Sierra

You may want to try using OSCAR to provide more detail on what is going on during your CPAP use. There may be room for improvements to the setup.

I am afraid I would be very skeptical about the effectiveness of EPAP. It only increases pressure on exhale, and I suspect by not very much as there is no indication of the pressure. My experience is that apnea events are more likely to occur in the inhale portion of each breath. In fact most CPAP machines reduce pressure on exhale without any impact on apnea frequency, and in some cases reduce the number of hypopnea events.

The second issue with an EPAP is that it does not monitor the effectiveness of the device by giving you an AHI score each night. You can even use some freeware called OSCAR to give you much more detailed daily report. My AHI at diagnosis was 34 which is in the severe range. With my CPAP I now average 0.85 for AHI. My wife does even better at 0.5 for AHI.

I use a very minimalist mask after unsuccessfully trying a number of other types. Each person has their preferences but I like the ResMed AirFit P10 Nasal Pillow. This mask is also very quiet and does not disturb the other person. My wife uses a bit different mask called the F&P Brevida. It is a bit larger, but is easier to adjust for fit.

Your best bet would be to try the CPAP again. Successful use usually depends on finding a mask type that works for you. What mask did you use last time and what were the issues?

My wife uses a mouth appliance for TMJ and uses it while using a CPAP and has no issues.

Here is a link to the posts made by @SleepDent in the past few years. You may want to check them out to see if any are of help.

https://myapnea.org/members/SleepDent/posts

There is a dentist that checks in here now and then. Hopefully he will see your post and give you a response. I have no experience in that type of approach.

I think masks are very personal choice. These are the masks I have tried with some brief comments about each and in roughly the order I tried them:

1. ResMed P10 AirFit Nasal Pillow - The original version of this mask was the one prescribed by the sleep clinic. I found it comfortable but really hard to keep on my head. The flimsy mask straps were awful.
2. ResMed N20 AirFit Nasal Mask - Only tried this one briefly. The headgear is much more substantial but it was not nearly as comfortable as the P10, and I found the fit over my nose almost claustrophobic.
3. ResMed Mirage Quattro Full Face - This was recommended by my son that has a beard and recommended it. I have no beard. This mask holds the record for being the very worst mask I have ever tried. I found it impossible to keep sealed. It was either too tight to be comfortable or it leaked, most often blowing air into my eyes. I did not make it through even one night with this mask.
4. ResMed F20 AirFit Full Face - This was significantly better than the Quattro but I still could not make it seal and the leaks kept waking me up. It may have made it 2-3 nights before it was dispatched to my growing mask boneyard.
5. F&P Brevida Nasal Pillow - This mask has better headgear than the P10 and it worked quite well except it seemed to irritate the dividing plate between my nostrils. I pawned it off on my wife and she liked it. She was using the Mirage FX for Her and it was leaving marks on her face that would not go away in a reasonable time during the day. She still uses the Brevida. She has larger leaks than I could tolerate, but she likes it and does not want to change.
6. ResMed Swift FX Nasal Pillow - I got this one as it seemed very similar to the P10 which I liked, but has a much better headgear component. It stayed on at night, but the vent system on the FX is very different than the P10. The P10 does an excellent job of diffusing the vent air flow so you can't feel or hear it. The FX however has straight holes that project air out at jet speed. I simply could not tolerate it blowing on my hand or arm, and it kept waking me up. Another reject.
7. P10/Swift Hybrid - As described in the link I adapted the Swift headgear to the P10. This actually worked very well, and that combination has seen the most use of the 5 years I have been using a CPAP. It was a bit difficult to clean, and it was getting to be time to replace it all, so I decided to try the improved headgear P10 as described in this review.
8. ResMed AirFit P10 Nasal Pillow Improved - Currently still using it. It leaks a little more than I like but is still pretty good. I average less than 1% of the time over the leak rate threshold. This compares to my wife's Brevida at about 8% of the time over the leak rate threshold. She beats me on AHI though by averaging 0.5 compared to my 0.84 long term average. I think I may have to get a needle and thread out to just retain the adjustment of the new and improved straps. But, other than that, this mask is the winner for me.

Chin Straps - Basically I have tried them all including a homemade one. The best was the Breathewear Halo you mentioned. However I found it was just too much with the mask straps and the chin strap to be comfortable. I have also found that using a satin pillow cover makes the pillow slippery enough to help keep the straps on my head, rather than having them "dragged" off by the standard pillow cover.

