Capsaicin-induced cough reflex is inhibited by deep inspiration in children with mild asthma

Background: Asthma is characterized by bronchospasms accompanied with frequent coughing, the pathogenesis of which is not clear. In healthy adults deep inspirations (DIs) provide a protective effect against bronchoconstriction triggered by metacholín, which correlates with the number of accompanying cough efforts. In adult asthmatics DIs have some spasmolytic effect, which decreases with age and severity of the disease. Our aim was to test the elicitability of cough reflex by capsaicin in children with mild asthma and their presupposed inhibition by DIs. Methods: In 21 children (8 girls and 13 boys of median age 13.3 yr) with mild asthma (FEV 1 >80%) the cough reaction to inhalation of increasing concentrations of capsaicin from a compressed air-driven nebulizer manifesting with 2 and 5 or more cough efforts (C2 and C5) was tested. The effect of previous DIs was also examined. Results: In control conditions 20.86 (14.58-29.8) umol/l of capsaicin provoked two cough reflexes (C2), but after 3-5 DIs similar reaction required significantly higher concentrations 29.02 (18.88-44.6) umol/l; P=0.016. Five or more cough efforts required increasing doses inhaled repeatedly in 1 minute intervals, which were not significantly higher after DIs 161.49 (77.31-337.33) umol/l, than without DIs 141.52 (68.77-291); P=0.54. Conclusion: A series of 5 DIs decreased the sensitivity of cough reflex provoked by capsaicin in children with mild asthma, but such inhibitory effect of DIs disappeared after repeated applications of increasing doses of capsaicin, suggesting reflex character of protective effect of DIs. Supported by a Grant of Ministry of Health of Slovak Republic 2007/50-UK-14.