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Sleep Heart Health Study

6.6.2.4 Rules for assigning sleep stages when arousal is present in the epoch

The following rules were established to maximize the amount of sleep identified and thus the number of respiratory events recorded (*):

Brief arousals (e.g. arousals < 15s. long) do not automatically require a change in sleep stage. The epoch is staged according to the sleep stage in the remaining parts of the epoch (not including the arousal).

If an arousal or an area of increased EMG causing artifact in the EEG channels is followed by Stage wake (W), then the arousal is considered part of the record scored as a stage Wake. If this part is > 15 s. long, then epoch is scored as a Stage Wake.

In Deep Sleep (unequivocal Stage 3/4), when fast frequency waves are visualized as “riding” on the top of the delta waves, and there are no frequencies characteristic of Stage Wake (*):

  • If there is any reason to suspect that the fast frequencies are result of artifact (like a sudden increase in EMG bleeding into EEG), an arousal is not scored.
  • When the fast frequencies are not the result of artifact, an arousal is scored. Deep Sleep is scored when delta waves persist despite the faster frequencies riding on top, independent of the length of the arousal.

Note for Delta Sleep: When an arousal includes bursts of Delta waves: these waves are not used for meeting Deep Sleep criteria (e.g. Deep Sleep is scored only if there is > 20 % of the epoch covered by delta waves outside of the arousal).


National Sleep Research Resource
Sleep Heart Health Study