The measurement of cough response to bronchoconstriction induced by methacholine inhalation in healthy subjects: An examination using the Astograph method

Background: We demonstrated that heightened cough response to bronchoconstriction is a fundamental feature of cough variant asthma (CVA). To evaluate this physiological feature of CVA in daily clinical practice, it is necessary to clarify the cough response to bronchoconstriction in healthy subjects. We evaluated cough response to methacholine (MCh)-induced bronchoconstriction in healthy subjects. A forced oscillometry technique was used to measure airway resistance changes with Mch.

Methods: Healthy never-smokers (21 men, 20 women; mean 22.3 ± 3.7 years) participated. None had a >3-week cough history, clinically significant respiratory or cardiovascular disorders, or disorders that might put subjects at risk or influence the study results or the subjects' ability to participate. Twofold increasing concentrations of Mch chloride diluted in phosphate-buffered saline (0.039 to 160 mg/mL) were inhaled from nebulizers at 1-minute intervals during subjects' tidal breathing after the baseline respiratory resistance (Rrs) was recorded. Mch inhalation continued until Rrs reached twice the baseline value and forced expiratory volume in 1 second (FEV₁) decreased to <90% of baseline value. Spirometry was measured before Mch inhalation and immediately after Rrs had increased twofold. Coughs were counted during and for 30 minutes after Mch inhalation. The cough reflex sensitivity to capsaicin was also examined.

Results: The number of coughs was 11.1 ± 14.3 (median, 7.0; range, 0 to 71; reference range, 0 to 39.7). There was no significant difference in the cough response between the sexes. The reproducibility of the cough response to bronchoconstriction was sufficient. No correlation existed between the bronchoconstriction-induced cough response and capsaicin cough-reflex sensitivity.

Conclusions: Using the Astograph method, cough response to bronchoconstriction could be measured easily, safely and highly reproducibly in healthy subjects.