Does 10 EEG arousals/hour mean sleep apnea?

[BigWing]

I was always pretty good at algebra but I can't make sense of this set of data.

Normal AHI is 0-5; above that and you have sleep apnea.

Normal RDI is 0-5; above that and you have sleep apnea.

RDI = AHI + RERAs/hour

So, if you have an AHI of 5, even a single RERA all night means you have sleep apnea!

Yet normal people have at least 10 EEG arousals PER HOUR - which are essentially RERAs!!**

Where have I misunderstood?

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*A RERA is an abnormal breathing event which does not meet the criteria of an Apnea or an Hypopnea, but is an “arousal” event associated with a respiratory effort as noted by EEG.

**"EEG Arousal Norms by Age" https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2564772/

[ChicagoGranny]

If you are trying to find an excuse to quit CPAP, you don't need an excuse. Just quit.

[BigWing]

If you are trying to find an excuse to quit CPAP, you don't need an excuse. Just quit.

Not at all....I'm trying to get more edukayshun!

[ChicagoGranny]

It's best to stay on the trail and out of the weeds. Especially if you tend to obsess over weeds.

[robysue1]

Where have I misunderstood?

Quite a bit.

Let's take it one step at a time:

Normal AHI is 0-5; above that and you have sleep apnea.

In any sleep test there has to be a way to determine the airflow in to the lungs. Apneas are scored when there is evidence of little or no airflow into and out of the lungs for at least 10 seconds while you are asleep. Classification of apneas into obstructive or central apneas requires some way of measuring the respiratory effort you are making during the apnea. If there is evidence that your body is trying to breathe, it's assumed that the upper airway is blocked and the apnea is scored as an obstructive apnea. If there is evidence that your body is not trying to breathe, it's assumed that a blockage in the upper airway is NOT the cause of the apnea, and the event is scored as a central apnea. (Last sentence has been edited to clean up a typo caught by BigWing in his response immediately below this post.)

Scoring hypopneas on a sleep test is a bit more difficult. Recall that in any sleep test there has to be a way to determine the airflow in to the lungs. And typically the tech running (or scoring) the test has to compute what is known as a "running baseline" for your respiration over each 2 minute period of sleep. On a sleep test, hypopneas are scored under one of two different scoring criteria: Your respiration has to (suddenly) drop by at least 30% AND there has to be a corresponding O2-desat of at at least 3 or 4 percent. No EEG arousal is required to score this kind of hypopnea. OR a hypopnea can be scored if your respiration drops by at least 50% AND there is a corresponding EEG arousal. In this case, it's not necessary to have the O2 desat to score the hypopnea. Ideally, the organization running the sleep test should tell you which criteria they use for scoring hypopneas, but not all of them do. Home sleep studies, which typically have fewer channels of data, particularly EEG data, often use "proxy" measures for scoring hypopneas and determining whether a given apnea is a obstructive or central. But oftentimes patients are stymied when they try to get information about how their sleep study was scored.

Next, the diagnostic AHI is computed by dividing the number of apneas and hypopneas that were scored during epochs when you were actually asleep. Basically an "epoch" is something like a 30-second snapshot from the time you were in bed. If the EEG evidence (or its proxy for at home sleep tests) shows you were awake during any part of a particular epoch, no apnea or hypopnea can be scored no matter how ragged your breathing might look. So if there were 10 OAs and 9 Hs scored on a sleep test where the total amount of sleep was recorded as 6.5 hours, then the diagnostic AHI is (10 + 9)/6.5 = 19/6.5 = 2.92 (which is rounded to 2.9 for reporting purposes), and you officially don't have a diagnoses of OSA. Now if all of those 19 events were recorded during a short period of REM or a limited amount of supine sleeping, a note might be made about the REM AHI or supine AHI being great enough to be classified as OSA.

Now if a different person also had 10 OAs and 9 Hs scored, but the total amount of their sleep time was 3.25 hours, their diagnostic AHI would be 18/3.5 = 5.85, which rounds to 5.9. And they'd wind up with a diagnosis of (very) mild obstructive sleep apnea.

Normal RDI is 0-5; above that and you have sleep apnea.

