Whether you're reading a printout from your sleep clinic, checking the myAir app, or loading your SD card into AirwayLab or OSCAR, the same set of numbers keeps appearing. Here's what each field actually represents.
Medical disclaimer: AirwayLab is a data-visualization tool, not a medical device. This article describes CPAP data fields — it does not constitute a diagnosis or a recommendation to change your therapy. Discuss your data with your sleep physician.
AHI — Apnea-Hypopnea Index
AHI is the count of apneas and hypopneas per hour of recorded time. An apnea is a pause in airflow lasting 10 seconds or more; a hypopnea is a partial reduction sustained for the same duration, typically accompanied by an arousal or an oxygen drop.
On CPAP therapy, the AHI your device reports is the residual AHI — events that occurred despite therapy being active. Most guidelines cite below 5/hr as the typical target range, though your sleep physician determines what's appropriate for your situation.
Night-to-night variation is expected. A single elevated night doesn't necessarily indicate a problem; a sustained multi-week trend in one direction is more meaningful data to bring to your clinician.
Further reading
For a deeper look at what AHI measures and what it misses, see Why AHI Is Lying to You and AHI vs RDI.
Event Breakdown: OA, CA, H, RERA
Many ResMed devices record not just total AHI but the component event types:
OA — Obstructive Apnea
The airway closes completely. Typically the predominant event type in obstructive sleep apnea.
CA — Central Apnea
Breathing pauses without an obstructive cause; the respiratory drive itself is temporarily absent. Some central events are normal during therapy. A high central count relative to obstructive is worth discussing with your clinician.
H — Hypopnea
Partial airflow reduction meeting the duration and arousal/desaturation criteria.
RERA — Respiratory Effort-Related Arousal
A run of increasingly restricted breaths that end in an arousal, without fully meeting the hypopnea threshold. ResMed devices report these separately. They contribute to sleep fragmentation even when AHI looks low.
For more on the distinction between detected apneas and estimated respiratory disturbances, see What Are RERAs?
Mask Leak Rate
Leak rate reflects how much air is escaping around your mask seal, reported in litres per minute. All CPAP masks have some intentional venting (required for CO₂ clearance) — your machine knows this "intentional leak" baseline and reports unintentional leak(sometimes called "large leak") separately.
Common reference ranges in ResMed documentation:
- < 24 L/min — typically within the acceptable range for most mask types
- > 24 L/min — elevated; may affect therapy delivery and event detection accuracy
Data quality note:High leak rates can inflate or distort AHI values. If you're seeing unexpectedly high AHI on nights with high leak, the two are often connected. Mask fit, cushion condition, and sleep position all affect leak. Your clinician can interpret recurring leak patterns in context.
For a detailed look at how leak is calculated and displayed, see the CPAP Leak Rate guide.
Pressure
CPAP therapy delivers a continuous positive pressure to keep the airway open during sleep. What your report shows depends on your device type:
Fixed CPAP
A single pressure value set by your prescriber. Your report confirms the pressure was delivered at the prescribed level.
APAP (Auto-Adjusting)
The device adjusts pressure breath-by-breath based on detected events and flow signals. Your report typically shows minimum pressure, maximum pressure, and a 90th or 95th percentile pressure (the level the device was at or below for 90–95% of the night). A rising 95th-percentile pressure over time is worth noting for your clinician.
BiPAP
Delivers separate inspiratory (IPAP) and expiratory (EPAP) pressures. Reports show both values.
Important: Do not adjust your own pressure settings without direction from your sleep clinician. Pressure changes affect therapy delivery in ways that require clinical judgment to evaluate.
Usage Hours
Simple and important: how long the mask was on your face during the recording. Many insurance and compliance programs define "compliant use" as 4+ hours per night on 70% of nights. Your usage hours tell you and your care team whether you're meeting therapeutic exposure targets.
Short sessions — under 4 hours — are worth noting because event data from very short recordings is less statistically reliable than from a full night.
What a Typical Therapy Report Looks Like
A therapy report from a ResMed APAP device might show:
The AHI is below 5/hr. Leak is low. The RERA count is higher than AHI — this is common and not inherently concerning, though it can contribute to daytime sleepiness if consistently high. These numbers give a clinician context for a follow-up conversation.
What These Numbers Don't Tell You
Standard CPAP reports don't capture:
- Breath shape patterns — flow limitation signatures that occur below the RERA threshold
- Oxygen saturation — SpO2 trends require a separate pulse oximeter
- Positional data— whether events cluster when you're on your back
- HRV and cardiac metrics — these require additional monitoring
Tools like AirwayLab layer in breath-shape scoring (Glasgow Index), flow limitation analysis (FL Score, NED), and oximetry metrics alongside standard CPAP data — giving you and your clinician a more complete picture. See Beyond AHI for more on what the standard report leaves out.
What to Bring to Your Clinician Appointment
Rather than describing your numbers verbally, consider:
- 1An SD card export or report printout covering the past 30–90 nights
- 2A note on any symptom changes — new snoring reports from a partner, increased daytime sleepiness, morning headaches
- 3Questions about any metrics that look different from your baseline
Your sleep physician interprets these numbers in context. The data tools give you the information; the clinical conversation is where it gets acted on.
Frequently Asked Questions
What is residual AHI on CPAP?
Residual AHI is the apnea-hypopnea index recorded while CPAP therapy is active — it counts events that occurred despite the pressure support. It differs from the AHI measured in your diagnostic sleep study, which was recorded without therapy. A residual AHI below 5/hr is a common reference point, but your sleep physician determines what's appropriate for your individual situation.
What does RERA mean in a CPAP report?
RERA stands for Respiratory Effort-Related Arousal. It describes a sequence of increasingly restricted breaths that end in an arousal before meeting the full criteria for a hypopnea. ResMed machines record these separately in the therapy data. RERAs contribute to sleep fragmentation and daytime symptoms even when AHI is low.
What is a good leak rate on CPAP?
ResMed documentation typically cites unintentional leak below 24 L/min as within the acceptable range. The exact threshold varies by mask type. What matters most is whether your leak rate is consistent and whether it correlates with nights where your AHI looks different from baseline. Your clinician can interpret recurring high-leak patterns in your therapy context.
What does 95th percentile pressure mean on APAP?
The 95th percentile pressure is the level your APAP device was at or below for 95% of the night. It gives a cleaner picture of typical operating pressure than the maximum, which can be driven by brief isolated events. A rising 95th-percentile pressure over multiple weeks is a data point worth discussing with your sleep clinician.
How can I see my full CPAP therapy report in AirwayLab?
Load the SD card from your ResMed device at airwaylab.app/analyze. AirwayLab reads your EDF files directly in the browser — your data never leaves your device. The overview tab shows AHI, event type breakdown, leak, pressure, and usage hours. Additional tabs cover breath-shape scoring, flow limitation analysis, and nightly trends across all loaded sessions.
See Your Full Therapy Picture
Load your ResMed SD card into AirwayLab and see AHI, event types, leak, pressure, breath-shape scores, and oximetry data together in one view — entirely in your browser, no upload required.
Medical disclaimer: AirwayLab is a data-visualization tool, not a medical device. Nothing on this page constitutes a diagnosis or a recommendation to change your therapy. Discuss your therapy data and any concerns with your sleep physician.