gone back to full mask

Ok so for the last week my AHI has been below 5 ...high pressure is max ie 20 and low is 13 ..so will increasing the low reduce my AHI further?

Yes...increase to 14.

What were your settings and general AHI before you went back to the FFM? It looks like you will need more min pressure, unfortunately.

Pretty much everything on the events graph that you see flagged is related to obstructive stuff going on in the airway with the exception of the CAs/centrals.
And more minimum pressure is usually what we suggest when we see more obstructive stuff happening than we want to see.

So yes...more minimum pressure is going to be needed to bring down that AHI. It won't help the central index though...more pressure doesn't fix centrals.

My low pressure with other mask was about 8.00 ... in laymen terms what are Centrals?

Central apneas are cessation of breathing but the airway is open. No effort to breathe. Hold your breath for 10 seconds...that's pretty much a 10 second central apnea.

A few centrals (real or not) isn't a big deal for most people. For the people who have so many centrals that it does create a problem then there are other machines that can actually breathe for you when you don't breathe on your own enough....would need at least 5 per hour average over many nights before we start worrying. Yours no where near worth worrying about.