RDI = AHI + RERAs/hour

So, if you have an AHI of 5, even a single RERA all night means you have sleep apnea!

Yet normal people have at least 10 EEG arousals PER HOUR - which are essentially RERAs!!**

EEG arousals and RERAs are not essentially the same thing.

RERA stands for Respiratory effort related arousal. Accurately scoring a RERA on a sleep test is difficult unless the test is done in a lab with special equipment to help measure the respiratory effort being made. It's kind of useful (but also a bit misleading) to think of a RERA as a "hypopnea wannabe". What I mean by this is that in a RERA, the airflow into/out of the lungs is never as restricted as it is in a "real" hypopnea, but there is evidence that the body is making an increased effort to get air into the lungs for at least 10 seconds. And then there's an EEG arousal scored and the breathing returns to normal after the person gets back to sleep. But without that increased respiratory effort, a RERA cannot be scored just because there's an EEG arousal.

In order to understand what's meant by "increased respiratory effort", a RERA is sometimes likened to the effort required to breathing through a straw: You can do it without any significant reduction in the amount of actual air getting into your lungs, but it takes more effort than normal breathing and the flow rate curve is likely to be distorted in predictable ways that indicate that increased effort needed to move the appropriate amount of air into the lungs.

Now what happens in a real RERA is the additional effort to maintain adequate airflow into your lungs wakes you up before the airflow becomes restricted enough to score a hypopnea and before any O2 desat takes place. Now on an in-lab sleep test, there must be an EEG arousal following a period of bad breathing that is not (by itself) severe enough to warrant scoring a hypopnea based on that 2-minute moving average of "normal airflow" into your lungs.

Now RERAs are still a bit controversial in sleep medicine, mainly because they are so darn difficult to measure with any accuracy (or repeatability) on in-lab sleep tests: The specialized equipment needed to measure the increasing respiratory effort is significantly uncomfortable and adds to the misery of an in-lab sleep test. And home tests typically don't even attempt to measure RERAs because of the limited data and the fact that to score a RERA, you really need the combination of the EEG data and the respiratory effort data that together demonstrate a particular arousal was respiratory related rather than spontaneous or related to period limb movements or some other cause.

And that last point is important: Many arousals scored during a sleep test are not related to any respiratory problems: Many people naturally arouse any time they want to turn over in bed. Many people arouse briefly at the end of each REM cycle. In many people chronic pain issues can cause spontaneous arousals. People with PLMD have arousals related to their periodic limb movements. Many people with sleep maintenance insomnia simply have far too many spontaneous arousals that are not related to their breathing. None of these kinds of arousals are RERAs even though they show up in the EEG data as arousals. And it's possible to have huge number of EEG arousals during a sleep test with none of them related to sleep disordered breathing---i.e. sleep apnea or UARS, which stands for upper airway resistance syndrome. In UARS the problem is all the RERAs disrupt the sleep enough so that the person wakes up feeling awful in the morning, the same way that in OAS, all the OAs and hypopneas with their O2 desats and arousals cause the sufferer to wake up feeling awful in the morning. And in that case, trying CPAP is not likely to improve the sleep since the problem is not sleep disordered breathing.

But here's the thing about the RDI definition of OSA vs. the AHI definition of OSA: It's now commonly believed that there is a very fuzzy line between scoring a real RERA and scoring a real "hypopnea with arousal"---a hypopnea where the amount of air going into the lungs has decreased by 50% but the event ends with an EEG arousal instead of having an accompanying O2 desat. And if a person is symptomatic, but many of the events scored on their diagnostic sleep test are in that fuzzy zone of "is it a RERA or a hypopnea with arousal?", then it really doesn't much matter whether those events are real RERAs or real hypopneas: What is clear from the data on the sleep test is that those events are respiratory related, end with an arousal, and are apparently disrupting the sleep severely enough for the person to be experiencing problems with waking up fatigued and/or experiencing excessive daytime sleepiness.
And because of that, it's reasonable to assume that a trial of CPAP is worthwhile.

