A Model of Cardiac Muscle Dynamics

A mathematical model is presented describing the timeand length-dependent behavior of cardiac muscle. The model describes a wider variety of experimental data than do previously published models. It incorporates a modification of the Hill equation describing the force-velocity relation. Based on the sliding filament theory, the revised equation includes the effects of finite cross-bridge compliance proposed by A. F. Huxley. The essential simplicity of the Hill equation is retained; however, the model successfully predicts force development during both isometric and isotonic contractions, observed deactivation of the contractile element during isotonic shortening, and the apparent dependence of series elastic stiffness on time after stimulation during quick-release and quick-stretch experiments.