Comparative Effects of Heart Rate and Aortic Blood Pressure on MVO₂ in the Anesthetized Open-Chest Dog

Abstract

Comparative effects of heart rate and aortic blood pressure on myocardial oxygen consumption (MVO₂) were studied in anesthetized openchest 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±5mmHg), an unit increase in heart rate per minute augmented MVO₂, by 0.027ml/min/100Gm of left ventricular muscle, while one mmHg elevation of BP caused 0.15ml increment in MVO₂ per minute per 100Gm of left ventricular muscle under the conscant heart rate (115±5beats/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.