Analysis of Left Ventricular Mechanics During Filling, Isovolumic Contraction, and Ejection

The left ventricle (LV) was modeled by two confocal ellipsoids truncated in a plane corresponding to the base of the LV. The ellipsoids were approximated by a series of cylindrical shells. During passive filling, the pressure within the ventricular chamber was determined from chamber volume and a stress-strain relationship for myocardium in the relaxed state. The rapid filling phase of diastole was not analyzed. During isovolumic contraction, the cylindrical shells assumed the properties of myocardium in active contraction. Contraction was sequential, beginning at the ventricular apex, and progressing toward the ventricular base. Geometric changes occurred in the LV model as a function of wall stress, material properties, and timing of myocardial activation. During ejection, viscous and inertial forces were determined as were model output pressure and flow waveforms.