Computational study of aortic hemodynamics for patients with an abnormal aortic valve: The importance of secondary flow at the ascending aorta inlet.

S Pirola,J R Pepper,G Asimakopoulos,O A Jarral,X Y Xu,T Athanasiou,D P O'Regan,J R Anderson

doi:10.1063/1.5011960

Abstract

Blood flow in the aorta is helical, but most computational studies ignore the presence of secondary flow components at the ascending aorta (AAo) inlet. The aim of this study is to ascertain the importance of inlet boundary conditions (BCs) in computational analysis of flow patterns in the thoracic aorta based on patient-specific images, with a particular focus on patients with an abnormal aortic valve. Two cases were studied: one presenting a severe aortic valve stenosis and the other with a mechanical valve. For both aorta models, three inlet BCs were compared; these included the flat profile and 1D through-plane velocity and 3D phase-contrast magnetic resonance imaging derived velocity profiles, with the latter being used for benchmarking. Our results showed that peak and mean velocities at the proximal end of the ascending aorta were underestimated by up to 41% when the secondary flow components were neglected. The results for helical flow descriptors highlighted the strong influence of secondary velocities on the helical flow structure in the AAo. Differences in all wall shear stress (WSS)-derived indices were much more pronounced in the AAo and aortic arch (AA) than in the descending aorta (DAo). Overall, this study demonstrates that using 3D velocity profiles as inlet BC is essential for patient-specific analysis of hemodynamics and WSS in the AAo and AA in the presence of an abnormal aortic valve. However, predicted flow in the DAo is less sensitive to the secondary velocities imposed at the inlet; hence, the 1D through-plane profile could be a sufficient inlet BC for studies focusing on distal regions of the thoracic aorta.

Highlights

Have a strong influence on the formation of atherosclerotic plaques and aneurysms
Our results showed that peak and mean velocities at the proximal end of the ascending aorta were underestimated by up to 41% when the secondary flow components were neglected
Overall, this study demonstrates that using 3D velocity profiles as inlet boundary conditions (BCs) is essential for patient-specific analysis of hemodynamics and wall shear stress (WSS) in the ascending aorta (AAo) and aortic arch (AA) in the presence of an abnormal aortic valve

Summary

Introduction

Have a strong influence on the formation of atherosclerotic plaques and aneurysms. WSS can be estimated from in vivo data acquired by phase-contrast magnetic resonance imaging (PC-MRI) (Piatti et al, 2017a; 2017b), accuracy is still a major concern due to uncertainties in determining where the wall is and inadequate spatial resolution for near wall velocity measurements (Piatti et al, 2017a). Advancements in imaging techniques have made it possible to acquire high resolution anatomical images and in vivo velocity measurements The former can be processed to reconstruct patient-specific geometries, while the latter allows the extraction of realistic boundary conditions for computational fluid dynamics (CFD) simulations (Tan et al, 2011; Cheng et al, 2016; Pirola et al, 2017; and Youssefi et al, 2017). This study aims to investigate and compare the influence of different inlet BCs on the results of CFD analysis of aortic hemodynamics in the presence of an abnormal aortic valve. For this purpose, two cases were analysed: one presenting a stenotic valve and the other with a mechanical valve (MV). Three inlet BCs were compared for each case: full 3D velocity profiles obtained from the patients’ PC-MR images; 1D velocity profile (through-plane component, TP) derived from the corresponding 3D velocity vector; and flat velocity profile for the same flow waveform obtained from PC-MRI

Objectives

Methods

Results

Discussion

Conclusion