Comprehensive Guide to Sleep Studies: What to Expect

Understanding Sleep Studies

What is a Sleep Study?  

A sleep study (medical term: polysomnography) is a test that is done to diagnose sleep disorders and decide on the treatment plan if a sleep disorder is diagnosed. 

Sleep disorders are conditions in which normal sleep patterns (sleep stages or sleep cycles) are disrupted. This can result in not getting enough sleep, not feeling rested, and getting excessively sleepy during the daytime. When people suffer from sleep disorders, they constantly feel tired throughout the day, affecting their performance at work and their quality of life.

Polysomnography involves spending the night in a sleep center or sleep lab in a hospital, usually overnight, but it can also be done during the daytime for night shift workers. You can also do home sleep apnea tests to find out if you have a condition called obstructive sleep apnea.

Purpose of a Sleep Study  

The purpose of a sleep study or sleep test is to help healthcare providers diagnose sleep disorders. During polysomnography, electrodes (sensors) are placed on your body to record several parameters while you are asleep, such as:

• Brain wave activity

• Blood oxygen level

• Heart rate

• Breathing rate

• Eye movements

• Limb movements

• Chest and abdomen movements

• Body position

• Snoring and other noises

Importance of Diagnosing Sleep Disorders

According to the American Academy of Sleep Medicine (AASM) and the Sleep Foundation, undiagnosed and untreated sleep disorders are associated with serious health risks, including but not limited to an increased risk of heart disease, stroke, and metabolic syndrome. In addition, sleep disorders can cause excessive daytime sleepiness, which can lead to potentially fatal motor vehicle accidents and errors in the workplace. 

What Can A Sleep Study Diagnose?

Obstructive Sleep Apnea and Other Breathing Disorders  

A sleep study can diagnose obstructive sleep apnea (OSA), a condition in which breathing repeatedly starts and stops during sleep. It can also be used to diagnose other sleep disordered breathing patterns.

Periodic Limb Movement Disorder and Restless Legs Syndrome

Periodic limb movement disorder (PLMD) and restless legs syndrome (RLS) are related conditions. PMLD is a condition in which there are repetitive movements of the limbs during sleep. Restless legs syndrome is a condition in which there is an irresistible urge to move and abnormal sensations in the limbs when sitting still or lying down.

Narcolepsy

Narcolepsy is a sleep disorder in which there is a disruption of normal sleep-wake cycles. It results in overwhelming sleepiness during the daytime and sudden sleep attacks. Compare narcolepsy treatments.

Parasomnias

Parasomnias are unusual or abnormal experiences that occur during normal sleeping hours, such as sleepwalking, sleep talking, and nightmares. They are classified according to the stages of sleep during which they occur. 

Non-rapid eye movement (NREM) sleep-related parasomnias include sleepwalking, sleep terrors, confusional arousals, and sleep-related abnormal sexual behaviors. Rapid eye movement (REM) sleep-related parasomnias include REM sleep behavior disorder (dream enactment behaviors), nightmare disorder, and recurrent isolated sleep paralysis.

Chronic Insomnia 

A sleep study may also be done in people with unexplained chronic (long-term) insomnia (trouble falling asleep or staying asleep). Learn about the effects of sleep deprivation.

Types of Sleep Studies  

Polysomnography (PSG)

As noted, a polysomnogram (sleep study) is a test done to find out if you have a sleep disorder such as obstructive sleep apnea (OSA). It involves measuring brain activity and other parameters like heart rate, breathing rate, blood oxygen levels, eye movements, and leg movements with monitoring equipment. If the PSG test shows OSA is present, you will need to undergo a second test called a titration study about 2 weeks later. 

Titration Study

During the titration study, you will again be hooked up to electrodes (sensors), but you will also use a CPAP or BiPAP machine. Continuous positive airway pressure (CPAP) and bilevel positive airway pressure (BiPAP) are devices that deliver pressurized air through a mask to keep your airways open while you sleep. The sleep technologist will adjust the air pressure in your mask during the titration study. The results of this sleep test will help your healthcare provider determine the correct pressure to control your OSA.

Split Night Study  

A split night study is a sleep study in which both the polysomnogram (PSG) and the titration study are done on the same night. Not everyone will meet the criteria to undergo a split-night study. 

Multiple Sleep Latency Test (MSLT)

A multiple sleep latency test (MSLT) is a daytime test that is done following an overnight sleep study. It involves monitoring to see how quickly you can fall asleep and how quickly REM sleep starts during daytime naps. Multiple sleep latency tests (MSLTs) are done to diagnose sleep-related conditions such as narcolepsy.

Home Sleep Apnea Testing  

A home sleep apnea test (HST or HSAT) is a convenient and affordable test that you can do overnight in the comfort of your own home and bed. The monitoring equipment is delivered to your home or you collect it from a doctor’s office. It collects data while you sleep overnight. 

An at-home sleep study is 98% effective in diagnosing sleep apnea. It is also more affordable than a polysomnogram (PSG) done in a sleep clinic ($3,000 for a PSG vs $200 for a home sleep apnea test). However, home sleep apnea tests collect less data than a PSG and may not be suitable for everyone.

What to Expect During a Sleep Study  

Preparing for a Sleep Study

Here are some tips on what to do in the afternoon and evening before an overnight sleep study:

• Avoid drinking alcoholic or caffeinated beverages. They can affect sleep patterns and worsen symptoms of certain sleep disorders. 

• Avoid taking a nap during the day. 

• If you are asked to shower or bathe, avoid using lotions, colognes, or other skin products. They can interfere with the electrodes (sensors) used during a sleep test.

Polysomnography Procedure: What Happens During a Sleep Study? 

