The study will compare a novel volumetric method (performed with the Aerogen Solo vibrating mesh nebulizer) with the standard two-minute tidal breathing protocol (performed with the Wright jet nebulizer) for methacholine challenge testing. The results will then give an indication as to whether the novel technique accurately assesses a given dose of methacholine with the new Aerogen Solo device. In addition, the reproducibility of test results with each method will be examined. Altogether, the findings from this investigation may provide means for better standardization of current testing guidelines.

Fifteen asthmatics will be recruited and tested at the University of Saskatchewan for this randomized, two-way crossover study. Two testing methodologies will be performed, the volumetric method with the Aerogen Solo nebulizer and the two-minute tidal breathing method with the Wright nebulizer.

Participants will undergo four methacholine challenges plus a screening methacholine challenge. However, screening is omitted with participants who have completed a methacholine challenge in the last six months. Of the four study challenges, two will utilize the Wright nebulizer with the two-minute tidal breathing method outlined in the 1999 American Thoracic Society Guidelines for Methacholine Challenge Testing. The remaining two challenges will utilize the Aerogen Solo nebulizer with the volumetric method. The timing of the spirometric manoeuvers and the duration of each inhalation cycle will be consistent with both testing methods. Each challenge will be stopped when the participant's forced expiratory volume in 1 second (FEV1) drops by at least 20%. This allows determination of aPC20 (provocative concentration of methacholine causing a 20% fall in FEV1), which will be converted to aPD20 (provocative dose). A minimum 24-hour washout period between challenges will be used.

Inclusion Criteria:

• Men and women aged 18 or older
• Stable asthma
• Baseline methacholine PC20 less than or equal to 16mg/mL
• Baseline lung function equal or greater than 65% of predicted FEV1

Exclusion Criteria:

• Use of long-acting bronchodilators within 7 days of visit 1
• Pregnant or nursing women
• Cardiovascular problems
• Upper respiratory tract infection within 4 weeks of visit 1
• Allergy-induced asthma exacerbation within 4 weeks of visit 1