How to Read Your CPAP Machine Data

Step 1: Know What Your Machine Records

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.

Step 2: Learn the Key Metrics

AHI (Apnea-Hypopnea Index)

AHI counts the number of breathing disruptions per hour. Under 5 is the clinical goal, and consistent readings under 2 are excellent. What matters more than any single night's number is the trend: if your weekly average is creeping up, bring it to your provider to discuss whether pressure, mask fit, or something else has shifted.

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 (opens in new tab).

Therapy Pressure

Therapy pressure is measured in cmH₂O (centimeters of water). On an auto-adjusting machine (APAP), pressure varies throughout the night based on what your airway needs. The number on the morning summary that most clinicians care about is the 95th percentile: the pressure your machine needed 95% of the time. If that value is creeping toward the ceiling of your prescribed range, the machine is running out of room to respond and a range adjustment is worth a conversation with your provider. The average pressure tells you where the machine spends most of the night, and pressure spikes usually correspond to event clusters or leak episodes rather than a problem on their own.

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

Your breaths per minute during sleep, typically 12 to 20. This is a secondary metric for most users, useful for tracking changes rather than making decisions. Consistently elevated rates can reflect discomfort, an approaching illness, or something worth mentioning at your next visit.

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.

Step 3: 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. If you're coming from myAir, see our guide to going beyond myAir.

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. For a full overview of what files are on the card and how to access them, see our CPAP SD card guide.

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. Import the data into 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 →

Step 4: Read 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 or central? The event type breakdown helps your provider determine the right approach.
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?

Step 5: Watch for Patterns Over Time

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. Our leak fix guide walks you through every step.

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.

Step 6: Understand What Each Metric Really Tells You

Here is a more detailed look at the key metrics with example values to give you a frame of reference.

AHI (Apnea-Hypopnea Index)

AHI counts full breathing pauses (apneas) and partial airflow reductions (hypopneas) per hour. Your CPAP machine breaks this into subcategories: obstructive apneas (OA), central apneas (CA), and hypopneas (H).

Example values:

• AHI 0.8 with 0 OA, 0 CA, 5 H over 6.2 hours: Excellent night. A handful of minor hypopneas is completely normal.
• AHI 4.2 with 3 OA, 1 CA, 22 H over 6.1 hours: Still in the normal range, but higher than average. Worth monitoring.
• AHI 12.5 with 28 OA, 2 CA, 45 H over 6.0 hours: Mild residual apnea. Discuss with your provider.

For a deep dive into AHI, see our complete AHI guide.

How AHI is calculated (and why different tools may show different numbers)

AHI is expressed as events per hour, but the exact formula depends on what you divide by.

The method your CPAP machine uses (and what CPAP Clarity displays): total respiratory events divided by total therapy hours. Every minute your mask was on the device counts as therapy time, including the occasional bathroom break where the machine kept running. This is what appears on your machine's screen in the morning and what lands in your sleep clinician's report.

An alternative method some independent analysis tools use: total events divided by total therapy time minus detected mask-off time. The idea is to exclude periods where no breathing data was being collected. This produces a slightly lower number on nights with significant mask-off time.

Both are valid under the American Academy of Sleep Medicine (AASM) guidance. The difference on most nights is small (0.1 to 1.0 events per hour). Neither is universally "correct"; they answer slightly different questions:

• Wall-clock method (machine / CPAP Clarity): "Across my whole therapy session, how often did a breathing event occur?"
• Time-in-apnea method (some third-party tools): "During the minutes I was actively breathing with the machine on, how often did a breathing event occur?"

Why it matters: if you cross-check your numbers against a third-party tool, expect a small drift on any night with mask-off time. What matters clinically is the trend and the severity band (under 5, 5 to 15, 15 to 30, 30 or higher), not the decimal place. All of these tools will show the same trend; only the exact number shifts by the small margin above.

What CPAP Clarity shows you: the wall-clock number. We pick this because it matches what your machine displays, what your sleep clinician reviews, and what lines up with insurance compliance reports. Changing your decision about pressure or mask fit should come from the trend and severity band, not from which calculation method a given tool uses.

Leak Rate

Leak measures unintentional air escape from your mask in liters per minute. Your machine's built-in vent leak is already subtracted.

