Colin Snow
The Respiratory Event Index (REI) is a measure sometimes used in home sleep studies to indicate the number of apneas or hypopneas recorded during the study per hour of device recording time. It is often used as an alternative to the Apnea-Hypopnea Index (AHI), which is a scale to measure the symptoms of sleep apnea. Sleep apnea is a condition where the tongue or tissues in the airways block airflow or challenges are related to the signals sent from the brain to control breathing during sleep. The AHI is the total number of times a person experiences apneas and hypopneas in one night, divided by the total number of hours of sleep. The REI is calculated based on the total analyzed time (TAT) rather than the total sleep time (TST), which can lead to an underestimation of the severity of sleep apnea.
| Characteristics | Values |
|---|---|
| Full Form | Respiratory Event Index |
| Used In | Home sleep study |
| Definition | Number of apneas or hypopneas recorded during the study per hour of device recording time |
| Compared To | Apnea-Hypopnea Index (AHI) |
| Difference From AHI | REI includes all apnea and hypopnea events during the sleep study, not just those that occur while the person is sleeping |
| Severity of OSA Based on REI | 42.1% and 72.8% for two datasets |
| REI-TRT vs REI-ACTI | Statistically significant difference, but clinically negligible |
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What You'll Learn
REI is the Respiratory Event Index
The AHI is the total number of times a person experiences apneas and hypopneas in one night, divided by the total number of hours of sleep. The result is the average number per hour. For example, a person with an AHI of 12 experiences an average of 12 episodes of apneas or hypopneas for each hour of sleep. This means that their breathing was either reduced by at least 30% or stopped completely for at least 10 seconds, 12 times per hour.
The REI is the number of apneas or hypopneas recorded during the study per hour of device recording time. Because the recording time is often more than the time spent asleep, the REI can sometimes underestimate the AHI. The REI is calculated based on the total analysed time (TAT) or total bedtime instead of the total sleep time (TST).
The Respiratory Disturbance Index (RDI) is another measure that is similar to the AHI because it includes apneas and hypopneas. However, the RDI also includes the number of times per hour a person is awakened or shifts to a more awake stage of sleep because they are having breathing difficulties.
Several studies have found that REI underestimates the severity of sleep apnea compared to the AHI. The REI had the lowest sensitivities (42.1% and 72.8%) and specificities (80.7% and 90.9%) in both datasets. However, one study found that there was no meaningful difference in the respiratory event index calculated using the actigraph estimated sleep time versus the total recording time.
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REI is used in home sleep studies
The Respiratory Event Index (REI) is a measure used in home sleep studies. It is often used as an alternative to the Apnea-Hypopnea Index (AHI) in sleep testing. While AHI is the standard measure for diagnosing sleep apnea, REI is often used in home sleep studies due to its simpler and more convenient nature.
REI is a measure of the number of apneas or hypopneas recorded during a sleep study per hour of device recording time. Apnea refers to a reduction in breathing to 10% of normal or less, including when breathing stops completely. Hypopnea refers to a reduction in breathing by at least 30%. These breathing irregularities can be caused by obstructions in the airways, such as the tongue or tissues, or issues with the signals sent from the brain to control breathing during sleep.
The key difference between REI and AHI is that REI includes all apnea and hypopnea events during the study, not just those that occur while the person is asleep. This means that REI is based on the total analysed time (TAT) or total recording time, whereas AHI is based on the total sleep time (TST). This distinction is important because the recording time in a home sleep study is often more than the time spent asleep, which can lead to an underestimation of the AHI.
However, it is important to note that REI tends to underestimate the severity of sleep apnea compared to AHI. This is because portable sleep monitoring devices used in home studies, such as polygraphy (PG), typically lack electroencephalography (EEG) sensing modalities. As a result, it is challenging to accurately estimate the total sleep time (TST) and identify hypopneas associated with arousals. Therefore, the severity of sleep apnea based on PG is often estimated using TAT or total bedtime, leading to a lower REI value compared to AHI.
Despite the tendency for REI to underestimate AHI, it still provides valuable information for assessing sleep apnea. In some cases, the difference between REI and AHI may not be significant enough to affect diagnostic decisions. Additionally, REI can be a reasonable alternative for individuals who prefer the convenience of a home sleep study or those with high pre-test likelihoods of moderate to severe OSA.
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REI measures apneas and hypopneas
The Respiratory Event Index (REI) is a metric used in sleep studies to measure the number of apneas and hypopneas a person experiences during sleep. Apneas and hypopneas are types of breathing disruptions where the airway becomes partially or fully blocked, leading to a reduction or cessation of airflow.
