Ghent University, IBiTech-bioMMeda, Belgium.
J Biomech. 2013 Jan 18;46(2):345-53. doi: 10.1016/j.jbiomech.2012.10.027. Epub 2012 Nov 13.
Although arterio-venous grafts (AVGs) are the second best option as long-term vascular access for hemodialysis, they suffer from complications caused by intimal hyperplasia, mainly located in vessel regions of low and oscillating wall shear stress. However, certain flow patterns in the bulk may reduce these unfavorable hemodynamic conditions. We therefore studied, with computational fluid dynamics (CFD), the impact of a helical AVG design on the occurrence of (un)favorable hemodynamic conditions at the venous anastomosis. Six CFD-models of an AVG in closed-loop configuration were constructed: one conventional straight graft, and five helical designed grafts with a pitch of 105 mm down to 35 mm. At the venous anastomosis, disturbed shear was assessed by quantifying the area with unfavorable conditions, and by analyzing averaged values in a case-specific patch. The bulk hemodynamics were assessed by analyzing the kinetic helicity in and the pressure drop over the graft. The most helical design scores best, being instrumental to suppress disturbed shear in the venous segment. There is, however, no trivial relationship between the number of helix turns of the graft and disturbed shear in the venous segment, when a realistic closed-loop AVG model is investigated. Bulk flow investigation showed a marked increase of helicity intensity in, and a moderate pressure drop over the AVG by introducing a lower pitch. At the venous anastomosis, unfavorable hemodynamic conditions can be reduced by introducing a helical design. However, due to the complex flow conditions, the optimal helical design for an AVG cannot be derived without studying case by case.
尽管动静脉移植物（AVG）是长期血液透析血管通路的第二选择，但它们会因内膜增生而导致并发症，主要发生在壁切应力低和波动的血管区域。然而，在体部的某些流动模式可能会减轻这些不利的血液动力学条件。因此，我们使用计算流体动力学（CFD）研究了 AVG 的螺旋设计对静脉吻合处（不利）血流动力学条件发生的影响。构建了闭环配置中 AVG 的六个 CFD 模型：一个常规的直移植物，和五个螺旋设计的移植物，螺距从 105mm 降低到 35mm。在静脉吻合处，通过量化具有不利条件的区域和分析特定补丁中的平均值来评估受扰剪切。通过分析移植物内部的动螺旋强度和压降来评估体部血液动力学。最具螺旋特征的设计得分最高，有助于抑制静脉段的受扰剪切。然而，当研究现实的闭环 AVG 模型时，螺旋移植物的匝数与静脉段的受扰剪切之间没有简单的关系。体部流动研究表明，通过引入较低的螺距，移植物内部的螺旋强度显着增加，并且压降适中。通过引入螺旋设计，可以减少静脉吻合处的不利血流动力学条件。然而，由于流动条件复杂，因此在没有逐个研究的情况下，无法为 AVG 推导出最佳的螺旋设计。
