Acta physiol. scand. 1976. 96. 277-280. From the Institute of Medical Biology, Sect. of Physiology, University of Tromsnr, Institute for Surgical Research, University of Oslo, Rikshospitalet, and Institute of Aviation Medicine, Royal Norwegian Air Force, Oslo, Norway
Myocardial Blood Flow in the Diving Seal BY ARNOLDUS SCHYITE BLIX,JOHNK. KJEKSHUS, IVARENGEand ANSTEIN BERGAN Received 18 August 1975
Abstract BLIX,A. S., J. K. KJEKSHUS,I. ENGEand A. BERGAN.Myocardial Blood Flow in the Diving Seal. Acta physiol. scand. 1976. 96. 277-280. Grey seals exhibit a marked drop in heart rate, a slight decrease in ventricular contractility, and an essentially unchanged stroke volume upon diving. In the present study, we have demonstrated that the resulting drop in cardiac output is associated with a 90% reduction of coronary blood flow. Such reduction of myocardial blood flow takes place despite a significant increase in effective coronary driving pressure, and is indicative of a 8 0 0 % increase in coronary vascular resistance. This means that the circulatory adjustments displayed by the diving seal (i.e. a reduction of the workload on the heart) are so effective that myocardial blood flow can be reduced to 10% of the pre-dive value without loss of cardiac function and blood pressure. I t is suggested that even partial simulation of such a circulatory state might be a successful approach in the treatment of ischemic injuries in the heart of man.
It has for long been acknowledged that the naturally diving vertebrates respond to submersion with a pronounced bradycardia and a marked redistribution of the circulating blood. Moreover, it is generally agreed that the redistribution of the blood involves that almost the total blood oxygen store is offered to the brain and the heart, while other tissues have to depend upon anaerobic metabolism. This principle for asphyxic defence was first advanced by Irving (1939) in his classical review on the respiration in diving mammals. His assumptions were based on his own observations (Irving 1938) of a retarded circulation in skeletal muscles of anesthetized animals, in concert with increased cerebral blood flow, during the arrest of breathing. Irving’s finding on muscle circulation was later well documented in the diving seal (Scholander 1940), while Johansen (1964) has reported a fourfold increase in myocardial blood flow in the diving duck. Neither this finding, nor that of Irving (1938) on cerebral circulation (which never has been re-examined), is, however, compatible with our present knowledge of a pronounced (90%) reduction of cardiac output in both the diving seal (Elsner et al. 1966) and the duck (Folkow et al. 1967). As the methods employed both by Irving and Johansen had some apparent shortcomings, we decided to re-examine some aspects of myocardial circulation in the diving seal by use of radioactively labelled microspheres injected into the left ventricle. By this approach, information of the distribution of cardiac output, which is important in relating our findings to those of recent reports, was obtained also. 277
278
ARNOLDUS SCHYTTE BLIX, JOHN K . KJEKSHUS, WAR ENGE AND ANSTEIN BERGAN
TABLE I. Tissue blood flow(m1/100 g.min-') in one seal while breathing air (control) and after 5 min of submersion (dive). The value obtained during the dive is also given in per cent ( % ) of the control value. n, is number of tissue samples examined. All numbers are means (if not single measurements)+S.E. S.E.=O, indicates a S.E. of less than 0.5. Cardiac output (litrelmin), heart rate (beats/min), arterial pressure (mmHg), Left ventricular (LV) max dp/dt (mmHg/s), Left coronary PRU and total PRU obtained at the moment of microsphere injection are also included. At the time of injection, arterial PO, was 92 torr and 47 torr in control and during diving, respectively. The difference in control/dive flow ratio between the two animals was less than 2 % in right and left ventricle, skeletal muscle, kidney and stomach, while the brain flow ratios differed with 12% (possibly due to a 10% difference in arterial pCO,, the PO, being identical, in the diving situation). 76
n
3f0 9f 1
4.2 10.3
3fO
2.0
49f6
33.9
5 15 4 4 3 3
Tissue
Control
Right ventricle Left ventricle M. psoas Kidney Stomach Cerebrum
70+4 90f3 14f I 135f5 14+0 143+8
Cardiac output Heart rate Arterial presure LV max dp/dt Left coronary PRU
7.9 132 I65 4 000 I .8
0.6 10 155 3 000 14.4
Total PRU
0.02 I
Dive
o+o
o*o
-
7 7 75
0.258
