Polysomnograms - a common sleep test

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.

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 oxymetry 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.

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 (PSG)?

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 oxymetry). In many cases it is also used to assess the severity of the condition, and diagnose associated health problems that arise during sleep alone. In addition, PSG is also used for a large group of other medical, neurological and psychiatric sleep related disorders like narcolepsy, sleep rhythm disorders etc.

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.

More about polysomnography

The study takes about 8-10 hours to complete. You may be asked to discontinue all medications before the study. There are no reported problems as a result of the test itself, so it is important to realize that there is no cause for anxiety – however, excessive anxiety may impair your ability to fall asleep, and have an adverse effect on the study quality.

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Hypnogogia

"O Sleep, rest of all things, mildest of the gods, balm of the soul..."

(Iris to Hypnos. Ovid, Metamorphoses)