To evaluate the effect of chronic airway inflammation on cough sensitivity and bronchial responsiveness, we measured the cough threshold to tartaric acid and bronchial responsiveness to methacholine (PC20-FEV1) in 13 asthmatic, 13 bronchitic (sino-bronchial syndrome) and 49 healthy non-atopic subjects. All subjects were non-smokers. The geometric mean value of the cough threshold was 9.55, 5.62 and 12.3% in asthmatic, bronchitic and normal subjects, respectively. The value in bronchitic subjects was significantly (p < 0.02) lower than that in normal subjects. The geometric mean value of PC20-FEV1 in asthmatic subjects (0.63mg/ml) was significantly lower than those in bronchitic (8.7 mg/ml) (p < 0.01) and normal subjects (21.4 mg/ml) (p < 0.01). There was no correlation between cough threshold and PC20-FEV1 values [correlation coefficient (r) = 0.06, p > 0.1]. 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.
