Toshiba Stroke Research Center, University at Buffalo, State University of New York, Buffalo, New York 14214, USA.
J Neurointerv Surg. 2012 Sep;4(5):351-7. doi: 10.1136/neurintsurg-2011-010089. Epub 2011 Sep 19.
Computational fluid dynamics (CFD) simulations of intracranial aneurysm hemodynamics usually adopt the simplification of the Newtonian blood rheology model. A study was undertaken to examine whether such a model affects the predicted hemodynamics in realistic intracranial aneurysm geometries.
Pulsatile CFD simulations were carried out using the Newtonian viscosity model and two non-Newtonian models (Casson and Herschel-Bulkley) in three typical internal carotid artery saccular aneurysms (A, sidewall, oblong-shaped with a daughter sac; B, sidewall, quasi-spherical; C, near-spherical bifurcation). For each aneurysm model the surface distributions of shear rate, blood viscosity and wall shear stress (WSS) predicted by the three rheology models were compared.
All three rheology models produced similar intra-aneurysmal flow patterns: aneurysm A had a slowly recirculating secondary vortex near the dome whereas aneurysms B and C contained only a large single vortex. All models predicted similar shear rate, blood viscosity and WSS in parent vessels of all aneurysms and in the sacs of B and C. However, large discrepancies in shear rate, viscosity and WSS among predictions by the various rheology models were found in the dome area of A where the flow was relatively stagnant. Here the Newtonian model predicted higher shear rate and WSS values and lower blood viscosity than the two non-Newtonian models.
The Newtonian fluid assumption can underestimate viscosity and overestimate shear rate and WSS in regions of stasis or slowly recirculating secondary vortices, typically found at the dome in elongated or complex-shaped saccular aneurysms as well as in aneurysms following endovascular treatment. Because low shear rates and low WSS in such flow conditions indicate a high propensity for thrombus formation and rupture, CFD based on the Newtonian assumption may underestimate the propensity of these events.
颅内动脉瘤血流动力学的计算流体动力学（CFD）模拟通常采用牛顿血流流变学模型的简化。本研究旨在探讨该模型是否会影响真实颅内动脉瘤几何形状下的预测血流动力学。
采用牛顿粘度模型和两种非牛顿模型（卡森和赫谢尔-布尔克利）对三个典型颈内动脉囊状动脉瘤（A，侧壁，长椭圆形伴子囊；B，侧壁，近球形；C，近球形分叉）进行脉动 CFD 模拟。比较了三种流变模型预测的每个动脉瘤模型表面剪切率、血液粘度和壁面剪切应力（WSS）分布。
所有三种流变模型都产生了相似的瘤内流动模式：动脉瘤 A 在瘤顶附近有一个缓慢再循环的二级涡流，而动脉瘤 B 和 C 只包含一个大的单一涡流。所有模型在所有动脉瘤的母血管和 B 和 C 的囊中预测了相似的剪切率、血液粘度和 WSS。然而，在 A 瘤顶区域，流动相对停滞，各种流变模型的预测剪切率、粘度和 WSS 存在较大差异。在该区域，牛顿模型预测的剪切率和 WSS 值较高，血液粘度较低。
牛顿流体假设可能低估停滞或缓慢再循环二级涡流区域的粘度，并高估剪切率和 WSS，这些区域通常位于长形或复杂形状的囊状动脉瘤的瘤顶以及血管内治疗后的动脉瘤中。由于这种流动条件下的低剪切率和低 WSS 表明血栓形成和破裂的倾向较高，基于牛顿假设的 CFD 可能低估了这些事件的倾向。
