Rheological properties of excised rabbit lung stiffened by repeated hyperinflation

Publisher Website
Google Scholar
Abstract
Two rheological properties, stress adaptation (S) and hysteresis loop area (H), were studied in normal fresh rabbit lungs and in lungs stiffened by 3 h repeated inflation at zero end-expiratory pressure. S was measured on the deflation limb at various volume levels ranging from 100-25% total lung capacity (TLC). H was obtained in another group of lungs before and after stiffening, for tidal volumes ranging from 5-30% TLC, at end-expiratory levels from 25-70% 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 monotonic 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. Above an equilibrium or transition pressure around 10 cmH2O the alveolar lining in stiff lung apparently may have film properties more resembling those of a viscous liquid, becoming solid-like below this pressure. Similar viscous liquid properties appear to exist on the inflation limb of normal lungs and near TLC on their deflation limb.