Independence of myocardial oxygen consumption from pressure-volume trajectory during diastole in canine left ventricle.

We have found that myocardial oxygen consumption is linearly correlated with the systolic pressure-volume area in the canine left ventricle. This pressure-volume area is a specific area in the pressure-volume diagram that is circumscribed by the end-systolic pressure-volume relation line, the end-diastolic pressure-volume relation curve, and the systolic segment of the pressure-volume trajectory. This area is equivalent to the total mechanical energy generated by ventricular contraction, consisting of the external mechanical work and the mechanical potential energy. In the present study, we specifically changed the course of the diastolic segment of the pressure-volume trajectory without changing the systolic segment of the pressure-volume trajectory and the systolic pressure-volume area. Although the fractions of external mechanical work and mechanical potential energy in the pressure-volume area were markedly changed, the simultaneously measured left ventricular oxygen consumption remained unchanged. This result indicates that the myocardial oxygen consumption is predominantly determined by the total mechanical energy generated during systole, or the systolic pressure-volume area, independent of how the total mechanical energy is converted effectively to external mechanical work during the cardiac cycle.