ASV Impact on Central Apneas

[Gideon]

When the “central event” is recognized by the ASV and (I guess) the Pressure Support kicks in to raise pressure, can this be detected by my body in some form of arousal that impacts my overall sleep quality…. negatively?
It can and does.  Not all the time and not for everyone. This is what you have to get used to with an ASV. With other therapies, other than ASV, we try to keep your pressures fairly, not absolutely, smooth with easy transitions.  With ASV it is the pressure differential that does the work, and it needs to be done on each breath that drops the Minute Vent. (G)
Then, if I don’t start regular breathing within that breath, does the machine kick the pressure up even higher? And, eventually produce a significant arousal?
Not on subsequent breaths, It raises it on the target breath up to the max PS. Getting this several breaths in a row, where multiple UAs are reported, that is your metric though you likely want to look at the UA and see what it looks like.[b](G)[/b]
If any of this is true, then wouldn’t it be advantageous if the machine (algorithm) counted these events and reported some metric other than AHI to test whether “central events” are impacting sleep quality?
Keep in mind that an ASV is a completely different animal.  EVERYTHING occurs in a single breath. It is not spread out like you see with other pap machines.[b](G)[/b]
Last questions for today:
I understand that I may not NEED to lower pressures, but is there any downside to lowering the pressures to reduce the incidences of “runaway” pressures? If the AHI doesn’t increase, why not operate at lower pressures?
We lower Max Pressures to limit runaway pressures from flow limits and obstructive events on non-ASV machines.  The ideal solution is not to lower pressures but to treat the obstructive events and thus prevent them from running away.  A lot of the runaway pressures are from positional apnea coming from chin tucking which is typically resolved with a soft cervical collar.  The collar may be needed with ASV as well.  When it is we see a lot of events which is unusual.[b](G)  [/b]
Gideon said:
“Lowering Max PS limits the response to a Central Apnea “
Does that mean the “central event” then becomes an apnea? .. maybe one of the “unclassified apneas” I see occasionally in Oscar?
Yes this can be one cause of UA events.  Note that non-ASV machines evaluate the event and then act on it in subsequent breaths to prevent future events.  With ASV all action occures in this initial breath which actually changes the shape of your breath in the flow rate and thus makes events harder to evaluate and classify.[b](G)[/b]

My reply is embedded.

[S. Manz]

Actually you are correct. The root causes of Central Apnea weren't even fully understood until recently in 2008 when Mayo Clinic researches found a link between not only opioid drug consumption but also the long term use of CPAP to treat Obstructive Apnea. (They call this graduation from Obstructive Apnea to Central, a "Complex Central Apnea" and some people mistakenly assume that Complex CSA means "several causes" driving their Central apnea.
Anyway, yes, with Central, one is not making an effort to breath like people with Obstructive do, so technically it shouldn't even be called Apnea

[Spy Car]

The “blow-back” routine to reset runaway pressures was new to me and I tried it. It works. But, of course, I can’t do that all night… The overall objective has to be to get a good night’s sleep!

Absolutely. Typically one or two series of blowbacks will "temper" a runaway machine for the night. 

Can't be doing that all night long.

As I said it is very typical (an my own) that a little struggle goes on between users and their ASVs. And times when one falls into perfect sync, which is dreamy.

Do post OSCAR results her and help the gurus cut your levels down to the point where they start to negatively impact results. 

Bill

[SarcasticDave94]

FWIW I had to enact the blowback several times, forgot specifically how many times, but only for say about the first 2 weeks it was needs as I drifted off to sleep then BAM! If you get the settings close to the needed area for your therapy, and as you get used to the patterns of breathing, it gets better.

[Spy Car]

FWIW I had to enact the blowback several times, forgot specifically how many times, but only for say about the first 2 weeks it was needs as I drifted off to sleep then BAM! If you get the settings close to the needed area for your therapy, and as you get used to the patterns of breathing, it gets better.

