Effects of smoking and smoking cessation on decline in pulmonary function

(Background) Natural course of pulmonary function after smoking cessation is still unclear. We sought to assess influences of smoking habits to lung function in subjects without pulmonary disorders. (Subjects and Methods) Total of 860 subjects were recruited from patients who attended to rural primary care clinics except for respiratory disorders. Each participant was asked to answer a questionnaire including smoking history and measure forced vital capacity (FVC) and forced expiratory volume in on second (FEV1). (Results) Both %FEV1 (measured FEV1 / predicted FEV1 X 100) in current smokers (CS) and %FEV1 in ex-smokers (ES) were lower than %FEV1 in non-smokers (NS). There was no difference in %FEV1 among the subgroups divided by age both in current smokers and ex-smokers. Also, there was no difference in %FEV1 among the subgroups divided by duration of smoking cessation in ex-smokers. Multivariate analysis showed that age, hight and amount of cigarette smoking were significantly related to FEV1 both in male CS and male ES. In male CS, the estimated decline of FEV1 per age was 26.9 mL and excess of decline pack-year of smoking was 2.6 mL. In male ES, The estimated decline of FEV1 per age was 25.9 mL and excess of decline pack-year of smoking was 1.3 mL. (Conclusion) Our data suggested that influences of smoking on FEV1 were observed even in healthy ex-smokers.