Modern life has been hard on sleep. Millions of people resort to sleep aids, either over the counter or by prescription, in an effort to pass the night without insomnia or disrupted sleep. But as common as it is for us to complain when we didn't get a good night's sleep, there's a very common disruption that tends to get overlooked: OSA, or obstructive sleep apnea. The name is becoming more common, unfortunately, because OSA has joined type 2 diabetes as a condition largely stemming from the national epidemic of obesity.
Many people think that sleep apnea is snoring, but although it's frequently associated with snoring (commonly a wife will bring her husband to the doctor with complaints about being kept awake), apnea is a different condition. OSA occurs when a person's pharynx or windpipe, the upper airway in the throat, collapses during sleep and breathing stops for at least 10 seconds; a single stoppage may last up to a minute. This may happen frequently, even hundreds of times a night. The person may be totally unaware; sometimes someone else in bed notices that breathing has stopped and becomes alarmed. Sleep apnea can cause more than drowsiness the next day -- it's associated with cardiovascular disease, cognitive problems, mood disorders and more.
Although it tends to slip by undiagnosed, OSA is very common. Estimates are that in Western countries roughly 1 out of every 5 adults has at least mild OSA, while 1 in every 15 has at least moderate OSA. Numerically, this amounts to about 18 million Americans who are thought to have the disorder.
Your greatest risk factor is being overweight. Because OSA is strongly linked with obesity, rates are climbing. It's thought that as many as 40 percent of obese people have sleep apnea, and about 70 percent of people with OSA are obese. There are very few studies on the prevalence of OSA in obese children, but they seem to have four to five times the risk of sleep apnea as non-obese children.
All sleep disorders would be easier to understand if sleep itself were understood. Yet nobody knows for sure why we need to sleep at all. The prominent sleep scientist William Dement conducted his research for 50 years and concluded, in effect, that the reason people need to sleep is that they grow sleepy. We do know, however, a good deal about the damage done by sleep deprivation. Animals that are completely deprived of sleep lose immune function and die in a matter of weeks. Losing as little as one night's sleep causes us to become drowsy and unable to concentrate the next day. Physical performance, including hand-eye coordination and reaction time, becomes impaired, along with judgment, memory and ability to do math. Continued lack of sleep leads to mood swings and hallucinations. It has also been found that there are long-term deficits to "getting by" on less than 8 to 9 hours of sleep a night. Despite the fact that you may think you've adapted to shorter sleep, your body knows the difference.
How does air flow get blocked?
The pharynx is located behind the tongue and soft palate. This upper portion of the airway from the lungs has little support from bones or cartilage and mostly relies on muscles to keep it open. Normally, the muscles surrounding the airway remain constricted enough to keep the airway taut. But in sleep apnea the throat relaxes, allowing the windpipe to collapse. In adults, OSA frequently occurs due to the buildup of fat or the general loss of muscle tone that accompanies aging. In children OSA is often caused by enlarged tonsils and adenoids.
When breathing is cut off in a sleep apnea episode, the blood vessels constrict and the level of blood oxygen falls. The low oxygen level signals the brain to wake up just enough to cause the throat muscles to tighten, which stiffens and opens up the windpipe, allowing air to rush in. Snoring may occur as the person inhales, but the snoring itself is not dangerous: It's a sign that air is getting in. Other audible signs are snorting or gasping. This cycle of the throat relaxing and tightening may be repeated many times a night.
OSA can develop in people of any age, gender or weight, but the main risk factors for the disorder are:
Other risk factors include:
Testing and diagnosis
If you suspect you have OSA because someone has noticed loud snoring, gasping or pauses in your breathing at night or because you have daytime symptoms (like drowsiness, headache and fatigue), then see your doctor. If it seems likely you have OSA, he or she may suggest you have diagnostic polysomnography. Your breathing, heart rate, brain activity, blood pressure and other functions will be monitored overnight while you sleep. You may be diagnosed as having mild, moderate or severe sleep apnea.
OSA and obesity
The close association with obesity is due to a number of factors. When someone is obese, fat cells infiltrate neck and throat tissues so that they lose tone and are more likely to collapse. The neck and chin become enlarged and press on the throat when the person is lying down. Excess fat compresses the chest and makes it difficult to inhale deeply. Finally, too much visceral fat (internal abdominal fat) pushes up on the diaphragm, the sheet of muscular tissue between the abdomen and the chest. This, too, prevents deep inhalation.
It appears that not only can obesity cause OSA, OSA can also lead to or worsen obesity. Sleep apnea causes imbalances in the levels of two hormones that are associated with feelings of hunger and satiety: leptin and ghrelin. Leptin produces feelings of satiety, and ghrelin has the reverse function: It's an appetite stimulant. Disrupted sleep causes levels of ghrelin to rise, levels of leptin to decrease.
But OSA can occur in people who aren't overweight, too. For them, the disorder may be due to chronic nasal congestion or having very large tonsils, an oversized uvula or a small, receding jaw. Untreated OSA can have deadly consequences. The afflicted have three times the risk of dying from any cause compared with people who don't have the disorder. One of the more likely causes of death is cardiovascular disease.
Why are cardiovascular disease and OSA linked?
High blood pressure is very likely a culprit. Some 50-60% of people with OSA have hypertension, and about 30 percent of those with hypertension are estimated to have OSA, often undiagnosed. Hypertension in someone with OSA may be due to activation of the sympathetic nervous system, which responds to the "threat" of low oxygen levels. Normal blood oxygen saturation values are 97-99 percent, but people with OSA may have oxygen saturation levels of 60 percent or even lower. The sympathetic nervous system reacts to these low levels (and possibly to other factors, such as disrupted levels of the hormone leptin) by severely constricting blood vessels and increasing heart rate. Surges in blood pressure as high as 250/110 mm Hg can occur as blood is forced into severely constricted blood vessels during an episode of sleep apnea.
Worse still, this sympathetic activation continues during the day, continuing to constrict blood vessels and increase heart rate. Hypertension, in turn, can lead to hardening of the arteries, or atherosclerosis, and all the problems that can come from it: heart attack and stroke, pulmonary vascular disease, congestive heart failure and heart arrhythmias.
Other problems can stem from OSA, such as
Sleep apnea damages the brain
MRI studies of people with sleep apnea have found that the concentration of the brain's gray matter -- the cerebral cortex of the brain, where most information processing takes place -- is actually reduced in people with sleep apnea. Affected were areas involved in memory, concentration, cardiovascular activity, breathing and executive functioning.
Raised glucose levels
OSA can raise insulin and glucose (blood sugar) levels and impair the body's ability to process glucose. People with moderate-to-severe sleep apnea may have twice the risk of developing insulin resistance, leading to diabetes.
Treating sleep apnea
Sometimes lifestyle modifications can be all that is necessary to cure sleep apnea:
Continuous positive air pressure (CPAP) is the most common treatment for sleep apnea, and it's usually very effective for moderate-to-severe sleep apnea. CPAP machines blow air out into the nose and possibly the mouth as well, depending on the interface. The gentle pressure of the air pushes your throat open so that it can't collapse while you sleep, thus preventing sleep apnea.
Tips for a good night's sleep
The amount of air flow delivered by the CPAP machine is individualized. To determine the best adjustment, it's necessary to sleep overnight in the sleep lab wearing the CPAP mask while the sleep technician monitors your sleep.
Oral appliances, or dental devices, are generally less effective than CPAP, but some people find them easier to use. They are usually plastic devices that are designed to prevent soft tissues from collapsing and pressing on the airway. There are many different kinds, and it's necessary to go to a dentist to have one custom-fitted for individual needs.
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