The study will assess how the inhalation technique used (deep inhalations versus tidal breathing) influences the results of a mannitol challenge test and a methacholine challenge test, if at all.

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.

Inclusion Criteria:

• signed informed consent
• men and women between 18 and 75 years of age
• FEV1 at first measurement of greater than or equal to 65% predicted
• methacholine provocative concentration causing a 20% in FEV1 at screening that is less than or equal to 16mg/ml
• generally good health
• stable asthma

Exclusion Criteria:

• respiratory infection within 4 weeks of screening visit
• worsening of asthma within 4 weeks of screening visit
• lung disease other than asthma
• significant medical comorbidity
• current smoker or ex-smoker with significant smoking history
• currently pregnant or breastfeeding