Effects of geometry and flow division on flow structures in models of the distal end-to-side anastomosis

Flow structures in models of the distal end-to-side anastomosis were visualised under steady and pulsatile flow conditions using planar illumination of suspended tracer particles. The effects of anastomosis geometry and flow in the proximal artery were investigated in models with anastomosis angles of 15, 30 or 45 degrees. The flow patterns in steady flow were highly three-dimensional and comprised two helical vortices in the distal artery, a recirculation vortex in the occluded proximal arterial segment and a stagnation point on the floor of the artery. Flow separation was observed at the toe of the anastomosis in the 30 and 45 degree models only. A second separation point was also found on the near wall of the 30 degree models at higher flow rates. Downstream flow in the proximal artery reduced and even eliminated the flow recirculation at the heel of the anastomosis, while upstream flow resulted in a captive vortex at the heel and flow reversal at the toe. In pulsatile flow, the secondary flow components in the distal artery became more pronounced during flow deceleration, particularly at higher Reynolds numbers. Significant flow reversal was observed at the toe of the anastomosis and this extended several vessel diameters along the near wall of the artery and upstream into the hood of the graft. The floor of the artery was subjected to a continually varying shear rate caused by the movement of the stagnation point during the pulsatile cycle. The results are in agreement with the observation that intimal hyperplasia occurs in regions of flow separation at the toe and the heel, and flow stagnation on the floor of the anastomosis.