Adler A, Cowley E A, Bates J H, Eidelman D H
Meakins-Christie Laboratories, McGill University, Montreal, Quebec, Canada H2X 2P2.
J Appl Physiol (1985). 1998 Jul;85(1):231-7. doi: 10.1152/jappl.1998.85.1.231.
The constriction of pulmonary airways is limited by the tethering effect exerted by parenchymal attachments. To characterize this tethering effect at the scale of intraparenchymal airways, we studied the pattern of parenchymal distortion due to bronchoconstriction in a rat lung explant system. First, we measured the elastic modulus under tension for 2% (wt/vol) agarose alone (37.6 +/- 1.5 kPa) and for agarose-filled lung (5.7 +/- 1.3 kPa). The latter is similar to the elastic modulus of air-filled lung at total lung capacity (4.5-6 kPa) (S. J. Lai-Fook, T. A. Wilson, R. E. Hyatt, and J. R. Rodarte. J. Appl. Physiol. 40: 508-513, 1976), suggesting that explants can be used as a model of lung tissue distortion. Subsequently, confocal microscopic images of fluorescently labeled 0.5-mm-thick explants prepared from agarose-filled rat lungs inflated to total lung capacity (48 ml/kg) were acquired. Images were taken before and after airway constriction was induced by direct application of 10 mM methacholine, and the pattern of parenchymal distortion was measured from the displacement of tissue landmarks identified in each image for 14 explants. The magnitude of the radial component of tissue displacement was calculated as a function of distance from the airway wall and characterized by a parameter, b, describing the rate at which tissue movement decreased with radial distance. The parameter b was 0.994 +/- 0.19 (SE), which is close to the prediction of b = 1 of micromechanical modeling (T. A. Wilson. J. Appl. Physiol. 33: 472-478, 1972). There was significant variability in b, however, which was correlated with the fractional reduction in airway diameter (r = 0.496). Additionally, parenchymal distortion showed significant torsion with respect to the radial direction. This torsion was similar in concentric zones around the airway, suggesting that it originates from inhomogeneity in the parenchyma rather than inhomogeneous airway constriction. Our results demonstrate the significance of the nonlinear mechanical properties of alveolar walls and the anisotropy of the parenchyma in determining the nature of airway-parenchymal interdependence.
肺实质附着所产生的束缚效应限制了肺气道的收缩。为了在肺实质内气道的尺度上表征这种束缚效应，我们在大鼠肺外植体系统中研究了支气管收缩引起的肺实质变形模式。首先，我们测量了单独的2%（重量/体积）琼脂糖（37.6±1.5千帕）以及琼脂糖填充的肺（5.7±1.3千帕）在张力下的弹性模量。后者与全肺容量时充气肺的弹性模量（4.5 - 6千帕）相似（S. J. Lai - Fook、T. A. Wilson、R. E. Hyatt和J. R. Rodarte。《应用生理学杂志》40: 508 - 513，1976），这表明外植体可作为肺组织变形的模型。随后，获取了从充气至全肺容量（48毫升/千克）的琼脂糖填充大鼠肺制备的0.5毫米厚荧光标记外植体的共聚焦显微镜图像。在直接应用10毫摩尔乙酰甲胆碱诱导气道收缩之前和之后拍摄图像，并从14个外植体每个图像中识别的组织标志物的位移测量肺实质变形模式。组织位移径向分量的大小作为距气道壁距离的函数进行计算，并通过一个参数b来表征，该参数描述组织运动随径向距离减小的速率。参数b为0.994±0.19（标准误），这与微机械模型预测的b = 1接近（T. A. Wilson。《应用生理学杂志》33: 472 - 478，1972）。然而，b存在显著变异性，且与气道直径的分数减少相关（r = 0.496）。此外，肺实质变形相对于径向方向表现出显著的扭转。这种扭转在气道周围的同心区域相似，表明它源于肺实质的不均匀性而非不均匀的气道收缩。我们的结果证明了肺泡壁的非线性力学特性和肺实质的各向异性在决定气道 - 肺实质相互依存性质方面的重要性。
