Capsaicin evoked cough responses
Participants inhaled four breaths of doubling concentrations of capsaicin (0.97-1,000µM: Stockport Pharmaceuticals Ltd, Stockport, UK) at 30 second intervals using a dosimeter (KoKo dosimeter; DeVilbiss Healthcare Inc., Somerset, PA). Only the coughs evoked in the first 15 seconds post each inhalation were counted. The challenge continued until the maximum tolerated dose or the final concentration was inhaled. The maximum number of coughs evoked at any concentration (Emax) and the concentration evoking 50% of the maximal response (ED50) were calculated.