PASSIVE MATERIAL PROPERTIES OF INTACT VENTRICULAR MYOCARDIUM DETERMINED FROM A CYLINDRICAL MODEL
PASSIVE MATERIAL PROPERTIES OF INTACT VENTRICULAR MYOCARDIUM DETERMINED FROM A CYLINDRICAL MODEL
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DOI：
10.1115/1.2894084
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发表时间：
1991-02-01
影响因子：
1.7
通讯作者：
WALDMAN, LK
中科院分区：
文献类型：
--
作者：
GUCCIONE, JM;MCCULLOCH, AD;WALDMAN, LK
犬左心室赤道区被模拟为由具有均匀指数特性的不可压缩超弹性材料组成的厚壁圆柱体。被动心肌的各向异性特性被假定为相对于纤维轴的局部横向各向同性，该纤维轴的取向沿壁呈线性变化。同时对圆柱体进行充气、拉伸和扭转，以产生先前在钾停滞犬心脏中测量的心外膜应变。通过将无应力构型视为翘曲圆柱弧，考虑了空载状态下的残余应力。在各向同性材料特性的特殊情况下，扭转和残余应力都显著降低了先前模型预测的心内膜高周向应力峰值。然而，合成的轴向力和力矩是导致观察到的心外膜变形所必需的。因此，各向异性材料参数被发现使这些结果最小化，并允许在已知的脑室压力负荷下发生规定的位移。该参数优化问题的全局最小解表明，对于较大范围的假设纤维角分布和残余应力，被动心肌(定义为20%等轴伸展)在纤维方向的刚度将是横向的2.4到6.6倍。这与双轴组织测试的结果一致。预测的跨壁纤维应力分布相对平坦，在心外膜下有轻微的峰值，纤维应变分布与实验观察到的肌节长度分布非常一致。结果表明，与纤维结构相关的扭转、残余应力和材料各向异性都可以降低被动左室心内膜的应力梯度。
The equatorial region of the canine left ventricle was modeled as a thick-walled cylinder consisting of an incompressible hyperelastic material with homogeneous exponential properties. The anisotropic properties of the passive myocardium were assumed to be locally transversely isotropic with respect to a fiber axis whose orientation varied linearly across the wall. Simultaneous inflation, extension, and torsion were applied to the cylinder to produce epicardial strains that were measured previously in the potassium-arrested dog heart. Residual stress in the unloaded state was included by considering the stress-free configuration to be a warped cylindrical arc. In the special case of isotropic material properties, torsion and residual stress both significantly reduced the high circumferential stress peaks predicted at the endocardium by previous models. However, a resultant axial force and moment were necessary to cause the observed epicardial deformations. Therefore, the anisotropic material parameters were found that minimized these resultants and allowed the prescribed displacements to occur subject to the known ventricular pressure loads. The global minimum solution of this parameter optimization problem indicated that the stiffness of passive myocardium (defined for a 20 percent equibiaxial extension) would be 2.4 to 6.6 times greater in the fiber direction than in the transverse plane for a broad range of assumed fiber angle distributions and residual stresses. This agrees with the results of biaxial tissue testing. The predicted transmural distributions of fiber stress were relatively flat with slight peaks in the subepicardium, and the fiber strain profiles agreed closely with experimentally observed sarcomere length distributions. The results indicate that torsion, residual stress and material anisotropy associated with the fiber architecture all can act to reduce endocardial stress gradients in the passive left ventricle.