What is polysomnography

Polysomnography is a sleep study, a test that records certain body functions as you sleep, or try to sleep. Polysomnography records your brain waves, the oxygen level in your blood, heart rate and breathing, as well as eye and leg movements during the study. Polysomnography is used to diagnose sleep disorders.

Polysomnography is usually done at a sleep disorders unit within a hospital or at a sleep center. The test records your nighttime sleep patterns. Polysomnography is occasionally done during the day to accommodate shift workers who habitually sleep during the day.

In addition to helping diagnose sleep disorders, polysomnography may be used to help adjust your treatment plan if you’ve already been diagnosed with a sleep disorder.

There are two stages of sleep:

1. Rapid eye movement (REM) sleep. Most dreaming occurs during REM sleep. Under normal circumstances, your muscles, except for your eyes and breathing muscles, do not move during this stage of sleep.
2. Non-rapid eye movement (NREM) sleep. NREM has three stages that can be detected by brain waves (EEG).

REM sleep alternates with NREM sleep about every 90 minutes. A person with normal sleep most often has four to five cycles of REM and NREM sleep during a night.

A polysomnography sleep study measures your sleep cycles and stages by recording:

• Air flow in and out of your lungs as you breathe
• The level of oxygen in your blood
• Body position
• Brain waves (EEG)
• Breathing effort and rate
• Electrical activity of muscles
• Eye movement
• Heart rate

Polysomnography can be done either at a sleep center or in your home.

Polysomnography study at a sleep center

Full sleep studies are most often done at a special sleep center.

• You will be asked to arrive about 2 hours before bedtime.
• You will sleep in a bed at the center. Many sleep centers have comfortable bedrooms, similar to a hotel.
• Polysomnography test is most often done at night so that your normal sleep patterns can be studied. If you are a night shift worker, many centers can perform the test during your normal sleep hours.
• Your sleep doctor will place electrodes on your chin, scalp, and the outer edge of your eyelids. You will have monitors to record your heart rate and breathing attached to your chest. These will remain in place while you sleep.
• The electrodes record signals while you are awake (with your eyes closed) and during sleep. The test measures the amount of time it takes you to fall asleep and how long it takes you to enter REM sleep.
• A specially-trained sleep technician or nurse will observe you while you sleep and note any changes in your breathing or heart rate.
• Polysomnography test will record the number of times that you either stop breathing or almost stop breathing.
• There are also monitors to record your movements during sleep. Sometimes a video camera records your movements during sleep.

Polysomnography at home

You may be able to use a sleep study device in your home instead of at a sleep center to help diagnose sleep apnea. You either pick up the device at a sleep center or a trained therapist comes to your home to set it up.

Home testing may be used when:

• You are under the care of a sleep specialist.
• Your sleep doctor thinks you have obstructive sleep apnea.
• You do not have other sleep disorders.
• You do not have other serious health problems, such as heart disease or lung disease.

Sleep Stages

Sleep occurs in 2 main phases, Non-Rapid Eye Movement (NREM) sleep, which has three stages (N1, N2, and N3), and Rapid Eye Movement (REM) sleep ¹. Each sleep phase and stage of sleep includes variations in muscle tone, brain wave patterns, and eye movements. Your body cycles through all stages approximately 4 to 6 times each night, averaging 90 minutes for each cycle ². Each sleep stage serves different functions, from the light transition into sleep (N1), to the restorative deep sleep (N3) and the active dreaming of REM sleep.

