Understanding EPR: Expiratory Pressure Relief

EPR (Expiratory Pressure Relief) is a ResMed CPAP comfort feature that drops the air pressure slightly each time you exhale, then returns it to your prescribed level when you inhale. It has three levels (1, 2, and 3 cmH2O of relief) and is one of the comfort features new CPAP users most commonly cite as the change that makes their first weeks tolerable.

This guide explains what each EPR level means, when to use Ramp Only vs. Full Time, how EPR shows up in your CPAP data, and when to talk to your provider about whether a different therapy mode might fit better.

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. (If exhaling against your CPAP still feels rough after dialing in EPR, the mask itself can be part of the comfort equation. The Mask Finder Quiz takes 30 seconds to recommend a style that matches your pressure range and sleep position.)

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. Pairing EPR with comfort accessories like a CPAP pillow (opens in new tab) or mask liner (opens in new tab) can further reduce the friction of getting started.
• 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 supports ResMed AirSense 10, AirSense 11, AirCurve 10, the AirCurve 11 ASV, BMC E-20A, BMC G3 A20, and React Health Luna G3 data. The BMC and Luna G3 equivalent of EPR is called Reslex and works the same way. The AirCurve 11 ASV uses dynamic pressure support rather than EPR because the therapy is fundamentally different.

EPR vs. BiPAP: When EPR Is No Longer Enough

EPR and BiPAP both make exhalation feel easier, but they are not the same therapy. Understanding the difference matters when you are deciding whether to push your EPR to the maximum or have a conversation about a different machine entirely.

EPR is a comfort feature on top of CPAP. Your prescribed therapy pressure stays the same; EPR just shaves up to 3 cmH2O off during the exhale phase. The machine still operates as a CPAP, and the pressure your airway sees during inhalation (when collapse is most likely) is unchanged. EPR maxes out at a 3 cmH2O difference between inhale and exhale.

BiPAP is a different therapy mode. A bilevel machine (the ResMed AirCurve family, for example) delivers two genuinely separate pressures: an IPAP for inhalation and a lower EPAP for exhalation. The gap between IPAP and EPAP (called pressure support) can be 4 cmH2O, 8 cmH2O, or higher, well beyond what EPR can provide. Bilevel also handles complex breathing patterns that pure CPAP cannot, including central apneas (with backup rate features in ASV variants) and severe restrictive lung disease.

If you have already enabled EPR 3 Full Time and exhalation still feels like work, the question to bring to your provider is whether a bilevel trial is worth running. The AASM 2019 guideline (Patil et al.) actually suggests clinicians use CPAP or APAP over BiPAP for routine OSA treatment, but notes that BiPAP may be appropriate when therapeutic pressure requirements exceed what CPAP or APAP can deliver, based on the clinician's judgment of the individual patient. The comfort-intolerance pathway to BiPAP is a clinical decision, not a guideline-driven one. For a deeper comparison of the two modes, see our BiPAP vs CPAP guide.

A practical signal: your therapy data. If your AHI is well controlled but your usage hours are dropping because of exhalation discomfort, EPR is the first lever. If EPR 3 Full Time is already in place and the discomfort persists, that is the conversation worth scheduling.

Common Mistakes With EPR

A few patterns we see often enough to call out.

Cranking EPR to 3 on the first night and giving up when it feels weird. EPR changes the breathing rhythm of the machine. A different sensation than what you have been getting is not the same thing as a worse sensation. Give any EPR change at least three full nights before deciding whether it works.

Confusing EPR with the ramp feature. The ramp slowly increases pressure from a low starting point to your prescribed level over the first few minutes; it is about easing into therapy. EPR drops pressure during each individual exhale; it is about making the breathing cycle feel more natural. They are two different features that can be used together.

Assuming EPR will fix every comfort problem. EPR helps the exhale-resistance class specifically. It will not fix a mask leak, a dry nose (try a saline nasal spray (opens in new tab) before bed and turn up the humidifier), a wrong mask size, or aerophagia from supine sleeping. If your discomfort survives EPR 3 Full Time, the next step is usually NOT to push pressure or therapy modes; it is to look at the mask + position + humidity stack.

Changing EPR yourself without telling your provider. Most CPAPs have a clinician menu that lets you change EPR settings. If you do, your provider sees the data and assumes the prescribed setting was tested at the time of titration; an undisclosed mid-stream change can muddy that picture and lead to less accurate adjustments downstream. The safer move is to schedule a brief phone or portal conversation before changing settings, even if the actual edit only takes a minute.

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 numbers are steady 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.

Frequently Asked Questions

What is EPR on a CPAP machine? EPR (Expiratory Pressure Relief) is a comfort feature on ResMed CPAP machines that drops the air pressure by 1, 2, or 3 cmH2O when you exhale, then returns to your prescribed pressure when you inhale. The reduced exhale pressure makes breathing out feel more natural, and new CPAP users frequently cite EPR as the comfort change that makes their first weeks of therapy bearable.

Does EPR reduce my AHI? EPR is a comfort feature, not a therapy adjustment, so it does not change your effective treatment pressure during the inhalation phase (when airway collapse is most likely). For most users, EPR has no measurable effect on AHI. In a small number of users with complex sleep apnea, EPR can slightly increase central apneas; if your central count rises after enabling EPR, mention it to your provider.

Should I use EPR 1, 2, or 3? A common starting point is EPR 3 Full Time because it provides the most relief with minimal downside; you can adjust downward over the first week if the relief feels excessive. Users on lower prescribed pressures may find EPR 1 or EPR 2 sufficient; users on higher pressures usually benefit from EPR 3. The right answer is the lowest setting at which exhalation feels comfortable.

What is the difference between Ramp Only and Full Time? Ramp Only enables EPR only during the first few minutes after you turn the machine on while pressure builds up to your prescribed level; after the ramp completes, EPR turns off for the rest of the night. Full Time keeps EPR active on every breath all night long. Full Time is the more common prescription.

Is EPR the same as BiPAP? No. EPR maxes out at a 3 cmH2O difference between inhale and exhale and is a comfort feature on a CPAP. BiPAP is a separate therapy mode that delivers two genuinely independent pressures with a gap that can be 4 cmH2O or much higher, and it can handle breathing patterns that CPAP cannot (central apneas, restrictive lung disease). If EPR 3 Full Time is not enough, BiPAP is the next conversation with your provider.

What is the Philips equivalent of EPR? Philips Respironics machines (DreamStation and earlier) call it Flex (C-Flex for fixed CPAP, A-Flex for APAP, Bi-Flex for BiPAP). Flex works on the same principle as EPR and uses the same 1 to 3 numbered settings. The BMC and Luna G3 equivalent is called Reslex.

Primary Sources

• Patil SP, Ayappa IA, Caples SM, Kimoff RJ, Patel SR, Harrod CG. Treatment of Adult Obstructive Sleep Apnea with Positive Airway Pressure: An American Academy of Sleep Medicine Clinical Practice Guideline. J Clin Sleep Med. 2019 Feb 15;15(2):335-343. The current AASM guideline for adult OSA. Suggests CPAP or APAP over BiPAP for routine treatment; BiPAP may be appropriate when therapeutic pressure requirements exceed what CPAP or APAP can deliver. Also recommends broader adherence support (education, troubleshooting) at therapy initiation. PubMed 30736887 (opens in new tab)
• National Heart, Lung, and Blood Institute. CPAP (NHLBI patient education page). Plain-language overview of how CPAP works and the common side effects to expect (congestion, dry mouth, nosebleeds). nhlbi.nih.gov CPAP (opens in new tab)