Continuous Positive Airway Pressure is the most common type, and delivers a steady flow of your prescribed pressure. When breathing on a CPAP, the air pressure is the same whether inhaling or exhaling. This positive air pressure acts like pillars in a tunnel, keeping your airway open during the night. A CPAP can be set to any single pressure between 4cm/H2O and 20cm/H2O.
Automatic Continuous Positive Airway Pressure is often referred to as an Auto CPAP. This type of therapy is set with a specific range of pressures. The machine will generally blow the lowest pressure programmed until it starts sensing apnea events. At that point the pressure will rise in strength until normal breathing resumes. APAP machines can be set with a range of pressures from 4cm/H2O to 20cm/H2O, and anywhere in between.
A BiLevel CPAP Machine is commonly known as a BIPAP, or a VPAP. These machines use two different pressures, one for inhales and another for exhales. These are generally used when CPAP has failed as a treatment for sleep apnea, and/or when higher pressures are necessary to eliminate apnea episodes. The purpose is to give the patient some relief during exhales, when pressures are high. BiLevel machines can set with two pressures between 4cm/H2O and 20cm/H2O, with some machines going as high as 25cm/H2O.