Hemodynamic parameters within aortal stent-grafts vs. their spatial configuration : a comparison based on computer simulations

Abstract

Background: It is difficult to find reliable premises which would enable a modification of the construction of stent-grafts to improve their durability and stability. Many systemic conditions make a comparison of homogeneous groups of operated patients a complicated task. Hence, it is helpful to use computer simulations and to verify them in a clinical observation. The hemodynamic parameters within aortal stent-grafts depending on their spatial configuration were compared using a computer simulation. Material/Methods: Computer simulations were made for 6 patients with abdominal aortal aneurysm (AAA) in whom bifurcated aortal stent-grafts were implanted. A basis for a spatial model were angio-CT data. Flow rate parameters were obtained in US-CD. In numerical calculations, CFD - Fluent® 6.2 software was used. Numerical grids (about 300,000 tetrahedral elements) were generated on the basis of three-dimensional geometries of AAA segmented from CT scans. A laminar character of flow was assumed. Blood viscosity was described by Quemada's rheological model. In all patients, two variants of the graft geometry were generated assuming that common long-body and shortbody grafts were applied. The patients’ real anatomical conditions were taken for the simulations. Pressure drop on the graft level and wall shear stress were analyzed. Results: It was found that the short-body graft caused a higher pressure drop along the inlet-outlet segment. The long-body graft offered smaller resistance to blood flow, and, consequently, the shear stress was lower. For the rate around 0.8 m/s, the difference reached 5500 Pa. In both variants, the highest value of shear stresses occurred near the bifurcation area. Conclusions: An increase of the shear stress is more distinct when the short- body graft is used, which can suggest that this part of the graft should be as long as possible