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The acting site of bronchodilator, methacholine and upper respiratory tract infection on airways
1Department of Medicine, Veterans General Hospital-Kaohsiung, Taiwan, R.O.C.
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.
Insights
Bronchodilators primarily act on small airways, while methacholine and upper respiratory infections (URI) affect large airways. Airway hyperresponsiveness does not impact spirometry recovery.
Area of Science:
- Pulmonary Medicine
- Respiratory Physiology
Background:
- Chronic obstructive pulmonary disease (COPD) management relies on bronchodilators.
- The precise sites of action for bronchodilators, methacholine, and upper respiratory infections (URI) remain debated.
- This study aimed to definitively identify these sites.
Purpose of the Study:
- To determine the primary sites of action for bronchodilators.
- To elucidate the major acting site of methacholine, a bronchial provocative agent.
- To investigate the impact of URI on airway function.
Main Methods:
- Thirty subjects underwent spirometry, methacholine challenge, and helium-oxygen (HeO2) inhalation.
- Bronchodilator response and HeO2 effects on VEMax50 were assessed.
- Isoflow volume (VisoV) analysis post-methacholine challenge identified methacholine's site of action.
Main Results:
- Bronchodilators predominantly act on small airways.
- Methacholine's primary site of action was identified as large airways.
- URI was found to affect large airways significantly.
Conclusions:
- Small airways are the main target for bronchodilators.
- Large airways are the primary sites affected by methacholine and URI.
- Bronchial hyperresponsiveness severity does not correlate with rapid spirometry recovery.