APAP pressure high enough to prevent most apneas?

[SelfSeeker]

I am thinking most APAPs should be set to prevent most apneas from happening, not stopping them after the fact, is this right?


Like if apneas are happening at pressures: a, b c and d. 90% is at c, then should the low number be set to pressure c and a high pressure one above d?

It makes sense to me, but then again, I may be way off the mark.

[Wulfman]

My "advice" would be to set your machine at a FIXED pressure somewhere between where you are spending the biggest percentage of the time and the 90% point. Remember, the 90% is the total of all the pressure points AT or BELOW the 90 percentile. In other words, you didn't spend 90% of the night at that (90%) pressure.....it's the point at which all the other numbers reached 90%.
I'll use my Auto test in July as an example.
I set my auto to a 10 - 15 pressure range. I'd already been on 10 for 10 months and 12 for about 3 months. My 90% number was between 13 and 14 depending on which night I looked at. Unfortunately, my machine was chasing my snoring at the same time. In any case, the vast majority of the nights I was spending between 10 and 12.....so I went back to 10 for awhile and then split the difference and set it on 11....which is where I've been for a couple of months now. I don't know why I skipped it back in March.....and went to 12, but (for now) 11 seems to offer a good balance for me.

Best wishes,

Den

[dsm]

It seems to me that repeatedly here there are mistaken assumptions about what an Auto is supposed to do.

The classic myths (IMHO) are ...

1) That an Auto will always prevent apneas
2) That an Auto can detect an Apnea occurring & raise the pressure to prevent that apnea


The reality ...

1) Autos are designed and always were designed, to prevent 'patterns' of apneas
2) No Auto in existence today (barring the emerging Adaptive response machines), are capable of adjusting their pressure fast enough to detect one apnea and to change pressure quickly enough to clear that same apnea
3) Autos try to pre-empt apneas by sensing the typical precursor conditions to an apnea & 'pre-emptively' adjusting pressure upwards in the hope they 'pre-empt' a subsequent apnea or pattern of apneas.


When is a glass half full or half empty ?
============================
One well known brand of Auto is known to adjust its pressure faster than one other well know brand but amusingly although many would consider such rapid response as being close to Auto heaven (isn't that what these machines are supposed to do ?0 , the way some people describe this machine's faster reaction response is call it 'aggressive' Now that poses the question that if this brand of auto is 'aggressive' what is the newer Auto Adaptive machine ? - 'a manic' ? The Auto Adaptive machines track the user's breathing in real time & respond in as good as real time.

The design choices used in Autos made by the major manufacturers do vary enough that one person will get different results from different brands however when it comes to cpap, the fundamentals are nearly the same (except for the algorithms that handle leak detection).

Barring the issues surrounding how effective a machines leak detection algorithm is and what that machine may or may not do when it thinks there is a leak, the different brands of cpaps tent to offer the same results to the same people. The major differentiator in cpaps has been the inclusion of exhalation relief (in Respironics that is cflex). Cflex has been a winning feature for Respironics & has served them well.

Why buy an Auto ?.
==============.

The real benefits of Autos were (and to a high degree remain) ...

1) That the machines do try to keep the pressure as low as is needed for a user & this is to minimise the problems associated with always running at higher fixed pressures like cpaps do - discomforts that include, mask leaks, aerophagia, exhalation against the pressure.

2) Many people want to monitor their own therapy and Autos because of their added sophistication, required the extra intelligence to record and respond to a nights changing events. People have discovered via Encore & Autoscan etc:, that they can extract their own data an take some level of responsibility for understanding and managing their own therapy. That is a gigantic plus in favour of Autos.

As Autos evolved, many of the data capture features were included in Bilevels, so today we have machines like the Respironics Auto Bipap and the Resmed VPAP III, that are very sophisticated and capable of managing a variety of user needs while providing lots of nightly detail.

The ability to closely monitor ones own nightly data is a powerful educator and tool for anyone wanting to exercise some control over their OSA SA.


DSM

[Guest]

I am thinking most APAPs should be set to prevent most apneas from happening, not stopping them after the fact, is this right?

