Wang Zhongjie, Xuan Yue, Guccione Julius M, Tseng Elaine E, Ge Liang
Department of Surgery, University of California San Francisco and San Francisco Veterans Affairs Medical Centers, San Francisco, CA.
J Heart Valve Dis. 2018;27(5):275-284.
Finite element analysis (FEA) can be used to determine ascending thoracic aortic aneurysm (aTAA) wall stress as a potential biomechanical predictor of dissection. FEA is dependent upon zero-pressure three-dimensional geometry, patient-specific material properties, wall thickness, and hemodynamic loading conditions. Unfortunately, determining material properties on unoperated patients using non-invasive means is challenging; and we have previously demonstrated significant material property differences among aTAA patients. Our study objective was to determine the impact of patient-specific material properties on aTAA wall stress. Using FEA, we investigated if patient-specific wall stress could be reasonably predicted using population-averaged material properties, which would greatly simplify dissection prediction.
ATAA patients (n=15) with both computed tomography (CT) imaging and surgical aTAA specimens were recruited. Patient-specific aTAA CT geometries were meshed and pre-stress geometries determined as previously described. Patient-specific material properties were derived from biaxial stretch testing of aTAA tissue and incorporated into a fiber-enforced hyper-elastic model, while group-averaged material properties were estimated using mean values of each parameter. Population-averaged material properties were also calculated from literature and studied. Wall stress distribution and its magnitude were determined using LS-DYNA FEA software. Peak and averaged stresses and stress distributions were compared between patient-specific and both group- and population-averaged material property models.
Patient-specific material properties had minimal influence on either peak or averaged wall stress compared to use of group- or population-averaged material properties. Stress distribution was also nearly superimposed among models with patient-specific vs. group- or population-averaged material properties and provided similar prediction of sites most prone to rupture.
FEA using population-averaged material properties likely provides reliable stress prediction to indicate sites most prone to rupture. Population-averaged material properties may be reliably used in computational models to assess wall stress and significantly simplify risk prediction of aTAA dissection.
有限元分析（FEA）可用于确定升主动脉瘤（aTAA）壁应力，作为夹层形成的潜在生物力学预测指标。有限元分析依赖于零压力三维几何形状、患者特异性材料特性、壁厚和血流动力学负荷条件。不幸的是，使用非侵入性方法确定未手术患者的材料特性具有挑战性；而且我们之前已经证明aTAA患者之间存在显著的材料特性差异。我们的研究目的是确定患者特异性材料特性对aTAA壁应力的影响。使用有限元分析，我们研究了是否可以使用群体平均材料特性合理预测患者特异性壁应力，这将大大简化夹层预测。
招募了15例同时有计算机断层扫描（CT）成像和手术切除的aTAA标本的患者。对患者特异性aTAA CT几何形状进行网格化，并如前所述确定预应力几何形状。患者特异性材料特性源自aTAA组织的双轴拉伸试验，并纳入纤维增强超弹性模型，而群体平均材料特性则使用每个参数的平均值进行估计。还从文献中计算并研究了群体平均材料特性。使用LS-DYNA有限元分析软件确定壁应力分布及其大小。比较了患者特异性与群体平均和总体平均材料特性模型之间的峰值和平均应力以及应力分布。
与使用群体平均或总体平均材料特性相比，患者特异性材料特性对峰值或平均壁应力的影响最小。在具有患者特异性与群体平均或总体平均材料特性的模型中，应力分布也几乎重叠，并对最容易破裂的部位提供了类似的预测。
使用群体平均材料特性的有限元分析可能提供可靠的应力预测，以指示最容易破裂的部位。群体平均材料特性可可靠地用于计算模型中，以评估壁应力，并显著简化aTAA夹层的风险预测。
