Influence of wall compliance on hemodynamics in models of abdominal aortic aneurysm.

Purpose: To determine complementary criteria to existing morphological criteria, which are not reliable but are used to justify surgical intervention to treat abdominal aortic aneurysm (AAA).

Methods: An experimental study was conducted in which 2 models of AAA, 1 rigid and 1 soft, were used to study the influence of compliance on aneurysm dynamics. The heart rate was 70 beats per minute, and the mean flow rate was 1.02 L/min. Velocity measurements were made with particle image velocimetry in 2 planes parallel to flow (1 vertical and 1 horizontal).

Results: The general flow patterns generated in the rigid AAA model were in agreement with the literature. In both models, a vortex occurred at the beginning of systolic deceleration in the proximal part of the AAA, near the anterior wall. The vortex remained confined to the proximal part during the entire cycle in the rigid model, whereas in the soft model, the vortex migrated to the distal segment during the cycle and impacted the AAA walls. This impact generated a local pressure increase on the wall. In the soft model, another vortex was created near the posterior wall. These vortices eroded and weakened the walls of the distal segment, which can cause rupture.

Conclusion: Compliance of the aneurysm wall might become another criterion to justify surgical intervention.