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EFFECT OF THE LOSS OF SYMMETRY ON THE DISTRIBUTION OF WALL SHEAR STRESSES IN ABDOMINAL AORTIC ANEURYSMS

Anne-Virginie L. B. Salsac
Department of Mechanical and Aerospace Engineering, University of California, San Diego La Jolla, California 92037, USA

Juan C. Lasheras
Department of Mechanical & Aerospace Engineering, University of California, San Diego, La Jolla, CA 92093-0411, USA

Abstrakt

Changes in the patterns of mechanical stimuli acting on the walls are thought to play a crucial role in the growth of abdominal aortic aneurysms (AAA). The goal of this study is therefore to measure the wall shear stresses (WSS) and gradients of wall shear stresses (GWSS) in idealized models of AAA under physiologically realistic pulsatile flow conditions. The spatial and temporal distributions of WSS have been derived from the Particle Image Velocimetry measurements of the velocity field inside the aneurysm. Similarly to axisymmetric aneurysms, the flow remains attached to the wall during the systolic acceleration up to very large asymmetry parameters. The geometric asymmetry prevents the formation of a close vortex ring. The non-symmetric vortex that resembles a hairpin engenders a helical flow pattern inside the AAA. The strength of the vortex shed from the proximal anterior wall increases with the asymmetry parameter, until it dominates the flow structure. Alternate patterns of WSS result along the walls, where the endothelial cells are exposed to quasi-steady very low and reversed WSS along the anterior wall and positive higher amplitude WSS along the posterior wall. GWSS are generated around the point of impact of the vortex on the posterior wall and at the aneurysm necks and are also expected to form in the circumferential direction.