Centrals on S9 ?

[beyondtired]

I was reading some about this at the forum here before. Though, I'm still a little confused. So it is common for central apneas to get scored aggressively on the S9 Autoset? During my sleep study, I didn't have any central apneas or obstructive apneas. I only had hypopneas. Though, when using the Autoset, I seem to be getting some centrals, which usually account for most of my AI. Since I didn't have any centrals the on sleep test, shouldn't I worry about this? Could some of the centrals actually be hypopneas that are getting scored as centrals?

[Otter]

Leaving Resmed's secret event definitions aside, there is an obvious reason why you might score more centrals at home than at the lab. The S9 doesn't monitor respiratory effort at all, and hence it can't actually tell if an apnea is caused by your CNS taking a break or by something else. It does have a way to detect whether or not your airway is clear, and this probably works most of the time, but it's not perfect. If you stop breathing and FOT says your airway is open, the S9 assumes you're having a central. But that belt you wear in the lab allows the the techs to tell whether or not you are trying to breath. Hence, some clear airway apnea events that score as centrals on the S9 might not have been scored as centrals in your sleep study.

Worrying it about it won't help, so don't bother.

[bkdraft]

I run into the same thing here. Sleep study showed NO centrals at all, only obstructive. Now at home with the S9 I am only have 1 or 2 obstructive all night, but Centrals are averaging around 3-4 per hour. At least its getting better, when I started 3 weeks ago my centrals were averaging 9-10, but after adding in some O2 they just keep getting better each night.

[Slartybartfast]

Centrals, or what passes for them outside of a sleep lab, are probably the least of your worries. Much ado about not so much. Look up "Hering-Breuer reflex" on the forum, or just Google it.

Exorcising the obstructive and hypopnic events, and ensuring you're getting good quality sleep are more important.

[bob007]

I just recently downloaded the software for the S9 and found that I have few obstructives but high centrals. I'm a year into CPAP and was just starting to feel a lot better about 2-3 months ago but recently noticed I was feeling a bit fatigued again. I noticed that particularly over the past week or so the apneas were increasing on the machine readout so I downloaded the software.

Any explanation for this?

I have an appointment with my sleep doc but she's never mentioned centrals at all.

Thanks,

Bob

[Slartybartfast]

I just recently downloaded the software for the S9 and found that I have few obstructives but high centrals. I'm a year into CPAP and was just starting to feel a lot better about 2-3 months ago but recently noticed I was feeling a bit fatigued again. I noticed that particularly over the past week or so the apneas were increasing on the machine readout so I downloaded the software.

Any explanation for this?

I have an appointment with my sleep doc but she's never mentioned centrals at all.

Thanks,

Bob

One possibility is that your pressure is set too high. You didn't say whether you're using an S9 Autoset or S9 in CPAP mode. If the latter, your pressure might be too high, triggering Hering-Breuer reflex events. Or they might be real Centrals. Outside of a sleep lab you really can't tell which one it is. The S9 assumes that any cessation of breathing with an open airway, as determined by the FOT (Forced Oscillation Technique) is, in fact, a Central Apnea. But that's only an assumption.

If that's what's causing the "centrals" then reducing the pressure slightly should decrease their frequency. Reduce the pressure too far and you'll start seeing more obstructive events. Optimum pressure is one at which you have few or no obstructive events and few or no "centrals."

In case you have an S9 Autoset and are using it in Automatic mode: Most of us who were titrated in the lab at a fixed pressure (mine was 11 cm) set our machines with a minimum of about 2 cm below the titrated pressure. In my case, 9 cm. Some folks advocate putting a high pressure limit on, too, but I've never seen the need to with my S9 Autoset.** So I just leave the maximum pressure at the 20 cm limit. Keeping the minimum pressure slightly below your titrated pressure hastens the machine's ability to respond to obstructive events.

**The Intellipap that I keep at my wife's place amongst the drippy big trees in Washington, where the roving herds of banana slugs frolic and play, ran away with me one night last week. I awoke and pressure was something like 18 cm and I was about to float away like a balloon. The nasal pillows disengaged from my schnoz and the hose took off, whipping around like the tail of a wet tomcat until I caught 'hold of it and wrestled it back to earth. I reset it with the Pmax at 13 cm and slept the rest of the week like the dead.

[AMUW]

During my sleep study, I didn't have any central apneas or obstructive apneas. I only had hypopneas. Though, when using the Autoset, I seem to be getting some centrals, which usually account for most of my AI...

