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

A significant number of late failures of arteriovenous fistulae for haemodi alysis access are related to the progression of intimal hyperplasia. Althou gh the aetiology of this process is still unknown, the geometry of the fist ula 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 degrees anas tomotic 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 condi tions corresponding to those recorded in patients. Quantitative measurement s of wall shear stress and turbulence were made using laser Doppler anemome try. The flow structures in pulsatile flow were similar to those seen in st eady flow with no significant qualitative changes over the cardiac cycle. T his was probably the result of the low pulsatility index of the flow wavefo rm in AV fistulae. Turbulence was the dominant feature in the vein, with re lative turbulence intensity > 0.5 within 10 mm of the suture line decreasin g to a relatively constant value of about 0.10-0.15 between 40 and 70 mm fr om 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 arter y, peak values of temporal mean and oscillating wall shear stress of 9.22 a nd 29.8 N/m(2), respectively. In the vein, both mean and oscillating wall s hear stress decreased with distance from the anastomosis. (C) 1999 Elsevier Science Ltd. All rights reserved.