reducing the magnesium ion concentration of blood perfusing a muscle by up to 84% has no immediate effect upon skeletal muscle vascular resistance to blood flow. Change in vascular resistance due to the combination of low blood potassium ion and 33 34 low blood magnesium ion concentrations appears to be not different from that produced by low blood potassium ion concentration alone. as can be seen from Figure 5. Potassium's Role in Active Hyperemia Potassium does not appear to control change in vascular resistance during active hyperemia. Depletion of 11% of the cellular potassium from a muscle does not change perfusion pressure response to electrical stimu- lation when blood flow rate is constant. The amount of potassium in blood entering or leaving the gracilis muscle during active hyperemia is not the controlling factor which influences change in vascular resistance. As shown in Table 4. change in vascular resistance during electrical stimulation when arterial potassium ion concentration was 3.89 meq/liter and venous potassium ion concentration was 5.57 meq/liter was the same as the change in resistance observed when arterial potassium ion concentration was 0.94 meq/liter and venous potassium ion concentration was 3.42 meq/liter. The amount of potassium released during active hyperemia does not control resistance changes since the same resistance change occurred when 1.68 meq/liter and 2.50 meq/liter of potassium were released into the blood passing through the muscle. Note that more potassium was released from the muscle during stimulation after one hour of hypokalemia perfusion than before the potassium depletion. RECOMMENDATIONS As research progresses. an increasing amount of data is generated which shows the specific effects of individual ions and chemicals on resistance to local blood flow. One of the purposes of such research is to discover the as yet unknown mechanism by which changes in resistance occur. Since hemodialysis has been shown to be an effec- tive method of studying the local effects of low blood ion concentrations. it is recommended that further hemodialysis studies be initiated to investigate the mechanism by which the observed changes in resistance to flow occur. The active constriction caused by low plasma potassium ion concentration may be associated with the active trans- port of potassium into and sodium out of cells. Chemicals such as digitalis are known to partially block the active transport of sodium and potassium across the cell membrane. If digitalis is effective in changing vascular response to hypokalemia and hyperkalemia. some mechanistic explan- ation may be possible. 