Hofer M, Rappitsch G, Perktold K, Trubel W, Schima H
Institute of Mathematics, Technical University of Graz, Austria.
J Biomech. 1996 Oct;29(10):1297-308. doi: 10.1016/0021-9290(96)00036-x.
In order to analyse the wall mechanics and the flow dynamics in compliant vascular distal end-to-side anastomoses, computer simulation has been performed. In a model study the effect of compliance mismatch on the wall displacements and on the intramural stresses as well as the influence of wall distensibility on the flow patterns are demonstrated applying two distensible models with different graft elasticity. In addition, the flow in a rigid model simulating a vein graft without adaption of the venous lumen has been investigated. The geometries for these models were obtained from a concurrent experimental study, where the formation of distal anastomotic intimal hyperplasia (DAIH) was studied in untreated and externally stiffened autologous venous grafts in sheep. In the flow study the time-dependent, three-dimensional Navier-Stokes equations describing the motion of an incompressible Newtonian fluid are applied. The vessel wall is modelled using a geometrically non-linear shell structure. In an iteratively coupled approach the transient shell equations and the governing fluid equations are solved numerically using the finite element method. In both compliant models maximum displacement and areas of steep stress gradients are observed in the junction region along the graft-artery intersection. The comparison of the normal deformations and the distribution and magnitude of intramural stress shows quantitative differences. The graft elasticity acts as a regulating factor for the deformability and the stress concentration in the junction area: In the model with high graft-elasticity maximum normal deformation at the side wall is 17%. This is twice as large as in the stiff graft model and maximum principle stress at the inner surface differs by one order of magnitude. The numerical results concerning the flow patterns indicate strongly skewed axial velocity profiles downstream of the junction, large secondary motion, flow separation and recirculation on the artery floor opposite the junction and at the inner wall downstream of the toe. In these regions a correlation between the time-averaged fluid wall shear stress and intimal thickening found in the animal experiment can be observed, whereas the pronounced formation of DAIH at the suture line seems to be mainly dependent on wall mechanical factors such as intramural stress and strain.
为了分析顺应性血管远端端侧吻合术中的血管壁力学和血流动力学，进行了计算机模拟。在一项模型研究中，应用两个具有不同移植物弹性的可扩张模型，展示了顺应性不匹配对血管壁位移和壁内应力的影响，以及血管壁可扩张性对血流模式的影响。此外，还研究了模拟未适应静脉腔的静脉移植物的刚性模型中的血流。这些模型的几何形状来自一项同期实验研究，该研究在绵羊未处理和外部加固的自体静脉移植物中研究了远端吻合口内膜增生（DAIH）的形成。在血流研究中，应用了描述不可压缩牛顿流体运动的随时间变化的三维纳维 - 斯托克斯方程。血管壁采用几何非线性壳结构进行建模。采用迭代耦合方法，使用有限元法对瞬态壳方程和控制流体方程进行数值求解。在两个顺应性模型中，沿移植物 - 动脉交叉处的连接区域均观察到最大位移和陡峭应力梯度区域。正常变形以及壁内应力的分布和大小的比较显示出定量差异。移植物弹性是连接区域变形能力和应力集中的调节因素：在高移植物弹性模型中，侧壁处的最大正常变形为17%。这是硬移植物模型中的两倍，内表面的最大主应力相差一个数量级。关于血流模式的数值结果表明，在连接下游轴向速度剖面强烈倾斜，在连接对面的动脉底部和趾部下游的内壁处有大的二次运动、流动分离和再循环。在这些区域，可以观察到动物实验中发现的时间平均流体壁面剪应力与内膜增厚之间的相关性，而缝合线处明显的DAIH形成似乎主要取决于壁力学因素，如壁内应力和应变。
