Bronchial responsiveness to inhaled methacholine in young asymptomatic smokers.

Methacholine inhalation challenges were performed in 10 young smokers who denied having respiratory symptoms and in 10 nonsmokers of the same age. There were five males and five females in each group. The bronchoconstriction was evaluated with specific lung conductance (sGL), maximum partial (initiated from end-inspiratory lung volume) expiratory flows assessed at 40% vital capacity breathing air (Vmax40p air), and a He-O2 mixture (Vmax40p He), and with maximum complete flows breathing He-O2 [forced expiratory volume at 1 s (FEV1), Vmax50c He]. Dose-response curves were studied for 1) threshold concentration (TC) where values depart by more than two SD from base line; 2) provocative concentration (PC) causing a fixed fall in a parameter. Smokers differed significantly from nonsmokers for TC and PC accessed by Vmax40p He (P less than 0.001 and P less than 0.01, respectively), Vmax40p air (P less than 0.01), and Vmax50c He (P less than 0.01 and P less than 0.05, respectively). TC and PC estimated by sGL and FEV1 were not significantly different. Males and females showed a similar reaction.