polysomnography (PSG)

Introduction

Comprehensive recording of the biophysiological changes that occur during sleep. It is usually performed at night, when when most people sleep. It is the gold standard for diagnosis of obstructive sleep apnea.

Indications

• excessive daytime sleepiness
• unexplained pulmonary hypertension
• unexplained polycythemia
• disturbances in respiratory control in patients with daytime hypercapnia
• violent sleep-related behaviors or parasomnias
• suspected periodic limb movement disorder
• suspected cataplexy
• assessment of optimal CPAP therapy
• assessment of response to therapy
• post-operative hypoxia, especially with risk factors for obstructive sleep apnea
• suspected obstructive sleep apnea OSA*
• used to diagnose
  • narcolepsy, cataplexy
  • restless legs syndrome
  • REM behavior disorder
  • parasomnias
  • sleep apnea

* OSA may be suspected on the basis of snoring, hypertension, obesity, low SaO2 on room air; MKSAP19 differs on indications for polysomnography (see OSA)

Methods

done in sleep lab

Components of polysomnography

• electroencephalogram (EEG) to measure brain activity
  • generally consist of 4 exploring electrodes & 2 reference electrodes (seizure disorder requires more electrodes)
  • exploring electrodes are usually attached to the scalp near the central & occipitial portions of the brain
  • readout of brain activity scored into different stages of sleep (1, 2, 3, 4, REM, & wakefulness)
• electrooculogram (EOG) to measure eye movements
  • 2 electrodes
  • one is placed superior & lateral to the outer canthus of the right eye
  • one is placed inferior & lateral to the outer canthus of the left eye
  • placement of electrodes picks up electropotential difference between the cornea & the retina (cornea is positively charged relative to the retina)
  • detects rapid eye movements
• electromyogram (EMG) to assess muscle activity (actigraphy)
  • 4 electrodes
  • 2 leads placed on chin, 1 above jaw line, 1 below
  • 2 leads placed on anterior tibialis of each leg
  • measures muscle tension
  • monitor excessive leg movements during sleep (see periodic Limb Movement Disorder)
• electrocardiogram (ECG) to measure heart rhythm
  • 2 or 3 leads
  • either placed under clavicle on either side, or
  • 1 under clavicle, the other 6 inches above the waist on either side
• pulse oximetry to measure arterial blood oxygenation
• nasal & oral airflow
  • measured using pressure transducers &/or a thermocouple
  • measures rate of respiration
  • respiratory effort measured by use of belts that expand & contract
• thoracoabdominal bands
• snoring sensor
• body position

Notes

• in many cases, polysomnography is replaced by actigraphy
• limited channel sleep study (which may be done at home) may be non-inferior for diagnosis of obstructive sleep apnea

More general terms

• sleep test