How Do Sleep Studies Work?

Sleep specialists can use multiple types of testing to monitor how a person sleeps and determine whether a sleep disorder is present. Overnight polysomnography conducted in a hospital or sleep lab is the test experts usually refer to as a “sleep study” and the gold standard for identifying a variety of sleep disorders. However, other types of testing are also available, and in casual conversation, everyday people often use the term "sleep study" to refer to other types of sleep-related tests.

In this article, we explore a variety of types of sleep testing, including polysomnography, home sleep apnea tests (HSAT), multiple sleep latency tests (MSLT), maintenance of wakefulness tests (MWT), actigraphy, oximetry, and sleep diaries. We also discuss who might want to pursue sleep testing and remote therapy for insomnia.

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Types of sleep studies

When a doctor or sleep specialist recommends a sleep study, they are generally referring to polysomnography. There are also other types of sleep tests that can be used to identify the presence of sleep disorders. 

Polysomnography (PSG)

A PSG normally collects data on the following:

• Brain waves: During a PSG, an electroencephalography (EEG) usually measures and records the sleeper's brain waves. To get these recordings, the sleeper must have 10 to 20 or more electrodes affixed to their scalp prior to going to sleep. Each electrode measures electrical activity in the brain. The data collected can help sleep specialists identify when a person is awake or asleep, as well as which sleep stages they enter, along with any abnormalities.
• Muscle activity and movement: Electrodes may also be placed on other parts of a sleeper's body during a PSG to monitor muscle activity and movement. Electrodes placed above, below, or next to the eye are for electrooculogram (EOG), which can identify when a person is experiencing rapid eye movement (REM) sleep. Meanwhile, electrodes placed on the chin, legs, or arms are for electromyogram (EMG). They typically show when muscles are tensed, which can also identify sleep stages. They can also show when a person moves their limbs, which tends to be associated with some sleep disorders, like periodic limb movement disorder (PLMD). A video recording of the sleeper may also be taken to monitor body movement.
• Heart activity and pulse: Often, electrocardiography (EKG or ECG) monitors heart activity throughout a sleep study. This data is usually collected through electrodes placed on the chest. At the same time, a pulse oximeter placed over the tip of a finger also measures the pulse from that location. Changes in heart activity during certain times of sleep may diagnose sleep disorders like sleep apnea.
• Breathing: A sensor called a nasal pressure transducer usually measures airflow through the nose during a PSG. This tool generally involves thin, clear tubing with two small pieces that are inserted into each nostril. A thermal sensor may also be used. This type of sensor can measure temperature to gather data about breathing. Finally, a band secured around the chest may also be used to record breathing. Breathing data can diagnose sleep apnea, which generally involves lapses in breathing during sleep. 
• Snoring: The sensors that measure breathing may also identify episodes of snoring. Additionally, the sleep study may involve recording audio in the room where the testing takes place. Audio recordings can confirm snoring episodes and measure the volume of snoring.
• Blood oxygen: In addition to measuring a person's pulse, the pulse oximeter placed on a fingertip can also measure blood oxygen levels. Blood oxygen levels often fall too low during sleep among people with sleep apnea.

If a person is diagnosed with OSA during the first few hours of their polysomnography, they may have a split-night study, during which a sleep technician may use the latter half of a sleeper's PSG to calibrate a continuous positive airway pressure (CPAP) machine. A CPAP machine is a tool frequently used to treat obstructive sleep apnea by pushing air into the airway so that it stays open during sleep and there aren't as many lapses in breathing.

Home sleep apnea test (HSAT)

A home sleep apnea test (HSAT) is a sleep test that is done overnight in a person's home. A doctor must prescribe an HSAT to a person specifically because they show signs and symptoms of obstructive sleep apnea. An HSAT doesn't usually record as many parameters as polysomnography, so it cannot be used to diagnose other sleep disorders, like narcolepsy or REM sleep behavior disorder. It also isn't meant to screen the general population for OSA. It's normally only used for those suspected of having OSA without further complications.

Generally, an HSAT measures breathing, snoring, pulse, and blood oxygen levels. Unlike a PSG, an HSAT does not usually measure brain waves, muscle activity, or heart activity beyond the pulse taken with a pulse oximeter. That means electrodes are not usually part of an HSAT. 

Sometimes, a tool called actigraphy is used to measure movement as part of an HSAT with a wristwatch-like device, but not always. In addition, actigraphy recordings typically collect data from one wrist, so they usually aren’t as detailed as the PSG movement recordings that involve electrodes on multiple muscles around the body.

