Metabolism and Sleep Apnea Treatment

Aim 1 Group: Inclusion criteria: * Age between 18-70 years * Ability to provide consent Exclusion criteria * Body Mass Index (BMI) \> 40 kg/m2 * Prevalent myocardial infarction, coronary revascularization, heart failure, and stroke * Type 1 or Type 2 diabetes mellitus * Current or prior use of PAP or oral appliance therapy for OSA * Use of oral corticosteroids * Unstable medical conditions that may preclude enrollment in the protocol such as: uncontrolled angina and/or congestive heart failure, uncontrolled blood pressure or resistant hypertension, severe chronic obstructive pulmonary disease, cancer, and active psychiatric disease (e.g., major depression) * Other sleep disorders (e.g., circadian rhythm disorder, self-reported habitual sleep duration \< 6h) * Use of supplemental oxygen during wakefulness or sleep * Central sleep apnea, obesity hypoventilation syndrome or Cheyne-Stokes respiration based on the home sleep test * Resting awake Oxygen Saturation (SpO2) \< 90% Aim 2 Group: Inclusion criteria: * Age between 18-70 years * Ability to provide consent * Moderate-to-severe OSA (AHI ≥ 15/h); * Demonstration of Positive Airway Pressure (PAP) use of \> 4 h/night on 70% of the nights during 1-week run-in period * Successful completion of all of the procedures for Aim 1. Exclusion criteria: * BMI: ≥ 40 kg/m2 * Type 1 or Type 2 diabetes mellitus * Current use of PAP or oral appliance therapy for OSA * Commercial driver or report of motor vehicle accident or near-miss due to sleepiness within the 2 previous years * Epworth sleepiness score of 18 or more * Use of oral corticosteroids * Participation in another clinical trial * Unstable medical conditions that may preclude enrollment in the protocol such as: uncontrolled angina and/or congestive heart failure, uncontrolled blood pressure or resistant hypertension, severe chronic obstructive pulmonary disease, cancer, and active psychiatric disease (e.g., major depression) * Other sleep disorders (e.g., circadian rhythm disorder, self-reported habitual sleep duration \< 6h) * Use of supplemental oxygen during wakefulness or sleep * Central sleep apnea, obesity hypoventilation syndrome or Cheyne-Stokes respiration based on the home sleep test * Resting awake SpO2 \< 90%