A Numerical Tool for the Coupled Mechanical Assessment of Anastomoses of PTFE Arterio-venous Access Grafts

Abstract

The anastomotic angle is assumed to affect the performance of arterio-venous (AV) access grafts by altering wall shear stress (WSS) and wall tension. The objective of this study was to develop a coupled numerical tool to assess fluid and structural anastomotic mechanics of a straight upper arm access graft. 3D computational fluid dynamics (CFD) and finite element (FE) models were developed for arterial and venous anastomoses with different graft attachment angles. The fluid simulations were executed using flow velocity profiles for anastomotic inlets obtained from a whole-graft CFD model. A mesh adaptation algorithm was developed to couple CFD and FE meshes and capture fluid structure interactions. The coupling algorithm enabled transfer of blood pressure (BP) and WSS predicted with the CFD models to the FE models as loadings. The deformations induced in the FE models were used to update the CFD geometries after which BP and WSS were recalculated and the process repeated until equilibrium between fluid and solid models. Maximum BP in the vein was 181 mmHg. WSS peaked at 2.3 and 0.7 Pa and the structural wall stress reached 3.38 and 3.36 kPa in arterial and venous anastomosis. Since flow-induced wall tension has been identified as a contributor to access graft failure along with WSS, the computational tool will be useful in studying the coupled mechanics in these grafts. Initial investigations of arterial and venous anastomotic end-to-side configuration indicated a slightly better performance of the 90° configuration over 135° arterial and 45° venous configurations.