Glossary

The number of apneas and hypopneas per hour of sleep. The most widely used measure of sleep apnea severity, but it misses flow limitation and RERAs.

A brief shift in brain wave activity lasting at least 3 seconds, indicating a partial awakening from sleep. Respiratory arousals are triggered by breathing events.

A specialised PAP mode for complex or treatment-emergent central sleep apnea. Provides variable pressure support that adapts to the breathing pattern in real-time.

ResMed's auto-adjusting PAP mode that automatically adjusts pressure within a set range based on detected breathing events. Also known as APAP.

A PAP device delivering two different pressures: higher during inspiration (IPAP) and lower during expiration (EPAP). Used when CPAP alone cannot resolve flow limitation.

A breathing pause caused by the brain temporarily failing to send signals to the respiratory muscles. Unlike obstructive apnea, the airway remains open.

The percentage of breaths classified as flow-limited by either NED (above 34%) or Flatness Index (above 0.85). Combines both detection methods for a more complete picture.

Simultaneous oxygen desaturation and heart rate surge occurring within 30 seconds. Strongly suggests a respiratory arousal and combined cardio-respiratory impact.

A therapy device delivering a single fixed air pressure through a mask to keep the upper airway open during sleep. The first-line treatment for obstructive sleep apnea.

A drop in blood oxygen (SpO2) from baseline, typically measured at 3% or 4% thresholds. Each desaturation event indicates a breathing disruption that affected oxygen delivery.

An estimate of cortical arousals per hour based on respiratory pattern changes. Detects spikes in respiratory rate and tidal volume that suggest micro-awakenings.

A standardised file format for multichannel time-series data used by ResMed PAP machines to store breath-by-breath flow waveform data on the SD card.

A ResMed comfort feature that reduces pressure during exhalation by 1, 2, or 3 cmH2O. Makes breathing out against positive pressure more comfortable.

A population-level metric measuring how much tidal volume variance is concentrated at flow peaks, indicating flat-topped (flow-limited) breathing. Reported as a percentage.

The ratio of mean inspiratory flow to peak inspiratory flow per breath. Values of 0.85 or above indicate significant flow limitation with a flat-topped breath pattern.

Partial narrowing of the upper airway during inspiration that restricts airflow without complete collapse. The core phenomenon that AirwayLab analyses.

A composite breath-shape scoring system that evaluates 9 flow limitation characteristics per breath on a 0-9 scale. Lower scores indicate better therapy.

Sudden increases in heart rate following a respiratory event, detected from pulse oximetry data. Often accompany oxygen desaturations as part of the autonomic stress response.

A partial reduction in airflow of at least 30% for at least 10 seconds, associated with an oxygen desaturation or arousal. More common than complete apneas on PAP therapy.

A characteristic inspiratory flow pattern with two peaks and a mid-inspiratory dip, suggesting upper airway oscillation or dynamic obstruction.

A per-breath measure of flow limitation calculated as the ratio of peak inspiratory flow to mid-inspiratory flow. Higher values indicate more airway narrowing during inhalation.

A condition where the upper airway repeatedly collapses during sleep, causing breathing pauses. The most common type of sleep apnea, typically treated with PAP therapy.

The number of times per hour blood oxygen drops by 3% or more from a 2-minute rolling baseline. Each drop indicates a breathing disruption that affected oxygen levels.

The number of times per hour blood oxygen drops by 4% or more. Uses a stricter threshold than ODI-3, capturing only more significant oxygen desaturations.

A cyclical pattern where breathing depth waxes and wanes over 30-100 second cycles. Associated with central sleep apnea, heart failure, and high-altitude exposure.

Detects cyclical breathing patterns with 30-100 second cycles using FFT spectral analysis. Elevated values suggest periodic breathing or Cheyne-Stokes respiration.

The difference between inspiratory pressure (IPAP) and expiratory pressure (EPAP) on a bilevel device. Higher pressure support provides more breathing assistance.

The total number of respiratory events per hour, including apneas, hypopneas, and RERAs. A more comprehensive measure than AHI alone.

A sequence of flow-limited breaths that terminates in a cortical arousal without meeting criteria for apnea or hypopnea. A hallmark of Upper Airway Resistance Syndrome.

A measure of breathing pattern regularity. On PAP therapy, highly regular breathing often indicates a persistently narrowed airway forcing uniform restricted breaths.

The detailed therapy data stored on your ResMed PAP machine's SD card, including breath-by-breath flow waveforms, pressure data, and machine settings.

The percentage of haemoglobin in the blood that is carrying oxygen. Normal resting SpO2 is 95-100%. Drops below 90% during sleep are clinically significant.

The percentage of recording time with blood oxygen below 90%. Indicates sustained hypoxemia that may affect organ function.

The time to peak inspiratory flow as a fraction of total inspiratory time. A low ratio may indicate early peaking and progressive airway narrowing.

A condition where airway narrowing causes sleep fragmentation through increased respiratory effort and RERAs, without producing the apneas or hypopneas that register on standard AHI testing.