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Sleep apnea

Description

An in-depth report on the causes, diagnosis, treatment, and prevention of sleep apnea.

Prognosis

Sleep apnea has a strong association with several diseases, particularly those related to the heart and circulation.

Adverse Effects of Sleep Apnea on Heart and Circulation

Researchers are intensively investigating why a problem in the upper airways is associated with serious conditions of the heart and circulatory system. Here are some of their findings:

• Major known risk factors for hypertension and heart disease (obesity, smoking, and alcohol abuse) are associated with sleep apnea. These factors, however, do not explain all cases of higher heart-related risks in people with sleep apnea. For example, among overweight people, those who have sleep apneas have a greater risk of heart problems than those without them.
• When breathing stops during episodes of apnea, carbon dioxide levels in the blood increase and oxygen levels drop. This effect may trigger a cascade of physical and chemical events that can then increase risk for heart problems.
• Apnea also causes decreased levels of the gas nitric oxide (NO), a potent substance that causes blood vessels to be elastic and expand. NO plays a crucial role in blood pressure control and heart health.
• Apnea may also increase levels of a substance called angiotensin-converting enzyme (ACE), which is known to play a role in high blood pressure and congestive heart failure.
• Researchers have reported high levels of certain immune factors called tumor necrosis factor-alpha (TNF-alpha) and interleukin 6 (IL-6) in people with sleep apnea, particularly those who are obese. High levels of TNF-alpha and IL-6 produce a damaging inflammatory response, which can harm cells in the body, including those in the arteries. Elevated TNF-alpha may be associated with fatigue, shortness of breath, and a diminished heart-pumping action.

At this time, however, evidence of a clear causal relationship with any of these health problems is still weak. Some studies have found no significant independent risk for heart disease from obstructive sleep apnea. The following are some discussions on the possible effects of apnea on specific health problems.

High Blood Pressure. A number of studies have found a strong association between sleep apnea and high blood pressure (hypertension). (In the past, the link between sleep apnea and hypertension was thought to be due to obesity, a risk factor for both conditions, but more recent studies contradict that theory.) A 2000 study followed patients for 4 years; the more nightly apnea episodes they had in the first year, the more likely they were to develop hypertension by the fourth year. A weak, but still higher-than-normal association with high blood pressure has also been observed in those who snore, wake frequently during the night, or have mild sleep apnea.

A 2004 data analysis of over 200,000 patient records revealed that people who took both antidepressants and antihypertensives were 18 times more likely to be diagnosed with obstructive sleep apnea than those who did not take the medications. The probability was highest among adults aged 20-39 years. These drugs do not cause sleep apnea, but antidepressants may be prescribed to treat hypertensive patients’ complaints of fatigue even if sleep apnea is the real cause. The researchers recommended that patients being treated for high blood pressure, depression, and fatigue should also be evaluated for sleep apnea.

One way that apnea may directly affect blood pressure, regardless of other risk factors:

• Blood pressure fluctuates widely and suddenly in response to episodes of apnea and hypopnea (shallow nighttime breathing).
• Such fluctuations are possibly due to a sudden surge in the sympathetic nervous system, which controls involuntary muscle responses, importantly those in the blood vessels and heart, and may also play a role in sleep apnea.
• These fluctuations lead to transient constriction of blood vessels that, over time, could possibly lead to sustained hypertension and heart damage.
• Effective treatment of sleep apnea with continuous positive airway pressure (CPAP) may reduce blood pressure. Sleep apneas must be significantly reduced, however, to have any effect on blood pressure. Even a 50% reduction in apneas has no effect.

