Distribution of systemic blood flow in lambs with aortopulmonary shunt during strenuous exercise
an
J. W. C. GRATAMA, J. J. MEUZELAAR, M. DALINGHAUS, J. H. KOERS, ’ S. GRATAMA, W. G. ZIJLSTRA, AND J. R. G. KUIPERS Departments of Pediatrics, Thoracic Surgery, and Physiology, University of 9713 EZ Groningen, 9713 EZ Groningen, The Netherlands GRATAMA, J. W. C., J. J. MEUZELAAR, M. DALINGHAUS, J.H. KOERS, S. GRATAMA, W. G. ZIJLSTRA, AND J. R. G. KUIPERS. Distribution of systemicblood flow in lambs with an aortopulmonary shunt during strenuous exercise. J. Appl. Physiol. 73(4): 1542-1548, 1992.-We studied regional blood flows with radioactive-labeled microspheres in 12 7-wk-old lambs with an aortopulmonary left-to-right shunt [59 * 3% (SE) of left ventricular (LV) output] and in 11 control lambs, at rest and during exercise at 80% of predetermined peak 0, consumption. At rest, systemic blood flow was similar in the two groups. Blood flow to the heart and diaphragm was substantially higher in the shunt than in the control lambs. Blood flow to the other organs was not significantly different between the two groups. During exercise, systemic blood flow increased substantially but less in shunt (81%) than in control lambs (134%). Blood flow to the heart and diaphragm increased, that to the heart still being higher in shunt than in control lambs. Blood flow to the brain did not change, whereas that to the kidneys and splanchnic organs decreased to the same extent (25%) in shunt and control lambs. Intrahepatic and intrarenal blood flow redistribution in the shunt lambs persisted during exercise. In conclusion, myocardial blood flow is not increased at the expense of one particular organ, nor is it associated with an essential change in exercise-induced redistribution in shunt lambs. exertion; redistribution; disease; chronic volume
regional load
blood
flow; congenital
heart
STUDY we demonstrated that lambs with a chronic left-to-right shunt amounting to 55% of left ventricular output can maintain systemic blood flow at the same level as control lambs by increasing left ventricular output (28). As a result of the increased myocardial work accompanying the increased left ventricular output, myocardial 0, consumption and hence myocardial blood flow are increased. As a consequence, the hearts of the shunt lambs obtain a fraction of systemic blood flow about three times higher than those of the control lambs (28). Because systemic blood flow is not significantly different from that in control lambs, the increased blood flow to the heart must have consequences for blood flows to other organs and tissues. In adult patients with moderate heart failure and adequate systemic blood flow, the increased myocardial blood flow is believed to be compensated by a decrease in renal blood flow (31). Redistribution of systemic blood flow is also seen during situations when a severe demand is made on systemic IN A PREVIOUS
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blood flow, e.g., during strenuous activity (3,22,31). This is especially true for individuals with decreased cardiac output reserve (X2), like those with large left-to-right shunts (11). However, if a redistribution of systemic blood flow is already present in shunt lambs during resting conditions, the reserve for exercise-induced redistribution will be smaller. Moreover, if myocardial 0, consumption were to remain higher in shunt than in control lambs during exercise, for which we have preliminary evidence, part of the blood flow that is redistributed at the cost of the abdominal organs would be needed to meet the higher 0, demands of the heart of the shunt lambs. This would reduce the effectiveness of exercise-induced redistribution, unless this redistribution were to be enhanced in shunt lambs. Recent reports showing that vasoactive hormones (catecholamines, renin, vasopressin) are increased during maximal exercise in humans with heart failure (9) and in dogs with left-to-right shunts (19) are compatible with the idea of an enhanced exercise-induced redistribution in shunt lambs. However, our recent report of substantially decreased maximal exercise capacity of shunt lambs (11) does not speak in favor of a substantially enhanced exercise-induced redistribution. The objective of our study was to determine the consequences of the increased myocardial blood flow in lambs with chronic left-to-right shunts on resting regional blood flows and exercise-induced redistribution. METHODS
We studied 23 7-wk-old lambs of mixed breed with documented dates of birth. They were divided into two groups, 12 lambs with an aortopulmonary left-to-right shunt and 11 lambs without a shunt. Until the day of study each lamb remained with its mother. Surgical Procedure Surgical preparation, catheter care, and antibiotic administration were performed as described previously (11). Briefly, after induction of halothane anesthesia, we performed a thoracotomy through the fourth intercostal space and sutured a Goretex conduit (6 mm ID; Gore, Flagstaff, AZ) between the descending aorta and the main pulmonary artery at the level of the fibrotic string of the ductus arteriosus. Precalibrated electromagnetic flow transducers (lo-15 mm ID; Skalar Medical, Delft, The Netherlands) were placed around the ascending
0 1992 the American
Physiological
Society
