Regional wall mechanics in the ischemic left ventricle: numerical modeling and dog experiments
TL;DR: The mechanics of the ischemic left ventricle during a complete cardiac cycle were simulated using a finite-element model accounting for the thick-walled ventricular geometry, the fibrous nature of the myocardial tissue, and the dependency of active muscle fiber stress on time, strain, and strain rate.
Abstract: The mechanics of the ischemic left ventricle during a complete cardiac cycle were simulated using a finite-element model accounting for the thick-walled ventricular geometry, the fibrous nature of the myocardial tissue, and the dependency of active muscle fiber stress on time, strain, and strain rate. Ischemia was modeled by disabling the generation of active stress in a region comprising approximately 12% of total wall volume. In the model simulations, the approximately 12% reduction in the amount of normally contracting tissue resulted in an approximately 25% reduction in stroke work compared with the normal situation. The more-than-proportional loss of stroke work may partly be attributed to storage of elastic energy in the bulging ischemic region. Furthermore the mechanical performance in the nonischemic border zone deteriorated because of reduced systolic fiber stress (if fibers were in series with those in the ischemic region) or reduced fiber shortening (if fibers were parallel). The deformation pattern of the ventricle was asymmetric with respect to the ischemic region because of the anisotropy of the myocardial tissue. Epicardial fiber shortening in and around the ischemic region, as predicted from the model simulations, was in qualitative agreement with shortening, as measured in four dogs in which ischemia was induced by occlusion of the distal part of the left anterior interventricular coronary artery.
Cites background or methods from "Regional wall mechanics in the isch..."
...Analytical equations have been developed to estimate LV wall stress (19), but more versatile approaches use the finite-element (FE) method, which can incorporate asymmetric geometry, tissue anisotropy (6, 14), and varying material properties (5, 15)....
...These biomechanical findings represent a fundamental change in modeling active myocardial contraction; before these studies were performed, myocyte contraction was modeled only in the direction of the muscle fiber (5)....
...Previous FE studies of the LV have validated stress calculations by showing good agreement with myocardial deformations (strains) measured with implanted markers (5, 14, 29, 38, 39)....
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