Understanding EPR: Expiratory Pressure Relief on Your CPAP

What Is EPR?

EPR stands for Expiratory Pressure Relief. It's a comfort feature on ResMed CPAP machines that reduces the air pressure when you breathe out.

Without EPR, your machine delivers the same pressure during both inhalation and exhalation. That constant pressure is what keeps your airway open, but it can also make exhaling feel like you're blowing against a wall. For many people, especially those on higher pressures, this sensation makes CPAP uncomfortable or even difficult to tolerate.

EPR solves this by briefly dropping the pressure each time you exhale, then returning to your prescribed level when you inhale. The result: breathing feels more natural, closer to how you'd breathe without a mask on.

How EPR Levels Work

ResMed machines offer three EPR levels. Each level reduces the exhalation pressure by a specific amount, measured in cmH2O (centimeters of water pressure).

EPR Level	Pressure Drop	Best For
EPR 1	1 cmH2O	Mild relief. Good starting point for users on lower pressures
EPR 2	2 cmH2O	Moderate relief. The most commonly prescribed setting
EPR 3	3 cmH2O	Maximum relief. Helpful for higher pressures or new users still adjusting

For example, if your therapy pressure is 12 cmH2O and your EPR is set to 3, the pressure drops to 9 cmH2O each time you exhale. When you inhale, it returns to 12.

You can also set EPR to Off, which delivers constant pressure throughout the breathing cycle. Some users prefer this, particularly those who've been on CPAP for years and are accustomed to steady pressure.

Ramp Only vs. Full Time

Your EPR setting has two modes that control when the pressure relief is active.

Ramp Only

EPR is active only during the ramp period, the first few minutes after you turn on the machine when the pressure gradually increases from a low starting point to your prescribed level. Once the ramp is complete, EPR turns off and you get constant pressure for the rest of the night.

This mode is designed for people who need the comfort boost to fall asleep but don't want reduced exhalation pressure once they're already sleeping.

Full Time

EPR is active all night long, on every breath. This is the more common setting and the one most sleep physicians prescribe. If breathing against pressure bothers you at any point during the night (not just when falling asleep), Full Time is the better choice.

Most new CPAP users start with EPR 3, Full Time for maximum comfort, then adjust from there if needed.

Who Benefits from EPR?

EPR is especially helpful if you:

• Feel like you're fighting the machine when you exhale. This is the most common complaint from new CPAP users. EPR directly addresses it.
• Are on higher pressure settings. Exhaling against 15 cmH2O is significantly harder than exhaling against 8 cmH2O. Higher pressures make EPR more noticeable and more valuable. For more on how pressure settings affect your therapy, see our dedicated guide.
• Are new to CPAP therapy. The adjustment period is real. EPR can make those first weeks much more tolerable, improving the odds that you'll stick with therapy long enough to feel the benefits.
• Wake up feeling like you can't catch your breath. Some users describe a feeling of air being "forced in" when they're trying to exhale. EPR smooths out that sensation.
• Have been told your compliance hours are low. If discomfort is causing you to remove your mask during the night, EPR may help you keep it on longer.

That said, EPR isn't for everyone. Some users find that pressure relief during exhalation feels odd or destabilizing. A few users with complex sleep apnea (mixed obstructive and central events) may find that EPR increases central apneas, since the pressure drop can sometimes interfere with the breathing signal. If your central apnea count goes up after enabling EPR, mention it to your provider.

How EPR Appears in CPAP Clarity

When you analyze your ResMed SD card data in CPAP Clarity, you'll see EPR-related information in a few places:

• EPR Pressure signal: Your AirSense 10 or 11 records a separate EPR pressure channel (labeled EprPress or EprPress.2s). This shows the actual exhalation pressure delivered on each breath, so you can see exactly how much relief you're getting throughout the night.
• Pressure chart: The main pressure graph shows your therapy pressure and your EPR pressure together. The gap between the two lines represents the pressure drop during exhalation.
• Session summary: Your EPR setting (level and mode) is recorded in the session data, so you can track whether changes to your EPR setting correlate with changes in your AHI, leak rate, or comfort.

Looking at your EPR pressure alongside your event data can reveal useful patterns. For example, if your events tend to cluster during periods when the EPR pressure is at its lowest, that might suggest the pressure drop is too aggressive for your needs.

Analyze your CPAP data for free →

What About Philips Machines?

If you use a Philips Respironics machine (like the DreamStation series), the equivalent feature is called Flex (sometimes labeled C-Flex, A-Flex, or Bi-Flex depending on the therapy mode). Flex works on the same principle: reducing exhalation pressure for comfort. The settings are also numbered 1 – 3, similar to EPR.

CPAP Clarity currently supports ResMed AirSense 10 and 11 data. Philips support may come in the future.

Should You Change Your EPR Setting?

EPR is a clinical setting, and any changes should be discussed with your sleep physician or equipment provider first. That said, here are some scenarios worth bringing up at your next appointment:

Signs to discuss increasing EPR with your provider:

• You consistently struggle to exhale comfortably against the pressure
• Your usage hours are low because you remove the mask out of discomfort
• You're on Ramp Only and find the second half of the night uncomfortable

Signs to discuss decreasing EPR with your provider:

• Your central apnea count has increased since EPR was enabled
• You feel like the pressure "disappears" during exhalation and it's disruptive
• Your AHI is well-controlled and you want a more consistent pressure feel

Bring these observations to your next appointment so your provider can make an informed adjustment.

Consider leaving it alone if:

• Your AHI is under 5 and you're sleeping comfortably
• You're using the machine 7+ hours per night without issues
• Your leak rate is normal and your therapy data looks good

The golden rule of CPAP settings: if your therapy is working well and you're comfortable, don't fix what isn't broken. EPR is a tool for comfort, and comfort is what keeps you using the machine night after night. Consistent use is the single biggest factor in successful CPAP therapy.

If you're curious about what your current EPR settings look like in practice, pull your SD card and explore your data in CPAP Clarity. Seeing the actual pressure curves can make the abstract numbers feel much more concrete. And if you want help interpreting the rest of your session data, our guide to reading CPAP data walks through each metric step by step.