Miya Pearson
RERAs, or Respiratory Effort-Related Arousals, are a type of sleep disruption caused by irregular breathing. They are characterized by a drop in airflow through the nose, followed by a spike in brain activity caused by a partial awakening. RERAs can only be detected during an in-clinic sleep study that monitors brain activity and breathing. While home sleep studies can diagnose OSA in some people, they cannot measure RERAs because they do not monitor brain activity. The addition of frontal EEG (electroencephalography) to adult home sleep apnea testing has been studied, and results show that removing EEG increased the number of respiratory events scored by ~13%.
| Characteristics | Values |
|---|---|
| RERA definition | A period of increasing upper airway resistance followed by an arousal, without meeting the criteria for hypopnea |
| RERA detection | Can only be detected during an in-clinic sleep study that monitors breathing and brain activity |
| RERA treatment | Isolated or infrequent RERAs may not require treatment |
| RDI | The combined total of apneas, hypopneas, and RERAs |
| RDI calculation | RDI = (# apneas + # hypopneas + # RERAs) × 60 / total sleep time in minutes |
| AHI | An index used to calculate sleep apnea severity based on the total number of complete cessations (apneas) and partial obstructions (hypopneas) of breathing per hour of sleep |
| AHI calculation | Apnea-hypopnea index (AHI) or respiratory disturbance index (RDI) for PSG or a respiratory event index (REI) for an HSAT |
| RERA and EEG | Home sleep apnea tests cannot measure RERAs because they do not monitor brain activity |
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What You'll Learn
- Home sleep studies without EEG may lead to an underestimation of sleep apnea severity
- RERAs are not detected in home sleep tests without EEG as they require brain activity monitoring
- EEG is used to identify arousal-based respiratory events during sleep apnea testing
- The Apnea-Hypopnea Index (AHI) is a metric used to assess sleep apnea severity
- The Respiratory Disturbance Index (RDI) includes RERAs, in addition to apneas and hypopneas
Home sleep studies without EEG may lead to an underestimation of sleep apnea severity
Home sleep apnea testing (HSAT) has become a popular option for diagnosing obstructive sleep apnea (OSA) due to its convenience, low cost, and ability to evaluate patients in their usual sleep environment. However, one of its major limitations is the lack of electroencephalography (EEG) channels to score sleep-wake stages, which can lead to an underestimation of sleep apnea severity.
EEG is a crucial tool for accurately determining sleep time and differentiating between sleep and wake states. Without EEG, HSAT kits rely on total recording time (TRT) instead of total sleep time (TST) to calculate the respiratory event index, which can lead to an underestimation of sleep apnea severity. This is because the TRT includes periods of wakefulness, resulting in a lower denominator for calculating the respiratory event rate.
Actigraphy, which estimates TST based on movement, is not a reliable substitute for EEG as it tends to overestimate sleep when movement is the only input. Furthermore, the absence of EEG can lead to an overestimation of the sleep period, particularly in patients with insomnia and low sleep efficiency. This, in turn, can reduce sleep-disordered breathing (SDB) indices and increase the risk of false-negative results.
The addition of frontal EEG channels to HSAT has been shown to improve the accuracy of sleep time determination. A study found that HSAT without EEG overestimated the sleep period by approximately 20% compared to HSAT with EEG, with a higher overestimation in patients with low sleep efficiency. Another study found that the removal of EEG increased the number of respiratory events scored by about 13%.
The underestimation of sleep apnea severity can have significant implications for patient management. The successful treatment of OSA relies on accurately assessing its severity, and the long-term complications of sleep apnea are directly correlated with its severity. Therefore, the limitations of HSAT without EEG should be recognized, and practitioners should exercise caution when interpreting HSAT results.
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RERAs are not detected in home sleep tests without EEG as they require brain activity monitoring
RERAs, or Respiratory Effort-Related Arousal, are a type of sleep disruption caused by irregular breathing. They are characterised by a period of increasing upper airway resistance, followed by an arousal or partial awakening. This occurs when there is a drop in airflow through the nose, followed by a spike in brain activity.
RERAs are often combined with apneas and hypopneas to form the Respiratory Disturbance Index (RDI). The RDI is calculated by adding the number of apneas, hypopneas, and RERAs, and then dividing this figure by the total sleep time in minutes. This index is used to assess the severity of sleep apnea.
While home sleep tests can be used to diagnose sleep apnea in some cases, they cannot measure RERAs. This is because home sleep tests do not monitor brain activity, which is crucial for detecting RERAs. Therefore, an overnight sleep study in a sleep lab is required to dependably identify RERAs. During this study, equipment is used to track various bodily functions, including brain activity, sleep stages, and breathing.
The addition of EEG (electroencephalography) to a home sleep test would allow for the monitoring of brain activity. However, there is currently no standard method for determining sleep time in the absence of EEG. As a result, valid signal time (VST) is used as a surrogate for total sleep time in the calculation of the AHI.
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EEG is used to identify arousal-based respiratory events during sleep apnea testing
Sleep apnea is a serious sleep disorder that affects a person's breathing during sleep. This can be potentially life-threatening and requires medical attention. Respiratory-related arousals during sleep are a key indicator of sleep apnea.
