How are stage III and IV sleep defined on normal sleep EEG?

Updated: May 15, 2018
  • Author: Selim R Benbadis, MD; Chief Editor: Helmi L Lutsep, MD  more...
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Answer

Answer

Stages III and IV sleep are usually grouped together as "slow wave sleep" or "delta sleep." Slow wave sleep (SWS) is usually 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 the images below.

Slow wave sleep with predominantly delta activity, Slow wave sleep with predominantly delta activity, especially in the first half.
Slow wave sleep with predominantly delta activity. Slow wave sleep with predominantly delta activity.

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. [4] 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.


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