Sensitivity of the cough reflex in patients with chronic cough

Cough may occur in association with excess bronchial secretions and may, therefore, be productive. However, in a proportion of patients the cough is non-productive and a possible association with an enhanced response of the cough reflex has been postulated. Using the irritant capsaicin, the sensitivity of the cough reflex was measured in 363 individuals. A questionnaire was used to divide subjects into three groups: Group A) non-coughing controls; Group B) subjects with non-productive cough; and Group C) subjects with productive cough. The group means (+/- 99% confidence interval (CI)) of the log capsaicin concentration causing two or more coughs (C2) for groups A, B, C were 0.98 (+/- 0.08), 0.64 (+/- 0.09) and 1.04 (+/- 0.23), respectively. The log capsaicin concentration causing five or more coughs (C5) for groups A, B, C were 1.78 (+/- 0.1), 1.16 (+/- 0.12) and 1.54 (+/- 0.25), respectively. Group B was significantly more sensitive to inhaled capsaicin than the other groups (p less than 0.01). No significant difference was observed between groups A and C. Some differences were found when subgroups were examined within groups B and C. In group B, patients with post-nasal drip were found to have a normal sensitivity of the cough reflex and were, therefore, different from the remainder of patients with non-productive cough. In group C, patients with bronchiectasis and current infection showed an increase in the sensitivity of their cough reflex. It is concluded that cough can occur in association with either excess mucus production leading to productive cough or an increase in the sensitivity of the cough reflex, possibly leading to non-productive cough.