A sleep study is an overnight test that monitors your sleep, breathing, heart rate, oxygen levels and movements to help diagnose sleep disorders. If you are experiencing symptoms of disrupted sleep and your doctor or respiratory consultant suspects you might have a sleep disorder, you may be referred for a sleep study, also called polysomnography.
This is an overnight diagnostic test that can be used to diagnose a range of sleep disorders including sleep apnoea (a condition that causes repeated interruptions to your normal breathing during sleep), as well as long-lasting insomnia, REM sleep disorder and restless legs syndrome.
Sometimes people feel a bit anxious about taking part in a sleep study, but it’s nothing to worry about and the results can help to determine what kind of treatment could help.
Why do I need to take part in a sleep study?
A sleep study is used to diagnose sleep disorders, as well as to create and manage the treatment plan for an existing condition. Polysomnography records your brain waves, breathing, heart rate and oxygen levels in your blood while you sleep, as well as your eye, leg and arm movements. The test is normally done at night at a specialist sleep disorders unit in a hospital or a sleep centre. While it is most often performed at night, it can sometimes be done during the daytime for shift workers.
When you fall asleep you enter a period of non-rapid eye movement (NREM) sleep. During this stage, your brain waves slow down. These are recorded with a test called an electroencephalogram or EEG. Following NREM sleep, brain activity increases and you enter rapid eye movement (REM) sleep. During REM sleep your eyes move quickly back and forth. This is when you are most likely to dream. Cycles of NREM and REM sleep typically last around 90 minutes and you go through multiple sleep cycles a night.
Preparing for a sleep study
You will receive detailed instructions on how to prepare for the sleep study. You should avoid alcohol or caffeine in the afternoon and evening before the test as these can interfere with your sleep patterns and may affect the results. Avoid taking a nap during the afternoon and do not apply lotions, gels or colognes to your skin as these can interfere with the electrodes.
If you are having the polysomnography at a sleep centre, you will arrive in the evening and stay overnight. You’ll be able to sleep in your own nightclothes and can bring items with you from home. You’ll have your own en-suite room, which will be dark and quiet. Rooms are equipped with a low-light video camera so the polysomnography technologist can see what is happening while you sleep. There is an audio system so they can hear you from outside the room.
What happens during a sleep study?
You will follow your normal bedtime schedule. Sensors will be placed on your scalp, temples, chest and legs. These will be connected by wires to a computer. They will monitor your brain waves, heart rate, eye movements, breathing patterns, snoring, limb movements and body position. A clip will be placed on your finger or ear. This will monitor levels of oxygen in your blood. The technologists will monitor you throughout the night and you can talk to them via the monitoring equipment if you need to.
During the sleep study, the team may invite you to try a positive airway pressure (PAP) machine for sleep apnoea. This piece of equipment delivers a gentle steam of air via a face mask into your nose and mouth to help you breathe. There are two different types – continuous positive airway pressure (CPAP) which provides a constant stream of air and bilevel positive airway pressure (BPAP) which delivers more pressure when you breathe in and less when you breathe out.
After the study, the sensors are removed and you will be able to go home. You’ll be given a follow-up appointment to discuss your results.
What will the sleep study show?
The sleep study will reveal a wide range of information about your sleep patterns, including:
- Eye movements and brain waves which can help identify whether disruptions occur during particular stages of sleep
- Changes in heart and breathing rates or levels of oxygen in the blood, which could indicate sleep apnoea
- Movements or behaviours during sleep, which can be signs of REM sleep behaviour disorder
- Frequent leg movements which can be a sign of restless leg syndrome
For more information about diagnosing and treating sleep apnoea, or if you are experiencing symptoms of a sleep-related breathing disorder, contact us.
Frequently Asked Questions
During an overnight sleep study, sensors monitor information such as your brain waves, breathing, heart rate, blood oxygen levels, eye movements and limb movements while you sleep. This information can help your clinician identify abnormal sleep patterns and investigate possible sleep disorders.
You do not normally need to sleep for the entire night for a sleep study to provide useful information. Many people find that they sleep differently from normal because they are in an unfamiliar environment and wearing monitoring equipment.
An overnight sleep study normally takes place over one night. You will usually arrive at the sleep centre in the evening, be connected to the monitoring equipment and sleep overnight before the sensors are removed in the morning.
The information recorded during your sleep study will be analysed and reviewed by your clinical team. You will normally have a follow-up appointment to discuss the results, whether a sleep disorder has been identified and any treatment or further investigation that may be recommended.
Some sleep studies can be carried out at home, particularly when investigating conditions such as sleep apnoea. Home testing can monitor measurements such as breathing, heart rate and blood oxygen levels. A hospital or sleep-centre study can record a broader range of information, including brain activity, eye movements and limb movements.
Yes. Sleep studies can be used to investigate and diagnose sleep apnoea by monitoring breathing and blood oxygen levels during sleep, alongside other measurements depending on the type of study.
