AHI, RDI, & outcomes

[Iowamv]

I noticed the research discussed in this thread
viewtopic/t93373/Sleep-Apnea-and-Cardiac-Risk.html

used RDI to categorize OSA severity. I think I read in another thread that RERAs are "hypopnea wannabes." And I guess I assumed that RERAs lead to loss of sleep, but might not be as harmful as full on apnea and hypopnea events. Does anyone have solid info on this? My reason for asking is that my AHI is 11 (mild), but my RDI is 21 (moderate). So I'm curious about whether someone in my situation is equally at risk for the various adverse health outcomes as someone whose AHI is moderate.

Had an appointment with my GP a few days ago. He said "I got the report from your sleep doc. Looks like your apnea is mild, but I'm glad you are treating it."

Which is it? Mild or moderate?

[Joe Snooze]

There is little evidence that CPAP treatment for mild Apnea reduces mortality but if it improves your quality of life that's all that counts.
If you feel more refreshed in the morning, especially if you were suffering from fatigue before CPAP, it's worth while.

[Iowamv]

Exactly! And I have moderate apnea as defined using the methodology used in that research. Which begs the question "is there a functional difference (in terms of likely adverse outcomes and benefits of CPAP treatment) between AHI-defined apnea and RDI-defined apnea?"

As an aside, I definitely do feel better, so I am committed to CPAP treatment.

[Rustsmith]

My numbers are very similar to yours - AHI =10 and RDI =26. If you read through information on this website as well as the internet, you will find a number of references to Upper Airway Resistance Syndrome (UARS). UARS is still quite controversial and is not an accepted diagnosis by many. Others (like my insurance company) feel that the benefits of PAP therapy for UARS is unproven. Some papers describe UARS as early stage sleep apnea and others believe that it is a separate disorder. What often seems to be consistent for the UARS supporters is belief that the patient population is different from that of OSA and that the patients tend to have lower BMIs, low blood pressure, small physical features of the face and throat creating narrow passages and that these lead to fewer true apneas/hyponeas and higher numbers of RERAs.

Getting back to the topic at hand about impacts to heart health, this pro-UARS publication -
http://www.journal-mhr.com/PDF_Files/vo ... 1N2_1.pdf‎

indicates that patients with UARS are not susceptible to the complications of OSA that lead to heart problems. The paper is only presenting a hypothesis about UARS and is not a study, but it does include a large number of references to relevant studies to support the proposed theory.

Steve

[robysue]

To muddy the waters further.

Back in January or July, my current sleep doc told me that the data from several long term studies show the following:

1) There is a strong positive correlation between untreated severe OSA and an increased mortality from stroke and congestive heart failure; and there is a strong positive correlation in reduction in mortality with sucessful CPAP treatment of severe OSA.

2) There is no correlation between untreated mild OSA and an increased mortality from stroke and congestive heart failure; and no correlation between treating mild OSA with CPAP and a reduction in mortality. In other words, untreated mild OSA does not statistically increase the risk of dying from a stroke or congestive heart failure. And successfully treating mild OSA by CPAP does not provide any measurable reduction in the risk of dying from a stroke or congestive heart failure.

3) The data is decidedly mixed for attempting to establish a correlation between untreated moderate OSA and mortality from stroke and congestive heart failure; and data is mixed for establishing the efficacy of treating moderate OSA with CPAP as a means of reducing mortality due to stroke and congestive heart failure in patients with moderate OSA. In other words, for the moderate OSA group:

• the data cannot be used to establish a positive correlation between untreated moderate OSA and increased mortality due to stroke and congestive heart failure---i.e. the data cannot be used to "prove" that people with untreated moderate OSA are at a higher risk of dying from stroke or heart disease.
• the data cannot be used to establish that untreated moderate OSA does not increase the risk of stroke or congestive heart failure----i.e. the data cannot be used to "prove" that people with untreated moderate OSA are NOT at a higher risk of dying from stroke or heart disease.
• the data cannot be used to establish a positive correlation between successful CPAP treatment of moderate OSA and a reduction of mortality due to stroke and congestive heart failure---i.e. the data cannot be used to "prove" that treating moderate OSA with CPAP will clearly lower your risk of dying from stroke or heart disease.
• the data cannot be used to establish there is no correlation between successful CPAP treatment of moderate OSA and a reduction of mortality due to stroke and congestive heart failure---i.e. the data cannot be used to "prove" that treating moderate OSA with CPAP will NOT lower your risk of dying from stroke or heart disease.

In other words, the data for folks with moderate sleep apnea is just not clear. (More long term data is needed.)

