Effects of cigarette smoke on methacholine- and AMP-induced air trapping in asthmatics

Objective: No information is available on the effect of cigarette smoke on bronchoconstrictor-induced air trapping in asthma. The aim of this study was to evaluate the additional influence of smoking on methacholine-and adenosine 50-monophosphate (AMP)-induced air trapping in subjects with asthma. Methods: Airway responsiveness to methacholine and AMP, bronchial (J'aw(NO)) and alveolar (CA(NO)) nitric oxide (NO) and exhaled breath condensate pH were measured in 68 adults (23 current smokers with asthma, 23 non-smokers with asthma and 22 current or former smokers with chronic obstructive pulmonary disease; COPD). The degree of air trapping induced by each bronchoconstrictor agent was expressed by the percent fall in forced vital capacity (FVC) at a 20% fall in forced expiratory volume in 1 s relative to FVC after saline inhalation (Delta FVC%). Results: The Delta FVC% for AMP was higher in both smokers with asthma and patients with COPD than in non-smokers with asthma (p < 0.001). By contrast, Delta FVC% for methacholine was similar in the three groups of subjects (p = 0.69). In smokers with asthma, but not in the other two groups, there was a correlation between the residual volume/total lung capacity at baseline and the Delta FVC% induced by each bronchoconstrictor agent. Mean values for J'awNO were higher in non-smokers with asthma than in the other two groups (p < 0.05). Conclusions: The results of this study suggest that factors underlying bronchoconstriction induced by indirect agonists are different in smokers and non-smokers with asthma. These observations might be clinically relevant, because triggers that frequently induce bronchial obstruction in the real world act by an indirect mechanism.