Influence of Smoking Status on Cough Reflex Sensitivity in Subjects with COPD

Cough reflex sensitivity has not been studied extensively in patients with chronic obstructive pulmonary disease (COPD). The aim of the study was to evaluate cough reflex sensitivity to capsaicin in current and former smokers with COPD and examine its association with potentially protussive mediators. Fifteen active smokers and 18 ex-smokers with moderate to severe COPD, 14 healthy active smokers, and 13 healthy never smokers were enrolled. Capsaicin aerosol was administered in order of ascending concentration until the concentrations inducing two or more coughs (C₂) and five or more coughs (C₅) were attained. The concentrations of leukotriene E₄ (LTE₄), leukotriene B₄ (LTB₄), and interleukin-8 (IL-8) in bronchoalveolar lavage (BAL) fluid were analyzed by ELISA. Cough reflex sensitivity in COPD smokers [mean log C₂ = 1.20 ± 0.23 (SEM) μM; log C₅ = 1.85 ± 0.21 μM] did not differ from that in COPD ex-smokers (log C₂ = 1.15 ± 0.14 μM; log C₅ = 2.10 ± 0.19 μM; p > 0.05). Mean C₂ and C₅ in both COPD groups were significantly lower than in healthy active smokers, but higher compared with the healthy never-smokers. BAL fluid concentrations of LTE₄ and LTB₄ were similar in all groups. IL-8 concentrations did not differ between COPD smokers, COPD ex-smokers, and healthy active smokers, but were significantly higher in all three groups compared with healthy never smokers. Cough reflex sensitivity to capsaicin does not differ between smokers and ex-smokers with COPD.