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aorta just above the coronary arteries and around the pulmonary artery proximal to the conduit. Polyvinyl catheters were placed in the ascending aorta, pulmonary artery, right ventricle, and left and right atrium. Finally, the chest wall was closed in layers, and the catheters and flow probe cables were led through a subdermal tunnel to a cloth pouch that was sewn to the left flank of the lamb. For the control lambs, surgical instrumentation was the same except for the conduit, the flow transducer around the pulmonary artery, and the right ventricular catheter. Experimental
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Treadmill practicing and peak 0, consumption (r'o, J test. In the week before surgery, the lambs were fami p” iarized with running on a motor-driven treadmill (Laufergotest Junior, Erich-Jaeger, Hoechberg, FRG) during one short daily run. No training effect was pursued. The lambs could be made to run freely on the treadmill without coercive measures. After surgery this attitude did not change. To give all lambs an equal stimulus for redistribution, we had them run at the same percentage of their maximal 0, consumption (vo2 peak)(22). Therefore we first determined the VO 2peakof each lamb during a graded treadmill test on the 8th day after surgery (11). . Exercise study. On the day of study, 3-5 days after the vo 2peaktest, the lamb was weighed and put on the treadmill. After 2-3 h of habituation, resting values were determined. Measurements were performed only when the lamb stood quietly on the treadmill. Systemic and pulmonary blood flows and aortic, pulmonary arterial, and left and right atria1 pressures were measured every 5 min for 30 min. At 15 and 30 min, blood samples (0.7 ml) were withdrawn with a dry heparinized syringe from the aortic and the mixed venous catheters, i.e., from the right ventricular catheter in the shunt lambs and the pulmonary arterial catheter in the control lambs. 0, saturation was determined in both samples and hemoglobin concentration, pH, Pco,, PO,, and plasma HCO, concentration only in the sample from the aorta. At 30 min an additional 1 ml of blood was withdrawn from the aortic catheter for determination of the lactate concentration. Immediately after this blood sample had been taken, radioactive microspheres labeled with 141Ce 51Cr, lo3Ru, or g5Nb (NEN-Trac, DuPont, Wilmington, DE) were injected into the left atrium, while a reference sample was withdrawn with a pump (Harvard Apparatus, Millis, MA) from the aortic catheter into a preweighed heparinized syringe for 1.25 min at a rate of 6 ml/min (14). We did not succeed in obtaining a correct arterial reference sample during the resting period in one shunt and in one control lamb. Ten minutes after the injection of the microspheres, the speed and inclination of the treadmill were set to the values obtained during the vo2 peaktest, imposing a work load corresponding to a VO, of 40% of \joZpeak on the lamb. When the lamb had been running for 7 min, and 25 min at this work load so that a steady state could be assumed to be present (3), blood flows and pressures were measured and blood samples withdrawn for determination of 0, saturation, hemoglobin concentration, pH, Pco,, PO,, and plasma HCO, concentration, as described, for the resting period. Immediately thereafter,
SHUNT
LA f\
T
RV
LV
9s
qP
qp- 9c
TER
FL
PULMONARY ARTERY
AORTA 9s
position of electromagnetic flow transFIG. 1. Diagram showing leftducers and Goretex conduit ( graft) in lambs with aortopulmonary to-right shunt. Flow transducer around pulmonary artery measures systemic blood flow (qJ, whereas flow transducer around aorta measures total left ventricular output or pulmonary blood flow (q,) minus coronary blood flow (9,). q,, Left-to-right shunt flow; RA, right atrium; RV, right ventricle; LA, left atrium; LV, left ventricle.
blood flow and pressure measurements and blood sampling were repeated. These were followed by the withdrawal of a sample for lactate determination and the injection of microspheres labeled with an isotope other than the one used during the resting period. When the reference sample for the microspheres had been withdrawn, the treadmill was stopped and the lamb was allowed to recover. Measurements and Calculations The precalibrated electromagnetic flow transducers were connected to Skalar MDL 400 flowmeters. Systemic and pulmonary blood flows in the shunt lambs were obtained from the pulmonary arterial and the aortic flow transducer, respectively (Fig. 1); systemic blood flow of the control lambs was obtained from the aortic flow transducer. The position of the aortic flow transducer was distal to the origin of the coronary arteries. To obtain total left ventricular output, coronary blood flow obtained with the microspheres was added to the aortic flow obtained with the flow transducer (16). Heart rate was obtained from the blood flow signal. Aortic, pulmonary arterial, and left and right atria1 pressures were measured with Gould P23 ID pressure transducers (Spectramed, Oxnard, CA) referenced to atmospheric pressure with zero obtained with the pressure transducer at right atria1 level. All variables were recorded on an Elema Mingograf 800 ink-jet recorder (Siemens-Elema, Solna, Sweden). 0, saturation was determined in duplicate with an OSM2 hemoximeter (Radiometer, Copenhagen, Denmark). pH, Pco,, PO,, and plasma HCO; concentration
Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (130.070.008.131) on January 12, 2019.
