Fluid mechanics of human fetal right ventricles from image-based computational fluid dynamics using 4D clinical ultrasound scans

Abstract

There are 0.6-1.9% of US children who were born with congenital heart malformations. Clinical and animal studies suggest that abnormal blood flow forces might play a role in causing these malformation, highlighting the importance of understanding the fetal cardiovascular fluid mechanics. We performed computational fluid dynamics simulations of the right ventricles, based on four-dimensional ultrasound scans of three 20-wk-old normal human fetuses, to characterize their flow and energy dynamics. Peak intraventricular pressure gradients were found to be 0.2-0.9 mmHg during systole, and 0.1-0.2 mmHg during diastole. Diastolic wall shear stresses were found to be around 1 Pa, which could elevate to 2-4 Pa during systole in the outflow tract. Fetal right ventricles have complex flow patterns featuring two interacting diastolic vortex rings, formed during diastolic E wave and A wave. These rings persisted through the end of systole and elevated wall shear stresses in their proximity. They were observed to conserve ∼25.0% of peak diastolic kinetic energy to be carried over into the subsequent systole. However, this carried-over kinetic energy did not significantly alter the work done by the heart for ejection. Thus, while diastolic vortexes played a significant role in determining spatial patterns and magnitudes of diastolic wall shear stresses, they did not have significant influence on systolic ejection. Our results can serve as a baseline for future comparison with diseased hearts.

Evaluating the roles of detailed endocardial structures on right ventricular haemodynamics by means of CFD simulations

“…Vortex analysis also demonstrated that the presence of detailed endocardial structures disrupted the main vortex ring in both constant and transient inflow simulations, generating small scale secondary vortices. Vortices in smoothed RVs were fewer and more compact and these results were in accordance with the few larger, tighter ones observed for the simplified RV models of Vruddhula et al, Wiputra et al, and from the large scale vortical motions observed by Pasipoularides et al…”

“…In future studies, it may be of interest to examine whether the distributions of endocardial structures would be correlated to reductions of WSS within a specific range, but many more subjects would be required to do so. It should also be noted that Wiputra et al suggested that the high vorticity regions were related to a higher WSS, through the generation of forces which they determined to be tangential to the ventricular walls. These relationships were observable also in our smoothed RV simulations, when comparing results in Figures and (constant inflow) and and (transient inflow): Higher WSSs were indeed found in the vicinities of larger vortices.…”

Organ Dynamics and Hemodynamic of the Whole HH25 Avian Embryonic Heart, Revealed by Ultrasound Biomicroscopy, Boundary Tracking, and Flow Simulations

“…For comparison purposes, we performed estimated the OSI in other cardiovascular structures, using plots from literature and simulation data from our previous work. We estimated OSI to be 0.04–0.2 in human adult aorta 37 , 0.22–0.31 in human adult ventricles 38,39 , about 0.17 in human fetal right ventricles 40,41 , and 0.1–0.3 in zebrafish ventricles 29 . OSI in our embryonic hearts thus had the same ranges as those observed in hearts of all scales, including human adult and fetal, and zebrafish hearts, but were higher than vascular structures, where flow tended to align in the stream-wise direction and OSI were low.…”

Mending a broken heart: In vitro, in vivo and in silico models of congenital heart disease

“…4D clinical ultrasound fetal heart images were obtained using spatio-temporal image correlation (STIC; Box 1) from structurally normal human fetuses between 20-32 weeks of gestation. These images were used to extract data on ventricular anatomy and ventricular wall motion, which were then used to generate fluid dynamic simulations (Lai et al, 2016;Wiputra et al, 2016). Collectively, Lai et al, and Wiputra et al described the same flow patterns for the left and right ventriclesa pair of vortex rings emanating from the mitral or tricupsid inlet during diastole, corresponding to E-and A-waves (Box 1)the primary mechanisms by which flow shear stresses are imposed on the endocardial wall.…”