Changes in lung function after smoking cessation: an assessment from a cross-sectional survey.

Cross-sectional lung function data of 51 ex-smokers (mean, 8 +/- 7 yr since smoking cessation) were compared with those of 54 nonsmokers and 105 current smokers. All subjects were steel workers 45 to 55 yr of age. In order to assess whether lung function indexes improve after smoking cessation, "expected" values were calculated for the ex-smokers, taking into account both duration of smoking and time since cessation. Observed values of forced expiratory volume in one second, vital capacity, residual volume, peak expiratory flow rate, slope of the N2 single-breath washout, and bolus closing volume were significantly different from "expected" ones. This suggested that smoking cessation not only stopped the smoking-induced fast decline in lung function, but even led to some reversal toward nonsmoking values. This was already apparent in 22 subjects who had quit smoking less than 5 yr previously.