Material and Methods A total of 3 grey seals (Halichoerus grypus) of both sexes, aged 6-7 months were used. The animals were sedated with 50 mg Valiumm Roche, i m . , and restrained on a specially designed board prior to each experiment. In the diving situation, the animals were totally submerged in fresh water of 15°C. Lehman pigtail catheters were advanced under fluoroscopic control, from the hind-flipper arteries, one to the left ventricle of the heart, and one to the thoracic aorta. Xylocain@Astra (1 %) was used as local anesthetics. The aortic catheter was used for blood sampling while the ventricular one was used for injection of the microspheres. Both W r and 86Srlabelled microspheres (3M) suspended and sonicated in saline were used. A mean diameter of the spheres of 25 p was chosen according to the rather large diameter of seal erythrocytes. The experimental procedure was essentially as described previously by Kjekshus (1973). The "Cr labelled spheres were used when the animal was on the surface breathing air, while the 86Srlabelled microspheres were injected 5 min after the commencement of the dive. The animals were killed after 15 min of submersion while still under water, with a massive dose of sodium pentobarbital. Tissue blood flow (m1/100 g min-I) and cardiac output were calculated as described by Rudolph and Heyman (1967). Two animals were used in these experiments, but from one of them we only got the relative change in flow upon submersion. Left ventricular and aortic blood pressure were measured by use of Statham transducers (P23H) connected to a Beckman RS Polygraph. Left coronary effective driving pressure (Berne 1964), heart rate and estimates of myocardial contractility (dp/ dt) were obtained from the recordings. Arterial PO, and PCO, were obtained by use of Radiometer@electrodes. Three animals were used in these experiments.
-
279
MYOCARDIAL BLOOD FLOW IN SEALS
E
mmHg
200
CONTROL
SUBMERGED
0 Fig. I . Typical aortic (upper tracing) and left ventricular (lower tracing) blood pressure of grey seals while breathing air (control) and during diving (submerged).
0
Results and Discussion The microsphere experiment revealed a more than 90% decrease in cardiac output in response to submersion (Table I). This decrease was of the same magnitude as the decrease in heart rate (Fig. 1, Table I), and is therefore in agreement with the findings of Elsner et al. (1966). Moreover, consistent with this reduction of cardiac output a pronounced decrease in blood flow to skeletal muscle, kidney and viscera took place in response to diving (Table I). This is again in good agreement with previous investigations (e.g. Scholander 1940, Bron et a/. 1966, and Elsner et al. 1966). Our investigation did, on the other hand, also reveal that even cerebral blood flow decreased markedly (Table I), in spite of a maintained perfusion pressure (Fig. 1). In striking contrast to Johansen (1964) we also observed a 90% decrease in left coronary blood flow in response to submersion, despite a significant increase in effective left coronary driving pressure (Berne 1964), (Fig. 1, Table I). This reduction of blood flow, which was even greater in the right ventricle is indicative of a 800% increase in left coronary peripheral resistance units (PRU) (diastolic aortic pressure (mmHg)/blood flow (mllmin)). It is unlikely that this reduction in coronary blood flow is associated with any ischemic dilatation of the heart (as would be the case in e.g. dogs and man, Lekven et al. 1973), since increased end-diastolic pressures never occurred, not even in dives lasting for as long as 15 min (Fig. 1). The reduction of left coronary blood flow was of the same magnitude as the reduction of cardiac output in the present study (Table I). Moreover, we found an essentially maintained stroke volume after 5 min of submergence, despite a 1200% increase in total peripheral resistance (mean aortic pressure (mmHg)/cardiac output (mllmin)), and a 25 % decrease in myocardial contractility. Our results therefore indicate that the reduction of workload on the heart due to the reduction of heart rate and contractility is the determinant of the reduced myocardial blood flow in the diving seal, irrespective of a marked increase in coronary driving pressure. This finding is supported by results on dogs, where coronary blood flow approaches the value found in resting skeletal muscle, in the potassium arrested heart, despite maintained perfusion pressure (Berglund et al. 1957). In conclusion, our study has revealed that the circulatory adjustments displayed by the diving seal are so efficient that myocardial blood flow can be reduced to 10% of the pre-dive value without loss of cardiac function and blood pressure. Finally, we wish to suggest that
280
ARNOLDUS SCHYTTE BLIX, JOHN K. KJEKSHUS, WAR ENGE AND ANSTEIN BERGAN
even partial simulation of such a circulatory state, by e.g. pharmacological means, might be a successful approach in the treatment of ischemic injuries in the heart of man. One of us (ASB) is sponsored by the Norwegian Research Council for Science and the Humanities. We wish t o thank Drs T. Kluge, S. 0. Wille, H. J. Grav, and H. Aune, Miss A. Ljosdal and 1. J. Blix, and Mr P. Gautvik for expert scientific and technical help throughout the experiments. We are also grateful to Dr T. Samuelsen, Bergen Aquarium, Bergen, for keeping and management of several of our seals.
