心血管支架設計與血管幾何形狀對血流動力學的影響

心血管支架為一項微型醫療器材，於施行氣球擴張術後，將血管支架部署於血管中，以其徑向強度維持血管管徑，恢復血流暢通性。目前血管支架手術已經成為心血管疾病的主要治療方式，並提供其他周邊血管病變治療新的選擇。然而，手術後仍有血管再狹窄化的風險。相關研究顯示，支架設計與血管幾何於血管再狹窄化的過程中扮演相當重要的角色。動脈粥狀硬化一般好發於較不利的血流動力學環境中，例如過低的血管壁面剪應力、剪應力方向震盪與回流生成區，這些位置也有較高的血管內膜增生現象。本研究在第一部分建立血管支架部署於直管及彎曲血管的計算流體力學模型，探討支架設計與血管幾何對於剪應力分布的影響；第二部分以頸動脈與腎動脈血管模型討論恆定流、脈動流、休息生理以及運動生理對於血流動力學的影響。研究結果顯示，血管支架設計對於血流動力學的影響並不顯著，然而部署血管支架於彎曲血管後，將使低剪應力面積上升。當血管彎曲角度自0°上升至90°時，低剪應力面積增加至原先的2倍，顯示支架部署於彎曲曲率越高的血管，有越高的血管再狹窄化風險。第二部分的頸動脈模型顯示，血管支架的部署同時影響到內、外頸動脈的流場分布。血液流至血管分岔處時，在兩者彎曲內側壁面產生回流區，造成剪應力下降與方向震盪，有較高的機率發生血管病變。至於腎動脈在休息生理與運動生理則呈現極為不同的血流動力學表現，其中影響的參數相當多，包含血管支架對於流場的干擾、血管彎曲幾何、分支血管角度、分支血管間的流場交互作用與脈動流流場分布形式等，任一項參術的變化都會影響到流場的表現。在脈動流流場部分，頸動脈與腎動脈的低剪應力面積與流量變化呈現時間差的反應，而恆定流分析所提供的資訊與結果具有一定的參考價值，但更貼近真實人體的研究仍以非牛頓流體與脈動流分析為佳。本研究所提供的方法與結論可協助血管支架的設計改良與醫事人員進行術前評估，以期降低術後血管再狹窄率並且達到最佳療效。

關鍵字

血管再狹窄；血管壁面剪應力；血管支架設計；血流動力學；彎曲血管；脈動流；剪應力方向震盪

並列摘要

Stents are miniature medical devices that can be inserted into arteries and expanded during angioplasty to maintain patency and re-establish flow through the vessel. They have been the primary treatment for cardiovascular diseases and the alternative treatment for various peripheral arterial occlusive lesions. However, after stenting, potential risks associated with restenosis may occur, and several studies have shown that stent design and artery geometry could be the critical factors in this process. The location of atherosclerotic lesion prone regions are subjected to abnormal hemodynamic behavior, such as low wall shear stress, oscillations in shear directions and flow recirculation where are also susceptible to intimal thickening. In this study, computational fluid dynamics models were established to investigate the effects of cardiovascular stent design on the wall shear stress distribution in straight and curved arteries in the first section. The model of stented carotid artery and renal artery were developed to study the hemodynamic behavior under steady flow, pulsatile flow, resting and exercise condition in the second section. Results showed that the stent design pattern alone did not have a significant impact on stent hemodynamics; however, stenting in curved arteries increased the low shear stress area which may lead to a higher restenosis rate. The total surface area of low wall shear stress almost doubled when the angle of artery curvature increased from 0° to 90° implied that stenting in a tortuous artery greatly increases the risk of restenosis. In the carotid artery simulation, the implantation of stent induced alterations of physiologic flow behavior in both internal and external carotid arteries. Flow through carotid bifurcation exhibited recirculation zone on the wall of inner curved in both carotid arteries, and these regions experienced low wall shear stress and oscillations in shear directions that are prone to lesions. In the renal artery simulation, hemodynamics behavior is quite different under resting and exercise conditions. However, since the parameters which affect the results are many, changes (e.g. stent-induced flow disturbance, curvature, angle, low interaction among branches, flow structures generated during the cycle, etc.) in these parameters may alter the flow patterns and wall shear stress distribution. In both carotid artery and renal artery model showed the time delay between low shear stress area and flow rate might be caused by aforementioned parameters. The flow features and results are still believed to be informative under steady flow simulation; however, more realistic studies should be conducted with non-Newtonian fluid and pulsatile flow. The proposed methodology and findings will provide great insight for the future design optimization and physician practice to help achieve the best possible clinical outcomes.

並列關鍵字

Restenosis ； Wall shear stress ； Cardiovascular stent design ； Hemodynamics ； Curved arteries ； Pulsatile flow ； Oscillations in shear directions

參考文獻

1. Sousa J.E., Serruys P.W., Costa M.A., “New frontiers in cardiology: drug-eluting stents: Part I”, Circulation. 2003; 107: 2274-9.

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3. Yadav J.S., Wholey M.H., Kuntz R.E., et al., “Protected carotid-artery stenting versus endarterectomy in high-risk patients”, N. Engl. J. Med.2004;351:1493-501.

4. Prinssen M., Verhoeven E.L., Buth J., et al., “A randomized trial comparing conventional and endovascular repair of abdominal aortic aneurysms”, N. Engl. J. Med.2004;351:1607-18.

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心血管支架設計與血管幾何形狀對血流動力學的影響

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