无支架四叶心包二尖瓣的应力分析

目的研究一种改进的无支架四叶心包二尖瓣的力学性能,通过数值模拟获得该种瓣膜的变形和应力分布.方法考虑材料非线性,大变形和接触条件建立有限元模型,采用有限元法进行应力分析.结果分析表明,数值模拟结果的瓣膜开启和闭合形态与体外流体动力学实验所观察到的相当接近,瓣叶闭合良好,瓣叶应力分布较均匀,应力大小在合理的范围内.结论有限元模型合理且有效,其分析结果可以作为评价该种瓣膜生物力学性能的参考.     

无支架心包二尖瓣的有限元分析

目的　通过无支架心包二尖瓣与有架三叶生物瓣对比，利用有限元法计算，观察在左心室舒张期瞬时跨瓣压差作用下的瓣叶静态应力分布。方法　采用八节点曲线薄壳单元，考虑大应变以及瓣叶闭合过程的接触，应用Newton-Raphson方法求解有限元非线性方程。结果　瓣膜开启状态下两种瓣膜应力水平均不高。在峰值跨瓣压差15.96 kPa作用下，无架心包二尖瓣第一主应力分布均匀，无明显应力集中、平均第一主应力为0.040~0.149 MPa；有架三叶瓣在临床上易发生撕裂的部位明显应力集中，最大第一主应力为2.352 MPa，平均第一主应力为0.223~0.724 MPa，明显高于无架心包二尖瓣。结论　(2)对于几何曲面形状不规则，高度接触的无支架心包二尖瓣，首次采用有限元方法进行应力计算是有效可行的；(2)本研究的有支架心包三叶瓣有限元模型得到的应力分布与临床结果一致；(3)无架心包二尖瓣较有架心包三叶瓣应力分布明显合理，有益于防止瓣叶撕裂和钙化、延长寿命。     

人体二尖瓣建模及生物力学分析

目的 建立人体心脏二尖瓣仿真模型,模拟二尖瓣闭合的工作过程,分析二尖瓣各组件应力分布,探讨二尖瓣瓣叶和腱索的相互作用,并探寻腱索受力大小与腱索粗细之间的相关性。方法 构建二尖瓣几何模型,在此基础上定义模型单元类型、材料属性、接触、载荷及约束,建立有限元模型,计算模型的应力、速度和位移等参数。结果 瓣膜上的应力分布不均匀,后瓣叶亚区之间的裂口位置所受应力最大;不考虑腱索连接至瓣叶时,瓣叶负载后外翻至心房一侧;考虑腱索连接至瓣叶时,前、后瓣叶关闭良好;各腱索受力不同,与前瓣叶相连的支持腱索受力最大,腱索受力大小与腱索粗细之间的线性相关系数为0.954。结论 瓣叶中心和后瓣叶亚区之间的裂口两处应力较大区域是临床上二尖瓣裂的常发生部位;与瓣叶相连的腱索可在瓣叶负载时,施加牵拉力使瓣叶不致发生翻转,前、后瓣叶恰好关闭;解剖结构粗壮的腱索受力较大。     

用于经导管二尖瓣置换术的支架有限元评估

目的：提出一种经导管二尖瓣置换术支架设计,评估支架与瓣叶植入后在体内相互作用产生的变形情况并分析其力学行为。方法：应用有限元方法,建立支架瓣叶组合模型,在瓣叶上施加压强载荷模拟其在人体内闭合的过程,分析其变形情况和应力应变结果以及受此影响的疲劳寿命。结果：本支架受瓣叶牵拉产生的最大顶端位移为0.24 mm,周期性应变的疲劳寿命约为2.05×10⁸次。结论：变形程度可接受但不可忽视,瓣叶的周期性牵拉对支架的影响可使其在人体内正常工作5～9年。     

