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APAP Discussion
#11
RE: [split] APAP Discussion
(12-13-2013, 09:34 AM)Sleepster Wrote: APAP's will indeed wait until you've had an event before raising the pressure in response to them. This is a fact that the manufacturers don't advertise.

I don't think this is true of many of the new APAPs if you define an "event" as an apnea or hypopnea (as per accepted definition of apneas and hypopneas). I sometimes have an AHI of 0.0 even though my pressure raises and lowers all through the night. If I look at the flow chart I can surmise that the pressure increases are usually due to plateaus forming in the flow waves (increased FL) and/or a slight increase in vibratory snoring. More often than not, pressure increases on my machine are NOT in response to an "event". Occasionally, but not very often, there is a tagged recorded event (usually H) and no pressure increase in response to it and usually no subsequent events even though the pressure remains static or in decrease (I haven't figured that one out yet Dont-know ). Also, I'm relatively assured that this isn't a malfunction because I have two different machines that I rotate in and out of use and the results are the same with both machines. I use S9 AutoSets, but I'm sure that I've read that PR Autos use indicators like these to attempt to avoid or preempt events as well. That being said, I am a firm believer in setting the minimum pressure high enough that the machine can respond more efficiently. I think that the rate of pressure increase used by these machines is not fast enough to prevent events if the minimum is set way too low and if the manufacturers raised the rate of increase enough to prevent events even at a low minimum pressure, then the rapid pressure increase would likely cause arousal.

I'm fairly certain, and it will be hard to convince me otherwise, that the reasons many HCPs are against APAPs is mostly due to the lucrative "titration" process at worst and/or ignorance of the newer Auto algorithms at best.

I personally think that there is a turf war going on and many HCPs see Home Sleep Studies and APAPs as the competition. JMHO
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#12
RE: Your Personal CPAP Success Story - Post Here
(12-11-2013, 04:25 PM)JohnNJ Wrote:
(12-11-2013, 03:37 PM)Sleepster Wrote: APAP's don't increase the pressure during an event. It's only after the event that the pressure is raised.

That's what my sleep doctor said and that's the reason he doesn't like auto machines. You have to have an event for the pressure to adjust instead of using a set pressure and not having any events.
Even with a properly set straight CPAP some events will get by on most nights for most users.

The biggest advantage of having an APAP over a CPAP is this: Any APAP can easily be set to run in straight CPAP; but no CPAP can be set to run in Auto mode. And the difference in cost between a full efficacy data CPAP and an APAP is just not that great.

Hence if you own an APAP but you do better on straight CPAP pressure, it's easy to set your machine up in straight CPAP mode. But if you own a straight CPAP and are finding it hard to tolerate your prescribed titrated pressure for some reason, there's no way to switch to APAP to see if you might do better in that mode and there's no way to verify your pressure needs by running an autotitration for a week or two on your own machine can't be done. And titration studies done in the lab do not always identify the optimal pressure and pressure needs can change over time. Owning an APAP (even if you use it in CPAP mode) can help you avoid an unnecessary trip back to the sleep lab in the future/

There are pros and cons to using APAP (Auto) mode vs. CPAP mode.

Pro CPAP mode: If you can easily tolerate your titrated CPAP pressure, then the benefit of switching to an APAP mode may be marginal at best. More events will likely be prevented in CPAP mode since the average pressure over the course of the night will be higher. And if you're sensitive to the pressure increases in the APAP's Auto algorithm, CPAP mode will likely be much easier to tolerate rather than APAP mode.

Pro APAP mode: If your apnea is strongly REM related or strongly positional, using APAP mode will allow an overall reduction in the needed pressure, but still allow the machine to gracefully respond to the times when your apnea is most pronounced. Another case where APAP is useful is when a person is having severe problems with aerophagia. Minimizing the pressure over the course of the night can lead to less swallowing of air, which in turn reduces the aerophagia. But in order to minimize the number of events that must happen before the machine reaches the needed pressure for the worst case scenarios for your OSA, the minimum pressure setting in the Auto range needs to be high enough. This typically means that the minimum pressure should be no more than 2-4 cm less than the titrated CPAP pressure.

Quote:He (the sleep doc) gave me an auto machine because I insisted but he kept the range narrow and based on my stats he may be correct.
A narrow APAP range based on your stats is really the best way of running in APAP mode.

