Polysomnography, how sleep tests work



There polysomnography it is a non-invasive test that is used to monitor the various stages of sleep when something is not working in our rest.

“It can be done at a sleep center and under the NHS: first of all in what we specialists call a sleep laboratory, with a short hospitalization, or in a hospital ward (usually in neurology), but also at home with a special device portable, ”he explains Luigi Ferini Strambione of the pioneers in this field.

“The difference between the examination performed in the laboratory and that in a hospital bed in the ward is that in the first case (more intimate and with few rooms) the patient’s behavior is also videotaped, as well as monitoring it with devices that evaluate many parameters “.

Qfour types of tailored tests to assess sleep

We therefore have 4 possibilities to choose from for each patient: either the polysomnogram plus video footage to be carried out in the sleep laboratory, or the portable polysomnogram to be used also on the move both in the ward (if the recording is to be made for several nights) and at home, or the polysomnography aimed at assessing respiration (in his own bed).

Finally, the actigraphic monitoring: the actigraph is a kind of clock that records wakefulness and sleep for several days (always at home).

But doesn’t sleeping in a hospital alter the results? “This is why we usually do the night of adaptation: the first is spent to get the patient accustomed to the new situation, and the second to record sleep,” explains the neurologist.

What is measured by the sleep test

Under the supervision of sleep doctors and technicians, anyone who spends the night in the ward is subjected to recording of various parameters (this is why we speak of “polysomnogram”), from respiratory to cardiovascular ones, but also those inherent to brain activity, through the electroencephalogram.

«The patient must not take any drugs, except those he usually uses for his possible pathologies, which should not be suspended precisely in order not to alter the results of the test. To do a polysomnography therefore sleep is not induced, what happens in natural conditions is monitored», Specifies the expert.

A very thorough electro-encephalogram is then done with electrodes that are positioned in strategic areas of the head (so as not to cause discomfort during rest, and increase in number depending on what the doctor wants to evaluate in the individual case).

“We also record the movements of the arms and legs, to evaluate motor activity. We therefore not only verify how the subject sleeps, but we must also identify all possible causes of sleep fragmentation»Explains the professor.

The main indication for prescribing this test is to study not only insomnia, but also to evaluate the particular activities that a person can do while sleeping. For example the sleepwalkingbut also of any Seizures.

And if there are certain “Troubled dreams”that is, those cases in which the patient seems to experience the dream during the REM phase (that of Rapid Eye Movements, characterized by involuntary eye movements): these dreams are generally very agitated because the subject must “defend himself” from someone who tries to attack him .

“This ailment can be indicator of neurological pathologies which manifest themselves after years, and mainly affects men after fifty. In these cases, instead of having the normal muscular “paralysis” typical of REM sleep, the person is particularly agitated and “lives” the dream », explains Ferini Strambi.

When you can do the sleep test at home

For other sleep disorders such as restless legs syndrome, the test can be done in the laboratory or even at home.

«Situations are tested in which the patient says he no longer sleeps well and a portable recorder. We have to see what happens during the day too? Do you need to do it for several days? Then polysomnography in these cases resembles the Holter, that device that measures cardiac parameters for a few days and during our normal activities. “If we have to evaluate only the presence of apneas, generally there is no need to put the electrodes on the head because we only monitor cardiac and respiratory activity”.


People with recurring headaches keep a diary of the attacks. The allergic person signs rhinitis, sneezing and strange reactions to foods. Even those with recurring fever today have dedicated apps. What about sleep? They range from the specific functions provided by many mobile phones that monitor the rest to hi-tech watches.

“Of course, they do not replace the classic tests, but they can sometimes provide important information both for a suspected diagnosis and for the continuation of patient checks after specific tests, also to see the effects of a therapy”, comments Professor Luigi Ferini Strambi.

«Through these devices you can obtain a history of the patient’s rest. The various technologies available today are generally of good quality and therefore also useful as additional information for the specialist: a bit like home blood pressure measurement with various automatic cuffs, which is then intended for evaluation by the general practitioner or cardiologist ” .

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