Gorman Cardiovascular Research Group, Glenolden, Pennsylvania, USA.
Am J Physiol Heart Circ Physiol. 2010 Dec;299(6):H1790-4. doi: 10.1152/ajpheart.00370.2010. Epub 2010 Oct 15.
Three-dimensional (3-D) echocardiography allows the generation of anatomically correct and time-resolved geometric mitral valve (MV) models. However, as imaged in vivo, the MV assumes its systolic geometric configuration only when loaded. Customarily, finite element analysis (FEA) is used to predict material stress and strain fields rendered by applying a load on an initially unloaded model. Therefore, this study endeavors to provide a framework for the application of in vivo MV geometry and FEA to MV physiology, pathophysiology, and surgical repair. We hypothesize that in vivo MV geometry can be reasonably used as a surrogate for the unloaded valve in computational (FEA) simulations, yielding reasonable and meaningful stress and strain magnitudes and distributions. Three experiments were undertaken to demonstrate that the MV leaflets are relatively nondeformed during systolic loading: 1) leaflet strain in vivo was measured using sonomicrometry in an ovine model, 2) hybrid models of normal human MVs as constructed using transesophageal real-time 3-D echocardiography (rt-3DE) were repeatedly loaded using FEA, and 3) serial rt-3DE images of normal human MVs were used to construct models at end diastole and end isovolumic contraction to detect any deformation during isovolumic contraction. The average linear strain associated with isovolumic contraction was 0.02 ± 0.01, measured in vivo with sonomicrometry. Repeated loading of the hybrid normal human MV demonstrated little change in stress or geometry: peak von Mises stress changed by <4% at all locations on the anterior and posterior leaflets. Finally, the in vivo human MV deformed minimally during isovolumic contraction, as measured by the mean absolute difference calculated over the surfaces of both leaflets between serial MV models: 0.53 ± 0.19 mm. FEA modeling of MV models derived from in vivo high-resolution truly 3-D imaging is reasonable and useful for stress prediction in MV pathologies and repairs.
三维（3-D）超声心动图可生成解剖结构正确且时间分辨的二尖瓣（MV）几何模型。然而，活体成像时，MV 仅在加载时呈现其收缩几何形状。通常，有限元分析（FEA）用于预测初始未加载模型施加负载时的材料应力和应变场。因此，本研究旨在为应用 MV 生理、病理生理和外科修复的体内 MV 几何形状和 FEA 提供框架。我们假设，体内 MV 几何形状可以合理地用作计算（FEA）模拟中未加载阀的替代物，产生合理且有意义的应力和应变幅度和分布。进行了三项实验以证明 MV 瓣叶在收缩期加载期间相对不变形：1）使用绵羊模型中的超声心动图测量体内瓣叶应变，2）使用经食管实时 3-D 超声心动图（rt-3DE）构建的正常人类 MV 的混合模型，使用 FEA 重复加载，3）正常人类 MV 的连续 rt-3DE 图像用于构建舒张末期和等容收缩末期的模型，以检测等容收缩期间的任何变形。体内 sonomicrometry 测量的等容收缩相关的平均线性应变值为 0.02 ± 0.01。正常混合人类 MV 的重复加载显示出应力或几何形状的变化很小：在前、后瓣叶的所有位置，von Mises 峰值应力的变化都小于 4%。最后，活体 MV 在等容收缩期间变形很小，通过在两个瓣叶表面之间的连续 MV 模型之间计算的平均值绝对值差进行测量：0.53 ± 0.19 毫米。源自体内高分辨率真正 3-D 成像的 MV 模型的 FEA 建模是合理且有用的，可用于 MV 病变和修复中的应力预测。
