Decrease in myocardial oxygen extraction with aortic constriction in the dog.

Abstract

In the open-chest dog constriction of the descending thoracic aorta, which raises central aortic pressure by 30-80 mmHg, increases cardiac oxygen usage (MVO2) and coronary blood flow (CBF) but reduces heart rate and myocardial oxygen extraction [(A-V)O2]. Pacing tachycardia superimposed on aortic constriction further increases MVO2 and CBF but does not alter (A-V)O2. Atropine or vagotomy abolishes the effect of aortic constriction on (A-V)O2, whereas vagal stimulation in the presence of alpha- and beta-adrenergic blockade reduces (A-V)O2. L-propranolol and phenoxybenzamine fail to modify the effect of aortic constriction on (A-V)O2. These results indicate that aortic constriction reduces (A-V)O2 by eliciting parasympathetically-mediated coronary vasodilation.