Palmen D E, van de Vosse F N, Janssen J D, van Dongen M E
Department of Mechanical Engineering, Eindhoven University of Technology, The Netherlands.
J Biomech. 1994 May;27(5):581-90. doi: 10.1016/0021-9290(94)90067-1.
This paper deals with the effect of geometric changes of mild stenoses on large-scale flow disturbances in the carotid artery bifurcation. Hydrogen-bubble visualisation experiments have been performed in Plexiglas models of a non-stenosed and a 25% stenosed carotid artery bifurcation. The flow conditions approximate physiological flow. The experiments show that shortly after the onset of the diastolic phase vortex formation occurs in the plane of symmetry. This vortex formation is found in a shear layer, which is formed in the carotid sinus. The shear layer is located between a region with low shear rates at the non-divider wall and a region with high shear rates at the divider wall. In order to gain insight into the parameters that are important with respect to the stability of the shear layer, experiments have been performed in which the influence of the shape of the flow pulse, the Reynolds number (Re), the Womersley parameter (alpha) and the flow division ratio (gamma) on the flow phenomena is studied. From these experiments it appears that the flow phenomena in the carotid artery bifurcation are significantly influenced by Re, alpha the systolic acceleration (sa) and deceleration (sd) and the duration of the peak-systolic flow (Tmax). With these results a simplified flow pulse is chosen, with which the experiments in the non-stenosed and the 25% stenosed bifurcation are performed. Comparison of the hydrogen-bubble profiles in the 0 and 25% stenosed models with similar flow conditions shows that the geometric change of the 25% stenosis only slightly influences the flow phenomena. The most striking influences are found in the stability of the shear layer. Quantitative experiments by means of laser Doppler anemometry measurements and numerical computations are needed to analyse the influence of the stenosis of the flow field more accurately.
本文研究了轻度狭窄的几何变化对颈动脉分叉处大规模流动扰动的影响。在无狭窄和25%狭窄的颈动脉分叉的有机玻璃模型中进行了氢气泡可视化实验。流动条件近似生理流动。实验表明，在舒张期开始后不久，对称平面内就会形成涡旋。这种涡旋形成发生在一个剪切层中，该剪切层在颈动脉窦中形成。剪切层位于非分隔壁处低剪切率区域和分隔壁处高剪切率区域之间。为了深入了解与剪切层稳定性相关的重要参数，进行了实验，研究了流动脉冲形状、雷诺数（Re）、沃默斯利参数（α）和分流比（γ）对流动现象的影响。从这些实验可以看出，颈动脉分叉处的流动现象受Re、α、收缩期加速度（sa）、减速度（sd）和收缩期峰值血流持续时间（Tmax）的显著影响。基于这些结果，选择了一个简化的流动脉冲，并据此在无狭窄和25%狭窄的分叉处进行了实验。对具有相似流动条件的0%和25%狭窄模型中的氢气泡轮廓进行比较表明，25%狭窄的几何变化仅对流动现象有轻微影响。最显著的影响体现在剪切层的稳定性上。需要通过激光多普勒测速测量和数值计算进行定量实验，以更准确地分析狭窄对流场的影响。
