Ths may seem like it is a bit OT, but I will come around to the point I am trying to make. Also, if you see some odd typos, it was because two of my cats were demanding 'pressure therapy' (in the form on a hand applied firmly to the back, and moved backwards) while I was typing, and tried to walk on the keyboard
As I get more experience with the IntelliPAP machine, I have personally observed that this machine can be 'squirrely', as was reported occasionally in the product challenge reviews on the machine. This condition is typified by the machine going to max or near max pressure and more or less staying there. I have since (at least for me) discovered why this is happening. If you are significantly below your 'titrated pressure', it can cause this machine to experience this 'runaway pressure syndrome'.
I have recently gotten my sleep study results, and was surprised by what I wasn't told. They could not successfully titrate me, and were recommending BiPAP or even Adaptive servo veltilator BiPAP titration if the high rate of pressure induced centrals could not be controlled.
I think my sleep doctor, in the interest of avoiding one or two additional expensive sleep studys and the possibility of having to have me use a machine that is priced in the mid thousands, decided to try an autoadjust CPAP set to just below the pressures where centrals were dominating the treatment picture. This was 10-13 cm/H2O.
I have always used a full-face mask of some sort. I currently use the Hybrid, which has worked very well for me.
After taking some time to get used to the IntelliPAP (my choice-- bought online), I found that the machine was 'maxing out' at the top end. I slowly increased the top end until I had a range of 10-16. I frequently maxed out this range as well. But after about two months of experimenting with variables such as hose length (and a lot of disruptive travel), I finally started walking up the minimum pressure. Each time I did this, I would have one terrible night with very high (12-16) AHI's. I would often see runaway pressure, and lots of NRI's. (NRI is what DeVilbiss considers to be a 'central'-- more later.) However, the NRIs were nowhere near the level of what was seen on my sleep study.
When I finally reached 12 cm/H2O, suddenly there was a change in the way the machine operated. The 'runaway pressure syndrome' seemed to be a lot less frequent, and seldom lasted most of the night. There was a significant reduction in my AHI (average 8 to average 6-- my AHI varies all over so it takes at least a couple of weeks to see a statistical change). The NRI rate has decreased, but EPI has become more variable, sometimes wildly variable.
My sleep doctor suggested (and I agreed that this seemed to me to be where I was 'headed') that I work up to a pressure range of 14-18. I first increased the high end from 16 to 17 and left it there for 3 nights. No real change, and the mask seemed to be able to deal with the pressure. So last night, I increased the low end to 13 cm/H2O. Much to my surprise, I had a AHI of 3.3, and an average pressure of just 13.5. No NRI's, and an EPI of 1.8. I also observed that the higher pressure was very comfortable in the sense it wasn't varying a lot.
So based on the above, I have reached a number of conclusions. The first conclusion is that the IntelliPAP is a great machine, provided that your minimum pressure is set high enough. Below that pressure, there is a tendency of this machine to experience 'runaway pressure'.
The second is that EPI is of questionable value. Why I am I showing any EPI at all with a full face mask? The average EPI is around 4, and it seems to have peaked right about the time I reached 12 cm/H2O. At that point, it would vary from about 1 to 14. I have one instance of 30. Only one instance of 0. How can this be? I did not see any clear correlation with mask leakage. It will be interesting to see if EPI stays this low as I work up in pressure.
The third conclusion is that NRIs are not necessarily centrals. I know that making a positive determination of a central is a very tough thing to do, short of having thoracic and abdominal movement sensors. In looking at my graphs, some NRIs are almost certainly centrals-- occurring at times when pressure is steeply increasing, or in clusters of what the machine flags as snores and obstructive apneas. Others just randomly occur (and these are infrequent). So, I suspect that like EPI's, a certain percentage of NRIs are some event the machine cannot fully 'understand'.
Lions can and do snore....