Transitional flow within an arteriovenous graft: A numerical study

Hemodialysis vascular access dysfunction has a significant impact on morbidity in end-stage renal disease patients. A major cause of hemodialysis vascular access failure is venous intimal hyperplasia near the venous anastomosis and proximal vein, which is followed by thrombotic occlusion. While the natural healing response from surgical injury causes some degree of intimal thickening, local hemodynamic factors have also been implicated. High flow rates in arteriovenous (AV) grafts, which create a significantly altered hemodynamic environment compared with normal venous circulation, are necessary for efficient hemodialysis performance.; In vivo measurements of flow rates and vein-wall vibration were performed on 30 AV grafts of varying geometric configurations (6mm constant diameter, 4 to 6mm and 6 to 4mm tapered) in 15 canine models. In addition, pulsatile flow numerical simulations, based on in vivo flow rates and geometry obtained from animal study, were conducted in order to elucidate detailed hemodynamics in an AV graft.; This research is the first extensive numerical study to investigate the physics of transitional blood flow in a subject-specific AV graft through direct numerical simulations. The spectral element technique is employed, which is a high-order discretization ideally suited to the simulation of transitional flows in complex domains.; The influence of flow division between the proximal venous segment (PVS) and distal venous segment (DVS) on the transitional nature of flow was examined for the Reynolds numbers in the range of 800 to 1400. Transition to turbulent flow was observed for Reynolds numbers lower than the critical value of 2100 when some portion of inflow goes to the DVS. The frequency spectra of velocity and pressure fluctuations indicated a significant intensity in high frequency downstream of the toe. An adverse pressure gradient, which enhances transition to turbulence, was developed in the PVS under flow division. These numerical findings were in good agreement with experimental data on the same geometry.; A better understanding of hemodynamic environment obtained in this study may lead to significant improvements in the durability of AV grafts. In addition, this work may help in the design of acoustic or vibration-based non-invasive diagnostic devices for information of AV graft patency.