35 APPENDIX: TABULATED EXPERIMENTAL DATA 37 Exp. No. %AP Arterial fiAK Venous %AK QB (ml/min) 1 10.3 44.0 27.5 13.0 2 15.8 64.3 42.9 - 3 21.8 68.4 18.1 8.4 4 5.85 30.7 23.1 19.0 6 9.35 33.8 5.0 15.2 7 8.9 37.5 29.2 16.2 9 7-9 39.6 31-0 15.7 10 5.2 29.0 25.7 20.5 11 15.2 55.0 39.2 8.6 12 24.2 72.0 53.6 13.5 13 17.6 81.6 38.5 8.5 14-1 25.1 96.0 63.5 7.9 14-2 18.4 89.0 70.3 12.4 15 18.2 82.8 23.5 - 16 22.6 72.2 32.3 - Table 5. Tabulated Results for the Short Term Vascular Response to Hypokalemia 38 wwsoamxomzm op nonsmomxm oopmonom new: «HSonxommm op omcommom cw omcmno wswsonm measmom copmaspma .m mance mm.ma o.oa mm.aa 0.3m .m>o «.mfi m.ma «.ma w.Hm mH m.nm o.mm H.om o.mn Na e.o~ s.sa m.m o.mm Ha fi:.m mo.m mm.fl w.mm o a.ea m.HH m.Ha n.5m A ~.Hfl m.HH m.oH w.mm e m.:H m.mfi a.aa m.:o m chamomxm m onsmonxm m mnemomxm a on c: an xqfi Hmauopn< .oz .mxm opswmopm :owmsmpom cw omcmno & 39 enummonm sowmsguom Homecoo pmom can mHEonxomzm mafiasa oasmmoum cowmzmnom com: nsox oco now :ofimsmnom owEonxomzm mo poommm wcflsonm mouSmmonm :oamsmnom uopmasnme .s magma oaH mmfl ms“ HHH o.mm ma mma ems ems oma m.am ea mom aim mSH baa H.Nn NH mm uofi an we o.mm “a wee omH oafi mma o.o~ ca nmfi mud mma mHH m.mm m nda oma NMH ONH n.5m h maa oaH NHH no” m.mm w mod aha méa oma 5.0m : was now mma mma m.ao m one oaum + on a a: H gas ca-m one o Homecoo pmom omcommon shop meoa mmcommou Show pnocm Homecoo max HmHuopp< .oz .axm “mm 88v mopsmmonm cowmswpom Luv} 1. .... .. ......i.,. .. . 1-41551... I...- v illi‘lfli. l .r L, I III. I 'I' [ llllll'l. 4O mm EXP. N0. PS PP]. Ppm AP sz area 3 135 125 162 37 140 258 4 137 113 132 19 115 87 6 82 93 115 22 98 104 7 138 110 135 25 120 131 9 128 115 147 32 118 1g; 10 195 90 103 13 93 12 125 121 170 49 129 865 14 12 104 124 0 102 228 15 13 89 1 4 5 9 3 2 avg. 123 107 136 29 113 253 a) Control PS = systemic blood pressure (mm Hg) Pp1 = preinjection perfusion pressure Pm = maximum pressure attained after levarterenol injection AP = Pm - Ppl sz = post injection perfusion pressure area = area under perfusion pressure curve caused by injection of levarterenol Table 8. Tabulated Results for Vascular Response to Levarterenol Injected During Normal and Hypokalemic Perfusion for One Hour 41 mm2 Exp. No. PS Pp1 Ppm AP sz area 3 133 170 175 5 170 85 4 127 145 157 12 150 41 6 85 113 135 22 110 41 7 138 125 150 25 133 138 9 90 123 140 17 135 56 10 120 75 86 11 83 77 12 125 143 170 27 133 357 14 125 137 153 16 133 88 15 129 102 139 37 102 378 avg. 119 126 145 19 128 146 b) After 5 Minutes of Hypokalemic Perfusion mmz Exp. No. PS Pp1 Ppm AP sz area 3 145 180 190 10 190 22 4 133 135 150 15 143 44 6 87 143 152 9 145 32 7 138 148 165 17 148 48 9 107 138 167 29 138 117 10 122 90 97 7 90 22 12 125 134 160 26 137 416 14 130 129 146 17 129 132 15 132 84 119 35 87 319 avg. 124 131 150 18 134 128 c) After 30 Minutes of Hypokalemic Perfusion Table 8 . to Levarterenol Injected During Normal and Hypokalemic Perfusion for One Hour Tabulated Results for Vascular Response 42 2 mm EXP. NO. PS Ppl Ppm AP sz area 3 146 205 210 5 217 0 4 