Sleep apnea is a condition characterized by brief interruptions of breathing during sleep. There are two types of sleep apnea: central and obstructive. Obstructive sleep apnea, in which the airway closes off and the person wakes up, gasping, is the more common type.
Central sleep apnea is a much less common condition in which the brain doesn't send the appropriate signals to muscles involved in breathing, and the patient alternates between hyperventilating and not breathing. Central sleep apnea may stem from a brain injury, congestive heart failure, or other health problems.
Some people have both types of sleep apnea.
More than 12 million Americans are estimated to have obstructive sleep apnea (OSA). Because people with sleep apnea don't get restful sleep at night, they may be excessively sleepy during the day, which can lead to trouble at school and work and even to car accidents. Untreated severe OSA is associated with a higher risk for insulin resistance, heart disease, heart attack, high blood pressure and stroke, and many people with these conditions have undiagnosed OSA. But once obstructive sleep apnea is diagnosed, it can be treated—which reduces the risk of diseases that often accompany the syndrome.
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Several structures of the nose, mouth, and throat can be involved in obstructive sleep apnea. The uvula is the piece of tissue that hangs down from the soft palate, at the back of the roof of the mouth. Tonsils are on either side of the throat at the back of the mouth; they are made of lymphoid tissue, part of the body's immune system. The position of the tongue can also affect nighttime breathing.
These structures can cause sleep apnea by obstructing airflow. This means the body has to work harder to pull in air, the airway can't stay open against the strong negative pressure produced by the body's effort to breathe, and it collapses.
In obstructive sleep apnea, air passage is blocked during sleep by the tongue and other soft tissues. Many people with sleep apnea are snorers. As soft tissues block the airway, the body has to work harder to pull air in; the increase in pressure can make the upper airway collapse so air cannot flow into the lungs, although efforts to breathe continue. Breathing stops for several seconds to over a minute, and levels of blood oxygen may drop during these episodes. When blood oxygen levels fall too low, the brain wakes you up enough to tighten the muscles around the upper airways, which opens them enough for air to flow through again. This arousal is so brief, the person likely won't even remember it. The repeated arousals decrease sleep quality, so people with sleep apnea often feel tired during the day.
Not all obstructive sleep apnea is caused by soft-tissue obstruction. The airway may also be narrowed by obesity or may just be naturally more narrow, making it more prone to collapse.
In children, obstructive sleep apnea is often caused by enlarged tonsils or adenoids.
Central sleep apnea, a much rarer condition, occurs when the brain intermittently fails to send the appropriate signals to the breathing muscles for respiration.
People who are overweight are more likely to develop obstructive sleep apnea, because fat around the neck makes it harder for the throat to stay open. Those who snore are more likely to develop sleep apnea. Smoking, drinking, and nasal congestion also increase the risk of sleep apnea—smoking irritates the tissue in your nose and throat, making the airway more likely to collapse while you are asleep.
Obstructive sleep apnea may have a genetic component, as it is more common among African-Americans, Asians, Native Americans, and Hispanics than Caucasians. It can also run in families. Men are more likely to have sleep apnea than women. Sleep apnea is more common in women after menopause than before.
While the classic patient with obstructive sleep apnea is male, middle-aged, and overweight, this stereotype leaves out most people with obstructive sleep apnea. While being overweight increases the risk of sleep apnea, a person who is not overweight can also have an airway that collapses in sleep.
Central sleep apnea is more common in older people. This may be because older people are more likely to have congestive heart failure, thyroid disease, stroke, or other conditions that can interfere with the nervous system's ability to regulate breathing.
Untreated obstructive sleep apnea is associated with a higher risk for insulin resistance, heart disease, heart attack, high blood pressure, and stroke. For this reason, treating sleep apnea is not simply a question of improving sleep quality and ending snoring; it may also decrease the risk of more serious disease.
The link between sleep apnea and these diseases is imperfectly understood. However, some events that happen during sleep apnea episodes may be bad for your heart.
In normal sleep, the deeper your sleep, the more your heart and blood vessels dilate. The heart beats more slowly and puts out less blood with each beat. Blood pressure is lower, and the blood vessels dilate.
But when a person with obstructive sleep apnea stops breathing, he or she wakes up. This interrupts sleep and stimulates the cardiovascular system. Blood vessels constrict and blood pressure goes up in the vessels and in the lungs, both because the person wakes up and because the blood is low in oxygen. The pressures that build up in the chest as you struggle to breathe against a closed airway can also affect the heart.
Even while awake, people with obstructive sleep apnea have higher heart rates and more variable blood pressure than people without sleep apnea.
In the Wisconsin Sleep Cohort, a long-term study, people with moderate to severe OSA at the time of the initial sleep study were three times more likely to have developed high blood pressure four years later.
Last reviewed on 09/20/2006
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