The bad rep of APAP in the eyes of many in the sleep medicine community is probably based as much on the real problems people run into when trying to use an APAP set wide open with a pressure range of 4-20 as anything else. There are two potential pitfalls with running an APAP wide open:
  • If your titrated pressure is anything above 9 or 10 cm: In this case too many events are going to have to happen before the pressure gets up to where you need it to be. And the machine is going to keep lowering the pressure back down to subtherapeutic levels as often as possible, which will in turn trigger even more events. In other words, the overall treated AHI may be much higher than it needs to be. And leaks are another potential problem. Even if you carefully fit the mask at 4-5 cm, once the pressure gets up to above 10cm, there's a good chance that you'll start having leaks.


  • If your titrated pressure is below 9 or 10 cm: Chances are you won't have as many problems running the APAP wide open. But there's always the off chance that under some bizarre circumstances the pressure setting could increase inappropriately on some nights. And on those nights, the chances of having problems with aerophagia increase as do the probability of having problems with pressure induced centrals. And the rare, but unneeded high peaks of pressure can lead to disturbances in your sleep patterns that can lead to further restlessnes which can trigger recording false events which can lead to more restlessness ... and you can get yourself trapped in a nasty feedback loop.


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#13
RE: [split] APAP Discussion
(12-13-2013, 11:49 AM)jgjones1972 Wrote:
(12-13-2013, 09:34 AM)Sleepster Wrote: APAP's will indeed wait until you've had an event before raising the pressure in response to them. This is a fact that the manufacturers don't advertise.

I don't think this is true of many of the new APAPs if you define an "event" as an apnea or hypopnea (as per accepted definition of apneas and hypopneas). I sometimes have an AHI of 0.0 even though my pressure raises and lowers all through the night. If I look at the flow chart I can surmise that the pressure increases are usually due to plateaus forming in the flow waves (increased FL) and/or a slight increase in vibratory snoring.
jgjones is correct here. Modern APAP Auto algorithms are designed to analyze the wave flow data pretty carefully to detect both flow limitations and snoring. The PR System One machines also have a proprietary algorithm for detecting wave flow patterns strongly associated with RERAs even though a real RERA requires an arousal in the EEG data and the System One has no way of definitively telling whether a flagged RERA is "real" or not.

Unlike the Resmed S9 machines, the PR Auto machines also have a "search" algorithm for attempting to determine the optimal pressure setting even when the sleep breathing pattern appears to be stable. The "search" algorithm has two main parts: A "test pressure increase" part that is used to proactively increase the pressure even before a FL can be scored and a "test pressure decrease" part that prevents the machine from lowering the pressure below a therapeutic level. It's this "search" algorithm that gives the pressure curve of PR Autos their characteristic sawtoothed shape.

The "test pressure increase" part of the PR "search" algorithm
When the sleep breathing appears to be stable, the PR Autos will proactively increase the pressure by 2cm over about a two minute period on a periodic basis. If no improvements in the shape of the wave flow are found after the test pressure increase, the pressure is lowered back down to the current baseline level over about 60 seconds or so. If improvements are found during the test pressure increase, then the PR System one continues to increase the pressure at a rate of 1 cm per minute as long as improvements continue to be found with the increased pressure OR the maximum pressure level is reached. At the end of the pressure increase, a new baseline pressure level is established at a new higher pressure level. The new baseline is typically 0.25-0.5cm less than the maximum tested pressure during the test cycle OR the max pressure setting if the pressure was increased that far.

You can read a bit about the PR's search algorithm at: http://www.healthcare.philips.com/us_en/...orithm.wpd

The "test pressure decrease" part of the PR "search" algorithm
The PR Auto machines use a similar "search" algorithm when they are attempting to decide whether it is safe to lower the pressure back down and to determine how far to lower the pressure. Once the breathing is stable at a given pressure for a long enough time, the machine will tentatively lower the pressure about 1 cm over the course of a minute. If any deterioration in the shape of the inhalations is detected, the pressure is then increased back up to the previous setting; if there was no deterioration in the shape of the wave flow detected during the test pressure drop, the machine will continue to decrease the pressure by 1cm per minute as long as no deterioration in the shape of the wave flow is detected. The pressure decrease will end whenever the min pressure setting is reached OR when the machine detects a slight deterioration in the wave flow, at which point it will increase the pressure back up by 1cm.

