Simulation of Pressure Losses in a Hemodialysis Graft Circuit with Computational Fluid Dynamics

Long-term hemodialysis is frequently provided with an arteriovenous (AV) graft implanted into an extremity. The useful life of AV grafts is limited by the development of stenosis at or downstream from the venous anastomosis. A better understanding of graft hemodynamics may allow improved assessment of the risk of thrombosis. Jones et al (J Biomech Eng 2005, 127: 60-66) developed a model of pressure losses for an experimental graft circuit using well-known hydrodynamic equations, and showed a reasonable prediction of pressure losses. Their model, however, had a number of assumptions based on the fixed geometry of a fabricated experimental model, whereas actual circuits have non-ideal geometries. The goal of this project was to create a 3D computational fluid dynamics (CFD) model using finite element analysis (FEA) based on the experimental graft geometry, simulate flow and pressure drops under the same experimental conditions, and compare results with both the experimental data and the hydrodynamic equation model. The FEA geometry was created in SolidWorks® using identical dimensions to the experimental graft circuit, consisting of an inlet artery, graft conduit, venous outflow, anastomoses and stenosis. The geometry was imported into COMSOL Multiphysics® and meshed with approximately 500,000 elements. Fluid flow was modeled using large eddy simulation with fluid parameters corresponding to the experimental model. Inlet boundary conditions were flow from 100 to 1200 ml/min. The results showed good general agreement with the experimental and hydrodynamic models. These results suggest that CFD can be applied, and would allow the study of various AV graft configurations seen clinically.