[Comparison of reproducibility to measure cough sensitivity between our original and astograph methods]

We have established a 15-seconds tidal breathing method using our originally developed apparatus to measure cough sensitivity to capsaicin. Astograph, an apparatus to measure bronchial responsiveness to methacholine, has been widely used in clinical practice in Japan. If Astograph is available for measurement of cough sensitivity, it will contribute to promoting the spread of cough sensitivity test.

Fifteen-seconds tidal breathing methods using our original apparatus and Astograph were compared in 29 healthy subjects. To assess the agreement of the two methods, increasing concentrations of capsaicin solution were inhaled for 15 seconds until 5 or more cough were elicited and cough threshold, the lowest concentration of capsaicin eliciting 5 or more coughs, was determined by each method on 2 separate days at one week interval. On each day, the cough threshold measurement was repeated twice at one-hour interval to assess the repeatability.

Difference and repeatability coefficient were 0.35 and 2.00 in our original method and 0.14 and 1.88 doubling concentration in Astograph method, respectively, indicating good repeatability of both methods. Difference and coefficient of agreement between the two methods was 0.30 and 2.44 doubling concentration, respectively.

Astograph is suitable for measurement of cough sensitivity to capsaicin because of its good repeatability and agreement with our original method already established.