Other notes on the PR "search" algorithm
I believe that the PR "search" algorithm also has an additional part to it that determines which way to make the test changes in pressure when the new baseline pressure is something that is between the minimum and maximum pressure settings. In other words, it appears that there are times when the "search" algorithm decides to do a test increase in pressure starting with the new (higher) baseline pressure and there are other times when the "search" algorithm decides to do a test decrease in pressure starting with the new (higher) baseline pressure.

I have not been able to sort out exactly how the PR Auto algorithm makes that decision because I almost always have my BiPAP in such a tight auto range: The difference between my min IPAP and max IPAP is only 2 cm most of the time and hence when Kaa finds an improvement in the inhalations, the increased IPAP is at my max IPAP and there's nowhere to go except for testing for decreases. (On a BiPAP, the "search" algorithm is applied only to the IPAP pressure.)

With my sleep doc's permission I was doing some autotitration earlier this fall where I did up the max IPAP and max PS settings to see just where the machine wants to take my pressures and whether using a bit more pressure would lead to better sleep. The sleep doc was skeptical that I'd find a better setting than my current one, but told me to go ahead and satisfy my curiosity. In the end the net result was indeed that higher pressures don't necessarily bring my AHI or FL down any further than my current range; higher pressures DO aggravate the aerophagia; higher EPAP pressures aggravate the aerophagia more than higher IPAP pressures do; and overall allowing the machine to increase my pressures further did nothing to increase the quality of my sleep.

But in going through that data I can find some really good illustrations of just how the PR search algorithm works. I'll put those in a separate post.

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#14
RE: [split] APAP Discussion
(12-13-2013, 03:41 PM)robysue Wrote:
(12-13-2013, 11:49 AM)jgjones1972 Wrote:
(12-13-2013, 09:34 AM)Sleepster Wrote: APAP's will indeed wait until you've had an event before raising the pressure in response to them. This is a fact that the manufacturers don't advertise.
I don't think this is true of many of the new APAPs if you define an "event" as an apnea or hypopnea (as per accepted definition of apneas and hypopneas).
jgjones is correct here.
I think everyone is correct, not always snoring and FL precede an obstructive apnea, some can come out of the blue without any warning

Edit: In case of clear airways events, snoring or/and FL are not relevant, only the 10 seconds or more required for scoring such apnea
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#15
RE: [split] APAP Discussion
(12-13-2013, 11:49 AM)jgjones1972 Wrote: Occasionally, but not very often, there is a tagged recorded event (usually H) and no pressure increase in response to it and usually no subsequent events even though the pressure remains static or in decrease (I haven't figured that one out yet Dont-know ).
The auto algorithm do not typically NOT respond to "isolated" events. In other words, it typically takes two apneas and/or hyponeas close together (like within about 5 minutes of each other) to trigger a pressure increase. Or it takes a FL and a OA/H close together to trigger a pressure increase that may be more substantial than just the increase that the FL would trigger.

On the PR machines, after the first 1cm increase in pressure the machine is going to wait for about 4 minutes minutes---even if events continue to happen----before increasing the pressure again. The Resmed S9 does seem to respond more aggressively to the individual events that occur close together in cluster.

Finally it is worth noting that the decision by the manufacturers to NOT increase the pressure in response to every single H or OA is actually following part of the AASM titration guidelines, which are available at http://www.aasmnet.org/Resources/clinica...040210.pdf. On a manually titrated PSG, the tech does not increase the pressure after every single OA or H. In particular once the tech increases the pressure in response to one or more events, the tech is supposed to wait for five minutes to see if the breathing stabilizes before increasing the pressure again.


Quote:I'm fairly certain, and it will be hard to convince me otherwise, that the reasons many HCPs are against APAPs is mostly due to the lucrative "titration" process at worst and/or ignorance of the newer Auto algorithms at best.

I personally think that there is a turf war going on and many HCPs see Home Sleep Studies and APAPs as the competition. JMHO
I agree with your assessment of this situation.

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#16
RE: [split] APAP Discussion
(12-13-2013, 04:02 PM)zonk Wrote: I think everyone is correct, not always snoring and FL precede an obstructive apnea, some can come out of the blue without any warning

Edit: In case of clear airways events, snoring or/and FL are not relevant, only the 10 seconds or more required for scoring such apnea
Scoring criteria for an OA on a PR System One or a Resmed S9 is based only on a reduction of airflow by at least 90% (or maybe it's 85%) from baseline that lasts at least 10 seconds. After about 6 seconds of "no airflow" both the S9 and the System One conduct a proprietary test for determining the patency of the airway. On both platforms, the CA detection algorithm is based on what happens to the back pressure at the machine end of the system when a pressure test is conducted. The S9 uses a series of small oscillations (the FOT algorithm), whereas the System One uses a brief puff of about 2cm of extra pressure (the PP algorithm).

