Comparison of a Demand Oxygen Delivery

Inclusion Criteria: 1. Age 5-17 years with or without Down Syndrome (DS). 2. Children with obstructive sleep apnea (OSA) and obstructive apnea hypopnea index (OAHI) 5-40 / hour: The rationale for selecting this range of OAHI is that a large number of children with DS with this range of OSA severity are untreated for months to years. It is important to understand the response to oxygen across the spectrum of disease severity. Notably, children with severe disease are left with few options (e.g., tracheostomy). 3. Absence of clinically significant hypoxia defined as oxygen saturation \< 88% for 5 minutes or episodic desaturation to 60% as these levels would otherwise identify children eligible to routinely receive oxygen. Exclusion Criteria: 1. Current CPAP use with documented compliance (\> 4 hrs/ night; \> 70% of nights). 2. Oxygen saturation \< 90% at rest during wakefulness 3. Chronic daytime or nighttime use of supplemental oxygen. 4. Unable to participate in a Polysomnogram (PSG). 5. Enrolled or planning to enroll in another study that may conflict with protocol requirements or confound results in this trial.