Flow Behaviour and Wall Shear Stress Derivatives in Abdominal Aortic Aneurysm Models: A Detailed CFD Analysis into Asymmetry Effect

Abstract

Assessing the risk of rupture is extremely important to reduce the mortality of the abdominal aortic aneurysm (AAA). Current clinical guidelines suggest considering the maximum diameter as a criterion for planning and surgical intervention; however, this approach is too simplistic and overlooks other morphological parameters that are associated with the risk of rupture. The aim of this paper is to study the thrombogenicity and to predict the risk of AAA rupture by taking into consideration the geometrical asymmetry of the aneurysm, studying its effect on blood flow behaviour and vortical structure, spatiotemporal distribution of wall shear stresses (WSS), and their related parameters. To show the effect of asymmetry on blood flow dynamics and hemodynamic forces, five virtual models were constructed using five values of geometrical asymmetry ratio β ranging from β=0.2 (asymmetric model; AM) to β=1 (symmetric model; SM). Simulations were run for each geometry under transient physiological flow conditions using finite volume discretization. Resting flow rate was investigated in these models and our results demonstrate that the asymmetry of the aneurysm has a clear effect on the flow behaviour, and consequently on WSS distribution, oscillatory shear index (OSI) and time averaged wall shear stress (TAWSS). Furthermore, these preliminary findings suggest that thrombus formation and rupture risk are more probable in an asymmetric abdominal aortic aneurysm.