Capsaicin cough sensitivity in smokers with and without airflow obstruction

Background: Cough is a frequent symptom of cigarette smokers that often precedes the development of airflow obstruction. We determined whether chronic cigarette smoking is associated with an increase in capsaicin cough response in the absence of cough. Methods: We examined this in asymptomatic smokers with normal lung function (n = 68, FEV₁ 99.3 ± 2.1% predicted) and in patients with established COPD without cough symptoms (n = 42; FEV₁ 57.0 ± 2.6% predicted), using healthy non-smoking volunteers as control (n = 92; FEV₁ 100.6 ± 1.7% predicted). Using an incremental capsaicin concentration challenge protocol, we recorded the concentrations that induced 2 (C2) and 5 or more coughs (C5). Results: Because females have a lower C2 and C5 than males in the control group, we analysed the data in each group according to gender. Log C5 was decreased both in asymptomatic smokers (1.56 ± 0.11 μmol/L, p < 0.05) and in COPD patients (1.44 ± 0.14 μmol/L, p < 0.01) when compared to non-smokers (1.90 ± 0.09 μmol/L). Log C2 did not differ between groups. Log C2 and log C5 were decreased in women (0.772 ± 0.071 μmol/L and 1.481 ± 0.094 μmol/L, respectively) when compared to men (1.045 ± 0.088 μmol/L and 1.923 ± 0.087 μmol/L, respectively) (p < 0.05 for log C2; p < 0.001 for log C5). Conclusion: We conclude that chronic cigarette smoking increases capsaicin cough reflex and that this remains so with the development of COPD.