Section 6. Brain, Spinal Cord, and Nerve Disorders

Chapter 81. Sleep Disorders

Topics: Introduction | Insomnia | Hypersomnia | Narcolepsy | Sleep Apnea Syndromes | Parasomnias | Sleep Disorders in People With Dementia

Sleep Apnea Syndromes

Sleep apnea syndromes are a group of serious sleep disorders in which breathing repeatedly stops long enough during sleep to decrease the amount of oxygen and increase the amount of carbon dioxide in the blood and brain.

Sleep apnea occurs when breathing is temporarily interrupted during sleep. There are three types.

Obstructive sleep apnea, the most common type, is caused by a blockage in the throat or upper airway. It affects about 4 to 6% of middle-aged men and 1 to 2% of middle-aged women in the United States. Obstructive sleep apnea most commonly occurs in obese people, who tend to sleep on their back. Obesity, perhaps in combination with aging body tissues and other factors, leads to narrowing of the upper airway. Smoking and excessive use of alcohol worsen obstructive sleep apnea. Lung disorders (such as emphysema) contribute to the lack of oxygen. Having a narrow throat and upper airway, which tend to run in families, increases the risk of sleep apnea. In children, enlarged tonsils or adenoids can cause obstructive sleep apnea.

Central sleep apnea, a much rarer type, is caused by dysfunction in the part of the brain that controls breathing (brain stem). Normally, the brain stem is very sensitive to changes in the blood level of carbon dioxide (a by-product of the metabolism of oxygen). When the level is high, the brain stem signals the respiratory muscles to breathe harder and faster to remove carbon dioxide through exhalation, and vice versa. In central sleep apnea, the brain stem is less sensitive to changes in the carbon dioxide level. Because the brain stem responds slowly to the buildup of carbon dioxide in the blood, the body's response is exaggerated, resulting in prolonged hyperventilation. Similarly, because the brain stem responds slowly to the removal of carbon dioxide from the blood, the body's response--a pause in breathing--is prolonged. Brain stem dysfunction that leads to central sleep apnea may be due to brain tumors. People who have heart failure may have central sleep apnea. In one form of central sleep apnea, called Ondine's curse, people may breathe inadequately or not at all except when they are fully awake. Central sleep apnea is not associated with obesity.

Mixed sleep apnea, the third type, is a combination of obstructive sleep apnea and central sleep apnea. For example, obstructive sleep apnea sometimes causes central sleep apnea--by decreasing oxygen levels and increasing carbon dioxide levels in the blood long enough to cause the brain stem to malfunction. Mixed sleep apnea is rare.

Symptoms

Because symptoms occur during sleep, they are usually first noticed by a sleep partner. In all types of sleep apnea, breathing may become abnormally slow and shallow, or breathing may suddenly stop for at least 10 seconds (sometimes up to 1 minute), then resume.

In obstructive sleep apnea, the most common symptom is snoring, with episodes of gasping, choking, pauses in breathing, and sudden awakenings. When obstructive sleep apnea is severe, repeated bouts of sleep-related obstructive choking occur at night and involuntary naps occur during the day. Eventually, these naps interfere with daytime work and reduce the quality of life. Memory may be impaired, sex drive may be reduced, and personality may change. In people with obstructive sleep apnea, the risk of such complications as stroke, heart attack, and high blood pressure is increased. If episodes of obstructive sleep apnea are more frequent than 20 per hour, the risk of death is increased.

People who are extremely obese often have obesity-hypoventilation syndrome (pickwickian syndrome) as well as obstructive sleep apnea. Excess body fat interferes with the movement of the chest wall, reducing the amount of air that reaches the lungs. Excess body fat below the diaphragm compresses the lungs, making breathing shallow. Excess body fat around the throat compresses the upper airway, reducing air flow.

In central sleep apnea, snoring does not usually occur. However, patterns of breathing may be abnormal. Cheyne-Stokes respiration (periodic breathing) is an example. In Cheyne-Stokes respiration, breathing gradually becomes more rapid, gradually slows down, stops for a short period, then starts again. Then the cycle repeats. Each cycle lasts 30 seconds to 2 minutes.

In all types of sleep apnea, the disturbances in sleep can result in daytime sleepiness, fatigue, irritability, headaches in the mornings, slowness of thought, and difficulty concentrating. Because oxygen levels in the blood may decrease significantly, abnormal heart rhythms may develop, and blood pressure may increase.

Prolonged, severe sleep apnea of any type eventually leads to heart failure and malfunction of the lungs. Then the heart cannot pump enough blood to the body, and the lungs cannot provide enough oxygen to or remove enough carbon dioxide from the body.

Diagnosis

In its early stages, sleep apnea is often diagnosed on the basis of information provided by the person's sleep partner. The partner may report that the person snores loudly, periodically stops breathing, awakens choking and frightened from sleep, and is becoming increasingly tired during the day. For example, the person may fall asleep while watching television, while attending a meeting, or even while driving.

The diagnosis is best confirmed and severity is best determined in a sleep laboratory. Electroencephalography (EEG) (see Section 6, Chapter 77) is used to monitor changes in levels of sleep. Eye movements can be recorded during REM sleep with electrodes placed near the eyes (a procedure called electro-oculography). Also, the oxygen level in the blood is measured with an electrode placed on a finger or an earlobe (a procedure called oximetry). Airflow is measured with a device placed in front of the nostrils, and the motion and pattern of breathing are measured with an electrode or gauge placed on the chest. This evaluation can help doctors distinguish between obstructive and central sleep apnea.

Treatment

Obstructive Sleep Apnea: Losing weight, quitting smoking, and not using alcohol excessively can help. Heavy snorers and people who often choke in their sleep should not consume alcohol or take sleep aids, antihistamines, or other drugs that cause drowsiness. Nasal infections and allergies should be treated.

Sleeping on the side or elevating the head of the bed can help reduce snoring. Special antisnoring pillows strapped on the back help prevent people from sleeping on their back. The various other devices marketed to reduce snoring usually help only when snoring is mild, and they do not relieve obstructive sleep apnea. If treatment is needed for heavy snoring, the small piece of tissue that hangs down at the back of the mouth (uvula) may be surgically removed in a procedure called uvulopalatoplasty.

Removable oral appliances, fitted by dentists, can help relieve obstructive sleep apnea (and snoring) for many people. These appliances, which are worn only while sleeping, help keep the airway open. Most appliances separate the jaws and push the lower jaw forward so the tongue cannot move backward to block the throat. Others hold the tongue forward.

If the above measures do not eliminate or relieve sleep apnea, people may benefit from continuous positive airway pressure (CPAP). With CPAP, room air that is under pressure is delivered through a face mask. The pressure keeps the airways open as the person breathes in. For the first two weeks of use, wearing the mask may seem uncomfortable and the nasal passages may dry out. But with continued use, many people can adapt. Also using a humidifier helps some people adapt.

Surgery to enlarge the airway through the throat (uvulopalatopharyngoplasty) is occasionally performed, but it is usually successful only in people who have mild sleep apnea.

Central Sleep Apnea: The underlying disorder is treated if possible. For example, drugs may be given to reduce the severity of heart failure (see Section 3, Chapter 25). As in obstructive sleep apnea, people with central sleep apnea also often benefit from CPAP. Oxygen delivered by nasal prongs (not under pressure) may also be helpful. Acetazolamide and theophylline are used occasionally. These drugs can stimulate the drive to breathe.