Debes J C, Fung Y C
Department of Bioengineering, University of California, San Diego, La Jolla 92093-0412, USA.
Am J Physiol. 1995 Aug;269(2 Pt 2):H433-42. doi: 10.1152/ajpheart.1995.269.2.H433.
A new method has been developed for measuring the stress-strain relationship in excised canine pulmonary arteries. Segments of dog main right pulmonary arteries were isolated by making two transverse cuts at each end of a segment near the bifurcations, yielding short cylinders, which were then cut radially, relieving the residual stress, causing the cylindrical shells to spring open to approximately flat rectangular slabs with dimensions approximately 1.0 x 3.0 x 0.1 cm. The specimens were then tested using a biaxial tensile testing machine. The resulting data show an approximately linear relationship between Kirchhoff stress and Lagrangian strain with very little hysteresis. The following pseudostrain energy function serves as a practical approximation for pulmonary arteries subjected to physiological levels of stress and strain: rho 0W(2) = 1/2(a1E2xx + a2E2yy + 2 a4ExxEyy), where rho 0 is the density of the wall (mass per unit volume), W is the energy per unit mass [superscript "(2)" indicates this is a 2-dimensional strain energy function], E is strain, a1, a2, and a4 are material constants with units of stress, and the subscripts x and y refer to the circumferential and axial axes, respectively, of the artery. To assess the physiological level of strain in the main right pulmonary artery, vessels were perfused in situ at physiological pressure (26 cmH2O) with silicone elastomer. The arteries were then excised and marked with small ink spots. Photographs of the spots on four tangent planes of the excised artery indicate a maximum circumferential strain of 21.5% and a maximum axial strain of 36.5% relative to the zero-stress state. These values are within the range of strain used in the biaxial tests. The relationship between Kirchhoff stress and Green's strain is approximately linear within the physiological range. The stress levels required to cause tissue failure are at least 10 times greater than the estimated normal physiological level.
已开发出一种新方法来测量切除的犬肺动脉中的应力-应变关系。通过在靠近分叉处的一段肺动脉两端各做两个横向切口，分离出犬主右肺动脉的节段，得到短圆柱体，然后将其沿径向切割，消除残余应力，使圆柱壳弹开成尺寸约为1.0×3.0×0.1厘米的近似扁平矩形板。然后使用双轴拉伸试验机对标本进行测试。所得数据显示，基尔霍夫应力与拉格朗日应变之间存在近似线性关系，滞后现象极小。以下伪应变能函数可作为承受生理应力和应变水平的肺动脉的实际近似：ρ₀W(²) = 1/2(a₁E₂ₓₓ + a₂E₂ᵧᵧ + 2a₄EₓₓEᵧᵧ)，其中ρ₀是壁的密度（单位体积质量），W是单位质量的能量[上标“(²)”表示这是二维应变能函数]，E是应变，a₁、a₂和a₄是具有应力单位的材料常数，下标x和y分别指动脉的圆周轴和轴向轴。为评估主右肺动脉中的生理应变水平，在生理压力（26厘米水柱）下对血管进行原位灌注硅橡胶弹性体。然后切除动脉并用小墨点标记。切除动脉的四个切面上墨点的照片显示，相对于零应力状态，最大圆周应变为21.5%，最大轴向应变为36.5%。这些值在双轴试验中使用的应变范围内。在生理范围内，基尔霍夫应力与格林应变之间的关系近似线性。导致组织破坏所需的应力水平至少比估计的正常生理水平大10倍。
