What is BiPAP, AVAP used for?
BiPAP, AVAP (and their predecessor, CPAP) are most commonly used for people with sleep apnea or with hypopnea. Both of these can occur in ALS.
- Obstructive Sleep Apnea (OSA)
The more commonly seen and therefore well-known apnea is obstructive. The muscles of the soft palate and throat weaken and the upper airway is narrowed or even collapsed when the muscles relax as the patient falls asleep. That blocks the airway and the patient wakes up repeatedly, often not aware that the reason he is awakening is because he quit breathing. Some people find they feel startled or even panicky with these awakenings, but others are so tired and groggy from lack of sleep they may not even be aware they are waking up over and over. Snoring generally occurs, but it is possible to have apnea and not snore at all. Similarly, obstructive sleep apnea is often associated with obesity however there are apneaics who are of normal or low weight.
- Central Apnea
Another type of apnea that can occur is "central apnea" in which the little nerve center in the brain stem that is supposed to regulate when we take a breath and how long we hold it, fails to work properly when we fall asleep. This can be a problem directly with the nerve center or with the motor nerves that carry the message to the muscles used in breathing. Even though we think of breathing as something that is continually on autopilot, sleep seems to somehow interfere with the autopilot mechanism and apnea occurs. All it takes is a little stimulation to get breathing going again -- for babies with sleep apnea, just jiggling the crib is often all it takes. For adults, a spousal elbow in the ribs usually does it! BiPAP gives a breath and that breath is either enough stimulation to get you to breathe again or is enough to tide you over until you do breathe again.
A third possibility is that the muscles of respiration are weak and during sleep when breathing is normally shallower, breathing becomes too shallow. The patient doesn't stop breathing but breathing is inadequate. BiPAP can be used to increase the volume of air taken in without increasing muscle effort.