Sleep Stages ³, ⁴:

• Stage 1 (N1 or light sleep) is the lightest stage of sleep and occurs as a person first falls asleep. This brief stage is when your drowsiness gives way to falling asleep. Your heartbeat and breathing start to slow down, but it’s still pretty easy to wake you up during this stage. Average length 1 to 7 minutes.
• Stage 2 (N2 or intermediate sleep) is where the body starts to relax more deeply. Your body temperature drops, your muscles relax, and your breathing and heart rate slow even more. Average length 10 to 25 minutes.
• Stage 3 (N3 or deep sleep) is the deepest and more restorative sleep, allowing your body to recover and grow. In stage 3 sleep, your breathing and pulse are slow and steady. Average length 20 to 40 minutes.
• Stage 4 (REM Sleep) is where most dreaming occurs, brain activity increases almost as if you were awake, and your muscles become temporarily paralyzed. Your heart rate and respiration speed up and become more erratic, and your eyes move quickly behind your eyelids. Dreams are most vivid during the REM stage. Average length 10 to 60 minutes.

Although the sleep stages are described numerically, you don’t always progress through them in this exact order. For example, in many sleep cycles, you transition from stage 3 sleep back to stage 2 sleep before beginning a period of REM sleep.

Sleep occurs in 5 stages: Wake, Non-Rapid Eye Movement (NREM) stage N1, then progress through N2 and N3, and after N3 you enter REM sleep ¹. You then return to NREM stages, often starting again at N2. Throughout the night, the REM periods lengthen, and deep N3 sleep decreases, with most N3 sleep occurring in the first half of the night, with each stage leading to progressively deeper sleep. Approximately 75% of sleep is spent in the NREM (Non-Rapid Eye Movement) stages, with the majority spent in the N2 stage ⁵. A typical night’s sleep consists of 4 to 5 sleep cycles, with the progression of sleep stages in the following order: N1, N2, N3, N2, REM ⁶. A complete sleep cycle takes roughly 90 to 120 minutes. The first REM period is short, and as the night progresses, longer periods of REM and decreased time in deep sleep (NREM) occur ¹. With each new cycle, you spend increasing amounts of time in REM sleep, so most of your REM sleep takes place in the second half of the night.

Sleep isn’t uniform. Sleep cycles can vary from person to person and from night to night based on a wide range of factors such as your age, recent sleep patterns, and alcohol consumption. Over the course of the night, you go through several rounds of the sleep cycle, which is composed of four stages. In a typical night, a person goes through four to six sleep cycles ¹. Not all sleep cycles are the same length, but on average they last about 90 minutes each.

The first sleep cycle is often the shortest, ranging from 70 to 100 minutes, while later cycles tend to fall between 90 and 120 minutes. In addition, the composition of each cycle — how much time is spent in each phase of sleep — changes as the night goes along.

Figure 1. Sleep Stages

Footnotes: A sleep episode begins with a short period of NREM stage N1 progressing through stage N2, followed by stage N3 and finally to REM. However, individuals do not remain in REM sleep the remainder of the night but, rather, cycle between stages of NREM and REM throughout the night. NREM sleep constitutes about 75 to 80 percent of total time spent in sleep, and REM sleep constitutes the remaining 20 to 25 percent. The average length of the first NREM-REM sleep cycle is 70 to 100 minutes. The second, and later, cycles are longer lasting—approximately 90 to 120 minutes ⁷. In normal adults, REM sleep increases as the night progresses and is longest in the last one-third of the sleep episode. As the sleep episode progresses, stage 2 begins to account for the majority of NREM sleep, and stages 3 and 4 may sometimes altogether disappear.

[Source ³ ]

Figure 2. Typical Sleep Pattern in Young Adults 

Footnotes: Average times and sequences of sleep cycles during the night. Over the course of a period of sleep, NREM and REM sleep alternate cyclically. The function of alternations between these two types of sleep is not yet understood, but irregular cycling and/or absent sleep stages are associated with sleep disorders ⁸. For example, instead of entering sleep through NREM, as is typical, individuals with narcolepsy enter sleep directly into REM sleep ⁹. Rapid eye movement (REM) sleep occurs cyclically throughout the night every 90 to 120 minute. Brief periods of wakefulness (stage W) occur periodically.  Sleep time is spent as follows:

• Stage N1: 2–5%
• Stage N2: 45–55%
• Stage N3: 13–23%
• REM: 20–25%

[Source ¹⁰ ]

Figure 3. EEG activity of the four stages of sleep

Footnotes: EEG activity during wakefulness with eyes open and closed and during the different stages of sleep. Brainwave activity changes drastically over the course of the different stages of sleep. REM sleep brain activity most closely resembles brain activity while awake.