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were determined with an ABL-2 blood gas analyzer (Rashunt (28) could lead to venous congestion of the liver, diometer, Copenhagen, Denmark) and corrected to the kidneys, and lungs and thus to an increase in the wet lamb’s rectal temperature. Hemoglobin concentration masses of these organs (23). If this were the case in the was determined with the methemoglobincyanide method shunt lambs, normalization of liver and kidney flows for (15). Lactate concentration was determined in whole organ mass would lead to wrong conclusions concerning blood by an enzymatic technique (5). organ perfusion. Therefore we performed microscopic exLeft-to-right shunt flow was calculated by subtracting amination of liver, kidney, and lung tissue samples to systemic blood flow from pulmonary blood flow. Left-toverify whether venous congestion were present. Heart right shunt fraction was obtained by dividing left-totissue was examined similarly to exclude venous congesright shunt flow by pulmonary blood flow. Mean organ tion. Splanchnic blood flow was obtained by adding the perfusion pressure was calculated as the difference be- flows to liver, gastrointestinal tract, pancreas, and tween mean aortic and right atria1 pressures. Systemic spleen. Portal venous flow was obtained by adding the and pulmonary vascular resistances were calculated ac- flows to gastrointestinal tract, pancreas, and spleen. cording to standard equations. Analogously, shunt resis- Carcass blood flow and mass were obtained by subtractance was calculated by dividing the difference between tion of the total blood flow and mass of the heart, diamean aortic and mean pulmonary arterial pressures by phragm, kidneys, liver, gastrointestinal tract, pancreas, shunt flow and organ vascular resistance by dividing or- spleen, and brain from systemic blood flow and body gan perfusion pressure by organ flow. Effective left ven- mass, respectively. Intrarenal blood flow distribution tricular stroke volume was calculated by dividing sys- was assessedby calculating the ratio of the blood flows temic blood flow by heart rate. Blood 0, concentration (ml min-’ al00 g-l) to the outer and the inner cortex. was calculated as the product of 0, saturation, hemoglo- Adequate mixing of the microspheres in each lamb was bin concentration, and a hemoglobin-binding capacity of confirmed by ascertaining that the blood flow per 100 g of 1.36 ml 0, per gram hemoglobin (20). VO, was calculated tissue to the two cerebral hemispheres, and also to the as the product of systemic blood flow and arteriovenous two kidneys, did not differ by >lO% (14). No organ re0, difference. ceived ~400 microspheres, and the average number of Blood flows to the different organs at rest and during microspheres in the arterial reference samples was exercise were determined with two of the four radionu>1,600 in both groups, corresponding to a mean accuracy elide-labeled microspheres (15 pm diam) injected in ran- in regional blood flow measurement of 5% (14). dom order. Each injection contained 1.5 X lo6 microStatistical Analysis spheres for control lambs and twice as much for shunt lambs. After the experiment, the lamb was killed with an Data are means t SE. The differences between the overdose of pentobarbital sodium intravenously, and the shunt and control lambs, at rest and during exercise, heart, diaphragm, lungs, kidneys, liver, gastrointestinal were compared by means of Student’s two-tailed t test tract (stomach and small and large intestines), brain, and for unpaired samples (30). The changes between rest and all muscles of upper and lower fore- and hindlimbs (be- exercise in each group were compared with Student’s tween hip and ankle joint) were removed and weighed. two-tailed t test for paired samples (30). P < 0.05 was Before weighing, the heart was cleared of its pericarconsidered significant. Correlation coefficients and redium, great vessels, chordae, and epicardial fat, and the gression equations were calculated according to standard stomach and small and large intestines were meticutechniques (30). We used the Mann-Whitney nonparalously cleared of their contents and stripped of their metric test, instead of the unpaired t test, to compare surrounding fatty tissue. To study the intrarenal blood differences in atria1 natriuretic factor concentrations beflow distribution, the left kidney was fixed in 8% Formatween shunt and control lambs, because there were large lin for 1 wk, after which it was reweighed (for correction differences in the variances of these variables between of mass changes during fixation) and divided into me- the two groups (30). dulla and cortex. The cortex was further subdivided into three equally thick layers parallel to the surface: outer, RESULTS middle, and inner cortex. These rough macroscopic diviAt Rest sions were microscopically verified as to histological characteristics and proved to be correct. All organs were At the time of study, there were no differences in age cut into pieces and put in vials for automatic handling by (48 t 2 vs. 47 t 2 days) and weight (12.5 t 1 vs. 12.9 t 1 the gamma counter (14). To reduce the number of vials, kg) between the shunt and the control lambs. The maxiwe took weighed samples amounting to 220% of total mal exercise capacity (11) and vo, peak(26 t 2 vs. 33 t 2 organ mass of liver, gastrointestinal tract, and leg mus- ml 0, min-l kg-‘, P < 0.05) were significantly lower in cles, after homogenizing the organs in a blender. The the shunt than in the control lambs. other organs were counted in toto. The left-to-right shunt led to significant hemodynamic The radioactivity in the different organs