含有镍钛合金丝的PET纺织瓣膜有限元分析及体外流体力学测试

目的 利用有限元方法分析径向织入镍钛金属丝的涤纶(polyethylene terephthalate, PET)基纺织瓣膜力学性能,结合体外血流动力学测试,分析金属丝数量和分布形式对PET瓣膜流体动力学性能的影响。方法 使用建模软件构建在径向方向上具有不同数量和分布的金属丝PET瓣膜和无金属丝PET瓣膜三维几何模型;根据文献和实验数据给定PET瓣膜和金属丝的材料属性;使用体外脉动流实验得到PET瓣膜的跨瓣压差曲线作为边界条件;利用有限元分析软件研究瓣膜在心动周期内的应力分布;通过体外脉动流实验评估金属丝瓣膜的流体力学性能。结果 有限元分析结果表明,径向织入镍钛金属丝可以增强对PET纺织瓣膜的支撑作用,金属丝均匀分布的瓣膜在瓣叶腹部区域的支撑力及作用区域随着金属丝数量增加而增大,金属丝分布在两侧位置的情况类似。金属丝的织入一定程度上改善PET瓣膜上的应力集中。脉动流实验结果表明,织入金属丝PET瓣膜开闭形态的稳定性、有效开口面积、反流分数和跨瓣压差等指标均优于无金属丝的纯PET瓣膜。结论 在PET纺织瓣膜的径向方向织入金属丝可以有效减少心动周期内PET纺织瓣膜上的应力集中,降低PET纺...     

起旋式人工主动脉瓣构型设计及血流动力学评价

目的 设计一种附起旋功能的双叶机械瓣,通过改善其血流状态预防术后并发症。 方法 基于导流片式局部起旋器结构,将瓣叶作为导流叶片,并定义瓣叶包角以探究具有较优血流动力学特性的瓣膜构型。 应用有限元分析软件,对心缩期峰值流量状态下的主动脉流场进行仿真,螺旋性、壁面切应力分布等血流动力学特征。 结果 相较于对照瓣膜,起旋瓣具有更大的有效开口面积与更小的跨瓣压差,一定瓣叶包角范围内的起旋瓣能促进右手螺旋流的生成,并使血流趋向流道中心;起旋瓣壁面切应力分布也更加均匀,具有较少的低应力区与高应力区,壁面切应力峰值也相对较小。 针对研究中的主动脉模型,具有最优血流动力学特性的瓣叶包角为 15° ~ 20°。 结论 该新型人工主动脉瓣能调节主动脉内的血流特征,降低主动脉瓣置换术引起主动脉扩张与主动脉瘤的风险,对未来机械瓣构型设计具有指导意义。     

脱细胞猪主动脉瓣叶的生物力学特性和免疫反应性

目的：探讨脱细胞猪主动脉瓣叶构建组织工程心脏瓣膜支架的可行性。方法：经胰酶-EDTA、表面活性剂、核酸酶处理，去除瓣叶的细胞成分，测定脱细胞瓣叶的生物力学特性，同时行大鼠皮下包埋实验，观察其免疫反应性。结果：瓣叶中的细胞成分能完全去除，获得无细胞的纤维网状支架。脱细胞瓣叶与新鲜瓣叶有基本相同的应力-应变曲线及应力-松弛曲线，而弹性模量、面积比、松弛强度、断裂强度和断裂伸长率两者无显著差异。脱细胞瓣叶的免疫反应性明显降低。结论：猪主动脉瓣叶经脱细胞处理后可以作为组织工程心脏瓣膜的支架材料。     

天然僧帽瓣的流体力学

一、引言如同主动脉瓣那样,也可认为僧帽瓣是一种在周围血液施加在瓣叶上的力影响下开和闭的被动瓣膜。以前,许多研究者为探讨心脏瓣膜功能的流体力学,己作出了不少的努力。这些努力的主要目的,就是要了解瓣膜的闭合机理。长期以来,人们认为,为了避免或减少心脏瓣口的倒流,在逆压力梯度开始前,心脏瓣膜已以某种方式部分闭合(对僧帽瓣的情形来说,是在心室开始收缩之前)。但是,对于所提出的这种瓣膜早期的部分闭合的机理,却还有许多争论。遗憾的是,包含在瓣膜闭合现象中的流体力学因     

