why a mask would make so mush difference in my AHI.

Can some one help me understand my AHI reading. I have been on auto-pap since 2005 and like others has tried about every mask our there. My AHI always was always run between 2 to 5 but never over 5 so figured it was OK. Most of the time my AHI would average about 2.5 to 3. Also I can not say I slept any better with cpap as I did before I used cpap. But the cpap machine seemed to do it job AHI wise. BUT I got a new mask ( ComfortGel Blue Full Face CPAP Mask) My sleep have been the best in years and my AHI has never gone above 2 for month's.
Why would a mask so greatly affect my AHI reading. The other mask also fit well and did there job it appeared but they must have had some affect on my AHI reading. I also noticed there is more dead space in the new mask then in other mask. Can anyone help me to understand why a mask would make so mush difference in my AHI.
Thanks
Gil

What was the old mask?

If you are now using a FF mask where before you were using a nasal mask, it is possible that before you had some minor leaks from mouth exhaling that were affecting you AHI, but not your sleep.

When i mention the old mask i would have to cover 20 different types of mask including all the popular ones and some not so popular. So its not one mask but all the old mask i have used in the last 7 years. Hope this helps
Gil

I have been using a full face mask for the last 2 or 3 years before that i did use nasal mask. but the results were the same except for the new mask
Gil

Sometimes is isn't all about the numbers...sometimes it is about the quality of sleep.
Perhaps in the change in the mask allows for more "good" sleep for some reason or another. Perhaps getting a little more hours of sleep has occurred or less fragmented sleep.

Also, some people do see a rather marked difference when there AHI happens to fall below a certain level when compared to another higher level even though that higher level is still under 5 AHI.

So perhaps a combination of factors have come together to let you finally feel better.
I had a similar thing happen to me when I experimented with a bipap machine. Minor improvement on an already quite acceptable AHI but a substantial difference in how I felt in general.

You are talking about a change in AHI of 1 per hour...that change is insignificant and could be the result of many factors. After 7 years of successful treatment, I don't know why you would be still checking your data daily.

Gil,

I should have asked: What type of mask?

Some people (like me) get better AHI results at the same fixed pressure with a nasal mask vs a full face mask. Example: with a nasal mask at 14cm pressure you are getting all of that air into your nasal airway; if you use a full face mask that same 14cm is diffused through 2 airways (mouth and nose) and might be less effective at that same pressure. I need to raise my pressure by 2 cm when I use a full face mask.