Here's the deal with pressure support (that difference between inhale and exhale)...in some people it can cause an imbalance in the gas exchanges that happen during respiration. It ends up causing central apneas to happen because of too much carbon dioxide wash out and it's actually carbon dioxide levels that the brain recognizes as a trigger to tell the body to breathe.
The weight loss has most likely caused a lot of changes in your entire metabolism and for some reason brought you to the point where your breathing has changed and you get too much carbon dioxide wash out with the bilevel pressure support settings you used to use without a problem. I have seen this happen with a couple of other people who had a significant weight loss...not only do they not need as much pressure to control their OSA...their bodies develop the unstable breathing gas exchange problem when using any form of pressure support or even just a little exhale relief.
You might find that with more weight loss the centrals want to creep up again and if that should happen we would first want to reduce PS even more. It's your body changing overall that likely causes it but I don't understand how the mechanics of how weight loss itself causes this problem.
I am not so sure you need the 8/11 settings at this point...you might be able to get by with less pressure. I don't know if the pressures are a factor in the complex sleep apnea or not but at some point if all you ever see are central apneas then a new sleep study done without cpap of any kind might be in order to see if you got lucky and your OSA went away with the weight going away. Of course gotta keep the weight off as well.
In your situation for right now....PS was your problem....it caused the centrals and that's not common but not totally unheard of either or I wouldn't have thought of it. Sometimes there is a very fine line where PS is the problem. I have a friend who gets about 20 centrals per hour with PS of 4 and essentially none with PS of 3. Go figure that one but sometimes a small change makes a big difference.
I don't know what you are going to tell your doctor about what you have done. They usually aren't too keen on "someone on the internet told me to do this"....
but I don't think you need 10/15 for sure and obviously PS is the culprit here. PS of 5 would likely have shown a small reduction in the centrals but not enough because we already know that the centrals were too numerous with PS of 4.
I would run with these settings for a week or so and see if they hold and if you wish to try maybe auto mode later to see if you really need 8/11 for OSA treatment...we could maybe give it a go and see if you can get by with even less pressure. Choice is yours.
Sort of do a DIY titration at home to get an idea what pressures are needed to deal with your OSA (assuming you still have it after the weight loss). I have a good friend who was able to lose her OSA and need for cpap after her weight loss surgery and the loss of weight (and she kept it off). I can't guarantee it for anyone but sometimes losing the weight does mean losing the OSA.
It's obvious that PS is your problem with the centrals though.....your body doesn't like it so don't let your doctors try to do it.
If you do decide you want to do a DIY at home titration...I am here to try to help.
Glad my little idea worked out. It was my only idea....
I may have to RISE but I refuse to SHINE.
