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Growth, buckling, and rupture of abdominal aortic aneurysms Hejazi, Masoud


The objective of this work was to assess the influence of buckling on the growth and rupture of Abdominal Aortic Aneurysms (AAAs). AAAs are one of the most common under-diagnosed cardiovascular diseases in North America. They manifest as localized bulges in arteries, posing a risk of rupture with fatal consequences. Assessing the rupture risk of AAAs is complicated by complex mechano-biological factors; size-based criterion is often used to guide surgical interventions. It is often found that AAAs can exceed the size recommended (≥ 5.5 cm) for surgical intervention, and yet do not rupture, and vice versa. AAAs exceeding the clinically recommended size are often found in a tortuous state. Since in-vivo testing is impossible to assess the rupture risk of AAAs, inflation tests on hyperelastic tubes were performed to advance the mechanistic modelling, and to inform our clinical study. Mechanical instability in a pre-tensioned finite hyperelastic tube subjected to an internal pressure produces a spatially localized bulge. The fate of the bulge under continued inflation is governed by the end- conditions and the initial tension in the tube. Buckling was found to confer protection against rupture. Failure maps in the stretch parameter space and in stretch–tension space are constructed by extending existing membrane theory for bulge formation and buckling. Biologically relevant constitutive models for arteries are implemented in Finite element analyses (FEA). Buckled AAAs were found to grow without rupture under favourable arterial pre-tensions. Failure maps incorporating post-bifurcation (bulging and buckling) response are constructed to delineate the regimes of growth, buckling and rupture of an AAA. Finally, a retrospective review is performed on a database of patients who had undergone AAA repair to assess whether buckling (tortuosity) confers protection against rupture. Greater aortic buckling was found in the unruptured AAAs compared with the ruptured AAAs at the same matched diameter, pointing to the need to incorporate not only the size but also tortuosity in clinical interventions.

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