Experimental evaluation of a patient specific Brachio-Cephalic Arterio Venous Fistula (AVF): Velocity flow conditions under steady and pulsatile waveforms

Arterio-Venous Fistulas (AVF) are the most popular form of vascular access used for hemodialysis. However they continue to present complications leading to early and late failure. To understand the reasons for failure, it is necessary to analyze the hemodynamics involved. Wall shear stress (WSS) is commonly studied in AVFs as it often relates to cardiovascular disease, although there is dispute over whether high or low WSS is detrimental to AVF patency. The goal of this paper is to investigate velocity flow conditions in a rigid, patient-specific brachio-cephalic AVF model in both steady flow (Re = 1817) and patient-specific pulsatile flow (Re_av=1817, Re_max=2233). Particle Image Velocimetry (PIV) measurements were performed at the anastomosis to capture the complex 3D-3C flow present. The results from this study found regions of recirculation and high velocity fluctuations in the distal artery and proximal vein, and flow impingement at the anastomosis toe. Steady and pulsatile flow demonstrated similar flow features, possibly owed to the low pulsatility index. In addition, the recirculation zone did not vary along the waveform. The directional variability was seen to be the highest at the regions of recirculation and flow impingement suggesting regions of high transWSS while the coefficient of variation was greatest at the walls and in areas of flow separation indicating high temporal wall shear stress.