Scoring criteria for H varies a bit between the PR System One and the Resmed S9. But in both cases the scoring of a H requires a reduction in airflow (of somewhere around 40-50% I believe) from baseline that lasts at least 10 seconds. One of the two may also require some kind of "recovery" breath at the end of the hypopnea, but I'm not sure about that.

Both machines track and respond to FL and snoring because they may indicate that the airway is becoming compromised. And while many OAs and Hs do occur in parts of the wave flow where the machine has detected FLs or snoring, as zonk says, some OAs and Hs can come out of the blue without any snoring or FL preceding them.
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#17
RE: [split] APAP Discussion
(12-13-2013, 11:49 AM)jgjones1972 Wrote:
(12-13-2013, 09:34 AM)Sleepster Wrote: APAP's will indeed wait until you've had an event before raising the pressure in response to them. This is a fact that the manufacturers don't advertise.

I don't think this is true of many of the new APAPs if you define an "event" as an apnea or hypopnea (as per accepted definition of apneas and hypopneas). I sometimes have an AHI of 0.0 even though my pressure raises and lowers all through the night. If I look at the flow chart I can surmise that the pressure increases are usually due to plateaus forming in the flow waves (increased FL) and/or a slight increase in vibratory snoring.

Does that plateau typically last for 10 seconds or more?
Sleepster

INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
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#18
RE: Your Personal CPAP Success Story - Post Here
(12-13-2013, 02:15 PM)robysue Wrote: Another case where APAP is useful is when a person is having severe problems with aerophagia. Minimizing the pressure over the course of the night can lead to less swallowing of air, which in turn reduces the aerophagia. But in order to minimize the number of events that must happen before the machine reaches the needed pressure for the worst case scenarios for your OSA, the minimum pressure setting in the Auto range needs to be high enough. This typically means that the minimum pressure should be no more than 2-4 cm less than the titrated CPAP pressure.

I guess this is why a BiPAP is often prescribed for aerophagia (was in my case). You can set the EPAP pressure another 3-5 cm lower.
Sleepster

INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
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#19
RE: [split] APAP Discussion
(12-13-2013, 10:04 PM)Sleepster Wrote:
(12-13-2013, 11:49 AM)jgjones1972 Wrote:
(12-13-2013, 09:34 AM)Sleepster Wrote: APAP's will indeed wait until you've had an event before raising the pressure in response to them. This is a fact that the manufacturers don't advertise.

I don't think this is true of many of the new APAPs if you define an "event" as an apnea or hypopnea (as per accepted definition of apneas and hypopneas). I sometimes have an AHI of 0.0 even though my pressure raises and lowers all through the night. If I look at the flow chart I can surmise that the pressure increases are usually due to plateaus forming in the flow waves (increased FL) and/or a slight increase in vibratory snoring.

Does that plateau typically last for 10 seconds or more?
No, it's not a plateau. It is an occurance of plateaus starting to form during each individual inhalation. These plateaus represent a split second hesitation or limitation during each individual inhale. These plateaus do not represent hypopnea though, as they do not present as a decrease in waves from trough to peak lasting several seconds, but more as regularly occurring split second small plateaus midway between the troughs and peaks of each inhalation.


EDIT

A picture is worth a thousand words:

[Image: Plateaus_zpsa6f761b7.png]


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#20
RE: [split] APAP Discussion
What I see in your graph is a series of plateaus forming on the leading edge of the crests. (A good way to remember which is the leading edge is to recall that the leading edge occurs at an earlier time than the trailing edge). Is this what you're referring to?

I see these a lot in my breathing patterns, too. These are pauses that occur just after the exhalation, but before the inhalation. As if the body is being careful to not draw in too quickly after an exhale for fear of a collapse. Perhaps it's just the way the body relaxes as it's passing through one or more of the sleep stages. It could be something that's seen in all people, or perhaps it's something that sufferers have conditioned their bodies to do over the decades of untreated OSA.

I'd really like to know the answer to that question!
Sleepster

INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
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