冠状动脉分叉病变单支架植入术后血流动力学分析

目的分叉病变在即刻手术成功率及远期心脏事件方面是最具有挑战的冠脉病变之一。血流动力学对动脉粥样硬化的形成有重要影响。对分叉病变单支架虚拟植入后的血流动力学参数分布进行分析,探讨其对支架后再狭窄的影响,可为临床治疗提供理论依据。方法本文选取一例冠状动脉分叉病变患者的冠状动脉血管造影(computed tomography angiography,CTA)图像,首先用Mimic软件对所获得冠脉CTA数据进行三维重建得到冠脉血流区域,然后运用类似虚拟去除斑块的方式建立不均匀壁厚血管壁模型,对所得模型在ABAQUS中进行单支架虚拟植入,最后根据虚拟植入前、后的冠脉模型分别生成支架前和真实变形后的血流域有限元模型,并利用ANSYS软件通过瞬态CFD分析模拟动脉血流的流动状态,获得目标血管段的血流动力学参数。结果支架植入后与支架植入前相比,目标血管段的血液流速、壁面剪切应力均降低;支架植入后主支血管远端有振荡的低剪切应力区域;支架边缘位置壁面剪切应力低于其他位置;分支血管直径变小;分支外侧壁壁面剪切应力低于内侧壁。结论分叉病变的单支架植入可改善冠脉主支的狭窄,但术后主支血管远端振荡的低剪切应力区域、支架边缘和边支外侧壁处的低壁面剪切应力,以及斑块和分叉嵴的移位有可能是分叉病变再狭窄的血流动力学机制。     

三角形截面丝裸支架治疗梭形颅内动脉瘤的流固耦合数值模拟研究

区别于传统圆形截面丝支架,本研究中提出新型的三角形截面丝支架。与相同孔隙率的传统支架进行对比研究,探讨新型支架治疗颅内动脉瘤的血流动力学有效性。分别建立植入圆形截面丝支架、三角形截面丝支架和不植入支架动脉瘤三维有限元模型;设置相同的边界条件,利用流固耦合数值模拟的方法对流动阻力、速度、压力、壁面切应力和网格变形等参数进行了计算和分析。研究发现,三角形截面支架的流动阻力值小于圆形截面支架,并且植入三角形截面支架后动脉瘤的速度、压力、网格变形等参数在数值上均大于植入圆形截面支架模型,壁面切应力的峰谷值也有所增加。三角形截面支架针对梭形动脉瘤的治疗效果并不如圆形截面支架。在临床应用时,应考虑各项因素,择优而定。真正的临床应用效果,还需要进一步的实验验证。     

不同截面和尺寸镁合金支架扩张过程中的应力变化

背景:降解带来的一个重要变化是支架尺寸的减小,从而影响支架的支撑力。由于支架的结构复杂性,导致其应力分布的复杂性。目的:分析不同截面形状和尺寸的镁合金支架在扩张过程中的应力变化。方法:利用有限元法分别计算正方形、八边形、圆形3种筋截面形状的镁合金支架扩张过程中主要受力部位的残余应力,同时计算120,140,160,180μm的4种不同尺寸下该处残余应力的变化情况。结果与结论:正方形、八边形、圆形这3种不同筋截面形状支架扩张后,圆形筋截面形状支架上主要受力部位的应力最大。对3种支架而言,随着筋截面尺寸的减小,该部位的应力减小,提示支架筋截面形状及尺寸均对支架扩张后的残余应力产生影响。     

