[Respiratory function impairment in idiopathic pulmonary fibrosis: with special emphasis on the apparently obstructive signs of small airways (author's transl)].

1. Respiratory function tests were performed in 6 cases with idiopathic pulmonary fibrosis (IPF) and 10 cases with pulmonary fibross associated with collagen disease. Obtained results were as follows: 2) In IPF, maximum mid-expiratory flow rate (MMF), maximal expiratory flows at 50 per cent (V50) and at 25 per cent (V25) of vital capacity significantly decreased, but no abnormal values was obtained in dynamic compliance test and multibreath N2 washout test. 3) The single model analysis of the lung functions suggested that the decrease of MMF, V50 or V25 in IPF was possibly resulted from the decrease of vital capacity. 4) These results suggest that the decrease of MMF, V50 or V25 observed in IPF is not the sign of the obstructive abnormalities in small airways, but the secondary sign caused by limitation of the lung volume.