Cough Reflex Sensitivity and Bronchial Hyper-responsiveness

Subjects inhaled increasing concentrations of citric acid, which induces coughing in a dose-dependent, reproducible matter. Following each inhalation, the number of coughs in the subsequent 15 seconds was counted and recorded. The challenge was terminated once the citric acid induced 5 or more coughs and the logarithmic (base 10) concentration provoking 5 coughs was recorded.

A baseline spirometry was used to assess how well the participant's lungs work by measuring how much air was inhale, how much was exhale and how quickly the participant exhaled. If this was normal, the subject inhaled slowly and deeply the methacholine test solution from a nebulizer and was told to hold their breath for 5 seconds. This was repeated until 5 inhalations were performed in no more than two minutes.