球扩式介入主动脉瓣膜支架的抗迁移力学行为

目的 研究球扩式主动脉瓣膜支架植入后的抗迁移力学行为。 方法 建立球扩式瓣膜支架介入主动脉瓣膜后的抗迁移力学模型,采用数值模拟方法研究不同瓣环椭圆率、摩擦因数、瓣膜支架材料及自体瓣叶钙化情况对瓣膜支架抗迁移力的影响规律。 结果 当主动脉瓣环椭圆率为 0. 2、0. 3、0. 4、0. 5 时,对应的最大抗迁移力分别为12. 37、10. 94、8. 50、4. 75 N;当摩擦因数为 0. 1、0. 2、0. 3 时,瓣膜支架的最大抗迁移力分别为 8. 98、11. 00、13. 10 N;L605 钴铬合金制成的瓣膜支架的锚定性要优于 316L 不锈钢制成瓣膜支架的锚定性,其对应的最大抗迁移力分别为 13. 10、9. 82 N;当自体瓣叶发生钙化时,最大抗迁移力为 13. 1 N,而未钙化时最大抗迁移力仅为 5. 51 N,相比而言降低了 57. 9% 。 结论 随着主动脉瓣瓣环椭圆率不断增大,瓣膜支架的锚定性逐渐降低;随着瓣膜支架与组织间的摩擦因数不断增大,最大抗迁移力也不断增大;L605 钴铬合金制成的瓣膜支架比 316L 不锈钢制成瓣膜支架的锚定性能优异;瓣膜发生钙化情况下瓣膜支架的锚定性要优于未发生钙化时的锚定性。 研究结果为抗迁移瓣膜支架的结构设计和临床选择提供重要的科学依据。     

理想主动脉瓣模型闭合机制的研究

目的；分析理想状态下主动脉瓣关闭机制。方法：建立理想的主动脉瓣模型，用几何学的方法对不同瓣叶情况下的瓣膜受力情况进行分析。结果：二叶瓣无法开放，不符合生理要求。四叶瓣完全开放后，瓣叶完全贴于瓣环，在血液返流的方向上没有受力面积，不利于瓣膜的关闭。三叶瓣在完全开放的状态下，在血液返流的方向上有一个大小较为合理的截面积，有利于瓣膜的闭合受力。结论；在完全开放状态下，主动脉瓣在血液返流方向上的截面积是其关闭动力的重要来源，从关闭角度来讲，三叶瓣是唯一理想的瓣膜。     

Application of finite element analysis to the design of tissue leaflets for a percutaneous aortic valve

Percutaneous Aortic Valve (PAV) replacement is an attractive alternative to open heart surgery, especially for patients considered to be poor surgical candidates. Despite this, PAV replacement still has its limitations and associated risks. Bioprosthetic heart valves still have poor long-term durability due to calcification and mechanical failure. In addition, the implantation procedure often presents novel challenges, including damage to the expandable stents and bioprosthetic leaflets. In this study, a simplified version of Fung's elastic constitutive model for skin, developed by Sun and Sacks, was implemented using finite element analysis (FEA) and applied to the modelling of bovine and kangaroo pericardium. The FEA implementation was validated by simulating biaxial tests and by comparing the results with experimental data. Concepts for different PAV geometries were developed by incorporating valve design and performance parameters, along with stent constraints. The influence of effects such as different leaflet material, material orientation and abnormal valve dilation on the valve function was investigated. The stress distribution across the valve leaflet was also examined to determine the appropriate fibre direction for the leaflet. The simulated attachment forces were compared with suture tearing tests performed on the pericardium to evaluate suture density. It is concluded that kangaroo pericardium is suitable for PAV applications, and superior to bovine pericardium, due to its lower thickness and greater extensibility.     

To what extent can 3D model replicate dimensions of individual mitral valve prolapse?

Determining the complex geometry of mitral valve prolapse is often difficult. We constructed 3D models of six prolapsed mitral valves for surgical assessment, and evaluated how accurately the models could replicate individual valve dimensions. 3D polygon data were constructed based on an original segmentation method for computed tomography images. The model’s replication performance was confirmed via dimensional comparison between the actual hearts during surgery and those models. The results revealed that the prolapsed segments matched in all cases; however, torn chordae were replicated in four cases. The mean height differences were 0.0 mm (SD 1.6, range ??2 to +?2 mm) for the anterolateral side, 0.0 mm (SD 1.7, range ??2 to +?2 mm) for the prolapsed leaflet center, and ??1.5 mm (SD 0.6, range ??1 to ??2 mm) for the posteromedial side. Regression analysis showed a strong and positive correlation, and Bland–Altman plots indicated quantitative similarity of the models to the actual hearts. We concluded that our 3D valve models could replicate the actual mitral valve prolapses within acceptable dimensional differences. Our concepts are useful for better 3D valve creation and better surgical planning with reliable 3D valve models.     

