Sleep Apnea
Medical Author: Andrew Verneuil MD
Medical Editor: Jay W. Marks, MD
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Sleep Apnea Symptoms and Warning Signs
Medical Author: Melissa Conrad Stöppler, MD
Medical Editor:
Barbara
K. Hecht, Ph.D.
 Sleep apnea is a disorder affecting about 18 million
Americans that has the potential for serious, and even fatal complications.
Persons with sleep apnea actually stop breathing for brief periods of time (usually 10-20 seconds) while
asleep. The pauses in breathing can be very frequent and occur 30 times or more
per hour. The most common kind of sleep apnea is termed obstructive sleep apnea,
and a less common form of sleep apnea is central sleep apnea.
Sleep apnea often results in feelings of
fatigue and excessive daytime sleepiness, since
the ability to reach deep,
restorative sleep stages is impaired. Other warning signs of sleep apnea are
often noticed by bed partners and include loud snoring and making snorting or
choking sounds at night. Those affected may experience awakening with brief
periods of shortness of breath.
The sudden decreases in oxygen levels that occur with sleep apnea place a
burden on the cardiovascular system, which must work harder in an attempt to deliver sufficient oxygen to
all tissues. This strain causes the development of high blood pressure in
approximately half of those suffering from sleep apnea, and this increases the
risks of stroke and heart failure.
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What is sleep apnea?
Sleep apnea is a disorder characterized by a reduction or cessation (pause of
breathing, airflow) during sleep. It is common among adults but rare among
children. There are two types of sleep apnea, the more common obstructive sleep
apnea and the less common central sleep apnea, both of which will be described
later in this article. Although a diagnosis of sleep apnea often will be
suspected on the basis of a person's history, there are several tests that can
be used to confirm the diagnosis. The treatment of sleep apnea may be either
surgical or nonsurgical.
An apnea is a period of time
during which breathing stops or is markedly reduced. In simplified terms, an
apnea occurs when a person stops breathing for 10 seconds or more. So, if normal
breath airflow is 70% to 100%, an apnea is if you stop breathing completely, or take less than 25% of a normal
breath (for a period that lasts 10 seconds or more). This definition includes
complete stoppage of airflow. (Other definitions of apnea that may be used
include at least a 4% drop in the saturation of oxygen in the blood, a direct
result of the reduction in the transfer of oxygen into the blood when breathing
stops.)
Apneas usually occur during sleep. When an apnea occurs,
sleep is disrupted. Sometimes this means the person wakes up completely, but
sometimes this can mean the person comes out of a deep level of sleep and into a more shallow level of
sleep. Apneas are usually measured during sleep (preferably in all stages of
sleep) over a two-hour period. An estimate of the severity of apnea is
calculated by dividing the number of apneas by the number of hours of sleep,
giving an apnea index (AI). The greater the AI, the more severe the apnea.
A hypopnea is a decrease in breathing that is not as severe as an
apnea. So, if normal breath airflow is 100% to 70%, a hypopnea is 69% to 26% of
a normal breath. Like apneas, hypopneas are associated with a 4% or greater drop
in the saturation of oxygen in the blood and usually occur during sleep. Also
like apneas, hypopneas usually disrupt the level of sleep. A hypopnea index (HI)
can be calculated by dividing the number of hypopneas by the number of hours of
sleep.
The apnea-hypopnea index (AHI) is an index of severity
that combines apneas and hypopneas. Combining them both gives an overall
severity of sleep apnea including sleep disruptions and desaturations (a low
level of oxygen in the blood). The apnea-hypopnea index, like the apnea index
and hypopnea index, is calculated by dividing the number of apneas and hypopneas
by the number of hours of sleep. Another index that is used to measure sleep
apnea is the respiratory
disturbance index (RDI). The respiratory disturbance index is similar to the
apnea-hypopnea index, however, it also
includes respiratory events that do not technically meet the definitions of apneas or hypopneas, but do disrupt sleep.
Sleep apnea is formally defined as an apnea-hypopnea
index of at least 15 episodes/hour in a patient without medical problems that
may be related to the sleep apnea. (That is the equivalent of one episode every
4 minutes.) In a patient with high blood pressure, stroke, daytime sleepiness, ischemic heart disease (low
flow of blood to the heart), insomnia, or mood disorders—all of which can be caused or
worsened by sleep apnea--sleep apnea is defined as an apnea-hypopnea index of at least 5
episodes/hour. This definition is stricter because the patient may be already
experiencing the negative medical effects of sleep apnea, and it may be
important to begin treatment at a lower apnea-hypopnea index.
Next: What are the types of sleep apnea? »
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