QUESTION TO DERIK--Re: MyEncore Software

[John M]

Hi Derik,

In the posting for your software, it states that you ("the author") consider the AHI vs. Pressure graph to be very important. I would like you to elaborate a little about this particular graph.

See, I was looking at similar data (manually sorted by hand) using info from my PB 420E Silverlining software, but I wasn't sure if it quite made sense. If AHI is correlated to pressure, for example, as shown in one of your graphs for "Otto Pap", then this indicates that raising the pressure beyond a certain point actually increases the AHI index. (Link below.)

myencore.php#PressAHI

This may be true for pressure induced central events, but otherwise doesn't make sense to me. Therefore, either your chart (and similar ones I have compiled from my own data) indicates that either (1) "normal obstructive events" increase with raised pressure (which I doubt), or (2) the events occuring as the pressure starts to go back up are central in nature (seems more likely to me).

There is also a possible 3rd case that seems even more likely and simple than the case (2), above--i.e., the increased pressures are not causing the events at all (except for a few centrals), but rather the events are causing the elevated pressures, which is exactly the purpose of having an APAP. In this case, I question the usefulness of such a chart. Maybe you can find a flaw in my thinking, or otherwise point out another useful purpose for such a chart. . .


Thanks,
-John M

[Guest]

This may be true for pressure induced central events, but otherwise doesn't make sense to me. Therefore, either your chart (and similar ones I have compiled from my own data) indicates that either (1) "normal obstructive events" increase with raised pressure (which I doubt), or (2) the events occuring as the pressure starts to go back up are central in nature (seems more likely to me).

Harvard researchers have recently identified a new SDB category called "Complex Sleep Disordered Breathing". While these patients are suspected to be rare, increases in CPAP pressure can cause an increase in central apneas and even an increase in obstructive apneas. This "Complex SDB" condition is based on CO2 dysregulation, and again is suspected to be somewhat rare.

[Wulfman]

John M,

I'm not going to answer FOR Derek on your questions, but here's my "take" on that graph and other details.
In the first place, I believe Derek was showing the graph as an example of what the software will show (statistics-wise). I'm pretty sure Derek has the same equipment that I do.....a REMstar Pro 2 CPAP......not an APAP. The graph was done over a period of time (February 11 to May 7), however it should show the same types of info over a night's period of time .

Bottom line: It shows the "Law of Diminishing Returns". It shows which pressure gives the best results.....be it fixed or a range from an APAP.

Also, we don't know from the graph whether he started at 14 and worked down or whether he started at 7 and worked up. Since this graph covers several months, we also don't know if his apneas and hypopneas were naturally decreasing with the therapy. If he was adjusting the pressure downward, there's also a point where not enough pressure would cause an increase in apneas and hypopneas because it would not be enough pressure to keep the airway open.

Just MY opinion.

Den

_________________

CPAPopedia Keywords Contained In This Post (Click For Definition): CPAP, APAP

[Guest]

John M:

The above POST by Den (WULFMAN) is perfectly stated in my opinion! Den has a brilliant way of clearly stating things which make it easy to understand that which would otherwise cause confusion! To me HE is one of the BEST, HELPFUL, and most INTERESTING people on this site. Go to the bank with what he tells you, and if you need clarification on something he responds to that too!

Best to you,

steve,
ufo13

[neversleeps]

Derek has the REMstar Auto, but uses it in CPAP-mode. Here is an interesting post he wrote that addresses this issue:

For the past three weeks I've been doing an experiment, comparing my nightly data using CPAP wiith that from the previous three months on APAP (REMSTAR Auto with C-Flex). Although the "experiment" is still a work-in-progress, I am convinced that I get significantly better therapy from CPAP. Here's the scoop:

As most of you know, I have been plotting my data using MyEncore, and I have frequently shown the following graph showing how my AHI depends on pressure:


This curve is based on 700 hours of APAP, with the minimum pressure set between 7 and 9 cm H2O. Now the shape of this curve has always bothered me for a couple of reasons: 1) The whole basis for the APAP algorithms is that the AHI should decrease with pressure. I was concerned that if I ended up on the positive slope above 10cm, if I had some event (snore?) that raised the pressure, then I was in fact in a worse position, and would be even more likely to have another event. In other words, on the positive slope we have a positive-feedback situation which can only make things worse, and even lead to pressure runaway - which I have found a few times. 2) I wondered if this curve really represented me, and was not an artifact of the APAP pressure control algorithm.

So I decided to do a study on myself using the CPAP mode. I decided to concentrate on the central region and have been buiding up AHI performance data for pressures of 9, 10, and 11 cm. Each night I have my wife choose one of the three pressures at random, and I looks at the total results in the morning. Here is the CPAP pressure-AHI plot for three weeks worth of data:



Now compare this to the same pressure range extracted from the first chart (ie 3 months of APAP data).



The plots are almost identical indicating that, at least in this data range, the APAP AHI-pressure plot provides a good picture of my true AHI-pressure dependence.

Now here's the thing: my nightly AHI's are significantly lower on the CPAP at any of the three pressures than on APAP at 9 - 14 cm, (I know that they are already low. ) and what's more the night to night variation in AHI is much, much reduced. I don't have the statistics yet, but looking at my nightly plots it is obvious that there is much less variation. I put this down to the fact that the nightly meanderings of the APAP pressure actually are inducing apneas/hypopneas.

So here's the question. If anybody has a concave AHI-pressure plot like mine, why would they ever want to set the maximum APAP pressure above the minimum in the plot (10 cm in my case)? You are, by definition, not going to get any better treatment from higher pressures. And if you can tolerate the 10 cm pressure, why bother with the lower pressures?

