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

脑动脉瘤形态复杂多样，对血流结构影响很大。然而，直接测量体内血流的细节几乎是不可能的。模型试验更适合于对细部流动结构进行评价。在本研究中，我们建立了解剖学上真实的脑动脉瘤模型，测量了详细的血流结构，并讨论了脑动脉瘤的几何特征和血流结构对破裂的影响。基于计算机断层成像图像，采用光成形方法建立了真实的脑动脉瘤模型。通过设置雷诺数和频率参数，将母动脉内的血流波形完全模拟为脑动脉内的生理脉动血流。我们用粒子图像测速仪和激光多普勒测速仪测量了速度剖面。动脉瘤内血流分为两种模式。一种是沿壁面的单循环流动，另一种是由循环流动和气泡内的低速再循环流动组成。脑动脉瘤破裂模型为后一种血流模式。脑动脉瘤破裂模型的壁剪应力峰值为5.1 Pa，是所有模型中最高的。脑泡内的循环血流和高壁剪应力与脑动脉瘤破裂有关，其破裂主要受动脉瘤宽高比和颈母动脉面积比作为几何参数的影响。我们还比较了WSS的分布和动脉壁组织退行性变的程度，认为在分支局部看到的低壁剪切应力有助于退行性改变，随后形成脑动脉瘤。

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.