How to Read Your CPAP Flow Rate Graph

What the Flow Rate Graph Is

Most CPAP charts summarize your night: one AHI number, a pressure line, a leak line. The flow rate graph is different. It is the raw signal from your machine's flow sensor, sampled many times per second, showing every single breath you took.

When you breathe in, the line rises above zero. When you breathe out, it dips below. A night of healthy breathing looks like a steady ribbon of evenly sized waves. The interesting moments are where that ribbon changes shape.

CPAP Clarity shows this graph in the dashboard's Detailed Charts section for machines that record it (ResMed AirSense and AirCurve SD cards, Philips DreamStation, and Löwenstein Prisma). At full-night view you see the envelope of your breathing; zoom in and individual breaths appear.

Breath Shapes Worth Knowing

Normal breaths. Rounded tops, roughly even spacing, similar heights. Most of your night should look like this.

Flattened tops. When the top of the inhale wave looks squared off or dented instead of rounded, airflow was partially restricted. Clinicians call this flow limitation, and machines score sustained versions of it in their flow limitation index. A few flattened breaths are normal; long runs of them can be worth a conversation with your care team.

Shrinking then recovering waves. A sequence where breaths get smaller, pause, then snap back with a big recovery breath is the classic shape of an obstructive event. Your machine usually flags these on the event timeline; seeing the shape underneath the flag helps the flag make sense.

Flat line with no effort. A stretch where the waveform goes nearly flat means airflow stopped. On its own the graph cannot tell you whether the airway was blocked or the breathing effort paused, which is one reason event classification belongs to your machine and your doctor, not to eyeballing a chart.

Ragged, chaotic stretches. Arousals, position changes, and mask adjustments all disturb the ribbon. If a messy stretch lines up with a leak spike on the leak chart, the mask is the usual suspect.

How to Use It Without Overreading It

The flow rate graph is context, not a verdict. Your machine's event detection already scores apneas and hypopneas using rules from its manufacturer, and CPAP Clarity keeps your headline numbers matched to what your machine reports. The waveform's job is to let you see what a flagged minute actually looked like.

A practical routine:

1. Start from a night that stood out, such as a high-AHI night or a night you felt rough.
2. Find a flagged event on the timeline, then zoom the flow graph to the minutes around it.
3. Compare a rough stretch against a calm stretch from the same night so you know what your normal looks like.
4. If a pattern repeats night after night, take a screenshot and bring it to your sleep physician rather than adjusting anything yourself.

Pressure changes and machine settings belong with your care team. What you can bring them is better evidence: your AHI trend, the leak picture, and now the breath shapes underneath both.

Envelope View vs Breath View

A full night at 25 samples per second is around 720,000 data points, far more than any screen can draw one by one. At full-night zoom, CPAP Clarity draws the envelope: for every column of pixels, the highest and lowest flow reached in that slice of time. The result reads like an audio waveform, and it is honest in a specific way: tall spans mean big breaths, narrow spans mean shallow ones, and gaps mean the mask was off. Nothing is averaged into existence.

Once you zoom in far enough that the screen has room for the real samples, the chart switches to drawing the actual line, and individual breaths appear with their true shapes. That switch is automatic; there is nothing to configure.

Where to Find It in CPAP Clarity

Import your SD card on the dashboard and open Detailed Charts. The Flow Rate row sits at the top, time-aligned with the event timeline and every other chart, so a flag and the breathing beneath it share the same instant on screen. Drag across the graph to zoom until individual breaths are readable. All processing happens in your browser; your night's several hundred thousand flow samples never leave your device.

If you imported before this chart existed, re-import your SD card once and the waveform appears for the nights the card still holds.

FAQ

Why does my flow rate graph look different from OSCAR or SleepHQ?

It mostly should not. CPAP Clarity reads the same raw file your machine writes and cross-checks the decoded signal sample by sample against OSCAR during development. Color, scale, and smoothing differ cosmetically, and the tools occasionally disagree about keeping a few seconds of a brief mask-on blip, but the breaths themselves are the same signal.

Why is there no flow rate graph for my machine?

Some devices never record the raw signal. The ResMed AirMini and AirStart 10, BMC machines, React Health Luna G3, and Yuwell machines either do not store breath-level flow or do not expose it in a readable form, so there is nothing to draw. The summary charts still work for those devices.

Can I diagnose sleep apnea from the flow waveform?

No. Diagnosis requires a sleep study interpreted by a clinician. The waveform helps you understand your data and have better conversations about it, and that is the job it should keep.