Relationship of pulmonary function response to ozone exposure and capsaicin cough sensitivity

Context: Challenge studies in humans have shown considerable interindividual variability in pulmonary impairment across ozone exposure. Objective: Since previous results suggested effect modulation by neural mechanism, we investigated sensory C-fiber reactivity in relationship to ozone-triggered response pattern. Methods: Cough reflex thresholds reflecting C-fiber sensitivity were evaluated by capsaicin single breath dose-response method. Capsaicin concentrations triggering, respectively, two and five or more coughs (C2, C5) were recorded. Sixteen healthy subjects were randomly exposed in an intermittent exercise protocol to ozone concentrations of 240 and 40 ppb (sham exposure). Ozone responsiveness was defined by a decrease in forced expiratory volume in 1 s (FEV1) of more than 5%. Results: Based on a dichotomous classification, subjects with enhanced reactivity to ozone had lower cough thresholds than non-responders (C2, p = 0.035; C5, p = 0.086). Over all, we could demonstrate relationships between capsaicin sensitivity and ozone-triggered changes in FEV1, peak expiratory flow and maximal expiratory flow at 50% vital capacity but not in specific airway resistance. Conclusion: Our results suggest that capsaicin challenge tests might be useful to characterize subjects with enhanced pulmonary function response towards inhalant irritants.