135 148 157 9 153 35 6 82 158 162 4 162 23 7 138 150 165 15 163 O 9 111 143 150 7 147 55 10 123 90 100 10 95 0 12 125 152 175 23 153 264 14 130 133 147 14 132 99 15 140 81 109 28 86 262 avg. 126 140 153 13 145 82 d) After 45 Minutes of Hypokalemic Perfusion mm2 Exp. No. Ps Ppl Ppm AP sz area 3 146 205 210 5 223 0 4 132 160 165 5 158 19 6 70 183 185 2 185 0 7 138 173 187 14 180 O 9 119 175 177 2 175 O 10 130 90 100 10 90 49 avg. 123 164 171 6 169 11 e) Control After 1 Hour of Hypokalemic Perfusion Table 8. Tabulated Results for Vascular Response to Levarterenol Injected During Normal and Hypokalemic Perfusion for One Hour 43 Exp. No. %AMg %AP Flow (ml/min) 26 37.7 0 28.7 27 33.8 0 30.0 28 83.4 0 4.4 29 79.2 0 5.3 30 66.7 0 7.3 31 60.8 -3.7 14.4 32 66.8 0 15.2 Table 9. Tabulated Data Showing Change in Perfusion Pressure When Arterial Magnesium Concentration is Lowered llll’lll '1 II] {II .Illlll I it.“ 44 Exp. No. Arterial flAMg Arterial fink %AP 30 72.6 87.5 30.2 31 59.1 84.2 17.0 33 60.9 77.0 18.6 Table 10. Tabulated Results for Vascular Response to Simultaneous Perfusion with Hypokalemic and Hypomagnesemic Blood oaowsz wflafiomuu comsmnom oHEonxommx one amenoz mo sofipmassfipm Hwowupooam op omcommom amasomm> mcfisosm mPHSmom copmasnma .fia manna 45 m.m:n om man 0.: +M Boa a: a wcwusu . oHH Hon mmm o.N o.N +m 30H A: H ohomon m.mau mu mam w.m Homecoo madman we saw com o.: H.a Hoapcoo oaomoo m n.mmu mm man :.m +2 sod an menses mNH man can H.H 0.0 +x 30H 9: whomon w.mmu on own n.m Hopvcoo mafiuso hmfi awn man 0.: m.m Hoppnoo muckon o.Hm- ooa mam e.~ +2 sea a: weapon mad mam H.H m.o +¥ Boa h: chomon :.NN1 no own m.w Hohvcoo mcfinsc nNH mam don m.: H.: Houwcoo ohomop 3.5- ooa Nam o.m +2 sea an H means. moa mom m.H 3.0 +m 30H h: H cuckoo m.mmu mm mom H.m Houpsoo wswnso moa com 0.: Homecoo ouoeon a.am- we can a.m +m sea a; means. mad omm m.H 0.H +x 30H u: ouomon n.0a1 ooH can n.m Honpcoo wswpsv oma wmm m.m Homecoo onomon H > m > a camp . . mom m Smo Emo +m +M mesmmamwc coflpmasswvm o: axe 46 oHomsz mHHHowHU cowsmnom OHEmmeomzm 0cm stpoz mo cOvaHzEHPm HmoHupoon o» omsommmm pmHsomm> wstonm mPHSmom copmHsnme .HH oHpme A.~m- we own 0.: +g :oH as H mcHeao 50H mHm m.H 5.0 +¥ 30H u: H ohomwp N.m:u 00 0mm 0.: Homecoo wansc OHH 5mm mHm N.m $.m HOMPCOO muchwn 0H m.m:s o0 on :.m +m soH an H mcHusc mHH mom Non m.H N.H +M 30H h: H 0HOMmQ 0.0m: 00 00m 0.: Hoapcoo wcHHsc ma non oom m.m 0.m Hoapcoo ouoeon a N.H:1 0m omm :.m +M 3oH an H mcHnsu. mm .00m mom m.H 0.0 +m 3oH a: H opomon n.mm1 m0 «mm m.m Homecoo wcHusc ma mom mom m.m w.m Hohvcoo shaken w n.0Hu om HHm m.m +2 30H a: H wsHuso ow amm amm m.H 0.0 +a :oH a: H oooeon 0.m:n mm 50m 0.0 Homecoo wcHusu mm mmm mmm N.: H.: Houvfloo muchon b H.0m1 m0 mmm m.m +x 30H H: H wcHHsu 00H mHm NHm m.H m.0 +x 30H h: H whommn m.Hm1 mm «Hm m.m Homecoo wcHnsc oHH don 00m 0.: N.: HOHPCOO «Momma 0 “4* m >Em0 demo >+V~ N+V~ QPNWhHNHU COflPMflMflHPm 0 0: .QNQ Lilli".lilflif lull! II 4? sonsmuom OHEmexogmm mo Hsom H wcHsoHHom can sOHPmHssva mpscHz m m wcHusa mHomss mHHHomuo mo mwcwno panmz 0cm Eonm Hm>o50m +0 wcHzonm «#00 umPMHsnme .0H 0Hme 0.0H 0.0HH 3:000. 