Department of Neurosurgery, Sapporo Kita Neurosurgical Clinic, Sapporo, Japan.
J Neurosurg. 2010 Oct;113(4):810-9. doi: 10.3171/2010.1.JNS09575.
The authors conducted a study to elucidate the relationship between the flow patterns and the formation of aneurysms at the bifurcation of the basilar artery (BA).
Six isolated, transparent vertebrobasilar arterial systems were prepared from humans postmortem, and flow patterns and velocity distributions were studied in detail using flow visualization and cinemicrographic techniques.
The authors found that if the diameters of 2 vertebral arteries (VAs) were nearly equal and they formed a symmetrical inverted Y-shaped junction with the BA, the BA flow was also symmetrical. The fluid elements that flowed into the BA from 2 VAs traveled almost parallel to the vessel wall of the BA without mixing with each other, and then they flowed out through ipsilateral superior cerebellar and posterior cerebral arteries. In contrast to this, if the diameters of 2 VAs were very different or the BA was badly bent, the BA flow was disturbed as a result of the formation of swirling and secondary flows. The approaching velocity profile at the BA's terminal bifurcation was flattened if the inverted Y-junction was symmetrical, and it was sharpened if the junction was asymmetrical. Thus, in the latter case, fluid elements impinged on the vessel wall around the flow divider of the bifurcation with much larger velocities and, hence, larger kinetic energy, compared with the case of a symmetrical inverted Y-junction, exerting high fluid pressures, wall shear stresses, and wall tensions on the vessel wall there.
The symmetrical structure of the inverted Y-junction in a normal vertebrobasilar arterial system provides a flattened approaching velocity profile at the terminal bifurcation of the BA, lowering the hemodynamic stresses (pressure, tension, and shear stress) exerted on the wall of the bifurcation. This may account for the relatively low incidence of aneurysm formation at this site.
作者进行了一项研究，阐明基底动脉（BA）分叉处的血流模式与动脉瘤形成之间的关系。
从人死后的尸体中准备了 6 个分离的透明椎基底动脉系统，并使用流动可视化和电影显微技术详细研究了流动模式和速度分布。
作者发现，如果两个椎动脉（VA）的直径几乎相等，并且它们与 BA 形成对称的倒置 Y 形连接，那么 BA 的流动也是对称的。从两个 VA 流入 BA 的流体质点几乎与 BA 血管壁平行流动，彼此之间没有混合，然后通过同侧小脑上后动脉流出。相比之下，如果两个 VA 的直径相差很大或 BA 严重弯曲，由于漩涡和二次流的形成，BA 的流动会受到干扰。如果倒置 Y 形连接是对称的，那么 BA 末端分叉处的接近速度分布会变平，如果连接是不对称的，那么速度分布会变尖。因此，在后一种情况下，流体质点以比对称倒置 Y 形连接时更大的速度撞击分叉处的流动分配器周围的血管壁，因此具有更大的动能，对那里的血管壁施加更高的流体压力、壁切应力和壁张力。
正常椎基底动脉系统中倒置 Y 形连接的对称结构在 BA 的末端分叉处提供了扁平的接近速度分布，降低了分叉处壁上的血流动力学应力（压力、张力和切应力）。这可能是该部位动脉瘤形成相对较低的原因。
