Flow-induced vein-wall vibration in an arteriovenous graft

The hemodynamic environment of an arteriovenous (AV) graft differs from that of arterial grafts because mean flow rates are typically 10 times greater. This increased flow rate can create a weakly turbulent state, which alters the biomechanical environment greatly and may play a role in AV graft failure. A canine animal study was conducted to simulate the hemodynamic environment of a human AV graft. In vivo measurements were obtained for vein-wall vibration (VWV), graft geometry, and blood flow rate. In order to investigate the complex flow structure at the venous anastomosis of an AV graft, which is thought to induce these vibrations, a computational fluid dynamics study was conducted by direct numerical simulation under pulsatile flow and geometry conditions based on the animal study. The simulation technique employs the spectral element method, which is a high-order discretization ideally suited to the simulation of transitional flows in complex domains. The minimum and maximum Reynolds numbers entering the graft, based on average velocities, were 875 and 1235, respectively. While velocity and pressure fluctuations are clearly present in the numerical simulations, their magnitude and frequency do not correlate well with the in vivo VWV measurements. Potential reasons for this discrepancy are threefold. First, a quiescent inflow condition was used in the present computations; a more realistic inflow condition might alter the velocity fluctuations significantly. Second, simulations were conducted with a rigid geometry; compliance may play an important role in flow stability within an AV graft. Third, the flow split between the graft and vein inlet may also play an important role in the stability of the flow structures.