Effects of cigarette smoking and short-term smoking cessation on airway responsiveness to inhaled methacholine

Threshold of airway responsiveness to methacholine aerosol was determined in 53 apparently healthy persons. In 18 nonallergic nonsmokers matched according to sex and age to 18 nonallergic smokers, the mean methacholine threshold of airway response (T), as measured using partial flow-volume curves, had a tendency to be greater in nonsmokers, but the difference was not significant for the group as a whole; it was, however, significant for a subset of 9 matched pairs with a cigarette consumption greater than 10 pack-years (mean T nonsmokers, 2.8 mg/ml; smokers, 0.3; p = 0.036). In 17 smokers who stopped smoking for 99 days in average, T was not significantly different for the group as a whole, although the majority of the smokers reported improvement of respiratory symptoms after cessation of smoking. The results of this study indicate that cigarette smoking is associated with increased airways responsiveness to inhaled methacholine and that this effect is dose related.