Coronary Artery Disease and Heart Attack. Sleep apnea has been associated with heart disease regardless of the presence of high blood pressure or other heart risk factors. In a 2001 study, researchers observed that the more episodes of apnea and hypopnea a patient had, the higher the risk for a heart attack. Many of the factors associated with stroke and sleep apnea (a risk for blood clots and narrowing of the arteries) may also increase the risk for heart attacks. Obstructive sleep apnea, however, may have other effects that increase the risk for heart problems:

• Some evidence suggests that obstructive apneas cause an increase in stiffness and inflammation in the arteries, which is now proving to be an important aspect of heart disease, particularly in older adults.
• A 2002 study reported that the white blood cells of patients with apnea have an increased number of proteins called adhesion molecules on their surface that may bind to the lining of blood vessels and cause inflammation. Increasingly, scientists believe that inflammation plays an important role in the development of coronary artery disease, heart attacks, and many other major ailments.

Stroke. Sleep apnea doubles the risk for stroke. The worse the sleep apnea, the greater the risk; moderate-to-severe obstructive sleep apnea can triple the risk of stroke. Sleep apnea is also associated with high blood pressure, a known risk factor for stroke. However, people who have sleep apnea, but not high blood pressure, are also still at increased risk for stroke. Sleep apnea in stroke patients is also associated with a higher risk for worse symptoms after a stroke, including delirium, depression, poor response to speech, and difficulty conducting daily chores.

• A 2000 study observed that blood becomes more viscous (stickier) in the morning in people with obstructive sleep apnea compared to people without the sleep disorder. Such "sticky" blood is more apt to form clots that can lead to strokes. To support this, another 2000 study reported that stroke victims with sleep apnea tended to have higher levels of the blood protein fibrinogen than stroke victims without sleep apnea. Fibrinogen is a factor in blood that causes it to clot. Higher levels of fibrinogen have been linked to both strokes and heart attacks.
• A 1998 study reported that the carotid artery, the major artery to the brain, is in far greater danger of becoming sclerotic (hardened and narrower) in people with obstructive sleep apnea than in the average person. People with both diabetes and sleep apnea are at particularly high risk for this effect.

Heart Failure. Studies suggest that 11 - 37% of patients with heart failure also have sleep apnea. Central sleep apnea is particularly linked with heart failure. The evidence for the association between heart failure and sleep apnea includes:

• High blood pressure, which is associated with sleep apnea, is a major cause of later heart failure.
• Sleep apnea reduces oxygen levels and causes abnormal changes in blood pressure and heart rate that add to the burden of the failing heart.
• Obstructive sleep apnea can affect breathing functions that are particularly harmful for patients with existing congestive heart failure.
• Sleep apnea is associated with poorer survival in patients with heart failure. Some studies have suggested that treating sleep apnea with CPAP may improve heart function in these patients. However, a 2005 New England Journal of Medicine study found that CPAP did not improve survival in patients with heart failure and central sleep apnea

Atrial Fibrillation. Sleep apnea is more common in people with atrial fibrillation (irregular heartbeat) than in patients with other heart conditions. In a 2005 study published in Circulation , 49% of patients with atrial fibrillation were at risk for developing apnea, compared with 32% of general cardiology patients. An earlier study indicated that patients with untreated obstructive sleep apnea may be at increased risk for recurrence of atrial fibrillation. Patients with atrial fibrillation who received CPAP treatment had a lower risk for recurrence.

Metabolic Syndrome. The metabolic syndrome (also called Syndrome X) is a cluster of abnormalities that cause insulin resistance. Some of these factors, including hypertension and obesity, are also associated with sleep apnea. A 2004 study found that metabolic syndrome was nine times more common among patients with obstructive sleep apnea, independent of obesity.

Sleep Apnea as a Cause of Obesity

When it comes to sleep apnea and obesity, it is not always clear which condition is responsible for the other. For example, obesity is often a risk factor and possibly a cause of sleep apnea, but it is also likely that sleep apnea increases the risk for weight gain. Some studies indicate that sleep apnea disrupts rapid eye movement (REM) sleep, which, in turn, increases the risk for obesity. Research indicates that animals deprived of REM sleep tend to eat more. People with apnea may also become too tired to exercise and so put on weight.

Other Adverse Effects on Health

Sleep apnea is associated with a higher incidence of many medical conditions, other than heart and circulation. The links between apneas and the conditions are unclear.

