Lung and alveolar wall elastic and hysteretic behavior in rats: effects of in vivo elastase treatment

Abstract

. Lung and alveolar wall elastic and hysteretic behavior in rats: effects of in vivo elastase treatment. J Appl Physiol 95: 1926-1936, 2003. First published July 18, 2003 10.1152/japplphysiol.00102. 2003.-We investigated the relationship between the microscopic elastic and hysteretic behavior of the alveolar walls and the macroscopic mechanical properties of the whole lung in an in vivo elastase-treated rat model of emphysema. We measured the input impedance of isolated lungs at three levels of transpulmonary pressure (Ptp) and used a linear model to estimate the dynamic elastance and hysteresivity of the lungs. The elastance of the normal lungs increased steeply with Ptp, whereas this dependence diminished in the treated lungs. Hysteresivity decreased significantly with Ptp in the normal lungs, but this dependence disappeared in the treated lungs. To investigate the microscopic origins of these changes, the alveolar walls were immunofluorescently labeled in small tissue strips. By using a fluorescent microscope, the lengths and angular orientations of individual alveolar walls were followed during cyclic uniaxial stretching of the tissue strips. The microstrains (relative change in segment length) and changes in angle of the alveolar walls showed considerable heterogeneity, which was interpreted in terms of a network model. In the normal strips, the alveolar walls showed larger angular changes compared with the treated tissue, whereas the alveolar walls of the treated tissue tended to be more extensible. Hysteresis in the average angle change was also larger in the treated tissue than in the normal tissue. We conclude that the decreased Ptp dependence of elastance and the constant hysteresivity in the treated lungs are related to microstructural remodeling and network phenomena at the level of the alveolar walls.

Early Emphysema in the Tight Skin and Pallid Mice

“…Hysteresivity is a macroscopic material property of the tissue (22), which also depends on the microscopic constituents of the alveolar walls. Since changes in the composition and structure of the parenchyma can alter hysteresivity in the emphysematous lung (31)(32)(33)(34), our data imply more viscous alveolar walls in the Tsk lung. Another unique observation is the low Raw values in the Tsk group (Figure 2A).…”

Static and dynamic imaging of alveoli using optical coherence tomography needle probes

“…Similar measurements have been performed with ex vivo tissue samples using light microscopy and multiphoton microscopy (10,15), and these small-scale measurements have been correlated against whole lung measurements of elastance (5). OCT is capable of performing highly localized measurements of the viscoelastic properties of tissue, a technique referred to as optical coherence elastography (21,22,49).…”

Biomechanics of the Aging Lung Parenchyma

“…The real part of the complex modulus is the storage modulus and the imaginary part is the loss modulus. The moduli are a function of the elastin, collagen, and PG content of the strip [1,21,27,43,45,51,105,146,161], alveolar size [21], anatomic makeup [125], tonicity of the surrounding fluid [27,99], cellular contractile state [44,54,106,160], genetic makeup [3], and the prestress implying nonlinear mechanical behavior [161]. By digesting collagen, elastin, or PGs, the respective contributions of these components can be estimated from stiffness measurements [1,75,105,161].…”