Prevalence and repeatability of the cough response induced by inhalation of low chloride ion solutions in normal subjects.

: Although the inhalation of low Cl- ion solutions has often been used to induce cough, the prevalence and repeatability of the challenge has never been studied in detail. We, therefore, examined cough response in a group of 59 volunteers (aged 15-57 yrs; 34 females and 25 males; 20 smokers) to ascertain prevalence and repeatability. Each subject performed, 2 weeks apart, two identical cough challenges by inhaling four isosmolar solutions with decreasing Cl- ion concentrations (150, 75, 37.5 and 0 mM). Each solution was delivered by a DeVilbiss 65 ultrasonic nebulizer (mean output: 1.9 mL.min-1) for 1 min, and the number of coughs was counted during the inhalation. Cough response was expressed as number of coughs.min-1. Significance of response to the cough challenge was assessed on the basis of mean number of coughs.min-1 and 95% upper confidence limit (CL) of response to the Cl- free solution in the whole population. Cough threshold for a significant response was greater than 8 coughs.min-1. Out of 59 subjects, only 20 exceeded the cough threshold (34%) after inhaling the Cl- free solution. A concentration-response effect was evident only when inhaling 37.5 and 0 mM Cl- ion solutions. A significant cough response was more likely among females (p = 0.03). Smoking did not significantly affect the prevalence of response. Coefficients of repeatability of cough response to 37.5 and 0 mM Cl- solutions in 20 responders were equal to 10.1 and 12.6, respectively. We conclude that a significant cough response to low Cl- ion solutions develops in approximately 1 out of 3 of challenged volunteers and that repeatability is not satisfactory. We suggest that cough threshold and repeatability should be preliminarily assessed, especially when the challenge is used to study the antitussive activity of drugs.