Central sleep apnea occurs when
the brain periodically fails to
activate the breathing muscles in the chest.
Unlike the heart, which continues beating no
matter what the brain does, the breathing muscles
work only when the brain gives them a
"breathe now" command.
Causes of Central Sleep Apnea
We are all familiar with several types of breathing
patterns commanded by the brain:
||Breathing during exercise
||Normal breathing, with sigh
In theory, many abnormal types of breathing patterns
could meet the criteria for central sleep apnea.
For example, simple repetitive breath-holding would
meet the criteria -- if it could be done while asleep.
In practice, however, the second pattern pictured below
is the most commonly seen form of central sleep apnea.
||Twice holding breath, in mid-breath
||Typical pattern in central sleep apnea
The second pattern is so distinctive that is has its own name:
Cheyne-Stokes breathing has alternate periods of no breathing (apnea)
changing smoothly into periods of hyper-breathing, which smoothly
change back to no-breathing.
Cheyne-Stokes breathing is
It may occur during sleep
or wakefulness. It is generally a sign of more advanced
disease when it occurs during wakefulness.
If a sleeping person has Cheyne-Stokes breathing, and if the
duration of the apneas are 10 seconds or longer, and if there
are more than 5 such apneas per hour of sleep, then the person
has central sleep apnea.
Because the brain controls breathing patterns, brain damage can
result in central sleep apnea. This is the simplest cause to
understand, but it occurs far less often than the most common
Heart Failure and Cheyne-Stokes Breathing
Heart failure is the most common cause of central sleep apnea.
About 40% to 60% of persons with heart failure have central sleep
|About heart failure
Heart failure is present when the heart is too weak to pump
enough blood to meet the demands of the body.
Heart failure is not the same
as a heart attack. Heart attacks damage the heart muscle.
If enough damage accumulates, heart failure occurs. As more people
survive heart attacks, heart failure is becoming more and more
High blood pressure is the other major cause of heart failure.
There are dozens of less common causes.
Why does the brain command abnormal breathing when the heart is weak?
References and Notes
A partial answer is as simple as your bathroom shower. (The complete
answer is still debated.) But, first, some background on the control of breathing.
The brain continuously monitors the body's status and continuously
decides the proper rate and depth of breathing to command. In particular,
the brain continuously monitors how much carbon dioxide is
contained in the bloodstream.
Breathing is normally controlled by a simple cycle of events:
Heart failure disrupts this cycle, and Cheyne-Stokes breathing is the result.
Heart failure is disruptive because the blood circulates more slowly through the
body in heart failure. As a result, the carbon dioxide levels seen by the brain
are not current information -- they represent carbon dioxide information from several
- When the level
of carbon dioxide gets too high, the brain sends a "breathe now" command to the
- The act of breathing lowers the level of carbon dioxide in the
- There is no stimulus to breathe until the level of carbon dioxide rises
again to the "too high" level.
- Since the body continuously produces carbon
dioxide, the "too high" level is reached again in a few seconds.
The cycle starts again at step 1).
The effect of having old information about carbon dioxide is the same as
trying to adjust the water temperature in a shower. We all know that in some
showers, it can take quite awhile before we can feel the effect of turning the "hot"
knob up. This slow circulation of water in the plumbing of the house can lead to
large swings in the temperature of the shower water.
An impatient person trying to adjust one of these showers will turn the "hot" knob,
wait a second, feel no change, turn it up more, feel no change, turn it up again, and
finally be scalded when a torrent of hot water finally comes out of the nozzle. The person
will then turn the hot knob way down, feel no change, turn it down again, and finally
be rewarded with a blast of ice water.
As the person gets familiar with how quickly the water temperature responds to
changes in the "hot" knob, the swings in water temperature decrease.
The situation in a patient with heart failure is similar. The brain is acting
on old information, and large swings in breathing depth and rate occur. The
difference is that the brain does not learn about the delay in carbon dioxide
levels, and that the swings in breathing continue.
The best treatment for Cheyne-Stokes respiration is to treat the heart failure.
The circulation of blood becomes shorter. It is always easier to adjust the
temperature of a shower where the water temperature changes the instant the
"hot" knob is turned.