CARDIAC OXYGEN METABOLISM AND CONTROL OF THE CORONARY CIRCULATION

Abstract

In heparinized dogs, anesthetized with pentobarbital Na, blood was circuited from a carotid artery through a bubble flow-meter into a cannulated anterior descending branch of the left coronary artery. The chest was then closed and the expt. carried out under spontaneous respiration. Venous blood samples withdrawn from a catheter placed into the coronary sinus were found to be unreliable as sources of true coronary venous blood. Consequently, coronary venous blood was obtained from a cannula placed into the great cardiac vein which represented true coronary outflow; O2 content of this blood consistently was 4-6 vols. % and left ventricular O2 consumption averaged 8.8 ml./l00 g./min. =*= 13.0% under normal conditions. This factor was found to have highly significant correlations with coronary flow, cor-onary resistance, blood pressure and cardiac work, but no correlation with cardiac output. Three groups of expts. of this type were completed in which 1) arterial blood pressure 2) cardiac output, or 3) arterial O2 content was altered primarily. Coronary blood flow under these conditions was found to adjust itself so as to meet primary changes either in the demand of the heart for oxygen or in the supply of available oxygen in the arterial blood and mechanical efficiency of left ventricle was found to vary inversely with aortic pressure, directly with cardiac output.