CPAP is better than APAP (for me..)

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

And, what better way to prove this than to get an APAP machine that can track this information for you.

I have a straight CPAP set at 10cm H2O and have inquired about getting the Remstar Auto w/CFlex. Pending the insurance/DME hassle, I hope to get it soon. Currently I have the Remstar Pro w/ CFlex.

I am not convinced of my one-time sleep study numbers showing 96 events per hour without CPAP and then not until I reach 10cm does this number come down to about 4 events...at about 14cm the events are about the same.

I guess what I am getting at is, if one was to figure all this out, one would have to have the smart card information that only the APAP machine has, since the CPAP has only the minimal insurance related information. So, even if I ran straight CPAP through the APAP, it still would be good to have the APAP vs. the CPAP to even read this information.

...done rambling.

Tim, who just found out today that he has to take meds for high blood pressure.

The argument, and it sounds like you've done enough sampling to invalidate it in your own case, is that your pressure may vary.

Deeper sleep, allergy season, cold/flu season, weight fluctuations, all of these could change the pressure at which you do best, something an Auto will adjust to but straight CPAP won't.

Also, although I think you corrected for this (I'm a little fuzzy headed right now, so I'm not sure what all you were writing), you have to be careful of the AHI numbers at various pressures.

I had one the other night where I had a really high spike in AHI at one pressure.

Well, when I looked at the data more closely, it was because I had a series of apnea events over the span of about 10 minutes, during which my pressure rose from my minimum to four points above it before everything settled back down again.

One of the intervening steps (it was minimum plus 2), I was at that pressure for only about 1 minute, during which I had two apnea events. Turned into an hourly figure, that showed up as an AHI at that pressure of around 120. On the other hand, had I stayed at that pressure all night, it would likely have had the same apnea count for the first 4 hours of the night that I had at my minimum pressure, and then the batch of apneas over 10-15 minutes (still don't know what happened during that time. Maybe I leaned on my mask wrong. Maybe I did some mouth breathing... Not sure), and then settled back down, and my overall AHI for the night at that pressure, as a fixed, would probably have been close to the same as my overall AHI with varying pressure... But if I'd graphed it out as you did, AHI vs pressure, I would have seen a serious spike at min+1, min+2 and min+3, and then a fairly low AHI at min and at min+4.

Just some rambling thoughts.

Liam, really starting to get this whole auto thing.

Wow Derek-- This is EXACTLY my experience also doing the self-titration experiment!! I really didn't understand the whole dreaded RUNAWAY problem... just chalked it up to some sort of shortcoming with the REMstar. Then rested gal helped me with my self-titration study, then wader explained how the algorithms may not be intended for my particular breathing patterns on this post:
viewtopic.php?t=2826
and now you've explained the phenomenon in terms of the curve.

It appears this is a problem for lots of people! So, I'll just use CPAP mode at my best rate of 12, still get the advantage of the CFLEX and not feel I should have bought the 420E instead.

I guess one should conduct occasional self-titrating studies to make sure the required pressure hasn't changed.

Just out of curiosity, is this true of the PB420E too? Or does turning off the magic button on the 420E prevent it from happening so it can always be left in auto?

Derek,

I think Liam has a point. It may be that in the auto mode the higher pressures occur for such a short duration and by design coincide with a time frame where it is more likely to have a missed event that this relationship will likely place the graph on an uphill path.

Just out of curiosity, has anyone ever verified their machine's different pressures with a manometer?

It would be awful if all these experiments were based on flawed pressure data.....

neversleeps wrote:Just out of curiosity, has anyone ever verified their machine's different pressures with a manometer?

It would be awful if all these experiments were based on flawed pressure data.....

That's true, but....

I don't care about absolute pressure with my auto. I care about how many apneic episodes I have, and what the machine has to do over the course of the night to treat me.

So really, what does 6cm vs 12cm really mean to me? However, I can chart my results and see that the machine sits at 6 for most of the night, and occasionally gets up to the 10 range (but usually with a 90% pressure of around , and it really doesn't matter to me if that's legitimately 6, 8 and 10, or whether in fact it's 5, 7 and 9, or 8, 10 and 12. It's just interesting to see how my body behaved over the course of the night.

