Cough threshold in patients with chronic obstructive pulmonary disease

Background-Cough is an important symptom of patients with chronic obstructi ve pulmonary disease (COPD). The cough threshold to citric acid and capsaic in in patients with COPD and in normal volunteers was measured, as well as bronchial hyperresponsiveness to methacholine. Methods-Nineteen patients with COPD and 22 controls were recruited. Subject s underwent a methacholine bronchoprovocation test and a cough challenge to citric acid and capsaicin. Results-The log citric acid cough threshold D-2 (concentration causing two coughs) was significantly lower in patients with COPD (mean 2.17 versus 2.5 6, mean difference (95% CI) 0.39 (0.04 to 0.74), p = 0.02) but not for caps aicin cough D-2 (0.66 versus 0.8, p= 0.41). Sixteen patients with COPD had bronchial hyperresponsiveness which was correlated with baseline FEV1 (r = 0.6, p = 0.01, 95% CI 0.15 to 0.84). Conclusions-Patients with COPD have a lower cough threshold to citric acid, possibly due to a differential effect of cigarette smoke on citric acid se nsitive cough receptors.