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Abstract
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 degrees 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/m2, 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/m2, respectively. In the
vein, both mean and oscillating wall shear stress decreased with distance from the
anastomosis.