AHI -- supposed to include CA apneas?

[RonWessels]

The other thing that looking at the detailed data might show you (it happens with me) is that if most of your "apnea events" occur while you are still awake, they should be ignored. Only apnea events while you are actually asleep count towards your true AHI value. Since your machine cannot tell whether you are awake or asleep, that summary AHI value might be artificially high.

[archangle]

It's been said in many places that "model X machine doesn't detect central apneas."

Unfortunately, this statement is wrong, or at least confusing. What it means is that the machine being discussed can't tell the difference between an obstructive apnea and a central apnea. It will detect that an apnea has happened, but can't tell whether it's obstructive or central.

If you have a central apnea, one of these machines will call it an "apnea" or may even call it "obstructive" apnea.

It's difficult for a CPAP machine to distinguish between central apnea and obstructive. In sleep tests, you use a "chest effort belt" worn around your chest to see if your chest is trying to breathe, but your airway is blocked.

More recent CPAP machines attempt to distinguish the two by using various kinds of pressure variations and pulses. Even now, the machines don't always get it right, but if it says "central" or "clear airway" apnea, it probably is a central apnea. If it says, "obstructive," it's possible it may actually still be a central apnea.

ResMed S9 and Philips Respironics System One (PRS1) machines can tell the difference, if it's one of the machines that collects data at all. Earlier models either don't try to tell the difference or are very much less good at it.

I have heard that some of the ASV machines will not ever report a central apnea, because, when they detect a central apnea, they will increase pressure enough to force you to breathe, so they don't flag an apnea.