How is stage N3 scored in sleep stage scoring?

Updated: Aug 19, 2019
  • Author: Andres A Gonzalez, MD, MMM, FACNS; Chief Editor: Selim R Benbadis, MD  more...
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Stage N3 sleep is scored when there is slow wave activity in at least 20% of the epoch, irrespective of age. If slow waves represent less than 20% of the epoch it will be scored under the rules for a different stage.

Stage N3. There is slow wave activity in greater t Stage N3. There is slow wave activity in greater than 20% of the epoch.

Stage N3 is the combination of R and K Stage II and IV, and often referred to as slow wave sleep. It is characterized by waves with a frequency of 0.5 to 2 Hz that have amplitudes of 75 microvolts peak to peak. These waves are usually best detected over the frontal leads, which were added in the 2007 AASM recommendations, and helps explain the increase in N3 sleep seen in AASM Manual versus R and K scored studies.

Although not required for scoring, sleep spindles may persist in stage N3 sleep. Also, K complexes may also be present but would be considered as slow waves if they meet the above definition of slow wave activity.

Eye movements are unusual in this stage and are typically not seen. EMG tone is variable but tends to be low, even approaching levels as low as Stage R.

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