The effect of altering airway tone on the sensitivity of the cough reflex in normal volunteers.

Cough is frequently the presenting symptom of bronchial asthma, although cough can result from a wide variety of other respiratory disease. Treatment of chronic cough has proved extremely difficult. It has been suggested that treatment with bronchodilators may reduce the symptom of cough. In this study the effect of altering airway tone on the sensitivity of the cough reflex was determined. Twelve normal, healthy volunteers took part. The number of coughs following inhalations of single breaths of doubling concentrations of capsaicin (1.95-500 microM) was recorded before and after doses of salbutamol, methacholine and saline which altered forced expiratory volume in one second (FEV1) by 6.2 +/- 2.6%, -8.8 +/- 3.2% and -0.18 +/- 1.38%, respectively. In a further study the cough response was recorded before and after doses of salbutamol and ipratropium bromide, both of which reduced baseline respiratory resistance and resistance measured after capsaicin. Ipratropium bromide, salbutamol and methacholine, despite having significant effects on airway tone, did not change the sensitivity of capsaicin-induced cough. Thus, if bronchodilator drugs are antitussive in non-asthmatic patients, then this is unlikely to be due to an effect on the sensitivity of the cough reflex.