The one area where the ResMed ASV algorithm could use some work in my estimation is better dealing with the moment on sleep transition. It seems to me that the normal slowing of breathing that occurs as one falls asleep can tripper these machines to overreact.

And for myself, having that transition broken can make it hard to reenter "sleep."

It gets better, but this is the one element in an otherwise great product that could use some work IMO.

And it is nice to see you Dave!

Bill

[RayBee]

I turned the Ramp feature on, on my ResMed ASV. It is only set to 5 minutes. Pretty short, but I can usually fall asleep in those five minutes. I think this is an important feature to turn on if you have a problem with the ASV occasionally going wild on you while falling asleep. It happened to me more often than I had hoped. So, the Ramp feature easily solved that problem for me.

[SarcasticDave94]

You have an interesting idea RayBee. Sure, if you keep it short, Ramp might be helpful. It's better to use the Ramp and get some use out of ASV therapy than not benefiting from therapy.

[conphil]

So…. I do a simple exercise that probably all of you have done sometime… I hold my breath. The ASV triggers this cessation of breathing, and within a couple of seconds the pressure support goes to work. It drives up IPAP pressure incrementally until PS reaches MAX PS (in just a few seconds).

Within this one breath I doubt that the algorithm can distinguish whether this is a “central” event (e.g. no effort) or an “obstructive” event (blocked airway). I suppose it’s both… my brain says don’t breathe so the muscles get no signal to breathe AND the airway is blocked (my throat is closed).

If I hold my breath long enough (>10 seconds), the ASV registers an apnea.
If the P.S. is set very high (say 15) and MAX EPAP is 15 (both ResMed factory default values), this results in MAX IPAP of 30.

I can attest that I can’t hold my breath for 10 seconds while keeping the mask on my face (try it). The pressure becomes so high, so fast that major leak occurs. I think the ResMed engineers expect that the settings we’ll be using are high enough (Max IPAP) that a central apnea will never develop. It will never persist for the 10 seconds required to meet the definition of a central apnea. Maybe it can persist long enough to register as hypopnea.

However, an obstructive blockage can persist sufficiently long that an apnea can result and be recorded as an obstructive apnea. And, that’s what the ResMed clinician manual says:

         any apneas reported by the device will be obstructive or indicative of a closed airway

Oscar records these apneas as Unclassified… My conclusion is that the ASV apneas are all Obstructive apneas.

Arguments? Feed back?

[SarcasticDave94]

I personally think, although the ASV doesn't monitor brain waves or have an effort belt input, I think the ResMed ASV is smart enough to know this is fake CA and isn't responding as it would for real CA. I would disregard/dismiss most of this exercise's results. I'd not trust it anyway.

[conphil]

I think the ResMed ASV is smart enough to know this is fake CA

Dave, I’m using this experiment only as an example of how the ASV probably functions. It can’t determine that it’s a “fake” anything.....It’s just a cessation of breathing. I thought of this as sort of a summary of where I am regarding the subject of this thread “ASV Impact on Central Apneas “… my thanks to all of you folks who have so generously communicated information that’s helping me learn a few things.

When a person stops breathing for any reason, the ASV device certainly can’t know why… it only recognizes that the cyclic breathing terminates. And, then it offers a shot of higher pressure air to try to re-establish the cyclic breathing…. And it happens so fast that a “central apnea” doesn’t have time to develop.

My observation supports that the ASV records only “obstructive” apneas like the clinician manual says. And, the follow-on conclusion I have postulated previously is that within the parameters that I can adjust, it doesn’t matter what settings I need to control obstructive apneas… the machine will record only obstructive apneas. Said another way.. central apneas are not impacted. They are never there.
However, some events that would have become centrals could morph into hypopneas (not sure if that happens… only a theory if the initiating event lasts long enough to meet the definition of hypopnea.)

Guess I’ve come full circle here because of all the fine inputs you all have been making…. Nothing new to you experienced folks, but very helpful in my learning curve… thanks again.