• Alpha activity is a smooth electrical activity of 8-12 Hz recorded from the brain; generally associated with a state of relaxation during wakefulness.
• Beta activity is a irregular electrical activity of 13-30 Hz recorded from the brain; generally associated with a state of alertness during wakefulness.
• Theta activity is EEG activity of 3.5-7.5 Hz that occurs intermittently during lighter stages of NREM sleep.
• Delta activity is a regular, synchronous electrical activity of less than 4 Hz recorded from the brain; occurs during the deepest stages of slow-wave sleep.
• Sleep spindle is a short burst of 12 to 14 cycle per-second waves observed during NREM sleep, decrease brain’s sensitivity to sensory input and keeps person asleep.
• K complex are single delta waves, sudden sharp wave forms, 1 per minute but can be triggered by noise.

[Source ¹¹ ]

Your sleep-wake cycle is regulated by the circadian rhythm (your body’s natural internal 24-hour clock that manages your sleep-wake cycle and other vital functions, like hormone release and body temperature, by synchronizing with the day-night cycle), which is driven by the suprachiasmatic nucleus (SCN) of the hypothalamus that acts as a “master clock” or “circadian pacemaker”, receiving light cues from your eyes to control the circadian rhythm ¹², ¹³, ¹⁴. The circadian rhythm also controls the nocturnal release of adrenocorticotropic hormone (ACTH), prolactin, melatonin, and norepinephrine (NE) ¹⁵. External factors like light exposure, meal timing, and activity can influence the circadian rhythm, and disruptions to the circadian rhythm, such as from shift work or jet lag, can negatively affect your health.

The suprachiasmatic nucleus (SCN) of the hypothalamus receives input from nerve cells in the retina that detect light to regulate the circadian rhythm and sleep via multiple pathways that cause the nocturnal release of adrenocorticotropic hormone (ACTH), prolactin, melatonin, and norepinephrine ¹⁶. One of the most commonly recognized pathways by which this occurs is via the stimulation of norepinephrine release by the suprachiasmatic nucleus (SCN), which in turn stimulates the pineal gland to release melatonin ¹⁷, ¹⁴. Wakefulness is maintained by subcortical structures and pathways activating the cortical system ¹⁷. This system is termed the “ascending arousal system” and utilizes several major neurochemicals, including:

• Norepinephrine (locus ceruleus)
• Serotonin (midline raphe nuclei)
• Histamine (tuberomammillary nucleus)
• Dopamine (ventral periaqueductal gray matter)
• Acetylcholine (pedunculopontine tegmentum and laterodorsal tegmentum of the pons)
• Orexin (perifornical area)

Transitions between sleep and wake states are influenced by multiple brain structures, including ¹:

• Hypothalamus: controls onset of sleep
• Hippocampus: memory region active during dreaming
• Amygdala: emotion center active during dreaming
• Thalamus: prevents sensory signals from reaching the cortex
• Reticular formation: regulates the transition between sleep and wakefulness
• Pons: helps initiate REM sleep. The extraocular movements (eye movements) that occur during REM sleep are due to the activity of PPRF (paramedian pontine reticular formation/conjugate gaze center).

Although it is apparent that humans need sleep, the current understanding of why sleep is an essential part of life is still yet to be determined ¹. The current hypotheses on the function of sleep include ¹⁸:

• Neural maturation
• Facilitation of learning or memory
• Targeted erasure of synapses to “forget” unimportant information that might clutter the synaptic network
• Cognition
• Clearance of metabolic waste products generated by neural activity in the awake brain
• Conservation of metabolic energy.

