Allergen exposure aggravates cough response to capsaicin
Exposure to allergens induces bronchoconstriction and increases the sensitivity of the cough reflex to capsaicin, a recent study has shown.
Researchers conducted a randomized, placebo-controlled, two-way crossover study including 12 steroid-naïve allergic asthma patients (mean age, 34.8 years; 50 percent female), whose response to inhaled capsaicin after allergen vs diluent control exposure was comparatively assessed. Spontaneous coughing was measured for 24 hours after allergen/diluent challenge.
The increase in the number of evoked coughs that induced the half-maximal response after capsaicin inhalation (ED50) was significantly greater after allergen vs diluent challenge (geometric mean coughs: 21.9 vs 12.1; p<0.001). Though the overall ED50 dropped after 24 hours, the difference between the allergen and diluent arms remained significant (16.1 vs 9.8; p=0.001).
Researchers also reported a significantly greater drop in lung function after allergen challenge in both the early (mean percent decrease: 38.2±13.0 percent vs 4.5±2.8 percent; p<0.001) and late (23.7±13.2 percent vs 2.2±2.1 percent; p<0.001) asthma response. This trend similarly persisted for 24 hours. Lung function was measured as the forced expiratory volume in 1 second.
There was also a significant increase in the rate of spontaneous coughs over 24 hours after allergen vs diluent challenge (geometric mean rate: 0.60 vs 0.25; p<0.001). This effect was statistically correlated with the drop in lung function (β, –0.72; p<0.001).