5种支架对颈内动脉瘤血液动力学影响的数值研究

目的 研究不同结构形状以及不同网丝截面的支架用于颈内动脉瘤治疗后对血液动力学及支架柔顺性的影响。方法 针对同一个体模型的颈内动脉瘤,构建5种不同支架介入治疗的模型。这些支架的支撑体网丝截面不同,但支架通透率近似相等。利用有限体积法进行数值仿真,获得其生物力学特性的定量信息。结果 5种模型中,矩形截面网格支架模型动脉瘤腔中平均流动速度的减小幅度最大;圆型截面支架和矩形截面螺旋支架模型中瘤面和瘤颈部分的壁面切应力减小面积较大;网格支架的柔顺性要远好于螺旋支架。结论 矩形截面网格支架对治疗颈内动脉瘤有较好的生物力学影响,这些发现可帮助临床医生在治疗脑动脉瘤时选择合适的支架。     

支架筋截面形状对血流动力学影响的数值分析

通过对方形、圆形和椭圆形三种横截面支架筋附近的血流动力学数值分析,对优化设计支架结构提供流体力学理论指导。利用边界元方法,计算了血液流场、血管壁切应力及支架筋所受压力。与方形和圆形截面支架筋比较,椭圆形截面支架筋对血流的扰动较小,支架筋所受压力较对称,并且支架筋间没有形成低切应力区。椭圆形截面支架筋对增加支架置入后的稳定性、防止再狭窄有一定的优越性。     

三种截面支架对动脉瘤血流动力学影响的比较研究

目的提出不同于传统支架的三角形网丝截面支架,并对其进行数值模拟,比较圆形、矩形、三角形截面支架在动脉瘤内的血流动力学效果。方法构建3个有支架植入的动脉瘤模型,分别为圆形(CM型)、矩形(RM型)和三角形(TM型)截面支架模型,并与1个无支架的动脉瘤模型(UM型)对照。在相同的边界条件下,利用有限单元法对4个模型进行流固耦合数值模拟。结果 RM型比TM型和CM型的速度更低、流阻更高、流转时间更长,所以矩形、三角形、圆形截面支架血液流动的影响效果依次降低。在削弱壁面切应力大小、降低壁面切应力波动性方面,RM型比TM型和CM型更加显著,但CM型和TM型的壁面升压低于RM型。壁面应力分布和变形结果表明动脉瘤沿远侧壁生长的可能性大于近侧壁,瘤顶破裂的风险最大。结论 3种截面支架展示了不同的血流动力学,这些结果为血管内支架的结构设计和优化提供了有意义的参考依据。     

半圆形截面支架介入串联囊状动脉瘤的血流动力学仿真

为了研究半圆形截面支架对颅内串联囊状动脉瘤血流动力学的影响,针对同一动脉瘤结构,构建无支架和4种截面支架介入动脉瘤的有限元模型,分别命名无支架为U型、圆形截面为C型、半圆形截面圆面朝向瘤腔为ES型、圆面朝向血管轴向为IS型,然后对模型中的生理脉动流进行计算流体动力学仿真。数值模拟的结果显示:有支架模型的腔内流速被有效削弱,壁面附近的流速很低;血流对瘤腔的冲击减弱,壁面切应力的量值和波动性降低,分布均衡;腔内压力在支架介入后略有升高。对比分析两个瘤腔,流动情况和壁面切应力基本相同,下游瘤腔的压力低于上游瘤腔。IS型的仿真结果更好,这为支架的结构设计提供了一些理论指导。     

几何参数对Z型覆膜支架柔顺性的影响

目的分析治疗胸主动脉瘤的常用Z型覆膜支架的几何参数对支架柔顺性能的影响及主次顺序。方法通过SolidWorks软件建立波峰数目、波峰高度、丝径及顶端圆角半径4种因素变化的覆膜支架模型,并导入ANSYS有限元软件进行仿真分析,对支架施加弯曲60°的转动变量,根据最大等效应力、节点反力、弯矩3个评价参数分析支架柔顺性。结果支架弯曲后,最大应力集中在弯曲内侧;减小支架丝径、波峰高度与波峰数目,支架的柔顺性增强;增大波峰顶端圆弧半径,支架柔顺性增强;丝径与波峰数目对支架柔顺性的影响强于顶端圆弧半径与波峰高度。结论波峰数目、波峰高度、丝径及顶端圆角半径对覆膜支架柔顺性均有显著影响。研究结果为以后临床支架的选择及优化设计提供理论依据,对减少新发破口等并发症的发生具有积极意义。     

