Changes in carbon monoxide transfer over 22 years in middle-aged men

Abstract

We measured single breath CO transfer (TL co), single breath alveolar volume (VA), CO transfer coefficient (Kco) and forced expiratory volume in 1 sec (FEV1) in 84 men, mean age 40·5 years at recruitment, in 1975 and in 1997. At recruitment, 42 men were cigarette smokers and 42 were not smoking. Mean annual decline in FEV1was similar in never- (34·2 ml yr−1) and ex- (33·1 ml yr−1) smokers and faster (51·0 ml yr−1) in continuing smokers.In contrast to predictions from cross-sectional reference values, there was no fall in TL coor Kcoin men who did not smoke over the period of follow-up. In the 16 men who smoked throughout follow-up there was a 10% fall in TL co(P=0·043) but most of this was due to a significant fall in VA(P=0·017), presumably reflecting uneven gas mixing.These results indicate the need for population-based longitudinal studies of TL coand Kco. If single breath estimates of VAare used in subjects with even mild airflow obstruction, Kcorather than TLcoshould be used to assess alveolar function.