Study A will consist of a cross-over controlled randomized trial to compare unintentional leak during auto-CPAP and during fixed CPAP after the progressive reduction of fixed CPAP, starting at the 90 th percentile obtained during a period of auto-CPAP. The order of interventions will be randomized. Auto-CPAP with a nasal mask will be used for 7 days. In the fixed CPAP arm, CPAP will be progressively reduced over a period of up to 21 days until leak is controlled or residual apnea-hypopnea index increases over 10 events/h. Subjects that persisted with excessive leak at the end of the Study A will be invited to Study B.