Spatial and temporal variations of wall shear stress within an end-to-side arterial anastomosis model.

Wall shear stress has been strongly implicated in the initiation of fibrous intimal hyperplasia that leads to arterial bypass graft failure. In this study, the photochromic tracer technique was used to determine the instantaneous value of the wall shear stress in order to provide a detailed description of its spatial and temporal variations within a 45 degrees end-to-side anastomosis model. At the heel and on the bed across from the heel, the shear stress was close to zero throughout the sinusoidal flow cycle. Flow separation was produced just beyond the toe where the peak phase-averaged shear stress was 6 dyn cm-2, whilst on the bed across from the toe it was 27 dyn cm-2. The stagnation point was seen to fluctuate quite sharply on the bed over a distance of about one tube radius upstream from the site across from the toe. This led to large spatial gradients of the wall shear stress with a peak value of 580 dyn cm-3. In addition, the sudden motion of the stagnation point around peak flow produced sharp temporal gradients of the wall shear stress with a peak absolute value of 3400 dyn cm-2 s-1. When compared to the sites where intimal hyperplasia tends to occur, a strong correlation is seen with low wall shear stress at the heel and toe, and with the sharp temporal variations of the magnitude and spatial gradient of the wall shear stress on the bed across from the junction.