Resmed flagging CAs vs OAs

Hi There,

I have a specific question, more of a general interest, does anyone know or can explain why some events are flagged as CAs va OAs?

I understand what the difference between a central and Obstructive apnea is, but how does the machine (Resmed specifically) choose what breathing events to flag as a CA vs an OA.

Image attached as the prime example, the Resmed flagged 3 CA and 2 OA, but looking at the waveform, all the events look pretty much identical. (and from personal experience - see other thread, i think these are all CA's..)
So is there some difference I am not seeing, or some other indicator the machine is using to differentiate, or is it just a best guess?
(I realize at the heart of it, it's just a math formula / equation of some sort making the determination, but still interested to know the inputs and outputs to come to this conclusion)

fyi, apologies if answered before, I did try searching for this topic, but ke-yworkind the search is kinda difficult.

APAP machines need to know the difference between the type of event (Obstructive vs Central). It uses a technique called Forced Oscillation Technique) FOT to determine the difference.

The reason it needs to know the difference is because OAs are treated with pressure, CAs are not.

If you zoom in on the apneas you will see after 4 seconds the pressure oscillations. A clear airway will have slightly more flow and slightly less pressure than a blocked one.

ahh that is super interesting..
I had noticed that "buzz" on the pressure graph, but didn't know what or why it was there..

here is a couple super zoomed in comparison between a CA and OA.
in the first one, about the only difference I can SEE is the waveform is slightly smaller at the end of the OA vs the CA. In the second shot, the OA has a larger oscillation vs the CA.

my guess was the presence or lack of an exhale breath prior to the event, as it seems the CA's have more of an exhale dip, where as the oa events seem more to be flat.

anyway, it's not a big deal one way or the other, at least now i have a term i can google for more reading (FOT). Thanks!

Watch this: https://www.youtube.com/watch?v=4GW97Xk06N8