Sleep is more than just closing your eyes; it’s a crucial part of feeling good and staying healthy. If your doctor suspects something might be wrong with your sleep, the most important test they might recommend is a sleep study.
A sleep study offers a detailed look into your sleep patterns and potential issues. While experts can easily interpret the results, for most people, the report can seem like it’s written in a secret code!
In this blog, we’re going to demystify the key terms and phrases in your sleep study report, making it easier to understand. From the complex-sounding “polysomnograms” (try saying that five times fast!) to tricky terms like “hypopneas,” we’ll break it all down together.
Sleep Study Dictionary
Polysomnography (PSG) / Sleep Study
Polysomnography, commonly known as a sleep study, is a test used to diagnose sleep disorders. It simultaneously records brain waves, blood oxygen levels, heart rate, and breathing during sleep, along with eye and leg movements. There are four types of sleep studies:
- Type 1 –A level 1 sleep study, also known as Polysomnography, is conducted exclusively in a sleep lab and continuously monitored in real-time by a Registered Polysomnographic Technologist (RPSGT). It tracks breathing patterns, oxygen levels, heart rate, brain activity, and muscle movements. The only significant difference between level 1 and level 2 studies is that level 1 can diagnose REM Sleep Behavior Disorder.
- Type 2 –A level 2 sleep study is similar to a level 1 study but isn’t monitored by an RPSGT. It can be conducted at home or in a sleep lab or hospital. This comprehensive test is sensitive enough to detect leg and body movements, identify periodic limb movement disorder (PLMD), and provide a detailed analysis of your overall sleep quality and duration.
- Type 3 – A level 3 sleep study, commonly known as a home sleep apnea test (HSAT), is conducted in the comfort of your own home rather than in a sleep lab or hospital. This study involves using a home sleep study kit that monitors breathing patterns, oxygen levels, and heart rate overnight. By analyzing this data, a level 3 sleep study can evaluate snoring, airflow, and determine whether you have obstructive sleep apnea.
- Type 4 – A sleep study with only 1 or 2 channels, usually including oximetry as one of the parameters. This test has limited value.
Sleep Related Breathing Disorder (SRDB) / Sleep-disordered breathing: A sleep-related breathing disorder is a condition where abnormalities in breathing occur during sleep, which may or may not be present while awake. The most common type is Obstructive Sleep Apnea (OSA).
Apnea: Apnea is defined by the American Academy of Sleep Medicine (AASM) as the complete cessation of airflow for at least 10 seconds. Apneas are of three different types
- Obstructive Sleep Apnea
- Central Sleep Apnea
- Mixed Sleep Apnea
Hypopnea: According to American Academy of Sleep Medicine (AASM), hypopnea can be defined based on one of the two below criteria.
- It can either be a reduction in airflow of at least 30% for more than 10 seconds associated with at least 4% oxygen desaturation (Medicare criteria) or
- A reduction in airflow of at least 30% for more than 10 seconds associated with at least 3% oxygen desaturation or an arousal from sleep on EEG (Recommended AASM criteria)
Obstructive Sleep Apnea (OSA): OSA is characterized by episodes of complete (apnea) or partial collapse (hypopnea) of the upper airway, leading to decreased oxygen saturation or arousal from sleep. This results in disruption of normal sleep architecture and is often associated with arterial desaturation.
- To know more about OSA read this article.
- Do you have Obstructive Sleep Apnea? Test it with this 2 minutes online tool.
Apnea-hypopnea index (AHI): The AHI measures the average number of apnea and hypopnea episodes per hour. OSA is represented by an AHI of more than 5/hour. OSA syndrome is defined as an AHI of 5 and above, with accompanying symptoms during the day or night. Based on the AHI, the disease severity of OSA is classified as below
- In adults –
- Mild OSA – AHI between 5-15,
- Moderate – AHI 15-30,
- Severe – AHI 30 and above.
- In kids –
- Mild OSA – AHI between 1-5,
- Moderate – AHI 5-15,
- Severe – AHI 15 and above
Upper Airway Resistance Syndrome (UARS): Patients with symptoms of OSA and evidence of sleep fragmentation on PSG, but with no or minimal obstructive apneas/hypopneas and no desaturation.
Respiratory Effort Related Arousal (RERA): An event characterized by increasing respiratory effort for 10 seconds or longer, leading to an arousal from sleep, but not meeting the criteria for hypopnea or apnea.
Respiratory Disturbance Index (RDI): Defined as the average number of respiratory disturbances (apneas, hypopneas, and respiratory event-related arousals [RERAs]) per hour. More specific than AHI.
Oxygen Desaturation Index (ODI): The number of times oxygen saturation falls by 4% or more, averaged out per hour. An ODI greater than 15 suggests OSA.
Sleep studies are powerful tools that offer detailed insights into your sleep health, helping to identify disorders like obstructive sleep apnea and others. By breaking down the jargon, this guide aims to make your sleep study results more accessible, empowering you to take informed steps toward better sleep and overall well-being.
If you have any questions about your report, don’t hesitate to consult a doctor specialized in sleep medicine —they’re there to help you navigate your path to healthier sleep.