The acting site of bronchodilator, methacholine and upper respiratory tract infection on airways.

BACKGROUND

The bronchodilator agent is an important drug for patients with chronic obstructive pulmonary disease. Methacholine is a popular bronchial provocative agent. Although the major acting site of bronchodilator, methacholine and upper respiratory tract infection (URI) has been evaluated in some studies, the sites are still in debate. This study investigated the exact major acting sites.

METHODS

Thirty subjects participated in this study. Episodes of URI were identified by a questionnaire. Spirometry, bronchial provocative test with methacholine, and five minutes' inhalation of a mixture of helium and oxygen (HeO2) were done on day one. Spirometry, bronchodilator test, with five minutes' inhalation of HeO2 and expiratory flow-volume (F-V) curve were performed on another day. The change of pre- and post-HeO2 VEMax50 was calculated as delta VEMax50. The pre- and post-bronchodilator VEMax50 and delta VEMax50 differences were counted to decide the acting site of bronchodilator. After bronchial provocative test with methacholine, the volume of isoflow (VisoV) was estimated from pre- and post-HeO2 F-V curve to establish the acting site of methacholine.

RESULTS

This study indicated that small airways are the major acting sites of bronchodilators, large airways are the major acting sites of methacholine and URI affects mainly large airways. Although airway hyperresponsiveness is more severe in subjects with positive methacholine response, the recovery of spirometry values is not significantly different between the methacholine-positive and -negative groups.

CONCLUSIONS

The major acting sites of the bronchodilator, methacholine, and URI are the small, large and large airways, respectively. Bronchial hyperresponsiveness is not a cause of quick restoration of spirometry values in subjects with positive methacholine response.