Velocity and wall shear measurements inside a vascular graft model under steady and pulsatile flow conditions

The velocity field in a scaled up model of a PTFE canine artery bypass graft has been studied through flow visualization techniques and laser Doppler anemometry. This research is clinically relevant because local fluid dynamic factors such as wall shear stress and particle residence time have been implicated as localization factors for intimal thickening, a major cause of human graft failure.;This research is the first comprehensive experimental study of the pulsatile fluid dynamics in a PTFE vascular graft utilizing an upscaled model from a canine cast. The graft geometry was idealized to be symmetric about the plane of the bifurcation and is defined by analytical expressions which may be useful for future numerical solutions to the Navier-Stokes equations on this geometry.;Velocity measurements were made under both steady and pulsatile flow conditions inside the vascular graft model for a flow division of 20% exiting through the proximal outlet segment and 80% exiting through the distal outlet segment. Wall shear stresses were estimated from near wall velocity measurements for steady and pulsatile flow.;The flow field inside this canine graft model is three-dimensional in nature with strong secondary motions under both steady and pulsatile conditions. The pulsatile flow phenomena cannot be accurately modeled using steady flow assumptions although the flow field is quasi-steady during the diastolic phase of the cycle.;The time averaged wall shear stress during the pulsatile cycle was estimated to be less than 4 dynes/cm;No evidence of turbulence and a small amount of separation was observed under pulsatile flow conditions. Low and oscillating wall shear stress values were found at several sites inside the graft model and these locations matched qualitatively with regions of intimal thickening reported in the literature.