Pulsatile flow measurements and wall stress distribution in a patient specific abdominal aortic aneurysm phantom

In this study, we develop a physiologic internal pressure and wall stress analysis procedure and apply it to a patient-specific abdominal aortic aneurysm model. Time-dependent pressure loading of the inner vessel wall was experimentally measured in a 3D printed aneurysm phantom. The results were used as boundary conditions for finite element calculations of von Mises stresses throughout the AAA model over the cardiac cycle. A nonlinear hyperelastic constitutive law with parameters based on biaxial stress-deformation data from aneurysmal tissue samples was used to describe the mechanical behavior of the aneurysm wall. The internal pressure was found to be fairly spatially uniform (within 10%) over most of the cardiac cycle, but average internal pressure varied by more than a factor of two between systole and diastole. The aneurysm wall stress was highly spatially nonuniform. The highest value of von Mises stress was localized in a small area within the aneurysm bulge and remained in the same place throughout the cardiac cycle, suggesting that this area was the most likely point of rupture. Large variations in wall stress over the cardiac cycle suggest calculations that assume steady flow are a poor approximation for physiological stresses.