Cough Sensitivity in Pure Cough Variant Asthma Elicited Using Continuous Capsaicin Inhalation

Cough variant asthma has recently been described, mainly as airway inflammation in relation to bronchial asthma, but the relationship between the two types of asthma remains unclear. Further studies of cough receptor sensitivity are necessary to fully characterize cough variant asthma. We assessed the relevance of testing cough sensitivity using an Astograph® with continuous capsaicin inhalation, and compared the results with those obtained using intermittent inhalation. We showed the clinical applicability of testing cough sensitivity (0.156-80pM capsaicin; five or more coughs, 1 minute of continuous inhalation at each concentration) using this method. We compared cough sensitivity among patients with pure cough variant asthma who did not develop bronchial asthma after an observation period of at least 1 year, patients with bronchial asthma and healthy individuals. The continuous cough sensitivity test using the Astograph® was reproducible and reliable. Cough sensitivity in patients with pure cough variant asthma was significantly higher than that in healthy individuals. The cough sensitivity of patients with cough variant asthma is not necessarily identical to that of healthy individuals.