Patient-specific computational modeling of blood flow in the pulmonary arterial circulation

Abstract

Computational fluid dynamics (CFD) modeling of the pulmonary vasculature has the potential to reveal continuum metrics associated with the hemodynamic stress acting on the vascular endothelium. It is widely accepted that the endothelium responds to flow-induced stress by releasing vasoactive substances that can dilate and constrict blood vessels locally. The objectives of this study are to examine the extent of patient specificity required to obtain a significant association of CFD output metrics and clinical measures in models of the pulmonary arterial circulation, and to evaluate the potential correlation of wall shear stress (WSS) with established metrics indicative of right ventricular (RV) afterload in pulmonary hypertension (PH). Right heart catheterization (RHC) hemodynamic data and contrast-enhanced computed tomography (CT) imaging were retrospectively acquired for 10 PH patients and processed to simulate blood flow in the pulmonary arteries. While conducting CFD modeling of the reconstructed patient-specific vasculatures, we experimented with three different outflow boundary conditions to investigate the potential for using computationally derived spatially averaged wall shear Stress (SAWSS) as a metric of RV afterload. SAWSS was correlated with both pulmonary vascular resistance (PVR) (R2 = 0.77, P < 0.05) and arterial compliance (C) (R2 = 0.63, P < 0.05), but the extent of the correlation was affected by the degree of patient specificity incorporated in the fluid flow boundary conditions. We found that decreasing the distal PVR alters the flow distribution and changes the local velocity profile in the distal vessels, thereby increasing the local WSS. Nevertheless, implementing generic outflow boundary conditions still resulted in statistically significant SAWSS correlations with respect to both metrics of RV afterload, suggesting that the CFD model could be executed without the need for complex outflow boundary conditions that require invasively obtained patient-specific data. A preliminary study investigating the relationship between outlet diameter and flow distribution in the pulmonary tree offers a potential computationally inexpensive alternative to pressure based outflow boundary conditions.

4D magnetic resonance flow imaging for estimating pulmonary vascular resistance in pulmonary hypertension

“…Based on computational modeling results, an increase in PVR has been shown to be proportional to a decrease in WSS, which is also a function of the velocity gradient (4). This is consistent with the fact that vorticity decreases concurrently with an increase in PVR in all generations of the vascular tree (31). In fact, vorticity appears to decrease towards the periphery, where outflow resistance can exponentially increase with every advancing generation of the vascular tree, providing further evidence of the outlet boundary condition impacts the local velocity profile.…”

Computational modeling and engineering in pediatric and congenital heart disease

“…[74] Simulations also revealed significantly lower shear stress in patient specific models of pulmonary hypertension, and correlated findings with gene regulation. [75]…”

Simulation of unsteady blood flows in a patient‐specific compliant pulmonary artery with a highly parallel monolithically coupled fluid‐structure interaction algorithm

“…For the solid domain, both the inlet and the outlets are fixed, and the outer wall is traction free. We have not explored other possible outflow boundary conditions, such as the resistance boundary condition or the structured tree based outflow boundary condition . The fluid is characterized with viscosity μ f = 0.03 g/(cm s) and density ρ f = 1 g/cm 3 .…”

“…The scalability is an useful metric for the parallel FSI algorithm since it implies that the algorithm is capable of solving the problem in a few hours, instead of days, and this is important for parameter studies or clinic applications. The impact of mesh density on the numerical solution is shown in Kheyfets et al for a steady fluid‐only simulation, where a mesh with a few millions elements is sufficient for the test problem since the solution is relatively smooth.…”

“…Millions of people die every year from cardiovascular diseases, representing more than 30 % of all global deaths . Computational fluid dynamics (CFD) is useful for understanding certain cardiovascular diseases, for example, in Kheyfets et al, it was shown that the wall shear stress obtained through a steady blood flow simulation is highly correlated to the resistive pulmonary arterial impedance. In most numerical simulations, the wall of the artery is assumed to be rigid, but it is widely believed that a simulation with an elastic wall would produce more valuable results than a fluid‐only simulation, even though, such calculations are computationally very expensive, and often take days or months of computing time on small computers without lots of processor cores.…”