Does the degree of coarctation of the aorta influence wall shear stress focal heterogeneity?

Abstract

The development of atherosclerosis in the aorta is associated with low and oscillatory wall shear stress for normal patients. Moreover, localized differences in wall shear stress heterogeneity have been correlated with the presence of complex plaques in the descending aorta. While it is known that coarctation of the aorta can influence indices of wall shear stress, it is unclear how the degree of narrowing influences resulting patterns. We hypothesized that the degree of coarctation would have a strong influence on focal heterogeneity of wall shear stress. To test this hypothesis, we modeled the fluid dynamics in a patient-specific aorta with varied degrees of coarctation. We first validated a massively parallel computational model against experimental results for the patient geometry and then evaluated local shear stress patterns for a range of degrees of coarctation. Wall shear stress patterns at two cross sectional slices prone to develop atherosclerotic plaques were evaluated. Levels at different focal regions were compared to the conventional measure of average circumferential shear stress to enable localized quantification of coarctation-induced shear stress alteration. We find that the coarctation degree causes highly heterogeneous changes in wall shear stress.

Suitability of lattice Boltzmann inlet and outlet boundary conditions for simulating flow in image‐derived vasculature

“…For the set of lattice points i in the slice, the relative error E of the velocity profile along a slice was computed with the following equation: where u and u r are the current and reference velocities, respectively . The naive implementation was previously validated by comparing simulated flow with experimental flow through 3D printed vasculature using particle image velocimetry (PIV) . Results showed that flow through the pipe in the two implementations was nearly identical (error E < 1.0e‐10).…”

“…Another example of a proposed inlet and outlet boundary condition is the nonlinear FD scheme, but this scheme has only been presented in literature for numerical experimentation . For these reasons, LBM simulations in vascular geometries have extensively used ZH and FD schemes. Therefore, we focus this study on ZH and FD boundary conditions because they are widely implemented in biomedical applications, and they are representative of the two broad categories of boundary condition implementations in LBM.…”

Computational Fluid Dynamics and Additive Manufacturing to Diagnose and Treat Cardiovascular Disease

“…The importance of these hemodynamic variables has been realized over the last few decades, with the identification of parameters such as low or oscillatory WSS [38, 39], pressure gradients [40], and velocity flow fields [41] as risk factors for both different vascular diseases and mechanobiologic drivers of vascular growth, remodeling, and adaptation. Large computational studies investigating the use of such hemodynamic markers in diagnosis have been completed for a range of diseases including but not limited to coarctation of the aorta [16, 42, 43], atherosclerosis [32, 44, 45], aortic aneurysms [46–48], cerebral aneurysms [49–51], coronary artery bypass grafting (CABG) [52], Kawasaki disease [53] (D. Sengupta, PhD thesis, University of California-San Diego, 2013), and congenital heart diseases [54–57]. …”

“…3D printed models offer a method to perform controlled fluid experiments for simulation validation. Such validation studies have been completed for aortic flow [43], cerebral aneurysms [50, 62], valve/leaflet interaction [74], coronary artery disease [32, 75–79], CABG [52, 80, 81] and in a left ventricular assist device (LVAD) [82]. An iterative feedback loop can be established to optimize the fluid simulations and ensure reproducible, robust, and accurate results.…”

“…In the two graphs on the right, average velocity over vertical slices of the images along the vessel is shown first, followed by a direct comparison of simulation values to in vitro measurements on the right. Image reproduced with permission from [43]. …”