and reference differences between the shunt and t,he control lambs at samples was determined on a Beckman 9000 gamma rest (Table l), which were similar to those reported previcounter (Beckman Instruments, Fullerton, CA). Organ ously from our laboratory (28). Despite a left-to-right blood flows were calculated with the aid of the computer shunt amounting to 59 t 3% of left ventricular output, program of Saxena et al. (26). Blood flows are expressed shunt lambs were able to maintain systemic blood flow at as either milliliters per minute per kilogram body mass or the same level as control lambs. This was realized by a a percentage of systemic blood flow. The increased atria1 substantial increase in left ventricular output through an pressures that are a consequence of the left-to-right increase in heart rate and left ventricular stroke volume. l
l
l
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BLOOD
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1. Hemodynamic data, 0, consumption-related variables, arterial blood gases, and lactate concentration at rest and during exercise at 80% of vozpeak
TABLE
Rest
Heart Blood
rate, beats/min flows, ml. min-’ kg-’ Systemic Pulmonaryb Left-to-right shunt Left-to-right shunt, % Pressures, mmHg Aortic Pulmonary arterial Left atria1 Right atria1 Organ perfusion Stroke volume, left ventricle, ml/kg Total Effective Vascular resistance, mmHg kg min? Systemic Pulmonary Shunt
Exercise
Control
Shunt
Control
Shunt
lO7k7
163+7"
230+8"
235+8"
12oe
123+6
120+5 183-tl5
306?13”
281+23" 281k23"
223+12dpe 420k17ape
l
l
46+3"
59-t3
72k2 15+1
5s
63+2" 28+2" 14+1" '
8223" 19k2f 4+1
72+2cpe 32+3"vg 16+1"
3+1 69-+2
10&l”
l&l
55t2"
8123"
10&l”
1.17+0.09 1.17+0.09
1.9O-tO.08” 0.78kO.05”
1.23kO.10 1.23&O. 10
1.82+0.10” 0.97&0.08d
582+26 84t8
450+19" 44+7"
302-t20" 57k7"
62-t2"*"
l
P-W g/l 0, saturation, % Aortic Mixed venous Caoz, ml 0,/l (a - v)02, ml 0,/l VO,, ml 0, min-’ kg-’
101+4
94kl
110+4"
291+19" 38+7g 237-t36 101+2"
92-tl
89&l
93&l”
91*1g
52+2
481~2
3Ok2"
214+28
126+5
1 14+2d
139+5”
28+2" 125+3d*e
5422
53+2
93+2"
6.520.2 2221
6.4kO.3 2722
25.9k1.8" 79k2"
19.1+1.4aTe 79k4"
PH Pco~, Torr PO,, Torr
7.4420.01
7.42kO.01
7.46~0.01
37&l 110+3
40+1” 102-t3
7.43~0.01 34+lape
HCO, [La],
23.9k0.8 24.6kO.8 0.85~10.08 0.8320.06
l
%
197+21
v”‘2
Arterial
l
peak
blood
, mmol/l mmol/l
86k4"
gases
OF
EXERCISING
SHUNT
LAMBS
1545
ences in regional blood flow (Table 2). Blood flow to the heart and the diaphragm was substantially higher in shunt than in control lambs. Blood flow to the other regions (brain, kidneys, splanchnic region, and carcass) did not differ significantly between the two groups. Vascular resistances of organs in shunt lambs that received higher blood flows than those in control lambs were significantly lower than in control lambs (Table 3). In addition, vascular resistance of the brain was significantly lower than in control lambs. Intrahepatic and intrarenal blood flow distributions were different between shunt and control lambs. The liver of the shunt lambs received more of its total blood flow through the hepatic artery (12 t 3% vs. 4 t 1% of total liver flow, P < 0.02). In the kidneys, the outer-to-inner cortex blood flow ratio was lower in shunt than in control lambs (2.5 t 0.2 vs. 3.1 t 0.3). This difference did not reach statistical significance (P = 0.09), but the ratio proved to be related to the left atria1 pressure, as evidenced by a significantly negative correlation in the shunt lambs (r = -0.73, P < 0.01). In the control lambs no significant relation existed (r = -0.37). Figure 2 depicts the organ flows as a percentage of systemic blood flow, showing that the heart, diaphragm, and hepatic artery received a significantly higher fraction of systemic blood flow in the shunt than in the control lambs. Exercise at 80% of V02peak The relative work load was equal in shunt and control lambs because the corresponding relative values of VO, (V02 as a percentage of V0, peak)were equal (79% of . vo 2 peak, Table 1). The absolute work load, however, was lower in shunt than in control lambs (inclination 6 t 1 vs. 10 + l%, P < 0.01; speed 3.5 t 0.1 vs. 3.6 t 0.2 km/h), because peak VO, and work load were lower in the shunt than in the control lambs (11). The hemodynamic reaction to exercise was similar in shunt and control lambs (Table 1). However, because of the smaller increase in heart rate, systemic blood flow increased less in shunt lambs and was, consequently, significantly lower than in control lambs during exercise. Most of the resting hemodynamic differences between shunt and control lambs persisted during exercise, such as increased pulmonary blood flow, pulmonary arterial and left and right atria1 pressures, left ventricular stroke volume, arterial PCO, and decreased aortic pressures, mean organ perfusion pressure, and arterial 0, concentration. Exercise-induced changes in regional blood flow in the two groups (Table 2, Fig. 2) are in accordance with the literature (3, 8, 21, 22, 27, 31). Blood flow to heart, diaphragm, and carcass, which is mainly to exercising muscles, increased substantially in the two groups. Blood flow to the heart was still larger in shunt than in control lambs, but that to the diaphragm was no longer significantly different. Carcass flow, however, was lower in shunt than in control lambs. In agreement, blood flow to the leg muscles was 30% lower in the shunt lambs (63 t 4 vs. 89 t 20 ml min-’ 100 g-l). This difference did not reach statistical significance because of the spread in the control lambs. Blood flow to the brain did not change in l
30&l” 1 16k4g
19.9kO.6" 3.9920.53"
10423”
21.3t0.8" 3.36kO.56"
