Polysomnography (Sleep Study): A Comprehensive Guide
Polysomnography (PSG), commonly known as a sleep study, is a comprehensive test used to diagnose sleep disorders. It records your brain waves, eye movements, muscle activity, heart rate, breathing patterns, and blood oxygen levels while you sleep. This information helps doctors identify any abnormalities in your sleep that may be contributing to sleep problems or other medical conditions. This article provides a detailed overview of polysomnography, including its purpose, types, what to expect, what it measures, how the results are used, and preparation tips.
Understanding what a sleep study entails can help alleviate anxiety and ensure you get the most accurate results.
Polysomnography (Sleep Study): A Comprehensive Guide
Purpose of a Sleep Study
A sleep study is used to diagnose a variety of sleep disorders, including:
Sleep Disorders Diagnosed by PSG
- Sleep Apnea: A condition in which breathing repeatedly stops and starts during sleep.
- Obstructive Sleep Apnea (OSA)
- Central Sleep Apnea (CSA)
- Complex Sleep Apnea Syndrome (CompSAS)
- Narcolepsy: A neurological disorder that causes excessive daytime sleepiness and sudden sleep attacks.
- Restless Legs Syndrome (RLS): A condition that causes an irresistible urge to move the legs, often accompanied by unpleasant sensations.
- REM Sleep Behavior Disorder (RBD): A condition in which people act out their dreams during REM sleep.
- Insomnia: Difficulty falling asleep, staying asleep, or getting restful sleep. (While PSG is not always necessary to diagnose insomnia, it can be helpful in ruling out other sleep disorders that may be contributing to insomnia.)
- Periodic Limb Movement Disorder (PLMD): Repetitive limb movements during sleep that can disrupt sleep.
- Parasomnias: Undesirable physical events or experiences that occur during sleep, such as sleepwalking, sleep terrors, and nightmares.
Types of Sleep Studies
There are two main types of sleep studies:
1. In-Lab Sleep Study (Polysomnography, PSG)
- Performed in a sleep lab or hospital: This is the traditional and most comprehensive type of sleep study.
- Overnight Stay: You’ll spend the night in a private room at the sleep center.
- Comprehensive Monitoring: A sleep technician will attach various sensors to your body to monitor your brain waves, eye movements, muscle activity, heart rate, breathing patterns, and blood oxygen levels throughout the night.
- Technician Supervision: A sleep technician will be present throughout the night to monitor the equipment and assist you if needed.
- Used to Diagnose a Wide Range of Sleep Disorders:
2. Home Sleep Apnea Test (HSAT)
- Performed at home: You’ll use a portable monitoring device to record data while you sleep in your own bed.
- Less Comprehensive: HSATs typically measure fewer parameters than in-lab studies, usually focusing on breathing patterns, heart rate, and blood oxygen levels.
- Primarily for Diagnosing Obstructive Sleep Apnea (OSA): HSATs are not suitable for diagnosing other sleep disorders.
- More Convenient and Less Expensive: Than in-lab studies.
- Not Suitable for Everyone: People with certain medical conditions (e.g., heart failure, lung disease) or those who are suspected of having a sleep disorder other than OSA may need an in-lab study.
What to Expect During an In-Lab Sleep Study (PSG)
If you’re scheduled for an in-lab sleep study, here’s a detailed breakdown of what you can typically expect:
Before the Study
- Instructions: You’ll receive detailed instructions from the sleep center about what to do before the study. This may include:
- Avoiding caffeine and alcohol on the afternoon and evening of the study.
- Avoiding napping on the day of the study.
- Following your usual medication routine, unless otherwise instructed by your doctor.
- Showering before arriving at the sleep center (avoid using lotions, oils, or makeup on your hair or skin).
- Medications: Discuss all your medications (prescription and over-the-counter) with your doctor. You may need to stop taking certain medications before the study, but *never* stop taking a medication without your doctor’s approval.
- What to Bring:
- Comfortable sleepwear (pajamas)
- Toiletries (toothbrush, toothpaste, etc.)
- Anything else you need for a comfortable night’s stay (e.g., your own pillow, a book, a favorite blanket)
- Any medications you normally take at night
During the Study
- Arrival and Check-In: You’ll typically arrive at the sleep center in the evening (usually a few hours before your normal bedtime). You’ll check in and be shown to your private room.
- Room Setup: The room will likely resemble a hotel room, with a bed, a nightstand, and a bathroom. There will also be monitoring equipment in the room.
