NUMERICAL STUDY OF WALL MECHANICS AND FLUID-DYNAMICS IN END-TO-SIDE ANASTOMOSES AND CORRELATION TO INTIMAL HYPERPLASIA

In order to analyse the wall mechanics and the flow dynamics in compli ant vascular distal end-to-side anastomoses, computer simulation has b een performed. In a model study the effect of compliance mismatch on t he wall displacements and on the intramural stresses as well as the in fluence of wall distensibility on the how patterns are demonstrated ap plying two distensible models with different graft elasticity. In addi tion, the flow in a rigid model simulating a vein graft without adapti on of the venous lumen has been investigated. The geometries for these models were obtained from a concurrent experimental study, where the formation of distal anastomotic intimal hyperplasia (DAIH) was studied in untreated and externally stiffened autologous venous grafts in she ep. In the flow study the time-dependent, three-dimensional Navier-Sto kes equations describing the motion of an incompressible Newtonian flu id are applied. The vessel wall is modelled using a geometrically non- linear shell structure. In an iteratively coupled approach the transie nt shell equations and the governing fluid equations are solved numeri cally using the finite element method. In both compliant models maximu m displacement and areas of steep stress gradients are observed in the junction region along the graft-artery intersection. The comparison o f the normal deformations and the distribution and magnitude of intram ural stress shows quantitative differences. The graft elasticity acts as a regulating factor for the deformability and the stress concentrat ion in the junction area: In the model with high graft-elasticity maxi mum normal deformation al the side wall is 17%. This is twice as large as in the stiff graft model and maximum principle stress at the inner surface differs by one order of magnitude. The numerical results conc erning the flow patterns indicate strongly skewed axial velocity profi les downstream of the junction, large secondary motion, flow separatio n and recirculation on the artery floor opposite the junction and at t he inner wall downstream of the toe. In these regions a correlation be tween the time-averaged fluid wall shear stress and intimal thickening found in the animal experiment can be observed, whereas the pronounce d formation of DAIH at the suture line seems to be mainly dependent on wall mechanical factors such as intramural stress and strain. Copyrig ht (C) 1996 Published by Elsevier Science Ltd.