Stevanella Marco, Votta Emiliano, Redaelli Alberto
Department of Bioengineering, Politecnico di Milano, Via Golgi 39, 20133 Milano, Italy.
J Biomech Eng. 2009 Dec;131(12):121010. doi: 10.1115/1.4000107.
Finite element modeling represents an established method for the comprehension of the mitral function and for the simulation of interesting clinical scenarios. However, current models still do not include all the key aspects of the real system. We implemented a new structural finite element model that considers (i) an accurate morphological description of the valve, (ii) a description of the tissues' mechanical properties that accounts for anisotropy and nonlinearity, and (iii) dynamic boundary conditions that mimic annulus and papillary muscles' contraction. The influence of such contraction on valve biomechanics was assessed by comparing the computed results with the ones obtained through an auxiliary model with fixed annulus and papillary muscles. At the systolic peak, the leaflets' maximum principal stress contour showed peak values in the anterior leaflet at the strut chordae insertion zone (300 kPa) and near the annulus (200-250 kPa), while much lower values were detected in the posterior leaflet. Both leaflets underwent larger tensile strains in the longitudinal direction, while in the circumferential one the anterior leaflet experienced nominal tensile strains up to 18% and the posterior one experienced compressive strains up to 23% associated with the folding of commissures and paracommissures, consistently with tissue redundancy. The force exerted by papillary muscles at the systolic peak was equal to 4.11 N, mainly borne by marginal chordae (76% of the force). Local reaction forces up to 45 mN were calculated on the annulus, leading to tensions of 89 N/m and 54 N/m for its anterior and posterior tracts, respectively. The comparison with the results of the auxiliary model showed that annular contraction mainly affects the leaflets' circumferential strains. When it was suppressed, no more compressive strains could be observed and peak strain values were located in the belly of the anterior leaflet. Computational results agree to a great extent with experimental data from literature. They provided insight into some of the features characterizing normal mitral function, such as annular contraction and leaflets' tissue anisotropy and nonlinearity. Some of the computed results may be useful in the design of surgical devices and techniques. In particular, forces applied on the annulus by the surrounding tissues could be considered as an indication for annular prostheses design.
有限元建模是一种已确立的方法，用于理解二尖瓣功能以及模拟有趣的临床场景。然而，当前模型仍未涵盖真实系统的所有关键方面。我们实施了一种新的结构有限元模型，该模型考虑了：（i）瓣膜的精确形态描述；（ii）对组织力学性能的描述，该描述考虑了各向异性和非线性；（iii）模拟瓣环和乳头肌收缩的动态边界条件。通过将计算结果与通过具有固定瓣环和乳头肌的辅助模型获得的结果进行比较，评估了这种收缩对瓣膜生物力学的影响。在收缩期峰值时，小叶的最大主应力等值线在前叶的支柱腱索插入区（300 kPa）和靠近瓣环处（200 - 250 kPa）显示出峰值，而后叶的值则低得多。两个小叶在纵向方向上都承受较大的拉伸应变，而在圆周方向上，前叶经历高达18%的名义拉伸应变，后叶经历高达23%的压缩应变，这与连合和副连合的折叠有关，与组织冗余情况一致。乳头肌在收缩期峰值时施加的力等于4.11 N，主要由边缘腱索承担（力的76%）。在瓣环上计算出高达45 mN的局部反作用力，导致其前、后段的张力分别为89 N/m和54 N/m。与辅助模型结果的比较表明，瓣环收缩主要影响小叶的圆周应变。当抑制瓣环收缩时，不再观察到压缩应变，峰值应变值位于前叶的中部。计算结果在很大程度上与文献中的实验数据一致。它们为正常二尖瓣功能的一些特征提供了见解，例如瓣环收缩以及小叶组织的各向异性和非线性。一些计算结果可能对外科手术器械和技术的设计有用。特别是，周围组织施加在瓣环上的力可被视为瓣环假体设计的一个指标。
