血管繞道手術揷接處流場受接合角度影響之數值研究

A Numerical Study of Arterial Flow Field in Distal End-to-Side Anastomoses for Different Anastomotic Angles

鄧志浩(Jyh-Haw Tang)

《中原學報》 28卷1期 (2000/03) Pp. 31-42

https://doi.org/10.6358/JCYU.200003.0031

摘要

執行血管繞道插接(arterial bypass graft)手術後，在插接處的尾端，臨床上常常發現血液流場容易發生異常現象。血管在插接處附近會因內膜增生而再度造成血管封閉，因而導致手術失敗。所以詳細了解人體血管插接處附近流場所造成的影響是十分重要的。本研究希望能藉由數値計算以有限元素方法，分析人工插接血管在不同角度接合模式的流場。研究中考慮流場爲週期及非穩態，並分別考慮二維及三維之幾何形狀。分析結果顯示：血管插接處附近的流場，因爲幾何形狀的改變，容易產生異常的流況；而且血管接合角度愈大，愈容易產生迴流域，壁剪應力變化也較爲劇烈。研究中發現，在不同的接合角度下，以三維模式分析在血管壁所承受的壁剪應力都較以二維模式分析所承受的壁剪應力爲大，其變化也較二維流場複雜；且在三維模式的非穩態流場中，有明顯的二次流存在，這亦是造成壁剪應力値變化劇烈的原因。而這些異常流況可能是導致內膜增生，造成血管內壁再度阻塞的原因。所以二維流場模擬所得之結果並不能完全取代三維流場之現象。分析三維非穩態的流場，結果發現迴流域內伴隨低壁剪應力、高壁剪應力變化及二次流渦流中心的位置等皆可能爲影響內膜增生之原因。同時愈小的接合角度對於防止內膜增生愈有利。

關鍵字

血管繞道揷接 ； 人工揷接血管 ； 內膜增生 ； 壁剪應力 ； 二次流

並列摘要

After the surgery of arterial bypass graft, the restenosis due to distal anastomotic intimal hyperplasia usually cause the failure of surgery again. The purpose of this study is to understand the possible role that hemodynamic effects may play in the end-to-side anastomosis by numerical finite element method. Pulsatile flow (femoral flow waveform) behavior in both two-dimensional (2-D) and three-dimensional (3-D) end-to-side anastomoses with four different anastomotic angles: 15, 30, 45, and 60 was simulated. Formodel verification, the simulated steady flow fields were compared and shown to match well with the general features of the experimental measurements. Based on the flow distributions, it was shown that the low shear stress in the recirculating area, high spatial gradient of shear stress; andthe variations of the secondary flow along the host artery might cause the intimal hyperplasia. It was shown that a bigger recirculating area, where known to be prone to intimal hyperplsia for longer residence times, in the distal anastomosis was accompanied with larger anastomotic angels; and more acute angel should be better for preventing the intimal thickening. The results of both 2-D and 3-D models showed larger shear stress at the heel and toe of the anastomoses; and along the floor opposite the anastomosis. By comparing the wall shear stress distributions between 2-D and 3-D models, it demonstrated the result obtained from 2-D model was underestimated. The secondary flow existing in the 3-D model under pulsatile flow may play some important roles on the high spatial gradient of shear stress. It is concluded that the numerical simulation of 3-D model should be more realistic than that of 2-D.

並列關鍵字

Arterial Bypass graft ； end-to-side anastomoses ； intimal hyperplasia ； wall shear stress ； secondary flow