Ventricular efficiency predicted by an analytical model

Based on the recent data from the literature, we derived analytic expressions for ventricular stroke work (SW), ventricular O2 consumption, and the ratio of the former to the latter, defined as ventricular efficiency, in terms of ventricular contractile properties and arterial afterloading properties. The ventricular properties were quantified by Ees and V0, the slope and volume axis intercept, respectively, of the linear end-systolic pressure-volume relationship. Ventricular afterload was represented by the effective arterial elastance (Ea), a parameter that is dependent on aortic input impedance parameters. O2 consumption was assessed by estimating ventricular pressure-volume area, which has been shown to be linearly related to O2 consumption. Model analysis indicated that SW is maximum when Ea = Ees, the afterload that results in the greatest efficiency is always less than that which provides the maximum SW, the SW and efficiency of a weak heart are more sensitive to changes in afterload than in a strong heart, and there is a sigmoidal relation between ventricular efficiency and end-diastolic volume that reaches its maximum at volumes outside the upper limit of the physiological range. Further analysis of the model indicated that under physiological conditions ventricular and arterial properties may be adjusted more toward optimization of efficiency than SW.