AHI vs facemask type

After 4 years of using a nasal mask I recently had to convert to a full face mask. While on the nasal mask my ahi ran 2-4. After finding a mask that fit me well and the leakage was acceptable I cannot seem to get my ahi stable. It wants to be anywhere between 5-10 and very erratic. Is there anyone that can explain why the difference or what I can do to improve my ahi? My pressure is 9cm H2O. I am using a Remstar pro m series with encore basic software. My titration pressure was 8-10cm.
Any help will be very much appreciated.
Jack

A few years back, I recall a post (can't recall from whom) with the opinion that a nasal mask might lead to a lower AHI over a FF for some patients, with the proposed reason being that the lower part of the FF mask might push the chin, and thus the mandible back toward the airway leading to airway occlusion.

The idea made sense, and anyone can try this themselves. Just breath normally, then try pushing your chin back toward you.

Alternatively, a nasal mask pushes on the top teeth, not physically affecting the airway.

The rationale made sense to me. Quite possibly described in the literature or discussed hereabouts in depth, but I haven't come across it. (No time now, will check later.)

This is one reason that I decline to use a FF, unless I have a bad cold.

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In theory pressure is pressure no matter which mask delivers it but in real life it isn't unusual for people going from a nasal mask to a full face mask to need a little more pressure to get the same job done.

I have seen full face mask users go to a nasal mask and end up being able to use 2 or 3 cm less pressure.
And I have seen nasal mask users go to a full face mask and need 2 or 3 cm more pressure.
Sounds like you need a little more pressure. I would start with 1 cm if it were me and move up slowly if that was what I had in mind to try to get the AHI down.

Thank you both, Captain Midnight and Pugsy. You have explained the reason why and a fix. I will make some adjustments.

I have experienced the same thing. I generally get a lower AHI with a nasal mask rather than a full face.
In my case I think I over breathe with the full face making my oxygen rise so my brain decides not to breathe and I get a lot of centrals.

G J writes...Thank you both, Captain Midnight and Pugsy. You have explained the reason why and a fix. I will make some adjustments.

Before we quit this discussion, might I ask why you are going from nasal to FF mask? If it is not something intolerable, it might be worth considering to stay w the mask that requires a lesser pressure for a therapeutic effect. (Think leaks and a longer list of potential "issues" that some folks get as pressure rises.)

This is not advice, just a suggestion to keep all paths as open as possible.

Good luck . . . Capt Midnight

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I have had bad sinus infections and just got over my fourth surgery two weeks ago. I am under care of a otolaryngologist and an infective disease doctor. I breath through my mouth and have tried various chinstraps to no avail. The thought is that the nasal having a smaller reservoir will tend to push air at a greater direct velocity tending to carry bacteria throughout my sinuses.
The FFM having a greater volume will cushion the pressure allowing it reach max more slowly. I know I pay for it by having a greater total pressure on my head.
I clean my mask and tank daily and sterilize with alcohol. Have even bought a So Clean2 trying to keep bugs to a minimum. I really prefer to use a nasal but trying to do everything to help. I have been on antibiotics for the best part of the last year and do everything to get rid of infections. My machine will be 5 yrs old August.
Any thoughts as to where I am going will be appreciated.Thanks CM.