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Polysomnography (PSG) is a multi-parameter type of sleep study [1] and a diagnostic tool in sleep medicine.The test result is called a polysomnogram, also abbreviated PSG.The name is derived from Greek and Latin roots: the Greek πολύς (polus for "many, much", indicating many channels), the Latin somnus ("sleep"), and the Greek γράφειν (graphein, "to write").
The terms obstructive sleep apnea syndrome (OSAS) or obstructive sleep apnea–hypopnea syndrome (OSAHS) may be used to refer to OSA when it is associated with symptoms during the daytime (e.g. excessive daytime sleepiness, decreased cognitive function).
Obstructive sleep apnea or sleep apnea is defined as either cessation of breathing (apnea) for 10 seconds, or a decrease in normal breathing (hypopnea) with an associated desaturation in oxygen and arousal during sleep that lasts at least 10 seconds. In adults, it is typical to have up to 4.9 events per hour.
The most severe of the sleep apneas is obstructive sleep apnea. Apnea is obstructive only when polysomnography reveals a continued inspiratory effort, evidenced by abdominal and thoracic muscle contraction. Sleep apnea is measured by the apnea-hypopnea index (AHI). An AHI is determined with a sleep study.
In the case of OSA, the outcome that determines disease severity and guides the treatment plan is the apnea-hypopnea index (AHI). [15] This measurement is calculated from totaling all pauses in breathing and periods of shallow breathing lasting greater than 10 seconds and dividing the sum by total hours of recorded sleep.
Hypopnea is overly shallow breathing or an abnormally low respiratory rate. Hypopnea is typically defined by a decreased amount of air movement into the lungs and can cause hypoxemia (low levels of oxygen in the blood.) It commonly is due to partial obstruction of the upper airway, but can also have neurological origins in central sleep apnea.
The respiratory disturbance index (RDI)—or respiratory distress Index—is a formula used in reporting polysomnography (sleep study) findings. Like the apnea-hypopnea index (AHI), it reports on respiratory distress events during sleep, but unlike the AHI, it also includes respiratory-effort related arousals (RERAs). [1]
Causes may include heart failure, kidney failure, narcotic poisoning, intracranial pressure, and hypoperfusion of the brain (particularly of the respiratory center). The pathophysiology of Cheyne–Stokes breathing can be summarized as apnea leading to increased CO 2 which causes excessive compensatory hyperventilation, in turn causing decreased CO 2 which causes apnea, restarting the cycle.