Why is increasing EPR eliminating h and fl

[yankees123]

I have noticed reading some threads that it is sometimes recommended to increase the EPR in order to eliminate or reduce hypopneas and or flow limitations.  Can someone explain how increasing the EPR does this?  I am trying to understand this but I must be missing something.
Thanks

[Sleeprider]

The use of EPR for people using CPAP therapy to resolve hypopnea is my own particular invention, and is based on an adaptation of standard VPAP-S or Vauto titration principles. Resmed nor any other titration protocol suggests that EPR is anything but a comfort setting.  Using the VPAP titration principle, I have observed a fairly high level of success in treating forum members that have residual hypopnea, after obstructive events have mostly cleared.  

The figure below is Resmed's recommendation for a VPAP-S Titration Protocol.  Note they start with IPAP 4-cm higher than EPAP (PS=4.0).  The titration begins by resolving OA by increasing EPAP as needed.  The protocol then goes on to recommend using increases in IPAP (pressure support) to resolve hypopnea.  So we know that EPAP treats OA and PS treats hypopnea.

Adapting this scheme to the Resmed Airsense 10 CPAPs, we can use CPAP pressure with zero EPR to establish EPAP and resolve OA. If we add in EPR, we must add 1-cm of pressure for ever 1-cm of EPR we add.  By adding pressure 1:1 with EPR increases, we have the same effect asn the VPAP-S titration of increasing IPAP and creating an increase in pressure support. The result is to keep EPAP (or CPAP pressure) at the therapeutic requirement for OA, while increasing IPAP.  In this case EPAP is equal to CPAP Pressure minus EPR, just the reverse of VPAP. Nevertheless, a pressure difference of up to 3-cm can be achieved between IPAP and EPAP and that is how we can use EPR, at least within its 3-cm limits, to treat hypopnea. In my experience, this does not work with Philips and the Flex pressure relief.

[Ron AKA]

I have noticed reading some threads that it is sometimes recommended to increase the EPR in order to eliminate or reduce hypopneas and or flow limitations.  Can someone explain how increasing the EPR does this?  I am trying to understand this but I must be missing something.
Thanks

Over the past couple of weeks I have done some comparison between what I call a High (3) EPR alternative, and a Low (0) EPR alternative for treatment. The pressures are not exactly the same in both alternatives as the High EPR requires higher minimum and maximum pressures, in theory by the 3 cm EPR, but in practice something less than that. In any case this is what I have found:

The Low EPR option reduced total AHI by 1.5
Low EPR reduced CA events by 1.1
Low EPR reduced OA events by 1.2
But Low EPR increased H events by 0.8

I'm sure these results are very individual specific, but at least in me, what low EPR seems to do in comparison to high EPR is convert some of the OA events to H events, but overall there is a total reduction. And I believe OA events are worse than H events, so at least in me, it is a good tradeoff. Why does it happen? Don't know.

I have done a similar but less rigorous comparison in my wife's case. Her AHI is much lower and she has far fewer central events. She gets a total AHI of about 1.2 with low EPR and 1.0 with high EPR. Why? Don't know. That is why I suggest individuals should try each way and see what works best for them. There are some comfort and leak issues to consider as well. Low EPR should mean lower maximum pressures and fewer mask leaks. High EPR may offer more comfort.

[yankees123]

Thank you SR for such a clear explanation.  Makes a lot of sense.

[Sleeprider]

Ron's observations are also pretty consistent with what I have seen. One prerequisite for success with EPR is that CA events are pretty low, and don't increase with the use of it. For those that benefit from the use of EPR in reducing hypopnea, there is probably a good argument to move to bilevel in place of CPAP.

[yankees123]

Ron AKA very interesting data.  
Can you explain why it is when you say low EPR should mean lower maximum pressures and fewer mask leaks. I don't understand how epr affects max pressure.  I thought it just drops the exhale(epap) pressure.
Thanks

[Ron AKA]

Ron AKA very interesting data.  
Can you explain why it is when you say low EPR should mean lower maximum pressures and fewer mask leaks. I don't understand how epr affects max pressure.  I thought it just drops the exhale(epap) pressure.

While I don't think there is a perfect relationship, in general obstructive apnea is related to EPAP pressure. So in theory if you have a set pressure or IPAP of 15 cm and you apply a 3.0 EPR you reduce your treatment pressure to the EPAP or to 12 cm. With no EPR, IPAP = EPAP. So at 15 cm, you have a treatment pressure of 15 cm. My experience is that the difference is not the full EPR value with the ResMed, and with FLEX on a Dreamstation it may even be less. But in general you should need less maximum pressure if you use no EPR. My estimate would be that if you have 15 cm with 3 EPR the equivalent treatment effect would be about 13 cm with no EPR in a ResMed. And there is the same effect on minimum pressure of course.

[Walla Walla]

Ron, How does a pressure of 12cm have the effect of a pressure of 13cm?

[Ron AKA]

Ron, How does a pressure of 12cm have the effect of a pressure of 13cm?

I have found that the impact that an EPR set EPAP is a bit different than an IPAP = EPAP pressure. Suspect the difference is greater in a Dreamstation as the FLEX impact is not as sustained as the EPR in ResMed. See this article for a little more detail on the differences between machines. You will have to google it, as I can't make the link work.

Comparing Expiry Relief in Different CPAP Machines

[yankees123]

I didn't know that epr effects both the minimum and the maximum pressures.  I though it only effected the minimum pressure when you exhale.