Force-time integral does not improve predictability of cardiac O2 consumption from pressure-volume area (PVA) in dog left ventricle

Summary We have proposed the systolic pressure-volume area (PVA) as a measure of the total mechanical energy generated by ventricular contraction, and we found a closely linear correlation between PVA and cardiac oxygen consumption (V_O2). Although the force-time integral (FTI) has long been considered to be the most reliable correlate of cardiac oxygen consumption (V_O2), we have already shown that V_O2 remained constant although FTI was changed while PVA was kept constant in the excised, cross-circulated dog left ventricle. This means that PVA is superior to FTI as a predictor of V_O2. In the present study, we studied whether a linear addition of FTI to PVA could improve the prediction of V_O2 from PVA in isovolumic and ejecting contractions with different afterload pressures in the same type of dog left ventricle preparation. Although left ventricular V_O2 was always closely correlated with either PVA (r=0.967, mean after z-transformation) or FTI (mean r=0.925), multiple regression analysis indicated that PVA alone accounted for as much as 94% (mean) of the variance of V_O2 and that FTI linearly added to PVA accounted for an additional few percent of the variance (statistically significant in less than half the cases). We conclude that the addition of FTI to PVA does not improve the predictability of V_O2 from PVA in ordinary contractions.