支架植入后趋直现象对血管壁局部生物力学环境的影响

目的研究支架植入后趋直现象对病变处血管壁力学环境变化的影响,探索支架植入后再狭窄的生物力学成因及支架优化方法。方法基于患者CT扫描图像,使用Mimics、Geomagic和Pro/E软件完成动脉、球囊以及理想与趋直两种支架模型的构建,应用ABAQUS软件建立球囊-支架-冠状动脉左前降至血管之间的力学模型,根据数值模拟计算结果,分析趋直对病变处血管壁力学环境的影响。结果在1.013 MPa充气压力下撑开支架后,与理想支架模型相比较,趋直支架模型的血管壁内表面出现Von Mises应力增大和明显的应力集中现象,尤其是在近心端、远心端及沿心肌表面区域。理想支架模型血管内壁平均和最大Von Mises应力分别0.39、5.12 MPa;趋直支架模型血管内壁平均和最大Von Mises应力分别为0.45、7.43 MPa。结论支架植入后发生的趋直现象将引起应力分布不均匀,出现应力集中,增大对血管壁造成的伤害,可能会引起血管的机械损伤及管壁重建,诱发支架内再狭窄的发生。研究结果可为术后支架内再狭窄的机理分析提供帮助,也为血管介入手术方案及支架优化设计提供参考。     

支架植入位置对狭窄血管段支架内再狭窄影响的力学分析

背景经皮冠状动脉介入作为治疗动脉粥样硬化等心血管疾病最有效的方式,近些年在临床上得到广泛应用,但血管晚期血栓和支架内再狭窄等问题却并没有得到彻底解决。研究表明,支架植入会使血管壁产生非生理性组织应力,支架植入后血管内血流动力学微环境的改变会诱发支架内再狭窄。支架植入位置的不同也会对血管内力学环境产生重要影响,但相关研究却少有报道。因此,深入了解支架植入不同位置对血管力学微环境的影响,对于临床上优化支架放置以及缓解支架内再狭窄有重要意义。方法采用有限元方法模拟了支架扩张过程中狭窄血管的力学响应,通过球囊损伤法构建了兔颈动脉狭窄模型,并根据支架与狭窄血管中心区域的相对位置构建了支架植入的近心、中心、远心三种模型,对术后血管内血流动力学特征进行了分析。随后将支架段血管划分为前、中、后三个区域,对三个区域内的血流动力学参数进行了与支架植入位置之间的等级相关性分析,探究了支架位置的变化对于支架不同区域血流动力学特征的影响,并通过血管形态学观察对计算结果进行了验证。结果(1)计算模拟结果显示,血管壁最大应力出现在支架前、后端,而低剪切应力、高震荡剪切等血流动力学特征主要出现在支架前端,在支架后端血流动力学特征不明显,因此支架前端血管出现再狭窄风险较高。(2)支架前端血流动力学特征与支架植入位置存在显著相关性(r_(TAWSS)=-0.718,r_(OSI)=0.898,r_(RRT)=0.818,P0.01)。随着支架位置向远心移动,即从近心模型到远心模型,支架前端血管内膜增厚的程度加重,而支架中后端血管内膜增厚无显著差异,表明支架位置的变化对支架前端血管重构产生显著影响。结论支架植入会显著改变血管内的力学环境,在支架前端形成促动脉硬化斑块新生的区域,随着支架位置的不断靠后,支架前端对支架内再狭窄的影响更加显著。因此,临床支架介入术中需对支架的放置做进一步优化。     

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。     

椎动脉狭窄临床病例介入治疗前后椎基底动脉血流状况分析

目的:基于血液和弹性血管壁相互作用的流固耦合方法,探究1例椎动脉颅内段狭窄的临床病例支架植入前后椎基底动脉的血流动力学特性。方法:应用医学建模软件对二维CT数据进行三维重建,得到支架植入前后的椎基底动脉血管模型,采用流固耦合方法对支架植入前后的椎基底动脉血流特性进行数值模拟,分析椎基底动脉的血流动力学特性。结果:支架植入前后椎基底动脉的血液流场、血液压力、血管壁面切应力以及管壁形变量有显著的变化。在支架植入后,基底动脉中间部位两侧受力变得均匀,椎基底动脉内血流速度明显增大,支架植入处压力增大,支架上游压力和支架处切应力减小。结论:在介入治疗后,椎基底动脉内的血流环境及受力情况得到明显改善,当椎动脉发生狭窄后应及时干预治疗,避免累及基底动脉和后循环系统。     