During a sleep study, the REI is calculated by counting the number of apneas and hypopneas that occur per hour of device recording time. This information is captured by monitoring devices, such as polysomnography (PSG) or portable devices like polygraphy (PG).
However, it is important to note that the REI may underestimate the true severity of sleep apnea compared to the Apnea-Hypopnea Index (AHI). This is because the recording time for REI includes periods when the person may not be asleep, resulting in a lower number of events per hour. On the other hand, AHI is calculated based on the total sleep time, providing a more accurate representation of breathing disruptions specifically during sleep.
The AHI is a crucial tool in diagnosing and determining the severity of obstructive sleep apnea (OSA). It is calculated by adding up all the apneas and hypopneas that occur during sleep and dividing that number by the total sleep time. A higher AHI score tends to reflect more severe OSA, and it is used to classify the condition as mild, moderate, or severe.
In summary, while REI measures apneas and hypopneas by counting these events per hour of device recording time, it is important to also consider AHI, which provides a more accurate indication of the severity of OSA by taking into account the total sleep time.
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REI underestimates AHI
The Respiratory Event Index (REI) is the number of apneas or hypopneas recorded during a sleep study per hour of device recording time. It is often used in home sleep studies to indicate the severity of obstructive sleep apnea. However, several studies have found that REI underestimates the Apnea-Hypopnea Index (AHI).
The underestimation of REI compared to AHI can be attributed to several factors. Firstly, REI is calculated based on total analysed time (TAT) or total recording time (TRT), while AHI is based on total sleep time (TST). This discrepancy in calculation methods can lead to an overestimation of sleep time and an underestimation of the number of respiratory events in REI, resulting in a lower index value.
Secondly, portable sleep monitoring devices used in home sleep studies often lack electroencephalography (EEG) sensing modalities. This limitation affects the accuracy of REI as it relies on TAT or TRT instead of TST. Without EEG, it is challenging to estimate TST and score arousals and related hypopneas accurately. As a result, the severity of sleep apnea may be underestimated when using REI.
Furthermore, studies have found that arousal-related hypopneas play a crucial role in accurately classifying the severity of obstructive sleep apnea. However, since REI does not consider these arousals, it may underestimate the true severity of the condition.
The underestimation of REI compared to AHI has significant implications for patient care. In one study, more than 50% of patients were classified into a less severe OSA group when using REI, and some individuals with moderate to severe OSA were classified into no-OSA or mild OSA groups. This underestimation could lead to underdiagnosis and inappropriate treatment decisions, highlighting the need for caution when using REI as a substitute for AHI.
While REI tends to underestimate AHI, it is important to note that AHI also has limitations. For example, AHI has been found to have a poor correlation with OSA-associated symptoms such as daytime sleepiness. Therefore, further studies are necessary to understand the relationship between these measurements and clinical symptoms fully.
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REI is calculated based on total analysed time (TAT)
The Respiratory Event Index (REI) is a measure that is sometimes used instead of the Apnea-Hypopnea Index (AHI) in home sleep testing. REI includes all the apnea and hypopnea events during the sleep study, not just those that happen while the person is sleeping.
The AHI is the total number of times a person experiences apneas and hypopneas in one night, divided by the total number of hours of sleep. REI, on the other hand, is calculated based on the total analysed time (TAT). TAT refers to the entire duration of the sleep study, including the time before falling asleep and after waking up.
In a sleep study, the device records the number of apneas or hypopneas per hour of recording time. Since the recording time is often longer than the time spent asleep, the REI can sometimes underestimate the AHI. This is because the REI does not account for the time spent awake during the study.
The REI is calculated by counting the number of apneas and hypopneas during the total analysed time of the study. This includes any breathing irregularities that occurred while the participant was awake or asleep. By including all respiratory events, the REI provides a comprehensive overview of the person's breathing patterns throughout the study.
While REI is based on TAT, the AHI is typically calculated based on total sleep time (TST). TST specifically focuses on the time spent asleep, excluding any periods of wakefulness. However, it's important to note that some studies have also calculated AHI based on TAT, referred to as AHITAT, to compare it with the traditional TST-based AHI.
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Frequently asked questions
REI stands for Respiratory Event Index.
REI is used in sleep studies, particularly home sleep studies, as an alternative to the Apnea Hypopnea Index (AHI).
REI is the number of apneas or hypopneas recorded during a sleep study per hour of device recording time.
REI is calculated based on total analysed time (TAT) rather than total sleep time (TST), which is used for AHI. REI can therefore underestimate the severity of sleep apnea compared to AHI.
