| Abstrakt: |
Myocardial oxygen consumption in isovolumic hearts with varying cardiac outputs was explored in heart-lung preparations from dogs, modified to measure coronary flow. The venous reservoir was raised in steps to increase stroke volume and with it left ventricular volume; myocardial oxygen consumption being determined at each step. The venous reservoir was then lowered to the starting level, thus restoring stroke volume to control and an intraventricular balloon was distended with saline again in steps, to increase left ventricular volume to the same extent as when the venous reservoir was raised, but maintaining stroke volume constant. Myocardial oxygen consumption was measured at each step and compared with that obtained at an identical left ventricular volume but with a higher cardiac output. The results of 10 comparative studies in six preparations indicate that at constant heart rate and mean systemic pressure, myocardial oxygen consumption was the same in preparations with identical left ventricular volumes but drastically different cardiac outputs. It may be concluded from this study that the oxygen cost of an increase in volume work of the heart, at constant mean aortic pressure and heart rate, is determined by the concomitant increase in the volume of the heart in so far as it affects the development of tension in accordance with the Laplace relationship. [ABSTRACT FROM PUBLISHER] |