不同支撑杆数目腔静脉滤器的生物力学性能和血流动力学分析

目的利用有限元与计算流体动力学的方法,分析不同支撑杆数目腔静脉滤器在植入过程中与血管的相互作用机制及对血流的影响,为滤器的临床治疗及设计开发提供更加科学的参考。方法应用Solidworks软件建立支撑杆数分别为4、6和8杆的3种滤器模型;应用ABAQUS软件模拟分析3种滤器在工作状态下血管与滤器表面上的应力分布以及径向支撑刚度;应用Fluent软件模拟分析3种滤器在血管内工作时血流流速、压力、剪应力的分布。结果 3种滤器的各项力学性能和流体性能都在安全范围内。6杆滤器的综合性能相对较好;8杆滤器工作时所受应力、支撑强度、出口速度、过滤网上的剪应力均较大,流迹状态逐渐由层流向过度流变化,容易造成血管壁的损伤;4杆滤器在工作时对血管的应力较大,出口速度较低,容易造成局部血管壁的损伤,并且不利于滤器在血管病变部位的正确定位。结论 6杆滤器具有较好的血流动力学效果和综合力学性能,潜在降低了滤器植入后对血管壁的损伤及本身破裂的可能性。腔静脉滤器的模拟分析为滤器的设计和临床选择提供良好的参考依据。     

血管内支架植入后的内皮损伤及其修复策略

动脉粥样硬化性心脏病是严重危害人类生命健康的心血管疾病。近年来其主要的治疗手段是将血管内支架植入到病变部位,支撑血管并重建血运。然而,大量研究表明,血管内支架植入的介入操作、抗增殖药物释放均会对血管内皮造成极大的损伤,大大增加了支架内再狭窄和晚期血栓形成的风险。维持血管内皮的完整和正常功能可明显降低支架植入带来的一系列风险。研究表明,干细胞动员、归巢、分化、增殖是血管内支架植入后血管内皮修复的主要机制,多种血管内因子、力学微环境变化等均参与此过程,进而影响植入部位的再内皮化。本文对支架植入造成血管内皮损伤的过程、损伤后的修复机制及其影响因素等进行详细阐述,并分析总结其修复策略,为深入理解支架内再狭窄、血管内皮化延迟和晚期血栓形成的机制以及新型药物洗脱支架和生物可降解支架的设计提供参考。     

支架植入颅内动脉瘤治疗效果的数值模拟研究

研究不同结构形状的血管支架用于治疗颅内动脉瘤后对血流动力学的影响。针对同一个体化颅内动脉瘤模型,设计了三种网丝截面相同、通透率近似相等、结构形状不同的支架。将这三种支架植入颅内动脉瘤模型,进行双向流固耦合数值模拟,分析血流速度、壁面切应力的变化情况。三种支架中,螺旋型支架对动脉瘤瘤腔内的血流旋涡改善效果最佳,对动脉瘤瘤颈和瘤顶部分较高的壁面切应力削弱也最明显;周期型支架的柔顺性优于其余两种类型的支架。螺旋型支架植入颅内动脉瘤的治疗效果最佳,但不适合几何形状复杂的血管,本研究也可为进一步优化支架结构提供依据。     

血管支架在真实狭窄血管模型中扩张过程的模拟研究

目的 研究血管支架在真实狭窄血管模型中不同扩张阶段的形变与受力特性,为支架的介入治疗与设计提供科学的参考意见。方法 利用三维建模方法构建患者颈动脉血管模型以及斑块模型,利用Pro/E软件构建1种I型血管支架;在ABAQUS/Standard软件中分析支架在真实狭窄血管模型中径向扩张（第1阶段）和径向收缩（第2阶段）的扩张过程,同时建立斑块与血管为一体的对比实验。结果 在第1阶段,支架发生径向扩张,支架与斑块和血管内壁接触面积最大,支架、斑块、血管壁所受应力最大值分别为515.000、2.482、1.053 MPa;在第2阶段,支架发生径向收缩,形成“狗骨效应”,支架与血管壁之间形成较多的间隙,支架、斑块、血管壁所受应力最大值分别为464.500、0.954、0.316 MPa。在对比实验中,狭窄血管与支架在第2阶段所受应力最大值分别为0.9、414.1 MPa。结论 相对于对比实验,区分血管组织成分的模型更符合狭窄血管的真实情况,更能真实反映血管与支架的受力情况;在第1阶段支架对于斑块及血管内壁造成的损伤最大,在第2阶段支架的“狗骨效应”是造成支架与斑块、血管间产生空隙的重要影响因素。研究结果对支架在介入治疗中的选择与支架的改进设计具有指导意义。     