Wake or Alert Stage

The first stage is the wake stage or stage W, which further depends on whether your eyes are open or closed. During wakefulness, the EEG is characterized by waves of low amplitude and high frequency. This kind of EEG pattern is known as low-voltage fast activity or activated. During eye-open wakefulness, beta waves predominate. Alpha waves (8–13 Hz) become the predominant pattern as you become drowsy and close your eyes, particularly in occipital regions ¹⁹. The Electromyography (EMG, a test that measures the electrical activity of muscles) reveals tonic muscle activity with additional phasic activity related to voluntary movements.

EEG recording: beta waves – highest frequency, lowest amplitude (alpha waves are seen during quiet/relaxed wakefulness)

Non-Rapid Eye Movement (NREM) Sleep Stages

• Stage N1 (Light Sleep): This is the transition between wakefulness and sleep, characterized by slowing heart rate and breathing.
• Stage N2 (Intermediate Sleep): Your heart rate and body temperature decrease further, and your body relaxes.
• Stage N3 (Deep Sleep): This is the deepest stage of Non-Rapid Eye Movement (NREM) sleep, when your body performs restorative work, and it is crucial for feeling rested.

Stage 1 or N1 Sleep

NREM Stage 1 (N1) or Light Sleep serves a transitional role in sleep-stage cycling. This is the lightest stage of sleep and begins when more than 50% of the alpha waves are replaced with low-amplitude mixed-frequency (LAMF) activity. Muscle tone is present in the skeletal muscle, and breathing occurs regularly. This stage lasts around 1 to 7 minutes in the initial cycle, comprising 5% of total sleep time and is easily interrupted by a disruptive noise.

Brain activity on the EEG in stage 1 transitions from wakefulness (marked by rhythmic alpha waves) to low-voltage, mixed-frequency waves. Alpha waves are associated with a wakeful relaxation state and are characterized by a frequency of 8 to 13 cycles per second ⁹.

EEG recording: Theta waves – low voltage.

Stage 2 or N2 Sleep

NREM Stage 2 (N2) represents deeper sleep as the heart rate and body temperature drop ¹. The presence of sleep spindles, K-complexes, or both characterizes it ¹. Sleep spindles are brief, powerful bursts of neuronal firing in the superior temporal gyri, anterior cingulate, insular cortices, and thalamus, inducing calcium influx into cortical pyramidal cells. This mechanism is believed to be integral to synaptic plasticity. Numerous studies suggest that sleep spindles are essential in memory consolidation, specifically procedural and declarative memory ²⁰. Individuals who learn a new task have a significantly higher density of sleep spindles than those in a control group ²¹.

K-complexes are long delta waves that last approximately one second and are known to be the longest and most distinct of all brain waves. K-complexes are shown to function in maintaining sleep and memory consolidation ²².

Stage 2 sleep lasts approximately 10 to 25 minutes in the initial cycle and lengthens with each successive cycle, eventually constituting between 45 to 55 percent of the total sleep episode. Stage 2 sleep is when bruxism (teeth grinding) occurs. An individual in stage 2 sleep requires more intense stimuli than in stage 1 to awaken. Brain activity on an EEG shows relatively low-voltage, mixed-frequency activity characterized by the presence of sleep spindles and K-complexes.

EEG recording: Sleep spindles and K complexes.

Stage 3 or N3 Sleep (Deepest Non-REM Sleep)

Sleep stage 3 or N3 sleep is also known as slow-wave sleep (SWS). This is considered the deepest stage of sleep and is characterized by signals with lower frequencies and higher amplitudes, known as delta waves ¹. Sleep stage 3 or N3 sleep is the most difficult to awaken from; for some people, loud noises (> 100 decibels) will not lead to an awake state ¹. As people age, they spend less time in this slow, delta-wave sleep and more time in stage N2 sleep ¹. Although this stage has the greatest arousal threshold, if someone is awoken during this stage, they will have a transient phase of mental fogginess, known as sleep inertia ¹. Cognitive testing shows that individuals awakened during this stage tend to have moderately impaired mental performance for 30 minutes to 1 hour ²³. Sleep stage 3 or N3 sleep stage is when the body repairs and regrows tissues, builds bone and muscle, and strengthens the immune system. Sleep stage 3 or N3 sleep is also the stage when sleepwalking, night terrors, and bedwetting occur ²⁴.

