What Happens During a Sleep Study?


In order to diagnose a possible sleep disorder, a doctor may recommend a sleep study, or nocturnal polysomnography, to collect more information. Sleep apnea, insomnia, narcolepsy, and REM sleep behavior disorder are a few examples of conditions that usually require a sleep study for diagnosis.

If you have an upcoming sleep study, understanding how it works and what to expect will prepare you for the experience and make it easier to feel confident about the process.

What Is A Sleep Study?

A sleep study involves the simultaneous collecting of many physiological signals (1) while you sleep. When looked at as a whole, this data offers insight into different aspects of your sleep health.

Data collection occurs via multiple small electrodes attached to wires, which are placed strategically around the head and body. The application is painless, and the study is noninvasive. However, the adhesive backing that holds the electrodes in place may cause some discomfort (2) or pull your hair slightly when they are removed.

Some of the sensors (3) that may be a part of a sleep study include:

  • Electroencephalograph (EEG): This sensor monitors changes in brain wave activity, which helps to determine the stages of sleep.
  • Electromyograph (EMG): An EMG tracks changes in skeletal muscle activity. This can help identify when REM sleep is happening, as well as specific disorders such as periodic limb movement disorder.
  • Electrooculogram (EOG): This sensor detects muscle movement around the eye. This helps corroborate the data collected from the EEG and EMG to pinpoint REM sleep.
  • Electrocardiograph (ECG): An ECG monitors heart rate and rhythm.
  • Oximeter: This device gauges oxygen saturation in the blood, which helps identify disorders such as sleep apnea.
  • Respirometry Device: This is used to measure airflow and help technicians determine if respiratory help is needed.
  • Thoracoabdominal Belt: This device can be used to assess breathing effort.

Sleep studies are conducted in a lab, usually located in a hospital or sleep clinic, that is equipped with private rooms and beds. Patients arrive in the evening and are required to stay overnight for continuous monitoring by a sleep technician.

The idea is to replicate a regular night’s sleep, so you will likely sleep in a regular bed rather than a hospital bed. The room may have a television, and you will be allowed to bring in personal items such as a book, snacks, change of clothing, and toiletries. The study will likely be videotaped to corroborate your physical movements with information from the sensors.

When you are asleep, the technician may wake you up with instructions specific to the study, or to request a change in sleep position. It may be necessary to call the technician before using the bathroom so that they can detach your monitoring system.

What If I Can’t Sleep During A Sleep Study?

You can bring up concerns over the ability to fall asleep during the study with your referring doctor, the sleep specialist, or the technician before the test. It may be possible to use an over-the-counter sleep supplement such as melatonin to help the process of falling asleep. The technicians present for your sleep study are likely well-versed in the apprehensions felt by patients, so talking it through with them may help settle any uneasiness.

Relaxing breathing techniques, meditation tracks, or a book on tape can be helpful to have as a backup, and it's a good idea to avoid caffeine and naps the day you check in for the study.

How Long Does A Sleep Study Last?

Polysomnography sleep tests run overnight and usually end soon after you wake up in the morning. Around seven hours of monitored sleep is a typical expectation. Patients should plan to arrive about two hours before going to sleep, so the technician has time to set up the monitoring systems. Some extra time to have the monitoring systems removed will also be required when the study is finished. You may also be asked to fill out a questionnaire before leaving.

A multiple sleep latency study (4) monitors daytime sleepiness and requires patients to stay through the afternoon to monitor scheduled naps. You can do a polysomnography test and a sleep latency test consecutively or separately. As a result, the length of time needed for each version, or for a combination of studies, will vary.

It may be possible to complete a sleep test as an at-home study. If a doctor suspects you may have sleep apnea, they can arrange for monitoring equipment to be used at home from the comfort of your own bed.

What Can A Sleep Study Diagnose?

Sleep studies can diagnose (5):

  • Breathing disorders such as sleep apnea
  • Seizure disorders
  • Narcolepsy
  • Periodic limb movement disorder
  • Restless legs syndrome
  • Circadian rhythm disorders
  • Parasomnias, including unusual movements and sleep behaviors such as sleepwalking or night terrors

What Happens After A Sleep Study?

After you complete a sleep study, the collected data is reviewed and scored by the sleep technicians and sleep physician. Once your referring doctor receives these results, they will explain what they have learned from the study. From this point, your medical team can make recommendations and write prescriptions to help remedy any problematic findings.

If you have been prescribed a Continuous Positive Airway Pressure (CPAP) machine – a common occurrence after the diagnosis of sleep apnea – a second sleep study may be required to determine the correct airway pressure setting.

While an overnight sleep study may feel strange at the time, it is worth doing. Once a sleep disorder is diagnosed, your doctor can take steps to correct it, leading to better sleep in the future.

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