In normal myocardium measurements of fiber orientation, patterns of deformation, and blood flow have demonstrated nonuniform behavior. Transmural deformation studies, in which local three-dimensional finite strains have been measured across the canine left ventricular wall by tracking implanted radiopaque markers, have revealed consistent trends in the magnitudes and directions of principal strains during systole. Strains measured in a cardiac coordinate system consist of significant normal strains (circumferential, longitudinal and radial strains) and frequently are accompanied by substantial in-plane and transverse shear strains, particularly near the endocardium. Moreover, the magnitude of deformation often increases dramatically with depth from the epicardium. Under conditions of abnormal activation, ischemia and infarct, regional function has been shown to have additional complexity. For example, in subendocardial ischemia gradients in blood flow, strains and properties exist as a function of distance from the ischemic region. While the experimental characterization of this complex behavior has become more sophisticated, its theoretical counterpart is far behind. Very few theoretical models of the left ventricle account for nonlinear material properties, large deformation and """"""""active state"""""""". Virtually no analyses have accounted for these nonlinear effects in conjunction with asymmetry in geometry, properties and loading and coupling between fibers of differing orientation. The effect of asymmetry is expected to be further amplified by local disturbances such as local epicardial activation and subendocardial ischemia and infarct. The primary objective of these studies is to provide the analytical tools needed to understand the influence of regionally nonuniform function on both local and global behavior of the left ventricle. In order to do so, the technique of nonlinear finite element analysis in continuum mechanics will be utilized. Detailed, nonsymmetric ventricular models will be constructed consisting of """"""""cardiac"""""""" finite elements. Measurements of transmural finite strain patterns throughout the ventricle will be incorporated in the analysis of both normal and abnormal function. It is anticipated that these studies will help elucidate the effects of mechanical interaction between muscle groups having different orientation and properties. These studies will provide new information on stresses and the range of material properties in normal and abnormal myocardium. In addition, they will provide a needed tool to quantify complicated experimental and clinical observations and to help in planning experimental protocols.
| Guccione, J M; McCulloch, A D; Waldman, L K (1991) Passive material properties of intact ventricular myocardium determined from a cylindrical model. J Biomech Eng 113:42-55 |
