Liao Jun, Vesely Ivan
Department of Biomedical Engineering, Lerner Research Institute, The Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195, USA.
J Biomech. 2003 Aug;36(8):1125-33. doi: 10.1016/s0021-9290(03)00109-x.
It has been reported previously that the mechanical properties of mitral valve chordae tendineae vary with chordal size and type. The popularity of mitral valve repair and chordal transposition warrant a better understanding of this phenomenon. The objectives of this study were to characterize the size- and type-related variations in chordal mechanics and explain them from the ultra-structural viewpoint. A total of 52 porcine mitral valve chordae from eight hearts were mechanically tested. We found that thicker chordae were more extensible than thinner chordae (4.2+/-1.5%, 8.1+/-2.5%, 15.7+/-3.9% and 18.4+/-2.8% strain corresponding to chordae with cross-sectional areas of 0.1-0.5, 0.5-1.0, 1.0-2.0, and 2.0-3.0mm(2), respectively), and had lower moduli (90.1+/-22.3, 83.7+/-18.5, 66.3+/-13.5 and 61.7+/-13.3 MPa corresponding to the same chordae groups). Polarized light microscopy was used to measure collagen fibril crimp. Thicker chordae had smaller crimp period than thinner chordae (11.3+/-1.4 microm vs. 14.8+/-3.0 microm), and were thus more highly crimped. Thicker chordae could therefore extend to greater strain before lock-up. Transmission electron microscopy (TEM) was used to measure choral fibril ultra-structure. Thinner chordae had lower average fibril diameter than thicker chordae but greater average fibril density. The cross-sectional area occupied by fibrils, however, was found to be constant at 49+/-2% regardless of chordal size or type. The difference in moduli between thick and thin chordae can therefore be explained by differences in fibril packaging and hence fibril-to-fibril interactions. According to a simple fibril interaction model, chordae with smaller diameter fibrils will have a greater number of fibril-to-fibril interactions, and hence a greater modulus.
先前已有报道称，二尖瓣腱索的力学性能随腱索大小和类型而变化。二尖瓣修复和腱索转位的普及使得有必要更好地理解这一现象。本研究的目的是表征腱索力学中与大小和类型相关的变化，并从超微结构角度对其进行解释。对来自8颗心脏的总共52根猪二尖瓣腱索进行了力学测试。我们发现，较粗的腱索比较细的腱索更具延展性（对应横截面积为0.1 - 0.5、0.5 - 1.0、1.0 - 2.0和2.0 - 3.0mm² 的腱索，应变分别为4.2±1.5%、8.1±2.5%、15.7±3.9%和18.4±2.8%），且模量较低（对应相同腱索组的模量分别为90.1±22.3、83.7±18.5、66.3±13.5和61.7±13.3MPa）。使用偏振光显微镜测量胶原纤维的卷曲。较粗腱索的卷曲周期比较细腱索小（11.3±1.4μm对14.8±3.0μm），因此卷曲程度更高。因此，较粗腱索在锁定前可延伸至更大应变。使用透射电子显微镜（TEM）测量腱索纤维的超微结构。较细腱索的平均纤维直径比较粗腱索低，但平均纤维密度更高。然而，发现无论腱索大小或类型如何，纤维所占的横截面积恒定为49±2%。因此，可以用纤维包装的差异以及由此产生的纤维间相互作用来解释粗、细腱索之间模量的差异。根据一个简单的纤维相互作用模型，具有较小直径纤维的腱索将具有更多的纤维间相互作用，并因此具有更大的模量。