Yes, you're right. The low end of the range should be set to the pressure you've determined prevents most apneas from happening. As Wulfman indicated, by scrutinizing your data you'll be able to determine what that pressure is. You're right on the mark!

[Snoredog]

I agree with DSM, the machine detects "patterns". Your sleep pattern may resemble or look like 2 hops a skip and a jump before you have an apnea. The machine will see this and store that pattern into its memory.

Then when the machine again sees again 2 hops a skip and a jump that matches what is contained in its memory it knows a apnea will be soon be following, so it will increase pressure in an attempt to prevent the following apnea. It then goes back to monitoring for another hop skip and jump, if it sees you are still hopping and skipping it will keep the pressure up.

But I disagree with the analogy that increasing the bottom pressure will lower the number of events seen. Not so, if that lower pressures masks the sleep pattern the machine needs to see (2 hops ski and a jump) and only sees the following apnea it may not have a long enough pattern to detect it.

Autopaps will always let a few events go by, but a few per night are not usually a problem.

[SelfSeeker]

Thank you Wulfman, DSM and Guest,

DSM, yes I thought that the AUTO, is designed to increase pressure to stop apnea or to at least open the airway.

I would love aggressive, but I have not bought the very aggresvie one.

Wulfman, I only have two naps and two nights data. Not much, but enough to see that apneas are happnening. And they do not necessarly happen at the 90%. But they do not happen at the same pressure each time either.

Guest thanks.

Snoredog, I am under the mind if I set the AUto a bit higher, my airways will be open so a lot of the ones at those lower pressure will not happen.


Why does the auto change pressure? I thought it was to stop apneas. In some terms apneas are 10secs long or longer.

Since the data shows apneas or Hypopneas, are these events stopped by the auto or by our own arrosal? I would assume that our blood pressure and oxygen would be effected with each one just like when not treated. Am I off the mark?

At least I have learned I have zero vibratory snore.

Non responsive apneas/hypopneas are those the central ones?

[dsm]

<snip>


Why does the auto change pressure? I thought it was to stop apneas. In some terms apneas are 10secs long or longer.

Since the data shows apneas or Hypopneas, are these events stopped by the auto or by our own arrosal? I would assume that our blood pressure and oxygen would be effected with each one just like when not treated. Am I off the mark?

At least I have learned I have zero vibratory snore.

Non responsive apneas/hypopneas are those the central ones?

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CPAPopedia Keywords Contained In This Post (Click For Definition): auto

SelfSeeker,

There is a perceptual trap in defining what Autos do, it is related to if one means an individual apnea or a pattern of apneas.

Q. Do Autos adjust pressure to prevent apneas ?
A. Yes (with qualification)

The qualification is that the Auto tries to 'pre-empt' apneas (apneas with an s).
An Auto is generally not fast enough in response to clear an individual apnea that may suddenly occur such as when someone moving from their side to their back. That is going to be cleared by the sleeper becoming aroused.

The machine doesn't say to itself "I see a sudden blockage, I will now boost cms rapidly until that blockage is cleared & the airway opened". Autos would like to be able to do that but have not yet reached that level of technology and sophistication (see 'Adaptive Ventilation Design' for a new breed of machine that do attempt to achieve real time clearing and airway control). The current Auto machine merely notes the 'pre-cursor' pattern and if it sees that pattern again will begin increasing cms in an attempt to 'pre-empt' another block.

So in reality, the Auto's realistic goal is to keep the cms as low as it believes it can allowing for its monitoring of the sleeper's breathing and airflow patterns and its memory of previous apnea 'patterns' *plus* the values stored in its lower & upper range settings.

When I say 'pre-cursor' conditions, I am referring to ...

- snoring (sets up a vibration in the airflow that gets sensed by the machine - snoring is a very good indication of a potential block)
- hypopneas (generally meaning that the airflow has dropped by 50% for more than 10 secs)
- other unusual airflow patterns (is it a leak?, is it the user's breathing? )

Each brand of Auto machine has its own unique ways of sampling these pre-cursor conditions and deciding what to do and how quickly to do it.
The really do vary quite a bit.

DSM

[wading thru the muck!]

DSM,

Thanks for several great explanations of what we can expect (and what we can't) from our autos.

