======================================================================
= Sleep apnea =
======================================================================
Introduction
======================================================================
Sleep apnea, also spelled sleep apnoea, is a sleep disorder where a
person has pauses in breathing or periods of shallow breathing during
sleep. Each pause can last for a few seconds to a few minutes and they
happen many times a night. In the most common form, this follows loud
snoring. There may be a choking or snorting sound as breathing
resumes. Because the disorder disrupts normal sleep, those affected
may experience sleepiness or feel tired during the day. In children it
may cause hyperactivity or problems in school.
Sleep apnea may be either obstructive sleep apnea (OSA) in which
breathing is interrupted by a blockage of air flow, central sleep
apnea (CSA) in which regular unconscious breath simply stops, or a
combination of the two. Obstructive (OSA) is the most common form.
Risk factors for OSA include being overweight, a family history of the
condition, allergies, a small breathing airway, and enlarged tonsils.
Some people with sleep apnea are unaware they have the condition. In
many cases it is first observed by a family member. Sleep apnea is
often diagnosed with an overnight sleep study. For a diagnosis of
sleep apnea, more than five episodes per hour must occur.
Treatment may include lifestyle changes, mouthpieces, breathing
devices, and surgery. Lifestyle changes may include avoiding alcohol,
losing weight, stopping smoking, and sleeping on one's side. Breathing
devices include the use of a CPAP machine. Without treatment, sleep
apnea may increase the risk of heart attack, stroke, diabetes, heart
failure, irregular heartbeat, obesity, and motor vehicle collisions.
OSA affects 1 to 6% of adults and 2% of children. It affects males
about twice as often as females. While people at any age can be
affected, it occurs most commonly among those 55 to 60 years old. CSA
affects less than 1% of people. A type of CSA was described in the
German myth of Ondine's curse where the person when asleep would
forget to breathe.
Signs and symptoms
======================================================================
People with sleep apnea have problems with excessive daytime
sleepiness (EDS), impaired alertness, and vision problems. OSA may
increase risk for driving accidents and work-related accidents. If OSA
is not treated, people are at increased risk of other health problems,
such as diabetes. Death could occur from untreated OSA due to lack of
oxygen to the body.
Due to the disruption in daytime cognitive state, behavioral effects
may be present. These can include moodiness, belligerence, as well as
a decrease in attentiveness and energy. These effects may become
intractable, leading to depression.
There is evidence that the risk of diabetes among those with moderate
or severe sleep apnea is higher. There is increasing evidence that
sleep apnea may lead to liver function impairment, particularly fatty
liver diseases (see steatosis). Finally, because there are many
factors that could lead to some of the effects previously listed, some
people are not aware that they have sleep apnea and are either
misdiagnosed or ignore the symptoms altogether.
Risk factors
======================================================================
Sleep apnea can affect people regardless of sex, race, or age.
However, risk factors include:
* being male
* obesity
* age over 40
* large neck circumference (greater than 16-17 inches)
* enlarged tonsils or tongue
* small jaw bone
* gastroesophageal reflux
* allergies
* sinus problems
* a family history of sleep apnea
* deviated septum
Alcohol, sedatives and tranquilizers may also promote sleep apnea by
relaxing throat muscles. People who smoke tobacco have sleep apnea at
three times the rate of people who have never done so.
Central sleep apnea is more often associated with any of the following
risk factors:
* being male
* an age above 65
* having heart disorders such as atrial fibrillation or atrial septal
defects such as PFO
* stroke
High blood pressure is very common in people with sleep apnea.
Mechanism
======================================================================
When breathing is paused, carbon dioxide builds up in the bloodstream.
Chemoreceptors in the blood stream note the high carbon dioxide
levels. The brain is signaled to awaken the person, which clears the
airway and allows breathing to resume. Breathing normally will restore
oxygen levels and the person will fall asleep again. This carbon
dioxide build-up may be due to the decrease of output of the brainstem
regulating the chest wall or pharyngeal muscles, which causes the
pharynx to collapse. People with sleep apnea experience reduced or no
slow-wave sleep and spend less time in REM sleep.
