The Series Elasticity of Cardiac Muscle in Hyperthyroidism, Ventricular Hypertrophy, and Heart Failure

The three-component model for muscle proposed by A. V. Hill (1) has been useful in describing the contractile activity of cardiac muscle in vitro (2) and in vivo (3). The contractile element (CE) of this model is assumed to be freely extensible at rest, but with activation it shortens according to a characteristic inverse relation between the velocity of shortening and the load (4). The CE is in series with an elastic element (SE) so that during isometric contraction, the activated CE shortens and stretches the SE, the rate of tension development (dP/dt) being determined by the CE velocity and the stress strain relation of the SE (1). Thus the external manifestations of CE activity depend to a large extent on the properties of the SE.Although the stiffness of the SE is unaffected by inotropic interventions, or the course of active state (5,6), it does become somewhat stiffer following damage from segmental compression (7). With the recent application of cardiac muscle mechanics to the study of pathologic ...