The Effect of Deep Inhalation on Mannitol Responsiveness

This study will look at airway responsiveness to inhaled methacholine and mannitol administered with and without deep inhalation. This study will also investigate the role of airway inflammation on these responses, using sputum differential cell counts and fractional exhaled nitric oxide. This is a single center, open label, randomized study. Individuals with stable asthma will be eligible for enrollment. The study will consist of two parts, screening and testing. Part 1: Screening Participants will undergo consent procedures and assessments of fractional exhaled nitric oxide levels, airway responsiveness to methacholine and sputum induction. If participants show airway responsiveness to methacholine (i.e. methacholine PC20 16mg/mL), they will be scheduled to undergo the testing part of the study. Part 2: Testing Participants will be randomized to undergo two methacholine or two mannitol challenges. Further randomization will occur with respect to whether the standard challenge method or the modified challenge method is performed first.