References BERGLUND. E., R. G. MONROEand G. L. SCHREINER, Myocardial oxygen consumption and coronary blood flow during potassium-induced cardiac arrest and fibrillation. Acra physiol. scand. 1957. 41. 261-268. BERNE,R. M., Regulation of coronary blood flow. Physiol. Rev. 1964. 44. 1-29. BLix, A. S.,The importance of asphyxia for the development of diving bradycardia in ducks. Acra physiol. srand. 1975. 95. 41-45.
BRON,K. M.,H. V. MURDAUGH, J. E. MILLEN,R. LENTHALL, P. RASKINand E. D. ROBIN,Arterial constrictor response in a diving mammal. Science 1966. 152. 540-543. Cardiovascular defence against ELSNER,R., D. L. FRANKLIN, R. L. VAN ClrrERs and D. W. KENNEY, asphyxia. Science 1966. 153. 941-949. FOLKOW,B., N. J. NlLssoN and L. R. YONCE,Effects of diving on cardiac output in ducks. Arra pl~ysiul. scand. 1967. 70. 347-361. IRVING, L., Changes in the blood flow through the brain and muscles during the arrest of breating. Amer. J . Physiol. 1938. 122. 207-214. IRVING, L., Respiration in diving mammals. Physiol. Rev. 1939. 19. 112-1 34. JOHANSEN, K., Regional distribution of circulating blood during submersion asphyxia in the duck. Arru physiol. scand. 1964. 62. 1-9. KJEKSHUS, J. K., Mechanism for flow distribution in normal and ischemic myocardium during increased ventricular preload in the dog. Circular. Res. 1973. 33. 489499. Compensatory mechanisms during graded myocardial ischemia. LEKVEN, J., 0.D. Micas and J. K. KJEKSHUS, Cardiology 1973. 31. 467473. RUDOLPH, A. M. and M. A. HEYMAN, The circulation of the fetus in utero. Methods for studying distribution of blood flow, cardiac output and organ blood flow. Circular. Res. 1967. 21. 163-184. P. F., Experimental investigations on the respiratory function in diving mammals and birds. SCHOLANDER, Hualrdders skrifrer, Norske Videnskaps-Akad., Oslo, 1940. 22. 1-1 3 I.
Myocardial Blood Flow in the Diving Seal BY ARNOLDUS SCHYITE BLIX,JOHNK. KJEKSHUS, IVARENGEand ANSTEIN BERGAN Received 18 August 1975
Abstract BLIX,A. S., J. K. KJEKSHUS,I. ENGEand A. BERGAN.Myocardial Blood Flow in the Diving Seal. Acta physiol. scand. 1976. 96. 277-280. Grey seals exhibit a marked drop in heart rate, a slight decrease in ventricular contractility, and an essentially unchanged stroke volume upon diving. In the present study, we have demonstrated that the resulting drop in cardiac output is associated with a 90% reduction of coronary blood flow. Such reduction of myocardial blood flow takes place despite a significant increase in effective coronary driving pressure, and is indicative of a 8 0 0 % increase in coronary vascular resistance. This means that the circulatory adjustments displayed by the diving seal (i.e. a reduction of the workload on the heart) are so effective that myocardial blood flow can be reduced to 10% of the pre-dive value without loss of cardiac function and blood pressure. I t is suggested that even partial simulation of such a circulatory state might be a successful approach in the treatment of ischemic injuries in the heart of man.
