These substances cause the soft tissues in the throat to sag and diminish the body's ability to inhale. The machine applies sufficient air pressure to prevent the tissues from collapsing during sleep. The amount of air pressure needs to be determined during sleep that is monitored in a sleep laboratory, but this may require only one night. Unfortunately, because it is inconvenient to use, less than half of those who have CPAP use it often enough for full benefit. Apart from the irritation with the nasal mask, side effects include headache and nasal congestion or dryness, which can be alleviated with nasal saline sprays or humidifiers.
Some patients complain that the system applies too much pressure making it difficult to exhale.
This may be alleviated using a mechanism called a ramp that allows pressure to gradually increase over five to 45 minutes. Behavioral or cognitive therapies may help improve compliance. These devices are more expensive than those that provide continuous airflow, but they may improve compliance in patients who find the steady flow of air from standard CPAP devices annoying and therefore. Even after using CPAP for an average of only four hours a night, patients are more alert, with improvements in memory, mood, concentration, and health. A 1997 study indicated that CPAP therapy may even reduce the risks of motor vehicle and domestic and work-related accidents associated with sleepiness.