Journal of Applied Physiology, Vol 47, Issue 2 360-368, Copyright © 1979 by American Physiological Society
Rheological properties of excised rabbit lung stiffened by repeated hyperinflation
K. Nagao, R. Ardila and J. Hildebrandt
Two rheological properties, stress adpatation (S) and hysteresis loop area
(H), were studied in normal fresh rabbit lungs and in lungs stiffened by 3
hr repeated inflation at zero end-expiratory pressure. S was measured on
the deflation limb at various volume levels ranging from 100 to 25% total
lung capacity (TLC). H was obtained in another group of lungs before and
after stiffening, for tidal volumes ranging from 5 to 30% TLC, at
end-expiratory levels from 25 to 70% TLC. In stiff lung, S after deflation
from TLC was biphasic (initial pressure rise, then a fall) whenever the
starting pressure exceeded approximately 10 cmH2O. At low lung volumes (25%
TLC) stress rose monotonically toward 10 cmH2O. Only monontonic adaptation
has previously been reported for normal lung. Tidal H in stiff lungs was
increased at all volume levels, occupying roughly 20% of a bounding
pressure-volume rectangle, resembling that of normal lungs near TLC but
twice that of normal loops at lower volumes. The results suggest that above
an equilibrium or transition pressure around 10 cmH2O the alveolar lining
in stiff lung may have film properties more resembling those of a viscous
liquid, becoming solidlike below this pressure. Similar viscous liquid
properties appear to exist on the inflation limb of normal lungs, and near
TLC on their deflation limb.
