Table 1.

Adult sleep staging and arousal scoring

	EEG characteristics	Relevance to OSA	Normal amounts
Wake	Low voltage, mixed frequency when eyes are open or alert; α activity (8–13 Hz) while relaxed with eyes closed	Typically increased in OSA	15–20% of time in bed
N1	Predominantly low amplitude and relatively fast θ activity (3–7 Hz) accompanied by slow rolling-type eye movements	Typically increased in OSA	4–6%, more in older patients
N2	Sleep spindles (12–14 Hz bursts lasting >0·5 s) and K complexes (large negative EEG wave followed immediately by a slower positive wave) on a background of low voltage, mixed frequency EEG	Typically increased in OSA	50–65%, more in older patients
N3	Slow (<2 Hz), high amplitude (> 75 μV) EEG waves for more than half the epoch	Often absent or reduced in OSA, but associated with improved severity or complete absence of OSA when present	15–20%, less in older patients
REM	Low voltage, mixed frequency EEG with periodic runs of sawtooth waves accompanied by irregular movements of both eyes and low muscle tone	Often absent or reduced in OSA; often accompanied by worsening of respiratory events and more pronounced desaturation than the non-REM stages	15–20%
Arousals	3–15 s return of waking or faster activity in the EEG; concurrent increase in EMG must be recorded in REM sleep	Commonly occur at the end of respiratory events, but also occur spontaneously or as a result of other stimuli (eg, leg movements)	20 per h of sleep

According to AASM scoring manual. REM=rapid eye movement. OSA=obstructive sleep apnoea. EEG=electroencephalogram. EMG=XXXX