AJP - Heart and Circulatory Physiology, Vol 249, Issue 6 1119-H1126, Copyright © 1985 by American Physiological Society
Coronary blood flow and myocardial segment dimensions during simulated dives in seals
R. Elsner, R. W. Millard, J. K. Kjekshus, F. White, A. S. Blix and W. S. Kemper
Three harbor seals Phoca vitulina richardsi and five spotted seals Phoca
vitulina largha were used in studies of acute episodes of local myocardial
ischemia in open-chest, anesthetized animals and of coronary blood flow and
regional function as indicated by left ventricular segment dimensions
during experimentally simulated dives of conscious, instrumented animals.
We observed that seal myocardium, in which there are few coronary
anastomoses, responded to brief local occlusion with prompt local
dysfunction and systolic bulging; coronary flow in the nondiving seal
oscillated irregularly and declined with spontaneous apnea and related
falling heart rate; flow continued to oscillate but was much reduced during
dives, frequently ceasing entirely for periods as long as 45 s; ventricular
segment dimension shortening was reduced intermittently during dives; and
elevated heart rate induced during dives by cardiac pacing or by
administration of atropine diminished or eliminated the reductions in
coronary blood flow. Responses of seal heart reflect the reduction in
cardiac metabolic demand during diving and the seal's myocardial adaptation
for enhanced anaerobic glycolysis. The seal heart can maintain mechanical
function during dives with minimal coronary perfusion, despite the
progressive and ultimately profound hypoxia, hypercapnia, and acidosis.
Reduced cardiac metabolism, copious glycolytic reserves, and metabolite
washout by intermittent brief bursts of coronary blood flow are apparently
sufficient to support continued cardiac function, even though the seal
heart has little tolerance for acute localized ischemia.
