2014B15 Write brief notes on the physiological changes associated with sleep.

 

List:

·         Intro

·         Sleep architecture

·         Sleep EEG signature

·         Sleep neurochemistry

·         Effect on body systems

 

Intro: sleep

Definition

·   Necessary natural state of rousable unconsciousness associated with rest and restoration of brain functions

·   Has a specific electrical and chemical signature distinct from anaesthesia

Effect of deprivation

·   CNS: cognitive impairment, affect dysregulation, oxidative stress in hippocampus and subcortex

·   Other: impaired endocrine, metabolic, immune function

 

Sleep architecture:

Cycle

·   NREM (non-rapid eye movement) 1 through 4 followed by REM

·   NREM3-4: for refreshment (a.k.a. slow-wave sleep)

·   REM: for vivid dreaming

Adult

·   Total 7-8 hours

·   Cycle duration 1.5 hours

·   15% REM (more if tired)

Neonate

·   Total 18 hours

·   12 cycles per day and night

·   50% REM

Elderly

·   Reduced total duration

·   Reduced %REM, especially >70 years

 

Sleep EEG signature:

Wave types

·   β: 13-30Hz – low amplitude

·   α (8-13Hz)

·   Θ (4-8Hz)

·   δ (<4Hz) – high amplitude

Drowsy

·   α

NREM 1

·   α and Θ

NREM 2

·   Θ

·   Sleep spindle (brief, high frequency low amplitude burst)

·   K complex (low frequency, high amplitude pattern)

NREM 3

·   Θ

·   δ 20-50%

NREM 4

·   Θ

·   δ >50%

REM

·   β

·   Similar to awake EEG, i.e. paradoxical

·   Pontogeniculoccipital spikes

 

Sleep neurochemistry:

Neuro-transmitters

 

 

Awake

NREM

REM

Aminergic

+++

+

+

Cholinergic

+++

+

+++

Awake/NREM
 flip-flop

(derived from Miller ‘s Anaesthesia)

NREM/REM
 flip-flop

(derived from Miller’s Anaesthesia)

 

Physiological effects of sleep:

 

NREM

REM

CNS

·   ↓Neuronal discharge

·   ↓CMRO2 25-45%

·   ↓SNS, ↑PSNS output

·   Dreams are non-vivid, not recalled

·   ↑Neuronal discharge

·   ↑CMRO2 20%, ↑CBF up to 2x

·   ↑SNS, ↓PSNS output

·   Dreams are vivid +/- recalled

Resp

·   ↓VT 15%, ↔RR = ↓MV

·   ↓response to ↓PaO2, ↑PaCO2

·   PaCO2 40->45mmHg

·   Brief centrally mediated apnoeas

·   ↓↔Pharyngeal dilator tone

·   ↓↓VT 25%, ↑RR and irregular = ↑MV

·   ↓↓response to ↓PaO2, ↑PaCO2

·   Atonia of non-diaphragm resp muscles

·   ↓↓Pharyngeal dilator tone
(highest risk OSA)

CVS

·   ↓HR, SV, CO, SVR, mAP

·   ↑HR and irreg, SV, CO, SVR, mAP

MSK

·   ↓Tone

·   ↓↓Tone

·   REM

·   Bruxism

Endocrine

·   ↑Melatonin at onset

·   ↓ACTH, cortisol

·   ↑GH, ADH, PRL

·   ↑ACTH, cortisol

Metabolic

·   ↓MR 10%

·   ↓T 0.5°C, lowest 3am

·   ↓Shivering threshold

·   ↑MR

 

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