But here in the US, Medicare still wants to only count hypopneas with desats even though not everyone experiences desats when they have a hypopnea. And so increasingly cases are made to both patients and insurance companies that if a patient is symptomatic and if the RDI is too high (including RERAs and "hypopneas with arousal" if the latter are not included in the AHI because of Medicare reasons), then the patient probably does have some kind of sleep disordered breathing and a trial of xPAP is worthwhile. Since Medicare and many insurance companies are reluctant to buy a machine for a patient with an official diagnosis of UARS, it's common to just fudge it and say since the RDI is at or above 5, the person has OSA.

I'll end with this little tidbit: If your AHI is exactly equal to 5, then you already have a diagnosis of (very) mild sleep apnea. Now, if your diagnostic AHI = 4.9, then it is possible that one additional event (of any kind: OA, H, or RERA), would push the RDI up to 5 and you'd get a diagnosis. And there's no real significance in insisting that the one additional event should be an OA or hypopnea so that the AHI increases to 5.0 instead of accepting that the one RERA pushed the RDI from 4.9 to 5.0. What this illustrates is that the numbers based definition of OSA, whether in terms of AHI or RDI, is a line that was drawn somewhat arbitrarily. Some folks feel really lousy and would probably benefit from a CPAP even though their diagnostic AHI is in the 4-5 range. Other people have a diagnostic AHI just over 5 and genuinely feel fine, but after being pushed by a doctor to try CPAP, find that they are no longer sleeping well because the machine itself is creating substantial disruption to their sleep. And if they were not symptomatic before being tested, a case can be made that if their diagnostic AHI is not much above 5, it may be best to just not worry too much until or unless they do become symptomatic.

[Miss Emerita]

Just to underline a point robysue has made: some arousals come after respiratory effort, and others don't. The latter are sometimes called "spontaneous" arousals. You're right that it's normal to have a fair number of arousals off and on throughout the night, but this will include both spontaneous and RER arousals.

[BigWing]

I really appreciate your highly-detailed response, robysue1 - it was fascinating.

Where have I misunderstood?

Quite a bit.

That seems a bit harsh, given that I made 5 statements and I think you only disagreed with the last part of the 5th one?

EEG arousals and RERAs are not essentially the same thing.

Fair enough - I hadn't studied the subtle differences in types of arousals. Rather than the 10 EEG arousals, my research suggests that normal people average 1.6 RERA's per hour.

It still seems daft to me that there are 2 different marking systems for sleep apnea, and not only is one clearly more exacting than the other but it requires measuring something (RERAs) which many machines don't seem to bother with and so they are just ignored....even though they could be sending you over the threshold!

If there is evidence that your body is not trying to breathe, it's assumed that a blockage in the upper airway is the cause of the apnea, and the event is scored as a central apnea.

Don't you mean: "...it's assumed that a blockage in the upper airway is NOT the cause of the apnea..."?

...trying CPAP is not likely to improve the sleep since the problem is not sleep disordered breathing...

Are you saying a RERA is NOT considered sleep disordered breathing? I'm surprised by that. For example, I see "Three breathing abnormalities used to quantify the severity of sleep-disordered breathing are Apnea, Hypopnea & RERA" [https://sleepapneamatters.com/apnea-vs- ... a-vs-rera/]

Thanks for all your extra detail though.

[robysue1]

EEG arousals and RERAs are not essentially the same thing.

Fair enough - I hadn't studied the subtle differences in types of arousals. Rather than the 10 EEG arousals, my research suggests that normal people average 1.6 RERA's per hour.

That was a critically important misunderstanding based on other, implicit misunderstandings.

It still seems daft to me that there are 2 different marking systems for sleep apnea, and not only is one clearly more exacting than the other but it requires measuring something (RERAs) which many machines don't seem to bother with and so they are just ignored....even though they could be sending you over the threshold!

You are correct: It is daft that there are two distinctly different criteria for scoring hypopneas on sleep tests.

And I'm keenly aware of the problems that creates: On my diagnostic sleep test way back in 2010, under the Medicare-approved definition of "hypopnea", my AHI was something like 3.6. But when you added the "hyponpeas with arousal" into the event total? My RDI/AHI soared to 23 and a diagnosis of "moderate sleep apnea" with strong pressure put on my by the sleep doctor and my primary care doctor to use CPAP even though I was not experiencing severe problems with daytime sleepiness.

