How to Read Your CPAP Machine Data

Your CPAP Machine Is a Data Goldmine

Every night, your CPAP machine records a detailed picture of your sleep therapy. Most people only see the basic AHI number on the machine's screen — but there's much more data available on the SD card.

Here's what your machine tracks and what each metric tells you.

The Key Metrics

AHI (Apnea-Hypopnea Index)

What it is: The number of breathing disruptions per hour.

What to look for: Under 5 is the goal. Consistent readings under 2 are excellent. If it's creeping up over time, something may need adjustment.

Leak Rate

What it is: How much air is escaping from your mask, measured in liters per minute (L/min).

What to look for:

• Under 24 L/min average — Good seal
• 24-40 L/min — Elevated, may reduce therapy effectiveness
• Over 40 L/min — High leak, likely needs attention

Some leak is intentional — your mask has built-in exhalation ports. Your machine reports unintentional leak (the excess beyond what's expected).

Leak spikes during the night usually mean your mask shifted during a position change. Consistently high leak suggests the mask doesn't fit properly or the cushion needs replacing.

Therapy Pressure

What it is: The air pressure your machine delivers, measured in cmH₂O (centimeters of water).

What to look for: If you're on an auto-adjusting machine (APAP), pressure varies throughout the night based on need. Key things:

• Average pressure — Where your machine spends most of the night
• 95th percentile — The pressure needed 95% of the time (if this is near your max setting, you may need a range adjustment)
• Pressure spikes — Usually correspond to event clusters or leak episodes

Usage Hours

What it is: How long you actually used the machine.

What to look for: Insurance typically requires 4+ hours per night for compliance. But for maximum health benefit, 7+ hours is ideal. Every hour counts — studies show a dose-response relationship between CPAP usage and health outcomes.

Respiratory Rate

What it is: How many breaths you take per minute.

What to look for: Normal is 12-20 breaths per minute during sleep. Significantly elevated rates may indicate discomfort or other issues.

Tidal Volume

What it is: The volume of air in each breath, measured in liters.

What to look for: Typical range is 0.3-0.6L per breath during sleep. This is mainly useful for tracking changes over time.

How to Access Your Data

Option 1: Machine Screen

Your ResMed AirSense shows basic stats (AHI, usage hours, mask fit) directly on the screen. Press the Home button and navigate through the menus. This gives you a quick snapshot but limited detail.

Option 2: myAir App

ResMed's official app provides a daily score and basic metrics. It's convenient but intentionally simplified — the "score" system obscures important details and has been criticized for inflating results.

Option 3: SD Card Analysis

Your machine's SD card contains the complete, detailed data — every breath, every event, every pressure change. This is what sleep physicians use and what gives you the most actionable information.

To get your SD card data:

1. Remove the SD card from your machine (small slot on the side/back)
2. Insert it into your computer using an SD card reader
3. Upload the data to an analysis tool

CPAP Clarity reads your ResMed SD card data directly in your browser — no installation needed, and your data never leaves your device. Try it free →

Reading Your Nightly Report

When you analyze a night's data, look at these things in order:

1. AHI first — Is it under 5? Great. Over 5? Look at the event breakdown.
2. Event types — Are they mostly obstructive (mask/pressure issue) or central (different cause)?
3. Leak rate — Is your seal good? Leak episodes often correlate with events.
4. Pressure graph — Is the machine working harder than usual? Flat pressure = easy night. Lots of variation = the machine is actively compensating.
5. Usage — Did you use it all night?

Patterns to Watch For

Rising AHI trend — If your AHI has been gradually increasing over weeks, something is changing. Common causes: weight gain, seasonal allergies, worn mask cushion.

Events clustered at specific times — Events grouped between 2-5am often relate to REM sleep (when muscles are most relaxed). Events early in the night may relate to body position as you settle in.

High leak + high AHI — These often go together. When your mask leaks, the machine can't maintain pressure, and events increase. Fix the leak first.

Good AHI but still tired — If your AHI is under 5 but you're still exhausted, look at usage hours, RERAs (subtle disruptions not counted in AHI), and consider discussing with your doctor. Other sleep disorders may be at play.