Student Abstracts: Medical & Health Sciences at ORNL

Mechanical Wall Stress in an Idealized Computer Model of Human Abdominal Aortic Aneurysm Following Endovascular Repair. WILLIAM JENKINS (University of Tennessee, Knoxville, TN 37996) KARA L. KRUSE (Oak Ridge National Laboratory, Oak Ridge, TN 37831) .
Rupture of an abdominal aortic aneurysm (AAA) is thought to occur when the mechanical stress in the aneurismal wall is greater than the strength of wall tissue. Because AAA rupture is a concern even after endovascular repair with a stent-graft, it is important to understand physiological factors that affect wall stress in post-operative AAAs. Upon generating an idealized AAA computer model, various cases of the model were studied including the aneurismal wall, intraluminal thrombus (ILT), and/or a stent-graft excluding the aneurismal sac. Additionally, a type I endoleak was simulated by creating a gap at the proximal attachment site of the stent-graft. Using commercial software, the wall stress was computed for each case following the application of physiologic intraluminal pressure. The highest wall stress occurred in the case of the wall by itself. Inclusion of the ILT lining reduced the wall stress significantly, and inclusion of the stent-graft reduced wall stress even further. In the simulated endoleak, with the aneurismal sac completely filled with ILT, no increase in the peak wall stress was observed. The results indicate that the ILT has a cushioning effect in the reduction of wall stress. Further, the stent-graft bears most of the pressure load with part of the load being transmitted to the wall due to stent-graft deformation. For wall stress to increase due to type I endoleak, we hypothesize that unclotted blood in addition to or in place of ILT must be present in the aneurismal sac to transmit the pressure load.