The term “CPAP” is often used somewhat generically, to refer to any of several types of machines used therapeutically to deliver Positive Air Pressure as a treatment for Sleep Apnea (a/k/a Sleep Disordered Breathing.)
If you are using a basic CPAP machine, or an APAP set for a single pressure, rather than a range of pressures, and find yourself waking several times a night with the mask off your face, or otherwise “fighting the mask”, you may require an APAP, rather than a CPAP machine to accommodate varying pressure requirements throughout the night.
But to get a little more specific, here’s a very brief description of the machines available in rising order of complexity, sophistication.
provides Continuous Positive Airway Pressure. The machines are usually capable of providing between 4 and 20 centimeters of water (that’s the standard measure of air pressure) at a constant level. This is the most basic machine and was the first to be developed. It can provide only a constant level of pressure, which may not be optimal for those requiring different levels of pressure in REM and non REM sleep (which is most patients.) However, some models do provide lower pressures during exhalation known as expiratory assist.
The “A” stands for “adjustable” or “Automatic” This is a self-adjusting machine that operates on an algorithm designed to anticipate your pressure needs as they change throughout the night. The most recent generations of these machines are often offered in gender specific models, because research has shown that women usually benefit from a slightly different algorithm. Your sleep doctor or technologist will often set a narrower pressure range than the full 4 to 20 cm of water possible, because if you experience a large leak, the machine will automatically increase the pressure and, in that case, you may awake feeling as though you are trying exhale against a hurricane. (not dangerous, but annoying.) Often expiratory assist is also available.
These are used by patients requiring higher pressures (usually large or heavy patients with a high AHI.) Bi-level is also sometimes used for patients who do not tolerate CPAP or APAP, for patients with COPD, and for patients with certain neurological diseases. Bi-Levels are designed to provide different pressure on inhalation and exhalation and may provide a higher range of pressures. These are a little less commonly used now that the APAP can provide expiratory assist.
The acronym stands for “Adaptive Servo Ventilator”- Essentially a machine with adaptive ventilatory function, used for patients suffering from central, or complex (combined central and obstructive) rather than purely obstructive, sleep apnea.