Kute S M, Vorp D A
Department of Surgery, University of Pittsburgh, PA 15213, USA.
J Biomech Eng. 2001 Jun;123(3):277-83. doi: 10.1115/1.1374203.
The formation of distal anastomotic intimal hyperplasia (IH), one common mode of bypass graft failure, has been shown to occur in the areas of disturbed flow particular to this site. The nature of theflow in the segment of artery proximal to the distal anastomosis varies from case to case depending on the clinical situation presented. A partial stenosis of a bypassed arterial segment may allow residual prograde flow through the proximal artery entering the distal anastomosis of the graft. A complete stenosis may allow for zero flow in the proximal artery segment or retrograde flow due to the presence of small collateral vessels upstream. Although a number of investigations on the hemodynamics at the distal anastomosis of an end-to-side bypass graft have been conducted, there has not been a uniform treatment of the proximal artery flow condition. As a result, direct comparison of results from study to study may not be appropriate. The purpose of this work was to perform a three-dimensional computational investigation to study the effect of the proximal artery flow condition (i.e., prograde, zero, and retrograde flow) on the hemodynamics at the distal end-to-side anastomosis. We used the finite volume method to solve the full Navier-Stokes equations for steady flow through an idealized geometry of the distal anastomosis. We calculated the flow field and local wall shear stress (WSS) and WSS gradient (WSSG) everywhere in the domain. We also calculated the severity parameter (SP), a quantification of hemodynamic variation, at the anastomosis. Our model showed a marked difference in both the magnitude and spatial distribution of WSS and WSSG. For example, the maximum WSS magnitude on the floor of the artery proximal to the anastomosis for the prograde and zero flow cases is 1.8 and 3.9 dynes/cm2, respectively, while it is increased to 10.3 dynes/cm2 in the retrograde flow case. Similarly, the maximum value of WSSG magnitude on thefloor of the artery proximal to the anastomosis for the prograde flow case is 4.9 dynes/cm3, while it is increased to 13.6 and 24.2 dynes/cm3, respectively, in the zero and retrograde flow cases. The value of SP is highest for the retrograde flow case (13.7 dynes/cm3) and 8.1 and 12.1 percent lower than this for the prograde (12.6 dynes/cm3) and zero (12.0 dynes/cm3) flow cases, respectively. Our model results suggest that the flow condition in the proximal artery is an important determinant of the hemodynamics at the distal anastomosis of end-to-side vascular bypass grafts. Because hemodynamic forces affect the response of vascular endothelial cells, the flow situation in the proximal artery may affect IH formation and, therefore, long-term graft patency. Since surgeons have some control over the flow condition in the proximal artery, results from this study could help determine which flow condition is clinically optimal.
远端吻合口内膜增生（IH）的形成是旁路移植失败的一种常见模式，已证实在该部位特定的血流紊乱区域会出现这种情况。取决于所呈现的临床情况，远端吻合口近端动脉段的血流性质因病例而异。旁路动脉段的部分狭窄可能使残余的顺行血流通过近端动脉进入移植血管的远端吻合口。完全狭窄可能导致近端动脉段血流为零，或者由于上游存在小的侧支血管而出现逆行血流。尽管已经对端侧旁路移植血管远端吻合口的血流动力学进行了多项研究，但对于近端动脉血流状况的处理并不统一。因此，不同研究结果之间的直接比较可能并不合适。这项工作的目的是进行三维计算研究，以探讨近端动脉血流状况（即顺行、零和逆行血流）对远端端侧吻合口血流动力学的影响。我们使用有限体积法求解完整的纳维 - 斯托克斯方程，以计算通过理想化远端吻合口几何形状的稳定血流。我们计算了整个区域内的流场、局部壁面切应力（WSS）和WSS梯度（WSSG）。我们还计算了吻合口处的严重程度参数（SP），它是血流动力学变化程度的一种量化指标。我们的模型显示，WSS和WSSG在大小和空间分布上都有显著差异。例如，顺行和零血流情况下，吻合口近端动脉底部的最大WSS大小分别为1.8和3.9达因/平方厘米，而在逆行血流情况下则增加到10.3达因/平方厘米。同样，顺行血流情况下，吻合口近端动脉底部的WSSG大小最大值为4.9达因/立方厘米，而在零血流和逆行血流情况下分别增加到13.6和24.2达因/立方厘米。逆行血流情况下的SP值最高（13.7达因/立方厘米），分别比顺行血流（12.6达因/立方厘米）和零血流（12.0达因/立方厘米）情况下低8.1%和12.1%。我们的模型结果表明，近端动脉中的血流状况是端侧血管旁路移植远端吻合口血流动力学的一个重要决定因素。由于血流动力学力会影响血管内皮细胞的反应，近端动脉中的血流情况可能会影响IH的形成，进而影响移植血管的长期通畅性。由于外科医生可以对近端动脉中的血流状况进行一定控制，本研究结果有助于确定哪种血流状况在临床上是最佳的。
