Effect of stenosis inlet geometry on shear rates of blood flow in the upstream region

Abstract

Abnormal shear rates of blood flow have been implicated in the processes of thrombosis, atherosclerosis, and restenosis after angioplasty. However, no study has quantitated the effect of stenosis inlet geometry on the shear rates in the region upstream to the stenosis. To quantitate this effect, we measured the velocity profiles of blood flow at Reynolds numbers 175 and 350 upstream to different axisymmetric model stenoses in an excised canine aorta. Two 40% and two 75% stenoses were tested, one each with a 45-degree inlet angulation and one each with a 90-degree angulation. For the velocity measurements we used a specially developed external single-channel Doppler ultrasound system capable of resolving blood flow velocity at 91 μm radial intervals across the aorta. We found that increasing the severity of stenosis narrowing and angulation resulted in a significant decrease in shear rate at the endothelial surface ( 40% 45 - degree stenosis: 189 ± 46 sec −1 vs 75% 90 - degree stenosis: 49 ± 12 sec −1 at Reynolds number 350; p < 0.002) and a significant increase in the maximum shear rate within the vessel lumen (189 ± 46 sec −1 vs 295 ± 8 sec −1, respectively; p < 0.05) in the region immediately upstream to the stenosis. These effects were less pronounced for Reynolds number 175. We conclude that stenosis inlet geometry has a significant impact on the flow conditions in the region immediately upstream to the stenosis, which is dependent on the Reynolds number. This may be an important determinant of thrombosis and atherogenesis in this particular region.