Values are means + SE of 12 lambs in shunt group and 11 lambs in control group. vo2peak, p eak 0, consumption; [Hb], hemoglobin concentration; Caop, aortic 0, concentration; (a - v)O,, arteriovenous 0, concentration difference; [La], lactate concentration. b Pulmonary blood flow equals total left ventricular output (see Fig. 1). Shunt vs. Control: a P < 0.01, ’ P < 0.02, d P < 0.05. Rest vs. Exercise: eP
an
J. W. C. GRATAMA, J. J. MEUZELAAR, M. DALINGHAUS, J. H. KOERS, ’ S. GRATAMA, W. G. ZIJLSTRA, AND J. R. G. KUIPERS Departments of Pediatrics, Thoracic Surgery, and Physiology, University of 9713 EZ Groningen, 9713 EZ Groningen, The Netherlands GRATAMA, J. W. C., J. J. MEUZELAAR, M. DALINGHAUS, J.H. KOERS, S. GRATAMA, W. G. ZIJLSTRA, AND J. R. G. KUIPERS. Distribution of systemicblood flow in lambs with an aortopulmonary shunt during strenuous exercise. J. Appl. Physiol. 73(4): 1542-1548, 1992.-We studied regional blood flows with radioactive-labeled microspheres in 12 7-wk-old lambs with an aortopulmonary left-to-right shunt [59 * 3% (SE) of left ventricular (LV) output] and in 11 control lambs, at rest and during exercise at 80% of predetermined peak 0, consumption. At rest, systemic blood flow was similar in the two groups. Blood flow to the heart and diaphragm was substantially higher in the shunt than in the control lambs. Blood flow to the other organs was not significantly different between the two groups. During exercise, systemic blood flow increased substantially but less in shunt (81%) than in control lambs (134%). Blood flow to the heart and diaphragm increased, that to the heart still being higher in shunt than in control lambs. Blood flow to the brain did not change, whereas that to the kidneys and splanchnic organs decreased to the same extent (25%) in shunt and control lambs. Intrahepatic and intrarenal blood flow redistribution in the shunt lambs persisted during exercise. In conclusion, myocardial blood flow is not increased at the expense of one particular organ, nor is it associated with an essential change in exercise-induced redistribution in shunt lambs. exertion; redistribution; disease; chronic volume
regional load
blood
flow; congenital
heart
STUDY we demonstrated that lambs with a chronic left-to-right shunt amounting to 55% of left ventricular output can maintain systemic blood flow at the same level as control lambs by increasing left ventricular output (28). As a result of the increased myocardial work accompanying the increased left ventricular output, myocardial 0, consumption and hence myocardial blood flow are increased. As a consequence, the hearts of the shunt lambs obtain a fraction of systemic blood flow about three times higher than those of the control lambs (28). Because systemic blood flow is not significantly different from that in control lambs, the increased blood flow to the heart must have consequences for blood flows to other organs and tissues. In adult patients with moderate heart failure and adequate systemic blood flow, the increased myocardial blood flow is believed to be compensated by a decrease in renal blood flow (31). Redistribution of systemic blood flow is also seen during situations when a severe demand is made on systemic IN A PREVIOUS
1542
0161-7567192
$2.00
Copyright
blood flow, e.g., during strenuous activity (3,22,31). This is especially true for individuals with decreased cardiac output reserve (X2), like those with large left-to-right shunts (11). However, if a redistribution of systemic blood flow is already present in shunt lambs during resting conditions, the reserve for exercise-induced redistribution will be smaller. Moreover, if myocardial 0, consumption were to remain higher in shunt than in control lambs during exercise, for which we have preliminary evidence, part of the blood flow that is redistributed at the cost of the abdominal organs would be needed to meet the higher 0, demands of the heart of the shunt lambs. This would reduce the effectiveness of exercise-induced redistribution, unless this redistribution were to be enhanced in shunt lambs. Recent reports showing that vasoactive hormones (catecholamines, renin, vasopressin) are increased during maximal exercise in humans with heart failure (9) and in dogs with left-to-right shunts (19) are compatible with the idea of an enhanced exercise-induced redistribution in shunt lambs. However, our recent report of substantially decreased maximal exercise capacity of shunt lambs (11) does not speak in favor of a substantially enhanced exercise-induced redistribution. The objective of our study was to determine the consequences of the increased myocardial blood flow in lambs with chronic left-to-right shunts on resting regional blood flows and exercise-induced redistribution. METHODS
We studied 23 7-wk-old lambs of mixed breed with documented dates of birth. They were divided into two groups, 12 lambs with an aortopulmonary left-to-right shunt and 11 lambs without a shunt. Until the day of study each lamb remained with its mother. Surgical Procedure Surgical preparation, catheter care, and antibiotic administration were performed as described previously (11). Briefly, after induction of halothane anesthesia, we performed a thoracotomy through the fourth intercostal space and sutured a Goretex conduit (6 mm ID; Gore, Flagstaff, AZ) between the descending aorta and the main pulmonary artery at the level of the fibrotic string of the ductus arteriosus. Precalibrated electromagnetic flow transducers (lo-15 mm ID; Skalar Medical, Delft, The Netherlands) were placed around the ascending
0 1992 the American
Physiological
Society
Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (130.070.008.131) on January 12, 2019.
