What Is a Sleep Study (Polysomnogram)?

A sleep study, called a polysomnogram, is a test used to help diagnose sleep apnea, restless legs syndrome (RLS), and other sleep disorders. People usually spend the night at a hospital sleep laboratory or an outpatient sleep clinic. Electrodes attached to their body monitor their brain waves, breathing, and movement while they sleep.

This article explains the purpose of a sleep study and how to prepare for one. It offers a step-by-step look at what happens during the study and explains how results are interpreted, as well as what may come next.

Purpose of a Sleep Study

Your healthcare provider may want you to undergo a sleep study if you have trouble falling asleep, wake up frequently, snore, or have other symptoms of a sleep disorder.

A polysomnogram might also be advisable based on a screening test for narcolepsy (excessive daytime sleepiness). The test is known as the Epworth Sleepiness Scale.

What Can a Sleep Study Diagnose?

Sleep studies are designed to diagnose sleep disorders, including:

• Circadian rhythm disorders
• Excessive daytime sleepiness
• Insomnia
• Narcolepsy
• Parasomnias (sleep behaviors)
• Periodic limb movements
• Sleep apnea (a total obstruction of breathing that lasts for more than 10 seconds)
  

Some healthcare providers ask their patients to write a self-report about the quality of sleep, how often they wake up, how rested they typically feel, and other issues. These reports may be helpful to a point, but they don't the full assessment a sleep study does.

What Does a Sleep Study Measure?

A sleep study provides a more complete picture of the quality of your rest and what may be going on in your body to affect it. The electrodes—small metal discs with wires attached—are used to monitor:

• Brainwave activity and sleep stages
• Heart rhythm
• Muscle tone
• Leg movements
• Breathing patterns
• Blood oxygen levels

A practitioner then interprets all the data that is collected and will discuss the results with you.

Timing and Location

Follow the instructions provided to you so you know where to go, when to arrive, and when you can expect to leave. Below is a general sense of timing and the various locations that sleep studies can be performed.

When Is Your Sleep Study?

Most sleep studies take place over the course of one night. A typical check-in time for a polysomnogram is between 8 and 10 p.m. The usual departure time after a person wakes up the next day is between 6 and 8 a.m.

The goal is for you to sleep for at least seven hours, though this isn't always possible. In some cases, sleep medication may be given to help you along.

That said, your provider may be able to make a diagnosis even if you don't sleep for this long.

If you work nights, some facilities can conduct studies during the day.

Where Are Sleep Studies Done?

This test typically is done at a sleep center or sleep lab. This may be a special department that is part of a hospital or clinic, or a standalone facility. Sleep studies are sometimes even set up in hotels.

Sleep labs may be accredited centers, which means they have met the standards of the American Academy of Sleep Medicine (AASM).

If your healthcare provider is ordering a sleep study for you, they will steer you in the direction of a lab that they are familiar with and trust. If you're seeking one on your own, be sure to research facilities in your area to find one that is accredited or has been reviewed favorably.

Typically, a sleep clinic is staffed with one or more healthcare providers who are trained in sleep medicine. Many also practice related disciplines, such as neurology, psychiatry, and pulmonary medicine.

Other medical professionals typically found at sleep centers include physician assistants, nurses, respiratory therapists, and medical assistants.

The Day of Your Sleep Study

On the day of the study, you should follow your regular diet and daily routine, but with some exceptions:

• Avoid caffeine in any form (e.g., coffee, tea, soft drinks, chocolate) after lunchtime.
• Refrain from drinking alcohol, which can interfere with sleep.
• Wash any hair gel or other styling products out of your hair. They can interfere with monitoring equipment.
• Do not nap during the day.
• Stop taking your regular medications if your healthcare provider has instructed you to do so.
  