Static and dynamic stresses during valve closure of a bileaflet mechanical heart valve prosthesis.

The effect of contact geometry and component compliance on the magnitude, distribution, and state of various types of stresses on a bileaflet mechanical heart valve prosthesis during valve closure was analyzed using an Edwards-Duromedics mitral valve as example. Static and dynamic stresses developing on both the leaflet and pivot ball during valve closure were modeled using finite element analysis (FEA). Uniform contact between the leaflet and housing as well as between the pivot ball and pivot slot can significantly reduce both static and dynamic stresses around the contact area. The level of the dynamic flexural stresses can be an order of magnitude higher than that of the static stresses. When both the radial and axial compliance of the housing are taken into consideration, peak dynamic stress was more than 40% less than that generated through the impact between a moving leaflet and a non-compliant rigid housing.     

Finite Element Investigation of Stentless Pericardial Aortic Valves: Relevance of Leaflet Geometry

Recent developments in aortic valve replacement include the truly stentless pericardial bioprostheses with single point attached commissures (SPAC) implantation technique. The leaflet geometry available for the SPAC valves can either be a simple tubular or a complex three-dimensional structure molded using specially designed molds. Our main objective was to compare these two leaflet designs, the tubular vs. the molded, by dynamic finite element simulation. Time-varying physiological pressure loadings over a full cardiac cycle were simulated using ABAQUS. Dynamic leaflet behavior, leaflet coaptation parameters, and stress distribution were compared. The maximum effective valve orifice area during systole is 633.5 mm² in the molded valve vs. 400.6 mm² in the tubular valve, and the leaflet coaptation height during diastole is 4.5 mm in the former, in contrast to 1.6 mm in the latter. Computed compressive stress indicates high magnitudes at the commissures and inter-leaflet margins of the tubular valve, the highest being 3.83 MPa, more than twice greater than 1.80 MPa in the molded valve. The molded leaflet design which resembles the native valve exerts a positive influence on the mechanical performance of the SPAC pericardial valves compared with the simple tubular design. This may suggest enhanced valve efficacy and durability.     

Design considerations and quantitative assessment for the development of percutaneous mitral valve stent

Percutaneous heart valve replacement is gaining popularity, as more positive reports of satisfactory early clinical experiences are published. However this technique is mostly used for the replacement of pulmonary and aortic valves and less often for the repair and replacement of atrioventricular valves mainly due to their anatomical complexity. While the challenges posed by the complexity of the mitral annulus anatomy cannot be mitigated, it is possible to design mitral stents that could offer good anchorage and support to the valve prosthesis. This paper describes four new Nitinol based mitral valve designs with specific features intended to address migration and paravalvular leaks associated with mitral valve designs. The paper also describes maximum possible crimpability assessment of these mitral stent designs using a crimpability index formulation based on the various stent design parameters. The actual crimpability of the designs was further evaluated using finite element analysis (FEA). Furthermore, fatigue modeling and analysis was also done on these designs. One of the models was then coated with polytetrafluoroethylene (PTFE) with leaflets sutured and put to: (i) leaflet functional tests to check for proper coaptation of the leaflet and regurgitation leakages on a phantom model and (ii) anchorage test where the stented valve was deployed in an explanted pig heart. Simulations results showed that all the stents designs could be crimped to 18F without mechanical failure. Leaflet functional test results showed that the valve leaflets in the fabricated stented valve coapted properly and the regurgitation leakage being within acceptable limits. Deployment of the stented valve in the explanted heart showed that it anchors well in the mitral annulus. Based on these promising results of the one design tested, the other stent models proposed here were also considered to be promising for percutaneous replacement of mitral valves for the treatment of mitral regurgitation, by virtue of their key features as well as effective crimping. These models will be fabricated and put to all the aforementioned tests before being taken for animal trials.     

