Reading Your CPAP Data

Your CPAP machine records a remarkably detailed picture of every night you sleep — but the app that came with it shows you almost none of it. Manufacturer apps like ResMed's myAir and the now-shuttered Philips DreamMapper distill a full night of breathing data down to a single feel-good score or a green checkmark. This guide is the hub for learning what's actually in your data, what each number means, and how to read the signals your machine quietly hides.

The goal here isn't to turn you into a sleep technician. It's to make you a confident, informed partner in your own therapy — someone who can look at their own numbers, understand what they're seeing, and have a sharper conversation with their clinician. Below we walk through the four headline metrics everyone should know, then the deeper signals that separate "my AHI looks fine" from "I actually understand my sleep."

The Four Numbers That Matter Most

Almost every CPAP report — whether from a manufacturer app, OSCAR, or SomniCharts — leads with the same four headline metrics. Learn these and you can read 80% of any report.

If you're starting from zero, the best place to begin is our plain-English walkthrough: How to Read Your CPAP Data explains AHI, leak rate, pressure, and usage hours without making you install OSCAR or learn medical shorthand.

AHI: the headline you can't read in isolation

AHI is the number most people fixate on, and it's genuinely important — but it's also the most misunderstood. The treatment goal for adults on CPAP is generally a residual AHI below 5 events per hour; many clinicians aim lower (for example, under 1–2) when that's comfortably achievable, though targets are individualized with your provider. There is no formal guideline establishing "below 2" as a universal standard, so don't panic if you land at 3 or 4.

What counts as a healthy number — and why a "good" AHI can still mask trouble like central apneas or flow limitation — is covered in What Is a Good AHI on CPAP. And if your number is running high, Why Is My AHI High on CPAP walks through the usual culprits: mask leak, back-sleeping (supine) position, emergent central events, alcohol, and sedatives — and how your own data points to which one is yours.

One crucial caveat: a single night's AHI is noise. Numbers swing for all kinds of harmless reasons. What matters is the trend over weeks. SomniCharts is built around exactly this idea — it imports every night and shows you the line, not just last night's dot.

Leak rate: the number that can quietly break everything

Here's the trust-building fact nobody tells new users: a large mask leak can invalidate your AHI. When air escapes faster than your machine can compensate, it can't reliably detect apneas and hypopneas — so your AHI may read artificially low while you're actually having a rough night.

Leak is also where vendors diverge. ResMed reports excess leak (air beyond the mask's intentional venting), with a commonly cited red line of 24 L/min at the 95th percentile. Philips reports total leak, a different baseline entirely — so you can't compare the two numbers head-to-head. Our CPAP leak rate guide breaks down the thresholds, the ResMed-vs-Philips difference, and concrete fixes. If your leaks trace to mouth breathing or a poor seal, CPAP mask leaks and mouth leak gets into the hands-on remedies.

Pressure: 95th-percentile vs median

If you're on an auto-adjusting machine (APAP), your pressure changes all night, so your report summarizes it with percentiles. The 95th percentile (P95) is the pressure your machine stayed at or below 95% of the night — a good proxy for "the most pressure you regularly needed." The median (P50) is your typical, middle-of-the-road pressure.

ResMed reports the 95th percentile; Philips reports the 90th — another reason cross-brand comparisons need care. CPAP 95th-percentile vs median pressure explains what the gap between these numbers tells you about whether your settings fit. Curious whether your pressure is off? Is your CPAP pressure too high or too low covers the symptoms and the data — though the right move is always to use that data for an informed conversation with your provider, not to change the setting yourself.

Usage hours: what "compliant" really means

Insurers and Medicare define "compliant" as using your machine at least 4 hours a night on 70% of nights over a 30-day window — a low bar that has nothing to do with whether therapy is working. How to read CPAP usage hours and what 'compliant' really means untangles the difference between meeting a billing requirement and actually treating your sleep apnea.

Beyond the Headlines: The Signals Your App Hides

This is where reading your data gets genuinely powerful — and where manufacturer apps fall silent. ResMed's myAir is ResMed-only, produces a 0–100 score weighted heavily toward usage hours, and shows no event-type, leak, or flow-limitation detail; its formula has never been published, and it can score a perfect 100 at an AHI of 4.9. DreamMapper shut down in January 2026 entirely. Neither ever showed you the signals below.

