The Effects of Methacholine Challenge Administered Using Three Different Nebulizers on Small Airways Function

The objective of this study is to examine the functional effects of methacholine challenge on small airways using three different nebulizers to generate particles with HMAD suitable for distribution in small, intermediate and large airways.Pulmonary function will be assessed using plethysmography and impulse oscillation techniques. Eight asthmatic subjects (>18 years, both sexes) who are stable clinically and require only intermittent ß2-agonist treatment will be recruited to undergo methacholine challenges for an in vivo, dose-finding observational study. Three separate methacholine challenges will be carried out using each of the three different nebulizers. After each challenge, pulmonary function tests will be performed on subjects to assess functional changes in large and small airways. Results of the tests will be compared between the three nebulizers. These experiments will demonstrate whether or not functional changes occur in small airways in response to methacholine, as measured by pulmonary function tests after selectively targeting small airways using the nebulizer which generates small particles. The results from these experiments will give us a better understanding of the role of small airways in methacholine-induced bronchoconstriction in asthmatics, and will compare sensitivity of plethysmography compared to forced oscillation for detecting changes in small airways.