血管支架对颅内动脉瘤血液动力学的数值模拟

血管支架作为治疗颅内动脉瘤的新方法被广泛运用到临床中,而且越来越普遍。但由于某些支架植入后不能满足力学要求或对瘤内血液动力学无明显影响,反而更易形成血栓,造成动脉瘤破裂。本研究首先通过结构静力学分析比较矩形截面网格状支架和网丝编织成的圆形截面螺旋形支架的弯曲变形能力及扭转变形能力;然后将网格支架植入实际脑动脉瘤模型,进行流－固耦合模拟仿真,分析血流速度、壁面压力及壁面剪切力变化。结果表明：两种支架能够在不损失径向支撑力的情况下,提供良好的轴向顺应性,且网格状支架的变形能力高于螺旋状支架;支架植入后血液动力学各项指标明显降低。血管支架对颅内动脉瘤血液动力学有很大影响,可为临床治疗动脉瘤提供理论依据。     

颈动脉分叉处血管粥样硬化斑块的体内应力分析

目的探究颈动脉分叉处血管斑块的体内应力分布,为颈动脉分叉处血管斑块破裂行为的研究和诊断治疗方案的设计提供力学机理参考。方法基于人体颈动脉分叉血管的平均几何参数,建立三维颈动脉分叉血管及其斑块的几何模型,通过"热-结构"耦合重建颈动脉分叉血管及其斑块的残余应力,并计算血压和血流分别作用下颈动脉分叉处血管斑块的体内应力。结果斑块的肩部同时存在着最大主应力和弹性剪切应力的应力集中。斑块肩部的弹性剪切应力随着狭窄率增大或血压升高均增加。斑块上游区域的流体壁面切应力明显高于斑块下游区域,斑块下游区域的振荡剪切指数则显著大于上游区域。且斑块的弹性剪切应力和流体壁面切应力大小随着狭窄率的变化呈现出不同的变化规律。结论斑块从内部中心位置到壁面肩部承受着非均匀的应力分布,血管严重狭窄时"内压外拉"的受力状态更容易导致斑块破裂。随着血压的变化,斑块结构应力的周期性变化可能使斑块产生结构疲劳,增加破裂风险。斑块上下游区域流体动力学参数的差异可能是斑块上下游组分、易损程度等性质不同的原因之一。     

Three-Dimensional Computational Fluid Dynamics Modeling of Alterations in Coronary Wall Shear Stress Produced by Stent Implantation

Rates of coronary restenosis after stent implantation vary with stent design. Recent evidence suggests that alterations in wall shear stress associated with different stent types and changes in local vessel geometry after implantation may account for this disparity. We tested the hypothesis that wall shear stress is altered in a three-dimensional computational fluid dynamics (CFD) model after coronary implantation of a 16 mm slotted-tube stent during simulations of resting blood flow and maximal vasodilation. Canine left anterior descending coronary artery blood flow velocity and interior diameter were used to construct CFD models and evaluate wall shear stress proximal and distal to and within the stented region. Channeling of adjacent blood layers due to stent geometry had a profound affect on wall shear stress. Stagnation zones were localized around stent struts. Minimum wall shear stress decreased by 77% in stented compared to unstented vessels. Regions of low wall shear stress were extended at the stent outlet and localized to regions where adjacent axial strut spacing was minimized and the circumferential distance between struts was greatest within the stent. The present results depict alterations in wall shear stress caused by a slotted-tube stent and support the hypothesis that stent geometry may be a risk factor for restenosis by affecting local wall shear stress distributions. © 2003 Biomedical Engineering Society. PAC2003: 8719Rr, 8710+e, 8780Rb, 8719Uv     

