Obstructive
Sleep Apnea
Sleep apnea is a disorder
that commonly affects more than 12 million people in the
United States. It takes its name from the Greek word apnea,
which means "without breath." People with sleep
apnea literally stop breathing repeatedly during their sleep,
often for a minute or longer and as many as hundreds of
times during a single night.
Sleep apnea can be caused
by either complete obstruction of the airway (obstructive
apnea) or partial obstruction (obstructive hypopnea—hypopnea
is slow, shallow breathing), both of which can wake one
up. There are three types of sleep apnea—obstructive,
central, and mixed. Of these, obstructive sleep apnea (OSA)
is the most common. OSA occurs in approximately 2 percent
of women and 4 percent of men over the age of 35.
Causes
The exact cause of OSA remains unclear.
The site of obstruction in most patients is the soft palate,
extending to the region at the base of the tongue. There
are no rigid structures, such as cartilage or bone, in this
area to hold the airway open. During the day, muscles in
the region keep the passage wide open. But as a person with
OSA falls asleep, these muscles relax to a point where the
airway collapses and becomes obstructed.
When the airway closes, breathing
stops, and the sleeper awakens to open the airway. The arousal
from sleep usually lasts only a few seconds, but brief arousals
disrupt continuous sleep and prevent the person from reaching
the deep stages of slumber, such as rapid eye movement (REM)
sleep, which the body needs in order to rest and replenish
its strength. Once normal breathing is restored, the person
falls asleep only to repeat the cycle throughout the night.
Typically, the frequency of waking
episodes is somewhere between 10 and 60. A person with severe
OSA may have more than 100 waking episodes in a single night.
Risk Factors
The primary risk factor for OSA is
excessive weight gain. The accumulation of fat on the sides
of the upper airway causes it to become narrow and predisposed
to closure when the muscles relax. Age is another prominent
risk factor. Loss of muscle mass is a common consequence
of the aging process. If muscle mass decreases in the airway,
it may be replaced with fat, leaving the airway narrow and
soft. Men have a greater risk for OSA. Male hormones can
cause structural changes in the upper airway.
Other predisposing factors associated
with OSA include:
Anatomic abnormalities, such as a
receding chin
Enlarged tonsils and adenoids, the main causes of OSA in
children
Family history of OSA, although no genetic inheritance pattern
has been proven
Use of alcohol and sedative drugs, which relax the musculature
in the surrounding upper airway
Smoking, which can cause inflammation, swelling, and narrowing
of the upper airway
Hypothyroidism, acromegaly, amyloidosis, vocal cord paralysis,
post-polio syndrome, neuromuscular disorders, Marfan's syndrome,
and Down syndrome
Nasal congestion
CPAP,
the more common of the three therapy modes, usually is administered
at bedtime through a nasal or facial mask held in place
by Velcro straps around the patient's head. The mask is
connected by a tube to a small air compressor about the
size of a shoe box. The CPAP
machine sends air under pressure through the tube into
the mask, where it imparts positive pressure to the upper
airways. This essentially "splints" the upper
airway open and keeps it from collapsing.
Approximately 55% of patients who
use CPAP do so on a nightly basis for more than 4 hours.
It is the most commonly prescribed treatment for OSA. The
advantages of CPAP are that it is very safe and completely
reversible. Generally, it is quite well tolerated. The main
disadvantage is that it requires active participation every
night; that is, patient compliance is necessary for it to
work.
Mask fitting is an essential element
of a patient's success with positive airway pressure therapy
since it affects compliance and effectiveness of treatment.
Higher pressures can result in air leak and patient discomfort.
Demands on mask stability increase as pressure increases.
Higher pressures may also require tighter head gear to maintain
an adequate seal contributing to the discomfort. When selecting
a CPAP mask the following
factors should be considered:
Comfort
Quality of air seal
Conveninence
Quietness
Airventing
Advertising Disclaimer
Side effects of CPAP include contact dermatitis, skin breakdown,
mouth leaks, nasal congestion, runny nose (rhinorrhea),
dry eyes, nose bleeds (rare), tympanic membrane rupture
(very rare), chest pain, difficulty exhaling, pneumothorax
(very rare), smothering sensation, and excessive swallowing
of air (aerophagia).
Nasal congestion often can be reduced
or eliminated with nasal steroid sprays and humidification
placed into the machine. Rhinorrhea can be eliminated with
nasal steroid sprays or ipratroprium bromide nasal sprays.
Epistaxis is usually due to dry mucosa and can be combatted
with humidification. Dry eyes are usually caused by mask
leaks and can be eliminated by changing to a better fitting
mask.
Autotitration devices are designed
to provide the minimum necessary pressure at any given time
and change that pressure as the needs of the patient change.
Autotitration devices respond to different parameters and
rely on different algorithm so they do not all operate the
same.
The AutoSet® by ResMed acts by
monitoring the patient's inspiratory flow-time curve. A
flattening of the inspiratory flow-time curve typically
precedes an upper airway obstruction, which causes apnea,
hypopnea, or snoring. Monitoring and responding to the flow-time
curve, reduces the number of respiratory events and arousals
improving sleep quality.
Bi-level positive airway pressure
is a variation of CPAP. Most of the problems patients experience
with CPAP are caused by having to exhale against a high
airway pressure. Because the air pressure required to prevent
respiratory obstruction is typically less on expiration
than on inspiration, bi-level positive airway pressure machines
are designed to sense when the patient is inhaling and exhaling
and to reduce the pressure to a preset level on exhalation.
Bi-level positive airway pressure machines usually are used
when the patient does not tolerate CPAP or when the patient
has more than one respiratory disorder.
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