Sleep Apnea

Description

Prognosis

As many as 200,000 automobile accidents in the US and 1,500 deaths from such accidents are caused by sleepiness. Studies continue to report that drowsy driving is as risky as drunk driving. Estimates on fatigue as a cause of automobile crashes range from 1% to 56%, depending on the study. In a major 1995 poll, for example, 33% of those surveyed said they had fallen asleep while driving, and 10% of these people had had accidents because of this. One study strongly suggested that it was habitual sleepiness, however, and not just being sleepy at the time of an accident that places people at higher risk.

Furthermore, some researchers believe that sleepiness associated with sleep apnea is the greatest risk factor for car accidents. Two studies in 1997 and 1998, respectively, reported that people with sleep apnea have two to three times as many car accidents, and five to seven times the risk for multiple accidents.

Sleep Apnea as a Cause of Obesity

Obesity and sleep apnea are a chicken and egg problem. 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.

Adverse Effects of Sleep Apnea on Heart and Circulation

Sleep apnea has a strong association with heart and circulation diseases. The links are not fully clear. Researchers are intensively investigating why a problem in the upper airways is associated with these serious conditions. Here are some findings:

• Obesity, smoking, and alcohol abuse, known risk factors for hypertension and heart disease, are also 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 these conditions.
• 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 was associated in one study 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). For example, a 2000 study followed patients for four years and reported that the greater the number of nightly apnea episodes they had in year one 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 even been observed in those who snore, wake frequently during the night, or have mild sleep apnea.

The relationship between sleep apnea and hypertension has been thought to be largely due to obesity, a risk factor common to both conditions. Recent and major studies, however, are suggesting a higher rate of hypertension in people with sleep apnea regardless of weight. In those whose hypertension is resistant to treatment, sleep apnea is likely to be particularly severe.

The following is 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 one 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 appears to increase the chance for a stroke independent of its association with high blood pressure (a known risk factor 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 verbal stimuli, and difficulty conducting daily chores. How sleep apnea increases these risks is under investigation. Some theories are as follows:

• One 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.

One small 1998 study reported a drop in blood flow in the brain during episodes of obstructive hypopnea (slow and shallow breathing associated with snoring). This may also increase the risk of stroke. Such declines in blood flow did not appear to occur with obstructive or central apnea, however.

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

• High blood pressure, which is associated with sleep apnea, is a major cause of later heart failure.
• Sleep apnea may directly contribute to the progression of heart failure by reducing oxygen levels and causing abnormal changes in blood pressure and heart rate that add to the burden of the failing heart.
• In any case, obstructive sleep apnea can affect breathing functions in a way that may be particularly harmful for patients with existing congestive heart failure. A 1999 study, in fact, indicated that sleep apnea is associated with poorer survival in patients with heart failure. Some evidence suggests that treating sleep apnea with continuous positive airway pressure (CPAP) may improve heart function in these patients.

Atrial Fibrillation. Results from a 2003 study indicated that patients with untreated obstructive sleep apnea may be at increased risk for recurrence of atrial fibrillation (a disturbance of the heart's rhythm.) 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 induce 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.

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.
• Diabetes.
• Kidney failure.
• Peripheral nerve damage (e.g., tingling, pain, or numbness in the hands and feet).
• Liver damage in obese individuals with sleep apnea.
• Seizures, epilepsy, and other nerve disorders. Sleep apnea appears to pose a particularly risk for nocturnal epilepsy (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. A condition called intracranial hypertension has been observed as well in some patients with sleep apnea, which may also damage vision.
• Possibly, Alzheimers disease.

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 exacerbate nightmares and post-traumatic stress disorder. In fact, 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. One study investigated the effects of the antidepressant paroxetine (Paxil) on patients with obstructive sleep apnea. The agent improved breathing during late sleep stages but had little effect on other aspects of obstructive sleep 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 even disrupt relationships. Diagnosis and treatment of sleep apnea in the patient can, of course, 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 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. In fact 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 eight. (Even children who snore and do not have sleep apnea may be at higher risk for poor concentration.)