What exactly is recorded in a sleep study?
The sleep study is called a polysomnography (PSG). The PSG entails recording an EEG (electroencephalogram), EOG (electrooculogram), EMG (electromyogram), ECG (electrocardiogram), respiratory flow and effort, oximetry, pulse, and body position. This article explains what a sleep technologist looks at in your EEG portion of the PSG.
What EEG characteristics are important for sleep?
The EEG determines the stages of sleep. When reviewing the recorded information the sleep technologist scores the EEG and assigns stages for each 30 second period, known as an epoch.
The stages are defined as follows:
Wake
Seems pretty evident at the start of the study, but we need to see what wake looks like throughout the study. It comprises more than 50% alpha/posterior dominant rhythm of the epoch. Alpha is when the frequency of the waveform is 8-13 Hz.
Stage 1
We see theta waves, 4-7 Hz
Stage 2
We see theta waves with K-complexes and sleep spindles.
Stage 3
We see delta waves, 0.5-3 Hz.
There are more characteristics that we look at in the rest of the recorded signals, but the above defines some of the EEG aspects. Stage 1 through to Stage 3 are defined as NREM sleep (non REM). Each can be marked as N1, N2, N3, respectively.
REM, it’s not just a 90s band
It stands for rapid-eye movement sleep. It’s the stage of sleep where we see rapid eye movements and the EEG is comprised of theta waves, slower alpha, and a defining feature called sawtooth waves (2-6 Hz) and they look serrated like a saw.
The sleep recording is a collection of waves that is looked at and scored in 30 second epochs. The data collected is interpreted by a sleep specialist.
If you think you may have a sleep disorder, or are experiencing any difficulty with getting to sleep, staying asleep, staying awake during the day, or have any other sleep related questions, feel free to contact Clinique Somnomed by clicking the link below.
We provide quick and convenient sleep testing in your home, in and around the greater Montreal area. We test patients every year for sleep disorders both common and rare.