BLOOD
FLOW
DISTRIBUTION
OF
EXERCISING
aorta just above the coronary arteries and around the pulmonary artery proximal to the conduit. Polyvinyl catheters were placed in the ascending aorta, pulmonary artery, right ventricle, and left and right atrium. Finally, the chest wall was closed in layers, and the catheters and flow probe cables were led through a subdermal tunnel to a cloth pouch that was sewn to the left flank of the lamb. For the control lambs, surgical instrumentation was the same except for the conduit, the flow transducer around the pulmonary artery, and the right ventricular catheter. Experimental
Y
1543
LAMBS
RA
Protocols
Treadmill practicing and peak 0, consumption (r'o, J test. In the week before surgery, the lambs were fami p” iarized with running on a motor-driven treadmill (Laufergotest Junior, Erich-Jaeger, Hoechberg, FRG) during one short daily run. No training effect was pursued. The lambs could be made to run freely on the treadmill without coercive measures. After surgery this attitude did not change. To give all lambs an equal stimulus for redistribution, we had them run at the same percentage of their maximal 0, consumption (vo2 peak)(22). Therefore we first determined the VO 2peakof each lamb during a graded treadmill test on the 8th day after surgery (11). . Exercise study. On the day of study, 3-5 days after the vo 2peaktest, the lamb was weighed and put on the treadmill. After 2-3 h of habituation, resting values were determined. Measurements were performed only when the lamb stood quietly on the treadmill. Systemic and pulmonary blood flows and aortic, pulmonary arterial, and left and right atria1 pressures were measured every 5 min for 30 min. At 15 and 30 min, blood samples (0.7 ml) were withdrawn with a dry heparinized syringe from the aortic and the mixed venous catheters, i.e., from the right ventricular catheter in the shunt lambs and the pulmonary arterial catheter in the control lambs. 0, saturation was determined in both samples and hemoglobin concentration, pH, Pco,, PO,, and plasma HCO, concentration only in the sample from the aorta. At 30 min an additional 1 ml of blood was withdrawn from the aortic catheter for determination of the lactate concentration. Immediately after this blood sample had been taken, radioactive microspheres labeled with 141Ce 51Cr, lo3Ru, or g5Nb (NEN-Trac, DuPont, Wilmington, DE) were injected into the left atrium, while a reference sample was withdrawn with a pump (Harvard Apparatus, Millis, MA) from the aortic catheter into a preweighed heparinized syringe for 1.25 min at a rate of 6 ml/min (14). We did not succeed in obtaining a correct arterial reference sample during the resting period in one shunt and in one control lamb. Ten minutes after the injection of the microspheres, the speed and inclination of the treadmill were set to the values obtained during the vo2 peaktest, imposing a work load corresponding to a VO, of 40% of \joZpeak on the lamb. When the lamb had been running for 7 min, and 25 min at this work load so that a steady state could be assumed to be present (3), blood flows and pressures were measured and blood samples withdrawn for determination of 0, saturation, hemoglobin concentration, pH, Pco,, PO,, and plasma HCO, concentration, as described, for the resting period. Immediately thereafter,
SHUNT
LA f\
T
RV
LV
9s
qP
qp- 9c
TER
FL
PULMONARY ARTERY
AORTA 9s
position of electromagnetic flow transFIG. 1. Diagram showing leftducers and Goretex conduit ( graft) in lambs with aortopulmonary to-right shunt. Flow transducer around pulmonary artery measures systemic blood flow (qJ, whereas flow transducer around aorta measures total left ventricular output or pulmonary blood flow (q,) minus coronary blood flow (9,). q,, Left-to-right shunt flow; RA, right atrium; RV, right ventricle; LA, left atrium; LV, left ventricle.
blood flow and pressure measurements and blood sampling were repeated. These were followed by the withdrawal of a sample for lactate determination and the injection of microspheres labeled with an isotope other than the one used during the resting period. When the reference sample for the microspheres had been withdrawn, the treadmill was stopped and the lamb was allowed to recover. Measurements and Calculations The precalibrated electromagnetic flow transducers were connected to Skalar MDL 400 flowmeters. Systemic and pulmonary blood flows in the shunt lambs were obtained from the pulmonary arterial and the aortic flow transducer, respectively (Fig. 1); systemic blood flow of the control lambs was obtained from the aortic flow transducer. The position of the aortic flow transducer was distal to the origin of the coronary arteries. To obtain total left ventricular output, coronary blood flow obtained with the microspheres was added to the aortic flow obtained with the flow transducer (16). Heart rate was obtained from the blood flow signal. Aortic, pulmonary arterial, and left and right atria1 pressures were measured with Gould P23 ID pressure transducers (Spectramed, Oxnard, CA) referenced to atmospheric pressure with zero obtained with the pressure transducer at right atria1 level. All variables were recorded on an Elema Mingograf 800 ink-jet recorder (Siemens-Elema, Solna, Sweden). 0, saturation was determined in duplicate with an OSM2 hemoximeter (Radiometer, Copenhagen, Denmark). pH, Pco,, PO,, and plasma HCO; concentration
Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (130.070.008.131) on January 12, 2019.
