Question on Pressure - Updated Info.

[ozij]

"Responding" to an apnea, for all autos:

1. Identifying an apnea
2. Noting when it has happened and how long it was
3. Raising pressure because an apnea has occured.

Resprionics will do no.3 at any pressure.
ResMed will never do no. 3 above 10 cms.
Puritan Bennett lets the response limit be set by the clinician / Users. The default is 10.
Devilbiss will raise the pressure if the flow drop is higher than 95% - according to Devilbiss apneas with that high a cessation in breathing are central apneas.

All four machines attempt to take pecautions against raising pressure when it should not be raised.
None is perfect about it.
Each machine (each algorithm) has a small part of the population for which it won't work for various reasons.

The Puritan Bennett and the Devilbiss are the most customisable algorithms, each in a different way.

O.

Edit: corrected percentage for Devilbiss

[dsm]

The A10 theory is that on reaching 10 CMs, the machine needs to respond more cautiously.

But before going into more detail, here is another monkey wrench into this whole Auto & responses debate. When an AUTO is above 10 CMs (Respironics or Resmed or whatever) and the nightly data reports that AIs have occurred & the user of the machine asks, "why did an AI occur, I thought the Auto would pre-empt them" - one response can be "but no Auto will treat a Central Apnea, so was the scored AI a central or an OSA event that got through the defence shield ?" - the subsequent answer to that posed question is likely to be "I don't have enough data to know if the AI was a central or a rogue OSA event".

ComplexSA is the condition where someone with OSA gets put on Cpap & when on Cpap therapy & starts exhibiting centrals that didn't show up in the initial sleep study. Does ComplexSA get worse at higher titration settings ?. IIRC, the answer is yes.

Geting back to A10
You post hits on the point I was making. That below 10 CMs - the A10 REMEMBERS Hypopneas and Apneas (as you defined) and it WILL raise pressure AFTER the Apnea, based on how long it lasted. As already discussed, like al Autos, IT WON'T ADJUST pressure while an no-flow apnea is in progress but below 10 CMs IT will raise pressure after the apnea whereas above 10 CMs it ignores the apnea, but still responds to Apnea pre-cursor signals.

So the answer is

Both below & above 10 CMs Autos don't adjust pressure when a no-flow apnea is in progress. Both the Respironics and the Resmed (A10) will adjust pressure AFTER an apnea when below 10 CMs (and they don't specifically differentiate between if it is a central or an OSA event (some brand of machines try)). Above 10 CMs the A10 IGNORES no-flow apneas but not the pre-cursor signals that indicate a no-flow apnea is about to occur.

Restated, when above 10 CMs, the A10 forgets a no-flow apnea just occurred, but below 10CMs it doesn't and it will adjust pressure. So in a nutshell the A10 when above 10 CMs will forget the effect of an apnea and only focus on adjusting pressure in response to apnea pre-cursor events that are associated with OBSTRUCTIVE apneas (snores & flattening of the INSP curve).

A10 does seek to pre-empt apneas when above 10 CMs. The Respironics, still remebers when an apnea occurs & tries out its special 'chair' pattern of pressure adjustment, over minutes, to probe the sleeper & looks to see what happened when it probed with pressure changes.

Therein lies part of the difference between these 2 approaches.

DSM

#2 Ozij's post also adds clarity to the whole story
#3 also saw SWS's post & it too clarifies

[ozij]

dsm, what in the world is a "no flow apnea"?
Your posts above are the first time I've run into that term.
An apnea is an apnea = non breathing. Air does not flow during an apnea.

An apnea can be obstructive= air cannot come in or out; or open airway = nothing obstructing the flow, but the brain is not sending instructions breathe.

ReMed assume that a "frank apnea" (ResMed term) above 10 cms has a great probability of being an open airway apnea, and it will not raise pressure when it sees that. It also assumes its response to flow limitations and snoring will create a pressure environment in which frank obstructive apnea will not occur. The assumption holds true for many, but not all.

All autos attempt to distinguish open airway apneas from obstructive apneas. They go about it in different ways, and they all err for lack or enough data.
The question is always: do I fall within this machine's errror group, or do I fall withing that machines error group?

O.

[dsm]

it is designed to "predict" onset of the apnea and thereby avoid it.

Right. That part is done the same way above 10 cm and below 10 cm. This is where the above and below 10 cm difference lies:

The pressure will not rise above 10 cm H2O when an apnea is detected, to prevent an inappropriate response to central apneas.

