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Heart Biomarker Evaluation in Apnea Treatment

Scoring Respiratory Events

The scorer will identify the following categories of discrete breathing events: obstructive apneas, central apneas and hypopneas

Obstructive Apneas are identified when the amplitude (peak to trough) of the airflow (thermistry) signal decreases to a flat or almost flat signal (showing a 90% reduction of the amplitude of "baseline" breathing for 90% of the duration, this will be known as the 90% criteria) if this change lasts for ≥ duration of 10 seconds. It will be classified as an obstructive event unless it meets the criteria for a central apnea (absence of effort on both bands). Baseline breathing is defined as a period of regular breathing with stable oxygen levels. Without reliable airflow, the event will default to hypopnea, if the event meets criteria for hypopnea. Identification of apnea does not require a minimum desaturation criterion.

Hypopneas will be identified if > 50% reduction of amplitude is visualized on either the nasal cannula or the respiratory SUM channel for a duration of at least 10 seconds and associated with >=3% desaturation. If the SUM and nasal cannula are not present, if a 50% reduction is seen on both belts (thoracic and abdominal), or 50% reduction on the airflow, and associated with >=3% desaturation, then a hypopnea may be scored. Discernable changes with desaturations that do not meet the rules of hypopnea are NOT scored as hypopneas. Identification of hypopnea does require a minimum desaturation >=3%.

A Central Apnea event is scored if NO displacement is noted on both chest and the abdominal inductance channels. Minimum duration of event is ≥10 seconds. Identification of an apnea does not require a minimum desaturation criterion. CA will be scored when all signals are "flat" unless signal deflection is due to cardiogenic artifact.

NOTE: CA is scored irregardless of desaturation

EXCLUDE: CA events that are post movement or post sigh (follows >= 150% of baseline effort) unless these are part of a series in which case scoring begins with the second event.

Hypopnea (H) must be associated with a 3% desaturation and characterized by either:

  • 50% reduction in a Nasal cannula or the respiratory SUM channel + 3% desat
  • 50% reduction in either belt + 3% desat
  • Discernable reduction or switch to paradox in a "reliable" airflow signal or either effort channels + 3% desat
  • When the airflow signal is unreliable ("choppy"), then obstructive events cannot be reliable scored. Then, they can be scored as hypopneas if they meet criteria.

Distinguishing Between Hypopneas and Apneas This distinction only can be made for events in which airflow by thermistry is interpretable. (If airflow is uninterpretable, the event-based on inductance data is considered by default to be a hypopnea but must be associated with >=3% desat to be scored as a hypopnea.) Apneas are marked if >90% of the event shows absent or nearly absent airflow on the thermistor channel (and this reduction is 90% the amplitude of the surrounding breaths).

Distinguishing Between Central and Obstructive Events Only events in which there is clear data from both the abdominal and chest signals can be distinguished as central or obstructive. (Events where one or both of these channels are missing or contain artifact are considered obstructive or hypopneic, but a hypopnea must be associated with ≥3% desaturation).

Often determining whether an event is central or obstructive is influenced by where the event is noted to begin and end. Sometimes small efforts are seen following a completely flat area, followed by a large (“breaking”) breath. If a single non-artifactual deflection less than 25% of baseline breathing is seen at the beginning or the end of the period of flat signal, the event will be marked as central. (This recognizes that shortening the event slightly would make it a central event). However, if two or more consecutive small breaths less than 25% of baseline breathing (providing airflow is flat) are seen in the period in question, the event is marked as obstructive.

Determining whether an event is central or obstructive in areas of periodic breathing can be difficult because of uncertainties in deciding when to start and end such events. Often these areas contain breaths that gradually increase and decrease, sometimes decreasing to an imperceptible level. Marking longer events in these areas would result in identifying obstructive events; shorter events are more likely to appear central. When it is unclear as to when to start an event, look for evidence of paradoxical breathing. Change in phase angle between thoracic and abdomen is an indicator of upper airway obstruction (such events will be designated as obstructive). When still unclear, the event duration will be marked using the airflow channel. Identify the areas where airflow stops and starts, then assess whether the period is also associated with effort on either channel/band. Then the inductance channels will be visualized to decide whether during this period, any effort occurred. If any effort was visualized, the event will be considered “obstructive,” otherwise, “central.”

Duration criteria: The beginning of an Apnea/Hypopnea is marked at the end of the last “normal” breath; the end of the event is identified as the beginning of the first breath that exceeds the amplitude of the first reduced breath used to mark the beginning of the event. Duration is based on a “trough to trough” marking lasting at least 10 seconds.

Clarification of amplitude threshold relative to baseline: If one non-artifactual deflection is less than 25% of baseline breathing, then it is a central. If two deflections are less than 25% of baseline breathing providing airflow flat, then it is obstructive. Flat excludes cardiogenic oscillation. If airflow reliable and not flat or airflow unreliable, then default to hypopnea if the hypopnea is associated with ≥3% desaturation.

Contiguous respiratory events that have a single respiratory effort in the middle of two periods of absent efforts, each <6 seconds, AND that are associated with a 3% or greater desaturation should be combined into a single Hypopnea event.

Nasal Flow Limitation

Nasal flow limitation is derived from the nasal cannula signal. A normal flow signal will present as a regular sinus rhythm and curve. Flow limitation may occur with increase upper airway resistance, not sufficient enough to cause discrete apneas and hypopneas. A regular sinus curve will transform into a signal that resembles a lowercase ‘H.”

Desaturation (D) events

Isolated desaturation (non-artifact-related) that are unassociated with either apneas or hypopnea, but which have a clear beginning and end should be marked as Desaturation (D) events if they include a 3% or great decrement in pOx tracing from a stable baseline. Prolonged events (>= 30 seconds) without a clear beginning or end should be deleted.

Summary of Scoring Process

Each study will be manually scored in the two passes:

During the first pass:

  • Review the channels and manually set time of “analysis start” and “analysis stop.”
  • The Respiratory signals from each study will be reviewed on a 2-5 minute basis (screen).
  • The saturation channel will be edited for artifact and respiratory events will be marked manually according to the rules stated above using all signals.
  • ECG is manually reviewed for any irregularities.

During second pass:

  • Respiratory data (abdominal/chest/saturation) will be reviewed on 5 minute pages. The saturation channel will be edited for artifact and respiratory events will be marked manually according to the rules stated above using only Respiratory belts.
  • Obstructive will be reclassified to either a Hypopnea or a Mixed Apnea (mixed apnea tag is chosen for report purposes only)
  • “Mixed Apnea” is marked for any events that have a 50% reduction in either belt or sum with < 3% desaturation.

During 12 week treatment pass:

  • Respiratory data (abdominal/chest/saturation) will be reviewed on 5 minute pages. The saturation channel will be edited for artifact and respiratory events will be marked manually according to the rules stated above using only Respiratory belts.
  • Obstructive events will not be scored. Studies are collected without flow signals.
  • Hypopnea, Central Apnea, and a “Mixed Apnea” will be scored using the same rules above.

Exclusion criteria during Embletta Screening

1) Severe OSA defined by

a)  nocturnal oxygen saturation < 85% for > 10% of the record or

b) AHI < 15 or > 50

2) Central sleep apnea index > 5

Those with markedly severe OSA (AHI >50; estimated prevalence 2-3%), will be excluded due to the severity of the physiological abnormality

National Sleep Research Resource
Heart Biomarker Evaluation in Apnea Treatment