Poroelastic Model of Intraluminal Thrombus in FEA of Aortic Aneurysm

The influence of the intraluminal thrombus (ILT) on the biomechanics of the abdominal aortic aneurysm (AAA) has been investigated for several years both numerically and experimentally. The FE analyses published till now simplified the material of the ILT as a homogenous continuum, but there is a contradiction between experiments and FE results. Therefore we use a poroelastic constitutive model for ILT. Poroelastic behaviour of the used finite element is based on the Biot theory of consolidation, the model consists of fluid and solid parts.

By using idealized AAA models, we showed that the pressure decrease through the ILT is small for an 18mm thick ILT. Therefore approx. 90% of the blood pressure is acting on the inner AAA wall surface. These results agree very well with all experimental results, which show either slight or no pressure reduction. The wall stresses calculated by our approach are almost the same as those obtained by using the homogenous material model for ILT.

Remarkably the model with poroelastic thrombus loaded by the blood pressure on the luminal surface of the ILT gives the same results as the model with homogeneous thrombus loaded on the inner surface of the AAA wall. These results support the theory that the stress reduction by ILT is caused by the adherent fibers, which serve as load bearing ropes stretched between different points on the arterial wall and consequently reduce the wall stress although the pressure is allowed to penetrate through without a substantial reduction.