Why not just set up in CPAP mode at the pressure with the lowest AHI? I'm going to stay in CPAP.
derek

[Wulfman]

neversleeps,

Thanks for the clarification.
I knew he was running single pressure, so I shouldn't have assumed he didn't have an APAP. On the other hand, running it in CPAP mode, it is then just like mine.


Steve (ufo13),



(thanks for your kind words)


Best wishes to all for a wonderful New Year.

Den

[ufo13]

Den:

Forgot to add in my other post my THANKS to YOU for the past info reference how wrong the titration studies can be! I like you were titrated at 18 cm H2O and I was on that fixed pressure 11 yrs, until recently (7-05) getting a remstar auto which had been set at a 16 to 20 range (tight around titrated pressure) still pretty high pressure. However I read your posts and info about how you were able to lower your av. pressure (around 10 I think) etc. My card reader was broke and I recently got a new one so I went into the testing mode and tracked it for weeks from the info you gave. Well after checking, most nights I never go past 13 once in a blue moon go to 15. My 90% pressure is av. 14! So for the last 2 weeks I have set my machine to a 12 to 20 range but hardly ever go past 15 so I will be lowering the top to about 16. Because of the much lower pressure I also was able to shut off the c/flex completely! I am feeling so much better and the stats look great for me at the lower pressures as well as much less side affects of the high pressures as you know!

So many, many THANKS to you for sharing your knowlege, I'm sure it has helped many people, I know it was a god-send to ME!

Thanks again to you Den, and HAPPY NEW YEAR TO YOU AND MY OTHER CPAP FRIENDS!!!


steve,
ufo13

[Wulfman]

Steve,

I'm really glad to hear you're doing (and feeling) better.....and at a lower pressure.
Since my experience with setting my pressure, I have wondered how many other people are either over or under "titrated".....and consequently suffer with not getting proper treatment.....not to mention finding the right mask to use.
My feeling (based on MY experience) is that a titration or split study may be somewhat questionable as to the longer term treatment. For example, after I got my machine and set my own pressure (10 cm), my AHI was still over 5.0 for the first day's usage.....then dropped to 0.5 the next night and then bounced around between 0.2 and 3.4 for the next several weeks before settling down to an average of 1.0 or below. My concern is that the "one night stand" at the sleep study may not give a true picture of what is really needed for the long term. This is why I think APAPs (or the ability for a person to change his/her own settings) over the course of their therapy is SOOOO important. Your needs DO NOT stay the same. The sleep studies are potentially valuable in finding some other underlying situations like RLS, low blood oxygen and other afflictions, but as far as using them for titration, I question their validity for long-term settings on a CPAP.

It's YOUR machine, it's YOUR therapy...."listen" to your body.....it'll tell you if something isn't right.....then be prepared to make "adjustments".

Just MY opinion.

Best wishes,

Den

[John M]

Thanks for the responses, everyone.

The "positive feedback" loop described by Derek is what concerns me. I've noticed that when my pressures go higher, my AHI is higher, but I assumed that it was the A's and H's that were causing the higher pressure. Later, I started to wonder if it wasn't the other way around (as it seems to be with Derek's data).

On the other hand, I have also noticed that the leak rate seems to be MUCH higher with these AHI's (more than can be explained by the increased mask exhaust rate). In my case I wonder if the higher pressures induce mask seal leaks and/or mouth leaks which in turn induce obstructive events and flow limitations which in turn causes the machine to bump up the pressure even more, thereby inducing even more leakage and therefore A's, H's and flow limitations. I should mention that months ago I limited my max pressure to 9 because beyond that, the leak rate went up exponentially--when I set the upper limit to 9, my compliance and AHI both improved quite a bit.

So, I wonder whether the positive feedback problem described by Derek may be largely (or at least partly) due to mask seal leakage--I think maybe it is, at least in my case.

I guess I need to perform an experiment similar to Derek's using constant pressure to know for sure. This seems to be the only good way to optimise therapy, anyway.

This sure points out the short comings of 1 night titrations and auto machines. No wonder so many people quit using xPAP.

Seems like there's still a great deal not understood about treating OSA, and a long way to go in APAP algorhythm and mask development. . .


Regards,
-John

[rested gal]

Steve,
I have wondered how many other people are either over or under "titrated".....and consequently suffer with not getting proper treatment.....not to mention finding the right mask to use.
My feeling (based on MY experience) is that a titration or split study may be somewhat questionable as to the longer term treatment.

--snipped--

My concern is that the "one night stand" at the sleep study may not give a true picture of what is really needed for the long term. This is why I think APAPs (or the ability for a person to change his/her own settings) over the course of their therapy is SOOOO important. Your needs DO NOT stay the same. The sleep studies are potentially valuable in finding some other underlying situations like RLS, low blood oxygen and other afflictions, but as far as using them for titration, I question their validity for long-term settings on a CPAP.

You said it so well, Den! My sentiments exactly, regarding a single pressure setting.

[rested gal]

I wonder if the higher pressures induce mask seal leaks and/or mouth leaks which in turn induce obstructive events and flow limitations which in turn causes the machine to bump up the pressure even more, thereby inducing even more leakage and therefore A's, H's and flow limitations.

I would wonder about that, too, John. Perhaps it's simply because I'm such an inveterate mouth air leaker, but I think mouth air leaks are a bigtime treatment breaker for many people.

Last night I tried using nothing to control my mouth air leaks. No tape, no mouthguard, nada. The difference in what happens was dramatic on my data results this morning. Machine had to really work hard to compensate for massive mouth air leaks. Quite a few more events slipped through. More pressure than usual had to be used. Had I been using a mask with an iffy seal, the increase in pressure would have forced even more leaks...mask air leaks to go along with the mouth air leaks!

[Colorado Jan]

Well, my mother always told me that one-night-stands were not a good thing. And here we are proving that she was right on the money!

Jan in Colo.