What is a

Sleep Study?

A sleep study measures how much and how well a patient sleeps. The type of sleep study your doctor will recommend depends on which sleep disorders you are at risk for. The most common and prescribed sleep study is a Polysomnogram (PSG), or an in-lab study. A Home Sleep Test (HST) is performed in the comfort of your own home. With recent technological advancements in HST devices and subsequent changes in medical insurance policies, portable studies are becoming a more common method for diagnosing obstructive sleep apnea in patients who don’t exhibit signs of other sleep disorders or major related health issues.

In addition to how much you sleep, sleep study results will tell you about quality of sleep, how much time you spend in different stages of sleep and whether you have a sleep disorder. A sleep study is required for an obstructive sleep apnea diagnosis.

Polysomnogram (PSG)

During a PSG attended sleep study, one stays overnight in a sleep center, either located in a hospital or an outpatient facility. You stay in a private room that is made up similar to a bedroom, some more comfortable than others. Before the sleep study begins, the sleep technician, who will be with you at the facility all night watching you on video from another room, apply patches and sensors on your scalp, face, chest, fingers, and limbs, as well as belts around your chest and abdomen.

Each sensor that is placed on your body during the PSG sleep study is responsible for recording one of many bodily functions that will be used to determine if you have a sleep disorder or not. Here are a few that are commonly used:

  • Electro-encephalogram (EEG) – measures electrical brain activity

  • Electro-myograph (EMG) – measures electrical activity in muscles

  • Electro-oculograph (EOG) – measures electrical activity associated with eye movement

  • Electro- cardiogram (EKG) – measures heart rate and rhythm

  • Respiratory airflow

  • Snore volume

  • Blood oxygen saturation

  • Body position

  • Respiratory effort

  • Eye movement

Throughout the attended sleep study, the sleep technicians keeps an eye on you and the channels of information being provided to them through all the sensors and belts, then they prepare the report for your physician who will decide what diagnosis, if any, is necessary.

Home Sleep Test (HST)

Many HST devices, otherwise known as portable sleep studies, can provide your doctors with detailed reports including much of the same information provided by a PSG, but you get to sleep in the comfort of your own bed. Home sleep tests are often recommended if a patient has no major co-morbidities, like cardiovascular disease, heart failure, stroke, etc. You will need to discuss with your health care provider if this is an option for you.

Home sleep test devices can have as few as 2-3 sensors, to as many at 20+ leads, depending on the sleep disorder you are being tested for. Some fit on the hand, or the head, and others are very similar to PSG leads and have sensors that attach to your face, chest and abdomen.

The most common use for an HST is to screen a patient who snores or is at high risk for having obstructive sleep apnea (OSA).

How Does a Sleep Study Measure Quality of Sleep?

During a sleep study, the stages and quality of sleep are determined. It is important to understand that each stage of sleep is important to your health. There are 4-5 stages of sleep and each have an important role in the process.

REM Sleep: Most dreaming takes place during REM sleep.

REM Sleep: Most dreaming takes place during REM sleep. REM sleep makes up about 20-25% of the sleep cycle in normal adults. REM sleep is characterized by:

  • Eyelid fluttering

  • Rapid eye movement

  • Muscle paralysis

  • Irregular breathing

  • Decrease in body temperature

  • Changes in heart rate and blood pressure

  • Eye movement

Non-REM Sleep: Approximately 75% of night's sleep is spent in non-REM sleep.

Non-REM sleep consists of four stages that range from light dozing to deep sleep.

Sleep Stage 1: Transition period from wakefulness to sleep. It is characterized by slow rolling eye movements. The dozing stage. Approximately 5% of the total night's sleep is spent in Stage 1.

Sleep Stage 2: Characterized by a lack of eye movements. Brain waves become larger. It is defined on PSG with sleep spindles and K-complexes. Approximately 45% of the total night's sleep time is spent in Stage 2 of non-REM sleep. This stage is often considered the official onset of consolidated sleep. Eye movements stop and brain waves become larger. Stage 2 Sleep is graphically defined with two distinct brain wave forms called sleep spindles and K-complexes. A sleep spindle is a pattern of EEG waves, consisting of a burst of 11 to 15 hertz waves that last for .5 to 1.5 seconds. A K-complex is high voltage EEG activity that consists of a sharp downward component followed by a slower upward component and lasts more than .5 seconds.

Sleep Stage 3: An individual becomes difficult to arouse. On the PSG, large and slow delta waves appear. Approximately 12% of the total night's sleep time is spent in Stage 3 of non-REM sleep.

Sleep Stage 4: Characterized by very deep sleep. When awakened, person feels groggy and disoriented. PSG shows delta waves almost exclusively. Approximately 13% of the total night's sleep time is spent in Stage 4 of non-REM sleep.

Does a Sleep Study Diagnose Sleep Apnea?

Whether you have obstructive sleep apnea, and the severity of your sleep apnea can be measured by the number of times you stopped or reduced breathing per hour. An apnea is an event in which a person stops breathing for 10 seconds or more. A hypopnea is a reduction in breathing causing a drop in blood-oxygen levels.

Together, these events are counted in your sleep study results and known as the Apnea-Hypopnea Index (AHI). The AHI determines whether your OSA is mild, moderate or severe based on the severity classifications of OSA:

  • Normal Limits: AHI less than 5 per hour

  • Mild OSA: AHI between 6 and 15 per hour

  • Moderate OSA: AHI between 16 and 30 per hour

  • Severe OSA: AHI greater than 30 per hour

Sleep study results also measure the drop in your blood-oxygen levels to help determine the severity of the disease. From there, your sleep physician will recommend the appropriate treatment options.

Find out if you should consider a PSG or HST for further evaluation.


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