Respiratory function in healthy ever-smokers is impaired by smoking habits in a dose-dependent manner.

BACKGROUND There is limited information about the respiratory function of ever-smokers without lung disorders. We sought to assess the effects of smoking habits on respiratory function in subjects without lung disorders. METHODS Subjects were recruited from among patients without any evidence of respiratory disorders who visited rural primary care clinics. Each participant was asked to answer a questionnaire that included questions smoking history. Their forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) were measured. RESULTS We analyzed 802 subjects (364 men and 438 women). The means of the lambda-mu-sigma method derived z-score of FEV1 (zFEV1) both in current-smokers and ex-smokers were lower than that in never-smokers. The mean zFEV1 in the ever-smokers with more than 30 pack-years of smoking history were lower than that in the ever-smokers with less smoking history. Univariate analysis showed that there were significant negative correlations between pack-years and zFEV1 both in the ex-smokers and current-smokers. There was no significant correlation between the duration of smoking cessation and zFEV1 in the ex-smokers. CONCLUSIONS Our data suggests that respiratory function in healthy ever-smokers is decreased based on smoking habits in a dose-dependent manner. Even after a long period of smoking cessation, the decreased respiratory function seems to be maintained in ex-smokers.

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