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Physiology of sleep

Normal Sleep is divided into two main stages:

NREM: (non-rapid eye movement)

  • There are four sub-stages of NREM: Stage 1 – Stage 4
  • Characterized as:
    • No eye movement
    • Slow EEG rhythms
    • High muscle tone

REM (rapid eye movement)

  • Characterized as:
    • Persistent eye movement
    • Aroused EEG rhythms
    • Muscular atony (except eye, ear and respiration)
    • Irregular breathing
    • Dreams

The sleep cycle

  • Cycles generally become shorter as the night goes on
  • 90 -110 mins x 4-5 times each night
The sleep cycle

The sleep cycle

Hypnogram of sleep cycles

Hypnogram. REM sleep periods are indicated in bold. The First Rem sleep cycle is usually short. REM cycles typically become longer, as the night progresses, but the overall sleep cycle shortens

 

Sleep Stage 1- NREM Stage 2- NREM Stage 3- NREM Stage 4 – NREM REM
% spent of total night 5% 45% 12% 13% 25%
Stage Dozing stage Consolidated sleep Deep Sleep, Slow wave sleep

 

Deep sleep Lightest stage of sleep
EEG waves Disappearance of Alpha wave (8-12 cycles) but appearance of Theta waves (3-7 cycles) Has K complexes and sleep spindles

(12-14 cycles per second)

Appearance of Delta wave

(<2 cycles per second)

Continuation of Delta wave Saw tooth wave

 

Neurotransmitters of sleep:

  • Serotonin: It initiates sleep & increases during sleep
  • Acetylcholine: Increased during sleep and increases REM sleep, reduces in NREM
  • Norepinephrine: Reduced during sleep and particularly in REM sleep
  • Dopamine: reduced during sleep but increases during arousal/ waking up
Sleep disorders summary chart

Sleep disorders summary chart

Narcolepsy

Definition: Excessive day time sleepiness & REM abnormalities (intrusion of REM into NREM and waking state) occurs for >3months. REM sleep occurs in less 10 minutes of falling asleep and patients feel well-rested on waking. Symptoms include:

  1. Cataplexy – sudden loss of tone whilst patient is awake, can be due to loud noise or intense emotion
  2. Hallucinations:
    1. Hypnagogic Hallucinations occur when falling asleep
    2. Hypnopompic hallucinations occur when as patient is waking
  3. Sleep paralysis occurs when patient is awake but unable to move
  4. Has ‘sleep attacks’ & falls sleep easily at night

Management

  • Sleep hygiene & lifestyle modifications
  • Stimulants (e.g. Modafinil) – to stimulate awakeness during the day – caution– can precipitate psychosis in those with a history of the disorder
  • Forced sleep during the day
  • Antidepressants (SSRIs in particular) – can supress REM sleep

Sleep Apnoea

Sleep apnoea when patient periodically stops breathing during sleep, typically for periods of seconds. Features include:

  1. Often a loud snorer, with audible pauses in breathing – may be detected by partner
  2. Morning headaches
  3. Sleepiness/ tiredness during the day
  4. May develop arrythmias, sudden death, hypoxemia and pulmonary hypertension
  5. Associated with obesity
  6. More common in men

There are 3 type of sleep apnoea:

  • Central (lack of respiratory effort)
  • Obstructive (muscle atony at oropharynx, nasal or tonsil obstructions)
  • Mixed type

Treatment: Advise weight loss, CPAP, Surgery may be indicated in some cases with altered pharyngeal or laryngeal anatomy (e.g. very large tonsils)

Insomnia

Definition: Difficulty in initiating or maintaining sleep. Often the result of general life stressors, but sometimes associated with a true underlying psychiatric disorder.

3 main patterns:

  1. Sleep-onset delay (trouble falling asleep)
  2. Early morning arousal (trouble staying asleep)
  3. Sleep fragmentation (repeated awakenings)

Symptoms: Yawning and tiredness during the day, patient complains of reduced daily functioning

Management

  • Sleep hygiene
  • Psychology referral if patient is amenable to this

Parasomnias

Definition:  Also known as abnormal behaviour of sleep, undesirable movements or behaviours that occur during sleep

Night Terrors

  • Also known as sleep terror disorder
  • Occurs during stages 3 & 4 of NREM sleep (delta waves on EEG)
    • In contrast to nightmares which occur in REM sleep
  • Patients may exhibit signs of being awake, including talking, screaming, signs of anxiety and signs of autonomic hyperarousal (pupillary dilatation, sweating, tachycardia). Typically patients sit upright in bed abruptly, following by loud screaming, flailing of limbs and sometimes walking
  • Patients often appear scared or inconsolable
  • Can last from a few minutes up to 30-40 minutes
  • Patients have no memory of the episodes
  • Most commonly occur in children and are typically benign
  • In adults, are more likely to be a sign of an underlying psychiatric disorder, such as PTSD or anxiety
  • Treatment is often not required but can be given benzodiazepines to supress stage 3 and 4 of NREM.

Somnambulism (Sleepwalking)

  • Sleepwalking also occurs during NREM stage 3 & 4.
  • Repeated episodes of walking in sleep and last about 10 minutes
  • Occurs without full consciousness – often sleepwalkers have no memory of the episodes
  • More common in children and usually benign. Treatment not usually required
  • Treatments: Can be given drugs to suppress stage 3 & 4 (e.g. benzodiazepines)

Nightmares

  • Bad dreams, occur during REM sleep
  • Patient has memory of events upon awakening.
  • Treatment: if recurrent and disturbing for the patient can use REM suppressants-such as SSRI

REM behaviour Disorder (RBD)

  • Occurs during REM breakdown
  • Patient acts out part of dreams.
  • Acute RBD found in drug withdrawal or intoxication states is generally a reversible condition

Chronic RBD requires ongoing pharmacotherapy, and is commonly associated with degenerative neurological diseases such as Parkinson’s disease, Lewy Body Dementia.

References

  • Nightmares and nightmare disorder - UpToDate
  • Murtagh’s General Practice. 6th Ed. (2015) John Murtagh, Jill Rosenblatt
  • Oxford Handbook of General Practice. 3rd Ed. (2010) Simon, C., Everitt, H., van Drop, F.
  • Beers, MH., Porter RS., Jones, TV., Kaplan JL., Berkwits, M. The Merck Manual of Diagnosis and Therapy

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