Your experience is similar to mine.
I started treatment about 20 years ago. My sleep study showed very high AHI, 70 I think, a mix of obstructive and central apneas. I was prescribed an ASV machine, an early Respironics M series. It was incredibly expensive, the copay was shocking. I didn't know anything then. They didn't configure the machine as an ASV, it wasn't until years later that I realized it was set up as an APAP. I felt better, but not great. My AHI was typically between 4 and 7 with it.
Until very recently I always had APAP machines, with the exception of a couple of dumb CPAP travel machines. I've had 4 sleep studies over the years. Basically an automatic CPAP can get my AHI down to 3 or 4 so they stop there and declare me OK. I functioned pretty well, but never feeling wonderful. My fixed pressure CPAP machines weren't much different than the APAP machines if I chose the pressure carefully. This was based on feel only since they were dumb, fixed pressure machines.
Since I had COVID in 2021 I've had a lot more problems with fatigue and daytime sleepiness so I have gotten serious about trying to improve my sleep. I have been using ResMed S10 machines, the first starting in 2016 which I replaced in 2024 with a new one. Having had a couple of machines fail over the years I've learned to always have at least two machines. I spent all of 2024 working through every setting on the S10 to find out how they affect my central apneas. My obstructive apneas are relatively easy to control, but the central apneas are extremely inconsistent and difficult to control. The first thing that I learned is that a night or even a week isn't enough to understand if a change in configuration is an improvement, there is just too much randomness. This is why it took me well over a year to understand the best settings and limitations of the S10. I analyzed the data in Excel to look at different combinations of settings across a couple years of data before I got close enough to be able to tease out the various effects.
I was able to get my AHI down to around 2 - 3 pretty consistently, but oddly only with my old S10. The new S10 consistently runs 3 to 4 with the same settings. They have different firmware and the pressure profile is different when it switches between EPAP and IPAP. But the old machine has over 18,000 hours and I don't want to rely on it. I know the pressure profile is different because I attached a pressure gauge and looked at what happens when I breathe. They are the same static pressure but behave very differently when breathing. The newer S10 software has a overpressure peak during the first part of the IPAP, especially when using the pillows mask setting. This is probably good for obstructive apneas but it triggers centrals in me. The full face setting is better, but not as good as the old machine which is more of a simple switch between EPAP and IPAP. If EPR is off on that machine the mask pressure remains fairly constant between inhale and exhale. You don't necessarily see this effect on OSCAR charts because the machine is doing the reporting.
My Z1 travel machine is interesting, it basically has the opposite of EPR, there is an increase in pressure during the first half of exhaling. Its uncomfortable but I feel pretty good when i use it. When I was working I traveled almost every week and used that machine quite a lot. Generally I felt as good if not better than when home with an APAP. Without data I don't actually know what numbers I get with it. I still use it once in a while if I'm away for just a day or two.
As for the S10. I'm sure everyone is going to be different, this is just what I found for one person (me). My central apneas are incredibly inconsistent, I can only work out the details with a lot of analysis. Before retirement I was an engineer who spent most of my 40+ year career optimizing analog and digital systems, the process is pretty similar to what I did then.
For me:
EPR at any level doubles or triples the number of central apneas + hypopneas. EPR during ramp doesn't help because I already get high number of central apneas during transition. I'd sometimes pop in and out of sleep for a half hour to an hour because of being aroused by central apneas.
Higher pressure increases centrals, I had the best overall results by reducing the maximum pressure until the obstructive apneas showed a slight increase. I look for pairs of apneas where the first is obstructive followed by a central right after when the machine increases pressure. Or a pair or series of obstructive apneas which showed the need for more pressure.
A cervical collar improved my obstructive apneas so the machine runs at lower average pressure improves my central count as well.
Using the full face mask setting with pillows was better than the nasal or pillow setting, more so on the 4G machine than the older machine. The full face setting has less pressure bump when switching from EPAP to IPAP.
The soft response setting isn't as good as the standard response setting, it tends to hang onto pressure increases longer.
The old firmware on the S10 with the 2G modem works better for me than the newer firmware on the 4G modem unit. My AHI on that machine is about half of the newer machine. (with the same settings)
Sleeping on my left side has a pretty dramatic bad effect, hugely increasing central apneas. My blood O2 often drops to the low 80's on my left side, especially during transition sleep. I learned this by setting an alarm on my O2 ring which would wake me up at 87 or so.
Sleeping on my back reduces my central apneas much more than it increases my obstructive apneas. My AHI is lowest on my back, but only a little higher on my right side. Left side is terrible.
It was common for settings to reduce the number of central apneas while increasing the number of hypopneas, leaving the total AHI about the same. This was especially true when a setting is better but something else wasn't optimum. To me its an indicator that things are better but still limited by something else.
Recently I purchased an AirCurve 10 ASV on craigslist. It consistently gets my AHI under 2, averaging just over 1. I feel better, but I'm still tuning for comfort because it sometimes wakes me up. I found the ASV at its default settings to be really brutal, like mouth to mouth from a jet engine or something. But it gives good results in almost any configuration I've tried. I still wake up more often than with the 2G S10 machine, but it gives me a lower AHI and fewer flow limitations. I'm getting used to it over time and working on settings to make it comfortable without reducing effectiveness. But its a totally different animal to tune....
In the end my used ASV machine cost me about the same as my mattress, it was well worth the price. I should have insisted on an ASV prescription years ago, with or without insurance. Life is too short to let the insurance company ruin it. The NP at my Pulmonologists office gives me a hard time about changing settings, it will be interesting to see her head explode when she see's my new machine
