Identification of the Time-Varying Properties of the Heart

Abstract

The mechanical behavior of both skeletal and cardiac muscle exhibits nonlinear time-varying properties. These nonlinearities and time variations present major difficulties to researchers attempting to identify a constitutive law for muscle to use in continuum models. Traditionally, quasistatic identification methods have been used on tetaninized skeletal muscle to determine its mechanical properties at various levels of activation. Such approaches are unsuitable for cardiac muscle where tetanic contractions are difficult or impossible to achieve. In this case one must resort to nonlinear time-varying identification methods. Here we present an identification scheme, together with the associated experimental apparatus, suitable for characterizing muscle models under time-varying conditions. Although this technique is used to identify the time-varying mechanical properties of isolated skeletal muscle throughout the time course of a single twitch, this approach is directly applicable to characterizing the constitutive properties of cardiac muscle.