The Influence of Asymmetric Inflow in Abdominal Aortic Aneurysm Hemodynamics

Inflow asymmetry has been found to strongly influence the hemodynamics in arterial geometries. Flow asymmetry is commonly found within the aortic conduit just proximal of the aneurysmal expansion and is caused by the remodeling of the abdominal aorta required to accommodate the excess volume of the distended vessel. In an effort to improve the accuracy of abdominal aortic aneurysm (AAA) rupture risk estimation the influence of parameters other than the peak transverse dimension, used routinely in clinical practice as a rupture risk index, on the distribution of wall stress is investigated. Towards this end, both experimental and computational flow studies in simplified geometry AAA models have been conducted. However, these studies neglect the presence of significant vessel tortuosity of the AAA inflow segment. This paper is primarily concerned with the effects of asymmetric inflow on abdominal aortic aneurysmal sac flow. To assess the influence of inflow asymmetry on the intra-aneurysmal flow features we compare the numerically computed time varying flow fields in two simplified geometry AAA models, one with a straight pipe inflow and another with an s-shaped inflow conduit. The tortuosity of the s-shaped AAA inlet was set to be equal to the mean inflow tortuosity derived from patient specific AAA wall surface models created by 3D reconstruction of in vivo acquired Computed Tomography images. The Womersley solution of a physiologic abdominal aortic flow waveform was used to compute the time varying velocity profile applied as the model inflow boundary condition. Our results show that the injection of an asymmetric velocity profile in the aneurysmal sac affects the distribution of wall stress thus influencing the progression of AAA wall disease and subsequently the risk of rupture.