Editing Polysomnography (section)

==Mechanism==
{{further|Electroencephalography{{!}}EEG|Electrooculography{{!}}EOG|Electromyography{{!}}EMG|Electrocardiography{{!}}ECG (EKG)}}
[[File:Polysomnography connections.jpg|thumb|Connections of polysomnography wires on an adult patient]]
[[File:Polysomnography tester.jpg|thumb|Use of equipment for overnight diagnosis in hospitalization records]]
A polysomnogram will typically record a minimum of 12 channels, requiring a minimum of 22 wire attachments to the patient. These channels vary in every lab and may be adapted to meet the doctor's requests. A minimum of three channels are used for the EEG, one or two measure airflow, one or two are for chin muscle tone, one or more for leg movements, two for eye movements (EOG), one or two for heart rate and rhythm, one for [[oxygen saturation]], and one each for the belts, which measure chest wall movement and upper abdominal wall movement. The movement of the belts is typically measured with [[piezoelectric sensors]] or [[respiratory inductance plethysmography]]. This movement is equated to effort and produces a low-frequency sinusoidal waveform as the patient inhales and exhales.

Wires for each channel of recorded data lead from the patient and converge into a central box, which in turn is connected to a computer system for recording, storing and displaying the data. During sleep, the computer monitor can display multiple channels continuously. In addition, most labs have a small video camera in the room so the technician can observe the patient visually from an adjacent room.

The [[electroencephalogram]] (EEG) will generally use six "exploring" electrodes and two "reference" electrodes, unless a seizure disorder is suspected, in which case more electrodes will be applied to document the appearance of seizure activity. The exploring electrodes are usually attached to the scalp near the frontal, central (top) and occipital (back) portions of the brain via a paste that will conduct electrical signals originating from the neurons of the cortex. These electrodes will provide a readout of the brain activity that can be "scored" into different stages of sleep (N1, N2, and N3 – which combined are referred to as [[NREM sleep]] – and Stage R, which is [[rapid eye movement sleep]], or REM, and wakefulness). The EEG electrodes are placed according to the [[10–20_system_(EEG)|International 10-20 system]].

The [[electrooculogram]] (EOG) uses two electrodes, one that is placed 1&nbsp;cm above the outer [[canthus (anatomy)|canthus]] of the right eye and one that is placed 1&nbsp;cm below the outer canthus of the left eye. These electrodes pick up the activity of the eyes in virtue of the electropotential difference between the cornea and the retina (the cornea is positively charged relative to the retina). This helps to determine when REM sleep occurs, of which rapid eye movements are characteristic, and also essentially aids in determining when sleep occurs.

The [[electromyogram]] (EMG) typically uses four electrodes to measure muscle tension in the body as well as to monitor for an excessive amount of leg movements during sleep (which may be indicative of [[nocturnal myoclonus|periodic limb movement disorder]], PLMD). Two leads are placed on the chin with one above the jawline and one below. This, like the EOG, helps determine when sleep occurs as well as REM sleep. Sleep generally includes relaxation and so a marked decrease in muscle tension occurs. A further decrease in skeletal muscle tension occurs in REM sleep. A person becomes partially paralyzed to make acting out of dreams impossible, although people that do not have this paralysis can develop [[REM behavior disorder]]. Finally, two more leads are placed on the [[tibialis anterior muscle|anterior tibialis]] of each leg to measure leg movements.

Though a typical [[electrocardiogram]] (ECG or EKG) would use ten electrodes, only two or three are used for a polysomnogram. They can either be placed under the collarbone on each side of the chest or one under the collarbone and the other six inches above the waist on either side of the body. These electrodes measure the electrical activity of the heart as it contracts and expands, recording such features as the "P" wave, "QRS" complex, and "T" wave. These can be analyzed for any abnormalities that might be indicative of an underlying heart pathology.

Nasal and oral airflow can be measured using pressure transducers, and/or a thermocouple, fitted in or near the nostrils; the pressure transducer is considered the more sensitive.{{Citation needed|date=December 2008}} This allows the clinician/researcher to measure the rate of respiration and identify interruptions in breathing. Respiratory effort is also measured in concert with nasal/oral airflow by the use of belts. These belts expand and contract upon breathing effort. However, this method of respiration may also produce false negatives. Some patients will open and close their mouth while obstructive apneas occur.  This forces air in and out of the mouth while no air enters the airway and lungs. Thus, the pressure transducer and thermocouple will detect this diminished airflow and the respiratory event may be falsely identified as a hypopnea, or a period of reduced airflow, instead of an obstructive apnea.

Pulse oximetry determines changes in blood oxygen levels that often occur with sleep apnea and other respiratory problems. The pulse oximeter fits over a fingertip or an earlobe.

[[Snoring]] may 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.  Also, snoring indicates airflow and can be used during hypopneas to determine whether the hypopnea may be an obstructive apnea.