Bronchial Responsiveness and Lung Function Related to Cigarette Smoking and Smoking Cessation

Abstract

Background: The relationships between bronchial respo- nsiveness and both cigarette smoking and smoking cessation are still controversial. Methods: To investigate the effects of cigarette smok-ing and smoking cessation on bronchial reactivity and the level of pulmonary function, bronchial respon- siveness to methacholine using the forced oscillation method, the transfer factor, and spirometry were measured in 180 nonsmokers, 109 current smoking, and 82 ex- smokers. The following indices of bronchial responsiveness were used: (1) baseline respiratory resistance(Rrs);(2) the cumulative dose of methacholine(DA) causing an increase in Rrs by twice the baseline values (bronchial sensitivity); and(3) the slope of linearly decreased respiratory conductance (SGrs) representing bronchial reactivity . Results: Current smokers had significantly higher baseline Rrs(p<0.001) and bronchial responsiveness than did nonsmokers and ex-smokers. In 24.7% of smokers, Rrs increased by twice or more upon challenge with methacholine( responders), compared with 0% of nonsmokers (p<0.0001) and 19.5% of ex-smokers (p=0.28). SGrs for responders among ex- smokers was found not to differ from that for responders among smokers. However, smokers had a sign- ificantly lower DA of inhaled methacholine than did ex - smokers. Cigarette smoking was also associated with an appreciable reduction in FEV1/FVC (forced expiratory volume in 1s/forced vital capacity), DLCO ( carbon monoxide diffusing capacity), and DLCO/VA ( alveolar volume). Conclusion: There seems to be a partially reversible phenomenon that leads to improvement in airway responsiveness and DLCO upon smoking cessation.