Abstract
RATIONALE: Studies have demonstrated that application of stress suppresses airway smooth muscle contractility. In animal models of asthma, continuous positive airway pressure (CPAP) reduced airway reactivity. Short-term studies of CPAP in patients with asthma showed reductions in airway reactivity. OBJECTIVES: To evaluate whether nocturnal CPAP decreased the provocative concentration of methacholine to reduce FEV(1) by 20% (PC(20)). METHODS: One hundred ninety-four individuals with asthma were randomized (1:1:1) to use CPAP with warmed, filtered, humidified air at night at pressures either less than 1 cm H(2)O (sham) or at 5 cm H(2)O or 10 cm H(2)O. The primary outcome was change in PC(20) after 12 weeks. MEASUREMENTS AND MAIN RESULTS: Adherence to CPAP was low in all groups. Regardless, all groups had a significant improvement in PC(20), with 12 weeks/baseline PC(20) ratios of 2.12, 1.73, and 1.78 for the sham, 5 cm H(2)O, and 10 cm H(2)O groups, respectively, and no significant differences between the active and sham groups. Changes in FEV(1) and exhaled nitric oxide were minimal in all groups. The sham group had larger improvements in most patient-reported outcomes measuring asthma symptoms and quality of life, as well as sinus symptoms, than the 5 cm H(2)O group. The 10 cm H(2)O group showed similar but less consistent improvements in scores, which were not different from improvements in the sham group. CONCLUSIONS: Adherence to nocturnal CPAP was low. There was no evidence to support positive pressure as being effective for reducing airway reactivity in people with well-controlled asthma. Regardless, airway reactivity was improved in all groups, which may represent an effect of participating in a study and/or an effect of warm, humid, filtered air on airway reactivity. Clinical trial registered with www.clinicaltrials.gov (NCT01629823).