Sleep Apnea (cont.)
What is obstructive sleep apnea and what causes it?
In obstructive sleep apnea (OSA), apneas have four components.
- First, the airway collapses or becomes obstructed.
- Second, an effort is made to take a breath, but it is
unsuccessful.
- Third, the oxygen level in the blood drops as a result of unsuccessful
breathing.
- Finally, when the amount of oxygen reaching the brain
decreases, the brain signals the body to wake up and take a breath. (This is
what the bed partner hears as a silence followed by a gasp for air.)
First, it is necessary to describe a "normal breath." A normal breath of air
passes through the nasal passages, behind the soft palate and uvula (part of the
soft palate), then past the tongue base, through the throat muscles, and between
the vocal cords into the lungs. An obstruction to the flow of air at any of
these levels may lead to apnea. The following are some examples:
- airflow can become diminished if a person has a deviated septum (the
middle wall of the nose that separates the two nostrils). A septum can be
deviated to one or both sides narrowing the air passages;
- there are filters in the nose called turbinates that can obstruct
airflow when they become swollen;
- if the palate and uvula (the part of soft palate that hangs down in the back of
the throat) are long or floppy, they can fall backwards and close the area
through which air flows;
- the back of the tongue can also fall backwards and obstruct breathing
especially when individuals lay flat on their backs; or
- the side walls of the throat can fall together to narrow or close the airway.
To break it down even further:
- the muscles of breathing work to expand the chest and lower the diaphragm to
degenerate a negative pressure between the airways of the lungs and outside;
- this negative pressure literally sucks air into the lungs;
- the nasal passages, palate, tongue, and pharyngeal
tissues can all contribute to narrowing of the airway;
- if during an attempt to breathe the airway
collapses or is obstructed the tissues of the airway are sucked together by
the negative pressure;
- the harder the chest tries to pull air in the
greater the negative pressure and the more the tissues of the airway are
sealed together; and
- finally,
when the oxygen in the blood stream decreases the person wakes up or the level
of sleep becomes more shallow in order to more consciously take a breath.
People with obstructive sleep apnea have an airway that is more narrow than
normal, usually at the base of the tongue and palate. When lying flat, the
palate is above the air passage. When the pharyngeal muscles (muscles of the
pharynx or throat ) relax the palate
can fall backwards and this can obstruct the airway.
The genioglossus muscle is
located where the base of the tongue attaches to the jawbone in front. Most
people have enough space behind the tongue to take a breath without needing to
pull the tongue forward. However, when obstructive sleep apnea patients are
awake, this muscle needs to be active to pull the base of the tongue forward to
open the airway. During sleep, most muscles including the genioglossus relax.
During the stage of rapid eye movement (REM), the
muscles completely relax. Relaxation of the genioglossus muscle during sleep allows the
base of the tongue to fall backwards and the airway closes.
Patients with obstructive sleep apnea often don't report waking up during the night with each
episode of apnea. Frequently, during the apnea the brain only awakens from a
deep sleep (stages 3, 4, or REM) to a shallow level of sleep. The genioglossus
muscle
then contracts and pulls the tongue forward so that a breath can be taken. The
patient may remain asleep, but the deep sleep that is important to be fully
rested the following day is disrupted.
Next: How common is obstructive sleep apnea? »
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