ASV Impact on Central Apneas

[conphil]

Hello, I’m a new member, 10 years a “brick” CPAP user. Recent test revealed high rate of central apneas, and sleep doctor prescribed ResMed AirCurve10 ASV Auto. 10 days of use; I’m getting satisfying AHI’s <3; but not sleeping well: fighting mask discomfort, leaks, and runaway high pressures.
Saw a blog suggesting lowering max EPAP and max PS to reduce runaway pressures. I’ve been doing this gradually while making sure AHI doesn’t increase… It’s working, and I’m fighting the mask less.

But I want to understand, generally, how my new machine attacks central apneas.

My Oscar charts show an occasional “unclassified apnea” that I thought might be a central apnea until I read the following in the MesMed clinician manual:

"AHI and Total AI: Central sleep apnea detection (CSAD) is not active in ASVAuto and ASV modes. The ASV algorithm eliminates central apneas. Therefore, any apneas reported by the device will be obstructive or indicative of a closed airway."
I suppose this means that the machine reacts to eliminate central apneas based on a set of instructions (an algorithm).

My questions:

• Does this machine truly eliminate central apneas? (or is it simply not able to record them?)
  
• I’m adjusting maxEPAP and maxPS… currently down to half of what was prescribed (maxIPAP28 down to 14). Will such adjustments impact central apneas?
  
• Pressure adjustments should impact only obstructive apneas / hypopneas… right?
  
• Can I conclude that: The ASV Auto machine will prevent ANY central apneas at ANY pressure settings?
  

• For lowest AHI and best comfort does it make sense to drive down the max pressure settings while keeping min settings high enough for unobstructed airway?
  

I’d sure appreciate a layman’s understanding of whatever anybody can share about the ASV algorithm and it’s impact on central apneas.

[Crimson Nape]

Hi conphil! -
I have moved your post out to the Main forum. Hopefully, you will get answers to your questions soon.

[Gideon]

What happens:

1. The ASV finds your 90 second average numbers, focusing on Minute Vent
   
2. You stop breathing, via either the start of a Central or Obstructive apnea
   
3. As a result your Minute Vend starts to drop
   
4. ASV increases PS enough to compensate for this loss of volume 
   
5. No Apnea occurs because the ASV stopped it on the same breath that it was occuring on maintaining your breathing as identified by your Minute Vent
   
6. Exhale occures 
   
7. ASV resets for your next breath.
   

Your Questions
1."Does this machine truly eliminate central apneas? (or is it simply not able to record them?)"
It eliminates them and thus has no reason to record them.

2."I’m adjusting maxEPAP and maxPS… currently down to half of what was prescribed (maxIPAP28 down to 14). Will such adjustments impact central apneas?"
Yes.  Lowering Max PS limits the response to a Central Apnea
Lowering Max EPAP does little for CA events but does limit the response to Obstructive events.  If EPAP gets too high it could interfere with the amount of PS that can be applied to treat the CA 

3."Pressure adjustments should impact only obstructive apneas / hypopneas… right?"
EPAP is adjusted primarily for OA events.
Max IPAP can impact both Obstructive and/or central events.
Min PS is used to treat hypopneas, flow limits, RERAs, and UARS.  
Max PS can affect both Obstructive and Central events.

4."Can I conclude that: The ASV Auto machine will prevent ANY central apneas at ANY pressure settings?"
No. Badly set settings will reduce the effectiveness of both treating both obstructive and central apneas.

5."For lowest AHI and best comfort does it make sense to drive down the max pressure settings while keeping min settings high enough for unobstructed airway?"
Yes and no.
Yes, It makes sense to keep min setting high enough for unobstructed airway.
No. You must leave the settings high enough to do their job. they only NEED to be lowered is something is causing an issue, such as aerophagia which requires a decrease inressures to eliminate.  This is a temporary settig and should return to the higher settng once resolved.

[Spy Car]

@conphil Your questions have been answered in greater detail that I could have offered.

What I can offer--as a ResMed10 ASV user is that with seems like a very common occurrence for new ASV users to struggle a little in the beginning. Like being in a dance where both partners want to that the lead. Mixed with times when man and machine are in sync.

Whether the machines train us or the algorithms get more used to us (don't know) but most users do find we get comfortable in in sync with the machines.

If when an ASV "goes wild" (and it is not unusual in my experience in the beginning) the key is what's known on the forum as "the lowback method"). This entails a quick series of very forceful exhalations into the mask. This will cause runaway pressure to cease. Once can retake "control" in this fashion.

The great thing is these are very high tech machines that are built to effectively eliminate Centrals. The initial adjustment curve that seems typical is not ideal, but it is a short term problem that will solve a long term problem.

Best wishes for getting in tune with your ASV.

