Gorman Cardiovascular Research Group, University of Pennsylvania, Glenolden, Pennsylvania, USA.
Ann Thorac Surg. 2012 Apr;93(4):1141-5. doi: 10.1016/j.athoracsur.2012.01.069. Epub 2012 Mar 6.
Using human mitral valve (MV) models derived from three-dimensional echocardiography, finite element analysis was used to predict mechanical leaflet and chordal stress. Subsequently, valve geometries were altered to examine the effects on stresses of the following: (1) varying coaptation area; (2) varying noncoapted leaflet tissue area; and (3) varying interleaflet coefficient of friction (μ).
Three human MV models were loaded with a transvalvular pressure of 80 mm Hg using finite element analysis. Initially leaflet coaptation was set to 10%, 50%, or 100% of actual coaptation length to test the influence of coaptation length on stress distribution. Next, leaflet surface areas were augmented by 1% overall and by 2% in the noncoapted "belly" region to test the influence of increased leaflet billowing without changing the gross geometry of the MV. Finally, the coefficient of friction between the coapted leaflets was set to μ = 0, 0.05, or 0.3, to assess the influence of friction on MV function.
Leaflet coaptation length did not affect stress distribution in either the coapted or noncoapted leaflet regions; peak leaflet stress was 0.36 ± 0.17 MPa at 100%, 0.35 ± 0.14 MPa at 50%, and 0.35 ± 0.15 MPa at 10% coaptation lengths (p = 0.85). Similarly, coaptation length did not affect peak chordal tension (p = 0.74). Increasing the noncoapted leaflet area decreased the peak valvular stresses by 5 ± 2% (p = 0.02). Varying the coefficient of friction between leaflets did not alter leaflet or chordal stress distribution (p = 0.18).
Redundant MV leaflet tissue reduces mechanical stress on the noncoapted leaflets; the extent of coaptation or frictional interleaflet interaction does not independently influence leaflet stresses. Repair techniques that increase or preserve noncoapted leaflet area may decrease mechanical stresses and thereby enhance repair durability.
利用从三维超声心动图获得的人二尖瓣（MV）模型，通过有限元分析来预测机械瓣叶和腱索的应力。随后，改变瓣叶几何形状，检查以下因素对应力的影响：（1）改变交界区面积；（2）改变非交界区瓣叶组织面积；和（3）改变瓣叶间摩擦系数（μ）。
使用有限元分析对三个 MV 模型施加 80mmHg 的跨瓣压。最初，瓣叶交界区设置为实际交界区长的 10%、50%或 100%，以测试交界区长对应力分布的影响。接下来，整体增加瓣叶表面积 1%，非交界区“腹部”增加 2%，以测试在不改变 MV 总体几何形状的情况下瓣叶膨胀增加对瓣叶的影响。最后，将瓣叶间的摩擦系数设置为μ=0、0.05 或 0.3，以评估摩擦对 MV 功能的影响。
瓣叶交界区长度均不影响交界区或非交界区瓣叶的应力分布；交界区瓣叶的峰值瓣叶应力在 100%时为 0.36±0.17MPa，在 50%时为 0.35±0.14MPa，在 10%时为 0.35±0.15MPa（p=0.85）。同样，交界区长度也不影响峰值腱索张力（p=0.74）。增加非交界区瓣叶面积可使瓣叶峰值应力降低 5±2%（p=0.02）。改变瓣叶间的摩擦系数不会改变瓣叶或腱索的应力分布（p=0.18）。
MV 瓣叶冗余组织减少了非交界区瓣叶的机械应力；交界区的范围或瓣叶间的摩擦相互作用不会独立影响瓣叶的应力。增加或保留非交界区瓣叶面积的修复技术可能会降低机械应力，从而提高修复耐久性。