It has for long been acknowledged that the naturally diving vertebrates respond to submersion with a pronounced bradycardia and a marked redistribution of the circulating blood. Moreover, it is generally agreed that the redistribution of the blood involves that almost the total blood oxygen store is offered to the brain and the heart, while other tissues have to depend upon anaerobic metabolism. This principle for asphyxic defence was first advanced by Irving (1939) in his classical review on the respiration in diving mammals. His assumptions were based on his own observations (Irving 1938) of a retarded circulation in skeletal muscles of anesthetized animals, in concert with increased cerebral blood flow, during the arrest of breathing. Irving’s finding on muscle circulation was later well documented in the diving seal (Scholander 1940), while Johansen (1964) has reported a fourfold increase in myocardial blood flow in the diving duck. Neither this finding, nor that of Irving (1938) on cerebral circulation (which never has been re-examined), is, however, compatible with our present knowledge of a pronounced (90%) reduction of cardiac output in both the diving seal (Elsner et al. 1966) and the duck (Folkow et al. 1967). As the methods employed both by Irving and Johansen had some apparent shortcomings, we decided to re-examine some aspects of myocardial circulation in the diving seal by use of radioactively labelled microspheres injected into the left ventricle. By this approach, information of the distribution of cardiac output, which is important in relating our findings to those of recent reports, was obtained also. 277
278
ARNOLDUS SCHYTTE BLIX, JOHN K . KJEKSHUS, WAR ENGE AND ANSTEIN BERGAN
TABLE I. Tissue blood flow(m1/100 g.min-') in one seal while breathing air (control) and after 5 min of submersion (dive). The value obtained during the dive is also given in per cent ( % ) of the control value. n, is number of tissue samples examined. All numbers are means (if not single measurements)+S.E. S.E.=O, indicates a S.E. of less than 0.5. Cardiac output (litrelmin), heart rate (beats/min), arterial pressure (mmHg), Left ventricular (LV) max dp/dt (mmHg/s), Left coronary PRU and total PRU obtained at the moment of microsphere injection are also included. At the time of injection, arterial PO, was 92 torr and 47 torr in control and during diving, respectively. The difference in control/dive flow ratio between the two animals was less than 2 % in right and left ventricle, skeletal muscle, kidney and stomach, while the brain flow ratios differed with 12% (possibly due to a 10% difference in arterial pCO,, the PO, being identical, in the diving situation). 76
n
3f0 9f 1
4.2 10.3
3fO
2.0
49f6
33.9
5 15 4 4 3 3
Tissue
Control
Right ventricle Left ventricle M. psoas Kidney Stomach Cerebrum
70+4 90f3 14f I 135f5 14+0 143+8
Cardiac output Heart rate Arterial presure LV max dp/dt Left coronary PRU
7.9 132 I65 4 000 I .8
0.6 10 155 3 000 14.4
Total PRU
0.02 I
Dive
o+o
o*o
-
7 7 75
0.258
Material and Methods A total of 3 grey seals (Halichoerus grypus) of both sexes, aged 6-7 months were used. The animals were sedated with 50 mg Valiumm Roche, i m . , and restrained on a specially designed board prior to each experiment. In the diving situation, the animals were totally submerged in fresh water of 15°C. Lehman pigtail catheters were advanced under fluoroscopic control, from the hind-flipper arteries, one to the left ventricle of the heart, and one to the thoracic aorta. Xylocain@Astra (1 %) was used as local anesthetics. The aortic catheter was used for blood sampling while the ventricular one was used for injection of the microspheres. Both W r and 86Srlabelled microspheres (3M) suspended and sonicated in saline were used. A mean diameter of the spheres of 25 p was chosen according to the rather large diameter of seal erythrocytes. The experimental procedure was essentially as described previously by Kjekshus (1973). The "Cr labelled spheres were used when the animal was on the surface breathing air, while the 86Srlabelled microspheres were injected 5 min after the commencement of the dive. The animals were killed after 15 min of submersion while still under water, with a massive dose of sodium pentobarbital. Tissue blood flow (m1/100 g min-I) and cardiac output were calculated as described by Rudolph and Heyman (1967). Two animals were used in these experiments, but from one of them we only got the relative change in flow upon submersion. Left ventricular and aortic blood pressure were measured by use of Statham transducers (P23H) connected to a Beckman RS Polygraph. Left coronary effective driving pressure (Berne 1964), heart rate and estimates of myocardial contractility (dp/ dt) were obtained from the recordings. Arterial PO, and PCO, were obtained by use of Radiometer@electrodes. Three animals were used in these experiments.
-
279
MYOCARDIAL BLOOD FLOW IN SEALS
E
mmHg
200
CONTROL
SUBMERGED
0 Fig. I . Typical aortic (upper tracing) and left ventricular (lower tracing) blood pressure of grey seals while breathing air (control) and during diving (submerged).
