Sleep study test polysomnography vector

Sleep Study: Overview and Practice Questions (2024)

by | Updated: Jun 12, 2024

A sleep study, or polysomnography, is a critical diagnostic tool used by medical professionals to assess sleep patterns and identify various sleep disorders.

This comprehensive test monitors several physiological parameters such as brain waves, breathing patterns, heart rate, and muscle activity.

These studies are important because they can provide insights into the underlying causes of sleep-related disturbances, which can significantly impact a person’s health and quality of life.

This article provides a comprehensive overview of sleep studies, including how they’re used to diagnose and treat various sleep disorders.

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What is a Sleep Study?

A sleep study, also known as polysomnography, is a comprehensive test that records various physiological activities during sleep to diagnose sleep disorders. It tracks brain waves, oxygen levels, heart rate, breathing, and eye and leg movements to assess issues like sleep apnea, insomnia, and restless legs syndrome.

Sleep study lab patient polysomnography vector


Sleep studies are typically indicated for diagnosing and managing various sleep-related disorders. Common indications include:

  • Sleep Apnea: Suspected obstructive or central sleep apnea characterized by breathing interruptions during sleep.
  • Restless Legs Syndrome (RLS): Uncontrollable urges to move the legs while resting, often accompanied by uncomfortable sensations.
  • Insomnia: Difficulty falling or staying asleep that affects daily functioning.
  • Narcolepsy: Excessive daytime sleepiness combined with sudden muscle weakness (cataplexy) and unexpected lapses into REM sleep.
  • Periodic Limb Movement Disorder (PLMD): Frequent involuntary movements of the limbs during sleep.
  • Parasomnias: Unusual behaviors during sleep, such as sleepwalking, night terrors, or REM sleep behavior disorder.
  • Unexplained Chronic Snoring: Evaluation of snoring that may indicate a more serious condition like sleep apnea.
  • Shift Work Sleep Disorder: Problems sleeping or staying alert due to work schedules that conflict with natural sleep rhythms.
  • Unexplained Daytime Sleepiness: Persistent sleepiness during the day that interferes with daily activities, not explained by other medical conditions.

Note: These studies help in making accurate diagnoses and formulating effective treatment plans for sleep-related issues.

How Does a Sleep Study Work?

A sleep study, typically conducted in a sleep lab or sometimes at home with portable equipment, involves several steps to monitor and analyze sleep patterns and behaviors:

  • Preparation: Before the study, you’ll usually meet with a sleep specialist who reviews your symptoms and medical history. You’ll receive instructions on how to prepare, such as avoiding caffeine and napping on the day of the study.
  • Setup: In a sleep lab, a sleep technologist will attach sensors to your body. These include electrodes on your scalp, face, and legs to measure electrical signals from the brain and muscle activity, as well as belts around your chest and abdomen to monitor breathing. An oximeter on your finger will track your oxygen levels and heart rate.
  • Monitoring: As you sleep, the equipment records several types of data, including brain waves, muscle activity, eye movement, heart rate, breathing interruptions, and oxygen saturation.
  • Analysis: A sleep specialist examines the recorded data to identify any abnormalities in sleep architecture or the presence of sleep disorders. This analysis helps in understanding the quality and quantity of sleep stages and diagnosing conditions like sleep apnea, restless legs syndrome, or other sleep-related issues.
  • Follow-up: After the study, you’ll have a follow-up appointment where the specialist will discuss the results with you and recommend treatments or lifestyle changes based on the findings.

Note: Home sleep tests are less comprehensive but can be effective for diagnosing obstructive sleep apnea. They typically measure breathing, oxygen levels, and heart rate.

What is Monitored During a Sleep Study?

During a sleep study, several physiological parameters are monitored to assess sleep quality and identify any sleep disorders.

The typical measurements taken include:

  • Electroencephalogram (EEG): This records brain wave activity to determine sleep stages, including deep sleep and REM (rapid eye movement) sleep.
  • Electrooculogram (EOG): This measures eye movements that are important for identifying REM sleep, where dreams typically occur.
  • Electromyogram (EMG): Muscle activity is recorded, particularly the lack of muscle tone that occurs during REM sleep. EMG also monitors leg movements to check for conditions like periodic limb movement disorder.
  • Electrocardiogram (EKG): Heart rate and rhythm are monitored to detect any abnormalities that may occur during sleep.
  • Respiratory Effort and Airflow: Sensors placed around the chest and abdomen measure the effort made to breathe, and nasal airflow sensors detect the airflow through the nose and mouth to identify breathing interruptions characteristic of sleep apnea.
  • Oxygen Saturation: A pulse oximeter attached to the finger monitors how well oxygen is being transported to the extremities away from the heart, helping to assess if breathing stops or becomes shallow during sleep.
  • Body Position: Monitors determine the position of the body throughout the night, as some sleep disorders are position-dependent (e.g., worse in the supine position).
  • Snoring: A microphone may be used to record snoring, which can indicate sleep apnea or other breathing problems during sleep.

