Does abnormal single-breath nitrogen wash-out predict an accelerated decline in FEV1 in lung-healthy subjects?

Single-breath nitrogen wash-out and forced expirograms measured on two occasions, 8 years apart, were analysed for 24 subjects with varying degrees of peripheral airway involvement. Correlation analyses were carried out between closing volume in percentage of vital capacity (CV%), the slope of the alveolar plateau (phase III) and forced expiratory volume in 1 s (FEV1) for both occasions. The correlations between CV% and phase III measured on the first occasion and the long-term change in FEV1 were also studied. It is concluded that large deviations are required for CV% as well as phase III before any pathological decreases in the large airways will occur. The prognostic value of an abnormal single-breath nitrogen wash-out seems to be limited, at least in lung-healthy subjects.