Comparative effects of heart rate and aortic blood pressure on MVO in the anesthetized open-chest dog.

Comparative effects of heart rate and aortic blood pressure on myocardial oxygen consumption (MVO2) were studied in anesthetized open-chest dogs. The left coronary artery was perfused through the external shunt with blood from the left common carotid artery. Heart rate was changed with the left atrial pacing and the constriction of the descending thoracic aorta was utilized to elevate the proximal aortic blood pressure (BP). The left ventricular enddiastolic pressure was insignificantly changed with the atrial pacing and with the aortic constriction. With the constant BP (100 +/- 5 mmHg), and unit increase in heart rate per minute augmented MVO2 by 0.027 ml/min/100 Gm of left ventricular muscle, while one mmHg elevation of BP caused 0.15 ml increment in MVO2 per minute per 100 Gm of left ventricular muscle under the constant heart rate (115 +/- 5 beats/min). Therefore an unit change in BP caused five- to six-fold greater increase in MVO2 compared with that in heart rate, indicating extremely important roles of BP in MVO2.