血管支架設計對血液動力學之影響

Effect of Stent Design on Intra-stent Hemodynamics

李冠輝(Kuang-Huei Lee)

指導教授 ： 蕭浩明

國立臺灣大學/工學院/機械工程學研究所/碩士(2012年)

https://doi.org/10.6342/NTU.2012.00082

摘要

血管支架在動脈硬化症造成的血管阻塞的治療上是一項極為重要的突破。然而，目前學界高度懷疑植入支架對血流造成的干擾將會造成動脈再狹窄──即裝有血管支架的動脈的再狹窄化。許多研究指出血管內的血液動力學性質是影響再狹窄形成最關鍵的因素：若裝有支架的血管管壁上的剪應力(Wall Shear Stress, WSS)過低、剪應力震盪過大、剪應力梯度(WSS Gradient, WSSG)過高或存在渦流都會刺激血管再狹窄發生。因此目前計算流體力學模擬被廣泛的運用在分析裝有支架的血管內的血液動力學。本研究提出了兩種計算流體力學模型(二維軸對稱血管模型與三維血管模型)幫助探討支架的設計樣式、支架結構的幾何形狀與血液的流變性質對流經支架的血流的影響。本研究主要包含了對各種不同情況下的血流速度分佈、渦流、剪應力分佈、剪應力震盪、剪應力梯度分佈的探討。結果顯示血液動力學性質與支架的幾何形狀高度相關。支架厚度與支架結構倒圓角對血流的影響最大，而支架結構寬度與支架結構彎曲處的曲率相對來說則影響很小。倒圓角的影響顯示支架表面處理製程的電化學拋光過程對血管再狹窄的過程有不小的影響，需要謹慎控制。至於血液的流變性質在二維軸對稱的模擬中對模擬結果的影響很小，牛頓流的假設只會使支架下游渦流較非牛頓流的模擬結果增長6%。然而流變性質對三維的模擬結果影響卻比較大。在三維的模擬結果中，牛頓流模擬對管壁上剪應力較低的面積的預測較非牛頓流模擬平均高14.7%，而且兩者之間的差距會隨支架設計樣式而不同。此外，三維的模擬結果也顯示支架設計樣式也對血液動力學有很大的影響。不對稱的支架設計與支架前後的毛邊分別會增加剪應力較低的區域3.9%、3.7%，降低平均剪應力梯度6.2%、3.5%，並增加剪應力的震盪程度50.2%、12.6%。論文中所提出的數值分析方法與發現將會幫助未來支架設計的最佳化，並成為支架測試流程中的一塊，加速支架的設計與測試過程，最終幫助未來的支架設計降低臨床上的血管再狹窄率。

關鍵字

動脈再狹窄 ； 剪應力 ； 血管支架設計 ； 血液動力學 ； 計算流體力學

並列摘要

The stent has been a major breakthrough for the treatment of atherosclerotic vascular disease. The permanent vascular implant of a stent, however, changes the blood flow hemodynamics and may consequently affect the restenosis process – a re-narrowing of stented artery. Computational Fluid Dynamics (CFD) has been widely used to analyze the hemodynamic behavior, such as wall shear stress (WSS) and wall shear stress gradient (WSSG) distribution, in stented arteries since clinical research indicated that low WSS, oscillatory WSS, flow recirculation, and high WSSG are the most critical factors in restenosis process. In this study, two CFD models (the axisymmetric model and the 3-D stent model) were developed to investigate the effects of stent design patterns, strut geometry, and blood rheology on the intra-stent hemodynamics. The velocity profile, flow recirculation, WSS distribution, oscillatory WSS, and WSSG distribution of various stent geometries were studied. Results show strong correlations between the intra-stent hemodynamics and strut geometry. The intra-stent blood flow is very sensitive to the stent thickness and fillet size, while the strut width and the radius of the most curved part of stent are relatively unimportant. The effect of fillet size suggests that electrochemical polishing, a surface-improving process during stent manufacturing, strongly influences the hemodynamic behavior in stented arteries and should be controlled precisely in order to achieve the best clinical outcome. Rheological effects on the wall shear stress are minor in axisymmetric model. Newtonian simulation increase distal recirculation length by only 6% as compared with non-Newtonian simulation; however, it becomes significant in the 3-D stented artery model, with Newtonian flow simulation tending to give more conservative estimates of restenosis risk. Newtonian simulation increase low shear area by average 14.7% as compared with non-Newtonian simulation. Moreover, the non-Newtonian effect varies with stent design. Besides, the simulated results based on 3-D stent model also show strong correlations between the intra-stent hemodynamics and stent design patterns. Asymmetric stent design and uneven head of a stent increase low shear area by 3.9% and 3.7%, decrease average WSSG by 6.2% and 3.5%, and intensify the WSS oscillation by 50.2% and 12.6%, respectively, while pulsatile blood flow is considered. The proposed methodologies and findings will provide great insights for stent design optimization, facilitate stent testing process, and then reduce potential restenosis rate of the future stent designs.

並列關鍵字

Restenosis ； Wall Shear Stress ； Stent Design ； Hemodynamics ； Computational Fluid Dynamics.

參考文獻

[5] D. L. Fischman, M. B. Leon, D. S. Baim, et al., “A Randomized Comparison of Coronary Stent Placement and Balloon Angioplasty in the Treatment of Coronary Artery Disease,” New England Journal of Medicine, Vol. 331, pp. 496-501, 1994.

[6] J. E. Sousa, P. W. Serruys, and M. A. Costa, “New Frontiers in Cardiology: Drug-Eluting Stents: Part I,” Circulation, Vol. 107, pp. 2274-2279, 2003.

[7] J. B. Hermiller, A. Raizner, L. Cannon, el al., “Outcomes with the Polymer-based Paclitaxel-eluting TAXUS Stent in Patients with Diabetes Mellitus: the TAXUS-IV Trial,” Journal of American College of Cardiology, Vol. 45, No. 8, pp. 1172-1179, 2005.

[8] P. W. Serruys, J. A. Ormiston, et al., “A Bioabsorbable Everolimus-eluting Coronary Stent System (ABSORB) - 2-year Outcomes and Results from Multiple Imaging Methods,” Lancet, Vol. 373, pp. 897-910, 2009.

[9] A. Kastrati, et al., “Restenosis after coronary placement of various stent types,” American Journal of Cardiology, Vol. 8, pp. 34-39, 2001.