The effect of 10 versus 0 cmH2O CPAP on airways responsiveness to inhaled methacholine will be studied using an adaptive "3+3" phase I/II study design.
Dose Titration Phase (phase I):
The efficacy of 8 hours of CPAP on airway responsiveness will be tested in three subjects.
Efficacy will be defined as a 25% improvement in the impedance response to methacholine in all three subjects. If this occurs in all subjects, shorter durations of CPAP will be studied (4 hours then one hour).
Conversely, if "dose escalation" is required, 3 nights, then 7 nights of CPAP will be studied.
Randomized-controlled study phase (phase II):
Participants will be randomized to CPAP 10 or Sham 0. The duration of CPAP will be determined in the dose titration phase. The effect on response to inhaled methacholine, lung function and asthma control will be determined in patients with asthma and a BMI ≥ 30 kg/m2, and also in healthy controls without asthma
