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Types of Sleep-Disordered Breathing Events - Definitions and Testing Procedures

 

By Admin

 

In addition to sleep apnea, there are a number of sleep-disordered breathing (SDB) events that can occur regularly and cause further health problems. While some of these events may not qualify as apneas, they still disrupt sleep and reduce blood-oxygen levels, potentially leading to more serious conditions. It is also important to distinguish the different types of respiratory events for differential diagnosis, which allows doctors to prescribe proper treatments for each condition. To test for these events, sleep clinicians use polysomnography, a sleep study method that records and measures body activity during a night of rest. The information collected includes brain waves, blood-oxygen levels, heart rate, and breathing patterns, as well as any eye or body movements. Tools such as the Apnea-Hypopnea Index (AHI) and the Respiratory Disturbance Index (RDI) are then used to perform diagnostics. When necessary, additional tests such as Electroencephalography (EEG) or arterial blood gases (ABG) tests can be included to measure brain activity and artery gases during each respiratory event or arousal. Together, these measures allow for precise assessments of breathing problems during sleep, whether they are singular events or the symptoms of a disorder.

What is a Sleep-Disordered Breathing Event?

As opposed to a syndrome, such as obstructive sleep apnea syndrome (OSAS), events simply refer to singular episodes of sleep-disordered breathing, rather than the symptoms or characteristics of a disorder. The FDA defines sleep-disordered breathing as partial or complete cessations in breathing during sleep. Complete cessations of breathing are considered apnea events, while other reductions are considered hypopnea or effort-related arousals. Doctors and sleep specialists observe the number and intensity of these events to diagnose a condition.

Apnea Events

Anyone familiar with sleep apnea knows that apnea events occur when breathing is cut off, either from blockage of the airway or blocked signals from the brain. As defined by both the American Academy of Sleep Medicine (AASM) and the International Classification of Sleep Disorders (ICSD),Third Edition, apneas must meet the following criteria:

 

1. Reduction in airflow by at least 90 percent of the patient’s baseline breathing, as recorded by oronasal thermistors or nasal pressure cannulas. (These devices are the tubes that connect to the nose or mouth to record airflow during testing.)

 

2. Event duration of at least 10 seconds.

 

3. Airflow reduction occurs at least 90 percent of the duration of the event (numbers 1 and 2 together).

 

Some clinicians consider reductions at least 70 percent above baseline to be mild apneas, though 90 percent more closely represents a cessation of breathing. Duration can also be defined as a minimum of two respiratory cycles, rather than by seconds. Most doctors and sleep specialists use the 90 percent standard and timed intervals.

Sleep Apnea Diagnostic Criteria

As mentioned above, the criteria used to assess breathing is based on the Apnea Hyponea Index (AHI) and the Respiratory Disturbance Index (RDI). AHI is the number of apneas or hypopneas recorded per hour of sleep, while RDI is the average number of respiratory disturbances per hour. Since RDI includes other breathing irregularities, and not just apneas and hypopneas, it may represent a more comprehensive assessment. Electroencephalography (EEG) or pulse oximetry can be included to confirm the results and provide more precise measures of brain activity and blood-oxygen levels, respectively.

AHI Criteria for Sleep Apnea Severity:

  • 0-4 events per hour: No apnea/minimal apnea.
  • 5-14 events per hour: Mild sleep apnea. Patients may either be asymptomatic or may experience daytime sleepiness. A subjective questionnaire such as the Epworth sleepiness scale (ESS) may be used to assess daytime sleepiness or fatigue.
  • 15-29 events per hour: Moderate sleep apnea. Patients are very likely to be symptomatic.
  • 30 or more: Severe sleep apnea. Symptoms are severe and will likely interfere with daytime activities.

 

The Three Types of Sleep Apnea

The three main types of sleep apnea are obstructive sleep apnea (OSA), central sleep apnea (CSA), and complex or mixed sleep apnea.

 

Obstructive sleep apnea (OSA), which involves physical blockage in the airway, is by far the most prevalent type of sleep apnea, accounting for over 95 percent of sleep apnea patients and roughly 20 percent of men with a body mass index (BMI) over 25. The primary reason for OSA prevalence is obesity, which can be both a cause and a comorbid condition among sleep apnea patients.

