Effect of a Disturbed Flow on Proliferation of the Cells of a Hybrid Vascular Graft

Atherosclerotic lesions and intimal hyperplasia develop preferentially in regions where blood flow is disturbed by the formation of secondary and recirculation flows. Hence, to investigate the mechanism of the localization of these vascular diseases, we constructed a sudden tubular expansion consisting of a 0.92 mm i.d. upstream tube and a 3.0 mm i.d. hybrid vascular graft, and by recirculating a cell culture medium through it in steady flow for 7 days, we tested the effect of a disturbed flow (an annular vortex) on proliferation of smooth muscle cells (SMC) of the hybrid graft. It was found that the thickness of the cell layer that was considered a measure of the proliferation of SMC underlying the endothelial cells was greatest around the reattachment point (the toe of the annular vortex) where the flow was the slowest and the wall shear stress was the lowest. The thickening of the cell layer also occurred around the stagnation point located at the origin of the expansion but was much less than that around the reattachment point. The cell layer was the thinnest in the middle portion of the vortex where the flow was the fastest and wall shear stress was the highest. These results indicated that a disturbed flow provides favorable conditions for the proliferation of SMC in regions where the flow is very slow and wall shear stress is very low. This may explain, in part, why intimal hyperplasia and atherosclerotic lesions develop preferentially in regions of slow flow.