Capsaicin responsiveness and cough in asthma and chronic obstructive pulmonary disease

Background-Chronic cough is associated with an increased sensitivity to inh aled capsaicin in a number of conditions but there are no data for patients with more severe asthma or chronic obstructive pulmonary disease (COPD). M oreover, the relationships between the capsaicin response (expressed as the concentration of capsaicin provoking five coughs, C5), self-reported cough , and routine medication is not known. Methods-The cough response to capsaicin in 53 subjects with asthma, 56 subj ects with COPD, and 96 healthy individuals was recorded and compared with a number of subjective measures of self-reported cough, measures of airway o bstruction, and prescribed medication. In asthmatic subjects the relationsh ips between the cough response to capsaicin and mean daily peak flow variab ility and nonspecific bronchial hyperresponsiveness to histamine were also examined. Results-Subjects with asthma (median C5 = 62 mM) and COPD (median C5 = 31 m M) were similarly sensitive to capsaicin and both were more reactive than n ormal subjects (median C5 >500 mM). Capsaicin sensitivity was related to sy mptomatic cough as measured by the diary card score in both asthma and COPD (r = -0.38 and r = -0.44, respectively), but only in asthma and not COPD w hen measured using a visual analogue score (r = -0.32 and r = -0.05, respec tively). Capsaicin sensitivity was independent of the degree of airway obst ruction and in asthmatics was not related to PEF variability or PC20 for hi stamine. The response to capsaicin was not related to treatment with inhale d corticosteroids but was increased in those using anticholinergic agents i n both conditions. Conclusions-These data suggest that an increased cough reflex, as measured by capsaicin responsiveness, is an important contributor to the presence of cough in asthma and COPD, rather than cough being simply secondary to exce ssive airway secretions. The lack of any relationship between capsaicin res ponsiveness and airflow limitation as measured by the FEV1 suggests that th e mechanisms producing cough are likely to be different from those causing airways obstruction, at least in patients with COPD.