I'm currently in a coffee shop after a morning yoga class and hence I don't have any of my records. I know that the doc gave me a piece of paper with the name of the meta-study he was telling me about. I'll try to locate it, but I won't make any promises ...

[Iowamv]

If you read through information on this website as well as the internet, you will find a number of references to Upper Airway Resistance Syndrome (UARS).

But don't you and I both have RDIs too high to qualify as UARS? I found this on the Cleveland Clinic site:
http://www.clevelandclinicmeded.com/med ... breathing/

The page says

A low respiratory disturbance index (RDI) is also needed to distinguish UARS from OSAHS.

I also experience desats in the low 80s.

Robysue, thanks for all the info. That's a lot to think about.

It is interesting to me that some sources define OSA using RDI while others use AHI. I suppose this is probably opening Pandora's box, but is AHI more commonly used because it is easier to gauge (especially at home)? Is it an insurance issue, or a distinction driven by clinical findings? In my sleep study, the tech said I was waking up on average once every 3 minutes (the RDI), confirmed by EEG. Even if the connection to heart health isn't as dramatic at that moderate level, I gotta believe it isn't just a question of fatigue and dark circles under my eyes.

I felt so different using my machine that I immediately thought "I don't ever want to sleep without that machine again."

[robysue]

I felt so different using my machine that I immediately thought "I don't ever want to sleep without that machine again."

This is the most important reason for treating mild-to-moderate OSA with CPAP according to my current sleep doc: The quality of life for most successful PAPers is substantially greater with PAP than without it. And the (potential) improvement in the quality of life is why it's worth treating mild-to-moderate OSA with PAP even if there isn't any real "benefit" in terms of reduced mortality due to stroke or heart disease.

Heck: Even with all of my problems with PAP, it's a net positive. The conversation between my doc and myself came up when he asked me to actually think about: Is BiPAP a net positive or not in your day to day life?

In my case, it's not a night-and-day answer. But: the absence of waking up with hand and foot pain every morning IS worth something. And the three nights without PAP this summer reminded me of just how much pain I used to wake up with. They also reminded me of just how restless my sleep patterns were in the sense of tearing up the covers and sleeping rather lightly. I may hate bedtime and putting the mask on and whole lot of other crap that I have to deal with at the beginning of the night. But waking up pain free is important to me. And not tossing and turning all night and kicking hubby mercilessly is important to him. So for now, yeah, I continue to work on making BiPAP work for me.

[Pugsy]

I suppose this is probably opening Pandora's box, but is AHI more commonly used because it is easier to gauge (especially at home)? Is it an insurance issue, or a distinction driven by clinical findings?

The medical community likes to put everything in a nice neat little box quantified by numbers...you know the old "normal range" of any test that we have done. They don't add many "buts" to the ranges. And as with anything where numbers are used there will always be a few "buts".
In my sleep study during non REM sleep my AHI of 12 barely made it worth talking about...BUT...there's the but...my Oxygen level dropped to 73% and I had most of those 12 per hour events lasting almost a minute long. There's no provision in the "numbers used for diagnosis criteria" to take into account duration of the events and/or oxygen levels.
Now in REM stage sleep my AHI was 53 but the numbers had to be extrapolated due to the fact that once they started occurring I would bounce right out of REM stage sleep and have to go through more non REM stage sleep to get to where REM stage sleep was rocking and rolling again. It's really hard to evaluate something when you don't get a chance to get much of it.

Were my pre cpap symptoms related to not getting the REM sleep or simply the low oxygen related to those rather long apnea events (but not all that frequent in number) in non REM sleep? I don't know and I don't know of anyway to know for sure.
Either one could easily be a sole culprit.

RDI is coming to be a "number" where people are looking at it as an indicator of something that can be used to put diagnoses in one of those nice little boxes that the medical community likes to put things. A few years ago I don't think it got much more than a passing nod and AHI was the end all of numbers used.

One nice thing about the medical community is that they will eventually change the criteria needed to fit in one of those nice little boxes...once enough studying and discussing about it has had a chance to occur.

I gotta believe it isn't just a question of fatigue and dark circles under my eyes.

For me I don't use the machine just because of potential cardiac or stroke risks....I use it so that I don't feel like crap right now.
Yeah..the potential for long term reduction of risks is important but I will be honest...right now this very minute...it's because it helps me feel better the next day. I don't wake up with a massive killer headache that takes 2 or 3 hours to fade away...I don't wake up every hour on the hour to pee (and a full bladder each time) and I don't nod off to nap at 9 AM after getting up at 7 AM.
Wake ups for any reason mess with how I feel and I have enough wake ups from other stuff and sure don't need to add more of them...whether they be minor arousals or full wake ups whatever the cause.

