Active Material Properties of the Myocardium: Correlation With Left Ventricular Function in Man

Author Institution: Department of Engineering and Physiology, Wright State UniversityThe effects of anisotrophy and nonhomogeneity of the ventricular myocardium as represented by a linear increase in the midwall effective modulus of elasticity were investigated in the present study, specifically as they effect the circumferential stress distribution. Various studies are presented suggesting a linear increase in the effective modulus of elasticity from endocardium to epicardium. In our study, this increase in the effective modulus was constrained by the approximation that stress per unit sarcomere length is constant. We evaluated 12 functionally normal cases and 9 functionally abnormal cases. The stress distribution for the 9 functionally abnormal cases was calculated, first with the normal and secondly with the abnormal variation in the modulus of elasticity. Assuming the myocardium has constant material properties that do not change with functional decomposition, the stress distributions in the first calculations indicated higher stresses through the inner half of the myocardium and lower stresses through the outer half of the myocardium as compared to the second. This finding suggests that the inner fibers are overloaded and the outer fibers are underloaded in left ventricular decompensation. The difference between the first and second stress distributions averaged 26% (range: 11% to 48%). A useful, clinical, and quantitative measure of stress loading of the sarcomeres in functionally normal and abnormal left ventricles is proposed