AJP - Heart and Circulatory Physiology, Vol 254, Issue 2 361-H368, Copyright © 1988 by American Physiological Society
Aortic pressure reduction redistributes transmural blood flow in dog left ventricle
J. J. Smolich, P. L. Weissberg, A. Broughton and P. I. Korner
Baker Medical Research Institute, Melbourne, Victoria, Australia.
We studied the effect of graded aortic blood pressure reduction on left
ventricular (LV) blood flow in anesthetized, autonomically blocked,
open-chest dogs at constant heart rate and mean left atrial pressure.
Aortic diastolic pressure (ADP) was lowered from rest (average 116 mmHg) to
90, 75, and 60 mmHg with an arteriovenous fistula. Global and regional LV
blood flow was measured with radioactive microspheres. Mean LV blood flow
fell stepwise from 145 ml.min-1.100 g-1 at rest to 116 ml.min-1.100 g-1 at
ADP of 60 mmHg, whereas the endocardial-to-epicardial flow ratio decreased
from 1.20 to 0.84. The transmural redistribution of LV blood flow was not
accompanied by increases in LV oxygen extraction, depression of LV
contractility, LV dilatation or LV electrical dysfunction and also occurred
in the presence of considerable coronary vasodilator flow reserve.
Electrical evidence of subendocardial ischemia appeared at ADP of 32 mmHg
and an endocardial-to-epicardial flow ratio of 0.41 in a subgroup of
animals. We conclude that the redistribution of LV flow during moderate
aortic pressure reduction was an appropriate physiological adjustment to
uneven transmural alterations in regional LV wall stress and that it
preceded a more pronounced redistribution evident with myocardial ischemia.
