Mechanical properties of mouse lungs: effects of degassing on normal, hyperoxic, and irradiated lungs.

We critically examined conventional techniques for studying static mechanical properties of the lungs using normal mice, mice exposed to high O2 concentrations, and mice with radiation pneumonitis and radiation fibrosis. Successive pressure-volume (PV) curves were performed in situ both before and after degassing the lungs in vacuo. In both hyperoxia and radiation pneumonitis the deflation limbs of the curves were shifted to the right compared with their corresponding controls. However, the curves were further shifted rightward and downward after degassing the lung, as compared with the curve obtained before degassing. This effect of degassing was most marked in abnormal lungs and was not corrected by repeating inflation-deflation cycles nor by inflating to higher pressures and allowing time for units to open. Histology showed that abnormal lungs fixed in inflation after degassing were unevenly reinflated. It is speculated that, in conditions such as hyperoxia and radiation pneumonitis, altered surface tension properties may result in uneven reinflation of the lungs after degassing and that nonuniform reinflation may produce spurious shifts in the shape as well as the amplitude of PV curves. Thus PV curves performed with air after degassing the lung may not correctly represent the mechanical properties of abnormal lungs.