CPAP, or Continuous Positive Airway Pressure, is a prescribed amount of pressurized air delivered through a mask worn on your face. The pressurized air holds or splints the airway open while you sleep and helps prevent the air passage from blocking.
APAP, or Auto-adjusting Positive Airway Pressure, constantly adjusts the pressure within a prescribed range and may be beneficial if you require a much higher pressure when you are lying on their back as compared to the pressure you need when lying on your side or between different stages of sleep.
BPAP, or Bi-level Positive Airway Pressure delivers one prescribed pressure when you are breathing in and a lower prescribed pressure when you breathe out.