And I still contend that running an auto in straight CPAP mode is better than most straight CPAPs, because you get better data out of it. That doesn't mean a straight CPAP couldn't report it, of course, but in order to keep the price of them down, why bother having the subtle measuring equipment necessary to detect "apnea precursors" when you're not going to do anything with that information anyway.

Even if I come to have some runaway pressures and decide to go with my standard 90% pressure of 8, I'll still be able to download my data every night and see if that 8 continues to give me a favorable AHI. Because THAT, and not the pressure, is the number that matters. If you have few or no apneic events, you're doing well regardless of the pressure. And if you're having a lot of events, you're doing poorly regardless of the pressure.

Liam, in full blown lecture mode, obviously.

Liam-

Point well taken!

Do we know for a fact the software is measuring the events properly???
(Just kidding.)

You're right of course. But I get such tremendous variations between CPAP and APAP data. I set my REMstar auto to CPAP 12, cflex 3 and I get far different results than when I set it to APAP 12/12, cflex 3. Wouldn't you think it should be the same? Have you tried it that way also?

Rats! Just when I felt I was starting to grasp this whole thing, I come to find I really haven't a clue.

Really? Hmmm, no I haven't tried APAP x/x vs CPAP x. Interesting, and I wonder why it would differ.

Actually, I think I might know...

One of the aspects of an APAP is the attempt to recognize a pressure-induced "central apnea" and drop the pressure. Perhaps that drop in pressure doesn't have to conform to the minimum set pressure (just as CFLEX doesn't), and thus, using #/# APAP still allows the machine to sense an apnea as a central and drop the pressure, while in CPAP mode, it says "Well, they want pressure X always, so we'll still sense stuff, but we won't adjust pressure at all, ever, except for exhalation".

Just a guess.

Liam, dis GUESS ting.

My wife's doctor does not like or thinks that an auto pap works at all he also said c flex does not work. He said the best is straight cpap with a pressure of 9... My wife has good numbers(AHI) when set to auto pap (RemStar auto clex) and her apnea is corrected at 6 or 7(MOSTLY 6)..It looks like around 2.0 to 2.5 on avg with the auto set at 5 to 10..when the auto is in CPAP set at 9 like the doctor wants she gets less than 1 on the avg. it looks like cpap might be better for her but she likes breathing in less air. She really wants to do what the doctor wants and it is better but she has less air and good numbers in the auto...here are her nights and numbers

5-10 1.4
5-10 3.1
5-10 1.9
5-10 3.3
5-10 3.9
6.5 - 6.5 3.7
6.5 - 6.5 3.8
6.5 - 6.5 3.8
8 -8 2.8
5-10 1.8
5- 10 2.8
5-10 2.5
4- 10 2.6
cpap 9 1.0
cpap 9 .07
cpap 9 .03
7- 10 1.0
7-10 3.8
7-10 2.5
7-10 2.7

I am now moving her back to 5-10 auto since she likes less air..What do you think? Should she be at straight cpap pressure of 9 or have auto 5 to 10 being corrected mostly at 6???

If she feels good in the morning and the 5-10 auto makes her more comfortable (translation: more willing to use the 'pap) then I say "stick with the auto."

She is feeling better. Her main problem now (to me) is PLMS. She had at her sleep study 9 (PLMS) and hour with 7 of them waking her out of her sleep cycle. Her doctor said that was not bad and would not give her any medicine.Told her not to worry about it. I told her doctor some nights are way worst than that. It gets so bad she runs me out of the bed. When it gets like that she does not feel as well the next day. I am trying to get my wife to see someone else but she wants to stick with the anti auto, non existent c flex doctor. I told her I was moving her pressure back to 5 to 10. She only smiled. I know she will blame me when she goes back to her doctor. I have no problem with that he is free to call........before 11:00 pm, we go to bed then

I wanted to add her doctor saw her AHI reports (APAP)I sent him. He said to use straight cpap 9. You can see where in the above chart where she went 3 nights with cpap set at 9 but she did not like all the extra air. So I made some adjustments. I think he really did not like that I had the software and reader for the machine. To get accurate numbers you need to come back for a $1500.00 sleep study every couple of years

I think as long as the AHI is below 5, I would go with whats the most comfortable. I struggle to get mine under 10 so I'm quite jealous.