Why would pressure increase while I'm sitting up awake?

[jrgood27]

I just started APAP therapy and I'm not tolerating it well so I'm using it in the evenings for an hour or two while I'm watching TV.

I'm on a Resmed s8 Vantage - no settling time. 4-18. In the hour I used it tonight the pressure increased to 9. When I checked the data there was a hypopnea index of 17.

Why is the machine increasing in pressure while I'm awake? And why is it counting hypops? Anyone know? Jenny

[Rastaman]

I have no idea but I'm curious too. I have the same machine right now.

[Handgunner45]

You might want to check out this thread.
viewtopic.php?t=9510

It doesn't really come to any conclusions. My best guess is that it has to do with the difference between your awake and asleep breathing patterns. We all breathe different while asleep and the machine's algorithm is designed around the normal sleeping breathing pattern

[Guest]

that machine increases pressure just for the heck of it. Check the programming it is probably NOT setup correctly by DME. Hold down the center down button and the right button at the same time to enter Clinical mode.

Most likely it is in cpap mode and a ramp instead of auto mode.

[neversleeps]

Here's a link to a 2002 interview (prior to the design of the Vantage) with Dr. Michael Berthon-Jones of Resmed that discusses the functionality of the APAP and contains quite a bit of interesting information about hypopneas:

http://resmed.com.au/Newsletters/Static ... 0906r1.pdf

Here's an excerpt:

When you are lying quietly awake, or when you
first go to sleep, or when you are dreaming, you
can have hypopneas (reductions in the depth of
breathing) which are nothing to do with the state of
the airway. For example if you sigh, which you do
every few minutes, you usually have a hypopnea
immediately afterwards. This can also happen if
you have just rolled over and are getting settled, or
if you are dreaming.

Apparently these things happen when we're awake too.

[GoofyUT]

Thanks for posting the link to this article, and I found that reading this article was extremely useful. I am a bit confused though.

I agree COMPLETELY with Dr. Berthon-Jones's thoughts about "central hypopneas" and how they are universal and NOT pathognomic. But, as I read the article, it sounds like the AutoSet alogorithm (at least in 2002) ignores hypopneas for just that reason.

Now, I am experiencing unmistakable clinical improvements since I started using my S8 AutoSet Vantage. But, i too have consistently noticed my S8 titrating up while I'm awake (I believe for the reasons that Dr. Berthon-Jones classifies as central hypops), and, though my AI has dropped dramatically (ALWAYS < 1.0), my HI can stay as high as 9.0, yielding an AHI of 8.0-10.0.

I've come to relax about the numbers and rely instead on how good I feel. And, i've been advised to discount the S8's tendency to report hypops aggressively.

But if the algorithm ignores hypops, why does it titrate when I'm awake, experiencing what are presumably "central hypopneas?" And why is it detecting hypops so aggressively if its ignoring them?

Chuck

[Guest]

Bump

[neversleeps]

But if the algorithm ignores hypops, why does it titrate when I'm awake, experiencing what are presumably "central hypopneas?" And why is it detecting hypops so aggressively if its ignoring them?

Chuck

Chuck, that is an excellent question for which I do not have an excellent answer. I don't even have a mediocre answer. My only thought is to suggest searching
-SWS's posts to shed some light on the subject. I just don't know.

[GoofyUT]

Here's my guess: the algorithm will detect and report flow limitations with positive flow occuring as a hypop, and then do nothing about it, except report it. However, flow limtations with no flow will be detected as an apnea, which it will let pass until flow resumes, and then bump pressure to head off the next one, on a breath by breath basis with a three breath-average. I know that it is much more sensitive to the shape of the hypop as well, but all in all, it seems that if it sees flow degrading, it'll report hypops until the flow stops, then reports an apnea and bumps pressure until the flow degradation ceases. However, that doesn't explain why it titrates during wakefulness even though it detects flow degradations such as might occur if one is reclining on their back.

BTW, I got ALL of this from my Magic Eight-Ball, which, whenever I ask it, says "It is probably so!!!"

Chuck

[Guest]

Here's an interesting thread from TAS

http://www.talkaboutsleep.com/message-b ... 7355#37355

[rested gal]

What a cool find, Guest. Thanks for posting that link!