Electroencephalographic (EEG) arousals are an awakening response of the brain that can be seen in EEG recordings. EEG is a method of measuring brain activity using sensors that detect brain wave changes. An arousal is when these sensors show that brain waves change to alpha wave form, indicating that the patient has woken up, even if they are not conscious of it.
EEG is an important tool in the diagnosis of sleep apnea. It can be used to identify arousal-based respiratory events during sleep apnea testing. The number of respiratory-related arousals during the night is directly related to the quality of sleep and the severity of the condition. Detecting EEG arousals is, therefore, a significant task in the clinical diagnosis of sleep medicine.
EEG arousals appear in the EEG record for several reasons, and the rate of occurrence can indicate the presence of sleep apnea. Respiratory arousals are particularly significant in the diagnosis of sleep apnea/hypopnea, such as OSAS and CSAS. EEG arousals can also be used to detect other conditions such as periodic limb movement (PLM) and restless legs syndrome (RLS).
In addition to EEG, other methods of diagnosis include electrocardiogram (ECG), electromyogram (EMG), electro-oculogram (EOG), oronasal airflow, ribcage movements, abdomen movements, and oxygen saturation. However, this method requires sleep technologists to monitor and diagnose sleep apnea events, which can be complicated, expensive, and time-consuming.
Recent studies have proposed a classification algorithm based on EEG sub-band signal feature extraction to help classify sleep apnea events. This method has shown high accuracy in automatically detecting the occurrence of sleep apnea events and determining the type of apnea event.
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The Apnea-Hypopnea Index (AHI) is a metric used to assess sleep apnea severity
The Apnea-Hypopnea Index (AHI) is a diagnostic tool that helps determine the presence and severity of obstructive sleep apnea (OSA). OSA is a sleep disorder characterised by repeated narrowing or collapse of the throat during sleep, causing breathing disruptions.
AHI quantifies the number of apneas and hypopneas occurring during sleep. Apneas are periods when breathing stops, while hypopneas are instances of blocked airflow resulting in shallow breathing. To register as an event, an apnea or hypopnea must last at least 10 seconds. The AHI is calculated by dividing the total number of apneic and hypopneic events by the total number of hours of sleep. A normal AHI is less than 5 events per hour, while an AHI of 30 or more events per hour indicates severe sleep apnea.
AHI is typically measured during a sleep study or polysomnogram, which monitors brain waves, blood oxygen levels, heart rate, and breathing while the patient sleeps. Polysomnography is usually conducted in a sleep laboratory, but simplified versions can sometimes be performed at home. Sleep studies provide valuable data on breathing disruptions and total sleep time, helping to diagnose and assess the severity of sleep apnea.
While AHI is a useful metric, it does not account for all factors contributing to OSA severity. For example, respiratory effort-related arousals (RERAs), which are not severe enough to be classified as apneas or hypopneas, are not included in the AHI calculation. RERAs are important indicators of OSA severity, and their inclusion can impact the accuracy of AHI scores.
In summary, the Apnea-Hypopnea Index is a valuable tool for assessing sleep apnea severity, but it should be considered alongside other metrics and clinical data to fully understand the condition's severity and guide treatment decisions.
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The Respiratory Disturbance Index (RDI) includes RERAs, in addition to apneas and hypopneas
The Respiratory Disturbance Index (RDI) is a formula used in reporting polysomnography (sleep study) findings. It is used to assess the severity of sleep apnea by measuring respiratory efforts or Respiratory Effort Related Arousals (RERAs). RERAs are arousals from sleep that do not meet the definitions of apneas or hypopneas but disrupt breathing during sleep and cause respiratory symptoms that may lead to an arousal. A RERA is characterised by increasing respiratory effort, such as dyspnea, for 10 seconds or more, leading to an arousal from sleep.
The RDI is calculated by adding the number of apneas, hypopneas, and RERAs, and then dividing this by the total sleep time (TST) in minutes. This formula can be expressed as (([RERAs + hypopneas + apneas] x 60) / TST). The RDI is often used interchangeably with the Apnea-Hypopnea Index (AHI). However, unlike the AHI, the RDI includes RERAs in addition to apneas and hypopneas. The AHI is the average number of combined apneas and hypopneas per hour, and it is used to determine the severity of a person's sleep apnea.
Some studies have found a strong correlation between high RDI and excessive daytime sleepiness. The RDI is also used to diagnose OSAHS, with a score of greater than 5 per hour and symptoms of daytime sleepiness. The RDI can be higher than the AHI due to the inclusion of RERAs and other subtle breathing irregularities.
The addition of frontal EEG to adult home sleep apnea testing has been studied, and it was found that removing EEG increased the number of respiratory events scored by approximately 13%. However, the impact on RDI was less significant, with the RDI by polygraphy only 8% lower than the RDI with EEG. This is because more RERAs were scored without EEG, as periods of inspiratory flow limitation (scored as a surrogate for RERA) did not show an associated arousal when EEG was added.
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Frequently asked questions
RERA stands for Respiratory Effort-Related Arousal. It is a period of increasing upper airway resistance followed by an arousal, without meeting the criteria for hypopnea.
RERAs can only be detected during an in-clinic sleep study that monitors breathing and brain activity. Home sleep apnea tests cannot measure RERAs because they do not monitor brain activity.
The removal of EEG increased the number of respiratory events scored by around 13%.
