Correlation between airway inflammation and loss of deep-inhalation bronchoprotection in asthma

Background: One of the characteristic features of the hyperresponsive airway smooth muscle in asthma is the loss of deep-inhalation bronchoprotection and bronchodilation. The airway of individuals with asthma is also characterized by inflammation. Objective: To evaluate whether the loss of deep-inhalation bronchoprotection is correlated with the degree of inflammation in the asthmatic airway. Methods: Eighteen study participants performed 2 methacholine challenges (identical doses), 1 with deep inhalations and 1 without separated by at least 24 hours. Airway inflammation was evaluated by measurement of fraction of exhaled nitric oxide (FENO) and induced sputum eosinophils. Results: A significant negative correlation was found between the degree of deep-inhalation bronchoprotection and airway inflammation when measured by FENO (P = .02, r = .54, n = 18) and by percentage of eosinophils (P = .002, r = .76, n = 12). A significant positive correlation was also found between the FENO and percentage of eosinophils (P = .009, r = .68, n = 12). Conclusions: Deep-inhalation bronchoprotection was significantly impaired in individuals with greater airway inflammation. This finding suggests that therapy directed at decreasing airway inflammation may promote the recovery of normal deep-inhalation bronchoprotection.