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( Polysomnogram)
Polysomnogram (PSG) is a multi-channel ("poly") recording ("gram") during sleep ("somno"), resulting from a sleep test, polysomnography. A doctor may order a polysomnogram because the patient has a complaint such as daytime fatigue or sleepiness that may be from interrupted sleep. Typically, doctors order a polysomnogram to diagnose or rule out obstructive sleep apnea. Although the PSG can be done during the day or night, the vast majority of sleep studies are done at night, when most people sleep. Shift workers and people with circadian rhythm sleep disorders can be accommodated in some labs by having the test at other times of day. For the standard test the patient comes to a sleep lab in the early evening, and over the next 1-2 hours is introduced to the setting and "wired up" so that multiple channels of data can be recorded when he/she falls asleep. The sleep lab may be in a hospital, a free-standing medical office, or in a hotel. A sleep technician should always be in attendance and is responsible for attaching the electrodes to the patient and monitoring the patient during the study. A polysomnogram usually records Thus, the typical polysomnogram has a minimum of 11 channels. (Note that this is different from the actual number of wires attached to the patient. For technical reasons, 2 wire attachments are actually required per individual recording channel in most cases.) The number of recorded channels can be more than 11 in certain situations. Some labs will measure air flow with both a thermistor and a pressure transducer (the latter considered more sensitive), so that the patient has 2 small probes in the nostrils, not one. Sometimes snoring will be recorded with a sound probe over the neck, though more commonly the sleep technician will just note snoring as "mild", "moderate" or "loud" or give a numerical estimate on "a scale of 1 to 10". Research labs and labs conducting special tests on selected patients (e.g., when nocturnal seizures are suspected) may also record additional data.
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