Normal Sleep Architecture in Adults

Adults have 2 types of sleep REM and Non-REM. The non-REM sleep is further divided into 4 stages (I,II,III and IV) according to R and K Scoring system (1968). In the modern AASM manual, Stage III and IV are taken together as Slow wave sleep reducing the stages of NREM sleep to 3- N1, N2 & N3.

Depends on the age. For most adults :NREM Stage 1 : 5-10%, NREM Stage 2: 45-55%, NREM Stage 3: 15-25%, REM : 20-25%. REM sleep is around 50% in newborns and gradually decreases with age. NREM Stage 3 also declines with age.

A sequence of NREM stage (s) and a REM stage make a sleep cycle. There are typically 4-5 sleep cycles in a night of sleep.

Sleep onset is the transition from wakefulness to any of the sleep stages(Usually NREM, sometimes REM as in Narcolepsy). Normal Sleep onset latency is the interval between ‘lights off’ and start of any Sleep stage based on an EEG recording. Normal range is 10 – 30 minutes.(Lichstein,2003).

REM sleep latency is the interval between onset of any stage of sleep and onset of first REM sleep stage. Normal REM Sleep latency is <120 minutes. Sleep Onset REM (SOREM) is also abnormal. A short REM latency time may result from narcolepsy, sleep apnea, and depression or withdrawal from tricyclic anti-depressants (TCAs), Monoamine Oxidase Inhibitor (MAOI) medications, amphetamines, barbiturates and alcohol. Long REM latency may happen due to Sleep apnea , periodic limb movement of sleep and use of REM-suppressing medications, including TCAs, MAOIs, amphetamine, barbiturates, and alcohol.

REM sleep increases in duration through each subsequent sleep cycle at night. Inital REM latency is usually 90-120minutes. On an average, latency between subsequent REM stages is decreased.

Lights off/out: The beginning of the study or the time at which the patient first attempts to fall asleep. The lights, television, and other devices that may distract the patient, are turned off. Impedence checks, amplifier calibrations and physiologic calibrations are comleted and artifacts are corrected before lights off/out.

Lights on: the end of the study, orr the point in time when the technician enters the room to wake the patient. Post-test calibration are performed after lights on.

Total recording time(TRT) = Light on time to Lights off time
Total sleep time(TST)= Total recording time(TRT) – WASO – Sleep latency(SL)
where WASO= time in wake stage after sleep onset till lights on time.

Sleep efficiency (SE) is the percentage of total recording time where the patient was a sleep.
SE(%)= (TST/TRT) *100 where, TST is Total sleep time, TRT is Total recording time. The normal value for sleep efficiency is at least 85%.

WASO is the total time in minutes spent awake after the first epoch of sleep.
WASO= TRT-TST-Sleep Latency Normal value for WASO increases with age from 10 minutes in newborn to around 100 minutes at 60years of age.

REM sleep and Slow wave sleep decline from around 25-30% each in young children to 15-20% in elderly. TST also decreases while time spent in N1 stage and WASO increase the most, with decline in sleep efiiciency.

1. Sleep latency is longer in women than men
2. Women <55 years report more sleepiness than men
3. Older women report 20 minutes less sleep than men
4. Women have more SWS and less NREM stage 1 sleep than men
5. Men have more NREM stage 1 and stage 2 sleep than women
6. Normalized delta activity in older women is lower than in older men

Cross ref: J Womens Health
(Larchmt). 2014 Jul 1; 23(7): 553–562.

Progesterone has a sleep promoting effect (GABA A agonist like benzodiazepines and barbiturates)

• Dec.Latency to NREM sleep
• Inc.Latency to REM sleep
• Dec.REM sleep percent

Oestrogen- Primary effects on REM sleep (↑)
Weakens the coupling between body temperature and sleep-wake cycle
Decreased SOL and WASO
Increased TST

Non-REM (NREM) sleep and stage 2 sleep significantly increases while REM sleep significantly decreases in the Luteal Phase (second half), (H.S Driver et al 1996). In menstrual pahse, Stage N3 latency increases.

Very low powered studies show increased total sleep time, decreased sleep efficiency, increased daytime naps, decrease in SWS (NREM stage 3), increased stage 1 and 2 sleep, and decreased REM sleep (during late pregnancy) along with increased WASO in entire pregnancy, which recover after delivery.

The first six months postpartum are associated with a significant increase in wake after sleep onset and a decrease in sleep efficiency compared to the last trimester of pregnancy, mostly ascribed to the baby’s erratic sleep-wake cycle. Sleep begins to normalize after around 3–6 months postpartum corresponding to slight regularization of baby’s sleep wake cycle.

After menopause, total sleep time and sleep efficiency decreases; WASO and sleep latency increases.