Changes in sensitivity to methacholine after inhalation with distilled water: the role of the bronchoconstrictive response

The inhalation of distilled water can induce bronchoconstriction and a transient increase in sensitivity to methacholine in asthmatics. The purpose of this study was to determine the role of the induced bronchoconstriction in the increased sensitivity to methacholine which follows the challenge with distilled water. Eighteen asthmatic children (age 9-17 yrs) were challenged by inhalation of distilled water. Bronchial responsiveness, the provocative concentration of methacholine producing a 20% decrease in forced expiratory volume in one second (PC20), was determined before inhalation of distilled water, and 1.5 and 24 h thereafter. Following inhalation of distilled water, eight patients (Group I) had a greater than 15% decrease in FEV1 (mean 23%); whereas, in the remaining 10 (Group II) the decrease was less than 7% (mean 1%). PC20 to methacholine, geometric mean and 95% confidence interval (CI), decreased transiently only at 1.5 h following inhalation of distilled water. The decrease was from 0.78 mg.ml-1 (95% CI 0.11-5.54 mg.ml-1) at baseline to 0.25 mg.ml-1 (95% CI 0.03-2.14 mg.ml-1) after challenge in Group I; and from 2.67 mg.ml-1 (95% CI 0.35-20.34 mg.ml-1) at baseline to 0.72 mg.ml-1 (95% CI 0.18-14.87 mg.ml-1) after challenge in Group II. The transient increase in sensitivity to methacholine observed following inhalation of distilled water occurred independently of the bronchoconstrictive response. This finding may have important clinical implications when hypo-osmolar solutions are used for delivery of drugs.