If you've recently switched from CPAP to BiPAP — or you're trying to make sense of a data file that suddenly has twice as many pressure columns — you're in the right place. BiPAP vs CPAP data isn't just a cosmetic difference. The underlying therapy mechanics are distinct, which means the data tells a different story.
This post walks through what changes in your data, what stays the same, and how tools like OSCAR and AirwayLab can help you read it all.
What makes BiPAP data different from CPAP?
CPAP delivers one continuous pressure — say, 10 cmH₂O — throughout every breath. The machine pushes air at that pressure whether you're inhaling or exhaling.
BiPAP works differently. It has two distinct pressure settings:
- IPAP (Inspiratory Positive Airway Pressure) — the higher pressure delivered when you inhale
- EPAP (Expiratory Positive Airway Pressure) — the lower pressure during exhalation
The gap between them is called pressure support(PS = IPAP − EPAP). If your BiPAP is set to IPAP 14 / EPAP 8, your pressure support is 6 cmH₂O.
That support actively assists your breathing effort on every inhale. This is why BiPAP data has more to look at — the machine is logging more interactions with your breathing pattern.
Key metrics in BiPAP data
Some things look exactly the same as CPAP:
AHI
Still your headline number: apneas and hypopneas per hour.
Leak rate
Unintentional air escaping from the mask or via mouth breathing.
Flow waveform
The shape of each breath, useful for spotting flow limitation and RERAs.
Snore index
Vibration-based snore detection (device-dependent).
What's new or more prominent in BiPAP data:
- IPAP and EPAP traces — Instead of one pressure line you get two, plus a pressure support channel on most modern devices.
- Tidal volume — The volume of air per breath (mL). More clinically relevant here because pressure support directly affects it.
- Minute ventilation — Breaths per minute × tidal volume; shows total breathing work across the session.
- Respiratory rate — Often logged more granularly on BiPAP machines.
- Ti (inspiratory time) — How long each inhale lasts; useful for spotting breathing pattern irregularities.
Not all BiPAP machines log all of these. ResMed AirCurve devices export the richest data; some older or simpler BiPAP units produce only basic summary statistics.
What the extra data points mean
Pressure support trends
If your device auto-adjusts IPAP while holding EPAP fixed (as in ASV or BiPAP Auto modes), you'll see IPAP vary across the night. A stable, narrow IPAP trace means your breathing was regular; a wide, shifting trace means the machine was working harder to compensate for irregular breathing. Neither reading is a diagnosis — it's context.
Tidal volume
A tidal volume in the 400–600 mL range is typical at rest for many adults, but what's relevant for your data depends on your pressure support setting and your own respiratory mechanics. In AirwayLab, tidal volume appears as a time-series alongside your pressure trace — useful for spotting nights where volumes ran low or unusually high compared to your own baseline.
Flow waveform and flow limitation
Flow limitation applies to both CPAP and BiPAP, but pressure support makes it more visible in the data. A clipped or flattened peak on the inspiratory flow waveform is called flow limitation— a data pattern you may see flagged in OSCAR or AirwayLab. Flow limitation scores may vary across sessions depending on pressure support settings and other factors. If you notice this pattern in your data, that's a specific observation to bring to your next appointment.
Viewing BiPAP data in OSCAR and AirwayLab
OSCAR
OSCAR handles BiPAP data well and has been the community standard for years. It displays IPAP/EPAP pressure graphs, leak rate, flow waveform, tidal volume (where the device logs it), and event flags. If you're familiar with OSCAR for CPAP, you'll find the same interface with additional pressure channels in the session view.
AirwayLab
AirwayLab reads the same SD card data OSCAR uses and is built to complement it — not replace it. A few things it adds for BiPAP users:
- Pressure support visualisation — see the IPAP/EPAP gap across the full night at a glance
- Flow limitation scoring alongside your dual-pressure trace
- RERAs, breathing pattern irregularities, and AHI, all in your browser with your data staying local
AirwayLab is free and always will be. It runs entirely in your browser — your data never leaves your device.
When to discuss your BiPAP data with your clinician
BiPAP data is information, not a diagnosis. If you notice patterns that concern you — persistent flow limitation, low tidal volumes, high AHI despite therapy, or large nightly pressure auto-adjustments — those are observations worth bringing to your prescribing clinician or sleep specialist.
“I pulled my SD card data and noticed X” is a much more productive starting point for a clinical conversation than “I don't think my therapy is working.” Your data gives a clinician something concrete to look at.
AirwayLab can generate a session summary you can print or screenshot to bring to an appointment. Always discuss any therapy changes with the clinician who manages your prescription.
Frequently asked questions
Can AirwayLab read BiPAP data the same as CPAP data?
Yes. AirwayLab reads the same SD card format OSCAR uses and supports ResMed AirCurve and compatible BiPAP devices.
What is pressure support in BiPAP data?
Pressure support is the difference between IPAP and EPAP — the extra pressure applied to assist each inhale.
Does tidal volume appear in all BiPAP data?
It depends on the device. ResMed AirCurve devices log tidal volume in SD card data; some other BiPAP machines do not export it.
What does a shifting IPAP trace mean in auto BiPAP mode?
It means the machine adjusted the inspiratory pressure during the night — typically in response to detected breathing changes. This is information to discuss with your clinician, not a cause for alarm on its own.
Ready to look at your BiPAP data?
Upload your SD card data on AirwayLab — no account needed, nothing uploaded, works entirely in your browser.
AirwayLab is an informational tool. Nothing in this article or in AirwayLab's output constitutes medical advice, a clinical diagnosis, or a recommendation to change your therapy settings. Always discuss therapy decisions with your prescribing clinician or sleep specialist.
Related reading
BiPAP Data Analysis: How to Read Your AirCurve 10 Data for Free — step-by-step guide to loading AirCurve EDF files.
How to Read Your CPAP Data — full guide to PAP data metrics including AHI and flow limitation.
Understanding Flow Limitation in Your PAP Data — the hidden metric beyond AHI, explained.
Glossary
Flow limitation — what it means and how AirwayLab measures it.
RERA — respiratory effort-related arousals explained.