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

We measured single breath CO transfer (T-Lco), Single breath alveolar volum e (V-A), CO transfer coefficient (K-co) and forced expiratory volume in 1 s ec (FEV1) in 84 men, mean age 40.5 years at recruitment, in 1975 and in 199 7. At recruitment, 42 men were cigarette smokers and 42 were not smoking. M ean annual decline in FEV1 was 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 T-Lco or K-co in men who did not smoke over the period of follo w-up. In the 16 men who smoked throughout follow-up then was a 10% fall in T-Lco (P = 0.043) but most of this was due to a significant fall in V-A (P = 0.017), presumably reflecting uneven gas mixing. These results indicate the need for population-based longitudinal studies o f T-Lco and K-co. If single breath estimates of V-A are used in subjects wi th even mild airflow obstruction, K-co rather than T-Lco should be used to assess alveolar function.