Digital on-line computation of a predictor of cardiac oxygen consumption. Left ventricular systolic pressure volume area.

Left ventricular systolic pressure volume area (PVA) has been proposed as a reliable predictor of cardiac oxygen consumption per beat (VO2). PVA is the area in the pressure-volume (P-V) diagram that is circumscribed by the end-systolic and end-diastolic P-V relation curves and the systolic segment of the P-V loop trajectory. It represents the total mechanical energy required for the ventricle to contract, to change its wall's elastic state from end diastole to end systole, and to eject blood against afterload. PVA has so far been measured manually with a planimeter applied to the P-V diagram. To measure PVA more accurately and on line during experiments, we devised a new method of computing PVA with a digital computer. The method consists of integrating during systole the infinitesimally narrow triangular pressure volume area swept by the straight line segment connecting Vd (ventricular volume at which peak isovolumic pressure is zero) and the instantaneously counterclockwise moving P-V data point in the P-V plane, and adding a small area between the end-diastolic P-V relation curve and the line connecting Vd and the end-diastolic P-V point. This method has proved useful in our study of the relation between VO2 and PVA to evaluate the PVA's ability to predict VO2.