A computational tool to support pre-operative planning of stentless aortic valve implant

In some cases of aortic valve leaflet disease, the implant of a stentless biological prosthesis represents an excellent option for aortic valve replacement (AVR). In particular, if compared to more classical surgical approaches, it provides a more physiological hemodynamic performance and a minor trombogeneticity avoiding the use of anticoagulants. The clinical outcomes of AVR are strongly dependent on an appropriate choice of both prosthesis size and replacement technique, which are, at present, strictly related to surgeon's experience and skill. Therefore, also this treatment, like most reconstructive procedures in cardiac surgery, remains "more art than science". Nowadays computational methodologies represent a useful tool both to investigate the aortic valve behavior, in physiologic and pathologic conditions and to reproduce virtual post-operative scenarios. The present study aims at supporting the AVR procedure planning through a patient-specific Finite Element Analysis (FEA) of stentless valve implantation. Firstly, we perform FEA to simulate the prosthesis placement inside the patient-specific aortic root; then, we reproduce, again by means of FEA, the diastolic closure of the valve to evaluate both the coaptation and the stress/strain state. The simulation results prove that both the valve size and the anatomical asymmetry of the Valsalva sinuses affect the prosthesis placement procedure.     

Aortic root performance after valve sparing procedure: a comparative finite element analysis

David and Yacoub sparing techniques are the most common procedures adopted for the surgical correction of aortic root aneurysms. These surgical procedures entail the replacement of the sinuses of Valsalva with a synthetic graft, inside which the cusps are re-suspended. Root replacement by a synthetic graft may result in altered valve behaviour both in terms of coaptation and stress distribution, thus leading to the failure of the correction. A finite element approach was used to investigate this phenomenon; four 3D models of the aortic root were developed to simulate the root in physiological, pathological and post-operative conditions after the two different surgical procedures. The physiological 3D geometrical model was developed on the basis of anatomical data obtained from echocardiographic images; it was then modified to obtain the pathological and post-operative models. The effectiveness of both techniques was assessed by comparison with the first two simulated conditions, in terms of stresses acting on the root, leaflet coaptation and interaction between leaflets and the graft during valve opening. Results show that both sparing techniques are able to restore aortic valve coaptation and to reduce stresses induced by the initial root dilation. Nonetheless, both techniques lead to altered leaflet kinematics, with more evident alterations after David repair.     

儿童主动脉瓣单叶置换术后瓣叶适应性的数值分析

目的 探究儿童主动脉瓣单叶置换（single aortic valve replacement, SAVR）术后主动脉瓣关闭不全（aortic insufficiency, AI）的生物力学机制,并提出应对措施。方法 构建理想化主动脉瓣模型及术后生长模型。改变置换瓣叶游离缘长度、瓣叶高度以及改进设计的一种凹型结构,比较不同结构尺寸对术后主动脉瓣运动同步性和关闭性能的影响。结果 置换瓣叶的闭合滞后于自体瓣叶,自体瓣叶贴合于置换瓣叶游离缘下方2 mm处。术后6年出现明显AI。增加瓣叶高度不能改善术后效果,且会增加瓣叶的最大应力。增加游离缘长度10%能够改善术后效果,当游离缘增加15%,会造成主动脉瓣过长,导致主动脉瓣产生不良的贴合。凹型主动脉瓣较传统结构更有利于瓣叶对合,能够有效降低最大应力20%,效果最佳。结论 儿童行SAVR术后,会使瓣叶运动不同步,对合点发生偏移,术后6年出现AI现象。建议裁剪为增加游离缘长度10%的凹型结构,不建议增加瓣叶高度。     

Characterizing the Collagen Fiber Orientation in Pericardial Leaflets Under Mechanical Loading Conditions

When implanted inside the body, bioprosthetic heart valve leaflets experience a variety of cyclic mechanical stresses such as shear stress due to blood flow when the valve is open, flexural stress due to cyclic opening and closure of the valve, and tensile stress when the valve is closed. These types of stress lead to a variety of failure modes. In either a natural valve leaflet or a processed pericardial tissue leaflet, collagen fibers reinforce the tissue and provide structural integrity such that the very thin leaflet can stand enormous loads related to cyclic pressure changes. The mechanical response of the leaflet tissue greatly depends on collagen fiber concentration, characteristics, and orientation. Thus, understating the microstructure of pericardial tissue and its response to dynamic loading is crucial for the development of more durable heart valve, and computational models to predict heart valves' behavior. In this work, we have characterized the 3D collagen fiber arrangement of bovine pericardial tissue leaflets in response to a variety of different loading conditions under Second-Harmonic Generation Microscopy. This real-time visualization method assists in better understanding of the effect of cyclic load on collagen fiber orientation in time and space.