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Objectives Reverse flow Retrograde flow (RF) of blood in the aortic isthmus can be observed in different types of fetal heart disease (FHD), including abnormalities in heart structure and function. This study sought to investigate the relationship between RF and blood flow parameters, and develop a computational fluid dynamics (CFD) model to understand the mechanisms underlying this observation. Material and methods A total of 281 fetuses (gestational age [GA] 26.6±.3 weeks) with FHD and 2803 normal fetuses (GA: 26.1±.1 weeks) by fetal echocardiography collected from May 2016 to December 2018. Principal component analysis (PCA) was performed to find the relationship and the CFD model reconstructed from 3D/4D spatio‐temporal image correlation (STIC) images to simulate hemodynamics. Results There was a significant difference in the percentages of RF between the study (80/201 (39%)) and control (29/2803 (1%)) groups (p < 0.05). The RF occur when the aorta flow rate (left heart) is reduced to 60% by CFD stimulation. Pearson correlation analysis showed significant correlations between flow rate and wall shear stress(WSS) (r = .883, p = 0.047) variables at the AI. Conclusion Volumetric flow rate of AO or left heart was the main component of the cause of RF. The hemodynamics of the cardiovascular system have highly complex behavior hinge on the turbulent nature of circulating blood flow.

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Background and Objectives: During critical windows of cardiac morphogenesis and remodeling, altered intrauterine hemodynamics may lead to congenital heart defects, such as aortic arch abnormalities. We sought to investigate the effects of diminished flow in the fetal aorta to understand the cause, improved diagnosis, and prognosis of coarctation of aorta (CoA) and interrupted aortic arch (IAA). Methods: Computational fluid dynamics (CFD) model of aortic and ductal arches was built based on dynamic 3D/4D spatiotemporal image correlation (STIC) fetal echocardiography (FE) and Doppler images from a normal fetus. Pulsatile hemodynamics, including velocity, pressure gradient, and wall shear stress (WSS), were stimulated as aortic flow decreased from 100% to 80%, 60%, 40%, and 20% by CFD, with accompanying ductal flow increased proportionally to maintain combined cardiac output (Figure). Results: As aortic flow diminished from 100% to 20% progressively, velocity, pressure, and WSS decreased in systole and diastole in aortic arch and isthmus. As aortic flow decreased, the flow structures changed, resulting in a reduction of WSS in the aortic isthmus, especially on the posterior wall. There was a “zero flow zone” between the left carotid and subclavian arteries when aortic flow decreased to 40% of baseline, and another one between innominate and left carotid arteries when it decreased to 20%. Pearson correlation analysis showed significant correlations between aortic flow, pressure, velocity, and WSS (r=0.883 - 1.000, P=0.047 - 0.001) at aortic isthmus. Conclusions: It is feasible to create a hemodynamic model of human fetal aortic arch using 3D/4D FE and CFD. The alterations of flow variables, especially WSS, and the “zero flow zones" in the aorta from progressive aortic flow reduction suggest the "flow-dependency” of the fetal aortic arch development and a unifying hypothesis of diminished flow in the pathogenesis of CoA and IAA.

The present study uses direct numerical simulations to calculate two different transitional flows from laminar flow to turbulence, that is, the two-scale wake flow and the two-dimensional Reyleigh-Taylor unstable flow, respectively. Both results show that the skewness of the longitudinal velocity gradient, S k , can become positive in the early transition stage, which is beyond our expectation since the turbulent equilibrium state always implies negative values of S k . These phenomena are explained analytically by considering only two dominant Fourier modes with harmonic relations. It is illustrated that the sign of S k is not only affected by the amplitudes of the perturbation velocities, but also related to their phases. We expect that the present results will be helpful for understanding the formation of turbulent equilibrium state and for constructing a new measurable criterion of the transition onset.