An investigation into how the geometry of an end-to-side arterial anastomosis affects its function.

The effects of altering the geometry of an end-to-side junction were investigated in a hydraulic model. The dimensions of the tubes, pressures and flow rate and the frequency of pulsation were calculated by dimensional analysis, to produce a model which simulated pulsatile flow in small arteries. The ratio between the impedance of the 'bypass' and the impedance downstream from the junction was greater than unity when the two tubes forming the junction were of unequal diameter. No increase in downstream impedance was measured when the angle of junction was increased from 45 degrees to 135 degrees. Cine photographs of streamlines at the junction showed that flow passed smoothly through the junction irrespective of angle and that perturbations occurred only during that part of the cycle when flow was reversed. The results indicate that the angle at which a junction is made affects flow. The effect is small and is only seen when the ratio of diameters of the tubes is unity. The ratio of the diameters of the two tubes which make up the junction has the greatest effect on flow through the junction.