Myocardial blood flow and oxygen consumption during moderate cardiac tamponade: role of reflex vasoconstriction.

SummaryThe influence of reflex vasoconstriction on aortic pressure and myocardial oxygen supply and demand during moderate cardiac tamponade was examined in anesthetized, open-chest dogs by comparing responses before and after systemic alpha adrenergic blockade. After α blockade, aortic pressure fell more during cardiac tamponade but there was no change in the ability of myocardium to satisfy its oxygen demand. The data suggest that although peripheral vasoconstriction attenuates the fall in aortic pressure during cardiac tamponade, adequate oxygen supply to myocardium depends on local metabolic vasodilatory systems that couple metabolism to coronary vascular tone, and not on this reflex adjustment.