Selfseeker,

The way I have understood the circumstance of an auto detecting and responding to apneas as they happen is that it would be likely that the rapid increase in pressure would cause an arousal thus defeating the ultimate purpose of the pap therapy in the first place.

It will be interesting to see if "Adaptive Ventilation Design" can avoid this stumbling block.

[rested gal]

Very nice description of the benefits of using an autopap, dsm.

Some people do find that they get more restful treatment using a single pressure, as Den does. Others, particularly those whose pressure needs change according to sleep position and stage of sleep, are better served by auto mode.

About this:

One well known brand of Auto is known to adjust its pressure faster than one other well know brand

Do you think the McCoy/Eiken tests that were discussed in the topics linked below contribute to that assertion? I hope after reading -SWS's words, no one still thinks those tests were useful at all in assessing how different brands of autopaps would be expected to respond to living, breathing people instead of to an artificial breathing machine.

-SWS talking about the first time older autopaps were hooked up to the breathing machine - the original Bliss/Eiken/McCoy study:
viewtopic.php?t=1715

"simply lobbing a single and unresponsive recorded or artificial sleep event into an AutoPAP is in and of itself inherently flawed and of little use. An AutoPAP algorithm will very often require several iterations of: 1) pressure adjustment, 2) patient breath detection, and 3) pressure re-adustment based on step 2.

The machine responds to the patient. The patient then responds to the machine. The machine then reiteratively responds back to the patient for crucial adjustments. That is the two-way loop that is broken in the study and your proposed machine. There must be a patient response (simulated or real) to truly test the algorithm. To rely on lobbing one obstructive sleep event (even repeatedly) is like assessing world-class tennis players using only a serving machine. It just doesn't make for any sort of useful comparison in my opinion."


-SWS's comments in a topic about the more recent test done by Eiken/McCoy, this time with modern apaps:
viewtopic.php?t=11981

"Regarding the methodology itself: toward serving the purpose of accurately comparing APAP algorithms and responses, a crucial patient feedback loop is open, thus clearly rendering the entire study null-and-void."
-----
"I also have no vested interest in the PAP market. However, I prefer to simply point to the study's methodology and point out that the patient-response feedback loop that is so crucial has been opened and thereby renders the entire study null-and-void."

[dsm]

DSM,

Thanks for several great explanations of what we can expect (and what we can't) from our autos.

Selfseeker,

The way I have understood the circumstance of an auto detecting and responding to apneas as they happen is that it would be likely that the rapid increase in pressure would cause an arousal thus defeating the ultimate purpose of the pap therapy in the first place.

It will be interesting to see if "Adaptive Ventilation Design" can avoid this stumbling block.

_________________

CPAPopedia Keywords Contained In This Post (Click For Definition): Arousal, auto

Wader,

From what I have learned of the Adaptive Servo Ventilation approach (I accidentally left off the 'Servo' word) it is a balance between a passive ventilator (which is what a cpap & apap basically are) and an active ventilator which is what we think of that hospital's use - esp in intensive care - that actively control the user's breathing).

So my use of 'passive' meaning that the ventilator (xpap machine), follows the users breathing while 'active' seeks to drive the user's breathing.

The Adaptive servo approach allows the ventilator to move from passive to active (backwards and forwards and very quickly if needed) if it determines that the user's breathing needs stabilizing or augmentation.

These new breed of machines are designed to cope with centrals as well as traditional Apnea blockages. As far as I can tell they do avoid the big no no of xpap therapy, which I believe are sudden pressure changes, these it seems, cause more problems than they solve.

In my own experience I learned the hard way that running a bilevel with too big a gap between ipap & epap was doing me more harm than good even though the clinical manual for the machine implied the settings I was using were quite ok ( 15/8 ). When I was finally able to do some serious measurements - my AHI was constantly showing as higher than my sleep study that got me into xpap therapy (AHI of 40). Once I dropped the range (by experimentation & nightly eval) to 10/13 cms, the AHI dropped to less than 2.5 from 50-60! (yes AHI of 50 to 60).

