POLL: Typical AHI for ResMed Users

[twokatmew]

As a new PAPper and ResMed user, I know that medical professionals claim AHI < 5.0 is "normal." Still most of what I initially read on this forum is about Respironics users seeking (and often getting) AHIs of 1.5 or less. Eventually I found posts by Rested Gal about ResMed machines over-scoring hypopneas and her reasoning for cutting the HI in half. (Velbor has weighed in on this interesting topic also.) Even so, my numbers have been consistently depressing. In recent polls and threads, I'm starting to read about ResMed users "doing just fine" (or not!) with significantly higher numbers. So I decided to start a new POLL/thread to hopefully encourage ResMed newbies (or oldsters) who may be struggling with higher AHIs.

I know there are ResMed users with near-Respironics AHIs, but I'm also realizing there are probably more ResMed users with significantly higher numbers, and this can be OK.

Anyway, off we go....

[billbolton]

Eventually I found posts by Rested Gal about ResMed machines over-scoring hypopneas and her reasoning for cutting the HI in half.

The only thing that is definitively established is that Resmed and Respironics machines score events differently.

There is emerging evidence that Respironics may under-score hypopneas...

In terms of your poll... you really need to think through what you want to achieve in much more detail as the current question is quite meaningless in terms of indicating anything useful.

Cheers,

Bill

[jnk]

If I understand rested gal's position, I believe it is that no machine overscores or underscores, since no home machine is telling you your actual AHI. Each brand of machine uses its own definition based on flow to report to you an ESTIMATE that is for TRENDING purposes only. In other words, the numbers are given solely for you and your doc to see if you are doing better or worse over extended periods of time--not to give you any indication of what your actual AHI would be during a PSG.

In fact, the clinical guide for my machine (a ResMed) states this:

"The AHI values reported . . . should be viewed as trending information only . . . The AHI reported . . . may be higher than the AHI determined by polygraphy scoring since the [machine] cannot detect the sleep state or the presence of arousals, nor does it incorporate SpO2 measurements into the AHI calculation."

The "below five" rule is for PSG tests, not home machines. And that rule is a line in the sand chosen as a way to arbitrarily define who gets to try a machine, not who might actually benefit from one.

Don't let those numbers depress you. It is not what they are for.

ps- I like the poll. Polls are fun. I think that is what they're for. Is ANY poll really supposed to be "useful"? None of mine have ever been.

[robertmarilyn]

I voted!

As jnk and twokatmew know, I fall in the 15-20 range (with apneas making about 5 of that 15-20).

mar

[twokatmew]

OK, I thought about changing the poll, but all I really wanted to see was a spread of numbers and perhaps some comments from ResMed users. Perhaps I should have also added two options, "satisfied w/ therapy" and "not satisfied w/ therapy." Perhaps I should have skipped the poll and just started a thread. Since people have already voted and commented, I'll leave the poll alone unless someone has specific suggestions.

Jnk, I should have been clearer. When I summed up Rested Gal's comments, I should have qualified by saying "ResMed overscores hypopneas compared to Respironics," (or the reverse). I realize this is simply trending data, but at the beginning when I'm not really noticing improvement, high numbers only serve to make me feel even less successful. Without data I would not have known I needed to significantly increase my pressure. But looking too closely at the numbers can be a hindrance. Even though I know the two machines score events differently, it seems to me we hear much more re data specifics from Respironics users than ResMed users.

Anyway, I simply wanted to gain some perspective from ResMed users.

It seems I get the best numbers when I have the poorest sleep. Last night I had my best AHI yet. I couldn't sleep, only spent a few hours in bed (awake) and had an AHI of 0.3, AI 0.0! Looks like I should just skip sleeping altogether!

[Muffy]

A better question would have been "How many users have Autos (where the AHI should be 0.0, having spent all that money on a machine to do exactly that)"?

Or "How many users have Autos with a too low starting pressure (that could get you a bunch of events)"?

It would seem that the aggessiveness of the Resmed A10 algorithm would have stomped out all the hypopneas, as suggested by the bench test by McCoy, Eiken and Diesem:



Maybe it's the "5 breath moving average" that adds in a few events during periods of artifact.

However, I'm sticking with Muffpothesis as the reason for the Respironics HI < ResMed HI (Respironics filters out poor sleep) until I see a comparison of ResMed vs Respironics with someone who has a Variable Breathing% of 0.0.

