Most people with obstructive sleep apnea tend to be obese and snore loudly. The disorder has been medically linked to hypertension, which in turn puts people at greater risk of heart failure and stroke. Weight reduction in persons who are overweight is an important factor in effective treatment. Alcoholic drinks near bedtime and sleeping pills should be avoided. Sometimes obstructive sleep apnea can be treated by surgically correcting the narrowing of the airway. Another option is continuous positive airway pressure, which involves wearing a mask over the nose and mouth during sleep; this treatment keeps the airway open by forcing air into the nasal passages. A different type of sleep apnea, called central sleep apnea, is believed to be caused by an abnormality in the brain's regulation of breathing during sleep.
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In humans, sleep occurs in cyclical patterns; in each cycle of 11/2 to 2 hr, the sleeper moves through four stages of sleep, from Stage 1 to Stage 4, and back again to Stage 1. In the first stage, low-frequency, low-amplitude theta waves characterize brain activity. The stage usually lasts only several minutes, before the individual drifts into Stage 2 sleep, and the brain moves into low-frequency, high-amplitude waves. Stage 3 signals an increase of low-frequency, high-amplitude delta waves, and at Stage 4 sleep these delta waves account for more than half of all brain wave activity (see electroencephalography). Rapid-eye-movement (REM) sleep occurs during Stage 1 sleep at the end of each cycle, and people woken up at this time usually report that they have been dreaming. Dream deprivation or sleep deprivation results in detrimental changes in personality, perceptual processes, and intellectual functioning. There is some evidence that emotional and environmental deprivation disrupts the sleep patterns of young children, which in turn inhibits the secretion of growth hormone, normally secreted maximally during sleep.
The amount of sleep needed depends on both the individual and the environment: For instance, worrying, critical individuals tend to need both more sleep and more dream sleep than easygoing ones, and stress and worry during the day result in an increase in REM sleep. It has been hypothesized that while deeper stages of sleep are physically restorative, REM sleep is psychically restorative. REM sleep is also believed to integrate new information in the brain and to reactivate the sleeping brain without waking the sleeper. There is evidence that the hypothalamus and thalamus of the brain initiate sleep and that part of the midbrain acts as an arousal system. See also dream; insomnia; narcolepsy; sleep apnea.
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Natural periodic suspension of consciousness during which the powers of the body are restored. Humans normally sleep at night, whereas nocturnal species sleep during the day. The average human sleep requirement is about 7.5 hours. Sleep is divided into two main types, REM (rapid-eye-movement) and NREM (non-REM); each recurs cyclically several times during a normal period of sleep. REM sleep is characterized by increased neuronal activity of the forebrain and midbrain, by depressed muscle tone, and by dreaming (see dream), rapid eye movements, and vascular congestion of the sex organs. NREM sleep is divided into four stages, the last of which is the deep, restorative, quiet sleep commonly associated with “a good night's rest.” Seealso insomnia, narcolepsy.
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