Fluid Dynamics of Ventricular Filling in the Embryonic Heart

Abstract

The vertebrate embryonic heart first forms as a valveless tube that pumps blood using waves of contraction. As the heart develops, the atrium and ventricle bulge out from the heart tube, and valves begin to form through the expansion of the endocardial cushions. As a result of changes in geometry, conduction velocities, and material properties of the heart wall, the fluid dynamics and resulting spatial patterns of shear stress and transmural pressure change dramatically. Recent work suggests that these transitions are significant because fluid forces acting on the cardiac walls, as well as the activity of myocardial cells that drive the flow, are necessary for correct chamber and valve morphogenesis. In this article, computational fluid dynamics was used to explore how spatial distributions of the normal forces acting on the heart wall change as the endocardial cushions grow and as the cardiac wall increases in stiffness. The immersed boundary method was used to simulate the fluid-moving boundary problem of the cardiac wall driving the motion of the blood in a simplified model of a two-dimensional heart. The normal forces acting on the heart walls increased during the period of one atrial contraction because inertial forces are negligible and the ventricular walls must be stretched during filling. Furthermore, the force required to fill the ventricle increased as the stiffness of the ventricular wall was increased. Increased endocardial cushion height also drastically increased the force necessary to contract the ventricle. Finally, flow in the moving boundary model was compared to flow through immobile rigid chambers, and the forces acting normal to the walls were substantially different.

Fluid Dynamics of Heart Development

“…Their simulations were performed for Reynolds numbers in the range of 1-10, corresponding to an HHstage 25 chick heart. Miller [65] also found that pressure and shear are of the same order of magnitude in a simplified two-dimensional beating heart model for Reynolds numbers on the order of 0.1. In this case, shear stress is maximized on the luminal side of the cushions, and pressure is maximized on the chamber walls during contraction.…”

Cyclic strain induces dual-mode endothelial-mesenchymal transformation of the cardiac valve

“…However, the influence of mechanical forces and its synergy with tissue architecture in influencing cardiac valve EMT is unknown. During embryonic development, valve morphogenesis has been correlated with an increase in fluid shear stresses, mechanical strains, and altered geometry of the developing heart (19)(20)(21)(22). These observations potentially suggests interaction between mechanical forces and the factors that regulate EMT.…”

Dimensionless analysis of valveless pumping in a thick-wall elastic tube: Application to the tubular embryonic heart

“…Some claim that pumping of embryonic blood is induced by myocardial contractions that induce peristaltic waves (Maes et al, 2011), while others hypothesized that valveless dynamic suction is the mechanism based on observations in zebrafish and quail embryos (Forouhar et al, 2006;Jenkins et al, 2007). Consequently, numerous computational models were published in support of either of these mechanisms (Manopoulos and Tsangaris, 2005;Taber et al, 2007;Loumes et al, 2008;Avrahami and Gharib, 2008;Santhanakrishnan and Miller, 2011;Miller, 2011).…”