Sacks Michael S, Enomoto Yoshiharu, Graybill Jeffrey R, Merryman W David, Zeeshan Ahmad, Yoganathan Ajit P, Levy Robert J, Gorman Robert C, Gorman Joseph H
Engineered Tissue Mechanics Laboratory, Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania 15219, USA.
Ann Thorac Surg. 2006 Oct;82(4):1369-77. doi: 10.1016/j.athoracsur.2006.03.117.
Surgical techniques have been developed for mitral valve repair for a wide range of pathologies. However, excessive tissue stress and damage have been identified as etiologic factors limiting long-term durability. Before computational models to optimize valve repair can be realistically developed, in-vivo dynamic mitral valve leaflet strain data are required. However, these data do not presently exist. In the present study, a sheep model and sonomicrometry were used to compute the in-surface Eulerian strain tensor of the anterior leaflet over the cardiac cycle at varying afterloads.
The anterior leaflet of nine Dorsett sheep (35 kg to 45 kg) was instrumented with nine 1-mm hemispherical piezoelectric transducers in a 15-mm square array. Three-dimensional crystal spatial positions were recorded at 250 Hz over several cardiac cycles, with peak left ventricular pressures varying from 90 mm Hg to 200 mm Hg. The in-surface Eulerian strain tensor was computed from the crystal displacements.
The mitral valve anterior leaflet experiences large anisotropic strains and peak strain rates of 400%/s, followed by an absolute cessation of any deformation during systole. Increasing left ventricular pressure also increased the effective leaflet stiffness but not the peak strains.
We report the first data on the dynamic in-vivo strain tensor of a functioning mitral valve anterior leaflet, which indicated large anisotropic strains and very high strain rates. Our observations also suggest that changes in left ventricular pressure and annular geometry result in altered effective leaflet stiffness, and may be an important factor in reducing leaflet stress and as such potentially affect mitral valve repair longevity.
针对多种病理情况，已开发出二尖瓣修复的手术技术。然而，过度的组织应力和损伤已被确定为限制长期耐久性的病因。在能够实际开发用于优化瓣膜修复的计算模型之前，需要体内动态二尖瓣叶应变数据。然而，目前尚无这些数据。在本研究中，使用绵羊模型和超声心动图测量法来计算在不同后负荷下心动周期中前叶的表面欧拉应变张量。
对9只多塞特绵羊（体重35千克至45千克）的前叶在一个15毫米见方的阵列中植入9个1毫米的半球形压电换能器。在几个心动周期内以250赫兹的频率记录三维晶体空间位置，左心室峰值压力在90毫米汞柱至200毫米汞柱之间变化。根据晶体位移计算表面欧拉应变张量。
二尖瓣前叶经历大的各向异性应变，峰值应变率为400%/秒，随后在收缩期任何变形完全停止。左心室压力增加也增加了有效瓣叶刚度，但未增加峰值应变。
我们报告了关于功能性二尖瓣前叶动态体内应变张量的首批数据，表明存在大的各向异性应变和非常高的应变率。我们的观察还表明，左心室压力和瓣环几何形状的变化导致有效瓣叶刚度改变，这可能是减轻瓣叶应力的一个重要因素，因此可能影响二尖瓣修复的寿命。
