BiPAP (and its predecessor, CPAP) are most commonly used for people with sleep apnea or with
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 other 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
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.
How does this apply to ALS?
All three of the problems discussed above can occur in ALS. Bulbar weakness (weakness of the
muscles controlled by the cranial nerves that arise from the bulb-shaped medulla portion of the
brainstem) causes swallowing and speech problems and may also allow collapse of the upper airway
during sleep when muscles relax. This results in obstructive apnea. If ALS affects the motor
pathways the brain stem uses to send the impulses to trigger breathing, central apnea can occur.
And of course ALS can affect the muscles used in breathing and cause hypopnea. Hypopnea is
probably the most common problem in ALS but it certainly is possible for a combination of these
problems to occur in ALS.
Whether it is a form of apnea or hypopnea, the patient does not get good quality sleep.
Quality of sleep is not just dependent on the total number of hours, but also how that time is
broken up by awakenings. In order to feel rested, it is necessary to get blocks of sleep that
lasts at least 90 minutes -- that is when REM sleep occurs and REM sleep is apparently the stage
of sleep where the brain has a chance to "recharge" itself. Without this good quality
sleep, the patient becomes increasingly tired, has trouble staying awake during the day (yet has
apnea and awakens if he falls asleep), finds it harder think clearly, concentrate, remember.
Depression is very common. In addition to the mental effects, the lack of sleep begins to affect
physical health too.
CPAP or BiPAP?
CPAP isn't bad for people with neuromuscular weakness of the respiratory muscles in the
sense that it is dangerous, it just doesn't work for them. CPAP is designed to give Continuous
Positive Airway Pressure to keep the airway from collapsing on exhalation. In effect, it keeps
the lungs partially inflated to the same amount during inhalation and exhalation. That makes it
more difficult to exhale and that is why it is difficult for anyone to adjust to. For
neuromuscular patients, the muscle weakness makes it even more difficult to exhale against the
pressure. BiPAP has separate pressure settings for inhaling (higher) and exhaling (lower). The
lower pressure during exhalation makes easy so it is the correct choice for ALS patients.