It has been suggested that in normal subjects inhaled anticholinergic agents have a preferential dilating effect on large central airways. We therefore studied 21 patients with asthma to see if response to inhaled ipratropium bromide was related to the initial central or peripheral site of major airway narrowing. Fourteen out of 21 patients with asthma increased their Vmax more than 10% after ipratropium but when assessed by air and helium/oxygen (He/O2) flow-volume curves, responders and non-responders to He/O2 breathing were divided equally between those who benefited from the drug, and those who did not. There were no significant differences in percentage improvement in Vmax between initial responders, and initial non-responders to He/O2 breathing. Furthermore the results from air and He/O2 flow-volume curves suggest that, contrary to some previous reports (not in asthmatics), inhaled ipratropium has a generalised action throughout the airways. There were no differences in severity of airflow obstruction, nor in age, sex, smoking history, or atopic status between those who benefited from ipratropium and those who did not. However, those improving after the drug had a significantly longer history of asthma than those who did not.
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