Haidekker, M., White, C.R., L'Heureux, N Frangos, J.A.
Analysis of temporal shear stgress gradients during the onset phase of flow over a backward-facing step. Implications on endothelia cell proliferation.
I Biomech Eng. 2001 123:455-463Endothelial cells in blood vessels are permanently exposed to blood flow and thus fluid shear stress. In arterial bifurcations and stenoses, a disruption of the flow causes zones of reirculation which are associated with both spatial and temporal gradients of shear stress. Such gradients have been linked to the generation of atherosclerotic plaques. For in-vitro studies of endothelial cell responses, the sudden-expansion flow chamber has been widely used and described. The goal of the current study was the elucidation of temporal gradients in shear stress occurring in sudden-expansion flow chambers under varying flow conditions. A model has been created based the 2D Navier-Stokes equations and the geometry of an existing flow chamber. For the onset phase of flow, the wall shear stress action on the bottom plate was computed as a function of time and distance from the sudden expansion. The results showed that depending on the time that the flow needs to getestablished, significant temporal gradients occur close to the reattachment point of flow. Slowly ramping the flow reduces the temporal gradients so that the effects of spatial and temporal gradientscan be observed separately. Cultured endothelial cells exposed to flow with a short (200ms) and along (15s) onset time showed significantly different proliferation rates close to the location wherethe highest temporal gradients occur. Proliferation rate and magnitude of temporal gradients match.This study shows that temporal gradients of shear stress are crucial in the understanding of theendothelium response to blood flow.