What is measured in polysomnography (PSG)?
Although there are some differences in the ways different labs perform PSG, the main parameters measured are
(i) Eye movements during sleep by electro-oculography (EOG)
(ii) Brain rhythms by electro-encephalography (EEG)
(iii) Heart rhythms by electrocardiography (EKG)
(iv) Movement of body muscles by electromyography (EMG), usually limb muscles.
Electroencephalography (EEG) involves placing electrodes at two different places on the scalp and measuring the voltage difference between them.
The measurements are sometimes called “brainwaves” which is somewhat contrived, but refers to the look of the patterns on the EEG printout.
In addition, oxygen levels in blood are recorded continuously by an oxygen monitor (pulse oximeter), and often, audio/video recordings are made for analysis of sleep quality, snoring and movements. Moreover, air flow through the nose is also measured by special flow meters. The data is analyzed by computers and various types of disorders during sleep, including obstructive sleep apnea, can be measured.
Do I to stay overnight for a PSG?
Yes, you do in most instances. The complexity of the test means that you have to sleep in a laboratory. Only basic sleep pulse oximetry is possible at home, which is often not capable of making the diagnosis or a full assessment of the severity of various sleep-related disorders, including obstructive sleep apnea. In-home PSG is debatable, with regards to its accuracy, and is not available or recommended in most settings. (There are home monitoring devices, but they are not considered good enough for medical diagnosis.)
Who interprets the results?
The results can be interpreted in most cases by sleep laboratory technicians, who are experts in interpreting sleep study results. However, in many cases the opinion of doctors with training in sleep medicine is required as well – particularly the more complex ones. In some hospitals however all results are interpreted by physicians.
Why might someone get a polysomnography?
The main reason for getting a PSG done would be to confirm a diagnosis of obstructive sleep apnea (OSA) which is suspected on the basis of a history or preliminary tests like pulse oximetry. In many cases it is also used to assess the severity of the condition, and diagnose associated health problems that arise during sleep alone. PSG is also used for a large group of other medical, neurological and psychiatric sleep related disorders like narcolepsy, sleep rhythm disorders etc.
Doctors do not usually send patients for polysomnography just because of insomnia, unless the insomnia is accompanied by another disorder. If insomnia is severe and does not respond to initial treatment regimens, PSG may be used to gather additional information.
Is it uncomfortable?
Some patients find sleeping with wires and monitors attached to them mildly uncomfortable. However, since there is no use of needles, or any other invasive testing, the procedure is totally painless. There is also no restriction on your movement on the couch too. Therefore nearly everyone manages to complete the test - the commonest complaint being difficulty to fall asleep in new surroundings. Sedation is practically never required except in children.
Do hospitals provide polysomnography or only special sleep clinics?
Both do so. Increasingly, hospitals are providing polysomnography as the science of sleep medicine is getting more and more popular among medical doctors and researchers. Sleep clinics are also part of many hospitals, apart from those on their own.
The hypnogram is a diagram showing the course of the stages over the night. More here.
More about polysomnography
PSGs are often done to confirm a diagnosis of obstructive sleep apnea (OSA) which is suspected on the basis of a history or preliminary tests. PSG is also used in diagnosis of medical, neurological and psychiatric sleep-related disorders like narcolepsy, bruxism, restless legs syndrome, periodic limb movement disorder, and REM sleep behavior disorder.