Corden J, David T, Fisher J
Department of Mechanical Engineering, University of Leeds.
Proc Inst Mech Eng H. 1995;209(4):243-53. doi: 10.1243/PIME_PROC_1995_209_351_02.
Leaflet tears originating from the free leaflet edge and calcification around the commissural region are common modes of failure exhibited by explanted bioprosthetic trileaflet heart valves. These may be a result of the cyclic bending and high levels of curvature that affect the leaflets within these areas during normal valve operation. These high levels of curvature occur in a short time period (approximately 20 ms) during rapid leaflet opening and to a lesser degree during leaflet closure. The curvatures that occur at the free leaflet edge of two designs of polyurethane trileaflet heart valve were determined in vitro at various stages during a cardiac cycle using a high-speed video camera (1000 frames/s). Significant deformations at the free leaflet edge were observed and bending radii as low as 0.55 +/- 0.125 mm (mean +/- standard deviation) were present during leaflet opening, 0.76 +/- 0.24 mm during leaflet closure and 1.01 +/- 0.27 mm while the valve was fully open during peak systole. The values of curvature were used to determine the values of bending strain and bending stress acting at the free leaflet edge using thin shell bending theory. The calculated values of bending strain were a maximum during the leaflet flexure associated with valve opening. These high levels of bending strain, which occur for short periods of time, are likely to be an important determinant of the valve's durability. It has been shown that the method of manufacture significantly influenced the level of bending strain in the valve leaflets. Valves manufactured using a dip-casting technique resulted in open leaflet bending strains up to 31 per cent lower than valves manufactured from solvent-cast sheets of polyurethane.
源于游离瓣叶边缘的瓣叶撕裂以及瓣叶联合区周围的钙化是植入的生物三叶形心脏瓣膜常见的失效模式。这些可能是由于在正常瓣膜运作期间影响这些区域内瓣叶的周期性弯曲和高曲率水平所致。这些高曲率水平在瓣叶快速打开期间的短时间内（约20毫秒）出现，在瓣叶关闭期间程度稍轻。使用高速摄像机（1000帧/秒）在心动周期的不同阶段体外测定了两种设计的聚氨酯三叶形心脏瓣膜游离瓣叶边缘处的曲率。在瓣叶打开期间观察到游离瓣叶边缘有显著变形，弯曲半径低至0.55±0.125毫米（平均值±标准差），瓣叶关闭期间为0.76±0.24毫米，在收缩期峰值瓣膜完全打开时为1.01±0.27毫米。利用薄壳弯曲理论，用曲率值来确定作用在游离瓣叶边缘的弯曲应变和弯曲应力值。计算得到的弯曲应变值在与瓣膜打开相关的瓣叶弯曲期间最大。这些短时间内出现的高弯曲应变水平可能是瓣膜耐久性的一个重要决定因素。已经表明，制造方法显著影响瓣膜瓣叶中的弯曲应变水平。采用浸铸技术制造的瓣膜，其打开瓣叶的弯曲应变比由聚氨酯溶剂浇铸片材制造的瓣膜低达31%。