Muffy

[jnk]

Thanks for linking to that article, Muffy! Very interesting.

I don't expect 0.0 from an auto, myself. I figure that a few bucks more (what, $75 more to go from an Elite II to an AutoSet II, right?) buys (1) a little more comfort as far as slightly lower mean pressure and (2) the ability maybe to give slightly better numbers on a night following a particularly exhausting day, or a high-allergy day, or the like. I don't expect a tech during a PSG to achieve 0.0 with a pressure, so I don't demand that from my machine either.

Maybe ResMed opts for efficacy over comfort in some instances when other brands might opt for comfort over efficacy, so some brands might be considered less "aggressive." But to my odd way of thinking, those differences between brands don't bother me. I figure that people (techs) make different decisions in the practice of their art/science, too, but I still like the idea of the PSG.

I assume my ResMed auto 'stomps out' the majority of hypopneas with its 'aggressiveness' but that it is also even more aggressive in scoring decreases in flow amplitude as possible hypopneas. So I don't let the high home-machine estimates of AHI bother me. I respect that the machine is being tough on itself in reporting its estimates of its own efficacy.

[Muffy]

And boy, I'll tell ya, since the Psearch patent suggests that hypoventilation

hypoventilation is defined as five (5) consecutive breaths with Vm less than 40 percent of the predicted awake supine Vm; and apnea is defined as a 10 seconds duration of no change in respiratory phase as determined by the leak adjusted threshold detection mechanism.

will elicit the same behavior as Variable Breathing:



one begins to wonder if the Respironics HI needs to be multiplied by a factor of 3 in select patients in order to try to reconcile these differences.

Muffy

[MoneyGal]

The gradation on the poll is really...weird. The jump between options 3 and 4 is startling.

FTR, my AIs with my ResMed are typically around 0.01; my HI around 2.2. I mentally slightly discount the HI and focus, instead, on the AI -- and on how I feel.

[jnk]

I have a mental limitation (OK, several, really) that keeps me from understanding flowchartish stuff like that.

But if I get the drift at all, it seems to me if a machine is going to run a test in a way that allows it to monitor whether or not the test makes things better or worse, that would require the machine to identify a clear baseline to compare the results of its test to. And similarly, whenever breathing is too unstable for the machine to discern a clear, relatively normal pattern of breathing, that would make it hard, I assume, for the machine to be confident about recognizing "hypopneas" and lesser decreases in flow (although maybe an "apnea" would be recognizable enough). So wouldn't it be an act of technological humility, in a sense, for an auto to hold off on making decisions about changing pressure, or scoring, whenever breathing is, in its judgment, too unstable to monitor well? Couldn't that be a very-well-thought-out design feature needed for the chosen Respironics approach, but one that isn't needed for ResMed, which doesn't run such tests at all with its autos in deciding on a pressure?

Or am I missing the point completely again?

[stanps]

I'm pretty lucky I guess. I'm a relative newby and my AHI is 1.8. AI is typically 0.0 to 0.1.

One odd thing I have noticed. On some occasions I will wake up early and check my data. I put my mask on to try to get a little more sleep. I don't fall asleep so I take the mask off and check data again and my hypopneas have gone up a bit. For some reason it thinks my breathing is worse awake than asleep. I don't get it.

[-SWS]

since the Psearch patent suggests that hypoventilation... will elicit the same behavior as Variable Breathing:

The patent suggests hypoventilation is a sustained drop in flow signal. By contrast, Variable Breathing (or VB) is inherently erratic breathing, with criteria based largely in peak-flow standard deviation. So hypoventilation criteria is altogether separate from VB criteria. But since those two conditions are not comprised of mutually exclusive criteria, that implies a breathing signal or flow condition can meet both criteria sets.

So what, in turn, does that mean regarding patients either meeting or failing to meet those separate criteria sets? It means that across the SDB patient population, some of those hypoventilation-positive detections will also be VB-positive while other hypoventilation-positive cases will not meet VB criteria. So let's follow both of those hopoventilation-positive cases through that flow chart:

Case One- Hypoventilation-Positve Criteria Combined With VB-Positive Criteria: Hypoventilation-positive cases or criteria always outrank VB-positive criteria regarding algorithmic priority. So in this case the flow signal is always sent back to the apnea-detection circuit for subsequent higher-priority reexamination---before dropping back down to that same hypoventilation-detection circuit for yet additional reexamination. That case never even has a chance to drop down to the lower-priority VB detection circuit until all higher-priority traces of apnea and/or hypoventilation are gone.