Example values:

• Average 4 L/min, max 18 L/min: Great seal. Occasional minor shifts.
• Average 22 L/min, max 55 L/min: Borderline. Spikes are pulling the average up. Check for position-related leaks.
• Average 38 L/min, max 72 L/min: Significant leak problem. Therapy effectiveness is compromised. See our leak fix guide.

Therapy Pressure

For auto-adjusting machines (APAP), pressure varies throughout the night. Your data shows minimum, average, 95th percentile, and maximum pressure in cmH2O.

Example values:

• Min 6.0, avg 8.2, 95th 10.4, max 12.0 (range set 6 to 16): The machine is comfortable in the lower half of its range. Good.
• Min 8.0, avg 13.5, 95th 15.8, max 16.0 (range set 8 to 16): The machine is frequently hitting the ceiling. Discuss with your provider whether the upper limit should be adjusted.
• Flat line at 10.0 all night: Fixed pressure (CPAP mode), not auto-adjusting. This is normal if your provider prescribed a fixed pressure.

Usage Hours

How long the machine was on and delivering therapy.

Example values:

• 7.5 hours: Excellent. Full night of therapy.
• 5.2 hours: Decent. Meets insurance compliance (typically 4+ hours), but more hours means more benefit.
• 2.8 hours: Short night. If this is a pattern, it affects treatment effectiveness. Research suggests a dose-response relationship: more hours of use correlates with better outcomes.

Step 7: Recognize Common Patterns

Understanding what typical nights look like helps you spot when something is off.

What a Good Night Looks Like

• AHI under 2. Very few events, mostly isolated hypopneas.
• Leak under 12 L/min average. Stable seal with only minor, brief spikes.
• Pressure in the lower to middle portion of your range. The machine is not working hard.
• 7+ hours of usage. Full night of therapy.
• Events spread evenly (or barely present). No clustering.

This is the pattern you are aiming for most nights. Not every night will look like this, and that is normal.

What a Bad Night Looks Like

• AHI above 5, especially if obstructive events dominate.
• Leak average above 24 L/min, particularly sustained elevation rather than brief spikes.
• Pressure frequently at or near the maximum of your auto range.
• Usage under 4 hours, meaning you removed the mask partway through the night.
• Events clustered in the second half of the night, which may indicate REM-related issues or mask displacement.

A single bad night is not a cause for concern. Everyone has them. The key question is whether bad nights are becoming more frequent.

Common Red Flags to Watch For

• Leak and AHI rising together. This usually means leak is undermining therapy. Fix the leak first, then reassess AHI.
• Central apneas increasing over time. This is a different pattern from obstructive events and may require a different treatment approach. See our central vs obstructive apnea guide.
• Pressure consistently near the ceiling. If your 95th percentile pressure is within 1 to 2 cmH2O of your maximum setting, discuss a range adjustment with your provider.
• Usage dropping over time. Declining usage often signals a comfort issue (leak, pressure discomfort, dry mouth, claustrophobia) that can be addressed.

Step 8: What to Do When You Spot a Problem

Your data is a tool for identifying issues and having productive conversations with your sleep provider. Here is a quick decision tree.

High leak rate? Start with our CPAP leak fix guide. Most leak issues can be resolved with strap adjustment, cushion replacement, or mask repositioning.

High AHI despite good seal? Review the event type breakdown. If events are mostly obstructive, discuss pressure optimization with your provider. If central apneas are appearing, report this to your provider as it may require a different approach.

Short usage hours? Identify what is causing you to remove the mask. Common causes include dry mouth (try increasing humidifier settings), mask discomfort (consider a different mask style), or pressure discomfort (discuss EPR settings with your provider).

Good numbers but still tired? If your AHI is low, leak is controlled, and you are using the machine 7+ hours, yet you still feel unrested, discuss this with your sleep physician. Other factors such as sleep fragmentation, periodic limb movements, or non-apnea sleep disorders may be involved.

Gradual worsening trends? If any metric is slowly getting worse over weeks, bring your data to your provider. CPAP Clarity's trend charts make it easy to show your provider exactly what is happening over time.

Analyze your CPAP data for free with CPAP Clarity →

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