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

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 (VO2). Although the force-time integral (FTI) has long been considered to be the most reliable correlate of cardiac oxygen consumption (VO2), we have already shown that VO2 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 VO2. In the present study, we studied whether a linear addition of FTI to PVA could improve the prediction of VO2 from PVA in isovolumic and ejecting contractions with different afterload pressures in the same type of dog left ventricle preparation. Although left ventricular VO2 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 VO2 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 VO2 from PVA in ordinary contractions.