So above we can see Resmed trying to prevent apneas above 10 cm, but not directly responding to them as they would have below 10 cm. That response occurs after the apnea in all cases, as dsm pointed out. The idea is to try and prevent subsequent apneas by getting the patient to a hopefully safer pressure zone.

Just adding ...

Above 10 CMs the A10 will still look for indications an obstructive apnea is looming - it still looks for snores and analyzes the INSP curve if flow starts to slow (flow lims). If it detects these it raises pressure IN ADVANCE of the looing OSA event. If a NO-FLOW event gets through the radar A10 does not remember it nor react. It takes the view that if there weren't any typical OSA pre-cursor signals, then the event was either a central or a rogue happening.

The point that must be remebered is that all Autos KEEP TRYING TO PREEMPT apneas above 10 CMs. A10 focuses on the pre-cursor signals & ignores the actual apnea events that may get through the defenses. As like Resmed, Respironics will stop adjusting pressure if an apnea occurs over 10 CMs but doesn't forget it & the fact that the apnea occurred causes it to probe with pressure adjustments. The Respironics looks to see if things are getting worse or better after making these probes & if better it *may* even raise pressure more. If things get worse (snores increase, or flow-lims increase, or flattening gets worse) it backs off the pressure. The Resmed only looks for events it believes indicate a looming apnea & will raise pressure - the Resmed doesn't probe with pressure bumps the way the Respironics machine does.

DSM

[JRI]

it is designed to "predict" onset of the apnea and thereby avoid it.

Right. That part is done the same way above 10 cm and below 10 cm. This is where the above and below 10 cm difference lies:

The pressure will not rise above 10 cm H2O when an apnea is detected, to prevent an inappropriate response to central apneas.

So above we can see Resmed trying to prevent apneas above 10 cm, but not directly responding to them as they would have below 10 cm. That response occurs after the apnea in all cases, as dsm pointed out. The idea is to try and prevent subsequent apneas by getting the patient to a hopefully safer pressure zone.

I am by no means an expert and may not even rise to the level of novice on this but I have a different understanding of the above.

The purpose of the APAP is to provide a range of pressure, as needed, to respond to the apnea event thereby avoiding further events. The CPAP provides a constant pressure which will prevent all apnea events up to the set pressure but does nothing for apneas above that set pressure. The APAP will work the same way as the CPAP for all apnea events up to the minimum set pressure. The difference comes into play for apnea events above the minimum set pressure.

In my case the minimum set pressure is 10 and the maximum is 20. Therefore, all apnea events under 10 should be prevented. Those above 10 will not be prevented but rather responded to after the first event. (within the parameters of the A-10 algorithm)

The 10 cm H2O pressure does not refer to a flow pressure but to a pressure increase above the flow setting.
So that a machine with a maximum set at 20 would function as follows:
My minimum setting of 10 allows the pressure to increase to the machine maximum of 20. If my minimum setting is 9 the machine can only increase pressure to 19 per the A-10 algorithm even though the machine max is 20. If my minimum setting was 4 the pressure could only increase to 14.

So, to my mind, the machine is responding to the apnea event in the same way regardless of wether it is an apnea above or below a flow pressure of 10 cm H2O.

I hope this is clear enough to make sense of. I am trying to understand and learn from the posts on this board and feel I have picked up a lot of knowledge.

**Edit to add** When I say "all apnea events" I mean to say all obstructive apnea events and do not mean include central apnea events. See, I am learning!

[ozij]

Respironics will respond to apneas above 10. ResMed will not.
Respironicse may err by raising pressure to a central apnea. ResMed will not make that error.
ResMed may err by not responding to an obstructive apnea above 10 cms. Respironics will not make that error.

This is how Respironics attempts to handle central apneas. All added emphasis mine.
http://sleepapnea.respironics.com/techn ... logic.aspx

Non-Responsive Apnea/Hypopnea (NRAH) logic
<snip>
The REMstar Auto actually identifies when patients do not respond to pressure increases triggered by apneas or hypopneas.

If a persistent string of these events is detected, the device activates the Non-Responsive Apnea/Hypopnea (NRAH) logic, which limits pressure increases to 3 cm H2O. If at this time the patient continues to have events, the REMstar Auto will lower the pressure by 2 cm H2O and hold pressure for an extended period to stabilize the airway. This pattern of increasing pressure, followed by subsequently decreasing pressure, allows the REMstar Auto to appropriately manage events that are non-responsive to increases in pressure.

If the REMstar Auto identifies additional evidence that the events may be obstructive, such as snoring or hypopneas with flow-limited breaths, the REMstar Auto will temporarily override the NRAH logic and will increase pressure until the events are resolved.