Note: These measurements collectively help to provide a comprehensive view of the sleeper’s physiological state during the night, enabling healthcare providers to diagnose and manage sleep disorders effectively.

Sleep Study Practice Questions

1. What is the definition of a sleep study?
A noninvasive clinical assessment of sleep in which the patient is monitored while spending the night in a sleep lab.

2. What is polysomnography?
Polysomnography is a comprehensive sleep study used to diagnose sleep disorders.

3. What does polysomnography record?
It records brain waves, eye movements, muscle activity, heart rate, respiratory effort, oxygen levels, and body position.

4. What measures brain waves?
An EEG (electroencephalogram) measures brain waves.

5. What measures muscle activity?
An EMG (electromyogram) measures muscle activity.

6. What measures heart rate and rhythm?
An ECG (electrocardiogram) measures heart rate and rhythm.

7. What is sleep physiology?
Sleep physiology refers to the study of the physical and biological processes associated with sleep and its stages.

8. What part of the brain controls sleep?
The hypothalamus primarily controls sleep, along with interactions from other brain regions like the brainstem and thalamus.

9. What is hypersomnolence?
Hypersomnolence refers to excessive daytime sleepiness, regardless of sufficient nighttime sleep.

10. What is an EEG?
An EEG, or electroencephalogram, is a test that measures the electrical activity of the brain.

11. What are the types of sleep apnea?
The types of sleep apnea include obstructive sleep apnea, central sleep apnea, and mixed sleep apnea.

12. What is mixed sleep apnea?
Mixed sleep apnea is a combination of both obstructive sleep apnea and central sleep apnea.

13. What is hypopnea?
Hypopnea is a partial obstruction of breathing during sleep, characterized by a significant reduction in airflow.

14. What is narcolepsy?
Narcolepsy is a sleep disorder characterized by excessive daytime sleepiness, often accompanied by sudden muscle weakness (cataplexy) and other REM sleep disturbances.

15. What should the patient avoid before a sleep study?
Caffeine and naps

16. What is a home sleep test?
A home sleep test is a simplified version of polysomnography done at home to primarily assess for obstructive sleep apnea.

17. What does a pulse oximeter measure?
A pulse oximeter measures the level of oxygen saturation in the blood.

18. What is REM sleep behavior disorder?
REM sleep behavior disorder is a sleep condition where individuals physically act out vivid dreams during REM sleep, typically due to lack of muscle paralysis.

19. What is the role of a sleep technologist?
A sleep technologist sets up the monitoring equipment, ensures its proper function during the study, and assists in the initial interpretation of the data collected.

20. What is the significance of body position in a sleep study?
Body position is monitored because some sleep disorders, particularly obstructive sleep apnea, can be position-dependent and worsen when lying on the back.

21. How is snoring assessed during a sleep study?
Snoring is assessed using a microphone that records the intensity and pattern of snoring, which can indicate the presence of sleep apnea.

22. What are sleep spindles?
Sleep spindles are sudden bursts of oscillatory brain activity visible on an EEG that occur during stage 2 of non-REM sleep and are thought to play a role in memory consolidation and learning.

23. What is a split-night study?
A split-night study combines diagnostic testing and CPAP (continuous positive airway pressure) titration in one night, first diagnosing sleep apnea and then adjusting CPAP levels if necessary.

24. What is CPAP titration?
CPAP titration is the process of finding the most effective CPAP pressure to keep the airways open during sleep, often conducted during the second part of a split-night study or a separate night.

25. How do sleep studies diagnose insomnia?
Sleep studies diagnose insomnia by measuring various sleep parameters like latency to sleep onset, frequency of awakenings, and total sleep time, helping to understand sleep patterns and rule out other sleep disorders.

26. What role do thermistors play in a sleep study?
Thermistors measure the temperature changes related to breathing patterns to detect airflow disruptions that occur during sleep.

27. Why are sleep stages important in a sleep study?
Analyzing sleep stages helps determine the quality of sleep and diagnose various sleep disorders by showing the distribution and timing of different sleep phases, including deep sleep and REM sleep.

28. What is periodic limb movement during sleep?
Periodic limb movement during sleep involves repeated muscle twitches, jerks, or spasms, usually in the legs, that occur at regular intervals, potentially causing sleep disturbances.

29. How does a sleep study detect circadian rhythm disorders?
A sleep study can help detect circadian rhythm disorders by recording the timing of various sleep phases, which may be delayed or advanced, helping to diagnose conditions like delayed sleep phase disorder.

30. What is actigraphy?
Actigraphy uses a wearable device that monitors movement to estimate sleep patterns over several days to weeks, often used for assessing sleep habits and circadian rhythm disorders outside of a sleep lab.