If there is evidence that your body is not trying to breathe, it's assumed that a blockage in the upper airway is the cause of the apnea, and the event is scored as a central apnea.[/quote

Don't you mean: "...it's assumed that a blockage in the upper airway is NOT the cause of the apnea..."?

Yes, thanks for catching the typo in my response. I'll edit it to clear up that point.

...trying CPAP is not likely to improve the sleep since the problem is not sleep disordered breathing...

Are you saying a RERA is NOT considered sleep disordered breathing? I'm surprised by that. For example, I see "Three breathing abnormalities used to quantify the severity of sleep-disordered breathing are Apnea, Hypopnea & RERA" [https://sleepapneamatters.com/apnea-vs- ... a-vs-rera/]

Too many RERAs---which are respiratory effort related arousals are part of sleep disordered breathing. If the problem is primarily documented RERAs, the formal diagnosis is UARS---upper airway resistance syndrome. And a trial of xPAP is recommended, but some insurance providers may balk at paying for an xPAP machine if the diagnosis is not OSA. So many labs won't report the problem as UARS, but OSA if the RDI, including RERAs, is at or above 5 events/hour.

If the problem is too many EEG arousals that are NOT due to respiration problems, then you don't get a diagnosis of any form of sleep disordered breathing (OSA, CSA, or UARS). And in the absence of severe snoring, you won't get a recommendation to try CPAP.

If you do have severe snoring, but not enough events (OAs, Hs, RERAs), the physician who "reads" the sleep study may conclude that your snoring may be causing some of the EEG arousals even if there's nothing in the breathing pattern that is significant enough to be labeled as an OA, an H, or a RERA; and severe snoring by itself can be treated with xPAP, but they often will first recommend other methods, such as "Breathe Right strips", which may help snoring, but are not effective in treating OSA or UARS, or sleep positional therapy if the snoring seems to be related to sleeping on your back. The reason is that simple snoring can be caused by nasal problems, but in OSA and UARS the problem is further down the upper airway---i.e. involves the tongue and the back of your throat and not your nostrils.

If the EEG arousals are related to periodic limb movements, you wind up with a diagnosis of PLMD--periodic limb movement disorder---which is NOT part of sleep disordered breathing. (But some people do have both OSA and PLMD, and the OSA can "mask" the PLMD in the initial diagnostic study.)

If the problem is too many EEG arousals without any apparent underlying cause? Then if there is a diagnosis, it's likely to be something along the lines of sleep maintenance insomnia---meaning you can get to sleep, but you don't seem to stay asleep. Treating sleep maintenance insomnia is something of a crap-shoot: Sleep medication is usually more effective at treating sleep onset insomnia (you can't get to sleep in the first place), than it is sleep maintenance insomnia. But many doctors will start with a sleep medication if the patient is interested in taking sleeping pills. Some forms of CBT-insomnia may help, and a doctor will recommend that if a patient is reluctant to try sleeping pills. Some efforts to clean up sleep hygiene might help. Or, if the patient is not particularly symptomatic, just ignoring the problem can be done. OR they may decide the sleep maintenance insomnia is related to some other medical problem and recommend treating the other problem effectively. Medical problems that can lead to sleep maintenance insomnia include many things like depression, anxiety, substance abuse problems, any medical condition that results in chronic pain (arthritis among others), and many prescription medications for a whole variety of medical conditions. Or they may just decide that the increase in EEG arousals is due to aging---older people tend to sleep less well overall than younger people do, even when there is no problem with things like sleep disordered breathing or PLMs.

[dataq1]

If there is evidence that your body is not trying to breathe, it's assumed that a blockage in the upper airway is NOT the cause of the apnea, and the event is scored as a central apnea.

Perhaps a better way: " If there is evidence that your body is not trying to breathe, it's assumed that the apnea is NOT caused by a blockage in the upper airway, and the event is scored as a central apnea."

[chunkyfrog]

Also, remember that the "official" definition of apnea is arbitrary.
(Just a silly number, pulled out of somebody's body cavity.)
And the insurance companies were allowed input to the decision!
WTF!