How Does a Sleep Study Work?
If your doctor suggests you undergo a sleep study, or polysomnography, you may be wondering what is involved in this test and what to expect. Sleep studies help doctors diagnose sleep disorders such as sleep apnea, periodic limb movement disorder, narcolepsy, restless legs syndrome, insomnia, and nighttime behaviors like sleepwalking and REM sleep behavior disorder. Often these disorders cannot be identified with a normal office visit—your doctor needs to gather more conclusive evidence while you're asleep.
A sleep study is a non-invasive, overnight exam that allows doctors to monitor you while you sleep to see what's happening in your brain and body. For this test, you will go to a sleep lab that is set up for overnight stays—usually in a hospital or sleep center. While you sleep, an EEG monitors your sleep stages and the cycles of REM and nonREM or NREM sleep you go through during the night, to identify possible disruptions in the pattern of your sleep. A sleep study will also measure things such as eye movements, oxygen levels in your blood (through a sensor—there are no needles involved), heart and breathing rates, snoring, and body movements.
A sleep study is done in a room that is made to be comfortable and dark for sleeping. You'll be asked to arrive roughly two hours before bedtime. You can bring personal items related to sleep, and you can sleep in your own pajamas. Before you go to bed in the exam room, a technologist will place sensors, or electrodes, on your head and body, but you'll still have plenty of room to move and get comfortable. Polysomnographic technologists monitor you during the night and can help you if you need to use the bathroom, for example. Many people wonder how they'll be able to sleep under these conditions. Don't worry about this too much—a full night of sleep is not required to gather useful information from your sleep study.
The data from your sleep study will usually be taken by a technologist, and later evaluated by your doctor. This may take up to two weeks, when you'll schedule a follow up to discuss the results.
What kind of sleep test will I take?
There are several different sleep disorders that typically involve a sleep study as part of the diagnosis, including: sleep apnea, narcolepsy, restless leg syndrome, and REM behavior disorder. Depending on your symptoms, your doctor will schedule one of several different types of sleep studies.
A polysomnogram test measures brain waves and other physiological
activity during sleep, including:
Blood oxygen levels
Capturing this data gives sleep technicians and other clinicians
information about your movement through stages and cycles of sleep.
Sleep follows a typical pattern, known as sleep architecture. Each cycle
of sleep is made up of four sleep stages:
Stages 1-4: Non-REM (NREM) sleep that ranges from Stage 1 light sleep to Stage 3-4 deep, slow-wave sleep
REM sleep: A sleep stage that’s characterized by brain activity that’s similar to when awake. REM sleep is a stage associated with vivid dreaming.
From beginning to end, one sleep cycle lasts from 90-110 minutes. A full night of sleep contains 4-5 complete sleep cycles.
A polysomnogram can pick up disruptions to the normal flow of sleep through stages and cycles, and this data provides valuable information in diagnosing several sleep disorders.
What’s a polysomnogram like?
When you go for a polysomnogram, you’ll sleep in a quiet, private room. During the night, you’ll sleep with electrodes attached to different parts of your body (27 electrodes, to be exact), which will collect data as you rest. The wires that connect the electrodes to monitoring equipment are long, allowing you to move around in bed in your natural way. There are typically video and audio systems in the room, allowing sleep techs to observe your activity as you sleep. If you need to get up at night, sleep techs will help you detach from the equipment temporarily so you can use the bathroom. Your doctor will review the results of your test and follow up with you, in person or on the phone, to go over your test results and discuss next treatment steps.
This sleep study is used to set and adjust individual CPAP levels. What is CPAP? Continuous positive airway pressure, or CPAP, is a treatment that keeps the airway open and breathing un-obstructed, during sleep. The CPAP machine pushes a gentle, consistent stream of air into the airway, which keeps it from becoming blocked.
CPAP is used to treat sleep-disordered breathing, specifically sleep apnea. Once you’ve been diagnosed with sleep apnea, your doctor will schedule a CPAP titration study to identify the precise degree of pressure needed to keep your airway open and allow you to breathe normally while asleep.
What’s a CPAP titration like?
Similar to a polysomnogram at a sleep center, when you have CPAP titration you will sleep in a quiet, private room. While you sleep, you will wear sensors and also a nasal mask, which directs the air from the CPAP device into your airway. During the night, a sleep technician will adjust the levels of air pressure, to determine what level is right for you. Your doctor will follow up with you with test results and details about using CPAP at home.
Split-night sleep study
Sometimes, a sleep study will combine a polysomnogram and CPAP titration study in the same night. This is known as a “split-night” study. This is mostly likely to be the case when a patient is showing clear symptoms of sleep apnea. You will know ahead of time if yours is to be a split-night study.
What is a split night study like?
Typically, sleepers will go through a polysomnogram during the first half of the night, and CPAP titration during the second half of the night.
Multiple Sleep Latency Test
The MSLT is used to diagnose narcolepsy, often in conjunction with a polysomnogram. The multiple sleep latency test is conducted during the day in a sleep center or laboratory. MSLT involves 5 20-minute naps at scheduled intervals throughout the day. Sleep specialists evaluate how quickly you fall asleep and what stages of sleep you enter, and for how long, during your naps.
What is MSLT like?
Often, an MSLT will directly follow a polysomnogram, requiring you to remain the controlled sleep environment for a full day after your overnight way. You’ll be given breakfast and lunch, and asked to relax quietly (watching television or reading) between naps, which take place two hours apart. If you can’t fall asleep during the nap window, that’s okay.
Home Sleep Test
In recent years, at-home sleep tests have become more common. It’s important to know: at-home tests are accurate for sleep apnea testing and sleep apnea testing only. These tests are done at home but are ordered by your physician, just as in-laboratory tests are. When your doctor raises the possibility of a study for sleep apnea, you can ask about an at-home option.
What is an at-home sleep study like?
Your doctor will arrange for you to receive the equipment you need for your at-home study. You may receive it through the mail or you may pick it up from your local hospital, doctor’s office, or medical center. You will receive instructions for using the equipment for 1-3 nights of at-home sleep assessment. Afterwards, you will return the equipment, and the data will be analyzed and delivered to your doctor, who will follow up with you about treatment plans.
The advantages of at-home sleep studies are pretty clear: comfort and convenience. You get to sleep in your own bed and maintain your natural nighttime routine while your sleep is measured. These tests are less expensive than sleep-laboratory testing. At-home sleep testing isn’t for everyone, so it’s important to follow through with a sleep-lab test if that’s what your doctor recommends.
Some tips to prepare for your sleep study:
• Stick to your regular routine in the days before your study. Keep your regular bedtime and wake time, exercise and eat your meals as you normally would.
• Don’t nap during the day, if possible.
• Limit your caffeine (and avoid altogether if your doctor recommends).
• Avoid alcohol.
• Your doctor may ask you to make adjustments to your medications ahead of a sleep study.
Bring comfortable sleep clothes, as well as toiletries you need for the night and next morning. Don’t forget a change of clothes for the next day and some reading material to keep you occupied.