Impact of Continuous Positive Airway Pressure on Breathing Motion Amplitude

CPAP requires subjects to wear a plastic pressurized mask/apparatus, which is connected via a filter and hose to a pump capable of supplying variable pressure (typically on the range of 4-20 cm H2O). The investigators plan to use a full-face mask to prevent subjects from reducing pressure by opening their mouths. If this cannot be tolerated or properly fitted, or is not compatible with the CPAP ventilator, subjects would use a nasal mask only and be asked to keep their mouths closed.