Stereoscopic particle image velocimetry of the impinging venous needle jet during hemodialysis

Stereoscopic particle image velocimetry (S-PIV) was used to quantify the dynamic flow field caused by the venous needle jet (VNJ) in an idealised model of hemodialysis cannulation. Scaling based on Reynolds number ensured dynamic similarity with physiological conditions. Measurements taken along the center plane indicate the presence of a steady secondary flow region, which develops downstream of the impingement region. Upon impingement, a wall jet forms on the floor of the vein and spreads along the curvature of the vessel. Circulating flow forms due to the interaction between the jet spreading and the wall jet. This secondary flow region represents a potential site of stenosis on the roof of the vein where flow is reversed. The effects of the circulating flows can be minimized by using shallow needle angles, low needle flow rates and placement of the needle away from the walls of the vein.