Evaluation of Time Course of Left Ventricular Isovolumic Relaxation in Humans

Abstract

Weiss and coworkers [1] first determined, in an open-chest, right-heart-bypass animal model, that left-ventricular-pressure decay during isovolumic relaxation can be approximated by a monoexponential function. Their technique required that the derived or best-fit monoexponential curve for the pressure data decay asymptotically toward zero pressure. [1, 2]. Subsequent evaluation of the time course of pressure fall during isovolumic relaxation has questioned whether the monoexponential decay of isovolumic pressure decline should proceed to a zero or nonzero asymptote [3–5]. Inherent in this calculation is the assumption that pressure decline during isovolumic relaxation is mono-exponential. This postulate is empiric and is not necessarily predicated by any physiologic mechanism [6]. However, in those cases where a monoexponential model applies, calculation of the time constant provides a single index which characterizes the shape of the pressure curve during isovolumic relaxation. Such an index is important if the effects of relaxation on diastolic performance and overall cardiac function are to be evaluated in diseases such as hypertrophic cardiomyopathy and exercise-induced myocardial ischemia.