Sleep stage 3 or N3 sleep lasts only a few minutes and constitutes about 3 to 8 percent of sleep. The EEG shows increased high-voltage, slow-wave activity.

EEG recording: Delta waves – lowest frequency, highest amplitude.

Rapid Eye Movement (REM) Sleep Stage

Rapid eye movement sleep or REM sleep is the fourth and final stage of sleep and is when you have your most vivid and intense dreams. During REM sleep your brain activity increases to near-waking levels, your eyes dart quickly under your eyelids with fluctuating in your breathing and heart rate and most vivid dreams occur in this phase of sleep. Your muscles become limp (atonia) to prevent you from acting out your dreams. EEG recording shows beta waves – similar to brain waves during wakefulness. You experience your first period of REM sleep about 60 to 90 minutes after falling asleep ¹⁶.

REM sleep is defined by the presence of desynchronized (low-voltage, mixed-frequency) brain wave activity, muscle atonia, and bursts of rapid eye movements ⁹. “Sawtooth” wave forms, theta activity (3 to 7 counts per second), and slow alpha activity also characterize REM sleep ⁷. During the initial cycle, the REM period may last only 1 to 5 minutes; however, it becomes progressively prolonged as the sleep episode progresses ⁷.

Most adults need about 2 hours of REM sleep each night, which contributes to brain development, brain function, memory consolidation, and emotional health ²⁵, ²⁶.

Infants and children need more REM sleep, because their brains are still rapidly developing. For example, newborn babies spend around eight hours in REM sleep each day.

How much time you actually spend in REM sleep can vary from night to night. On a night when you’re short of sleep, your total REM time can get cut short. This can trigger your brain to initiate more REM sleep the following night, which is known as a REM rebound ²⁷. Some research also suggests that REM sleep may increase after learning new information ²⁸.

Because REM sleep enables better brain function, memory, and emotional regulation, a lack of REM sleep can cause a range of issues. On top of that, a lack of REM sleep circumvents healthy sleep overall, contributing to sleep deprivation. In the short term, signs of sleep deprivation can include ²⁹:

• Difficulty concentrating
• Excessive daytime sleepiness
• Forgetfulness or poor memory
• Irritability or frustration
• Greater risk of accidents

Over the long term, insufficient sleep can weaken your immune system and raise your risk of conditions like heart disease, diabetes, depression, and anxiety.

How Much Deep Sleep Do I Need?

Different people need different amounts of sleep. Most adults need 7 to 8 hours of sleep a night for good health and mental functioning. Some adults need up to 9 hours a night ³⁰. During a healthy night’s sleep for most adults, deep sleep (stage 3 or N3 sleep) makes up between 10% and 20% of total sleeping time ³¹. People who sleep less than approximately 7 hours a night are at a greater risk for heart disease, stroke, asthma, arthritis, depression, and diabetes. Nearly 20% of all car crashes, both fatal and nonfatal, are attributed to drowsy driving. Without enough sleep, your brain may struggle to perform basic functions. You may find it hard to concentrate or remember things. You may become moody and lash out at co-workers or people you love.

If you’re not sure about how much sleep you really need, you can use an online Sleep Calculator (https://www.sleepfoundation.org/sleep-calculator). However, your doctor is in the best position to make a detailed sleep recommendation for you based on your age, your overall health and your unique situation.

Table 1. Recommended Sleep Duration

	Age Range	Recommended Daily Sleep
Infant	4–12 months	12-16 hours (including naps)
Toddler	1–2 years	11-14 hours (including naps)
Preschool	3–5 years	10-13 hours (including naps)
School-age	6-12 years	9-12 hours
Teens	13-18 years	8-10 hours
Adults	18 years and older	7 or more hours

[Source ³² ]

Just as your brain needs sleep to restore itself, so does your body. When you do not have enough sleep, your risk goes up for several illnesses.

