Sleep Apnea (cont.)
What is central sleep apnea and what causes it?
Central sleep apnea (CSA) occurs when the brain does not
send the signal to breathe to the muscles of breathing. This usually occurs in
infants or in adults with heart disease, cerebrovascular disease, or congenital diseases, but
it also can
be caused by some medications and high altitudes.
Central sleep apnea may occur in premature infants (born before 37 weeks of gestation) or in
full term infants. It is defined as apneas lasting more than 20 seconds, usually
with a change in the heart rate, a reduction in blood oxygen, or hypotonia
(general relaxation of the body's muscles). These children often will require an
apnea monitor that sounds an alarm when apneas occur. Central sleep apnea in
children is not the same thing
as sudden infant death syndrome (SIDS).
Under normal circumstances, the brain monitors several
things to determine how often to breathe. If it senses a lack of oxygen or an
excess of carbon dioxide in the blood it will speed up breathing. The increase in breathing
increases the oxygen and decreases the carbon dioxide in
blood. Some people with heart or lung disease have an increase in carbon dioxide in
their blood at all times.
When there is a chronic (long term) increase in blood
carbon dioxide, the brain starts to ignore the oxygen level and monitors the
blood carbon dioxide level to determine when to take the next breath. The control of breathing also becomes slower to respond to changes in carbon
dioxide levels; so when a person takes more or deeper breaths and "blows off"
carbon dioxide the drive to breathe decreases and the rate of breathing
decreases. As a result of slower rate of breathing, the carbon dioxide builds back up in the blood and the rate of
breathing increases again. The brain, slow to adjust, continues to signal for more
rapid breathing until the carbon dioxide level drops too low. Breathing then
slows down or stops until the carbon dioxide level rises again. This pattern of
abnormal breathing is called
Cheyne-Stokes breathing (after the men who described it). It is characterized by
repetitive cycles of fast breathing followed by slow breathing and apnea. This
breathing pattern happens when the person is awake or asleep, but becomes more
of a problem when asleep. Some patients with heart failure have central sleep
apnea associated
with a Cheyne-Stokes pattern of breathing.
Central sleep apnea usually occurs in adults with other medical problems. In
infants, it usually occurs with prematurity or other
congenital disorders. In both patient groups it is usually suspected by the
primary care doctor. Central sleep apnea can be diagnosed with a sleep study or
overnight monitoring while the patient is in the hospital.
In infants, central
sleep apnea is treated with an apnea alarm. This alarm monitors the infant's
breathing with sensors and sounds a loud noise when the infant experiences an
apnea. The alarm usually wakes the infant and the parents. Most infants usually
"out-grow" the central apnea episodes, so the alarm monitoring is stopped after
the episodes resolve. In infants with other congenital problems, apnea
monitoring may be needed for a longer period.
In adults with central sleep
apnea, the apneas are treated by treating the underlying heart disease,
medication interaction, high altitude, or
other primary problem.
Next: What is obstructive sleep apnea and what causes it? »
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