Lung mechanics in subjects showing increased residual volume without bronchial obstruction.

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Abstract
Fourteen subjects showing an increase of residual volume (RV) without any clinical or functional signs of bronchial obstruction were studied. Maximum expiratory flow volume (MEFV) curves were obtained with a pressure-corrected volume plethysmograph. Static pressure-volume curves were obtained by stepwise interruption of a slow expiration from total lung capacity (TLC) to RV. Static compliance was measured by the slope of pressure-volume curve between functional residual capacity (FRC) and FRC+20% of TLC. Maximum flow static recoil (MFSR) curves were constructed by plotting MEF obtained from MEFV curves against elastic pressure (Pst) obtained from pressure-volume curves at the same lung volumes. Most patients demonstrated a decrease of MEF 50% and 25% of VC. From the MFSR curves it was clear that this reduction was not the result of increased airways resistance, but rather of loss of elastic recoil. Most patients showed a significant decrease of Pst at different volumes and changes seem likely to be evidence of emphysema.