Diagnosis
======================================================================
Sleep apnea may be diagnosed by the evaluation of symptoms, risk
factors and observation, (e.g., excessive daytime sleepiness and
fatigue) but the gold standard for diagnosis is a formal sleep study
(polysomnography, or sometimes a reduced-channels home-based test). A
study can establish reliable indices of the disorder, derived from the
number and type of event per hour of sleep (Apnea Hypopnea Index
(AHI), or Respiratory Disturbance Index (RDI)), associated to a formal
threshold, above which a patient is considered as suffering from sleep
apnea, and the severity of their sleep apnea can then be quantified.
Mild obstructive sleep apnea (OSA) ranges from 5to 14.9 events per
hour, moderate OSA falls in the range of 15-29.9 events per hour, and
severe OSA would be a patient having over 30 events per hour.
Despite this medical consensus, the variety of apneic events (e.g.,
hypopnea vs apnea, central vs obstructive), the variability of
patients' physiologies, and the inherent shortcomings and variability
of equipment and methods, this field is subject to debate.
Within this context, the definition of an event depends on several
factors (e.g., patient's age) and account for this variability through
a multi-criteria decision rule described in several, sometimes
conflicting, guidelines. One example of a commonly adopted definition
of an apnea (for an adult) includes a minimum 10-second interval
between breaths, with either a neurological arousal (a 3-second or
greater shift in EEG frequency, measured at C3, C4, O1, or O2) or a
blood oxygen desaturation of 3-4% or greater, or both arousal and
desaturation.
Oximetry
==========
Oximetry, which may be performed over one or several nights in a
person's home, is a simpler, but less reliable alternative to a
polysomnography. The test is recommended only when requested by a
physician and should not be used to test those without symptoms. Home
oximetry may be effective in guiding prescription for automatically
self-adjusting continuous positive airway pressure.
Classification
================
There are three types of sleep apnea. OSA accounts for 84%, CSA for
0.4%, and 15% of cases are mixed.
Obstructive sleep apnea
=========================
No airway obstruction during sleep. Airway obstruction during sleep.
Obstructive sleep apnea (OSA) is the most common category of
sleep-disordered breathing. The muscle tone of the body ordinarily
relaxes during sleep, and at the level of the throat, the human airway
is composed of collapsible walls of soft tissue which can obstruct
breathing. Mild occasional sleep apnea, such as many people experience
during an upper respiratory infection, may not be significant, but
chronic severe obstructive sleep apnea requires treatment to prevent
low blood oxygen (hypoxemia), sleep deprivation, and other
complications.
Individuals with low muscle-tone and soft tissue around the airway
(e.g., because of obesity) and structural features that give rise to a
narrowed airway are at high risk for obstructive sleep apnea. The
elderly are more likely to have OSA than young people. Men are more
likely to suffer sleep apnea than women and children are, though it is
not uncommon in the last two population groups.
The risk of OSA rises with increasing body weight, active smoking and
age. In addition, patients with diabetes or "borderline" diabetes have
up to three times the risk of having OSA.
Common symptoms include loud snoring, restless sleep, and sleepiness
during the daytime. Diagnostic tests include home oximetry or
polysomnography in a sleep clinic.
Some treatments involve lifestyle changes, such as avoiding alcohol or
muscle relaxants, losing weight, and quitting smoking. Many people
benefit from sleeping at a 30-degree elevation of the upper body or
higher, as if in a recliner. Doing so helps prevent the gravitational
collapse of the airway. Lateral positions (sleeping on a side), as
opposed to supine positions (sleeping on the back), are also
recommended as a treatment for sleep apnea, largely because the
gravitational component is smaller in the lateral position. Some
people benefit from various kinds of oral appliances such as the
Mandibular advancement splint to keep the airway open during sleep.