血管支架在真实狭窄血管模型中扩张过程的模拟研究

目的 研究血管支架在真实狭窄血管模型中不同扩张阶段的形变与受力特性,为支架的介入治疗与设计提供科学的参考意见。方法 利用三维建模方法构建患者颈动脉血管模型以及斑块模型,利用Pro/E软件构建1种I型血管支架;在ABAQUS/Standard软件中分析支架在真实狭窄血管模型中径向扩张（第1阶段）和径向收缩（第2阶段）的扩张过程,同时建立斑块与血管为一体的对比实验。结果 在第1阶段,支架发生径向扩张,支架与斑块和血管内壁接触面积最大,支架、斑块、血管壁所受应力最大值分别为515.000、2.482、1.053 MPa;在第2阶段,支架发生径向收缩,形成“狗骨效应”,支架与血管壁之间形成较多的间隙,支架、斑块、血管壁所受应力最大值分别为464.500、0.954、0.316 MPa。在对比实验中,狭窄血管与支架在第2阶段所受应力最大值分别为0.9、414.1 MPa。结论 相对于对比实验,区分血管组织成分的模型更符合狭窄血管的真实情况,更能真实反映血管与支架的受力情况;在第1阶段支架对于斑块及血管内壁造成的损伤最大,在第2阶段支架的“狗骨效应”是造成支架与斑块、血管间产生空隙的重要影响因素。研究结果对支架在介入治疗中的选择与支架的改进设计具有指导意义。     

血管支架在真实狭窄血管模型中扩张过程的模拟研究

目的研究血管支架在真实狭窄血管模型中不同扩张阶段的形变与受力特性,为支架的介入治疗与设计提供科学的参考意见。方法利用三维建模方法构建患者颈动脉血管模型以及斑块模型,利用Pro/E软件构建1种I型血管支架;在ABAQUS/Standard软件中分析支架在真实狭窄血管模型中径向扩张(第1阶段)和径向收缩(第2阶段)的扩张过程,同时建立斑块与血管为一体的对比实验。结果在第1阶段,支架发生径向扩张,支架与斑块和血管内壁接触面积最大,支架、斑块、血管壁所受应力最大值分别为515.000、2.482、1.053 MPa;在第2阶段,支架发生径向收缩,形成"狗骨效应",支架与血管壁之间形成较多的间隙,支架、斑块、血管壁所受应力最大值分别为464.500、0.954、0.316 MPa。在对比实验中,狭窄血管与支架在第2阶段所受应力最大值分别为0.9、414.1 MPa。结论相对于对比实验,区分血管组织成分的模型更符合狭窄血管的真实情况,更能真实反映血管与支架的受力情况;在第1阶段支架对于斑块及血管内壁造成的损伤最大,在第2阶段支架的"狗骨效应"是造成支架与斑块、血管间产生空隙的重要影响因素。研究结果对支架在介入治疗中的选择与支架的改进设计具有指导意义。     

药物洗脱支架植入病灶部位后的血流特性

目的 研究冠脉内植入药物释放支架后的血液流动特性,为临床应用及改善药物洗脱支架的设计提供理论指导。方法 建立病灶部位植入药物洗脱支架后的数值模型,利用计算流体动力学方法进行药物浓度分布及壁面剪切力分布的数值分析研究,并将计算结果与裸金属支架植入后的计算结果进行比较。结果 药物洗脱支架在血流过程中产生的低壁面剪切力区域几乎都伴随着较高的药物浓度分布,而低药物浓度区域则伴随的是较高的壁面剪切力分布,显著地减少了低壁面剪切力区域或低药物浓度区域独立存在的区域。理论上,药物释放支架在药物释放阶段比植入裸金属支架具有优越性。结论 药物洗脱支架能够显著降低支架内的再狭窄率。详细了解药物洗脱支架的流场分布规律将有利于改善药物洗脱支架的设计,进一步提高支架的整体性能,为临床应用提供理论依据。     