000.0 +0 soH a: H o.mH 0.00H o o Homecoo 0H 0.00 0.00 0000. omm.H +0 :oH an H 0.0N M.H® O O HOHPQOO m n.0H o.~HH moHo. 030.0 +0 :oH an H 0.0H 0.00 0 0 HoHPCoo 0 0.0 0.00 03000. 000.0 +0 SoH a: H 0.0 0.00 0 0 Honvcoo 0 0.:H 0.30 0H000. 000.0 +0 BoH H: H 0.:H 0.00 0 0 HoHHCoo 0 0.00 0.0HH mmHo. 00N.H +0 30H a: H 0.00 0.00H o 0 Honpaoo m 0.0H 3.00 0HHO. 0H0.0 +0 30H a: H 0.0H 0.00 0 0 Houpsoo 3 0.:H 0.00 omHo. 000.0 +0 30H a: H N.eH 0.:e o o Houeaoo m 0.mH 0.00H 0H000. 000.0 +0 soH a: H o.mH c.0oH o o Houpcoo m 0.00 0.00H 00000. :mH.H +0 :oH H: H 0.00 H.0NH 0 0 Homecoo H :Hs\Ha A200 93 oHomsa mHomss aw H00 cm>oson mvdmszHc .o: .000 3OHM 00>oamn +0 008 +0 008 NOMENCLATURE D - inner diameter gc - standard acceleration of gravity K - plasma potassium ion concentration L - tube length Mg - plasma magnesium ion concentration "U I perfusion pressure 0 - flow rate (volume/time) v - viscosity .A, - change Spbscripts B - blood c - control e - experimental 48 I'll! ‘1 1| l: I ululil‘ Illnl III II. I'lll I’ll). 1. 2. 3. 4. 6. 7. 8. 9. 10. 11. LITERATURE CITED Guyton. A. 0.. Functions of the Huma Bod . W. B. Saunders Co.. Philadelphia. Pa. 1964. Haddy. F. J.. J. B. SCOtt. M. A. Florio. R. M. Daugherty. and J. N. Huezenga. “Local Vascular Effects of Hypo- kalemia. Alkalosis. Hypercalcemia and Hypomagnesemia.” Am. J. of Physiology. 2041202. 1963. Bohr. D. F. and P. L. Goulet. "Role of Electrolytes in the Contractile Machinery of Vascular Smooth Muscle." Am. J. of Cardiology. October. 1961. Grimsrud. L.. "A Theoretical and Experimental Inves- tigation of a Parallel-Plate Dialyzer in the Laminar Flow Regime with Applications to Hemodialyzer Design." Ph. D. Thesis. University of Washington. 1965. Grimsrud. L.. and A. L. Babb. Biomechanical and Human Factors Symposium. ASME. New York. N.Y. 1967. Babb. A. L. and L. Grimsrud. "A New Concept in Hemo- dialyzer Membrane Support.” Trans. Am. Soc. Artificial Organs. 10:31. 1964. Grimsrud. L.. and A. L. Babb. ”Optimization of Dialyzer Design for the Hemodialysis System." Trans. Am. Soc. Artificial Int. Organs. 101101. 1964. Nagle. F. J.. J. B. Scott. B. T. Swindall and F. J. Haddy. "Venous Resistances in Skeletal Muscle and Skin During Local Blood Flow Regulation." Am. J. of Physiol. 214:885. 1968. Roth. S. A.. D. K. Anderson. D. P. Radowski. J. B. Scott. and F. J. Raddy. Physiologist. 12:343. 1969. Roth. S. A.. "The Use of Hemodialysis in the Study of the Local Vascular Effects of Potassium Depletion.” Ph. D. Thesis. Michigan State University. 1970. Unpublished Data. 49 l l llllllll Illlllllllllllllll lllll llllllll llll ll 93003771296