Principles of Polysomnography

A polysomnography is a diagnostic test used to evaluate sleep disorders. It includes a series of multiple examinations, given to sleeping patients, that analyzes various physiological changes associated with sleep. Sleep is a state of rest marked by disengagement from the environment, quiescence, decreased responsiveness and a recumbent posture. There are two kinds of sleep: nonrapid-eye-movement (NREM), which is divided into four stages, and rapid-eye-movement (REM).

Sleep Stages

• Stage 1 of NREM is characterized as a light sleep that you drift in and out of easily. In Stage 2 of NREM, eye-movements stop and brain waves decrease with occurrences of sporadic bursts called sleep spindles. Except for during infancy, humans generally spend 50 percent of their sleeptime in Stage 2. Stage 3 is distinguished by the emergence of delta brain waves, with a steady decline in brain activity. In Stage 4 the brain almost exclusively generates delta waves. Stages 3-4 are considered to be phases of "deep sleep," with Stage 4 being the deepest level. After Stage 4, REM begins. It is distinguished by irregular breathing, rapid jerking movements of the eye and temporary limb paralysis. Dreams occur in REM.

  A foundational principle of polysomnography is the belief that a normal range of changes that occur in the body during each sleep stage can be compared to a patient's reactions during their sleep stages in order to diagnose sleep disorders.

Diagnostic Tools

• Some of the diagnostic tools that are used to create a polysomnography, or sleep study, include an electroencephalogram, electro-oculogram, electromyography, thermistors and pulse oximetry. Polysomnography is conducted overnight in a controlled laboratory environment.

  It is thought that the specificity of each diagnostic tool working together is a cornerstone of effective polysomnographic analysis.

Electroencephalography

• An electroencephalography (EEG) is a devise that records brain activity during sleep stages. It can detect seizures, and thus identify nonsleep-related medical disorders such as encephalitis and Parkinson's diseases. However, the premise for using an EEG for a polysomnography is because it is a neurological testing tool, and abnormal brain wave activity is symptomatic of sleep disorders.

Electro-oculography

• An electro-oculography (EOG) monitors eye movement throughout the sleep stages, and particularly REM. This device is used for polysomnography because it helps determine total sleep time, sleep latency, total arousals during sleep and the time of each stage of sleep. Substantial deviations from the standard ranges of these factors are characteristic of sleep disorders.

Electromyography

• An electromyography (ECM) is a device that evaluates skeletal muscle condition and activity. In polysomnography, it monitors the length and intensity of atonia, which is temporary limb paralysis that normally occurs during REM. An abnormal reading can indicate potential sleep disorders.

Thermistor and Pulse Oximetry

• A thermistor is a device that measures the air flow of a patient's mouth and nose. A pulse oximetry monitors the amount of oxygen in the blood to detect any levels of oxygen starvation. Deviations from a standard range of air flow and oxygen in the blood during sleep are symptomatic of sleep disorders.

Sleep Disorders

• Some of the most common sleep disorders that are diagnosed via polysomnography include sleep apnea, which is an intermittent stoppage of breathing; sleep hypopnea, which is consistent inadequate breathing levels; narcolepsy which is frequent and sudden periods of daytime sleep episodes; and periodic limb movement which is characterized by sporadic, involuntary leg and arm movements every 20-30 seconds.