Role of catecholamines on energetics of the heart and its blood supply.

The effects of continuously infused intravenous l -epinephrine and l -norepinephrine (5 gamma/ kg/min.) were determined in the open-chested anesthetized dog prepared for measurement of total coronary flow and myocardial oxygen consumption. When catecholamines were infused at any fixed cardiac output, cardiac oxygen consumption rose in association with increases in blood pressure and heart rate, while cardiac external mechanical efficiency declined. The significance of the product (blood pressure times heart rate) as an index of the total cardiac effort, as indicated by the myocardial oxygen requirement, is considered in view of the alterations brought about by catecholamines in this relationship. The decline in the coronary A-V oxygen difference, the percentage of oxygen extracted by the heart and the ratio (cardiac oxygen consumption/oxygen availability) and the rise in coronary venous oxygen, are all attributed to a direct action of catecholamines on the coronary vessels. Despite their new levels, the coronary venous oxygen, content and the coronary A-V oxygen difference remain fairly constant as the cardiac effort and its oxygen requirement vary during catecholamine infusion.