Schulze-Bauer Christian A J, Mörth Christian, Holzapfel Gerhard A
Institute for Structural Analysis, Computational Biomechanics, Graz University of Technology, 8010 Graz, Schiesstattgasse 14-B, Austria.
J Biomech Eng. 2003 Jun;125(3):395-406. doi: 10.1115/1.1574331.
Inflation and extension tests of arteries are essential for the understanding of arterial wall mechanics. Data for such tests of human arteries are rare. At autopsy we harvested 10 non-diseased external iliac arteries of aged subjects (52-87 yrs). Structural homogeneity was ensured by means of ultrasound imaging, and anamneses of patients were recorded. We measured the axial in situ stretches, load-free geometries and opening angles. Passive biaxial mechanical responses of preconditioned cylindrical specimens were studied in 37 degrees C calcium-free Tyrode solution under quasistatic loading conditions. Specimens were subjected to pressure cycles varying from 0 to 33.3 kPa (250 mmHg) at nine fixed axial loads, varying from 0 to 9.90N. For the description of the load-deformation behavior we employed five "two-dimensional" orthotropic strain-energy functions frequently used in arterial wall mechanics. The associated constitutive models were compared in regard to their ability of representing the experimental data. Histology showed that the arteries were of the muscular type. In contrast to animal arteries they exhibited intimal layers of considerable thickness. The average ratio of wall thickness to outer diameter was 7.7, which is much less than observed for common animal arteries. We found a clear correlation between age and the axial in situ stretch lambda is (r = -0.72, P = 0.03), and between age and distensibility of specimens, i.e. aged specimens are less distensible. Axial in situ stretches were clearly smaller (1.07 +/- 0.09, mean +/- SD) than in animal arteries. For one specimen lambda is was even smaller than 1.0, i.e. the vessel elongated axially upon excision. The nonlinear and anisotropic load-deformation behavior showed small hystereses. For the majority of specimens we observed axial stretches smaller than 1.3 and circumferential stretches smaller than 1.1 for the investigated loading range. Data from in situ inflation tests showed a significant increase of the axial stretch with intraluminal pressure. Thus, for this type of artery the axial in situ stretch of a non-pressurized vessel is not representative of the axial in vivo stretch. None of the constitutive models were able to represent the deformation behavior of the entire loading range. For the physiological loading range, however, some of the models achieved good agreement with the experimental data.
动脉的膨胀和伸展测试对于理解动脉壁力学至关重要。关于人类动脉此类测试的数据很少。在尸检时，我们采集了10条老年受试者（52 - 87岁）的非病变髂外动脉。通过超声成像确保结构均匀性，并记录患者的病史。我们测量了轴向原位拉伸、无负载几何形状和开口角度。在37摄氏度无钙台氏液中，在准静态加载条件下研究了预处理圆柱形标本的被动双轴力学响应。标本在九个固定轴向载荷（从0到9.90N）下承受从0到33.3 kPa（250 mmHg）变化的压力循环。为了描述载荷 - 变形行为，我们采用了动脉壁力学中常用的五个“二维”正交各向异性应变能函数。比较了相关本构模型表示实验数据的能力。组织学显示这些动脉为肌性类型。与动物动脉不同，它们表现出相当厚的内膜层。平均壁厚与外径之比为7.7，远低于常见动物动脉的观察值。我们发现年龄与轴向原位拉伸λis之间存在明显相关性（r = -0.72，P = 0.03），以及年龄与标本的扩张性之间存在明显相关性，即老年标本的扩张性较小。轴向原位拉伸明显小于动物动脉（1.07 +/- 0.09，平均值 +/- 标准差）。对于一个标本，λis甚至小于1.0，即血管在切除时轴向伸长。非线性和各向异性的载荷 - 变形行为显示出小的滞后现象。对于大多数标本，在研究的载荷范围内，我们观察到轴向拉伸小于1.3，周向拉伸小于1.1。原位膨胀测试的数据显示轴向拉伸随腔内压力显著增加。因此，对于这种类型的动脉，未加压血管的轴向原位拉伸并不代表轴向体内拉伸。没有一个本构模型能够表示整个载荷范围的变形行为。然而，对于生理载荷范围，一些模型与实验数据达成了良好的一致性。
