Does normal pulmonary impedance constitute the optimum load for the right ventricle?

Abstract

Right ventricular performance of isolated supported cat hearts was experimentally characterized by a relationship among ventricular pressure (P), volume (V), and time after onset of systole. This characterization was combined with a hypothetical load network consisting of lumped central and peripheral lung vascular resistances (Rc and Rp), inertance (L), and compliance (C). We calculated ventricular and load pressure, flow, external ventricular work (Wext), static ventricular P-V energy (Wstat), and pump efficiency Q = Wext/Wstat over a broad range of load conditions. Magnitudes of load network variables resulting in a maximum value of Q would define the load impedance matching the ventricle. A practical optimum magnitude of lumped vascular compliance was obtained at C = 150 x 10(-6) g-1 . cm4, above which no substantial change in Q took place. We obtained maximum Q at approximately 4 ml stroke volume (heart rate = 2 Hz) and at characteristic impedance between 0.75 and 1.1 x 10(3)g . cm-1 . s-1. As these values are quite close to those encountered in the intact animal, we conclude that the right ventricular and the pulmonary arterial tree appear to constitute a matched pump-load system.