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     

Computational fluid dynamics analysis of balloon-expandable coronary stents: Influence of stent and vessel deformation

In many computational fluid dynamics (CFD) studies of stented vessel haemodynamics, the geometry of the stented vessel is described using non-deformed (NDF) geometrical models. These NDF models neglect complex physical features, such as stent and vessel deformation, which may have a major impact on the haemodynamic environment in stented coronary arteries. In this study, CFD analyses were carried out to simulate pulsatile flow conditions in both NDF and realistically-deformed (RDF) models of three stented coronary arteries. While the NDF models were completely idealised, the RDF models were obtained from nonlinear structural analyses and accounted for both stent and vessel deformation. Following the completion of the CFD analyses, major differences were observed in the time-averaged wall shear stress (TAWSS), time-averaged wall shear stress gradient (TAWSSG) and oscillatory shear index (OSI) distributions predicted on the luminal surface of the artery for the NDF and RDF models. Specifically, the inclusion of stent and vessel deformation in the CFD analyses resulted in a 32%, 30% and 31% increase in the area-weighted mean TAWSS, a 3%, 7% and 16% increase in the area-weighted mean TAWSSG and a 21%, 13% and 21% decrease in the area-weighted mean OSI for Stents A, B and C, respectively. These results suggest that stent and vessel deformation are likely to have a major impact on the haemodynamic environment in stented coronary arteries. In light of this observation, it is recommended that these features are considered in future CFD studies of stented vessel haemodynamics.     

Proximal atherosclerotic lesion as a cause of very late stent thrombosis

Very late stent thrombosis is defined as in-stent thrombosis occurring after 1 year of an intra-coronary artery stent placement. Drug eluting stents have lately been criticized for increased reports of very late stent thrombosis. The exact cause of these very late stent thromboses is not clearly understood. Virchow's triad describes the three main factors of thrombus formation to be stasis of blood flow, endothelial injury and hypercoagulability. Based on Virchow's triad, we propose the cause of very late stent thrombosis to be formation of a de novo atherosclerotic lesion in the proximal segment of a stented artery. The de novo atherosclerotic lesion narrows the vessel lumen and causes stasis of blood flow in the distal stent. The de novo lesion can also cause myocardial ischemia creating a prothrombotic environment in the stented region. Stasis of blood flow and prothrombotic environment in the stented region can lead to the formation of very late stent thrombosis. Since atherosclerosis is a dynamic aging process in humans, we propose de novo proximal lesions in the coronary arteries can predispose to very late stent thrombosis.     

Computer assisted design for the implantable left ventricular assist device (LVAD) blood pump using computational fluid dynamics (CFD) and computer-aided design and manufacturing (CAD/CAM)

Thrombus formation and hemolysis are critical issues in the design of a long-term implantable LVAS (left ventricular assist system). The fluid dynamic characteristics of the blood flow are one of the main factors that cause thrombus formation and hemolysis. In this study, we optimized blood chamber geometry, port design, and fluid dynamics in our implantable LVAS to ensure minimization of shear-stress-related blood damage. A blood pump chamber (stroke volume, 65 ml) and an inflow and outflow port were designed with three-dimensional CAD (computer-aided-design) software (Pro-Engineering version 20) and estimated by FEM (fine-element method) computational fluid dynamic (CFD) analysis (Ansys version 5.5). We adopted three-dimensional distribution of CFD results for qualitative evaluation, and we also tried to estimate the normalized index of hemolysis (NIH) and time-series change of hematocrit from the results of CFD analysis as quantitative index of optimization for geometry of the blood pump chamber. With the use of this design, the blood pump geometry was optimized as the decrease of NIH from 2.72 g/1001 in the first model to 0.098 g/1001 in the second model, corresponding to the decrease in shear stress. The hematocrit also improved from 0.7% in the first model to 11.5% in the second model 2 years after implantation of the pump. Areas where flow stagnation was observed in the first model were free of stagnation in the second model. The results show that computer-aided design of the blood pump contributes to optimizing a blood pump chamber for reducing thrombus formation and hemolysis, and also contributes to reducing cost and time in developing the implantable LVAS.     

