Isn't Resmed's Expiratory Pressure Relief really Inspiratory Pressure Support??

[Reznik]

I've been thinking about this issue for quite a while and haven't really seen any posts that directly address it, and so I'd like to start a discussion on this to see what the experts think.

I believe that Resmed's Expiratory Pressure Relief ("EPF") is mis-named.  It should be called Inspiratory Pressure Support, and when you enable it, the machine should be showing the lower expiratory pressure on the display instead of the higher insporatory pressure as it shows now.  Here's why.

Resmed claims that Expiratory Pressure Relief ("EPR") is a "comfort feature" that reduces the pressure during expiration to make it easier to adapt to CPAP.  But, as far as I can tell, the pressure isn't relieved just during expiration.  It is also relieved when you are neither inspirating nor expirating.  The pressure only comes back up to full pressure when you start to inspirate. In essence, a Resmed machine in CPAP or Auto mode with EPR enable is really just a spontaneous (non-timed) bi-level machine with the IPAP at the level shown on the display and EPAP at that level minus the EPR setting.

So, for example, a Resmed Airsense 10 that is set in CPAP or Auto mode with a stated pressure of 8.0 cm with EPR set to 3 is really a Bi-level machine with IPAP set at 8 and EPAP set at 5.  In Bi-level mode, it is accepted that the EPAP is what prevents obstructive events and the pressure support (the difference between EPAP and IPAP) is what helps to prevent central apneas and hypopnea.

That's why, if you are titrated to CPAP at 8.5 with no EPR, and you decide you want EPR, you should increase the programmed pressure on your machine by the amount of EPR you want.  If you're going to enable EPR when you haven't used it in the past, you really need to adjust the pressure level up to match the EPR.  So, if you're set at 8.5 with no EPR, and you want to enable EPR at 3 cm, then you need to increase your pressure setting to 10.5.  That way, you'll be at 10.5 IPAP and 8.5 EPAP, and be getting the same level of pressure during expiration as you were before.  Plus, you'll be getting 3.0 units of inspiratory pressure support on top of the EPAP that you're accustomed to.

If, instead, you leave your pressure at 8.5, you're reallly now in a Bi-level mode with 8.5 as the IPAP and 5.5 as the EPAP.  You've essentially reduced your prescribed expiratory pressure by 3.0.  That's why I see posts from people who say that they after they enable EPR, they see their AHI go UP.

And this is why I say that EPR is really mis-named.  It should be called Inspiratory Pressure Support, and the machine should show the lower EPAP number on the screen instead of the IPAP number like it does today.  

Now, this is also true with A-Flex and C-Flex+ in the Respironics products, but NOT with C-Flex.  C-Flex truly is an expiratory pressure relief mode, because as soon as you're done expirating, the machine returns to the IPAP pressure without awaiting you to inhale.  But, A-Flex/C-Flex+ are more like the Resmed EPR, in that they keep the pressure BELOW the pressure listed on the machine until you start to inhale (though as far as I can tell, A-Flex/C-Flex+ always puts EPAP at 2 cm below IPAP, and the numerical levels of 1, 2, and 3 reflect a additional pressure relief that occurs right at the beginning of expiration).

I welcome any thoughts on what I've written here.

[Walla Walla]

The IPAP does NOT prevent central apneas. In a BPAP the IPAP is determined by the pressure support you set. In a APAP the EPR determines how far down the pressure drops. Almost the same but different. As far as a name I don't care what they call it as long as I know what it does.

[Reznik]

Hi Walla Walla,

Thanks for responding.

The reason that I think the name is misleading is that Resmed's pressure relief is not merely expiratory.  It also gives pressure relief at idle, i.e. when you are neither inhaling nor exhaling, and that's typically when an obstructive apnea starts.  So, if you're titrated at CPAP 8.5, and you then switch on EPR on a new machine at level 3, you're now only getting 5.5 EPAP (and at idle) and you're going to see your AHI go up.  Again, that's not the case with Respironics C-Flex, which truly is an expiratory pressure relief and which returns to the machine's stated pressure as your exhalation completes.  The advantage of Resmed's protocol is that it may eliminate the need for more expensive Bipap machines in cases where people only need 1, 2, or 3 cm of Pressure Support.  

You've indicated that EPR is almost the same as BiPap.  But in the case of Resmed machines, I disagree.  EPR is exactly the same as Resmed's bi-level machines if EPAP and IPAP are set within 3 cm of each other.  If you have a Aircurve 10 S or VAUTO set in S mode with the EPAP and IPAP within 3 cm of each other, you can get the exact same therapy from an Airsense 10.

