Lei M, Giddens D P, Jones S A, Loth F, Bassiouny H
Department of Biomedical Engineering, The Johns Hopkins University, Baltimore, MD 21205, USA.
J Biomech Eng. 2001 Feb;123(1):80-7. doi: 10.1115/1.1336145.
Various hemodynamic factors have been implicated in vascular graft intimal hyperplasia, the major mechanism contributing to chronic failure of small-diameter grafts. However, a thorough knowledge of the graft flow field is needed in order to determine the role of hemodynamics and how these factors affect the underlying biological processes. Computational fluid dynamics offers much more versatility and resolution than in vitro or in vivo methods, yet computations must be validated by careful comparison with experimental data. Whereas numerous numerical and in vitro simulations of arterial geometries have been reported, direct point-by-point comparisons of the two techniques are rare in the literature. We have conducted finite element computational analyses for a model of an end-to-side vascular graft and compared the results with experimental data obtained using laser-Doppler velocimetry. Agreement for velocity profiles is found to be good, with some clear differences near the recirculation zones during the deceleration and reverse-flow segments of the flow waveform. Wall shear stresses are determined from velocity gradients, whether by computational or experimental methods, and hence the agreement for this quantity, while still good, is less consistent than for velocity itself from the wall shear stress numerical results, we computed four variables that have been cited in the development of intiimal hyperplasia-the time-averaged wall shear stress, an oscillating shear index, and spatial and temporal wall shear stress gradients in order to illustrate the versatility of numerical methods. We conclude that the computational approach is a valid alternative to the experimental approach for quantitative hemodynamic studies. Where differences in velocity were found by the two methods, it was generally attributed to the inability of the numerical method to model the fluid dynamics when flow conditions are destabilizing. Differences in wall shear, in the absence of destabilizing phenomena, were more likely to be caused by difficulties in calculating wall shear from relatively low resolution in vitro data.
多种血流动力学因素与血管移植物内膜增生有关，内膜增生是导致小口径移植物慢性功能衰竭的主要机制。然而，为了确定血流动力学的作用以及这些因素如何影响潜在的生物学过程，需要全面了解移植物的流场。与体外或体内方法相比，计算流体动力学具有更高的通用性和分辨率，但计算结果必须通过与实验数据的仔细比较来验证。虽然已经报道了许多关于动脉几何形状的数值模拟和体外模拟，但在文献中很少有这两种技术的直接逐点比较。我们对端侧血管移植物模型进行了有限元计算分析，并将结果与使用激光多普勒测速仪获得的实验数据进行了比较。发现速度剖面的一致性良好，在流动波形的减速和逆流段，再循环区域附近存在一些明显差异。壁面剪应力由速度梯度确定，无论是通过计算方法还是实验方法，因此对于这个量的一致性虽然仍然良好，但不如速度本身的一致性。根据壁面剪应力数值结果，我们计算了在内膜增生发展过程中被引用的四个变量——时间平均壁面剪应力、振荡剪应力指数以及空间和时间壁面剪应力梯度，以说明数值方法的通用性。我们得出结论，对于定量血流动力学研究，计算方法是实验方法的一种有效替代方法。当两种方法发现速度存在差异时，通常归因于在流动条件不稳定时数值方法无法对流体动力学进行建模。在没有不稳定现象的情况下，壁面剪应力的差异更可能是由于从相对低分辨率的体外数据计算壁面剪应力存在困难所致。
