Flow patterns in the radiocephalic arteriovenous fistula: an in vitro study

A significant number of late failures of arteriovenous fistulae for haemodialysis access are related to the progression of intimal hyperplasia. Although the aetiology of this process is still unknown, the geometry of the fistula and the local haemodynamics are thought to be contributory factors. An in-vitro study was carried out to investigate the local haemodynamics in a model of a Cimino-Brescia arteriovenous (AV) fistula with a 30° anastomotic angle and vein-to-artery diameter ratio of 1.6. Flow patterns were obtained by planar illumination of micro-particles suspended in the fluid. Steady and pulsatile flow studies were performed over a range of flow conditions corresponding to those recorded in patients. Quantitative measurements of wall shear stress and turbulence were made using laser Doppler anemometry. The flow structures in pulsatile flow were similar to those seen in steady flow with no significant qualitative changes over the cardiac cycle. This was probably the result of the low pulsatility index of the flow waveform in AV fistulae. Turbulence was the dominant feature in the vein, with relative turbulence intensity >0.5 within 10 mm of the suture line decreasing to a relatively constant value of about 0.10–0.15 between 40 and 70 mm from the suture line. Peak and mean Reynolds shear stress of 15 and 20 N/m 2, respectively, were recorded at the suture line. On the floor of the artery, peak values of temporal mean and oscillating wall shear stress of 9.22 and 29.8 N/m 2, respectively. In the vein, both mean and oscillating wall shear stress decreased with distance from the anastomosis.