Sleep studies

Polysomnography (PSG) observed by a technician in the sleep laboratory is the reference method for the diagnosis of patients with suspicion for sleep apnea-hypopnea syndrome (SAHS) and other nonrespiratory sleep disorders

• used to diagnose, or rule out, many types of sleep disorders including SAHS, narcolepsy, and parasomnias
• often ordered for patients with complaints of daytime fatigue or sleepiness that may be caused by interrupted sleep. Although it is not directly useful in diagnosing circadian rhythm sleep disorders, it may be used to rule out other sleep disorders

Polysomnography is a multi-parametric test that is used to study/record in detail all the biophysiological changes that occur in the human body when the person is asleep

• the PSG or polysomnogram, as the test is referred to, measures or monitors many body functions including the eye movements (EOG), brain (EEG), heart rhythm (ECG), skeletal muscle activation (EMG), and breathing or respiratory effort during sleep, and based on the observations, a decision can be made whether the patient PSG suffers from SAHS
• PSG usually is performed at night except in certain special cases when the tests are done over two days time
• procedure
  • no fixed rule that specifies the number of channels that should be fixed to the patient, for a typical polysomnogram, it is twelve
    • twelve is the minimum number of channels required for efficiently carrying out the test. If to observe more attributes, like the snoring volume or airflow using a transducer, a higher number channels may be required
    • polysomnogram will typically record a minimum of twelve channels requiring a minimum of 22 wire attachments to the patient
    • of the twelve channels
      • three are for EEG - to determine if the person is indeed sleeping and in what stage of sleep he/she is at a given time
      • to measure air flow - one channel
      • to sense chin and leg movements - one channel each
      • to measure REM - two channels
      • ECG - one channel
      • oxygen saturation - one channel
      • chest and abdominal wall movements - one channel
    • a live video of the sleeping patient is also recorded so that the supervising technician could observe the patient from an adjacent room
      • same clips may also be used by the doctor for further diagnosis of the patient
    • after the test is done, a scorer - usually a different person than the technician - analyzes the collected data by reviewing the study in "epochs" of 30 seconds each, looking for:
      • sleep latency, the moment the patient slept since the lights were switched off (NB it is the EEG that says whether the patient was awake or was sleeping)
      • sleep efficiency, which is the minutes of total sleep divided by the minutes spent on bed
        • in normal cases, it falls between 85%-90%
      • sleep stages, which are based on the data coming from the six channels, EOG (2), EEG (usually 3channels), and chin EMG
        • depending on the collected information, each 30 second "epoch" is classified as either "awake" or any one of the five sleep stages - 1,2,3,4, and REM. The sleep stages 1 and 2 are further classified as "light sleep" while 3 and 4 as "deep sleep"

Notes:

• sleep pattern differs with age
  • for example, for older people the duration of the REM stage will be lesser in comparison with younger people. REM generally occupies 25%-35% of the total sleep time while the most observed sleep stage across all ages is stage 2 (except in infancy)
  • consumption of drugs (anti-depressants) and alcohol could also affect the duration of sleep stages
• the PSG also allows analysis of:
  • breathing irregularities like apnoea or hypopnoea, if there is any
    • apnoea is the complete cessation of breathing for at least 10 seconds in sleep
    • hypopnoear refers to partial cessation, again lasting for at least 10 seconds
    • apnea/ hypopnea index (API) is calculated from these observations
      • for normal persons, it must be below 5
  • "arousals" indicated by a sudden shift in the brain wave activity
    • a higher than normal number of "arousals" could be indicative of disturbed sleep or other symptoms like fatigue and/or sleeplessness
  • cardiac rhythm abnormalities, body position during sleep, leg movement patterns, and oxygen saturation

Reference:

• 1) Kushida CA, Littner MR, Morgenthaler T, Alessi CA, Bailey D, Coleman J, et al. Practice parameters for the indications for polysomnography and related procedures: an update for 2005. Sleep. 2005;28:499-521.