Mouth Taping - This is my preferred choice and what I have been using for a few years now since I gave up on the chin strap.

As I said in the beginning I think everyone has to experiment to see what they like and can tolerate for a mask. I also think one has to "make friends" with the mask and learn how to live with it. The new P10 does it for me.

I am not familiar with that condition. The condition or medication used to treat it, may be a factor in CSR. It is worth investigating.

One thing to be aware of is that some sleep doctors/technicians may want to use a BiPap for treatment. It is very similar to an APAP like you have but it can up to 25 cm in pressure and the "pressure support" can go up to 10 cm. Pressure support is using more pressure on inhale than on exhale and is essentially the same thing as EPR except EPR is limited to 3 cm, and pressure support can be as much as 10 cm. Based on your use of EPR having benefit for hypopnea but aggravating CA events this device is unlikely to be successful for you. However, if you are involved in the DME system in the US, it may be a hoop you have to jump through to get an ASV, which is much more likely to work for you. Just make sure you get a free trial before buying a BiPap as it is not likely to work. I recall that the DME system may require you to fail on use of a BiPap before they are allowed to supply an ASV.

I did a little more checking into the impact of elevation on CSR or PB (periodic breathing). From what I saw, it seems healthy non apnea sufferers can tolerate up to 9,000 feet of elevation without suffering from CSR. However, those with other issues can be impacted at elevations as low as 4,500 feet. You (and I) may be in that category. If you are seeing specialists in Denver, they should be familiar with the altitude issue.

On the sleep test, be aware there are two steps to an in lab sleep test. First they test you with no pressure to see the type and frequency of apneas you are having. Next they do a step test (titration) where they keep increasing pressure in steps to see the impact on the apneas. This step test would be useful in determining if pressure is a factor causing your central apneas and CSR.

Here is a link that looks worth reading about CSR causes and treatment.

https://nchmd.org/health-library/diseases-and-conditions/con-20166460/

Altitude is likely causing your issues to be worse than average. I live at about 2,000 feet and CA's are my most significant contributor to AHI. I also have CSR flagged from time to time. When I vacation at sea level my AHI almost always goes down. I have not traveled to an area at 5,000 feet and I am sure my issues would get much worse at that elevation.

Thinking about this a little longer I would suggest these steps as the best approach.

1. Determine if there are any underlying medical conditions which could be causing it.
2. If not, then consider an ASV instead of an APAP.
3. Or, consider drug treatment to reduce the negative impact of elevation using acetazolamide.

Although your machine has not flagged it as Cheyne-Stokes respiration (CSR), I am pretty sure that it is. CSR is a period of increased depth of breathing followed by decreasing depth of breathing, followed by a period of apnea with the airway open (CA). The reason that it repeats over and over is that the CO2 intensity signal is not getting back to the control system quickly enough. High CO2 causes you to breath more deeply, while low CO2 causes you to breath less deeply, and even stop breathing (CA). Your breathing rate gets out of sync with what it needed. You are breathing more and more deeply when CO2 has already recovered, but the control system does not know it. The control is essentially unstable. It never catches up like a dog chasing their tail.

While what is happening is fairly obvious, the root cause is not. In the worst case it could be a sign of heart failure, or a neurological issue. It can also be caused simply by the APAP machine pressure, but I am not so sure that is your case. In your previous post I see the multiple CA events even when your pressure is quite low and under 10 cm. Your could experiment with lower pressures or even fixed pressures in the CPAP mode, but I can't say I would be all that optimistic about it working. Because of your altitude the issue is likely aggravated by the elevation effect. The test of this would be to see if this still happens at an altitude closer to sea level. Another option would be to get a sleep apnea test where the pressure is not increased by the machine to see how frequent the CA events are.

Probably the first thing you should do is be seen by a cardiologist. Be sure to take the printouts of your overall results and some printouts of the expanded examples of your CSR. Potential solutions could be the prescription of the elevation sickness drug I mentioned earlier, or an ASV machine. Something needs to be done, as the AHI is currently way too high to leave things as they are now.

I would be interested in seeing a zoomed in detail shot of the mask pressure, Flow Rate, and Minute Ventilation in a couple of the areas where you are having a high frequency of CA events. This may help understand what is causing the CA events. Here is an example from my data of what you might see.