MECHANICAL EFFECTS OF LOOPING IN THE EMBRYONIC CHICK HEART

During early embryonic development, the heart bends into a curved tube in a vital morphogenetic process called looping. Since looping involv es poorly understood biomechanical forces that are difficult to measur e, this paper presents a theoretical model for the tubular chick heart , whose development is similar to that of the human heart. Representin g the basic morphology of the looped ventricle, the model is a thick-w alled, isotropic, pressurized curved tube composed of three layers rep resenting the myocardium, cardiac jelly, and endocardium. The model is analyzed with nonlinear elasticity theory, modified to include residu al strain and muscle activation, and material properties are determine d by correlating theoretical and experimental pressure-volume relation s. The results show that longitudinal curvature significantly influenc es the biomechanical behavior of the embryonic heart. As the curvature increases, the compliance of the tube increases, especially at end sy stole. Stress concentrations, which develop in the endocardium during diastole and in the myocardium during systole, also increase with the curvature. The largest wall stress during the cardiac cycle occurs nea r the beginning of systolic ejection in the myocardial layer at the in ner curvature of the tube. Relative to end diastole, the model predict s epicardial strains that are nearly equal in the circumferential and meridional directions, in agreement with experimental measurements. Th ese results provide insight into the interrelation between biomechanic al forces and morphogenesis during cardiac looping.