药物洗脱支架高度对药物浓度和壁面切应力分布影响的数值分析

目的研究药物洗脱支架(drug-eluting stent,DES)突起高度对药物释放动力学和血流动力学的影响,为DES的优化设计提供依据。方法采用计算流体动力学(computational fluid dynamics,CFD)方法,对血流动力学和药物释放动力学进行耦合分析,考虑3种不同突起高度支架,研究血管壁组织中药物含量和壁面切应力的分布。结果支架突起高度的增加将有利于药物的沉积,但将增加低切应力区长度。比较而言,血管壁中药物含量随着突起高度增加的幅度远小于低切应力区长度的增加。结论综合考虑药物浓度和壁面切应力两种因素,建议适当降低支架的突起高度,以便更有效地降低再狭窄产生的几率。     

支架置入椎动脉开口处狭窄后突出距离的血流动力学分析

目的探讨支架置入椎动脉开口处狭窄后突出到左锁骨下动脉的距离对局部血流动力学的影响。方法分别构建未置入支架(模型1)以及置入支架无下移(模型2)、下移1 mm(模型3)、2 mm(模型4)、3 mm(模型5)的椎动脉模型。利用计算流体力学方法进行数值模拟,比较不同模型的血流流速、壁面切应力等血流动力学差异。结果支架置入术后,模型2的支架段壁面切应力降低85.33%、血流速度降低35.36%、旋动流现象消失。支架下移不同程度的几个模型相比,狭窄段的壁面切应力相差最大0.76%、血流速度相差最大0.45%。结论支架的置入椎动脉开口狭窄后的血流动力学变化显著,而支架下移距离对椎动脉流速和壁面切应力的影响不明显。     

The Influence of Strut-Connectors in Stented Vessels: A Comparison of Pulsatile Flow Through Five Coronary Stents

The design of coronary stents has evolved significantly over the past two decades. However, they still face the problem of in-stent restenosis, formation of neointima within 12 months of the implant. The biological response after stent implantation depends on various factors including the stent geometry which alters the hemodynamics. This study takes five different coronary stent designs, used in clinical practice, and explores the hemodynamic differences arising due to the difference in their design. Of particular interest is the design of the segments (connectors) that connect two struts. Pulsatile blood flow analysis is performed for each stent, using 3-D computational fluid dynamics (CFD), and various flow features viz. recirculation zones, velocity profiles, wall shear stress (WSS) patterns, and oscillatory shear indices are extracted for comparison. Vessel wall regions with abnormal flow features, particularly low, reverse, and oscillating WSS, are usually more susceptible to restenosis. Unlike previous studies, which have tried to study the effect of design parameters such as strut thickness and strut spacing on hemodynamics, this work investigates the differences in the flow arising purely due to differences in stent-shape, other parameters being similar. Two factors, the length of the connectors in the cross-flow direction and their alignment with the main flow, are found to affect the hemodynamic performance. This study also formulates a design index (varying from 18.81% to 24.91% for stents used in this study) that quantifies the flow features that could affect restenosis rates and which, in future, could be used for optimization studies.     

Hemodynamically Driven Stent Strut Design

Stents are deployed to physically reopen stenotic regions of arteries and to restore blood flow. However, inflammation and localized stent thrombosis remain a risk for all current commercial stent designs. Computational fluid dynamics results predict that nonstreamlined stent struts deployed at the arterial surface in contact with flowing blood, regardless of the strut height, promote the creation of proximal and distal flow conditions that are characterized by flow recirculation, low flow (shear) rates, and prolonged particle residence time. Furthermore, low shear rates yield an environment less conducive for endothelialization, while local flow recirculation zones can serve as micro-reaction chambers where procoagulant and pro-inflammatory elements from the blood and vessel wall accumulate. By merging aerodynamic theory with local hemodynamic conditions we propose a streamlined stent strut design that promotes the development of a local flow field free of recirculation zones, which is predicted to inhibit thrombosis and is more conducive for endothelialization.     