What to Bring

It will be important to check with your sleep center to see if they have special restrictions for you. In general, though, you should bring the same items you would pack for an overnight stay at a hotel:

• Medications that you take at night or in the morning that your healthcare provider has said you can continue during the test
• Toiletries
• Comfortable sleepwear and slippers or non-skid socks
• Clothes to go home in
• Favorite pillows or blankets
• A bedtime snack (there may be a small refrigerator in your room)
• Phone charger
• Book or other reading material (if it's part of your nighttime routine)
• Something to eat for breakfast (coffee or juice may be provided, but food likely won't)

Who Can Go With You

No one can stay with you overnight, though exceptions may be made for parents of children undergoing a sleep study or patients with a condition that makes it unsafe for them to be alone, such as dementia.

In these cases, a rollaway cot may provided. Keep in mind that the room will be monitored throughout the night.

You won't be able to bring a pet, with the possible exception of a service animal. The animal will require proper documentation before it is granted entry.

During Your Stay

You'll be asleep for most of the time you're being tested, but it's important to know what will happen so you can do your part to ensure that the results are as accurate and useful as possible.

Check-In Process

When you arrive for your sleep study, the process will be similar to checking in for any healthcare provider's appointment. There may be paperwork to fill out, including a consent form. You may need to present your health insurance card and/or co-pay if you have one.

Once you're checked in, a sleep technician will take you to your bedroom for the night. They will show you the bathroom and where you can put your things.

You will then have time to change into your sleepwear and go through your regular nighttime routine of brushing your teeth and washing your face.

Testing Set-Up

The technician will spend about 45 to 60 minutes setting you up for your sleep study. Some studies for seizures, for example, may take as long as 90 minutes to two hours to set up.

An electroencephalogram (EEG), which measures electrical activity in the brain, is one of the tests that will take place while you sleep. To prepare you, the technician will:

1. Measure the dimensions of your head and use a special pencil to mark places on your scalp and face where the electrodes will be attached
2. Use a cotton swab to apply a mildly abrasive paste to each spot in order to remove the oil from your skin so the electrodes can adhere properly
3. Apply a dab of a special paste to each disc to help it stay in place and allow it to better conduct the electrical waves from your brain
4. Gently place the electrodes on the marked spots on your face and scalp; some of the wires may be taped in place

If you're sensitive to or allergic to medical tapes or glues, let the technician know ahead of time so that they can use a type that won't bother you.

Other Equipment

In addition to the electrodes, several or all of the following may be part of your sleep study setup:

• A flat, plastic microphone taped to your neck to record snoring
• Sticky pads on your chest to monitor your heart rhythm via an electrocardiogram (EKG)
• Stretchy cloth belts that go across the chest and stomach to measure breathing
• Sticky pads or electrodes applied to the shins or forearms to monitor muscle movements via electromyography (EMG)
• A peripheral capillary oxygen saturation monitor (usually clipped to a finger), measuring continuous oxygen saturation
• An electro-oculogram (EOG), which uses electrodes placed near the eye to measure eye movements

All of these wires will be connected to a small, portable box that you can easily carry with you if you need to get out of bed to use the bathroom. If you use continuous positive airway pressure (CPAP) during the night, you may be fitted with a mask.

Finally, just before you go to bed, the technician will place a nasal cannula—plastic tubing that sits in the nose—that will measure airflow while you sleep. Most sleep clinics also use a thermistor, a pronged wire that sits in the nostrils and measures temperature changes.

Going to Bed

The technician will help you into bed and connect the wire box to a computer so that they can monitor you from another room. There will likely be a small infrared camera and two-way speaker in the room. If you need to get up during the night, this is how you will call for help to do that.

Just prior to going to sleep, the technician will test the equipment. As part of this testing, they will have you open and close your eyes, move them around, snore, take breaths in and out, and move your arms and legs.

If something goes wrong with a wire, or if one comes loose during the night, your technician will fix it.

Once you're set up, the technician will leave you alone to read, watch television, or listen to music. It's important to not fall asleep until it's your usual bedtime or you feel drowsy enough to drift off.

What If You Can't Sleep?

Not being able to sleep is a common concern of people undergoing a sleep study. Surprisingly, most people do sleep despite the unfamiliar environment and all the wires. In fact, it's rare that someone isn't able to sleep at all.

If you're really worried about falling and staying asleep, your healthcare provider may have you take a medication that won't interfere with the various tests. The most common sleep aid is Ambien (zolpidem). Do not take this medication or any other without the approval of your healthcare provider.

