Cardiac output and its distribution through capillaries and A‐V shunts in diving seals

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Abstract
Regional blood flow and cardiac output were determined by distribution of radioactive microspheres injected via catheter into the left ventricle during experimental diving and recovery in juvenile spotted seals (Phoca vitulina largha) and grey seals (Halichoerus grypus). Cardiac output was 9.8 l/min before diving, declined 90% during submersion and increased to 12.1 l/min after 40 s of recovery. Left ventricular myocardial perfusion declined from 179 .+-. 24 to 25 .+-. 2 ml/min .cntdot. 100 g at 2 min submersion and measured 23 .+-. 3 after 10 min of submersion. Cerebral cortical flow was reduced from a predive value of 115 .+-. 3 to 40 .+-. 5 and 49 .+-. 6 at 2 and 5 min of diving, respectively, but increased to 253 .+-. 14 ml/min .cntdot. 100 g at 10 min along with elevated PCO2 [partial pressure of CO2] (84 torr) and lowered pH (7.10) in arterial blood. It remained at that level in recovery. Brain stem perfusion after 10 min submersion was still identical with control but increased to 275% of control in recovery. Adrenal flow decreased to 4 and 27% of control at 2 and 5 min of diving, respectively. Recovery flow after 10 min of diving was 200% of control. Liver, kidney, fat, skin and stomach were ischemic throughout the dive. Recovery flow increased slowly in these tissues. Skeletal muscle (m. [musculus] psoas) was perfused at a low rate (3 ml/min .cntdot. 100 g) predive and was ischemic during diving. Recovery muscle perfusion was variable at different sites (from 5-105 ml/min .cntdot. 100 g). Predive pulmonary capillary perfusion was 58 .+-. 8 ml/min .cntdot. 100 g, decreased to 7 .+-. 0 ml/min .cntdot. 100 g after 10 min of submersion and had increased to 50% of predive value after 40 s of recovery from a 10 min dive. The following conclusions were reached: previous information from implanted flow transducers was confirmed; detailed data for discrete tissues elaborate the concept of selective redistribution of cardiac output in diving seals; nonuniform reperfusion contributes to the maintenance of arterial pressure during recovery; and substantial A-V [atrioventricular] shunting of cardiac output took place in the first 2-5 min of the dive, when total capillary/nutritive flow was low. Late in the dive, CO was routed through systemic capillaries, mainly in the cerebral circulation and < 15% through A-V shunts.