Decoding EPR and the Flex Technologies on CPAP Machines

March 15, 2019

Comfort settings on CPAP machines such as EPR and Flex are able to mimic natural breathing patterns making CPAP therapy more comfortable.

If you’re researching or shopping for a new CPAP machine, chances are you are either new to CPAP therapy or you’re replacing the one you already have. We’ve said this many times before, CPAP machines these days are packed with incredible technology. But what exactly is this technology? 

CPAP machines have integrated wireless and battery-powered options, Bluetooth capabilities, remote monitoring and reports at your fingertips through apps on your phone. Another technology which we will be focusing on is a technology called Expiratory Pressure Relief (EPR) or FLEX which are both features to increase comfort and compliance for all users. 

What exactly is EPR or FLEX? Continue reading as we break down some fancy acronyms and abbreviations. Learn what EPR means and the difference between the types of Flex available as we simplify the terms much as we can. Here we go!

What Is Expiratory Pressure Relief (EPR)?

CPAP machines have “comfortable” settings that allow CPAP therapy to mimic your natural breathing pattern as much as possible. ResMed calls this feature EPR while Philips Respironics calls this comfort feature, Flex.

ResMed defines their comfort setting as EPR - Expiratory Pressure Relief. In other words, making it easier for you to exhale or providing a deeper exhale with each breath while on CPAP therapy. For example, your CPAP pressure setting is 10cmH20 with function EPR 3 would be inhaling at 10chH20 and exhaling at a dropped pressure of 7cmH20 and will return to 10cmH20 on the inhale.

Diagram showing how the Expiratory Pressure Relief comfort setting on ResMed CPAP machines work to make CPAP therapy more comfortable

There are 4 settings for Expiratory Pressure Relief on a ResMed machine: OFF, Setting 1 = mild comfort (1 cm H20), Setting 2 = medium comfort (2 cm H20), Setting 3 = maximum comfort (3 cm H20).

What Is Flex Technology? 

Philip Respironics calls their comfort setting Flex. Flex comfort feature provides users with pressure relief on various (CPAP, APAP or BiPAP) modes of therapy. There are various types of Flex available. C-Flex, A-Flex, Bi-Flex and C-Flex+.


C-Flex Pressure: Breakdown

C-Flex, identical to EPR on ResMed, lowers pressure during exhalation for users to adjust to CPAP therapy and works on a breath-by-breath basis.  Using the same example from earlier, if your CPAP pressure setting is 10cmH20 with function EPR 3 on...then, you would be inhaling at 10cmH20 and exhaling at a dropped pressure of 7cmH20 and will return to 10cmH20 on the inhale.

Diagram showing the C-Flex pressure profile as part of Respironics Flex technologies that feature on their CPAP machines

C-Flex also has 4 settings for on their machines: OFF, Setting 1 = mild comfort (1 cm H20), Setting 2 = medium comfort (2 cm H20), Setting 3 = maximum comfort (3 cm H20)

Following along so far? Good, let’s keep going.


Bi-Flex Pressure: Breakdown

Bi-Flex works on BiPAP mode and offers pressure relief at both inhalation and exhalation. The Bi-flex setting offers pressure relief at 3 important areas - the transition from exhalation to inhalation, the transition from inhalation to exhalation and during the exhalation.

The Bi-Flex comfort setting works on BiPAP modes and offers pressure relief at three important times to make breathing transitions more seamless

A-Flex Pressure: Breakdown 

A-Flex works within Auto-CPAP mode. Like C-Flex, A-Flex provides pressure relief at the beginning of exhalation and like Bi-Flex softens transition avoiding spike ups from inhalation to exhalation. It's a smoother and more comfortable feeling. A-Flex mimics your natural breath the most.

The A-Flex pressure profile offers pressure relief as you begin to exhale and makes transitions between inhaling and exhaling smoother

C-Flex+ (Plus) Pressure: Breakdown

C-Flex+ (Plus) is a newer setting within the more advanced CPAP machines when in fixed-CPAP mode.  Like C-Flex, C-Flex+ provides pressure relief at the beginning of exhalation. Like A-Flex, C-Flex+ offers a smoother and softer transitioning from inhalation to exhalation providing additional comfort when in fixed-CPAP mode.

C-Flex+ works best with CPAP machines in fixed CPAP mode. This comfort setting aims to mimic natural breathing patterns while allowing you to gain the benefits of sleep apnea therapy

If you got a blank stare and feeling a bit confused, we don’t blame you - it can be confusing. The take-home message is Expiratory Pressure Relief (EPR) and Flex are both comfort settings available on ResMed and Respironics machines. They come in different modes to ultimately make your adjustment to Sleep Apnea therapy more comfortable by mirroring your most natural breathing patterns possible regardless of your CPAP pressure.

Which Comfort Function Is Best For You And Your CPAP Machine?

Which function is best for you? Ultimately, it comes down to personal comfort and preference. You’ll need to give the functions at various settings a test drive. Some people like EPR and Flex, some don’t use them and others even dislike these comfort settings. These settings may bring on other problems - possibly make your apnea better or worse or the pressure changes may increase your chances of experiencing CPAP mask leaks.

After all, that’s said, many do find the comfort functions helpful. This is the part where we say try it, see what setting works best for you!


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