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A sleep study is a series of tests that measures physiological aspects of sleep in an effort to diagnose sleep disorders. It is usually conducted in a sleep center and is  indicated when a patient experiences non-restorative sleep. Sleep studies may be performed for patients who have trouble falling asleep or staying asleep (insomnia), have an excessive need for sleep (hypersomnia), or have other conditions that may affect their ability to sleep, such as restless legs syndrome.

Many people also undergo sleep studies because it is suspected they may have  sleep apnea, a condition in which they stop breathing multiple times during the night. For instance, children with conditions such as Down syndrome and Prader-Willi syndrome (a rare condition characterized by chronic hunger and overeating) may benefit from sleep studies as sleep apnea and abnormal sleep patterns are very  common among these populations.

Sleep studies can measure the stages of a person’s sleep cycle in addition to many physiological activities that occur during sleep. Patients do not usually experience discomfort while tests are being performed.

The physiological measurements of a sleep study may include:

• Electrical activity of the brain (electroencephalography or EEG). Performed by placing electrodes on the scalp. An EEG can identify the specific stages of sleep and any disturbances, which may help diagnose a specific sleep disorder.
  
  
• Respiratory effort. Two bands are placed around the chest and abdomen to monitor movements while breathing, and measurements are made electronically.
  
  
• Airflow. Performed with electrical sensors placed just under the patient’s nose.
  
  
• Oxygen saturation. Performed using a pulse oximeter, a device placed on the patient’s finger or earlobe that measures the oxygen level in the body.
  
  
• Eye movement (electro-oculogram or EOG). Performed by placing electrodes on the face near the eyes.
  
  
• Muscle movement (electromyography or EMG). Performed by placing electrodes on legs and usually on the chin.
  
  
• Electrical activity of the heart (electrocardiogram or EKG/ECG). Performed by placing electrodes on the chest.
  
  
• Body position. The patient’s body positions throughout the night are recorded on video and monitored.
  
  
• Volume and frequency of snoring. Audio recordings of patients’ snoring are sometimes taken during a sleep study.

From the physiological information obtained, physicians can better understand aspects of sleep including how much time patients spend in each sleep stage, how often they wake up and how their breathing changes or stops during the night. Some unusual behaviors (e.g., sleepwalking) may also be observed, although these may not occur in a single sleep study.

Physicians use the sleep study information to diagnose certain sleep disorders, including:

• Insomnia. Difficulty falling asleep or staying asleep, resulting in inadequate length of sleep and/or poor quality of sleep.
  
  
• Hypersomnia.  An unexplained increased need for sleep.
  
   
• Sleep apnea. A disorder in which a person’s breathing stops and starts many times during sleep. Snoring is a common symptom of sleep apnea.
  
  
• Narcolepsy. A neurological sleep disorder characterized by sudden and uncontrollable sleepiness and frequent daytime sleeping.
  
  
• Restless legs syndrome. Sleep disorder characterized by unpleasant sensations in the legs that are described as creeping, crawling, tingling, pulling or painful.