 

Central sleep apnea (CSA) is sleep apnea that is not caused by physical blockage, but rather by a disruption of the autonomous signals that control breathing. In terms of respiratory effort, CSA is a more heterogeneous group in which effort events are diminished or absent. In most cases it is also associated with OSA syndromes or another medical condition. When a CSA event occurs, breathing will stop without patient response, dilaying arousal.

 

Complex sleep apnea (CompSA) is also referred to as “mixed sleep apnea” because it involves both OSA and CSA as a distinct syndrome. Often, this condition begins as OSA but presents CSA events during treatment with PAP therapy. The reasons for this syndrome are not completely understood.

Hypopnea Events

Hypopnea events are defined as follows:

1. Airflow is reduced by at least 30 percent of the patient’s baseline, as recorded by nasal pressure cannulas, induction plethysmography, or oronasal thermistors.

 

2. Events last at least 10 seconds.

 

3. Airflow reduction occurs at least 90 percent of the duration of the event.

 

4. Reduction in blood oxygen at least 4 percent from baseline SpO2 percent (percentage of oxygenated blood) prior to the event.

 

Some clinicians use more stringent criteria for hypopnea, for example, the AASM’s “Chicago Criteria” guidelines describe two types of hypopneas: Those with an airflow reduction of at least 50 percent from baseline, without a requirement for oxygen desaturation or arousal, and those with a lesser airflow reduction (30 percent) in association with oxygen desaturation above 3 percent or an associated arousal. Hypopnea events are very similar to apnea events, and interpretations can vary, but generally, hypopnea means abnormally slow or shallow breathing, while apnea means the cessation of breathing. This is why some diagnostic manuals such as the Diagnostic and Statistical Manual, Fifth Edition (DSM-5), now refers to obstructive sleep apnea hypopnea syndrome (OSAHS) as the primary syndrome for sleep apnea.

AHI Criteria for Hypopnea:

Since the Apnea Hypopnea Index (AHI) measures both the number of apneas and hypopneas a patient experiences per hour, a doctor can use it to assess the severity of hypopnea as follows:

  • Less than 5 events per hour: No hypopnea/minimal hypopnea.
  • 5-15 events per hour: Mild hypopnea. Patients are often asymptomatic.
  • 15-30 events per hour: Moderate hypopnea. Patients can be symptomatic.
  • More than 30 events per hour: Severe hypopnea. Symptoms are more severe, and can very easily develop into full apnea events.

Three Types of Hypopnea

As with sleep apneas, there are three different types of hypopnea:

 

Central hypopnea: Both airflow and breathing effort are reduced.

 

Obstructive hypopnea: Only the flow of air is reduced, not breathing effort.

 

Mixed hypopnea: There is a mix of both central and obstructive hypopnea episodes, including reduced airflow and effort events.

 

Respiratory Effort, Disturbances, and Arousals

Sleep disturbances such as arousals or increases in respiratory effort are signs of a sleep-disordered breathing condition. While singular events can result from stress, anxiety, or life changes, more frequent occurrences are often the result of a progressive illness or disorder. Mild increases in respiratory effort can be very similar to snoring, while more serious disturbances can cause strain or discomfort and often end in arousal. This spectrum has been more clearly defined over time.

 

Arousal: An arousal is a rapid shift in EEG frequencies from sleep to waking, but more specifically, it is defined by waveforms (alpha and theta waves, but not sleep spindles) with frequencies greater than 16 Hz and a duration lasting 3-15 seconds. Normal sleep is recorded before and after an event to establish a baseline for patient sleep and waking patterns. An arousal is not the same thing as wakefulness, and patients are often unconscious of an arousal and have no memory of it occurring. One example in respect to sleep apnea is an unconscious removal of a CPAP mask during the night, a common problem for those struggling with treatment adherence.

 

Respiratory Effort: Respiratory effort, or labored breathing, is defined by the FDA as breathing abnormalities characterized by increased effort, including the use of accessory muscles of respiration, straining, grunting, or other signs of respiratory distress. While much of the effort takes place in the lungs, the accessory muscles of respiration, such as the sternocleidomastoid and the scalenes (anterior, middle, and posterior) are used to a greater degree when the lungs fail to take in oxygen effectively. Respiratory effort can take many forms, from mild to severe, but can sometimes be mistaken for snoring.

 

Respiratory Effort Events for the Three Types of Sleep Apnea:

1. Obstructive apnea: respiratory effort is recorded throughout the event.

 

2. Central apnea: there is no respiratory effort during the event.

 

3. Mixed or Complex apnea: there is absence of respiratory effort at the beginning of the event followed by increasing respiratory effort during the second half.

