Yettram A L, Beecham M C, Gibson D G
Department of Mechanical Engineering, Brunel University, Uxbridge, Middlesex, UK.
Heart Vessels. 1998;13(6):290-301. doi: 10.1007/BF03257233.
In systole the left ventricle of the heart behaves mechanically in two modes simultaneously, passive and active. When in the former mode, the ventricle has to carry and react to the pressure increase within the cavity, while in the latter, force is generated within the myocardium itself through the contraction, i.e., active self-shortening, of the muscle fibers. When the deformations of these two opposing modes balance, isovolumic contraction occurs. After this phase, when the aortic valve has opened, the active mode dominates. Many models of the left ventricle under passive internal pressure have been reported, usually for analyzing the situation in diastole. Only a few attempts have been made to incorporate the self-activation effect present in systole. In this paper, a model for systole is described in which the active component has been treated by analogy to thermal stress analysis methods common in dealing with conventional engineering structures. The model was applied to the pressure and volume data for the ventricles of four patients with cardiac disease. A parametric study was then undertaken to investigate the influence of some of the mechanical factors on ventricular behavior. It was found that fiber angle has a very significant effect on the deformation of the ventricle and also that for ventricles with stiff myocardia, the passive component to the reaction of the ventricle was negligible.