- Sensor Application: A sleep technician will attach various sensors to your body. These sensors are usually painless and non-invasive. The process typically takes 30-60 minutes.
- Electrodes on your scalp (EEG): Small, flat metal discs (electrodes) will be attached to your scalp with a conductive paste or adhesive to measure brain waves.
- Electrodes near your eyes (EOG): Electrodes will be placed near your eyes to measure eye movements.
- Electrodes on your chin and legs (EMG): Electrodes will be placed on your chin and legs to measure muscle activity.
- Electrodes on your chest (ECG): Electrodes will be placed on your chest to measure heart rate and rhythm.
- Belts around your chest and abdomen: Elastic belts will be placed around your chest and abdomen to measure breathing effort.
- A nasal cannula or sensor near your nose and mouth: A small tube (nasal cannula) or a sensor will be placed near your nose and mouth to measure airflow.
- A clip on your finger (pulse oximeter): A small clip will be placed on your finger to measure blood oxygen levels.
- Calibration: Once the sensors are in place, the technician will ask you to perform some simple tasks (e.g., blinking your eyes, moving your legs) to calibrate the equipment.
- Monitoring: The technician will monitor you throughout the night from a separate room. They will be able to see and hear you, and you will be able to communicate with them if needed.
- Sleep: You’ll be encouraged to sleep as normally as possible. The room will be dark and quiet.
- Video and Audio Recording: The sleep study may be video and audio recorded to help the sleep specialist interpret the data.
- Bathroom Breaks: If you need to go to the bathroom during the night, you can simply call for the technician, who will disconnect the sensors so you can go.
After the Study
- Wake-Up: The technician will wake you up in the morning, usually around your normal wake-up time.
- Sensor Removal: The sensors will be removed. This may involve some pulling on the skin, but it should not be painful.
- Departure: You can usually leave the sleep center after a brief period of observation. You may be asked to complete a questionnaire about your sleep.
- Results: The sleep study data will be analyzed by a sleep specialist (a doctor who specializes in sleep disorders), and the results will be sent to your doctor. This typically takes 1-2 weeks.
What to Expect During a Home Sleep Apnea Test (HSAT)
- Instructions: You will receive detailed instructions from your doctor or a sleep specialist on how to use the portable monitoring device. You may pick up the device from a clinic or have it mailed to you.
- Setup: You will apply the sensors yourself before going to sleep. The sensors typically include:
- A nasal cannula or sensor to measure airflow.
- A belt around your chest to measure breathing effort.
- A clip on your finger to measure blood oxygen levels.
- Possibly a sensor to measure heart rate and body position.
- Sleep: You will sleep in your own bed, as you normally would.
- Return: The next day, you will return the device to the clinic or doctor’s office, or mail it back according to the instructions provided.
- Results: The data from the device will be downloaded and analyzed by a sleep specialist, and the results will be sent to your doctor.
What Does a Sleep Study Measure?
A sleep study measures various physiological parameters during sleep, providing a detailed picture of your sleep patterns and any abnormalities.
Parameters Measured (In-Lab PSG)
- Brain Waves (EEG – Electroencephalogram):
- Electrodes placed on the scalp record the electrical activity of the brain.
- Different brain wave patterns correspond to different stages of sleep (wakefulness, light sleep, deep sleep, REM sleep).
- Helps identify sleep stages and detect any abnormalities in brain activity during sleep.
- Eye Movements (EOG – Electrooculogram):
- Electrodes placed near the eyes record eye movements.
- Helps identify REM (rapid eye movement) sleep, a stage of sleep associated with dreaming.
- Muscle Activity (EMG – Electromyogram):
- Electrodes placed on the chin and legs record muscle activity.
- Chin EMG helps identify sleep stages (muscle tone decreases during REM sleep).
- Leg EMG can detect leg movements associated with restless legs syndrome (RLS) or periodic limb movement disorder (PLMD).
- Heart Rate and Rhythm (ECG – Electrocardiogram):
- Electrodes placed on the chest record the electrical activity of the heart.
- Monitors heart rate and rhythm during sleep.
- Can detect arrhythmias (irregular heartbeats) that may be related to sleep disorders.
- Breathing Effort:
- Elastic belts placed around the chest and abdomen measure the movement of the chest and abdomen during breathing.
- Helps identify respiratory events, such as apneas (pauses in breathing) and hypopneas (shallow breathing).