I know that my reasons sometimes can't jive with others who either don't have horrible symptoms without cpap or cpap makes sleep quality worse. My heart goes out to those people.

After working in the medical field for 30 some years and seeing all the changes...sleep apnea treatment is still a work in progress and actually just now more getting the attention that it deserves. Technology is catching up real fast.
Maybe in 5 years we will see RDI used more and it's ramifications understood more clearly and maybe they will have more "buts" in the criteria pigeon hole boxes of numbers that can be used to evaluate things.
My personal opinion...RDI is pretty damn important and I base that solely on awakenings or arousals that I know I have that are related to something other than OSA. If I don't control those non related arousals...I feel like crap and would feel like crap even without OSA. It's not hard to think that simple arousals from minor flow reductions are just as detrimental to sleep quality and thus impacting how we feel and the jury is out on how much damage is done long term with long term crappy sleep quality.
I would rather play it safe and do what I can now...just in case 10 years from now they determine that there is indeed significant damage done to the body.

I just don't know what to do or offer to people like RobySue or 49er (whose sleep quality sucks and in some cases cpap makes it worse). Talk about damned if you do and damned if you don't.
It's pretty sad when a person's RDI is made worse with cpap. I know it can't be good but I don't know which is worse long term.

[Rustsmith]

But don't you and I both have RDIs too high to qualify as UARS?

As both Robysue and Pugsy indicate, a lot of it has to do with how the data is scored and the the "boxes" that they try to put the results into to get a diagnosis. I also suspect that in my case the AHI value might have been a bit inflated and was insurance driven. My insurance covers xPAP for OSA but not UARS.

One of the differences between us is that my minimum oxygen desat value was 92% and from the comments I got during the followup, I suspect that even that value was not characteristic of the rest of the night.

Another possible difference between our tests was that my test included esophageal pressure monitoring (Pes), which is usually described as the gold standard for determining UARS. My test included PeS probably because I fit all the criteria for the classic description of a UARS patient other than that I am not a mid-30s female. Pes is not commonly performed and to be honest, it was uncomfortable enough that I am not really sure how I ever got to sleep. I was not able to tolerate it for the full night when I returned for my titration study. But it provided the data required in both tests and combined with the high number of RERAs and micro-arousals, showed me to be pretty typical for UARS (if the medical community can only agree whether that box really exists and how to define it).

I just don't know what to do or offer to people like RobySue or 49er

Pugsy, you will probably eventually be able to add my name to that of RobySue and49er. I have been 100% compliant now for a month and still cannot see that I am seeing much benefit either in the way of the machine's AHI number or in improvements to how I feel in the morning. I guess that is part of the reason my insurance company will not cover xPAP for a diagnosis of UARS.

Steve

[hegel]

Iowamv: those low oxygen levels would seem to be enough of a concern to keep using cpap regardless of everything else.

I've had a couple of episodes of atrial fibrillation that comes on during sleep. My doctors all know that I have apnia. In all of the discussions, not one doctor has mentioned this. Now I've learned (on my own) about how the heart slows way down during oxygen desaturation and then "jolts" back up (Resmeds term) to normal rates during sleep arousal and gasping for air. This constant oscillation of the heart rate can't be good. Perhaps it can even induce afib? (I have no other heart issues.)

My encore numbers are pretty good and I generally sleep well enough. I'm pretty certain that my O2 levels are good--no more headaches and a funny feeling in the morning that goes away after 10-15 minutes, which I think was associated with low O2. So yeah I'm a very dedicated cpap user too.

(Sorry for the bit of thread drift here.)

[Iowamv]

I feel for those who are struggling with treatment too. I hope all of you find answers soon!

I found this set of guidelines just now: http://emedicine.medscape.com/article/2 ... fferential

No universal consensus exists on whether the AHI or the RDI should be the standard index used to determine treatment by specialists and insurance carriers, with Medicare being the most confusing as it varies by region as to whether AHI and RDI can be used. This needs to be resolved as soon as possible. One study found that 30% of symptomatic patients would have been left untreated if the AHI were used rather the RDI.[35]

In the authors’ view, the RDI is preferable to the AHI because it includes flow-limitation events that end with arousals. The RDI is better suited to meet the new American Academy of Sleep Medicine (AASM) diagnostic criteria for OSA (see below). One study has demonstrated that use of the AHI alone leads to the underdiagnosis of OSA in 30% as compared to the use of the RDI.[35]

Sounds like there's a reason for the confusion.