Bronchial Responsiveness to Dry Air Hyperventilation in Smokers May Predict Decline in Airway Status Using Indirect Methods

BACKGROUND: Disabling respiratory symptoms and rapid decline of lung function may occur in susceptible tobacco smokers. Bronchial hyperresponsiveness (BHR) elicited by direct challenge methods predicts worse lung function outcomes. The aim of this study was to evaluate whether BHR to isocapnic hyperventilation of dry air (IHDA) was associated with rapid deterioration in airway status and respiratory symptoms. METHODS: One hundred twenty-eight smokers and 26 age- and sex-matched healthy individuals with no history of smoking were investigated. All subjects completed a questionnaire. Spirometry and impulse oscillometry (IOS) measurements were recorded before and after 4 min of IHDA. The tests were repeated after 3 years in 102 smokers and 11 controls. RESULTS: Eighty-five smokers (66 %) responded to the challenge with a ≥2.4-Hz increase in resonant frequency (F (res)), the cutoff limit defining BHR, as recorded by IOS. They had higher F (res) at baseline compared to nonresponding smokers [12.8 ± 3.2 vs. 11.5 ± 3.4 Hz (p < 0.05)] and lower FEV(1) [83 ± 13 vs. 89 ± 13 % predicted (p < 0.05)]. Multivariable logistic regression analysis indicated that wheezing (odds ratio = 3.7, p < 0.01) and coughing (odds ratio = 8.1, p < 0.05) were significantly associated with hyperresponsiveness. An increase in F (res) was recorded after 3 years in responding smokers but not in nonresponders or controls. The difference remained when subjects with COPD were excluded. CONCLUSIONS: The proportion of hyperresponsive smokers was unexpectedly high and there was a close association between wheezing and coughing and BHR. Only BHR could discriminate smokers with rapid deterioration of airway status from others.