Perktold Karl, Leuprecht Armin, Prosi Martin, Berk Thomas, Czerny Martin, Trubel Wolfgang, Schima Heinrich
Institute of Mathematics, Graz University of Technology, Austria.
Ann Biomed Eng. 2002 Apr;30(4):447-60. doi: 10.1114/1.1477445.
Intimal hyperplasia at vascular anastomoses seems to be promoted by altered flow conditions and stress distributions within the anastomotic region. In order to gain deeper insight into postoperative disease processes, and subsequently, to contribute to the development of improved vascular reconstructions, detailed studies, also on local flow dynamics and related mass transport and wall mechanical effects, are required. In context with in vivo studies, computer simulation based on casts of femoro-popliteal bypasses implanted into sheep were performed to analyze the flow dynamics, the oxygen transport, and the wall and suture mechanics in anatomically correct bypass configurations related to three established surgical techniques and resulting geometries (conventional type anastomosis, Taylor-patch and Miller-cuff anastomoses with venous interposition grafts of different modifications). The influence of geometry, compliance of the graft, the interponated vein patch and vein cuff, and of the artery was included. Time-dependent, three-dimensional Navier-Stokes equations describing the flow field, and a nonlinear shell structure for the vessel walls were coupled using finite element methods. The numerical results demonstrate nonphysiological flow patterns in the anastomotic region. Strongly skewed axial velocity profiles and secondary velocities occur in the junction region. In the Miller-cuff a vortex may induce a wash-out effect which protects the host artery. On the artery floor opposite the junction flow separation and zones of recirculation were found. The analysis of oxygen transport illustrates a correlation between zones of low wall shear stress and reduced oxygen flux into the wall. Wall mechanics show that increased compliance mismatch leads to increased and discontinuous intramural stresses. Comparison to histomorphological findings on intimal hyperplasia shows certain correlations, particularly increased compliance mismatch has a proliferate influence on suture line hyperplasia. The reduction of compliance mismatch using vein interposition results in decreased generation of intimal hyperplasia, and therefore, contributes to improvement of patency rates, while the geometrical modification and the resulting change of the flow pattern seems to be less important for the growth of anastomotic intimal hyperplasia.
血管吻合处的内膜增生似乎是由吻合区域内改变的血流状况和应力分布所促进的。为了更深入地了解术后疾病过程，并进而为改进血管重建的发展做出贡献，需要进行详细的研究，包括局部血流动力学、相关的质量传输和壁面力学效应。结合体内研究，基于植入绵羊的股腘动脉旁路移植模型进行计算机模拟，以分析与三种既定手术技术及相应几何形状（传统型吻合、泰勒补片和米勒袖套吻合，以及不同改良的静脉间置移植）相关的解剖学正确旁路构型中的血流动力学、氧输送以及壁面和缝合力学。研究包括了几何形状、移植物顺应性、间置静脉补片和静脉袖套以及动脉的影响。使用有限元方法耦合描述流场的时间相关三维纳维 - 斯托克斯方程和血管壁的非线性壳结构。数值结果表明吻合区域存在非生理性血流模式。在交界区域出现强烈倾斜的轴向速度剖面和二次速度。在米勒袖套中，一个涡流可能会产生冲刷效应，从而保护宿主动脉。在与交界相对的动脉底部发现了血流分离和再循环区域。氧输送分析表明低壁面切应力区域与进入壁面的氧通量减少之间存在相关性。壁面力学表明顺应性失配增加会导致壁内应力增加且不连续。与内膜增生的组织形态学结果比较显示出一定的相关性，特别是顺应性失配增加对缝合线增生有增殖影响。使用静脉间置减少顺应性失配会导致内膜增生的产生减少，因此有助于提高通畅率，而几何形状的改变以及由此产生的血流模式变化对于吻合口内膜增生的生长似乎不太重要。
