Dependency of myocardial reactive hyperemia on coronary artery pressure in the dog

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Abstract
We studied the effects of coronary artery pressure on myocardial reactive hyperemia following brief flow arrests in 20 closed-chest anesthetized dogs. The circumflex artery was perfused from a pressurized arterial reservoir with a cannula inserted through the right carotid artery. Increasing coronary pressure from 60 to 160 mmHg did not alter heart rate, systemic pressure, or left ventricular dP/dtmax. For 10-s inflow occlusions, 20-mmHg increments in coronary pressure from 40 to 160 mmHg resulted in proportional increases in peak hyperemic flow [40 +/- 4 to 257 +/- 18 (SE) ml/min], total hyperemic flow (2 +/- 1 to 42 +/- 4 ml), and the duration of hyperemic flow (9 +/- 2 to 37 +/- 3 s). These results were unchanged when preocclusion pressure was held constant and postocclusion pressure varied. The influence of coronary artery pressure on hyperemic flow was progressively less pronounced after occlusions of shorter duration. These data indicate that coronary artery pressure has a major influence on the characteristics of myocardial reactive hyperemia after brief periods of arterial flow arrest. The observed pressure dependency suggests that coronary reactive hyperemia may be, in part, a passive flow response that could be explained by a transient depression of the normal vascular reactivity to postocclusion pressure. A passive component to reactive hyperemia could account for the overrepayment of bloow flow debt characteristically observed in the heart.