Bill

[SarcasticDave94]

Great description from Gideon on the ASV questions. It does excellent CA combat. Along the way, all the other Apnea get eradicated. The ASV can't record an event it caused to disappear. It does need correct pressure settings for the individual.

I used an ASV myself until COPD came to visit. So I used the ASV and you bet it will only give you excellent results at a minimum. If you can handle the ASV uniqueness on doing business, it'll only kill all Apnea as they begin to hatch.

Let's see the data. Show us OSCAR. If there's any tweaks needed, we can work it. How are you sleeping? Well, OK, poor? Details from you mean we help with passing on what we learned by doing. Good luck.

[S. Manz]

Actually I disagree with the first respondent who seems to have way too much faith in the ASV "algorithm". 
We design custom robotics that rely on "Servo" mechanisms" for their entire functionality and the ASV machines are no different.
A "Servo system" (ASV=Adaptive(or Auto) Servo Ventilation) relies on "feedback" in order to function, just like all other "Servo systems".
In the case of ASV machines, the feedback is "YOU" while you sleep...Rather it is "your breathing" pattern.
Now I don't care how sophisticated a Servo mechanism is and how fast its response time (aka response lag), when you stop breathing upon your Central events, all that the ASV can do is to supply you with breaths (a bit like blowing in your lungs during a resuscitation event). It provides you with breaths while monitoring your feedback which is all well and good, unless you decide you are not going to take the next breath by yourself, in which case the "algorithm" really has no other choice but to keep providing you with breath and eventually you WILL breath by yourself, but NOT necessarily because the ASV caused you to resume breathing after your central event, but depending on some individual factors, all Central sufferers eventually start breathing by themselves until the next event.

What we can conclude therefore is that even though the ASV machines are monumentally more sophisticated as compared to regular dumb PAP machines that simply provide positive pressure whether you need it or not, the ASV are not by themselves complete yet, because they simply function based on feedback and when that feedback is not provided, they can be just as dumb as a regular pap machine while they get into a loop.

That said, ASV machines are still very superior in providing therapy but we need to tone it down when it comes to our biases towards the machine...It is NOT as sophisticated as some imagine, because your feedback (or lack thereof) can render them pretty useless.

[Gideon]

Sorry I didn't provide a more technical explanation but the OP requested a layman's explanation so I dumbed it down. If you follow me me you will see I often do that.

[conphil]

You guys are all great with your responses. Thank you very much.

Yes, I need it in layman’s terms just now until I get into it. Everybody’s words are helping me.

Once I get past my startup mask issues (being worked with my DME supplier), I intend to get into fine-tuning and I’ll gladly share some Oscar charts. Right now I’m not sleeping too well, but the AHI’s are all less than 3 (lowest I’ve had in years)… so when I reach some stability I’ll focus on reducing hypopneas… the bulk of what I’m seeing so far.

For now, I’d like to continue probing in generalities.

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!

So, continuing on the subject of central apneas and the algorithm:

I especially liked use of the phrase “central events”… because since they do not result in cessation of breathing, they cannot be called “apneas” and will never be counted in AHI.

So, here are my follow-on “general” questions:

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?

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?

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?

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?
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?

[S. Manz]

In apnea world the medical classification for an apnea event is described as "The complete absence of airflow through the nose and mouth, despite an effort to breathe as measured at the chest and abdomen, is called an "apnea event" if it continues for 10 seconds or more. "
Since your ASV breaks up your central apnea events before they become an "event" as described above, then there's no logical or medical reason for the algo to record the number of events.
I have to checkup on this but if you see a lot of "Hypopnea" events on your chart, I believe those are precursors to Central Apnea events which the ASV breaks up and registers as Hypopnea because the ASV won't allow the event to become a full Central event when you completely stop breathing for 10 seconds or more..
If you zoom in onto a hypopnea event for ab=out 20 seconds before and after each event, you will see that about 8 seconds or se befor a Hypopnea event is registered , the "Flow rate" slows down is reduced by more than half the "moral" rate and when the eventis broken up by increase in "Pressure" and the whole episode is over within 10 seconds.
Please magnify a hypopnea event into a 1 minute scale and post with your next post so we can discuss it.

[SarcasticDave94]

S. Manz,
So what you described is in fact an Apnea, an Obstructive Apnea because you included "effort to breathe". Since we need to be technical, I am obligated to mention this critical difference. On top of that, I think an Apnea has a range of 80-100% cession of airflow for 10 or more seconds. A Central Apnea has no effort present. Even so, this ResMed's algorithm takes care of all things Apnea.

OK back to the regular program.

conphil, it would depend on taking a trend snapshot so to speak and see what your ASV needs for pressures on EPAP, PS, and IPAP to treat you and to maintain comfort. If you never crossed into 20 plus IPAP, it can be edited if it maintains comfort and therapy effectiveness. Sure it can be done, but let's gather a little trend data to base the edits on.