Airway cough sensitivity to inhaled capsaicin and bronchial responsiveness to methacholine in asthmatic and bronchitic subjects

The objective of this study was to evaluate the effect of chronic airway inflammation on airway cough sensitivity and non-specific bronchial responsiveness, and the relationship between them. The capsaicin cough threshold, defined as the lowest concentration of capsaicin causing five or more coughs, and non-specific bronchial responsiveness, defined as the methacholine concentration causing a 20% fall in forced expiratory volume in 1 s (FEV1) (PC20-FEV1), were measured in 18 asthmatic, 13 bronchitic (sinobronchial syndrome) and 28 healthy non-atopic subjects. All subjects were non-smoking men. The geometric mean values (mumol) of the cough threshold were 18.9 (GSEM 1.29), 8.69 (GSEM 1.29) and 27.6 (GSEM 1.31) in asthmatic, bronchitic and normal subjects, respectively. The value in bronchitic subjects was significantly lower (P < 0.02) than that in normal subjects. The geometric mean value of PC20-FEV1 in asthmatic subjects (0.48 mg/ml (GSEM 1.38)) was significantly lower than that in bronchitic subjects (18.5 mg/ml (GSEM 1.75)) (P < 0.001). There was no correlation between cough threshold and PC20-FEV1 values (correlation coefficient (r) = 0.155). These results indicate that cough sensitivity is potentiated by chronic airway inflammation in bronchitis but not in asthma, and suggest that cough sensitivity and bronchial responsiveness may be independently potentiated by different mechanisms resulting from chronic airway inflammation.