0
Results and Discussion The microsphere experiment revealed a more than 90% decrease in cardiac output in response to submersion (Table I). This decrease was of the same magnitude as the decrease in heart rate (Fig. 1, Table I), and is therefore in agreement with the findings of Elsner et al. (1966). Moreover, consistent with this reduction of cardiac output a pronounced decrease in blood flow to skeletal muscle, kidney and viscera took place in response to diving (Table I). This is again in good agreement with previous investigations (e.g. Scholander 1940, Bron et a/. 1966, and Elsner et al. 1966). Our investigation did, on the other hand, also reveal that even cerebral blood flow decreased markedly (Table I), in spite of a maintained perfusion pressure (Fig. 1). In striking contrast to Johansen (1964) we also observed a 90% decrease in left coronary blood flow in response to submersion, despite a significant increase in effective left coronary driving pressure (Berne 1964), (Fig. 1, Table I). This reduction of blood flow, which was even greater in the right ventricle is indicative of a 800% increase in left coronary peripheral resistance units (PRU) (diastolic aortic pressure (mmHg)/blood flow (mllmin)). It is unlikely that this reduction in coronary blood flow is associated with any ischemic dilatation of the heart (as would be the case in e.g. dogs and man, Lekven et al. 1973), since increased end-diastolic pressures never occurred, not even in dives lasting for as long as 15 min (Fig. 1). The reduction of left coronary blood flow was of the same magnitude as the reduction of cardiac output in the present study (Table I). Moreover, we found an essentially maintained stroke volume after 5 min of submergence, despite a 1200% increase in total peripheral resistance (mean aortic pressure (mmHg)/cardiac output (mllmin)), and a 25 % decrease in myocardial contractility. Our results therefore indicate that the reduction of workload on the heart due to the reduction of heart rate and contractility is the determinant of the reduced myocardial blood flow in the diving seal, irrespective of a marked increase in coronary driving pressure. This finding is supported by results on dogs, where coronary blood flow approaches the value found in resting skeletal muscle, in the potassium arrested heart, despite maintained perfusion pressure (Berglund et al. 1957). In conclusion, our study has revealed that the circulatory adjustments displayed by the diving seal are so efficient that myocardial blood flow can be reduced to 10% of the pre-dive value without loss of cardiac function and blood pressure. Finally, we wish to suggest that
280
ARNOLDUS SCHYTTE BLIX, JOHN K. KJEKSHUS, WAR ENGE AND ANSTEIN BERGAN
even partial simulation of such a circulatory state, by e.g. pharmacological means, might be a successful approach in the treatment of ischemic injuries in the heart of man. One of us (ASB) is sponsored by the Norwegian Research Council for Science and the Humanities. We wish t o thank Drs T. Kluge, S. 0. Wille, H. J. Grav, and H. Aune, Miss A. Ljosdal and 1. J. Blix, and Mr P. Gautvik for expert scientific and technical help throughout the experiments. We are also grateful to Dr T. Samuelsen, Bergen Aquarium, Bergen, for keeping and management of several of our seals.
References BERGLUND. E., R. G. MONROEand G. L. SCHREINER, Myocardial oxygen consumption and coronary blood flow during potassium-induced cardiac arrest and fibrillation. Acra physiol. scand. 1957. 41. 261-268. BERNE,R. M., Regulation of coronary blood flow. Physiol. Rev. 1964. 44. 1-29. BLix, A. S.,The importance of asphyxia for the development of diving bradycardia in ducks. Acra physiol. srand. 1975. 95. 41-45.
BRON,K. M.,H. V. MURDAUGH, J. E. MILLEN,R. LENTHALL, P. RASKINand E. D. ROBIN,Arterial constrictor response in a diving mammal. Science 1966. 152. 540-543. Cardiovascular defence against ELSNER,R., D. L. FRANKLIN, R. L. VAN ClrrERs and D. W. KENNEY, asphyxia. Science 1966. 153. 941-949. FOLKOW,B., N. J. NlLssoN and L. R. YONCE,Effects of diving on cardiac output in ducks. Arra pl~ysiul. scand. 1967. 70. 347-361. IRVING, L., Changes in the blood flow through the brain and muscles during the arrest of breating. Amer. J . Physiol. 1938. 122. 207-214. IRVING, L., Respiration in diving mammals. Physiol. Rev. 1939. 19. 112-1 34. JOHANSEN, K., Regional distribution of circulating blood during submersion asphyxia in the duck. Arru physiol. scand. 1964. 62. 1-9. KJEKSHUS, J. K., Mechanism for flow distribution in normal and ischemic myocardium during increased ventricular preload in the dog. Circular. Res. 1973. 33. 489499. Compensatory mechanisms during graded myocardial ischemia. LEKVEN, J., 0.D. Micas and J. K. KJEKSHUS, Cardiology 1973. 31. 467473. RUDOLPH, A. M. and M. A. HEYMAN, The circulation of the fetus in utero. Methods for studying distribution of blood flow, cardiac output and organ blood flow. Circular. Res. 1967. 21. 163-184. P. F., Experimental investigations on the respiratory function in diving mammals and birds. SCHOLANDER, Hualrdders skrifrer, Norske Videnskaps-Akad., Oslo, 1940. 22. 1-1 3 I.