Continuous positive airway pressure (CPAP) is the most effective
treatment for severe obstructive sleep apnea, but oral appliances are
considered a first-line approach equal to CPAP for mild to moderate
sleep apnea, according to the AASM parameters of care. There are also
surgical procedures to remove and tighten tissue and widen the airway.
Snoring is a common finding in people with this syndrome. Snoring is
the turbulent sound of air moving through the back of the mouth, nose,
and throat. Although not everyone who snores is experiencing
difficulty breathing, snoring in combination with other risk factors
has been found to be highly predictive of OSA. The loudness of the
snoring is not indicative of the severity of obstruction, however. If
the upper airways are tremendously obstructed, there may not be enough
air movement to make much sound. Even the loudest snoring does not
mean that an individual has sleep apnea syndrome. The sign that is
most suggestive of sleep apneas occurs when snoring 'stops'.
Other indicators include (but are not limited to): hypersomnolence,
obesity BMI >30, large neck circumference ( in women, in men),
enlarged tonsils and large tongue volume, micrognathia, morning
headaches, irritability/mood-swings/depression, learning and/or memory
difficulties, and sexual dysfunction.
The term "sleep-disordered breathing" is commonly used in the U.S. to
describe the full range of breathing problems during sleep in which
not enough air reaches the lungs (hypopnea and apnea).
Sleep-disordered breathing is associated with an increased risk of
cardiovascular disease, stroke, high blood pressure, arrhythmias,
diabetes, and sleep deprived driving accidents. When high blood
pressure is caused by OSA, it is distinctive in that, unlike most
cases of high blood pressure (so-called essential hypertension), the
readings do 'not' drop significantly when the individual is sleeping.
Stroke is associated with obstructive sleep apnea.
It has been revealed that people with OSA show tissue loss in brain
regions that help store memory, thus linking OSA with memory loss.
Using magnetic resonance imaging (MRI), the scientists discovered that
people with sleep apnea have mammillary bodies that are about 20
percent smaller, particularly on the left side. One of the key
investigators hypothesized that repeated drops in oxygen lead to the
brain injury.
Obstructive sleep apnea is associated with problems in daytime
functioning, such as daytime sleepiness, motor vehicle crashes,
psychological problems, decreased cognitive functioning, and reduced
quality of life. Other associated problems include cerebrovascular
diseases (hypertension, coronary artery disease, and stroke) and
diabetes. These problems could be, at least in part, caused by risk
factors of OSA.
Central sleep apnea
=====================
In pure central sleep apnea or Cheyne-Stokes respiration, the brain's
respiratory control centers are imbalanced during sleep. Blood levels
of carbon dioxide, and the neurological feedback mechanism that
monitors them, do not react quickly enough to maintain an even
respiratory rate, with the entire system cycling between apnea and
hyperpnea, even during wakefulness. The sleeper stops breathing and
then starts again. There is no effort made to breathe during the pause
in breathing: there are no chest movements and no struggling. After
the episode of apnea, breathing may be faster (hyperpnea) for a period
of time, a compensatory mechanism to blow off retained waste gases and
absorb more oxygen.
While sleeping, a normal individual is "at rest" as far as
cardiovascular workload is concerned. Breathing is regular in a
healthy person during sleep, and oxygen levels and carbon dioxide
levels in the bloodstream stay fairly constant. Any sudden drop in
oxygen or excess of carbon dioxide (even if tiny) strongly stimulates
the brain's respiratory centers to breathe.
