Vesely I, Lozon A
John P. Robarts Research Institute, University of Western Ontario, London, Canada.
J Biomech. 1993 Feb;26(2):121-31. doi: 10.1016/0021-9290(93)90043-e.
The mechanics of glutaraldehyde-fixed aortic valve leaflets depend largely on the amount of stress present during fixation. Our previous work has suggested that even when the aortic valve is flaccid, the leaflet components are preloaded. We have, therefore, hypothesized that fixing valve leaflets in this naturally preloaded state will affect the function of their components, the fibrosa and the ventricularis. We have compared the elastic response of fibrosa and ventricularis fixed under 'low' and 'zero' tensile and compressive preload by testing 120 of these layers: (i) fresh, (ii) glutaraldehyde-fixed, and (iii) isolated from whole porcine aortic valve leaflets fixed while intact. In both the radial and circumferential directions, the fibrosa from intact-fixed valves was more extensible than the fresh (39.2 vs 29.2% strain to high modulus phase at p < 0.0122, and 12.7 vs 8.1% strain, at p < 0.0003, respectively). The ventricularis from intact-fixed valves, however, was less extensible than when fresh (35.4 vs 63.7% strain, at p < 0.00001 in the radial direction). The fibrosa must have, therefore, been fixed under compression and the ventricularis under tension, when fixed together in the intact aortic valve cusp. The tensile stresses in the intact-fixed ventricularis produced a greater circumferential elastic modulus than in separately fixed tissue (9.62 vs 4.65 MPa, at p < 0.00001), likely through a fibre recruitment process. Compressive stresses in the fibrosa produced a decrease in the elastic modulus both radially and circumferentially (from 3.79 to 2.26 MPa at p < 0.0023, and from 9.55 to 4.65 MPa at p < 0.00001, respectively). Fixing porcine aortic valves at even minimal tensile and compressive preload, such as that which occurs naturally, significantly alters both the extensibility and the elastic modulus of the valve leaflet components.
戊二醛固定的主动脉瓣小叶的力学特性在很大程度上取决于固定过程中存在的应力大小。我们之前的研究表明，即使主动脉瓣处于松弛状态，小叶各成分也处于预加载状态。因此，我们推测在这种自然预加载状态下固定瓣膜小叶会影响其纤维层和心室层成分的功能。我们通过测试120层这样的组织来比较在“低”和“零”拉伸及压缩预加载下固定的纤维层和心室层的弹性反应：（i）新鲜的，（ii）戊二醛固定的，以及（iii）从完整固定的猪主动脉瓣小叶中分离出来的。在径向和周向方向上，完整固定瓣膜的纤维层比新鲜的更具延展性（分别在p < 0.0122时，高模量阶段的应变从29.2%变为39.2%，在p < 0.0003时，从8.1%变为12.7%）。然而，完整固定瓣膜的心室层比新鲜时延展性更差（在径向方向上，应变从63.7%变为35.4%，p < 0.00001）。因此，当在完整的主动脉瓣叶尖中一起固定时，纤维层必定是在压缩状态下固定的，而心室层是在拉伸状态下固定的。完整固定的心室层中的拉应力产生的周向弹性模量比单独固定的组织更大（9.62对4.65 MPa，p < 0.00001），这可能是通过纤维募集过程实现的。纤维层中的压应力导致径向和周向的弹性模量均降低（分别从3.79 MPa降至2.26 MPa，p < 0.0023，以及从9.55 MPa降至4.65 MPa，p < 0.00001）。即使在最小的拉伸和压缩预加载下固定猪主动脉瓣，比如自然发生的那种预加载，也会显著改变瓣膜小叶成分的延展性和弹性模量。
