Pressure relief on the ResMed AirSense 11 is a comfort feature called Expiratory Pressure Relief, or EPR. It slightly lowers the air pressure delivered by your machine each time you breathe out, so you’re not exhaling against the full force of your therapy pressure. The goal is to make breathing on CPAP feel more natural, closer to how you’d breathe without a mask on.
How EPR Works
Your CPAP machine delivers a set pressure (measured in centimeters of water pressure, or cmH2O) to keep your airway open while you sleep. Without EPR, that pressure stays constant whether you’re breathing in or breathing out. Breathing in against that pressure feels fine because air is flowing into your lungs. But breathing out against it can feel like blowing into resistance, which many people find uncomfortable, especially at higher pressure settings.
EPR solves this by detecting when you transition from inhaling to exhaling. During each exhale, the machine briefly drops the pressure by 1, 2, or 3 cmH2O, then brings it back up for your next inhale. If your therapy pressure is 10 cmH2O and your EPR is set to 3, you’ll breathe in at 10 but breathe out at 7. This small drop makes a noticeable difference in comfort, particularly for people prescribed pressures above 8 or 9.
EPR Settings: Off, 1, 2, and 3
The AirSense 11 offers four EPR options:
- Off: No pressure drop during exhalation. You breathe against the full therapy pressure in both directions.
- EPR 1: Pressure drops by 1 cmH2O on exhale. A subtle change that some people barely notice.
- EPR 2: Pressure drops by 2 cmH2O. A moderate reduction that works well for many users.
- EPR 3: Pressure drops by 3 cmH2O. The maximum relief, best for people who feel like they’re fighting the machine when they exhale.
Most people starting CPAP therapy find EPR 2 or 3 more comfortable. If you’re adjusting to a new machine or a new pressure, starting at 3 and working down can make the first few weeks easier.
Does EPR Affect Your Therapy?
The pressure drop only happens during exhalation, so your airway still receives full therapy pressure during inhalation, which is when obstructive events (apneas and hypopneas) are most likely to occur. A study comparing pressure-relief CPAP to constant CPAP found that both approaches maintained effective therapy. Nightly usage was comparable between the two groups, though patients using pressure relief reported less mouth dryness during their first night of treatment.
Some sleep professionals raise the concern that lowering expiratory pressure too aggressively could contribute to central apneas in certain patients. This is because the brain uses the resistance it feels during exhalation as one signal for regulating breathing rhythm. If you notice your AHI (the number your machine reports each morning) climbing after turning EPR on or increasing it, that’s worth discussing with your sleep provider. For the majority of users, EPR at any setting doesn’t cause problems.
How to Access EPR Settings
Here’s the catch: EPR is located in the clinical menu, not the standard user menu. ResMed locks certain settings behind the clinical menu so they can be managed by your sleep provider. To access it yourself, go to the home screen on your AirSense 11 and press two fingers anywhere on the touchscreen for about three seconds. You’ll see “Clinical Home” appear in the top left corner. From there, navigate to the Comfort section, where you’ll find the EPR toggle (on or off) and the level setting (1, 2, or 3).
If your provider has set your EPR to a specific level and asked you not to change it, there’s usually a clinical reason. But if you’re finding therapy uncomfortable and your provider hasn’t discussed EPR with you, it’s one of the simplest adjustments that can improve how CPAP feels night to night.
EPR on AutoSet vs. Fixed Pressure
The AirSense 11 AutoSet model automatically adjusts your therapy pressure throughout the night based on what your airway needs. When EPR is active on an AutoSet machine, the pressure relief tracks with whatever pressure the algorithm is currently delivering. So if the machine ramps up to 12 cmH2O during a period of obstruction and your EPR is set to 3, you’ll exhale at 9. When the machine drops back to 6 during stable breathing, you’ll exhale at 3 (though most machines won’t let the expiratory pressure fall below a minimum floor).
On a fixed-pressure CPAP model, the math is simpler: your set pressure minus your EPR level equals your exhalation pressure, all night long.
When Higher EPR Feels Worse
More pressure relief isn’t always better. Some people find that EPR 3 makes their breathing feel unstable, as though the machine can’t decide what pressure to deliver. Others feel like they’re not getting enough air on the exhale because the drop is too dramatic. If EPR 3 feels strange, try 2 or 1 before turning it off entirely. The right setting is whichever one lets you fall asleep without noticing the machine’s pressure shifts.
People who breathe through their mouth while sleeping sometimes find that higher EPR levels increase air leak, since the lower expiratory pressure makes it easier for air to escape through parted lips. If your machine reports high leak numbers and you’re using EPR 3, dropping to 2 may help more than switching to a different mask.