Lung elastic recoil during breathing at increased lung volume

During dynamic hyperinflation with induced bronchoconstriction, there is a reduction in lung elastic recoil at constant lung volume (R. Pellegrino, O. Wilson, G. Jenouri, and J. R. Rodarte. J. Appl. Physiol. 81: 964-975, 1996 ). In the present study, lung elastic recoil at control end inspiration was measured in normal subjects in a volume displacement plethysmograph before and after voluntary increases in mean lung volume, which were achieved by one tidal volume increase in functional residual capacity (FRC) with consta nt tidal volume and by doubling tidal volume with constant FRC. Lung elasti c recoil at control end inspiration was significantly decreased by similar to 10% within four breaths of increasing FRC. When tidal volume was doubled , the decrease in computed lung recoil at control end inspiration was not s ignificant. Because voluntary increases of lung volume should not produce a irway closure, we conclude that stress relaxation was responsible for the d ecrease in lung recoil.