What makes a machine say CA (central apnea / clear airway)?

When I was getting acquainted with my machine (it's an ibreeze, in case the auto text isn't working), trying it out while awake, I wanted to understand what it was responding to.

I could generate as many "obstructive apnea" flags as I wanted, just by pausing for fourteen seconds between breaths. Usually, ten seconds is enough, but when I think I stop and start a breath isn't always the same as when the machine does. Fourteen seconds is a pause that's short enough to be easy to repeat with every breath, and long enough to guarantee that every single breath will be flagged as an obstructive apnea event. Hypopnea flags and flow-limitation flags aren't as easy to generate consistently, but they show up.

No matter what I did, I could not get the machine to flag anything as a "central apnea". I pause between breaths with my airway open, breathing through my nose as usual, and it's marked as obstructive. I pause between breaths with my mouth open, and it's still marked as obstructive. Nor have I ever seen it flag an event as "central" that happens while I'm asleep.

I thought I found a description some time, but now I can't find it. I think it was something to do with percentage of baseline amplitude over the previous however-many seconds, same general idea as for flagging events as obstructive, just with some difference in details. I've also seen stuff that seems to say it's about the flow in response to the pressure fluctuations that the machine makes after I haven't been breathing for a few seconds.

Anyone know?

The iBreeze creates small pressure oscillations (pulses) that flow through the tubing and into the mask. The algorithm then compares this pressure with the corresponding flow response.

Thank you. That's what I thought -- as far as it goes. But what kind of flow response is it looking for, and what can cause that? As I said, i tried holding my breath while keeping my airway open, with all the variations I could think of, and none of them got flagged as a "central apnea" by the machine.

dsws wrote: ↑

Sun Aug 10, 2025 7:56 pm

i tried holding my breath while keeping my airway open

Bet you can't do it.

The vocal folds, along with the surrounding tissues, form a structure known as the glottis. When holding your breath, the vocal folds adduct (move closer together), effectively closing the glottis and preventing air from entering or leaving the lungs.

The algorithm is on to your attempted trickery.