My CPAP lowered pressure and AHI increased- why?

[Naama]

Hi there,
I have been using my CPAP for a little over six months now, am a able to say I got used to it and mostly manage it well. 
Ever since I started using, and with the help of a strict diet, I lost weight, not too much, but enough for now (around 5 KG). 
Either because of that, or maybe because I got used to sleeping with the machine, and due to airophasia, I lowered my original high-end pressure from 10 to 9.5, and have been sleeping this way for at least three months now. My AHI were great (between 2-3, sometimes less than 2 even), and all was well. 
Then, for a reason I don’t know, three nights ago, the CPAP lowered the average high-end pressure to 8.5, and my AHI spunk to around 5... any idea why the machine should do that? Needless to say I didn’t change anything in the setting and pressure range is still the same as it was - 4-9.5 cmH2O. 
Would appreciate your insight on that, and if anyone can also explain the mechanism by which the CPAP works, aka chooses the top pressure level nightly, would be happy to hear. 
Many many thanks and good day to all,
Naama.

[Naama]

Just as a clarification: the pressure range is still programmed the same - still 4-9.5, only the 90% measure (indicating which pressure has been used for 90% of the night), says 8.5... 

Why didn't the machine use it's maximum pressure of 9.5 to decrease the AHI below 5??
Would appreciate you help here..
Could it be that something is wrong with the machine? Should I contact my provider?
Thanks!

[OpalRose]

Hi Naama,
The Apap will not use the maximum pressure set if it detects for example, Clear Airway Events, as the Apap will not raise the pressure in response to Clear Airway Events. That may be one reason why your AHI is higher, and we would simply be guessing without seeing your data.

Download the free OSCAR software.  (Be sure there is an SD card in your machine.)

How is your Aerophagia? That is key to what we advise as far as pressure changes.

Use the links below in my signature line to guide you in taking a screenshot of the daily page.
Organization is important.  Then use the Attachment Feature to post a screenshot here.

[ragtopcircus]

Well, you should download Oscar and post some charts. Others with more expertise than I will be able to help more if they have data to work with.

However, from what you have said, the minimum pressure of 4 is probably too low. It is too low for almost everyone.

I would raise the minimum pressure to 7, use an SD card to collect breath-by-breath data (only basic data collected without SD), and use Oscar to post the results here for the experts to review.

[Sleeprider]

The Philips CPAP Auto works best when you optimize the minimum pressure. Since you are using a range starting a 4.0 cm, it's clear you have not done so. Philips is overly reliant on apnea precursors like snores and even hypopnea to increase pressure to where it is effective against obstructive events. I suspect that with your weight loss you may be snoring a bit less, but still need the higher pressure. I'm certain if you changed your minimum pressure to 8.0 your results would significantly improve, and you might even start beating the 2 AHI.