[-SWS]

I just started APAP therapy and I'm not tolerating it well so I'm using it in the evenings for an hour or two while I'm watching TV.

I'm on a Resmed s8 Vantage - no settling time. 4-18. In the hour I used it tonight the pressure increased to 9. When I checked the data there was a hypopnea index of 17.

Why is the machine increasing in pressure while I'm awake? And why is it counting hypops? Anyone know? Jenny[/url]

Jenny, we know that autopaps by design attempt to detect wakefulness. However, I have yet to see any manufacturer specs regarding sensitivity or specificity of wakefulness detection. A little food for thought regarding how accurately wakefulness is detected by autopaps: if wakefulness were detected with a high degree of sensitivity and specificity, then there would be absolutely no reason for autopaps to even employ a "settling time" at the beginning of any sleep session. In other words a high degree of sensitivity and specificity regarding "wakefulness detection" would completely obviate the need for "settling time". So the bottom line in my own opinion is that your wakefulness was probably not accurately detected, and your settling period had also expired. Your autopap was thus attempting to treat you as if you were sleeping and as if obstructive events had been detected and needed to be treated.

Regarding why any autopap would "aggressively" detect hypopneas. All autopaps should indiscriminately detect all hypopneas, limited only by their own hypopnea detection sensitivity and specificity capabilities. Do not confuse the recording of sleep events---namely detection---with the algorithmic response to hypopneas. Sleep event detection should always be a complete recording of that which has occurred. And in the case of xPAP-based sleep event detection these events would all be "residual" events.

Hypopneas are detected by xPAP machines primarily via amplitude reduction---be it a central or obstructive hypopnea. Very specifically detection of lesser flow limitations that are obstructive are detected primarily via wave shape. That is because the wave shape itself gives off unique pattern-based clues regarding characteristics such as extreme respiratory effort (hence obstructive versus central), occlusive or restrictive tissue resonance (again obstructive versus central), etc. The main challenge with hypopnea detection has to do with the fact that a single airflow data channel cannot differentiate central versus obstructive hypopneas or even wakeful versus wakeless hypopneas with an extremely high degree of accuracy. The autopaps that do trigger in direct response to hypopneas will typically trigger only on those hypopneas that also show concurrent obstructive flow-limitation type waveforms.

In a PSG test, a flow limitation is typically scored as a less severe flow-limited breath than either an apnea or hypopnea. These three events are typically scored and tiered as mutually exclusive events. Autopap algorithms, however, will attempt to detect or score hypopneas based on amplitude reduction alone---and do so with reasonable specificity and sensitivity. However, that reasonable sensitivity and specificity is in regard only to undifferentiated hypopneas. Thus, some autopap algorithms will attempt to differentiate those hypopneas via those same concomitant wave shape characteristics that are also used to differentiate obstructive flow limitations from central events (such as central hypoventilation). The autopaps that perform this differentiation will thus typically trigger only on those hypopneas that show a high probability of concomitant airway obstruction. In general, autopap treatment for hypopneas are largely based on proactive pressures such as snore and flow limitation as precursor events to more severe hypopneas and apneas.

[jrgood27]

Well I'm not sure I can see a definitive answer - not that I would understand it anyway. The flow dynamics stuff is a little too close to physics for me, lol.

I did double check that I'm set to APAP and not CPAP. So that's all set. My settling time was off - so now when I'm sitting with it in the evenings I will leave it on.

I'm a bit concerned because my SDB is on the unusual side - all hypopneas, no desats, not much flow obstruction and a zillion arousals. And it seems like there's some murkiness in the whole APAP treating hypopnea arena.

I can't for the life of me fall asleep with my machine. Well, I fall asleep and wake up every 1 to 10 minutes with a strange little startle or gasp. I'll keep this up for 1 to 3 hours depending how sleep deprived I am before I give up for the night. This is with sleep meds.

But I digress...

This is all really interesting though thanks for all the food for thought. Jenny

[Guest]

Jenny-maybe ask your dme to switch from the Resmed auto to the PB auto and see if it does a better job for you.

[Darth Vader Look]

Well, I fall asleep and wake up every 1 to 10 minutes with a strange little startle or gasp.

This is telling me that your span is way to large. You need to, at the very least, reset that lower pressure setting of 4 cms to 6 or 7 cms and see how things progress.