Airway closure and trapped gas during low volume breathing

We used a plethysmographic technique to estimate the trapped gas volume (TGV) in seven normal subjects after breathing air or o 2 normally at functional residual capacity (FRC-air, FRC-O 2) and near residual volume (RV) with small breaths (LVB-air, LVB-O 2). If airway closure occurs, lung units subtended by closed airways would tend to collapse as TGV is absorbed; rapidly if the gas is O 2 and slowly if it is air. Both inspiratory and expiratory quasi-static and static pressure-volume curves after LVB-O 2 for 180 sec demonstrated a shift to the right and increased hysteresis, reduced vital capacity (VC) and significantly increased transpulmonary pressures at 25% and 50% control VC (P L 25, P L 50) as compared with those of FRC-O 2 controls (P