Multiple sleep latency test (MSLT)

The multiple sleep latency test (MSLT) is a test usually done during the daytime to measure how sleepy a person is. MSLT results normally show how quickly a person can fall asleep during the daytime, which tends to be an indicator of daytime tiredness. In addition to defining how tired a person is, this test can also help diagnose narcolepsy and idiopathic hypersomnia, a disorder in which a person is excessively tired and requires more sleep than is considered normal.

The MSLT is often conducted the day after polysomnography, which ensures that any tiredness found isn't the result of sleep deprivation from the night before. Before an MSLT, a person is generally told to avoid alcohol, caffeine, and substances that may cause sedation or increased alertness.

Electrodes are normally applied before the MSLT to measure brain activity, heart activity, and eye movement. During the MSLT, a person may lie down on a bed in a dark, quiet room. They are usually instructed to keep their eyes closed and allow themselves to fall asleep. Usually, an MSLT involves five "nap trials" that begin like this. The purpose is usually to see if a person falls asleep during a nap trial and, if so, how quickly. 

Maintenance of wakefulness test (MWT)

The maintenance of wakefulness test (MWT) tends to be similar to the MSLT, except instead of measuring how quickly a person can fall asleep during the daytime, the test measures how long a person can stay awake. Often, the MWT is given after a sleep disorder has been diagnosed and treated. MWT results may determine whether a person's treatment is successful. If treatment for narcolepsy or OSA is working, a person generally shouldn't immediately fall asleep during the MWT.

The MWT is often conducted very similarly to the MSLT, except instead of lying down, a person may sit either in a chair or on a bed after being connected to electrodes and other measurement devices. They may then be instructed to sit still, look straight ahead, and stay awake for as long as they can. If a person falls asleep quickly during the daytime despite trying to stay awake, then they may need a treatment adjustment or further sleep testing.

Actigraphy, oximetry, and sleep diary

Actigraphy, oximetry, and sleep diary techniques are often used in the early stages of exploring sleep changes or difficulties, as well as in conjunction with sleep studies.

• Actigraphy: An actigraphy can be described as a wristwatch-like device that measures movement during sleep. These can identify sleep and wake times, body movements, and estimations of sleep stages, though these are usually not as accurate as those provided by polysomnography. Sometimes, sleep specialists have people wear an actigraphy at home for a few nights to a couple of weeks when they are having trouble with sleep or daytime tiredness.
• Oximetry: A pulse oximeter is usually part of polysomnography, HSAT, MSLT, and MWT, but sometimes, a sleep specialist may have a person wear a pulse oximeter on its own at home, or along with actigraphy. Oximetry usually measures a person's pulse through their fingertip, and it also can estimate blood oxygen levels. These can provide insight on what happens while the person is asleep.
• Sleep diary: A sleep diary normally involves keeping manual sleep-related records either on paper or digitally. A person may track what time they go to sleep, what time they wake up in the morning, and any awakenings they have during the night, along with ratings of how well they slept and notes on any factors they believe affected their sleep.

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Who needs a sleep study?

Doctors generally recommend a sleep study when a person has signs of obstructive sleep apnea, such as excessive snoring, observed lapses in breathing during sleep, and morning headaches. Signs and symptoms of narcolepsy are other reasons a doctor may recommend a sleep study, and these can include excessive daytime sleepiness and suddenly falling asleep during the day without warning.

Generally, sleep studies are not recommended as a first-line test for people who have symptoms of restless legs syndrome or insomnia. Other treatments and tests are usually tried first for these types of problems, and a sleep study may be recommended later if other options are exhausted without providing help.

Remote therapy for sleep

If you have a sleep disorder, therapy isn't a substitute for medical treatment. However, many people with insomnia stemming from stress or mental health concerns benefit from receiving therapy. Remote therapy can be useful because it generally allows you to receive treatment from the comfort of your home or any location you prefer. BetterHelp is a remote therapy platform that can connect you with a therapist suited to your unique needs.

Many research studies have looked at the effects of cognitive behavioral therapy on insomnia, which usually involves trouble falling asleep, staying asleep, or waking up earlier than desired. Cognitive behavioral therapy for insomnia (CBT-i) is usually considered the first-line treatment for insomnia. One study of 65 adults with insomnia found that remote therapy can be just as effective as in-person therapy, while providing treatment more efficiently. In the study, remote CBT-i usually improved people's sleep and daytime functioning.