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Nocturnal polysomnography (NPSG)

Your doctor would like you to have a Nocturnal Polysomnography investigation (NPSG)

What is a nocturnal polysomnography (NPSG)?

The NPSG is an overnight sleep study. It measures your sleep cycles and stages by recording brain waves (EEG), electrical activity of muscles (EMG), eye movement (EOG), breathing rate, blood oxygen saturation, and heart rhythm (ECG). A Clinical Physiologist will perform the test and staff in training may be present during your investigation. This will be explained at the time of your appointment and consent for this will be discussed with you

What should I do before the test?

  • Please wash your hair and do not use any hair products (gel, hairspray etc)
  • Take your medication as normal unless otherwise directed by your doctor
  • Eat as normal
  • Please bring a list of medication that you take with you
  • Please wear comfortable, baggy clothes

You are welcome to bring a friend or relative to accompany you to your appointment

What will happen during the test?

  • A qualified Clinical Physiologist will explain the test to you and answer any questions you may have
  • They will measure your head with a tape measure, mark some points with a special pencil and then apply several small electrodes to your head with a sticky paste and special glue.
  • You will also have several electrodes placed around your eyes, on your chin and cheek, on your legs and on your finger. Additional electrodes may also be applied depending on what your Consultant has requested.
  • These electrodes will then be attached to a small recorder box which is held in place by using a belt around your waist
  • The set up procedure takes approximately 45-60 minutes and you will then be able to go home. You may wish to bring a loose-fitting hat or scarf to wear.
  • You will be able to move around freely and sleep as normal
  • You will not be able to have a bath or shower, wash or comb your hair once the electrodes have been attached
  • You must keep the belt around your waist at all times even when you are in bed
  • You will be asked to press a special button when you go to sleep and then again when you wake up. This does not stop or start the recording, but helps us keep track of the amount of sleep you had.
  • You must not drink any products that contain caffeine once you have been set up
  • You will need to change the batteries in the recorder box at midday on the Thursday. If you do not feel comfortable doing this then you may return to the department on the Thursday morning and the Clinical Physiologist will do this for you (please discuss this on the day of set-up).

How long will the test take?

The set up procedure on the first afternoon takes approximately 45-60 minutes and you will then be able to go home. The NPSG test will be a 1-2 night study and you will return to the department later that week.

What will happen after the test?

  • If you are not having any further tests then your electrodes will be removed following the investigation
  • The small electrodes will be taken off with warm water or a solution to dissolve the special glue
  • You will then be able to go home or back to work and carry on as usual
  • There are no after effects from this test
  • You will not be told any results on the day of the tests The results will go back to your Consultant for the test within two to three weeks.

If your Consultant has requested a Multiple Sleep Latency and Multiple Wakefulness test (MSLT/MWT) then you will return to the department on the Friday at 08:45am and this test will then last all day until approximately 5-6pm. (Please see the additional patient information leaflet on MSLT).

How will the results of this test assist my consultant?

A NPSG will help your doctor in the diagnosis and management of your complaint or condition.

Are there any risks?

No, there are no reported risks to this test.

Is a NPSG test painful?

No, this is a painless test.

What are the consequences of not having a NPSG?

A NPSG is a well established method of helping doctors to diagnose and treat a wide range of medical conditions. Your doctor would not have as complete a picture as they require and hence your diagnosis may take longer and/or your treatment may not be the most appropriate.

Are there any alternative ways of getting the same information that a NPSG provides?

There is no alternative test performed at The Walton Centre. If for any reason you are unable to make this appointment or have any specific requirements or questions (before or after the test) please ring 0151 556 3416.

Patient co-operation is required for the duration of the test; if due to a learning disability you feel more time is needed, please contact the department. In addition
we can also provide a visit to the department in advance of the appointment for patients who may require it to familiarize yourself with the surroundings and staff.

Further information about NPSG is available is available from numerous organisations including;
1. The Brain Charity: 0151 298 2999 or visit or if you live locally call into their library at Neurosupport, Norton Street. Liverpool. L3 8LR.
2. The British Sleep Society: visit

  • Last Updated:
    03 October 2022
  • Review Date:
    03 October 2026
  • Author:
    : Caroline Finnegan/Sue Kirkham/Neurophysiology Department
  • Summary:

    Your doctor would like you to have a nocturnal polysomnography investigation (NPSG).

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