BTW- I didn't say that IPAP prevents central apnea, and it doesn't.  However, spontaneous Pressure Support can prevent hypopnea and also periodic breathing.  Both hypopnea and periodic breathing can lead to a central apnea in some people, especially if they have several hyponeas followed by a very deep breath.  Typically, what follows after the very deep breath is more hypopneas or a central apnea.  So, Pressure Support can help prevent central apnea by keeping inspiration consistent.  Timed Pressure Support (which forces IPAP when you fail to initiate it spontaneously) definitely can prevent central apneas, by provoking inspiration.  ASV (which adjusts IPAP on a real-time basis to prevent periodic breathing) uses variable pressure support specifically to prevent CSR and central apneas with great success.

Likewise, excessive Pressure Support can also cause central apneas, by causing inspirations that are too deep.  As with everything in CPAP, you need to find the individual balance.  And that ties back to what I was saying in the first post- the name EPR is misleading and can make it harder for people to find that balance if they don't actually know what their machine is doing.

[HalfAsleep]

I don't understand what you mean by "idle"?

AFAIK, a person is either exhaling or inhaling. An apnea would result from a struggle to either exhale or inhale.

[Walla Walla]

Hypopnea's don't cause centrals either. I've also had Periodic breathing without centrals. They may happen at the same time but one doesn't cause the other. As far as EPR being misleading most people don't even set their own pressures. Only the ones that care enough to research on the internet get involved enough to set their machines. They learn what EPR is and how to use it. The rest just let the DME's do everything. I guess you could write ResMed and Complain about the EPR name. Good luck with that.

[Reznik]

There are times when you are neither inhaling nor exhaling.  Sometimes it only lasts for a short period of time.  If it lasts for more than ten seconds, we call it an apnea.  I used the term "idle" to refer to that state.  You could transitioning from inhalation to exhalation, or just holding your breath of a few seconds.

In Resmed's EPR (and in all spontaneous bi-level machines), the machine remains at the EPR pressure until you start inhaling again.  Respironics C-Flex (but NOT C-Flex+/A-Flex) does just the opposite.  It returns to the machine's stated pressure as soon as you stop breathing out.  It doesn't wait for you to start inhaling.

[Reznik]

Hypopnea's don't cause centrals either.  I've also had Periodic breathing without centrals. They may happen at the same time but one doesn't cause the other. As far as EPR being misleading most people don't even set their own pressures. Only the ones that care enough to research on the internet get involved enough to set their machines. They learn what EPR is and how to use it. The rest just let the DME's do everything. I guess you could write ResMed and Complain about the EPR name. Good luck with that.

I didn't say that hypopnea's cause centrals.  But, hypopnea's can lead to central apneas, and bipap is often prescribed as a first line for people who have mixed apneas because pressure support can sometimes resolve them.  When it doesn't, that's when they turn to Timed Bilevel or ASV.

I don't really care what Resmed calls it.  Since a lot of people who come here DO set their own pressures, I think its important for us to understand what it really does, and from what I've seen here, a lot of people don't understand that EPR really is a bi-level with a pressure support of 1, 2, or 3 cm.  For example, if you own an Aircurve 10 in S-mode and you have EPAP of 10 and IPAP of 8, you could get the very same therapy at 50% of the cost from an Airsense 10 set at 10 with EPR of 2.

[Walla Walla]

Hypopnea's don't cause centrals either.  I've also had Periodic breathing without centrals. They may happen at the same time but one doesn't cause the other. As far as EPR being misleading most people don't even set their own pressures. Only the ones that care enough to research on the internet get involved enough to set their machines. They learn what EPR is and how to use it. The rest just let the DME's do everything. I guess you could write ResMed and Complain about the EPR name. Good luck with that.

I didn't say that hypopnea's cause centrals.  But, hypopnea's can lead to central apneas,

What's the difference?

[Reznik]

If hypopnea caused central apnea, then every hypopnea would lead to a central apnea.  That's not the case, and I didn't say it was.

But, hypopneas can lead to central apnea in certain cases.  In some cases, a hypopnea can be the start of a chain of events that ultimately ends in a central apnea.  In those cases, preventing the hypopnea can prevent the central.

For example (and this is just one), if you have a three hypopneas (which lowers your oxygen levels and increases CO2 levels), you then take a very large breath (which raises oxygen and lowers CO2), that large breath might be followed by a central apnea.  But, if you prevented the hypopneas in the first place (with pressure support), you never would have taken the large breath, and thus might never have had the central.

That's why I said "may lead to" and "may help prevent" and not "causes" and not "prevents."  They're different.

[HalfAsleep]

In Resmed's EPR (and in all spontaneous bi-level machines), the machine remains at the EPR pressure until you start inhaling again.  Respironics C-Flex (but NOT C-Flex+/A-Flex) does just the opposite.  It returns to the machine's stated pressure as soon as you stop breathing out.  It doesn't wait for you to start inhaling.

Some people get apneas on inhale not on exhale.....