1544
BLOOD
FLOW
DISTRIBUTION
OF
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LAMBS
were determined with an ABL-2 blood gas analyzer (Rashunt (28) could lead to venous congestion of the liver, diometer, Copenhagen, Denmark) and corrected to the kidneys, and lungs and thus to an increase in the wet lamb’s rectal temperature. Hemoglobin concentration masses of these organs (23). If this were the case in the was determined with the methemoglobincyanide method shunt lambs, normalization of liver and kidney flows for (15). Lactate concentration was determined in whole organ mass would lead to wrong conclusions concerning blood by an enzymatic technique (5). organ perfusion. Therefore we performed microscopic exLeft-to-right shunt flow was calculated by subtracting amination of liver, kidney, and lung tissue samples to systemic blood flow from pulmonary blood flow. Left-toverify whether venous congestion were present. Heart right shunt fraction was obtained by dividing left-totissue was examined similarly to exclude venous congesright shunt flow by pulmonary blood flow. Mean organ tion. Splanchnic blood flow was obtained by adding the perfusion pressure was calculated as the difference be- flows to liver, gastrointestinal tract, pancreas, and tween mean aortic and right atria1 pressures. Systemic spleen. Portal venous flow was obtained by adding the and pulmonary vascular resistances were calculated ac- flows to gastrointestinal tract, pancreas, and spleen. cording to standard equations. Analogously, shunt resis- Carcass blood flow and mass were obtained by subtractance was calculated by dividing the difference between tion of the total blood flow and mass of the heart, diamean aortic and mean pulmonary arterial pressures by phragm, kidneys, liver, gastrointestinal tract, pancreas, shunt flow and organ vascular resistance by dividing or- spleen, and brain from systemic blood flow and body gan perfusion pressure by organ flow. Effective left ven- mass, respectively. Intrarenal blood flow distribution tricular stroke volume was calculated by dividing sys- was assessedby calculating the ratio of the blood flows temic blood flow by heart rate. Blood 0, concentration (ml min-’ al00 g-l) to the outer and the inner cortex. was calculated as the product of 0, saturation, hemoglo- Adequate mixing of the microspheres in each lamb was bin concentration, and a hemoglobin-binding capacity of confirmed by ascertaining that the blood flow per 100 g of 1.36 ml 0, per gram hemoglobin (20). VO, was calculated tissue to the two cerebral hemispheres, and also to the as the product of systemic blood flow and arteriovenous two kidneys, did not differ by >lO% (14). No organ re0, difference. ceived ~400 microspheres, and the average number of Blood flows to the different organs at rest and during microspheres in the arterial reference samples was exercise were determined with two of the four radionu>1,600 in both groups, corresponding to a mean accuracy elide-labeled microspheres (15 pm diam) injected in ran- in regional blood flow measurement of 5% (14). dom order. Each injection contained 1.5 X lo6 microStatistical Analysis spheres for control lambs and twice as much for shunt lambs. After the experiment, the lamb was killed with an Data are means t SE. The differences between the overdose of pentobarbital sodium intravenously, and the shunt and control lambs, at rest and during exercise, heart, diaphragm, lungs, kidneys, liver, gastrointestinal were compared by means of Student’s two-tailed t test tract (stomach and small and large intestines), brain, and for unpaired samples (30). The changes between rest and all muscles of upper and lower fore- and hindlimbs (be- exercise in each group were compared with Student’s tween hip and ankle joint) were removed and weighed. two-tailed t test for paired samples (30). P < 0.05 was Before weighing, the heart was cleared of its pericarconsidered significant. Correlation coefficients and redium, great vessels, chordae, and epicardial fat, and the gression equations were calculated according to standard stomach and small and large intestines were meticutechniques (30). We used the Mann-Whitney nonparalously cleared of their contents and stripped of their metric test, instead of the unpaired t test, to compare surrounding fatty tissue. To study the intrarenal blood differences in atria1 natriuretic factor concentrations beflow distribution, the left kidney was fixed in 8% Formatween shunt and control lambs, because there were large lin for 1 wk, after which it was reweighed (for correction differences in the variances of these variables between of mass changes during fixation) and divided into me- the two groups (30). dulla and cortex. The cortex was further subdivided into three equally thick layers parallel to the surface: outer, RESULTS middle, and inner cortex. These rough macroscopic diviAt Rest sions were microscopically verified as to histological characteristics and proved to be correct. All organs were At the time of study, there were no differences in age cut into pieces and put in vials for automatic handling by (48 t 2 vs. 47 t 2 days) and weight (12.5 t 1 vs. 12.9 t 1 the gamma counter (14). To reduce the number of vials, kg) between the shunt and the control lambs. The maxiwe took weighed samples amounting to 220% of total mal exercise capacity (11) and vo, peak(26 t 2 vs. 33 t 2 organ mass of liver, gastrointestinal tract, and leg mus- ml 0, min-l kg-‘, P < 0.05) were significantly lower in cles, after homogenizing the organs in a blender. The the shunt than in the control lambs. other organs were counted in toto. The left-to-right shunt led to significant hemodynamic The radioactivity in the different organs and reference differences between the shunt and t,he control lambs at samples was determined on a Beckman 9000 gamma rest (Table l), which were similar to those reported previcounter (Beckman Instruments, Fullerton, CA). Organ ously from our laboratory (28). Despite a left-to-right blood flows were calculated with the aid of the computer shunt amounting to 59 t 3% of left ventricular output, program of Saxena et al. (26). Blood flows are expressed shunt lambs were able to maintain systemic blood flow at as either milliliters per minute per kilogram body mass or the same level as control lambs. This was realized by a a percentage of systemic blood flow. The increased atria1 substantial increase in left ventricular output through an pressures that are a consequence of the left-to-right increase in heart rate and left ventricular stroke volume. l