Comparison of Two Stents in Modifying Cerebral Aneurysm Hemodynamics

There is a general lack of quantitative understanding about how specific design features of endovascular stents (struts and mesh design, porosity) affect the hemodynamics in intracranial aneurysms. To shed light on this issue, we studied two commercial high-porosity stents (Tristar stent and Wallstent) in aneurysm models of varying vessel curvature as well as in a patient-specific model using Computational Fluid Dynamics. We investigated how these stents modify hemodynamic parameters such as aneurysmal inflow rate, stasis, and wall shear stress, and how such changes are related to the specific designs. We found that the flow damping effect of stents and resulting aneurysmal stasis and wall shear stress are strongly influenced by stent porosity, strut design, and mesh hole shape. We also confirmed that the damping effect is significantly reduced at higher vessel curvatures, which indicates limited usefulness of high-porosity stents as a stand-alone treatment. Finally, we showed that the stasis-inducing performance of stents in 3D geometries can be predicted from the hydraulic resistance of their flat mesh screens. From this, we propose a methodology to cost-effectively compare different stent designs before running a full 3D simulation.     

The Effect of Stent Porosity and Strut Shape on Saccular Aneurysm and its Numerical Analysis with Lattice Boltzmann Method

The analysis of a flow pattern in cerebral aneurysms and the effect of stent strut shapes are presented in this article. The treatment of cerebral aneurisms with a porous stent has recently been proposed as a minimally invasive way to prevent rupture and favor coagulation mechanism inside the aneurism. The efficiency of stent is related to several parameters, including porosity and stent strut shapes. The goal of this article is to study the effect of the stent strut shape and porosity on the hemodynamic properties of the flow inside an aneurysm using a numerical analysis. In this study, we use the concept of flow reduction to characterize the stent efficiency. Also, we use the lattice Boltzmann method (LBM) of a non-Newtonian blood flow. To resolve the characteristics of a highly complex flow, we use an extrapolation method for the wall and stent boundary. To ease the code development and facilitate the incorporation of new physics, a scientific programming strategy based on object-oriented concepts is developed. Reduced velocity, smaller average vorticity magnitude, smaller average shear rate, and increased viscosity are observed when the proposed stent shapes and porosities are used. The rectangular stent is observed to be optimal and to decrease the magnitude of the velocity by 89.25% in the 2D model and 53.92% in the 3D model in the aneurysm sac. Our results show the role of the porosity and stent strut shape and help us to understand the characteristics of stent strut design.     

弯曲圆管入口段定常流动的三维数值模拟

目的 研究定常流动条件下弯曲圆管入口段内的流动情况。方法 用有限体积法对弯曲圆管入口段定常流动作三维数值模拟。结果 分别计算了管内流线、截面等速度线、沿对称面直径的速度剖面和壁面切应力分布等。沿对称面直径的速度剖面计算值与实验结果吻合很好。结论 弯管的外侧壁是高切应力区，内侧壁是低切应力区，证实内侧壁是动脉粥样斑块的高发区。     

不同连接筋结构的支架治疗椎动脉狭窄的血流动力学数值模拟

目的 研究具有不同连接筋结构的支架治疗椎动脉狭窄后的血流动力学效果,以期为支架的设计以及介入治疗提供更加科学的指导。方法 采用Pro/Engineer建立带有狭窄的椎动脉模型和3种不同连接筋的支架模型（根据连接筋形状分别称为L-支架、V-支架和S-支架）;利用有限元分析软件ABAQUS模拟这些支架在狭窄椎动脉中扩张后的结果,并分别建立3种支架治疗椎动脉狭窄后的流场有限元模型。利用有限元分析软件ANSYS-CFX对3个模型进行血流动力学数值模拟。结果 与V型和S型连接筋相比,L型连接筋造成了较小的低壁面切应力分布面积及较少的血流停滞区。结论 L型连接筋具有较好的血流动力学效果,潜在地可降低支架内再狭窄发生的可能性,从而为支架选择、支架设计和手术规划等提供科学依据。