Effect of Intraluminal Thrombus Thickness and Bulge Diameter on the Oxygen Diffusion in Abdominal Aortic Aneurysm

The intraluminal thrombus (ILT) commonly found within abdominal aortic aneurysm (AAA) may serve as a barrier to oxygen diffusion from the lumen to the inner layers of the aortic wall. The purpose of this work was to address this hypothesis and to assess the effects of AAA bulge diameter (d_AAA) and ILT thickness (δ) on the oxygen flow. A hypothetical, three-dimensional, axisymmetric model of AAA containing ILT was created for computational analysis. Commercial software was utilized to estimate the volume flow of O₂ per cell, which resulted in zero oxygen tension at the AAA wall. Solutions were generated by holding one of the two parameters fixed while varying the other. The supply of O₂ to the AAA wall increases slightly and linearly with d_AAA for a fixed δ. This slight increase is due to the enlarged area through which diffusion of O₂ may take place. The supply of O₂ was found to decrease quickly with increasing δ for a fixed d_AAA due to the increased resistance to O₂ transport by the ILT layer. The presence of even a thin, 3 mm ILT layer causes a diminished O₂ supply (less than 4 × 10⁻¹⁰ μmol/min/cell). Normally functioning smooth muscle cells require a supply of 21 × 10⁻¹⁰ μmol/min/cell. Thus, our analysis serves to support our hypothesis that the presence of ILT alters the normal pattern of O₂ supply to the AAA wall. This may lead to hypoxic cell dysfunction in the AAA wall, which may further lead to wall weakening and increased potential for rupture.