Editing Polysomnography (section)

==Interpretation==
[[File:Sleep Stage N3.png|thumb|200px|right|[[Electrophysiology|Electrophysiological]] recordings of stage 3 sleep]]
After the test is completed, a "scorer" analyzes the data by reviewing the study in 30-second "epochs".<ref>Rechtschaffen, A. & Kales, A. (Eds.) (1968). ''A manual of standardized terminology, techniques, and scoring system for sleep stages of human subjects''. Washington D.C.: Public Health Service, U.S. Government Printing Service</ref>

The score consists of the following information:{{citation needed|date=February 2022}}
* 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 "waking" 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 (usually 4 channels), 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|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, stages 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 medication], alcohol taken before bedtime, 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%<ref>{{Cite web|url=https://www.fda.gov/media/112603/download|archive-url=https://web.archive.org/web/20191214190528/https://www.fda.gov/media/112603/download|url-status=dead|archive-date=December 14, 2019|title=Current Definitions for Sleep Disordered Breathing in Adults|website=FDA}}</ref> oxygen desaturation; [[hypopnea]] is a 30% or greater decrease in airflow for at least 10 seconds followed by an arousal and/or 4% oxygen desaturation.<ref>Berry, Richard et al. (2012). ''A The AASM Manual for the scoring of Sleep and Associated Events: Rules Terminology and Technical Specifications, Version 2.0''. Darien, IL: American Academy of Sleep Medicine</ref> (The national insurance program [[Medicare (United States)|Medicare]] in the US 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.

Once scored, the test recording and the scoring data are sent to the sleep medicine physician for interpretation. Ideally, interpretation is done in conjunction with the medical history, a complete list of drugs the patient is taking, and any other relevant information that might impact the study such as napping done before the test.

After interpreting the data, the sleep physician writes a report that is sent to the referring provider, usually with specific recommendations based on the test results.