31. What is the significance of delta waves in a sleep study?
Delta waves are the slowest and highest amplitude brain waves, prominent during deep sleep (non-REM stage 3), and are important for assessing sleep depth and quality.

32. How are audio recordings used in sleep studies?
Audio recordings are used to capture snoring and breathing sounds, which are analyzed to detect sleep apnea and other respiratory or sleep-related disorders.

33. What factors can influence the accuracy of a sleep study?
Factors such as the sleep environment, adherence to pre-study instructions, the presence of medical conditions, and even the type of equipment used can influence the accuracy and outcomes of a sleep study.

34. What is sleep architecture?
Sleep architecture refers to the structure of different sleep stages over the course of the night, including the cyclic alternation between REM and non-REM sleep.

35. How is total sleep time calculated in a sleep study?
Total sleep time is calculated by summing all periods of sleep (excluding awakenings) throughout the duration of the sleep study.

36. What is sleep efficiency?
Sleep efficiency is a measure calculated by dividing the total sleep time by the total time spent in bed, expressed as a percentage, to assess the effectiveness of sleep during the study.

37. What does an irregular sleep-wake rhythm indicate in a sleep study?
An irregular sleep-wake rhythm typically indicates a type of circadian rhythm sleep disorder where sleep episodes are fragmented and occur at irregular times over a 24-hour period.

38. How are respiratory disturbances scored in a sleep study?
Respiratory disturbances are scored by observing reductions (hypopneas) or cessations (apneas) in breathing, with their impact on oxygen saturation and arousal from sleep being particularly noted.

39. What is an arousal index?
The arousal index is a measure used in sleep studies to indicate the number of times a person wakes up per hour of sleep, helping to evaluate sleep continuity and quality.

40. What is the difference between Type I and Type II sleep studies?
Type I sleep studies are full polysomnographies conducted in a lab with extensive monitoring, while Type II sleep studies are comprehensive but can be conducted at home with fewer channels of data.

41. How does a sleep study differentiate between obstructive and central sleep apnea?
The study differentiates these conditions based on respiratory effort: obstructive sleep apnea shows persistent effort despite airflow blockage, whereas central sleep apnea is marked by a lack of respiratory effort during episodes.

42. What is a hypnogram?
A hypnogram is a graphical representation of the different sleep stages throughout a sleep study, showing how a person cycles through stages of sleep, including light sleep, deep sleep, and REM periods.

43. Is a sleep study a diagnostic or therapeutic test?
A sleep study is primarily a diagnostic test used to identify sleep disorders, though it can have therapeutic aspects, such as CPAP titration.

44. What if a patient is nervous during a sleep study?
If a patient is nervous, technicians can help by explaining the process thoroughly, ensuring comfort with the environment, and sometimes using relaxation techniques or allowing a familiar item from home.

45. What disorders can a sleep study detect?
Sleep studies can detect disorders such as sleep apnea, narcolepsy, restless legs syndrome, periodic limb movement disorder, and various forms of insomnia and parasomnias.

46. How long does a patient need to sleep during a sleep study?
Ideally, a patient should sleep for at least 6-7 hours during a sleep study to ensure that sufficient data across all sleep stages is collected, though some meaningful data can often be gathered in shorter durations.

47. Can a patient lay on their stomach during a sleep study?
Yes, a patient can lay on their stomach during a sleep study. The equipment is adaptable to different sleeping positions to accurately record sleep data.

48. When should you recommend a sleep study for a patient?
A sleep study should be recommended when a patient exhibits symptoms of a sleep disorder, such as excessive daytime sleepiness, chronic snoring, observed apneas, or unrefreshing sleep, especially if these symptoms impact their daily life.

49. How is sleep related to the respiratory system?
Sleep significantly affects the respiratory system; during sleep, breathing patterns change, and disorders like sleep apnea directly involve respiratory function disruptions, impacting overall health.

50. What is the role of a respiratory therapist during a sleep study?
A respiratory therapist during a sleep study may assist in managing and monitoring equipment related to breathing, such as CPAP machines, and evaluating respiratory-related data to help diagnose and treat sleep-related breathing disorders.

Final Thoughts

A sleep study is an invaluable procedure for diagnosing patients with various sleep disorders.

By recording and analyzing physiological data while a patient sleeps, healthcare providers can tailor specific treatments and interventions to improve sleep quality and overall health.

The insights gained from these studies not only help in managing symptoms but also in enhancing the long-term well-being of individuals suffering from sleep-related issues.

John Landry, BS, RRT

Written by:

John Landry, BS, RRT

John Landry is a registered respiratory therapist from Memphis, TN, and has a bachelor's degree in kinesiology. He enjoys using evidence-based research to help others breathe easier and live a healthier life.


  • Gerstenslager B, Slowik JM. Sleep Study. [Updated 2023 Aug 14]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024.

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