sleep

sleep

1. sleeping patterns vary amongst people

   • we spend about a 1/3 of our lives sleeping

2. What happens when someone is sleep deprived?

   • grumpiness
   • grogginess
   • irratability
   • forgetfullness
   • language, memory, planing and sense of time - severely affected

3. How to measure sleep?

   • questionnaire
     • results can be limiting! increased error due to BIAS
   • physiological measurements
     • results are limited by methods used, mostly free from bias and are reproducible
     • Neurochemial
       • normally via blood samples
     • neurophysiological
       • electroencephalography (EEG)
         • involves the recording of a gross average of electrical potentials of the cells and fibres in the brain areas closed to each electrode attached to the scalp
         • an EEG shows the electrical activity of a particular brain region relative to another, usually one region being higher then the other
           • increased activity is displayed as larger amplitude, or bigger peaks, than the baseline recording

4. Stages of sleep

   • stage 1 non-REM sleep: awake and relaxed
     • dominated by irregular, jagged, low voltage waves brain activity is still high but will start to decline
     • stage 2 non-REM sleep
       • contains: -sleep spindles: 12-14Hz bursts for at least 500msec - generated by oscillating interactions between cells in thalamus and the cortex -K-complex: sharp high-amplitude positive wave followed by a smaller slow negative wave - occur randomly and in response to auditory stimuli
       • stage 3 non-REM sleep
         • Delta waves: slow, large amplitude waves neural activity is highly synchronised
         • stage 4 non-REM sleep
           • increased delta wave activity stages 3 and 4 are known as alow-wave-sleep (SWS) sleepwalking, nightmares, bedwetting can occur at this stage of sleep
           • (rapid eye movement) REM sleep
             • irregular, low voltage, fast waves similar to those in stage 1 of non-REM sleep increased brain activity may be associated with a state of dreaming
             • physiological changes
               • postural muscles become more relaxed - deep REM sleep
               • HR, BP, breathing rate are all much more variable than in other stages of sleep
               • increased blood supply to reproductive organs
   • sleep cycle lasts approx 60-90 mins

5. physiological changes during sleep

   • cardiovascular
     • NREM sleep
       • reduction in heart rate, CO, BP
     • REM sleep
       • HR and BP increase, vasoconstriction in skeletal muscle
   • respiratory system
     • NREM sleep
       • slight hypoventilation, PCO2 levels rise, PO2 levels decrease
       • decrease in firing of inspiratory neurons, breathing is under chemical and mechanical control (no active mechanism present)
     • REM sleep
       • higher and variable respiratory rate, lower tidal volume, probably driven by higher cortical control
       • increase of resistance in upper airway due to loss of muscle tone during REM sleep
     • sleep apnea
       • lack of breathing during sleep for at least 10 seconds -older patients or infants -in adults associated with daytime sleepiness and snoring -sudden infant death syndromme (SIDS) -most death occur in the morning when SIDS babies have increased REM sleep -increased incidence odSIDS in younger mothers, low birthweight, paternal cocaine use -placing babies on backs when sleeping reducesSIDS
   • renal system
     • decreased urine production, increased conc
     • decrease in GFR and renal plasma flow
     • secretion of aldosterone and ADH increase
   • GI
     • decreased motility
     • decreased gastric acid secretion
     • swallowing reflex slows down
   • nervous system
     • overall reduced discharge rate and metabolism during NREM sleep
     • the increase/decrease in neuronal activity is very much dependent on the brain region

6. Insomnia

   • the inability to sleep
   • chronic insomnia
     • lasting for weeks, months or years
   • transient insomnia
     • short lived, lasting for only a few nights or weeks, usually resulting from a stressful event
   • 1st line: non drug treatments
     • change in the environment
       • bed, light etc
     • change in lifestyle
       • exercise, establish a routine
     • avoiding stimulants eg caffeine
   • drug treatments
     • benzodiazepines
       • act allosterically to increase affinity of GABA for its receptors -increase chloride conductance
       • decrease the time taken to get to sleep and increase the duration of sleep
       • reduce REM sleep
       • next day residual effects: headache, nausea, 'hangover syndrome', psychomotor impairment
     • sedative antihistamines
     • z-drugs
       • zaleplon
         • t1/2 = 1 hour for patients who have difficulty falling asleep. severe case
       • zolpidem
         • t1/2 = 2.5 hours for short term treatment in patients where insomnia is debilitating or is causing severe distress treatment <4 weeks
       • zopiclone
         • t1/2 = 3.5-6.5hours for patients suffering from severe sleep disruption doses should be as low as possible and treatment should not last longer then 4 weeks