- Airflow:
- A nasal cannula (a small tube that fits into the nostrils) or a sensor placed near the nose and mouth measures the flow of air in and out of the lungs.
- Helps identify apneas and hypopneas.
- Blood Oxygen Levels (Pulse Oximetry):
- A small clip (pulse oximeter) placed on a finger measures the percentage of oxygen in the blood.
- Detects drops in oxygen levels (desaturations) that occur during apneas and hypopneas.
- Body Position: A sensor may be used to track your body position during sleep (e.g., on your back, side, or stomach).
- Snoring: A microphone may be used to record snoring sounds.
Parameters Measured (Home Sleep Apnea Test)
- Airflow
- Breathing Effort
- Blood Oxygen Levels
- Heart Rate (often)
- Body Position (sometimes)
How are Sleep Study Results Used?
The data collected during a sleep study is analyzed by a sleep specialist. The results are used to:
Uses of Sleep Study Results
- Diagnose Sleep Disorders: The sleep specialist will look for patterns and abnormalities in the data to diagnose sleep disorders such as sleep apnea, narcolepsy, restless legs syndrome, REM sleep behavior disorder, and insomnia.
- Determine the Severity of Sleep Apnea: The Apnea-Hypopnea Index (AHI) is calculated, which is the number of apneas and hypopneas per hour of sleep. The AHI is used to classify the severity of sleep apnea:
- Normal: AHI < 5
- Mild Sleep Apnea: AHI 5-15
- Moderate Sleep Apnea: AHI 15-30
- Severe Sleep Apnea: AHI > 30
- Guide Treatment Decisions: The results of the sleep study help determine the most appropriate treatment plan. For example, if sleep apnea is diagnosed, the sleep study can help determine the optimal CPAP pressure.
- Monitor the Effectiveness of Treatment: Follow-up sleep studies may be performed to assess the effectiveness of treatment and make adjustments as needed.
Preparing for a Sleep Study
To ensure accurate results, follow these guidelines when preparing for a sleep study:
- Avoid caffeine and alcohol on the afternoon and evening of the study.
- Avoid napping on the day of the study.
- Follow your usual medication routine, unless otherwise instructed by your doctor.
- Shower before arriving at the sleep center (for an in-lab study) and avoid using lotions, oils, or makeup on your hair or skin.
- Bring comfortable sleepwear, toiletries, and anything else you need for a comfortable night’s stay (e.g., your own pillow, a book).
- Inform the sleep center staff about any medical conditions you have or medications you are taking.
- Arrive on time for your appointment.
- Relax and try to sleep as normally as possible.
FAQ – Frequently Asked Questions About Sleep Studies
Q1. Will I be able to sleep during the sleep study?
A1. Many people worry about this, but most people are able to fall asleep and get enough sleep for the study to be useful. Sleep centers are designed to be as comfortable as possible, and the technicians are trained to help you feel relaxed.
Q2. What if I have to go to the bathroom during the night?
A2. If you need to go to the bathroom during an in-lab sleep study, you can simply call for the technician, who will disconnect the sensors so you can go. For a home sleep study, you can usually disconnect the sensors yourself.
Q3. How long does it take to get the results of a sleep study?
A3. It typically takes 1-2 weeks to get the results of a sleep study. The data needs to be analyzed by a sleep specialist, and a report needs to be generated.
Q4. Are sleep studies covered by insurance?
A4. Most insurance plans cover sleep studies, but it’s always a good idea to check with your insurance provider beforehand to confirm coverage and any out-of-pocket costs.
Q5. What’s the difference between a sleep study and a CPAP titration study?
A5:
- Sleep Study (Diagnostic PSG): Used to *diagnose* sleep disorders.
- CPAP Titration Study: Used to determine the optimal CPAP pressure for treating sleep apnea. During a titration study, the CPAP pressure is gradually increased throughout the night until apneas and hypopneas are eliminated. A titration study is *only* done if a diagnostic study has already confirmed sleep apnea. Sometimes a “split-night” study is done, where the first part of the night is diagnostic, and if sleep apnea is found, CPAP titration is done during the second part of the night.
Conclusion: Unlocking the Secrets of Your Sleep
A sleep study is a valuable tool for diagnosing and managing sleep disorders. If you’re experiencing symptoms of a sleep disorder, such as excessive daytime sleepiness, loud snoring, or difficulty falling asleep or staying asleep, talk to your doctor about whether a sleep study is right for you. Getting a proper diagnosis is the first step towards improving your sleep and overall health.