Abstract
In order for computational fluid dynamics to provide quantitative parameters to aid in the clinical assessment of type B aortic dissection, the results must accurately mimic the hemodynamic environment within the aorta. The choice of inlet velocity profile (IVP) therefore is crucial; however, idealised profiles are often adopted, and the effect of IVP on hemodynamics in a dissected aorta is unclear. This study examined two scenarios with respect to the influence of IVP—using (a) patient-specific data in the form of a three-directional (3D), through-plane (TP) or flat IVP; and (b) non-patient-specific flow waveform. The results obtained from nine simulations using patient-specific data showed that all forms of IVP were able to reproduce global flow patterns as observed with 4D flow magnetic resonance imaging. Differences in maximum velocity and time-averaged wall shear stress near the primary entry tear were up to 3% and 6%, respectively, while pressure differences across the true and false lumen differed by up to 6%. More notable variations were found in regions of low wall shear stress when the primary entry tear was close to the left subclavian artery. The results obtained with non-patient-specific waveforms were markedly different. Throughout the aorta, a 25% reduction in stroke volume resulted in up to 28% and 35% reduction in velocity and wall shear stress, respectively, while the shape of flow waveform had a profound influence on the predicted pressure. The results of this study suggest that 3D, TP and flat IVPs all yield reasonably similar velocity and time-averaged wall shear stress results, but TP IVPs should be used where possible for better prediction of pressure. In the absence of patient-specific velocity data, effort should be made to acquire patient’s stroke volume and adjust the applied IVP accordingly.
Highlights
The choice of inlet boundary condition is crucial to ensure accuracy and validity of numerical solutions in any computational fluid dynamic (CFD) simulation
For validation of the computational methods used throughout this study, the streamlines obtained with 3D inlet velocity profile (IVP) for P1 and P2 were compared to their respective 4D magnetic resonance imaging (MRI) streamlines
The velocity patterns are well captured in the descending aorta, with lower FL velocities in P1 seen in both the 3D IVP and 4D MRI results, while the higher TL velocities observed in the 4D MRI streamlines for P2 are correctly modelled with the 3D IVP
Summary
The choice of inlet boundary condition is crucial to ensure accuracy and validity of numerical solutions in any computational fluid dynamic (CFD) simulation. The impact of inlet boundary condition on aortic hemodynamics has been assessed by various researchers (Chandra et al, 2013, Morbiducci et al 2013, Pirola et al 2018 and Youssefi et al 2018). These studies show that the type of IVP, in the form of a spatially varying TP velocity profile or 3D profile containing all three velocity components, has a strong impact on the hemodynamics and related parameters in the ascending aorta and aortic arch, but it has limited influence on flow in the descending aorta. In many type B aortic dissections, the PET is located just distal to the left subclavian artery (LSA) on the aortic arch where the influence of inlet velocity profile could still be significant
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