On the evening of your sleep study, you will arrive at the sleep center and stay overnight. You can sleep in your own pajamas and bring any items you need for your usual nighttime routine, such as a book, water bottle, or blanket. The room where you’ll sleep is similar to a hotel room. It is dark and quiet, with a private bathroom. You won’t share the room with another person. 

Before the sleep study begins, a sleep technician will place various electrodes (sensors) on areas of your body, including your scalp, temples, chest, abdomen, and limbs, as well as a clip on your finger. These electrodes are connected to a computer system and record various indicators. 

A sleep technologist will monitor you throughout the night. If you want something, you can talk to them. If you need to use the bathroom, you can ask them to come in and disconnect the wires. 

If you are having a split night study, the sleep technician may have you try a continuous positive airway pressure (CPAP) machine during the second half of the test if you test positive for sleep apnea in the first half of the sleep test. 

Equipment Used in a Sleep Study

Equipment in a sleep clinic room includes a computer system with wires and electrodes that are placed on your body. There is also a low-light video camera in the sleeping area that allows the sleep technologist to observe the room when the lights are out. An audio system is present that allows two-way communication between you and the sleep technician and also allows them to hear any sounds from the room, such as snoring. 

Interpretation of Sleep Study Results  

Sleep study results can be interpreted by looking at a number of key indicators, including:

Apnea-Hypopnea Index (AHI)

Apnea-hypopnea index (AHI) is the number of apnea and hypopnea events per hour of sleep. Apnea is a complete pause in breathing lasting 10 seconds or more. Hypopnea is a significant reduction in breathing lasting 10 seconds or more. AHI results are interpreted as follows:

Other Indicators

• Arousals are brief awakenings from sleep lasting 3 seconds or more as a result of apnea or hypopnea. They are brief and you don’t usually recall them, but they disrupt sleep and can cause daytime sleepiness and fatigue.

• Sleep Efficiency is the percentage of time you sleep compared to the amount of time you spend in bed. A sleep efficiency of 80% or higher is considered normal. So, if you spend 8 hours in bed, you should spend at least 6.4 of these hours sleeping to have healthy sleep efficiency. 

• Sleep Latency is the amount of time it takes you to fall asleep. For instance, if you go to bed at 10 pm and fall asleep at 10:30 pm, your sleep latency is 30 minutes. Normal sleep latency is between 5 and 15 minutes. Sleep latency under 5 minutes suggests excessive sleepiness and above 15 minutes suggests problems with sleep initiation.

• Sleep Architecture is the structure of sleep or the amount of time you spend in each sleep stage during a sleep cycle. There are 4 stages of sleep that constitute one sleep cycle which lasts about 90-120 minutes. A healthy person has 4-5 sleep cycles during the night.

• REM Latency is the amount of time it takes you to achieve REM sleep after falling asleep. This is the final stage of the sleep cycle and the first REM period should therefore occur 70-110 minutes after sleep initiation. 

• Oxygen Saturation (SaO2) is the oxygen level in the blood. Healthy levels are 94-100%.  People with sleep apnea and lung conditions have low oxygen saturation levels. 

• Periodic Limb Movement Index (PLMI) is the number of leg jerks during each hour of sleep. 

• Electromyogram is a record of muscle movement and is used to diagnose neurological disorders such as PLMD and RLS.

• Electroencephalogram and electrooculogram are used to record brain waves and eye movements, respectively. They can help to identify disruptions in sleep stages that occur in sleep disorders such as REM sleep behavior disorder or narcolepsy.

• Electrocardiogram, heart rate, breathing rate, and oxygen saturation are indicators used to diagnose sleep apnea.

Next Steps and Treatment Options  

After a sleep specialist interprets the data from your sleep study, they will arrive at a diagnosis. You will be called in for a follow-up visit to discuss the findings and treatment options for your condition. 

Follow-Up and Monitoring Procedures

Follow-up and monitoring after your sleep study will consist of three phases: Treatment initiation, treatment optimization, and long-term follow-up. For example, if you are diagnosed with sleep apnea:

• Your healthcare provider may recommend using a CPAP machine at night to initiate treatment. 

• At follow-up visits, they will adjust the settings on your CPAP device. 

• Long-term management will consist of follow-up visits to ensure you continue using the CPAP machine every night, monitor you for side effects, evaluate you for complications and health conditions that can develop as a result of sleep apnea, and ensure continued resolution of your symptoms. Find out if you can control sleep apnea with medication.

Frequently Asked Questions  

How Many Hours of Sleep Are Required?

Experts recommend that adults get 7 to 9 hours of sleep every night. People with sleep-disordered breathing, such as sleep apnea, can have multiple brief awakenings during the night, leaving them feeling unrested and sleepy during the daytime.

What if I Cannot Sleep During the Study?

You can tell the sleep technologist that you’re having trouble falling asleep during the sleep study. Most people are able to fall asleep by following their usual bedtime routine, such as getting into comfortable pajamas, reading a good book, and getting under their favorite blanket. However, if you still cannot sleep, the sleep specialist may prescribe a sedative to help you fall asleep in the unfamiliar surroundings of the sleep clinic. 

Is a Sleep Study Safe?

A sleep study (polysomnogram) is a safe, painless, and non-invasive test. The only possible side effect is minor skin irritation from the adhesive on the electrodes.

How Many Hours of Sleep Do You Need For A Sleep Study?

You must sleep for at least 2 hours for the results of a sleep test to be considered valid. It’s common for people to have trouble falling asleep during sleep studies due to the unfamiliar environment. However, this does not affect the sleep apnea sleep study results. In other words, you don’t need a full night's sleep to get accurate sleep study results.