Polysomnography (PSG) or Baseline sleep study is used to diagnose, or rule out, many types of sleep disorders including narcolepsy, hypersomnia, periodic limb movement disorder (PLMD), REM behavior disorder, parasomnias, and sleep apnea. It is often ordered for patients with complaints of daytime fatigue or sleepiness that may be caused by interrupted sleep. Although it is not directly useful in diagnosing circadian rhythm sleep disorders, it may be used to rule out other sleep disorders It is a comprehensive recording of the biophysiological changes that occur during sleep. It is usually performed at night, when most people sleep, though some labs can accommodate shift workers and people with circadian rhythm sleep disorders and do the test at other times of day. The PSG monitors many body functions including brain (EEG), eye movements (EOG), muscle activity or skeletal muscle activation (EMG) and heart rhythm (ECG) during sleep. After the identification of the sleep disorder sleep apnea in the 1970s, the breathing functions respiratory airflow and respiratory effort indicators were added along with peripheral pulse oximetry.
Sticky patches with sensors called electrodes are placed on your scalp, face, chest, limbs, and a finger. While you sleep, these sensors record your brain activity, eye movements, heart rate and rhythm, blood pressure, and the amount of oxygen in your blood.
Elastic belts are placed around your chest and belly. They measure chest movements and the strength and duration of inhaled and exhaled breaths.
Wires attached to the sensors transmit the data to a computer in the next room. The wires are very thin and flexible. They are bundled together so they don’t restrict movement, disrupt your sleep, or cause other discomfort.
The image shows the standard setup for a polysomnogram. In figure A, the patient lies in a bed with sensors attached to the body. In figure B, the polysomnogram recording shows the blood oxygen level, breathing event, and rapid eye movement (REM) sleep stage over time.
If you have signs of sleep apnea, you may have a split-night sleep study. During the first half of the night, the technician records your sleep patterns. At the start of the second half of the night, he or she wakes you to fit a CPAP (continuous positive airway pressure) mask over your nose and/or mouth.
A small machine gently blows air through the mask. This creates mild pressure that keeps your airway open while you sleep.
The technician checks how you sleep with the CPAP machine. He or she adjusts the flow of air through the mask to find the setting that’s right for you.
At the end of the PSG, the technician removes the sensors.
After the test is completed a “scorer” analyzes the data by reviewing the study in 30 second “epochs”.
The score consists of the following information:
(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 meds), alcohol taken before bed time, and sleep deprivation.)