 

Respiratory Effort- Related Arousal (RERA)

A RERA is a very common event characterized by increasing respiratory effort for 10 seconds or more, and leading to an arousal from sleep that does not qualify as apnea or hypopnea. The standard for measuring RERAs is esophageal manometry, as recommended by the American Academy of Sleep Medicine (AASM). Diagnostic criteria are as follows:

 

1. A series of respiratory cycles of increasing/ decreasing effort or flattening, as recorded by nasal manometry and leading to an arousal that cannot be defined as apnea or hypopnea.

 

2. An event duration of at least 10 seconds.

 

Hypoventilation

Hypoventilation is saturation of carbon dioxide in the arteries. Technically, it is defined as an increase of PaCO2 (partial pressure of carbon dioxide) level by a minimum of 10 mm Hg (millimetre of mercury) during sleep compared to baseline PaCO2 levels before the test, but it is generally referred to as an increase in CO2 levels in the blood. Partial pressure of carbon dioxide (PaCO2) is one of several measures calculated by an arterial blood gases (ABG) test. While hypoventilation can be a singular event, Chronic Hypoventilation Syndrome or Sleep-related Hypoventilation are common conditions with a variety of causes and comorbidities. Hypoventilation can also be closely related to hypoxemia, the reduction of oxygen in the blood, but loss of oxygen alone does not always account for increases in CO2. Hypoxia can be the result of apnea events, other respiratory conditions such as COPD, or sleep-related hypoxemia disorder In addition, increased levels of PaCO2 in a blood sample taken immediately after arousal is suggestive of hypoventilation.

Cheyne-Stokes Respiration

Cheynes-Stokes respiration is a condition and not an event, but it involves at least three dramatic fluctuations in respiration, often described as “crescendo-decrescendo” events due to the dramatic increase and decrease of the breathing patterns. In addition to these respiratory events, Cheynes-Stokes Respiration must also include the following:

 

1. Five or more central apneas or hypopneas per hour of sleep.

 

2. Rising and falling fluctuations in respiration (crescendo-decrescendo) lasting at least 10 continuous minutes.

 

Upper Airway Resistance Syndrome (UARS)

Like Cheynes-Stokes syndrome, UARS is not an event but a syndrome made up of persistent events over time. UARS involves RERAs rather than apneas, and often includes other gas exchange abnormalities such as snoring. UARS is often caused by narrowing of the airway, but can take a variety of forms as long as it does not lead to apnea or hypopnea events (or at least over 50 percent of the time). This close distinction to sleep apnea is one of the reasons why UARS is so important. At times, UARS will resemble a mild case of OSA, and must be diagnosed accurately for proper treatment. As a close variant of sleep apnea, some classification systems such as the International Classification of Sleep Disorders define UARS as a subgroup of OSA. Together, these events represent the most common sleep-disordered breathing problems, often resulting from underlying health conditions such as obesity, heart disease, or respiratory failure. While there are a large number of respiratory conditions, these events are related to SDB specifically and occur during sleep. Causes range from physical obstructions, often from chest or airway changes, to autonomic issues such as CSA, to other gas exchange abnormalities. The gold standard treatment for sleep apnea is CPAP or other forms of PAP therapy, while tissue reduction surgery or oral appliances can be used as alternatives. With more isolated events such as mild hypopnea, lifestyle changes alone may be all that is necessary to reduce the symptoms, but more persistent events or syndromes often require a combination of treatments and lifestyle changes to manage the condition.  

 

Sources

American Academy of Sleep Medicine - https://aasm.org/

Chest - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3021364/

FDA.gov - https://www.fda.gov/media/112603/download

Hippokratia - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2765300/

International Classification of Sleep Disorders, Third Edition - https://j2vjt3dnbra3ps7ll1clb4q2-wpengine.netdna-ssl.com/wp-content/uploads/2019/05/ICSD3-TOC.pdf

Journal of Thoracic Disease - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4561280/

Karger.com - https://www.karger.com/Article/FullText/335839

Physiological Reviews - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3970937/

Seminars in Respiratory and Critical Care Medicine - https://pubmed.ncbi.nlm.nih.gov/16052414/

Sleep - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2635578/

Sleep Education - http://sleepeducation.org/treatment-therapy/surgery/surgical-procedures