l
l
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BLOOD
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DISTRIBUTION
1. Hemodynamic data, 0, consumption-related variables, arterial blood gases, and lactate concentration at rest and during exercise at 80% of vozpeak
TABLE
Rest
Heart Blood
rate, beats/min flows, ml. min-’ kg-’ Systemic Pulmonaryb Left-to-right shunt Left-to-right shunt, % Pressures, mmHg Aortic Pulmonary arterial Left atria1 Right atria1 Organ perfusion Stroke volume, left ventricle, ml/kg Total Effective Vascular resistance, mmHg kg min? Systemic Pulmonary Shunt
Exercise
Control
Shunt
Control
Shunt
lO7k7
163+7"
230+8"
235+8"
12oe
123+6
120+5 183-tl5
306?13”
281+23" 281k23"
223+12dpe 420k17ape
l
l
46+3"
59-t3
72k2 15+1
5s
63+2" 28+2" 14+1" '
8223" 19k2f 4+1
72+2cpe 32+3"vg 16+1"
3+1 69-+2
10&l”
l&l
55t2"
8123"
10&l”
1.17+0.09 1.17+0.09
1.9O-tO.08” 0.78kO.05”
1.23kO.10 1.23&O. 10
1.82+0.10” 0.97&0.08d
582+26 84t8
450+19" 44+7"
302-t20" 57k7"
62-t2"*"
l
P-W g/l 0, saturation, % Aortic Mixed venous Caoz, ml 0,/l (a - v)02, ml 0,/l VO,, ml 0, min-’ kg-’
101+4
94kl
110+4"
291+19" 38+7g 237-t36 101+2"
92-tl
89&l
93&l”
91*1g
52+2
481~2
3Ok2"
214+28
126+5
1 14+2d
139+5”
28+2" 125+3d*e
5422
53+2
93+2"
6.520.2 2221
6.4kO.3 2722
25.9k1.8" 79k2"
19.1+1.4aTe 79k4"
PH Pco~, Torr PO,, Torr
7.4420.01
7.42kO.01
7.46~0.01
37&l 110+3
40+1” 102-t3
7.43~0.01 34+lape
HCO, [La],
23.9k0.8 24.6kO.8 0.85~10.08 0.8320.06
l
%
197+21
v”‘2
Arterial
l
peak
blood
, mmol/l mmol/l
86k4"
gases
OF
EXERCISING
SHUNT
LAMBS
1545
ences in regional blood flow (Table 2). Blood flow to the heart and the diaphragm was substantially higher in shunt than in control lambs. Blood flow to the other regions (brain, kidneys, splanchnic region, and carcass) did not differ significantly between the two groups. Vascular resistances of organs in shunt lambs that received higher blood flows than those in control lambs were significantly lower than in control lambs (Table 3). In addition, vascular resistance of the brain was significantly lower than in control lambs. Intrahepatic and intrarenal blood flow distributions were different between shunt and control lambs. The liver of the shunt lambs received more of its total blood flow through the hepatic artery (12 t 3% vs. 4 t 1% of total liver flow, P < 0.02). In the kidneys, the outer-to-inner cortex blood flow ratio was lower in shunt than in control lambs (2.5 t 0.2 vs. 3.1 t 0.3). This difference did not reach statistical significance (P = 0.09), but the ratio proved to be related to the left atria1 pressure, as evidenced by a significantly negative correlation in the shunt lambs (r = -0.73, P < 0.01). In the control lambs no significant relation existed (r = -0.37). Figure 2 depicts the organ flows as a percentage of systemic blood flow, showing that the heart, diaphragm, and hepatic artery received a significantly higher fraction of systemic blood flow in the shunt than in the control lambs. Exercise at 80% of V02peak The relative work load was equal in shunt and control lambs because the corresponding relative values of VO, (V02 as a percentage of V0, peak)were equal (79% of . vo 2 peak, Table 1). The absolute work load, however, was lower in shunt than in control lambs (inclination 6 t 1 vs. 10 + l%, P < 0.01; speed 3.5 t 0.1 vs. 3.6 t 0.2 km/h), because peak VO, and work load were lower in the shunt than in the control lambs (11). The hemodynamic reaction to exercise was similar in shunt and control lambs (Table 1). However, because of the smaller increase in heart rate, systemic blood flow increased less in shunt lambs and was, consequently, significantly lower than in control lambs during exercise. Most of the resting hemodynamic differences between shunt and control lambs persisted during exercise, such as increased pulmonary blood flow, pulmonary arterial and left and right atria1 pressures, left ventricular stroke volume, arterial PCO, and decreased aortic pressures, mean organ perfusion pressure, and arterial 0, concentration. Exercise-induced changes in regional blood flow in the two groups (Table 2, Fig. 2) are in accordance with the literature (3, 8, 21, 22, 27, 31). Blood flow to heart, diaphragm, and carcass, which is mainly to exercising muscles, increased substantially in the two groups. Blood flow to the heart was still larger in shunt than in control lambs, but that to the diaphragm was no longer significantly different. Carcass flow, however, was lower in shunt than in control lambs. In agreement, blood flow to the leg muscles was 30% lower in the shunt lambs (63 t 4 vs. 89 t 20 ml min-’ 100 g-l). This difference did not reach statistical significance because of the spread in the control lambs. Blood flow to the brain did not change in l
30&l” 1 16k4g
19.9kO.6" 3.9920.53"
10423”
21.3t0.8" 3.36kO.56"
Values are means + SE of 12 lambs in shunt group and 11 lambs in control group. vo2peak, p eak 0, consumption; [Hb], hemoglobin concentration; Caop, aortic 0, concentration; (a - v)O,, arteriovenous 0, concentration difference; [La], lactate concentration. b Pulmonary blood flow equals total left ventricular output (see Fig. 1). Shunt vs. Control: a P < 0.01, ’ P < 0.02, d P < 0.05. Rest vs. Exercise: eP
