Trapped air in extrinsic allergic alveolitis.

Non-ventilated lung volume (trapped air) during tidal breathing and several other lung function parameters were determined in 19 patients with extrinsic allergic alveolitis, most of them with farmer's lung, and in 28 non-smoking healthy subjects. The trapped air was significantly larger (p < 0.01) in the patients (mean 0.73 litres) than in normal subjects (mean 0.32 litres); in 7 patients (37%) it was definitely enlarged. The results suggest that the frequent increase of trapped air may be caused by patchy small airways occlusion due to bronchiolitis.