This safe and effective method is unique to the REMstar Auto, and each occurrence is noted in our enhanced Encore reporting as NRAH events. Having the ability to identify and react to Non-Responsive Apnea/Hypopnea events at higher pressures allows the REMstar Auto to successfully titrate obstructive apnea events above 10 cm H2O.

Respironics sometimes has to backtrack because it raised the pressure when it shouldn't have. ResMed never has to backtrack for that reason.

The algorithms are very different in their approach to avoiding a vicious cycle of raised pressure caused by responding to central apneas.

O.

[dsm]

it is designed to "predict" onset of the apnea and thereby avoid it.

Right. That part is done the same way above 10 cm and below 10 cm. This is where the above and below 10 cm difference lies:

The pressure will not rise above 10 cm H2O when an apnea is detected, to prevent an inappropriate response to central apneas.

So above we can see Resmed trying to prevent apneas above 10 cm, but not directly responding to them as they would have below 10 cm. That response occurs after the apnea in all cases, as dsm pointed out. The idea is to try and prevent subsequent apneas by getting the patient to a hopefully safer pressure zone.

I am by no means an expert and may not even rise to the level of novice on this but I have a different understanding of the above.

The purpose of the APAP is to provide a range of pressure, as needed, to respond to the apnea event thereby avoiding further events. The CPAP provides a constant pressure which will prevent all apnea events up to the set pressure but does nothing for apneas above that set pressure. The APAP will work the same way as the CPAP for all apnea events up to the minimum set pressure. The difference comes into play for apnea events above the minimum set pressure.

In my case the minimum set pressure is 10 and the maximum is 20. Therefore, all apnea events under 10 should be prevented. Those above 10 will not be prevented but rather responded to after the first event. (within the parameters of the A-10 algorithm)

The 10 cm H2O pressure does not refer to a flow pressure but to a pressure increase above the flow setting.
So that a machine with a maximum set at 20 would function as follows:
My minimum setting of 10 allows the pressure to increase to the machine maximum of 20. If my minimum setting is 9 the machine can only increase pressure to 19 per the A-10 algorithm even though the machine max is 20. If my minimum setting was 4 the pressure could only increase to 14.

So, to my mind, the machine is responding to the apnea event in the same way regardless of wether it is an apnea above or below a flow pressure of 10 cm H2O.

I hope this is clear enough to make sense of. I am trying to understand and learn from the posts on this board and feel I have picked up a lot of knowledge.

**Edit to add** When I say "all apnea events" I mean to say all obstructive apnea events and do not mean include central apnea events. See, I am learning!

JRI

The A10 & Respironics will each go as high as the upper pressure setting allows. If an S8 were set to 8 & 20 then under the right circumstances (lots of snores & flattening of INSP curve) the upper pressure can keep rising until it hits 20.

The reason Resmed chose 10 CMs a the delimiting point in their A10 algorithm is that at 10 CMs the airway of the majority of people is being held open & thus pressure increases above 10 are less likely to be dealing with no-flow obstructive apneas but increase the potential for no-flow central apneas.

CompSA is a growing disorder & reflects how using cpap can & does introduce centrals into a significant number of people on cpap therapy. CompSA is an example of the cure compounding the problem.

Again, all autos seek to pre-empt obstructive apneas whilst ignoring central apneas (unless lowering the pressure reduces them, if they can be recognized at all). A10 just looks at different data to the other brands once pressure goes over the 10 CMs mark.


Hope this helps

DSM

[dsm]

Respironics will respond to apneas above 10. ResMed will not.

<Snip>

I'd rather phrase it this way

Resmed will selectively respond to OSA event patterns above 10 CMs.

The way it does this is that Resmed ignores actual no-flow apneas above 10 CMs but not the signals (snores & flow limitations) preceding them, which, it will react to. The goal is to pre-empt the apneas not try to eliminate active apneas that are already taking place.

The Respironics machine above 10 CMs will respond to apneas by waiting for the event to pass then probing with pressure adjustments & then waiting for a short period to see what the adjustment did. If the situation worsens, the pressure goes back to where it was & normal pre-emptive sensing resumes.

DSM

[ozij]

Respironics will respond to apneas above 10. ResMed will not.

<Snip>

I'd rather phrase it this way

Resmed will selectively respond to OSA event patterns above 10 CMs.

The way it does this is that Resmed ignores actual no-flow apneas above 10 CMs but not the signals (snores & flow limitations) preceding them, which, it will react to. The goal is to pre-empt the apneas not try to eliminate active apneas that are already taking place.

DSM

No automatic machine tries to aeliminate active apneas that are already taking place.
O.

