Nonlinear finite element analysis of an abdominal aortic aneurysm.

摘要

Abdominal aortic aneurysms (AAAs) are defined as permanent, localized dilations of the abdominal aorta, and are induced by localized weakening of the arterial wall. Although mortality on aneurismal rupture exceeds 90 percent, surgical repair options are available for AAAs diagnosed prior to rupture. Currently, surgical management is recommended when the risk of rupture exceeds risks associated with surgery, which is thought to occur when the lesion maximum diameter is greater than 5.5 cm. However, from a biomechanical standpoint, rupture is to be expected when wall stress, not diameter, is greater than sustainable limits. In this project, a nonlinear, multilayer, finite element model of the diseased vessel wall replicating the shape of a specific patient aneurysm as evaluated from CT imaging has been developed. Stress-strain calculations have been performed in this model under three loading conditions: (i) steady, uniform internal wall pressure at 120 mmHg, a typical value for systolic blood flow in vivo, (ii) pulsatile internal wall pressure approximating the cardiac cycle with a sine function and (iii) spatially non-uniform internal wall pressure based on experimental fluid flow measurements taken from a physical replica of this patient model. The maximum values for principal stresses under the three aforementioned loading conditions are 654 kPa, 654 kPa, and 650 kPa, respectively. A straight tube healthy abdominal aorta model resulted in a maximum value for principal stress of 207.8 kPa. The stresses in the aneurysm have about tripled from the stresses reported in the straight tube healthy aorta under constant systolic pressure loading. Although the difference in maximum stresses between uniform and non-uniform loading conditions for the aneurysm is less than one percent, the resulting stress difference for another patient's geometry could be very significant.