• Diabetes. Your body does not do as well controlling blood sugar when you do not get enough sleep.
• Heart disease. Lack of sleep can lead to high blood pressure and inflammation, two things that can damage your heart.
• Obesity. When you do not get enough rest from sleep, you are more prone to overeat. It is also harder to resist foods high in sugar and fat.
• Infection. Your immune system needs you to sleep so it can fight colds and keep you healthy.
• Mental health. Depression and anxiety often make it hard to sleep. They also can become worse after a string of sleepless nights.

The cancer research branch of the World Health Organization has determined that disruption of regular sleep is “probably carcinogenic to humans”, putting it in the same risk category as the infectious agents malaria and human papillomavirus (HPV), as well as the biochemical weapon mustard gas. Sexual health is affected by sleep deprivation as well, as men with the worst sleeping habits have significantly lower sperm counts, decreased circulating testosterone, and even testicular shrinkage.

Adults generally need about 1.5 to 2 hours of deep sleep per night, which equates to roughly 13-23% of their total recommended sleep time. This stage of sleep is crucial for physical recovery, immune function, and cognitive health, so ensure you are getting sufficient overall sleep and practicing healthy sleep habits to obtain enough deep sleep

Why Deep Sleep is Important?

While all stages of sleep are necessary for good health, deep sleep is important because it is when your body undergoes essential physical restoration, immune system strengthening, and hormone production, while your brain processes and stores memories, consolidates learning, and clears waste products ⁴. During deep sleep, your body works to build and repair tissue, muscles, and bones, including by producing high levels of growth hormone ³³. Achieving sufficient deep sleep helps you wake feeling refreshed, promotes long-term physical and mental health, and supports healthy weight and cardiovascular function ⁴. Deep sleep also promotes immune system functioning. Research suggests that it helps you build stronger immune responses and reduce unwanted chronic inflammation ³⁴.

Slow-wave sleep also helps regulate blood sugar levels. As a result, the risk of developing type 2 diabetes may be higher if you don’t get enough deep sleep ³⁵. And a shortage of deep sleep has also been linked to high blood pressure ³⁶.

Deep sleep is important for cognitive function and memory. Although brain activity slows during deep sleep, this may actually facilitate learning by keeping the brain from becoming oversaturated with information. Evidence suggests that deep sleep also helps eliminate waste material from the brain, which may help protect against dementia ³⁷.

Because deep sleep is an essential component of your nightly rest, a shortage of deep sleep contributes to broader impacts of sleep deprivation. In addition to causing tiredness, a shortage of deep sleep can cause general symptoms of sleep deprivation, including ³⁸:

• Reduced alertness and attention
• Trouble learning and remembering things
• Irritability
• Symptoms of depression or anxiety
• Increased likelihood of accidents and injuries

On top of these immediate effects, a chronic lack of quality sleep can increase the likelihood of multiple health problems, such as:

• Infections and reduced immune system function
• Obesity
• Type 2 diabetes
• Cardiovascular problems, including high blood pressure, stroke, and heart disease
• Kidney disease

If you want to get more deep sleep, focus on enhancing your overall sleep. If your sleep quality and quantity are good, it usually means you’re getting plenty of restorative deep sleep. You get the most deep sleep during the early part of the night.