Case Two- Hypoventilation-Positve Criteria Lacking VB-Positive Criteria: Since no VB-positive criteria is present, but hypoventilation-positive criteria exists, the flow signal once again always gets sent back to the higher-priority apnea-detection circuit for subsequent reexamination. Once all traces of either apnea or hypoventilation are gone, then the algorithm is finally allowed to look for signs of lower-priority VB.


Above, we have hypoventilation-positive cases always being sent back to the higher-priority apnea-detection circuit for apnea reexamination---before dropping down for yet another pass at hypoventilation reexamination. The only flow-signal conditions that are allowed to be treated by the lower-priority VB circuit, are those VB flow signals lacking both higher-priority apnea and higher-priority hypoventilation criteria.

since the Psearch patent suggests that hypoventilation... will elicit the same behavior as Variable Breathing:

That control layer running Psearch happens to be lower priority than both the VB and hypoventilation detection circuits. So if criteria for either VB or hypoventilation surfaces during a Psearch, then algorithmic control reverts to the highest-priority control layer for which criteria matches.

[Muse-Inc]

...wouldn't it be an act of technological humility, in a sense, for an auto to hold off on making decisions about changing pressure, or scoring, whenever breathing is, in its judgment, too unstable to monitor well? Couldn't that be a very-well-thought-out design feature needed for the chosen Respironics approach, but one that isn't needed for ResMed, which doesn't run such tests at all with its autos in deciding on a pressure?

I think that the crux of the matter. From what I've read here, it seems to me that the Respironics APAPs respond with larger increases to events and flow limitations (thus faster response to max) and detect VB (and PB) which might have been induced by the most previous pressure change and then back out of that change...all in addition to the expected pressure changes in response to events. Plus, if I remember correctly/understood properly, the 'recovery' from pressure increases is in stages over several minutes. This seems to me to be a significant number of changes...plus now in the new machines they use FOT (FOB?) which again is a 2-breath temporay pressure 'change' that might lead to breathing/arousals. In contrast, it seems to me that ResMed APAPs respond more cautiously to flow limitations and events, thus conceiviably might have fewer pressure changes. As we've seen posted here, many have reported that the changing pressures of an APAP result in higher overnight AHIs or just not feeling as well the next day. Confusing because they approach CPAP therapy from different perspectives. I think that's why some do better on one vs the other and that's not even addressing the other manufacturers machines!

And as -SWS-Muffy just posted, there's the whole issue of hypoventilation that factors in these calculations.

[jnk]

Muse-Inc,

Just between you and me, all the questions about algorithms are a good distance over my head. I do enjoy reading when -SWS, Muffy, Velbor, and the rest of the technologically savvy experts talk among themselves about them, but I am only able to glean bits and pieces. Maybe one day . . .

It amazes me that some here are able to understand not just what the machines do in general but also the differences in approaches from one brand as compared to another. Frankly, though, although I found the article very interesting, that article Muffy linked to confused me and raised more questions than it answered in my mind. I think I'm just going to sit quietly, reread Muffy's and -SWS's posts in this thread a few more times, reread the article, run some searches for some older threads on it, and see what I can learn. I am not even sure I understand the concept of "aggressive" anymore, when it comes to autos. They keep score, and they choose a pressure. From the advertising literature, all the approaches sound pretty good to me.

What would be cool is if titrations could be done with three or more autos all hooked to one tube so that a tech could switch from one machine to the other seemlessly during the night to see which one each patient reacted to the best. See, it's crazy ideas like that one that make it clear my sanity should be tested before being allowed in such discussions!

[twokatmew]

I'm with you, jnk! My poor brain just doesn't make much sense of this very technical info. I wish it did, and I'm still grateful for the technical responses, as I hope to understand a bit more one day.

Although we have a very small sample for the poll, so far I see more than half have AHIs over 5, and just as many have AHIs over 10 as do 2.5 and below. I hope this will help ResMed newbies feel a bit better about higher numbers.

As for me, I suspect I do quite a bit of irregular breathing which may push my numbers even higher. I'll do more testing with my oximeter once my batteries arrive.

Thanks all, keep the posts and votes coming!