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The sleep-wake cycle varies in relation to the age and gender of the individual. The newborn may sleep as much as 20 hr each day; a child, 8–14 hr, depending on age; adults, 3–12 hr with a mean of 7–8 hr, which may decrease to 6.5 hr in the elderly. Women over 35 tend to sleep more than men. There is great individual variation in the amount and depth of sleep.
Sleep has two states: non–rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. NREM sleep and REM sleep alternate during the night; each cycle requires 90–100 min. NREM sleep makes up approx. 75% of the sleep cycle, and REM sleep approx. 25%, with individual variations.
People deprived of sleep for several days or more become irritable, fatigued, unable to concentrate, and usually disoriented. Performance of mental and physical tasks deteriorates. Some people experience paranoid thoughts and auditory, visual, and tactile illusions or hallucinations. Deprivation of REM sleep may cause anxiety, overeating, and hypersexuality. The effects of sleep deprivation are reversed when the normal sleep-wake cycle is resumed. See: non–rapid eye movement sleep; rapid eye movement sleep
Physiological Changes during Sleep
The following physiological changes occur during sleep: body temperature falls; secretion of urine decreases; heart rate and respiration become slower and more regular during NREM sleep and then more rapid and less regular during REM sleep. During REM sleep, blood flow to the brain is increased; breathing is more irregular; heart rate and blood pressure vary; cerebral blood flow and metabolic rate increase; and penile erections may occur. There is an increased secretion of growth hormone during the first 2 hr of sleep; surges of adrenocorticotropic hormone (ACTH) and cortisol secretion occur in the last half of the sleep period. Luteinizing hormone secretion is increased during sleep in pubescent boys and girls, and prolactin secretion is increased in men and women, esp. immediately after the onset of sleep.
In evaluating sleep, it is important to know that hand waving, arm swinging, laughing, and flatus occur during normal sleep. Snoring may be clinically insignificant but, when accompanied by apnea, can be harmful.