Sleep Disorder – Baseline Sleep Study

Polysomnography (PSG) or Baseline sleep study is used to diagnose, or rule out, many types of sleep disorders including narcolepsy, hypersomnia, periodic limb movement disorder (PLMD), REM behavior disorder, parasomnias, and sleep apnea. It is 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 It is a comprehensive recording of the biophysiological changes that occur during sleep. It is usually performed at night, when most people sleep, though some labs can accommodate shift workers and people with circadian rhythm sleep disorders and do the test at other times of day. The PSG monitors many body functions including brain (EEG), eye movements (EOG), muscle activity or skeletal muscle activation (EMG) and heart rhythm (ECG) during sleep. After the identification of the sleep disorder sleep apnea in the 1970s, the breathing functions respiratory airflow and respiratory effort indicators were added along with peripheral pulse oximetry.

Before The Test

  • Remain on all routine medication, unless otherwise instructed by the physician. Bring any medications that you may need while in the lab
  • NO NOT take any naps the day of your study.
  • No caffeine after 1pm. Please try to avoid all chocolate and limit your intake of caffeine to 1-2 cups of coffee, tea, or soda on the day of the procedure.
  • Shower and wash your hair prior to arriving for the study. DO NOT use hair spray, oils, gels, or lotions on your hair or on your body.
  • Bring sleepwear such as a two piece pajama set with sleeves or gym shorts and t-shirt.
  • Showers are available in the morning after the sleep study is complete. Bring your own toiletries, hair dryers, etc. Towels and washcloths are available upon request.
  • You should eat dinner before arriving a the sleep lab, but you may bring your own snack.
  • Patients requiring nursing level of care, or unable to get into or out of bed without assistance must have someone stay with them all night.
  • If you are currently using CPAP or BiPAP, bring the unit with you to the center.
  • Please be prepared to leave the lab by 6 am.

During The Test

Sticky patches with sensors called electrodes are placed on your scalp, face, chest, limbs, and a finger. While you sleep, these sensors record your brain activity, eye movements, heart rate and rhythm, blood pressure, and the amount of oxygen in your blood.

Elastic belts are placed around your chest and belly. They measure chest movements and the strength and duration of inhaled and exhaled breaths.

Wires attached to the sensors transmit the data to a computer in the next room. The wires are very thin and flexible. They are bundled together so they don’t restrict movement, disrupt your sleep, or cause other discomfort.

The image shows the standard setup for a polysomnogram. In figure A, the patient lies in a bed with sensors attached to the body. In figure B, the polysomnogram recording shows the blood oxygen level, breathing event, and rapid eye movement (REM) sleep stage over time.

If you have signs of sleep apnea, you may have a split-night sleep study. During the first half of the night, the technician records your sleep patterns. At the start of the second half of the night, he or she wakes you to fit a CPAP (continuous positive airway pressure) mask over your nose and/or mouth.

A small machine gently blows air through the mask. This creates mild pressure that keeps your airway open while you sleep.

The technician checks how you sleep with the CPAP machine. He or she adjusts the flow of air through the mask to find the setting that’s right for you.

At the end of the PSG, the technician removes the sensors.

After the test is completed a “scorer” analyzes the data by reviewing the study in 30 second “epochs”.

The score consists of the following information:

  • – Onset of sleep from time the lights were turned off; this is called “sleep onset latency” and normally is less than 20 minutes. (Note that determining “sleep” and “awake” is based solely on the EEG. Patients sometimes feel they were awake when the EEG shows they were sleeping. This may be because of sleep state misperception, drug effects on brain waves, or individual differences in brain waves.)
  • – Sleep efficiency: the number of minutes of sleep divided by the number of minutes in bed. Normal is approximately 85 to 90% or higher.
  • – Sleep stages; these are based on 3 sources of data coming from 7 channels: EEG (4 channels usually), EOG (2) and chin EMG (1). From this information each 30-second epoch is scored as “awake” or one of 4 sleep stages: 1, 2, 3, and REM or Rapid Eye Movement sleep. Stages 1–3 are together called non-REM sleep. Non-REM sleep is distinguished from REM sleep, which is altogether different. Within non-REM sleep, stage 3 is called “slow wave” sleep because of the relatively wide brain waves compared to other stages; another name for stage 3 is “deep sleep”. By contrast, stage 1 and 2 are “light sleep”. The figures show stage 3 sleep and REM sleep; each figure is a 30-second epoch from an overnight PSG.

(The percentage of each sleep stage varies by age, with decreasing amounts of REM and deep sleep in older people. The majority of sleep at all ages (except infancy) is Stage 2. REM normally occupies about 20-25% of sleep time. Many factors besides age can affect both the amount and percentage of each sleep stage, including drugs (particularly anti-depressants and pain meds), alcohol taken before bed time, and sleep deprivation.)


  • – Any breathing irregularities; mainly apneas and hypopneas. Apnea is a complete or near complete cessation of airflow for at least 10 seconds followed by an arousal and/or 3% oxygen desaturation; hypopnea is a 50% decrease in airflow for at least 10 seconds followed by an arousal and/or 3% oxygen desaturation. (Medicare requires a 4% desaturation in order to include the event in the report.)
  • – “Arousals” are sudden shifts in brain wave activity. They may be caused by numerous factors, including breathing abnormalities, leg movements, environmental noises, etc. An abnormal number of arousals indicates “interrupted sleep” and may explain a person’s daytime symptoms of fatigue and/or sleepiness.
  • – Cardiac rhythm abnormalities.
  • – Leg movements.
  • – Body position during sleep.
  • – Oxygen saturation during sleep.