Polysomnography (Sleep Study)

Polysomnography means recording many body signals during sleep at the same time. In a full laboratory study, small electrodes on the scalp and face record brain waves, eye movements and chin muscle activity, which show whether you are awake and which stage of sleep you are in, including dreaming sleep. A soft tube under the nose and a small heat sensor measure airflow, belts around the chest and abdomen show breathing effort, and a clip on a finger measures oxygen levels. Sensors on the legs record movements, a small microphone records snoring and stickers on the chest follow the heart rhythm. A video camera and a position sensor show your sleeping position and any unusual behaviour. A trained technologist follows the recording through the night from a nearby room. A home sleep apnea test is a simpler version that records breathing, airflow, oxygen and pulse, but not brain waves, so it cannot measure sleep itself.

A sleep study is recommended when symptoms suggest a sleep disorder that needs confirming. The most common reason is suspected obstructive sleep apnea: loud snoring, breathing pauses noticed by a partner, waking up choking or gasping, morning headaches and daytime sleepiness, especially together with high blood pressure, a thick neck or excess weight. It is also used to look for central sleep apnea, in which the brain briefly stops sending the signal to breathe, for example in heart failure. A full laboratory study is preferred for suspected narcolepsy, often followed by a daytime nap test, for violent or unusual movements during sleep, for frequent limb movements and when a home test was negative despite strong symptoms. People with significant heart or lung disease or with nerve and muscle conditions are usually studied in the laboratory rather than at home. A study may also be repeated to check how well a treatment is working.

You usually arrive at the sleep centre in the early evening. A technologist explains the process and spends about 30 to 60 minutes attaching the sensors, which does not hurt and still lets you turn over in bed. The room is private and quiet, much like a hotel room, and you go to bed close to your usual time. The recording runs through the night while the technologist watches from another room and can help if a sensor slips or you need the bathroom. In a split-night study, if clear sleep apnea is seen in the first part of the night, the technologist fits a CPAP mask, which delivers gently pressurised air to keep the airway open, and adjusts the pressure for the rest of the night. This adjustment is called CPAP titration and can also be done on a separate night. In the morning the sensors are removed, and you can shower and leave.

Almost anyone can have a sleep study, including children, older adults and people with other health conditions; children are usually studied in a dedicated pediatric sleep service with a parent staying overnight. On the day of the study, avoid caffeine from the early afternoon, alcohol and daytime naps, as these change your sleep. Wash your hair and avoid oils or gels so the scalp sensors stick well, and remove nail varnish from at least one finger for the oxygen clip. Take your usual medicines unless told otherwise and bring a list of them, since sleeping tablets and some antidepressants can affect the results. Bring comfortable night clothes and anything that helps you sleep at home. Many sleep services ask you to complete a sleepiness questionnaire and a sleep diary beforehand. For international patients, earlier test results and a short medical summary can usually be reviewed remotely, so the right type of study is booked before travel.

There is no physical recovery after a sleep study. You may feel tired if you slept less than usual, so arrange for someone else to drive if you feel sleepy. The whole night's recording is then scored in detail by a trained technologist and interpreted by a sleep specialist, which usually takes a few days. Many international patients plan a short visit: a consultation, the study night and a results appointment a few days later, at which treatment is discussed. If sleep apnea is confirmed and CPAP is recommended, the mask can often be fitted and the pressure set during a titration night before you leave, and many machines let the clinic follow your use remotely. If you later travel with a CPAP machine, most airlines allow it on board as a medical device, but ask in advance. Arrange follow-up with a sleep or chest specialist near home for long-term care and mask adjustments.

Polysomnography is a safe, non-invasive test. The main drawbacks are mild skin irritation from the adhesive or paste and a night of poorer sleep in an unfamiliar room, although most people still sleep enough for a reliable result. The key breathing result is the apnea-hypopnea index, or AHI: the average number of times per hour of sleep that breathing stops, called an apnea, or becomes very shallow with a fall in oxygen, called a hypopnea. In adults, fewer than 5 events an hour is generally considered normal, about 5 to 15 mild, about 15 to 30 moderate and more than 30 severe; children are judged by lower thresholds. The report also describes oxygen levels, sleep stages, sleep quality, snoring, limb movements and heart rhythm. A home test can underestimate sleep apnea because it does not measure actual sleep time, so a negative home test with strong symptoms is often followed by a laboratory study.