Finite-sized gas bubble motion in a blood vessel: non-Newtonian effects.
Finite-sized gas bubble motion in a blood vessel: non-Newtonian effects.
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DOI：
10.1103/physreve.78.036303
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发表时间：
2008-09
期刊：
影响因子：
--
通讯作者：
Eckmann DM
中科院分区：
文献类型：
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作者：
Mukundakrishnan K;Ayyaswamy PS;Eckmann DM
我们对有限尺寸的几乎闭塞的气泡通过在圆形横截面的血管中流动的剪切稀化卡森流体的轴对称运动进行了数值研究。数值求解需要求解两层流体模型——无细胞层和非牛顿核心以及气泡。这个问题引起了流变学领域和健康科学气体栓塞研究的兴趣。数值方法基于改进的前向跟踪方法。血液（散装液体）Casson 模型中的粘度表达式包括血细胞比容 [红细胞 (RBC) 的体积分数] 作为显式参数。研究了 0.2、2 和 200 附近的三种不同的流动雷诺数 Reapp=ρlUmaxd/μapp。式中，ρl 为血液密度，Umax 为入口 Casson 剖面中心线速度，d 为血管直径，μapp 为全血表观粘度。还考虑了三种不同的血细胞比容：0.45、0.4 和 0.335。所考虑的血管尺寸对应于正常人的小动脉以及小动脉和大动脉。气泡闭塞程度用气泡与血管半径之比（长径比）λ来表征，范围为0.9≤λ≤1.05。对于动脉血流，在相关的情况下，会考虑 Fahraeus-Lindqvist 效应。水平和垂直容器的几何形状都已被研究。我们的研究揭示了许多重要的见解：（i）当气泡接近细胞、在其上方移动并通过时，气泡运动会在血管壁内衬的“内皮细胞”（EC）表面产生大的时间和空间剪切应力梯度； (ii) 气泡运动过程中施加到细胞表面的剪切应力 (+ → − → +) 的符号发生快速反转； (iii) 大的剪切应力梯度和符号反转可归因于气泡后部再循环涡流的发展； (iv)计算出的剪切应力梯度的大小及其符号反转可能对应于通过脉冲压缩和拉伸造成膜破裂而导致细胞损伤的水平； (v) 对于所研究的容器尺寸和流速，重力影响可以忽略不计。
We have numerically investigated the axisymmetric motion of a finite-sized nearly occluding air bubble through a shear-thinning Casson fluid flowing in blood vessels of circular cross section. The numerical solution entails solving a two-layer fluid model—a cell-free layer and a non-Newtonian core together with the gas bubble. This problem is of interest to the field of rheology and for gas embolism studies in health sciences. The numerical method is based on a modified front-tracking method. The viscosity expression in the Casson model for blood (bulk fluid) includes the hematocrit [the volume fraction of red blood cells (RBCs)] as an explicit parameter. Three different flow Reynolds numbers, Reapp=ρlUmaxd/μapp, in the neighborhood of 0.2, 2, and 200 are investigated. Here, ρl is the density of blood, Umax is the centerline velocity of the inlet Casson profile, d is the diameter of the vessel, and μapp is the apparent viscosity of whole blood. Three different hematocrits have also been considered: 0.45, 0.4, and 0.335. The vessel sizes considered correspond to small arteries, and small and large arterioles in normal humans. The degree of bubble occlusion is characterized by the ratio of bubble to vessel radius (aspect ratio), λ, in the range 0.9≤λ≤1.05. For arteriolar flow, where relevant, the Fahraeus-Lindqvist effects are taken into account. Both horizontal and vertical vessel geometries have been investigated. Many significant insights are revealed by our study: (i) bubble motion causes large temporal and spatial gradients of shear stress at the “endothelial cell” (EC) surface lining the blood vessel wall as the bubble approaches the cell, moves over it, and passes it by; (ii) rapid reversals occur in the sign of the shear stress (+ → − → +) imparted to the cell surface during bubble motion; (iii) large shear stress gradients together with sign reversals are ascribable to the development of a recirculation vortex at the rear of the bubble; (iv) computed magnitudes of shear stress gradients coupled with their sign reversals may correspond to levels that cause injury to the cell by membrane disruption through impulsive compression and stretching; and (v) for the vessel sizes and flow rates investigated, gravitational effects are negligible.