Kunzelman K S, Reimink M S, Cochran R P
Division of Cardiothoracic Surgery and Center for Bioengineering, University of Washington, Seattle 98195, USA.
J Heart Valve Dis. 1998 Jan;7(1):108-16.
The study objective was to compare coaptation, and leaflet and chordal stresses in normal and dilated mitral valves (18% annular dilatation) versus valves with flexible (Duran) and rigid (Carpentier-Edwards classic) ring annuloplasty, using a computer model. We have developed a 3D finite element model which allows us to evaluate valvular function in terms of coaptation and stresses in both leaflets and individual chordae.
The mitral valve was simulated using ANSYS 4.4A software. Normal model geometry, collagen fiber orientation, tissue thickness and material properties were determined from fresh porcine valves. For annular dilatation, the annular circumference was increased by 18% versus normal. For annuloplasty, a simulated flexible ring was attached to the annulus, and a simulated rigid ring then attached. Valves were evaluated during systolic pressure loading, after which timing of coaptation and leaflet and chordal stresses were determined.
In the normal valve, the anterior leaflet was subject to higher tensile stresses than the posterior leaflet which was under compression. With annular dilatation, all stresses were increased, particularly in the posterior leaflet. The flexible ring returned leaflet and chordal stresses closer to normal than did the rigid ring. Leaflet coaptation began at 5 ms in the normal state, was delayed by dilatation, and returned towards normal with both rings. The flexible ring returned coaptation and stresses closer to normal than did the rigid ring.
Ring annuloplasty reduces the stresses and improves coaptation relative to annular dilatation. The success of mitral annuloplasty is likely due to the re-establishment of posterior leaflet compressive stresses and near-normal coaptation.
本研究的目的是使用计算机模型，比较正常二尖瓣和扩张二尖瓣（瓣环扩张18%）与采用柔性（杜兰）和刚性（卡彭蒂埃-爱德华兹经典型）瓣环成形术的瓣膜在瓣叶对合及瓣叶和腱索应力方面的差异。我们开发了一个三维有限元模型，该模型使我们能够从瓣叶对合以及瓣叶和单个腱索的应力方面评估瓣膜功能。
使用ANSYS 4.4A软件模拟二尖瓣。正常模型的几何形状、胶原纤维方向、组织厚度和材料特性由新鲜猪瓣膜确定。对于瓣环扩张，瓣环周长相对于正常增加18%。对于瓣环成形术，先在瓣环上连接一个模拟的柔性环，然后连接一个模拟的刚性环。在收缩期压力加载过程中对瓣膜进行评估，之后确定瓣叶对合时间以及瓣叶和腱索应力。
在正常瓣膜中，前叶承受的拉应力高于受压的后叶。随着瓣环扩张，所有应力均增加，尤其是后叶。柔性环比刚性环使瓣叶和腱索应力更接近正常水平。在正常状态下，瓣叶对合始于5毫秒，扩张使其延迟，两种环均使其恢复至接近正常。柔性环比刚性环使对合和应力更接近正常水平。
相对于瓣环扩张，瓣环成形术可降低应力并改善瓣叶对合。二尖瓣瓣环成形术的成功可能归因于后叶压应力的重建和接近正常的瓣叶对合。
