This question started when Mongo threw into a thread that his S-8 was a 24V system. Well, yes, ResMed had started using 24 for their Bi/VPAP machines back then, but my point was it was a really small portion of the universe and that they didn't really go in for a non-standard 24 V standard until the S-9s.
So, to answer your question, if the machine says BiPAP or ASV or Auto Servo or VPAP anywhere it is in the BiPAP/VPAP group which probably make up 10-15% of the world - auto machines are really considered CPAPs as lumped together by the medical/insurance/government cabal and probably make up 85-90%. You are really talking features, not major functionality differences that would exist between say someone needing to treat central vs. obstructive apneas.
The purpose here was to have an anecdotal, wild assed guess as to what ratio of the two kinds of machines there are in use. It has no realistic statistical validity. I just wanted to be somewhere on the paper when I try to conceptualize the split in the PAP community. 8:1 or 9:1 or somewhere in between I think would be reasonable.
Somehow you've managed to say a lot, but still leave me pretty confused =) I'll blame myself this time.
I think I'm just gonna start saying ABPAP. If one distinguishes an APAP from a CPAP, then I feel it's reasonable to distinguish an ABPAP from a BPAP. I don't know where to draw the line between what's considered a feature vs a function. They sound like the same thing, to me, when it comes to these machines.
As for ResMed going to 24 V on their S8 bilevel machine (VPAP), I would suggest that the wider split between IPAP and EPAP requires a more responsive blower motor; and 24 V makes that easier.*
* The blower may have to raise pressure by perhaps 6 cm in 300 msec.
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