Cough-reflex sensitivity to inhaled capsaicin in COPD associated with increased exacerbation frequency

Background and objective:   The causes of exacerbations in COPD patients are poorly understood. This study examined the association between cough-reflex sensitivity in patients with stable COPD and the frequency of subsequent exacerbations.
Methods:   The sampling frame for cases and controls for this study was patients attending a hospital outpatient clinic. cough-reflex sensitivity was evaluated using the log concentration of capsaicin causing five or more coughs (log C₅). Subsequent COPD exacerbations were identified prospectively via symptom-based diaries over a 12-month period.
Results:   The study group comprised 45 COPD subjects and 10 controls. Mean log C₅ was lower in the COPD group than in the control group (0.97 (95% confidence interval (CI): 0.76–1.18) versus 1.26 (95% CI: 0.81–1.71), P  = 0.095). In the COPD group, log C₅ was negatively correlated with serum CRP level ( r  = ?0.36, P  = 0.02) and significantly associated with the exacerbation frequency ( r  = ?0.38, P  = 0.01). Stepwise multiple regression analysis showed that cough-reflex sensitivity was significantly associated with exacerbation frequency ( r ² = 0.15, P  = 0.01).
Conclusions:   Hypersensitivity of the cough reflex to inhaled capsaicin might reflect airway inflammation in stable COPD patients, which predisposes to frequent exacerbations.