One of the most reliable ways to improve your sleep is by practicing good sleep hygiene. Good habits include ³⁹:

• Establishing a consistent bedtime and wake-up time
• Ensuring you have a quiet, cool, and dark sleep environment
• Creating a relaxing bedtime routine to wind down in the evening
• Reducing caffeine intake in the afternoon and evening
• Limiting use of mobile devices, tablets, laptops, and other screens for 30 minutes or more before bedtime

There are some additional steps you can try to encourage more deep sleep:

• Take a warm bath: Some research suggests that heating your body with a warm bath before bedtime may induce more slow-wave sleep ⁴⁰. A warm bath raises body temperature, which promotes blood circulation, and the subsequent cooling may help ease the transition to sleep.
• Change your diet: What you eat and drink before bedtime impacts your sleep. One small study found that people eating a diet high in saturated fats obtained less slow-wave sleep ⁴¹. People who ate more fiber were more likely to have increased amounts of deep sleep.
• Listen to binaural beats: Binaural beats are created by listening to two slightly different tones, one in each ear. The difference between the frequencies of those tones creates a perceived third tone, or binaural beat. Limited research suggests that listening to certain binaural beats may contribute to more stage 3 sleep ⁴².

Why is polysomnography sleep study done?

Polysomnography monitors your sleep stages and cycles to identify if or when your sleep patterns are disrupted and why.

The normal process of falling asleep begins with a sleep stage called non-rapid eye movement (NREM) sleep. During this stage, your brain waves, as recorded by electroencephalography (EEG), slow down considerably.

Your eyes don’t move back and forth rapidly during NREM, in contrast to later stages of sleep. After an hour or two of NREM sleep, your brain activity picks up again, and rapid eye movement (REM) sleep begins. Most dreaming occurs during REM sleep.

You normally go through multiple sleep cycles a night, cycling between NREM and REM sleep in about 90 minutes. Sleep disorders can disturb this sleep process.

Your doctor may recommend polysomnography if he or she suspects you have:

• Sleep apnea or another sleep-related breathing disorder. In this condition, your breathing repeatedly stops and starts during sleep.
• Periodic limb movement disorder. In this sleep disorder, you involuntarily flex and extend your legs while sleeping. This condition is sometimes associated with restless legs syndrome.
• Narcolepsy. You experience overwhelming daytime drowsiness and sudden attacks of sleep in this condition.
• REM sleep behavior disorder (parasomnia). This sleep disorder involves acting out dreams as you sleep.
• Unusual behaviors during sleep. Your doctor may perform this test if you do unusual activities during sleep, such as walking, moving around a lot or rhythmic movements.
• Unexplained chronic insomnia. If you consistently have trouble falling asleep or staying asleep, your doctor may recommend polysomnography.

Polysomnography procedure

Whether the polysomnography test is at a sleep study center or at home, you prepare the same way. Unless directed to do so by your doctor, do not take any sleep medicine and do not drink alcohol or caffeinated beverages before the test. They can interfere with your sleep.

How you prepare

You may be advised to avoid drinks or food containing alcohol or caffeine during the afternoon and evening before polysomnography. Alcohol and caffeine can change your sleep patterns, and they may make symptoms of some sleep disorders worse.

Napping in the afternoon before a sleep study is discouraged. You’ll usually be asked to bathe or shower before your sleep study. But don’t put on lotions, gels, colognes or makeup before the test, as these can interfere with the use of the electrodes.

During polysomnography sleep study

You arrive at the sleep center in the evening for polysomnography and stay overnight. You may bring items you use for your bedtime routine, and you can sleep in your own nightclothes.

The room where polysomnography is done is similar to a hotel room, and it’s dark and quiet during the test. You won’t share the room with anyone else. Each room has its own bathroom.

The sleeping area will typically have a low-light video camera, so the polysomnography technologists monitoring you can see what’s happening in the room when the lights are out. It also has an audio system, so they can talk to you and hear you from their monitoring area outside the room.

After you get ready for bed, one of the technologists will place sensors on your scalp, temples, chest and legs using a mild adhesive, such as glue or tape. The sensors are connected by wires to a computer, but the wires are long enough to let you move around in bed. A small clip also is placed on your finger or ear to monitor the level of oxygen in your blood.

While you sleep, a sleep technologist monitors your:

• Brain waves
• Eye movements
• Heart rate
• Breathing pattern
• Blood oxygen level
• Body position
• Chest and abdominal movement
• Limb movement
• Snoring and other noise you may make as you sleep

Polysomnography technologists monitor you throughout the night. If you need assistance, you can talk to them through the monitoring equipment. They can come into the room to detach the wires if you need to get up during the night.

