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, FEV(1) 99.3+/-2.1% predicted) and in patients with established COPD without cough symptoms (n=42; FEV(1) 57.0+/-2.6% predicted), using healthy non-smoking volunteers as control (n=92; FEV(1) 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 micromol/L, p<0.05) and in COPD patients (1.44+/-0.14 micromol/L, p<0.01) when compared to non-smokers (1.90+/-0.09 micromol/L). Log C2 did not differ between groups. Log C2 and log C5 were decreased in women (0.772+/-0.071 micromol/L and 1.481+/-0.094 micromol/L, respectively) when compared to men (1.045+/-0.088 micromol/L and 1.923+/-0.087 micromol/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.