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Clear/Central Apneas, BiPAP, CO2 washout confusion.
Hi. I was hoping someone could explain (or point me to the best threads) on here concerning the relationship between central/clear apneas, pressure, and treatment type.

I have read people use BiPAP or ASV treatment to reduce central or clear apnea (CA) events, because normal CPAP/APAP treatment with higher pressures increases CA events. - So pressure relief on exhale reduces CA events. RIGHT?

BUT . . . to the contrary:Thinking-about
others talk about lowering the exhale pressure causing "CO2 washout" - which in turn causes an increase in CA events.Huhsign

These scenarios seem contradictory. Does lowering exhale pressure reduce or increase CA events? Or is there a sweet spot for exhale pressure and CAs increase both directions from that differential?
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To add to the mix, look at what is actually going on:
1. obstructive is when you are exerting an effort to breathe, but not succeeding-your airway is physically blocked-someplace
2. Central is when, timing wise you should be taking a breath, but you are not even trying to breathe, zero effort to breathe.

So what can make your brain not even try to breathe? Damage to the brain stem-yes. something that makes you "catch" your breath-yes. taking a breath and holding it while you toss and turn-sleep/wake junk. Some people catch their breath when air is puffed into their face, or when the pressure changes-same thing. Anything that interrupts or disturbs the natural rhythm of your breathing.

Pressure changes, exhaling into pressure, moving, and of course your breathing is triggered by your CO2/O2 levels, if your brain stem thinks they are fine, it will not trigger a breath. Breathing has two purposes, maintaining proper O2 levels and making sure that CO2 does not build up in your system.

A central can be caused by many things and several things.
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Building on PoolQ's answer: ASV machines treat real central apneas by using enough pressure to pretty much force you to breathe in. BiPAP, in its many various names, does not treat CA. It is for people who need higher pressures or a higher level of pressure relief on exhalation. But exhalation pressure relief can lead you to exhale more fully than you normally would which reduces the CO2 in your body and that results in your body not triggering a breath. At least I think that is how exhalation relief can cause CA.
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There is some confusion because, at least with Resmed and I think Philips Respironics, the machines intended to treat central apneas are also bilevel machines but they also have a back up system to help the patient to trigger a breath when one is not being triggered by the patient soon enough. The terms bilevel, bipap, VPAP can include the ST, T, ASV mode machines that are for central apnea as well as the straight bilevel machines that have no backup rate like the VPAP Auto that I use.

Best Regards,


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