In the worst-case scenario, the testing can be repeated to ensure that the results are valid.

Sleep Study Results

You likely will not be given any information about your study until a sleep healthcare provider has had a chance to review the results. This probably will take some time.

Sleep study reports can be as many as five pages long. They can be packed with hundreds of pieces of data about everything from the stages of sleep you went through and your breathing, to your heart rate, oxygen levels, muscle movements, and snoring episodes.

Sleep study results typically include data about:

• Sleep efficiency, the total number of minutes you slept divided by the total amount of time you were recorded sleeping. The higher the sleep efficiency, the higher the percentage of sleep time versus awake time. Some reports also add up the amount of time a person is awake, as well as how much REM sleep and stage 1, 2, 3, and 4 sleep they get.
• Apnea Hypopnea Index (AHI). This looks at how often a person experiences sleep apnea and hypopnea (partial obstruction). Five or more episodes usually lead to a diagnosis of sleep apnea.
• Oxygen Desaturation Index (ODI). This refers to the number of times a person's oxygen level drops while they're asleep—useful information if someone is being assessed for sleep-disordered breathing. Oxygen levels above 90% are considered normal.
• Heart rate. In general, a normal heart rate is between 60 and 100 beats per minute (BPM). If it exceeds this number, it's called tachycardia. Less than 60 BPM is known as bradycardia.

Your healthcare provider will review your study results with you and discuss possible treatments, if needed.

Follow-Up

For those with excessive daytime sleepiness, multiple sleep latency testing (MSLT) may follow a diagnostic polysomnogram. This testing consists of opportunities to take naps at two-hour intervals the day following the overnight testing.

It is somewhat simplified from the baseline study, with fewer measurements involved. The MSLT can identify narcolepsy, hypersomnia, or whether a normal amount of daytime sleepiness is present.

A maintenance of wakefulness test may also be performed as a follow-up. It's usually reserved for people who work in professions that require sustained alertness in order to preserve public safety.

Truck drivers, airline pilots, train conductors, and other transportation professionals may be prime candidates for this test. Its goal is to ensure that in a quiet, somewhat darkened space, the patient can stay awake while slightly reclined. Transient dozing (or falling asleep) may be a problem if identified.

Repeat Sleep Studies

Sometimes it's necessary to repeat a sleep study. Your healthcare provider may suggest this course of action in certain situations.

Health Changes

A relatively modest change in weight—say, a loss or gain of 10% of your body weight—may justify a repeated sleep study, Sleep issues often improve with weight loss and worsen after weight gain.

Abnormal sleep behaviors such as REM behavior disorder may develop later in life and should be assessed with a formal sleep study. Significant health changes could necessitate a second look, too. Heart failure, stroke, or the introduction of narcotic medications may all be reasons to ensure changes in breathing during sleep have not occurred.

Checking to See if Other Treatments Are Working

You may have tried alternative treatments and your physician wants to measure their effectiveness.

Some people turn to alternative therapies to treat sleep apnea, including the use of an oral appliance from a dentist or a surgical treatment. A second sleep study can be a useful way to check how the appliance works or whether the surgery was a success.

Unresolved Sleep Apnea

If you're still too sleepy, it may be a sign to dig a little deeper. Persistent and excessive daytime sleepiness may also require a reassessment of other conditions that may be triggering the fatigue.

The Epworth Sleepiness Scale may be used again to gauge sleepiness. More intensive evaluation often proves necessary to sort out the underlying cause of the apnea.

Summary

Your healthcare provider may ask you to undergo a sleep study if you have trouble falling asleep, wake up frequently, snore, or have other symptoms of a sleep disorder. The study requires that you spend a night at a sleep center or sleep lab so that you can be hooked up to several types of monitors that literally track your every breath and movement.

In the end, the report should give your primary care physician a good picture of your sleep quality (or lack thereof). To prepare for your visit, it's smart to pack as if you were going to a hotel but not actually staying at one (since you can't drink caffeine or alcohol before the study begins). Many people fear that they won't fall asleep (or stay asleep) during a sleep study, but the majority do.