The Prospective Study on the macro-microscopic intra-aneurysmal flow causing the rupture

脑动脉瘤形态复杂多样，对血流结构有很大影响。然而，几乎不可能直接详细测量体内血流。而模型试验更适合于评估详细的水流结构。本研究建立了具有解剖学真实感的脑动脉瘤模型，测量了动脉瘤的血流结构，讨论了动脉瘤的几何特征和血流结构对破裂的影响，并基于CT图像采用光成形方法建立了具有真实感的脑动脉瘤模型。通过设置雷诺数和频率参数，将载瘤动脉内的血流波形完全模拟为脑动脉内的生理脉动流。我们用粒子图像测速仪和激光多普勒测速仪测量了动脉瘤内的流速分布，并将动脉瘤内的血流分为两种模式。一种是由沿着壁面的单循环流组成，另一种是由循环流和气泡内的低速回流组成。破裂脑动脉瘤模型为后一种流型。此外，破裂脑动脉瘤模型的壁面切应力峰值为5.1 Pa，是所用模型中最高的。脑动脉瘤破裂与滤过泡内的再循环血流和高切应力有关，主要受动脉瘤和瘤颈的长宽比影响，我们还比较了WSS的分布和动脉壁组织的退变程度，并认为分叉局部的低壁切应力有助于动脉壁组织的退变。脑动脉瘤形成后的变化。

Cerebral aneurysms have a variety of complicated shapes, and it greatly influences on blood flow structure. However, it is almost impossible to measure directly in vivo blood flow in detail. Instead, model experiment would be more appropriate to evaluate the detailed flow structure. In our present study, we built anatomically realistic models of cerebral aneurysm, measured detailed flow structure, and discussed the influence of geometric features and blood flow structure of cerebral aneurysms on the rupture.We built realistic cerebral aneurysm models by photoforming method based on computed tomography images. The flow waveform in the parent arteries was completely simulated to the physiological pulsatile flow in cerebral arteries by setting Reynolds number and frequency parameter. We measured velocity profiles with particle image velocimetry and laser Doppler velocimeter.Intra-aneurysmal flow was classified into two patterns. One consists of single circulating flow along the wall, and the other consists of circulating flow and low-velocity recirculating flow in bleb. Ruptured cerebral aneurysm model had the latter flow pattern. Furthermore, wall shear stress had a peak of 5.1 Pa in the ruptured cerebral aneurysms model, which was the highest in the employed models. The recirculating flow and high wall shear stress in bleb seem to be associated with the rupture of cerebral aneurysms, and that was influenced mainly by aspect ratio of aneurysm and neck-parent artery area ratio as a geometric parameter.We also compared the distribution of WSS and the extent of degeneration of arterial wall tissues and suggested that low wall shear stress seen in the local portion of the bifurcation contributed to the degenerative changes followed by formation of cerebral aneurysms.