Having learned that lesson and had time to asses the improvements I then saw the wisdom of limiting EPR to a max 3 cms variation between inhale/exhale that the Resmed Elite & Vantage incorporate. I am guessing (educated guess) that any bigger range would begin to reverse the benefits of xpap therapy for a number of people just as it did for me. The problem of dropping the gap too low though is losing the benefit of exhalation relief.
Cflex is one valid approach, EPR (with max 3 cms gap) is another.

Getting back to Adaptive Servo Ventilation. Because the machine can so quickly adjust and adapt, it is not so much responding to events as managing them in near real time thus there appear to be no dramatic pressure changes such as happens with bilevels set with too big an ipap/epap gap and that can also occur in some autos trying to respond to rapidly changing user input. I now believe that the variation in pressure rise from one brand to another will affect people differently. I think Chuck has highlighted his observation of this when discussing his use of a Remstar Auto and a Resmed Vantage.

My comments here are not a statement that these newer Adaptive Servo Ventilation machines are God's gift to xpap therapy (what is new can often appear so until fully evaluated over time), just that the technology is evolving and examples of newer approaches are already among us. And, that these new machines do appear to be able to do what many people mistakenly think today's Autos already do.

With xpap therapy, there is always so much to learn. The learning can be by reading & observation or it can be by way of 'ordeal by fire' (try it out & sometimes get burned ).

Cheers

DSM

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CPAPopedia Keywords Contained In This Post (Click For Definition): resmed, wader, Arousal, CPAP, AHI, auto, APAP

[dsm]

Rested Gal,

I will go back & read the links you provided.

But I do agree very much with the point that it is going to be very difficult to devise a lab test that doesn't involve a real sleeping human, that hopes to provide any meaningful evaluation of an Auto machine.

As always SWS has many helpful insights and explanations of the way these machines can and do work. I doubt we would be in any disagreement on the issue of non-human testing of Auto responsiveness.

Cheers

DSM

[wading thru the muck!]

DSM,

Thanks again for another great explanation. I have one question regarding the Adaptive Servo Ventilation... Is the concept similar to a continuously variable transmission that is found in many of the fuel efficient hybrid vehicles marketed today? The concept in practice as I understand it provides maximum efficiency in transfer of power from the drive system to the wheels and at the same time does so without any noticeable "change of gears" or as analogous to our situation no noticeable change in pressure.

[dsm]

Gee Wader, That is a challenging comparison

I don't know enough about the transmission in the current hybrids to be sure.
I do understand variable ratio gearboxes that allow for smooth variation in transferring engine revs to wheel revolutions using variable ratio V-wheels & belts.

I know that the long term design of automotive transmissions is heading towards independent brushless motors mounted in each wheel and use of electric power converted via hydrogen fuel cells to feed the motors. GM already have one of these prototypes in Germany (they did it a few years ago - they just keep quiet about it). see http://www.gm.com/company/onlygm/fastlane_Blog_2.html

The today vehicles I have seen (Toyota Prius) use a combo of small petrol engine & battery power to drive an electro/mechanical transmission. See http://www.hybridsynergydrive.com/en/se ... allel.html

While I understand what Ford & Toyota are trying to do. I can't find a way to relate that to the Adaptive Servo Ventilation machines other than in very broad and general terms.

Perhaps the hybrid synergy drive provides a valid comparison ? - it uses both petrol and electric drive and can run as electric only (like passive ventilation) or add petrol power drive as well as the electric drive (perhaps akin to active ventilation).

Anyway, there is an attempted analogy but I think it is a rough comparison.

Adaptive Servo Ventilation relies heavily on maintaining the users breathing pattern allowing that this pattern will vary steadily during different phases of sleep. If it detects a sudden decline in breathing it can very quickly move to active mode & nudge the user's breathing back into the pattern and back to the air flow volume it has been observing.

Cheers

DSM

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CPAPopedia Keywords Contained In This Post (Click For Definition): wader, Power

[dsm]

[quote="wading thru the muck!"]DSM,

Thanks again for another great explanation. I have one question regarding the Adaptive Servo Ventilation... Is the concept similar to a continuously variable transmission that is found in many of the fuel efficient hybrid vehicles marketed today? The concept in practice as I understand it provides maximum efficiency in transfer of power from the drive system to the wheels and at the same time does so without any noticeable "change of gears" or as analogous to our situation no noticeable change in pressure.