Event types: your AHI is a blend

A single AHI number lumps together very different events. An AHI of 5 made of obstructive apneas means something different from an AHI of 5 made of central (clear-airway) events. CPAP event types decoded explains obstructive apnea, central apnea, hypopnea, and RERA, and why the same AHI can have completely different meanings.

This matters most with central events. CPAP is designed to splint the airway open and reliably treats obstructive apneas, but it doesn't directly correct the unstable breathing drive behind central (clear-airway) events. A rise in central events on CPAP can signal treatment-emergent central sleep apnea (TECSA, also called complex sleep apnea), which appears in roughly 5–15% of PAP titrations and resolves on its own in about 60–80% of cases within weeks to a few months of continued CPAP. The wrong response is to raise your pressure to chase them — higher pressure doesn't fix central apneas and can sometimes provoke them. Central apneas showing up on CPAP explains when watchful waiting is appropriate and when persistent events warrant a clinician's evaluation. For the underlying anatomy, see central vs obstructive apnea.

The flow rate waveform: the most revealing chart

The flow rate waveform is the raw, breath-by-breath shape of your airflow — the single most detailed view of your night. Healthy breaths look rounded and smooth; flat-topped breaths signal that your airway is partially narrowing even when no apnea is scored. Learning to read it is the most advanced skill in CPAP self-analysis, and How to read the CPAP flow rate waveform teaches you the patterns.

Flow limitation: the hidden metric beyond AHI

Here's the one that explains why so many people feel exhausted despite "perfect" numbers: you can have hundreds of flow-limited breaths an hour and still register an AHI of 0. Flow limitation is partial airway narrowing that never crosses the threshold to be counted as a hypopnea or apnea — so it's invisible in your headline AHI, and myAir and DreamMapper never showed it at all. CPAP flow limitation: the hidden metric beyond AHI explains what it is and why it's the prime suspect when you're still tired on CPAP with good numbers. It's also the core of UARS, the diagnosis your AHI misses — covered in UARS (upper airway resistance syndrome).

Periodic breathing and Cheyne-Stokes

A waxing-and-waning, crescendo-decrescendo breathing pattern is periodic breathing; its most distinctive form is Cheyne-Stokes respiration. When your machine flags this, it's a "see your doctor" signal — periodic breathing patterns can be associated with heart conditions and other serious causes. Periodic breathing and Cheyne-Stokes on your CPAP chart explains what the flag means and why it's worth a clinician's attention rather than a settings tweak.

Reading Your Data Without Becoming an Expert

You don't have to learn all of this the hard way. The traditional route is OSCAR — free, powerful desktop software, but with no automatic scoring, no plain-language explanations, and no Chromebook support. There's a whole ecosystem of tools, and choosing among them depends on which machine you own.

A few facts worth knowing before you pick a tool:

• OSCAR is free and excellent for power users, but it's desktop-only and won't interpret anything for you.
• Philips DreamStation 2 stores its SD-card data encrypted — OSCAR and most third-party tools can't read it at all. (SomniCharts does support DreamStation 2.)
• Cloud tools vary in which brands they handle and which sit behind a paid tier.

SomniCharts takes a different approach: it imports ResMed, Philips Respironics (including the DreamStation 2), and Löwenstein prisma data and explains all of the above — AHI, leaks, pressure, event types, flow limitation, and waveform patterns — in plain language, automatically, across vendors, in your browser. No software install, no manual scoring. If you've been switching brands, it also keeps your full history in one place so you don't lose years of trends — see switching CPAP brands.

To go deeper on the tooling landscape, online CPAP data analyzer shows the upload-and-understand workflow, and myAir and DreamMapper limitations lays out exactly what the manufacturer apps leave out.

Where to Go From Here

Use this page as your map. If you're brand new, start with the plain-English data guide and what a good AHI looks like. If your numbers look off, jump to why your AHI is high or the leak rate guide. And if your numbers look great but you still feel terrible, the answer is almost always in the deeper signals — flow limitation and the flow rate waveform.

Whatever the metric, remember the single most important habit: read your data as a trend over weeks, not a verdict from one night. One night is noise. The line is the story.