Polysomnogram: What Is It, And How Does It Work?
Let's continue talking about obstructive sleep apnea (OSA). We already discussed some of the symptoms and signs, as well as the significance of untreated OSA and the related diseases such as stroke, heart attack, and diabetes.
Today we will focus on the polysomnogram (PSG), the test used to diagnose OSA, as well as most other sleep disorders. Again, if we break down the words it won't seem so mysterious- poly means many, somno means relating to sleep, and gram means recording- in simple terms it is just a recording of different things during sleep.
The parameters that are recorded during PSG by attaching wires to different parts of the body include:
- brain waves or electroencephalography (EEG) - this allows the sleep specialist to know when a person is awake or asleep, and to determine if they have arousals, or brief awakenings during their sleep
- eye movements or electrooculography (EOG) - this tells us when the subject is in rapid eye movement sleep better known as REM sleep
- limb movements or electromyography (EMG)- which tells us when the patient moves, and are especially important to diagnose other sleep disorders (besides OSA) and are also useful to help identify decreased muscle tone (or lack of it) during REM sleep
The channels (or leads) that are most useful to identify breathing-related sleep disorders, OSA being the most common, include:
- respiratory effort monitors, which consist of bands around the chest and abdomen to see if the patient is using increased effort to breathe
- monitors for airflow through the mouth and/or nose
- sound recording for the intensity of snoring
- heart rate
- percentage of oxygen in the blood or pulse oximeter
- video monitoring to determine if there are any unusual movement disorders during sleep, called parasomnias (see blog on REM behavior disorder)
The PSG is usually performed at night, when the typical person sleeps, and requires the patient to sleep in a sleep lab. If the patient's normal sleep is different, such as in shift workers, the test can be done during the day. Obviously, it can be somewhat challenging to sleep in a strange place, particularly with all these wires attached to you, but the basic idea when diagnosing sleep problems is to have the patient try to sleep in an environment which is as close to normal as possible and during their normal sleep period.
In obstructive sleep apnea we typically see loud snoring, increased respiratory effort in the chest and abdomen, without air flowing into the nose or mouth on the airflow monitors. This can then lead to a drop in the oxygen percentage in the blood, often an increased and/or decreased heart rate, and frequently causes arousals which are noted on the EEG. This combination of signs is how obstructive sleep apnea is diagnosed in the sleep laboratory.
In my next blog we will cover the "newer" diagnostic technology that is becoming better and may soon be more widely available. Stay tuned, see you online