How does cpap work?

Air pressure. Continuous or Bi Level positive airway pressure pushes air with or without supplemental oxygen as needed past the obstruction in the back of the throat (palate, pharyngeal walls, tonsils if present, base of tongue) into the lungs. This will prevent the pharyngeal collapse, providing more restful sleep and decreased risk of motor vehicle accident, stroke, and heart attack.
Airway splint. CPAP forces positive pressure into the nose/ mouth or both. It acts as a pneumatic splint to open up a closed airway. It can provide pressure when you breath in only or both when you breath in and out. CPAP works for mild, moderate and severe sleep apnea.