New biocompatible polymer surface coating for stents results in a low neointimal response

Clinical studies indicate a more pronounced endothelial response after stent implantation than after balloon inflation. This might be related to the metal surface of the stent, and therefore it is speculated that coating of the stent might partially prevent hyperplasia. One coated and one noncoated Palmaz-Schatz stent were implanted in two separate coronary arteries of seven pigs. The coating was composed of methylmethacrylate (MMA) (hydrophobic, 70 mol %) and 2-hydroxyethyl methacrylate (HEMA) (hydrophilic 30 mol %). After sacrifice (3 weeks), cross sections were made of the stented areas. Vessel wall reaction was calculated both independently and dependently of local vessel wall injury due to the stent struts. Overall, vessel wall reaction of the coated stents was lower than that of the noncoated stents. The degree of hyperplasia was linearly related to the degree of stent-induced vessel wall injury. Analyses of all the struts showed that significantly less hyperplasia occurred in the coated versus noncoated stents. In this porcine coronary artery model, the MMA/HEMA stent coating resulted in significantly reduced vessel wall response. However, it remains to be determined whether this favorable outcome will also be present in humans.     

冠脉分叉病变及支架后再狭窄的血流动力学研究进展

全球每年约有100万例经皮冠脉介入(PCI)治疗患者,其中分叉病变约占20%,而其支架后再狭窄率高达30%。频繁的再狭窄不仅和支架与血管的变形、支架与血管顺应性不匹配有关,也和支架后局部血流动力学变化引起的内膜增生有关。文中回顾了分叉冠脉的血流动力学研究发展,分析了分叉病变的血流动力学因素研究现状,详细阐述了其支架后再狭窄相关的计算流体力学(CFD)研究进展。CFD研究为探讨分叉冠脉的血流动力学环境与斑块形成、支架植入术与支架后再狭窄之间的关系提供了很好的技术手段,对临床医生理解斑块形成、工程师改善支架结构设计技术起到一定的作用。     

Potential mechanical blood trauma in vascular access devices: a comparison of case studies

Since vascular access devices may cause disturbances in blood flow, possibly damaging red blood cells (RBCs), the correlated risk of lysis must be assessed. The monodimensional approach for the evaluation of cannulae hydrodynamic behaviour (in vitro measured flow curves) does not furnish information on the local flow field occurring in specific clinical conditions. Researchers consider the prediction of blood trauma, induced by mechanical loading, to optimize the design phase, and to furnish indications on their optimal clinical use. In this study, a model of cannula inserted in a non compliant wall vessel was used as a test bench in a Computational Fluid Dynamics (CFD) problem. By means of CFD the flow field was 3D analysed to achieve information on velocity and shear stress local values, when cannula is used for inflow and outflow cannulation. A prediction of potential blood corpuscle damage, based on a power law, quantified the potential blood damage. Several numerical simulations, with different cannula/vessel flow rate ratios were provided, to investigate the incidence of local sites in the design on blood damaging potential during cannulation. Several regions appeared to be sensitive to the flow rate not only inside the cannula but also in the space between cannula and vessel, suggesting new indications for the assessment of a quality factor based on the evaluation of induced blood cells injury.     

冠脉可降解支架介入的血管力学特性数值模拟与实验研究

目的探究可降解支架在动态降解过程中,血管应力变化对内皮功能恢复以及血管再狭窄抑制作用的影响。方法拟合超弹性血管本构关系的材料参数,通过数值模拟计算支架介入前以及动态降解过程中血管内膜应力分布;采用体外培养实验,设置硅胶腔体拉伸率分别为0%、5%、10%、15%,模拟不同降解阶段的力学环境,探究不同拉伸率下对内皮细胞生长状态的影响。结果支架完全降解后,血管内膜周向应力、应变恢复到0.137 MPa、5.5%,与支架介入前生理参数(0.122 MPa、4.8%)接近;体外实验表明,在0.1 MPa周向应力、5%应变条件下,内皮细胞成活率最高,能实现全部黏附生长。结论支架随降解进程的发生,内膜周向应力、应变恢复到接近生理参数范围,促进内皮细胞的生长,完整内皮功能的维持有效抑制了血管再狭窄进程。结果可为研究冠脉介入治疗血管再狭窄问题提供理论依据和实验平台。