Bronchial responsiveness and lung function related to cigarette smoking and smoking cessation

The relationships between bronchial responsiveness and both cigarette smoking and smoking cessation are still controversial.

To investigate the effects of cigarette smoking and smoking cessation on bronchial reactivity and the level of pulmonary function, bronchial responsiveness to methacholine using the forced oscillation method, the transfer factor, and spirometry were measured in 180 nonsmokers, 109 current smokers, 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.

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 significantly 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).

There seems to be a partially reversible phenomenon that leads to improvement in airway responsiveness and DLCO upon smoking cessation.