[CPAP] Increased EPR reduces flow limits even when EPAP is simultaneously decreased

[G. Szabo]

I decided to start a separate thread with this specific title so it is easier to find and one can refer to it directly when advising members. 

There has been controversy over the correct setting up of EPR on this forum. 

One argument emphasizes that expiratory pressure keeps the airways open; hence, once some EPR is added to an already established constant-pressure CPAP therapy, the expiratory pressure should be increased by the same amount as the EPR drops the pressure during expiration. 

The other line of arguments, based on experience, emphasized that adding EPR in the above situation might benefit and reduce flow limitation even without increasing the expiratory pressure.

Below, I provide some measurements that support the latter view.

I run my AirCuve 10 with the following settings for 4 days: 
EPAP=5.4, IPAP=7.4, PS/EPR=2.0
With the following outcomes

FL(95%)=0.05; 0.01; 0.02; 0.03
Average FL (95%)=0.028
The standard deviation of FL (95%)= 0.017

FL(99.5%)= 0.26; 0.08; 0.10; 0.12
Average FL (99.5%)=0.14
The standard deviation of  FL (95%)= 0.082

I run my AirCuve 10 with the following settings for 4 days: 
EPAP=4.4, IPAP=7.4, PS/EPR=3.0
With the following outcomes

FL(95%)= 0.00; 0.00; 0.00; 0.00
Average FL (99.5%)=0.00
The standard deviation of FL (99.5%)= 0.00

FL(99.5%)= 0.08; 0.05; 0.05; 0.06
Average FL (99.5%)=0.06
The standard deviation of (95%)= 0.014

Outcome: 
When the EPR was increased from 2 to 3 by decreasing EPAP, the 95% flow limit was also reduced from 0.028 to 0.000. A similar FL decrease (from 0.14 to 0.06) can be observed at 99.5%. 

Conclusion: 
Adding EPR to the treatment plan is beneficial unless it permanently increases CAs. It is not necessary to increase the EPAP simultaneously. Nevertheless, the best practice is adding the EPR in the APAP regime when the instrument automatically increases pressure if, and only if,  it is needed. 

An added benefit of EPR is better exhalation efficiency, which reduces some inhalation limitations by more efficiently removing the stuck air from the lung.         

[Sleeprider]

I agree with what you're saying here, however it is possible to lower EPAP enough to lose airway patentcy. Also, the way EPR is set, it is possible to set minimum pressure lower than the available CPAP range, resulting in EPAP being stuck at 4.0 without the ability to respond to a need for higher pressure, so we always suggest minimum pressure is at least set to 4.0 cm plus EPR equals minimum pressure. The response of flow limits to increases in EPR and pressure support has been something I have advocated for a very long time, and is is also demonstrable that flow limits will not respond to positive air pressure increases in the same way they respond to pressure support increases. In nearly every case where flow limitation is reduced, individuals report better sleep integrity and better rest.

There has been a trend among the YouTube experts to advocate for fixed pressure, no EPR and the use of VCOM. None of these makes much sense to me based on results we have seen on the forum with bilevel pressure support or EPR. One of the guiding principles I have tried to live by here is that there is no single rule that applies to all. There is a great deal of individual response to any changes we make and those need to be observed and accommodated by being flexible with our suggestions. Positive Air Pressure therapy is inherently a trial and error experiment, from the titration protocols to more refined setting adjustments to improve an individual's comfort and efficacy. Another member Dormeo put is most simply, "EPR reduces pressure when you exhale, but by the same token, it increases pressure when you inhale. It's the increased pressure for inhalation that helps reduce flow limitation".