Respiratory impairment relating to smoking habits evaluated by lambda-mu-sigma method derived z-score in healthy ever-smokers

Background: Natural course of pulmonary function in healthy ever-smoker is still unclear. Objectives: We sought to assess influences of smoking habits to pulmonary function in subjects without lung disorders. Methods: Subjects were recruited from patients who attended to rural primary care clinics without any evidence of respiratory disorders. Each participant was asked to answer a questionnaire including smoking history and to measure forced vital capacity (FVC) and forced expiratory volume in one second (FEV1). Results: Eight hundred two subjects (339 of never smokers, 222 of ex-smokers and 241 of current smokers) were analyzed. Means of Lambda-Mu-Sigma method derived z-score of FEV1 (zFEV1) both in current-smokers (-0.061 +/- 0.923) and ex-smokers (-0.058 +/- 0.854) were lower than that in never-smokers (0.161 +/- 0.959). Univariate analysis showed that there were significant negative correlations between the pack-years and zFEV1 both in the ex-smokers and the current smokers. There was no significant correlation between the duration of smoking cessation and zFEV1 in the ex-smokers. Conclusion: Our data suggested that the respiratory function in healthy ever-smokers are decreased by smoking habits in dose-dependent manner. Despite the long duration of smoking cessation, the decreased respiratory function remains in the ex-smokers.