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Excerpt from EEG Atlas: Normal Sleep EEG - Stages III and IVSynonyms, Key Words, and Related Terms: delta sleep, delta waves, sleep stages, slow wave sleep, SWS, sleep stages, REM sleep, NREM sleep, rapid eye movement, nonrapid eye movement, EEG atlas, normal sleep stage III, normal sleep stage IV, sleep cycles Please click here to view the full topic text: EEG Atlas: Normal Sleep EEG - Stages III and IVLoomis provided the earliest detailed description of various stages of sleep in the mid-1930s, and in the early 1950s Aserinsky and Kleitman identified rapid eye movement (REM) sleep. Sleep generally is divided in two broad types: nonrapid eye movement sleep (NREM) and REM sleep. On the basis of EEG changes, NREM is divided further into 4 stages (stage I, stage II, stage III, stage IV). NREM and REM occur in alternating cycles, each lasting approximately 90-100 minutes, with a total of 4-6 cycles. In general, in the healthy young adult NREM sleep accounts for 75-90% of sleep time (3-5% stage I, 50-60% stage II, and 10-20% stages III and IV). REM sleep accounts for 10-25% of sleep time. Total sleep time in the healthy young adult approximates 7.5-8 hours. In the full-term newborn, sleep cycles last approximately 60 minutes (50% NREM, 50% REM, alternating through a 3-4 h interfeeding period). The newborn sleeps approximately 16-20 hours per day; these numbers decline to a mean of 10 hours during childhood. Stages III and IV usually are grouped together as "slow wave sleep" or "delta sleep." Slow wave sleep (SWS) usually is not seen during routine EEG, which is too brief a recording. However, it is seen during prolonged (>24 h) EEG monitoring. Representative examples of SWS EEGs are shown in Images 1-2. Men aged 20-29 years spend about 21% of their total sleep in SWS, those aged 40-49 years spend about 8% in SWS, and those aged 60-69 spend about 2% in SWS (Williams et al, 1974). Notably, elderly people's sleep comprises only a small amount of deep sleep (virtually no stage IV sleep and scant stage III sleep). Their total sleep time approximates 6.5 hours. SWS is characterized by relative body immobility, although body movement artifacts may be registered on electromyogram (EMG) toward the end of SWS. Patient Education For excellent patient education resources, visit eMedicine's Procedures Center. Also, see eMedicine's patient education articles Sleep: Understanding the Basics and Electroencephalography (EEG). Please click here to view the full topic text: EEG Atlas: Normal Sleep EEG - Stages III and IV |
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