Stiffening of the Cardiac Wall by Coronary Blood Volume Increase: A Finite Element Simulation
A porous medium finite element model of the beating left ventricle is used to simulate the influence of the intracoronary blood volume on left ventricular mechanics. The spongy material is composed of incompressible solid (myocardial tissue) and incompressible fluid (coronary blood). The model is axisymmetric and allows for finite deformation, including torsion around the axis of symmetry. The total stress in the tissue is the sum of the intramyocardial pressure, effective passive stress due to myocardial deformation and the contractile fiber stress. The model is able to simulate a full cardiac cycle. Three-dimensional end-systolic deformation computed relative to the end-diastolic state is shown to be consistent with experimental data from the literature. The direction of maximal shortening varied less than 30° fiuni endocardium to epicardium while fiber direction varied by more than 100°. It is shown that the ventricular model exhibits diastolic stiffening following an increase of intracoronary blood volume. End-diastolic left ventricular pressure increases from 1.5 kPa to 2.0 kPa when raising intracoronary blood volume from 9 to 14 ml per 100 g myocardial tissue. The model simulation suggests that the mechanism underlying the increase in end-diastolic pressure at higher coronary blood volumes, is an increase in passive stiffness of the myocardial fibers. This increased stiffness is the combined result of an overall increase in strain in myocardial tissue and the non-linear stress-strain relationship of myocardial tissue.
KeywordsLeft ventricle porous medium mixture erectile properties diastole coronary perfusion.
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