Left ventricular pressure-volume relationship based on the intracellular control mechanisms: analysis of the time-varying elastance

Left ventricular (V) performance is governed by the intracellular control of contraction. Analysis of cardiac fiber dynamics, based on the biochemistry of crossbridge cycling and calcium kinetics, suggests the existence of two dominant feedback mechanisms: a negative and a positive feedback loop. The interplay between the feedback loops and the loading conditions determine the LV end-systolic pressure-volume relationship (ESPVR) the commonly used index of contractility. It explains the observed dependence of the “pressure deficit” on the ejected volume and the isovolumic pressure. The analysis reveals the basic physiological parameters and intracellular biochemical kinetics which explains the dependence of the pressure deficit on E(t), the time-varying elastance. The study suggests a new approach for evaluating the LV function based on intracellular control mechanisms