In central sleep apnea, the basic neurological controls for breathing
rate malfunction and fail to give the signal to inhale, causing the
individual to miss one or more cycles of breathing. If the pause in
breathing is long enough, the percentage of oxygen in the circulation
will drop to a lower than normal level (hypoxaemia) and the
concentration of carbon dioxide will build to a higher than normal
level (hypercapnia). In turn, these conditions of hypoxia and
hypercapnia will trigger 'additional' effects on the body. Brain cells
need constant oxygen to live, and if the level of blood oxygen goes
low enough for long enough, the consequences of brain damage and even
death will occur. However, central sleep apnea is more often a chronic
condition that causes much milder effects than sudden death. The exact
effects of the condition will depend on how severe the apnea is and on
the individual characteristics of the person having the apnea. Several
examples are discussed below, and more about the nature of the
condition is presented in the section on Clinical Details.
In any person, hypoxia and hypercapnia have certain common effects on
the body. The heart rate will increase, unless there are such severe
co-existing problems with the heart muscle itself or the autonomic
nervous system that makes this compensatory increase impossible. The
more translucent areas of the body will show a bluish or dusky cast
from cyanosis, which is the change in hue that occurs owing to lack of
oxygen in the blood ("turning blue"). Overdoses of drugs that are
respiratory depressants (such as heroin, and other opiates) kill by
damping the activity of the brain's respiratory control centers. In
central sleep apnea, the effects of sleep 'alone' can remove the
brain's mandate for the body to breathe.
* Normal Respiratory Drive: After exhalation, the blood level of
oxygen decreases and that of carbon dioxide increases. Exchange of
gases with a lungful of fresh air is necessary to replenish oxygen and
rid the bloodstream of built-up carbon dioxide. Oxygen and carbon
dioxide receptors in the blood stream (called chemoreceptors) send
nerve impulses to the brain, which then signals reflex opening of the
larynx (so that the opening between the vocal cords enlarges) and
movements of the rib cage muscles and diaphragm. These muscles expand
the thorax (chest cavity) so that a partial vacuum is made within the
lungs and air rushes in to fill it.
* Physiologic effects of central apnea: During central apneas, the
central respiratory drive is absent, and the brain does 'not' respond
to changing blood levels of the respiratory gases. No breath is taken
despite the normal signals to inhale. The immediate effects of central
sleep apnea on the body depend on how long the failure to breathe
endures. At worst, central sleep apnea may cause sudden death. Short
of death, drops in blood oxygen may trigger seizures, even in the
absence of epilepsy. In people 'with' epilepsy, the hypoxia caused by
apnea may trigger seizures that had previously been well controlled by
medications. In other words, a seizure disorder may become unstable in
the presence of sleep apnea. In adults with coronary artery disease, a
severe drop in blood oxygen level can cause angina, arrhythmias, or
heart attacks (myocardial infarction). Longstanding recurrent episodes
of apnea, over months and years, may cause an increase in carbon
dioxide levels that can change the pH of the blood enough to cause a
respiratory acidosis.
Mixed apnea
=============
Some people with sleep apnea have a combination of both types; its
prevalence ranges from 0.56% to 18%. The condition is generally
detected when obstructive sleep apnea is treated with CPAP and central
sleep apnea emerges. The exact mechanism of the loss of central
respiratory drive during sleep in OSA is unknown but is most likely
related to incorrect settings of the CPAP treatment and other medical
conditions the person has.
Management
======================================================================
The treatment of obstructive sleep apnea is different than that of
central sleep apnea. Treatment often starts with behavioral therapy.
Many people are told to avoid alcohol, sleeping pills, and other
sedatives, which can relax throat muscles, contributing to the
collapse of the airway at night.
Continuous positive airway pressure
=====================================
For moderate to severe sleep apnea, the most common treatment is the
use of a continuous positive airway pressure (CPAP) or automatic
positive airway pressure (APAP) device. These splint the person's
airway open during sleep by means of pressurized air. The person
typically wears a plastic facial mask, which is connected by a
flexible tube to a small bedside CPAP machine.
With proper use, CPAP improves outcomes. Whether or not it decreases
the risk of death or heart disease is controversial with some reviews
finding benefit and others not. This variation across studies might be