Oxygen costs of cardiac mechanical energy and contractility

To maximize ventricular pumping efficiency, determinants of cardiac oxygen (or energy) consumption should be better understood. The authors have proposed a new framework to predict cardiac oxygen consumption per beat (Vo/sub 2/) from left ventricular pressure-volume (P-V) data. The essence of the method is to obtain both Emax and PVA to correlate with Vo/sub 2/, where Emax=slope of the end-systolic P-V relation or maximum elastance, as an index of contractility, PVA=systolic P-V area as a measure of total mechanical energy of contraction=external work EW+mechanical potential energy PE. The empirical equation the authors have obtained is Vo/sub 2/=aPVA+b=aPVA+cEmax+d. Pumping efficiency (EW/Vo/sub 2/) is then given by EW/(aPVA+cEmax+d). Therefore, a maximum efficiency is achieved by minimizing the denominator by decreasing a (O/sub 2/ cost of PVA) and c (O/sub 2/ cost of Emax) besides choosing an optimal combination of PVA and Emax for a required EW per min.