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Polysomnography (PSG) is used to evaluate abnormalities of sleep and/or wakefulness and other physiologic disorders that have an impact on or are related to sleep and/or wakefulness.

A polysomnogram consists of a simultaneous recording of multiple physiologic parameters related to sleep and wakefulness. The interaction of various organ systems during sleep and wakefulness also is evaluated.

  • By international standards, a polysomnogram must have a minimum of 4 neurophysiologic channels.One electroencephalography (EEG) channel (central with an ear reference provides the best amplitude) to monitor sleep stage
  • Two electrooculogram (EOG) channels to monitor both horizontal and vertical eye movements (electrodes are placed at the right and left outer canthi, 1 above and 1 below the horizontal eye axis)
  • One electromyography (EMG) channel (usually chin or mentalis and/or submentalis) to record atonia of rapid eye movement (REM) sleep

Other parameters often monitored include the following :

  • Additional EEG channels, particularly in patients with sleep-related epilepsy
  • Additional EMG channels, particularly anterior tibialis, to detect periodic limb movements of sleep
  • Airflow
  • Electrocardiogram
  • Pulse oximetry
  • Respiratory effort
  • Sound recordings to measure snoring

Optional parameters include the following :

  • Continuous video monitoring of body positions
  • Core body temperature
  • Incident light intensity
  • Penile tumescence
  • Pressure and pH at various esophageal levels

The different stages of sleep

Normal sleep is divided into non-rapid eye movement (NREM) and rapid eye movement (REM) sleep. The stages of sleep are stage I (light sleep), stage II, stages III and IV (deep or delta-wave sleep), and stage V, REM sleep; NREM sleep comprises stages I-IV. Sleep is an active process that cycles at an ultradian rhythm of about 90 minutes.

Waking usually transitions into NREM sleep. REM follows NREM sleep and occurs 4-5 times during a normal 8- to 9-hour sleep period

In adults, sleep of 8-8.4 hours is considered fully restorative. In some cultures, total sleep often is divided into an overnight sleep period of 6-7 hours and a midafternoon nap of 1-2 hours.

  • Stage I is considered a transition between wake and sleep. It occurs upon falling asleep and during brief arousal periods within sleep and usually accounts for 5-10% of total sleep time.
  • Stage II occurs throughout the sleep period and represents 40-50% of total sleep time.
  • Stages III and IV delta sleep occur mostly in the first third of the night. They are distinguished from each other only by the percentage of delta activity and represent up to 20% of total sleep time.
  • Stage V or REM represents 20-25% of total sleep time. Stage V or REM is characterized by muscle atonia, cortical activation, low-voltage desynchronization of the EEG, and rapid eye movements. REM may be considered to have both tonic and phasic characteristics. Other phasic features of REM sleep include periodic skeletal muscle twitches, increased heart rate variability, pupil dilation, and increased respiratory rate

During Stage V or REM sleep, blood flow increases in the thalamus and the primary visual, motor, and sensory cortices, while remaining comparatively decreased in the prefrontal and parietal associational regions. The increase in blood flow to the primary cortical regions may explain the vivid nature of REM dreaming, while the continued decrease in blood flow to the prefrontal cortex may explain the unquestioning acceptance of even the most bizarre dream content.

Normal sleep diagram

Sleep cycles

Sleep rhythms progressively take place owing to sleep/awake shift from foetal period till the age of 20.

A good night's sleep depends on the proper balance of these components.

Biologics rythms

In industrialized countries, 20% of active people are extended hours employees or shiftworking employees These working people contradict their own biologic rhythms and are opposite to their surrounding rhythms. Most of the time it induces family and social difficulties

Sleep apneas

Sleep obstructive apnea have a direct impact on sleep quality. These night breathing stops, followed by micro-wake-up lead to a fragmentation of sleep. Each new breathing effort fragment sleep rhythms, and disorganise the sleep stages. More than 60 Micro-wake-up can occur each hours. NREM sleep appears rarely with an increasing slow and light sleep, and a decrease of slow deep sleep. At the same time, REM sleep is shorten.

Perturbated sleep diagram

Read more : Snoring and sleep apnea