Comparison between tidal breathing and dosimeter methods in assessing cough receptor sensitivity to capsaicin

Dosimeter method and tidal breathing method have been used to assess cough sensitivity to inhaled capsaicin, a C-fibre ending stimulator. The aim of the present study was to evaluate the repeatability of and the agreement between the two methods.

Cough threshold, the lowest concentration of capsaicin causing five or more coughs, was measured twice 1-3 weeks apart by each method in 26 normal subjects. Increasing concentrations of capsaicin were inhaled by a single breath in the dosimeter method or by 15 s tidal breathing in the tidal breathing method in 1 min intervals.

Coefficients of repeatability of the cough threshold measurement were 1.89 and 2.71 doubling concentration in the tidal breathing method and the dosimeter method, respectively, suggesting good repeatability in the cough threshold measurement by both methods. The cough threshold was significantly (P < 0.0001) greater by 1.75 doubling concentration on the dosimeter method than the tidal breathing method. The coefficient of agreement between the two methods was 2.53 doubling concentration. Five subjects complained of burning sensation in the throat in the dosimeter method but no patient complained about the tidal breathing method (P < 0.05).

Although the agreement between the two methods was considered to be good, higher concentrations of capsaicin solution were required to determine the cough threshold in the dosimeter method, resulting in an unpleasant sensation in the throat.