[dsm]

Respironics will respond to apneas above 10. ResMed will not.

<Snip>

I'd rather phrase it this way

Resmed will selectively respond to OSA event patterns above 10 CMs.

The way it does this is that Resmed ignores actual no-flow apneas above 10 CMs but not the signals (snores & flow limitations) preceding them, which, it will react to. The goal is to pre-empt the apneas not try to eliminate active apneas that are already taking place.

DSM

No automatic machine tries to aeliminate active apneas that are already taking place.
O.

I thought that was clearly stated ?

DSM

[-SWS]

Also, I'd like to add a link to a discussion by ozij, wulfman, jnk, et al that DoriC nicely pointed out:
viewtopic.php?f=1&t=36570&p=316992&#p316992

That's a very good discussion IMHO.

[dsm]

Here is a baseline summary

ABOVE 10 CMs - normal monitoring.
==============================

Resmed:
Sniffs the signals from the sleeper looking for typical signs that an obstructive apnea is looming. When these signals (as defined by Resmed's algorithm) are seen, it adjust pressure upward.

Respironics:
Sniffs the signals from the sleeper looking for typical signs that an obstructive apnea is looming. When these signals (as defined by Respironics algortithm) are seen, it adjusts pressure upward.

ABOVE 10 CMs after an apnea has been scored.
========================================
(point here is, the Resmed & Respironics machines don't really know if that apnea was central or obstructive - Sandman takes an educated guess as does the Weinman SOMNObalance e machine)

Resmed:
Ignore the event - Resmed A10 says, "I was looking for all signs (signature) that an obstructive apnea was looming & saw none so that apnea may well have been a central. Had it been obstructive I would have seen the signature & already pre-empted it" or "That apnea (whatever it was) happened to fast that my normal pre-emptive sniffing for signatures didn't work, but it may have been a central anyway - who knows ? ".

BUT REMEMBER: OBSTRUCTIVE APNEAS ARE LIKE COMPUTER VIRII, THEY HAVE A SIGNATURE !!! THEY DON'T JUST 'HAPPEN' SUDDENLY ! THEY USUALLY show their signature !!! - (this OSA happens suddenly is a line that some among us have sort of pushed in some of the linked to threads. It is not accurate. Obstructive apneas typically go through a signature cycle starting with flow limitations etc:.).

Respironics
Wait until this apnea passes (it may be a central & it may be an obstructive apnea - if it was obstructive my sniffing should have recognized the signature & pre-empted it). But unlike Resmed, when it has passed I will do my 'chair probe' that is, I will up the pressure a bit, sniff the effect of doing that, if no change, try another dose, but if no improvement or the signs show deterioration then back off the pressure & revert to normal signature sniffing again.

*******************************************************************************

So what is the real difference ?

Both Resmed & REspironics say "if it walks like a duck & quacks like a duck it is a duck (pre-cursor signals that are the signature of looming OSA).

Respironics adds that it backs the horse both ways & goes into its pressure probing routine to see what effect that has. Was it central or OSA. I'll probe then sniff to see what effect my probing has.

********************************************************************************

To some people the Resmed approach works well, to others it doesn't & guess what. Exactly the same applies to the Respironics approach. The chairs (pressure probes) are either helpful or not. This is pretty well agreed I think

DSM

#2

Another perspective

IF BOTH RESMED & RESPIRONICS COULD ACCURATELY RECOGNISE CA vs OSA events in a standard Auto, then the A10 algorithm would be probably obsolete as would Respironics pressure probing.

Puritan Bennett (via Sandman) are honing in on that cpap Auto nirvana as are Weinmann of Germany. So it seems to me both Resmed & Respironics need to make some advances soon else they may be left behind. But knowing both those companies, they won't let that happen (too quickly when you dominate the market you can afford to be a tad tardy )

DSM

[JRI]

Here is a baseline summary...DSM

Great post!

[mars]

Hi All

This has been a great thread, and I now understand things that before I only knew that words existed, but the meaning eluded me.

Not that descriptions in other threads have not been good, simply that new information using new words needs some revisiting and digesting. Many years ago when I was learning computer programming (when machines were as big as houses) I had to approach it the same way. A first reading would only make me familiar with a new word, subsequent readings, and especially in a different format, would provide the knowledge.

And this is what the repeated discussions on this forum do, I keep on reading, and slowly something clicks. Ah! Now I understand this, now I understand that.

Brilliant.

cheers

Mars

[track]

Good stuff guys.... Given I don't appear to have any centrals...I have sure had a lot more luck lowering my AHI with a remstar than I ever did with my resmed.