During the study, the technologist may have you try a positive airway pressure (PAP) machine for sleep apnea. This is a device that consists of a tight-sealing nosepiece through which a gentle stream of air is delivered to enhance your breathing.

Continuous positive airway pressure (CPAP) is one type of PAP machine. CPAP devices deliver a constant stream of air that keeps the airway passages open while you sleep.

For some people, bi-level positive airway pressure (biPap or bPap) machines may be a more comfortable choice. These devices deliver more pressure while you’re breathing in, and lower pressure when you exhale.

You may have the opportunity to try on a PAP device before the sleep study begins so that you are not surprised by it if the technologist suggests you try the device later in the night. If necessary, oxygen also may be used during the study to bolster your breathing.

Although you probably won’t fall asleep as easily or sleep as well at the sleep center as you do at home, this usually doesn’t affect the test results. A full night’s sleep isn’t required to obtain accurate polysomnography results.

After polysomnography sleep study

In the morning, the sensors are removed, and you may leave the sleep center. You’re given an appointment for a follow-up visit with the doctor who recommended the test. You can return to your usual activities after polysomnography

Polysomnography sleep study results

The measurements recorded during polysomnography provide a great deal of information about your sleep patterns. For example:

• Brain waves and eye movements during sleep can help your health care team assess your sleep stages and identify disruptions in the stages that may occur due to sleep disorders such as narcolepsy and REM sleep behavior disorder.
• Heart and breathing rate changes and changes in blood oxygen that are abnormal during sleep may suggest sleep apnea.
• Correct settings for positive airway pressure (PAP) or oxygen in case your doctor would like to prescribe these for home use.
• Frequent leg movements that disrupt your sleep may indicate periodic limb movement disorder.
• Unusual movements or behaviors during sleep may be signs of REM sleep behavior disorder or another sleep disorder.

The information gathered during polysomnography is evaluated first by a polysomnography technologist, who uses the data to chart your sleep stages and cycles. Then that information is reviewed by your sleep center doctor.

At a follow-up appointment, your doctor reviews the results with you. Based on the data gathered, your doctor will discuss any treatment or further evaluation that you may need.

The polysomnography test helps diagnose possible sleep disorders, including obstructive sleep apnea (OSA). Your provider may think you have OSA because you have these symptoms:

• Daytime sleepiness (falling asleep during the day)
• Loud snoring
• Periods of holding your breath while you sleep, followed by gasps or snorts
• Restless sleep

Polysomnography can also diagnose other sleep disorders:

• Narcolepsy
• Periodic limb movements disorder (moving your legs often during sleep)
• REM behavior disorder (physically “acting out” your dreams during sleep also called parasomnias)

Normal polysomnography sleep study results

A polysomnography sleep study tracks:

• How often you stop breathing for at least 10 seconds (called apnea)
• How often your breathing is partly blocked for 10 seconds (called hypopnea)
• Your brain waves and muscle movements during sleep

Most people have short periods during sleep where their breathing stops or is partly blocked. The Apnea-Hypopnea Index (AHI) is the number of apnea or hypopnea measured during a sleep study. Apnea-Hypopnea Index (AHI) results are used to diagnose obstructive sleep apnea.

Normal test result show:

• Few or no episodes of stopping breathing. An apnea-hypopnea index (AHI) of less than 5 is considered normal.
• Normal patterns of brain waves and muscle movements during sleep.

What abnormal polysomnography sleep study results mean

In adults, apnea-hypopnea index (AHI) results above 5 may mean you have sleep apnea:

• 5 to 15 is mild sleep apnea
• 15 to 30 is moderate sleep apnea
• More than 30 is severe sleep apnea

To make a diagnosis and decide on treatment, the sleep specialist must also look at:

• Other findings from the sleep study
• Your medical history and sleep-related complaints
• Your physical exam

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