Effect of Variations in Intraluminal Thrombus Constitutive Properties on Abdominal Aortic Aneurysm Wall Stress: A Parametric Study

Abstract

The prevalence of abdominal aortic aneurysm (AAA) is growing together with population age, being 8.8% in a population above 65 years according to a recent study [1]. Deciding between elective surgical repair of AAA and watchful management is a complex issue due to the lack of reliable rupture risk indices. The maximum transverse diameter of AAA is most commonly used in clinical practice to base this decision. From a biomechanical viewpoint, AAA rupture is related to the balance between the stresses acting on the wall and strength of the wall tissue. Many different factors contribute to the stress within the aortic aneurysm wall, including the presence of intraluminal thrombus (ILT) [2–5], the local surface curvature [6] and material characteristics of the AAA wall [7], and the presence of local “stress concentrators” due to calcifications or local thinning. As regards the ILT, its role with respect to aneurysm wall stresses has given rise to many hypotheses. Some studies show that the pressure inside the thrombus is not reduced with respect to the arterial blood pressure, some, including studies from the authors, state a possible protective role [2–5]. Previously in our laboratory, a nonlinear, hyperelastic constitutive model was developed for ILT, and the parameters for which were determined through ex-vivo experimentation [8]. The purpose of this study was to investigate the reliability of using the same population-mean values of ILT constitutive parameters for estimates of wall stress distribution in all AAA. For this, we performed a parametric study in which the ELT constitutive parameters were varied within a physiological range and aortic wall stresses were evaluated.