• Pulmonary hypertension.
• Asthma. Sleep apnea may worsen asthma symptoms and interfere with the effectiveness of asthma medications. Treating the apnea may help asthma control.
• Diabetes.
• Kidney failure.
• Peripheral nerve damage (tingling, pain, or numbness in the hands and feet).
• Liver damage in obese individuals with sleep apnea. Recent research suggests that severe apnea may increase the risk of liver disease regardless of weight.
• Seizures, epilepsy, and other nerve disorders. Sleep apnea appears to pose a particularly risk for nocturnal epilepsy, a condition in which seizures occur during sleep.
• Headaches. Some studies strongly suggest that for some people sleep disorders, including apnea, may be the underlying causes of some chronic headaches. In some patients with both chronic headaches and apnea, treating the sleep disorder has been known to cure the headache, even the very severe and disabling form known as a cluster headache.
• Irregular menstrual periods. This occurs in about 40% of premenopausal women. It is not clear how they are related, but one study reported that treating apnea helped normalize periods.
• High-risk pregnancies. Some evidence suggests that there are higher rates of pregnancy complications in women with sleep apnea.
• Eye disorders, including glaucoma, conjunctivitis, dry eye, and various other infections and irritations. Findings presented at the 2003 annual meeting of the American Academy of Ophthalmology suggested that patients with sleep apnea may be at increased risk for glaucoma and should be tested for this eye disease. A vision-damaging condition called intracranial hypertension has also been observed some patients with sleep apnea.

Effects on Emotions and Thinking in Adults

Mental Issues in Adults . Some studies have reported that older people with sleep apnea and daytime sleepiness have lower scores on tests for mental functions, such learning and attention. One expert suggested that treating sleep apnea in older patients may correct some cases of dementia that are caused by sleep disturbances. Elderly people with sleep apnea may also be more prone to depression.

Emotional Effects of Sleep Apnea. Studies report an association between severe apnea and psychological problems. In one study, 32% of patients had symptoms of depression. Sleep-related breathing disorders can also worsen nightmares and post-traumatic stress disorder. In one study, treatment of sleep apnea eased these complaints. Certainly, daytime sleepiness interferes with quality of life. It is also possible that severe emotional problems might worsen the apnea.

Effects on Bed Partners

Because sleep apnea so often includes noisy snoring, the condition can also adversely affect the sleep quality of a patient's bed partner. Spouses or partners may also suffer from sleeplessness and fatigue. In some cases, the snoring can disrupt relationships. Diagnosis and treatment of sleep apnea in the patient can help eliminate these problems.

Effects in Infants and Children

Failure to Thrive. Small children with undiagnosed sleep apnea may "fail to thrive," that is, they do not gain weight or grow at a normal rate and they have low levels of growth hormone. In severe cases, this may affect the heart and central nervous system. Most often sleep apnea in children is caused by overgrown tonsils or adenoid. Their removal often completely solves all of these problems, including resolution of sleep apnea and restoring weight gain and normal growth hormone levels.

Attention Deficits and Hyperactivity. Problems in attention and hyperactivity are common in children with sleep apnea. There is some evidence that such children may be misdiagnosed with attention-deficit hyperactivity disorder. Snoring, rather than sleepiness, is a stronger risk factor for hyperactivity in many of these children, especially boys under 8 years old. (Even children who snore and do not have sleep apnea may be at higher risk for poor concentration.)

Sleep Apnea and Automobile Accidents

Some researchers believe that sleepiness associated with sleep apnea is the greatest risk factor for car accidents. As many as 200,000 automobile accidents in the U.S. and 1,500 deaths from such accidents are caused by sleepiness. Studies continue to report that drowsy driving is as risky as drunk driving. Several studies have suggested that people with sleep apnea have two to three times as many car accidents, and five to seven times the risk for multiple accidents.

• Review Date: 7/19/2006
• Reviewed By: Harvey Simon, M.D., Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital

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