Maybe the following qns and comments can help:
- are you comparing home CPAP against your lab titration study on CPAP? ... which was performed with a similar mask, in a similar body position, at a similar pressure range? what were your results for the basic study? In my case the basic study tried out the worst scenario, while the titration study tried to optimize
- note that in the lab or at home you could be having apneas shorter than 10 seconds, which aren't scored; then something can happen in the setup to make those apneas or hypopneas slightly longer ... and bang: the machine or the technician scores one for you; this becomes obvious when you get to look at your curves
- some reasons for increased apneas: change of body position to create upper airway constriction, going into REM sleep, nasal congestion due to different air temperature and / or humidity, cumulative upper airway congestion that some people develop to CPAP use (hopefully resolves in time), mask leakage, etc.
- if you can read your flow curves in ResScan, you'd also get an impression whether the apneas appear during sleep onset (duration?) or maybe before you wake up (total sleep time?), and whether they come in clusters

[ozij]

Leaving Resmed's secret event definitions aside, there is an obvious reason why you might score more centrals at home than at the lab. The S9 doesn't monitor respiratory effort at all, and hence it can't actually tell if an apnea is caused by your CNS taking a break or by something else. It does have a way to detect whether or not your airway is clear, and this probably works most of the time, but it's not perfect. If you stop breathing and FOT says your airway is open, the S9 assumes you're having a central. But that belt you wear in the lab allows the the techs to tell whether or not you are trying to breath. Hence, some clear airway apnea events that score as centrals on the S9 might not have been scored as centrals in your sleep study.

Worrying it about it won't help, so don't bother.

I'm afraid, Otter, you are begging the question, and confusing some terms.
The S9 does not monitor sleep or wake states, and does not monitor chest or abdominal effort. An open airway apnea means you're airway is open (not obstructed), you're supposed to be breathing, and yet there is no airflow because your brain in not giving your muscle the commands to start breathing. There can be many reason's for the brain behaving like that.
In a sleep lab, the scoring is based on your sleep / wake status. If there is no airflow, and no chest/abdominal effort, that's a central apnea -- open airway or not. The APAP tries to figure out if the airway is open -- in order not raise the pressure should that be the case.

The significance of central or open airway apnea really depends on how many of them are reported by the machine (a couple an hour? a dozen?), and most importantly, on whether you are awake or asleep during that time - something the machine does not know.

Tossing and turning sleeplessly may have the machine reporting open airway apneas simply because you sigh and stop breathing during that process - totally innocuous.

On the other hand(my emphasis):

I run into the same thing here. Sleep study showed NO centrals at all, only obstructive. Now at home with the S9 I am only have 1 or 2 obstructive all night, but Centrals are averaging around 3-4 per hour. At least its getting better, when I started 3 weeks ago my centrals were averaging 9-10, but after adding in some O2 they just keep getting better each night.

[idamtnboy]

I was reading some about this at the forum here before. Though, I'm still a little confused. So it is common for central apneas to get scored aggressively on the S9 Autoset?

From what I've seen on my own flow graphs I would say not particularly, at least while sleeping.

Could some of the centrals actually be hypopneas that are getting scored as centrals?

That's not likely because of how the flow is interpreted. In my graphs HIs are very definitely hypos because the flow graph shows definite inhalation/exhalation cycles. They're just less than normal. Centrals always show no flow periods.

Are you looking at the graphs with Resscan? If so, are the CAs occurring during times when you are actually awake? I find on my graphs many CAs are scored when I'm awake, especially in the morning before I crawl out of bed. It's surprising how irregular my breathing is when I'm awake compared to when I'm asleep.

[Otter]

Leaving Resmed's secret event definitions aside, there is an obvious reason why you might score more centrals at home than at the lab. The S9 doesn't monitor respiratory effort at all, and hence it can't actually tell if an apnea is caused by your CNS taking a break or by something else. It does have a way to detect whether or not your airway is clear, and this probably works most of the time, but it's not perfect. If you stop breathing and FOT says your airway is open, the S9 assumes you're having a central. But that belt you wear in the lab allows the the techs to tell whether or not you are trying to breath. Hence, some clear airway apnea events that score as centrals on the S9 might not have been scored as centrals in your sleep study.

Worrying it about it won't help, so don't bother.

I'm afraid, Otter, you are begging the question, and confusing some terms.

If wrote the last sentence either of these two ways, would some of your fears be allayed?

Hence, some events that score as centrals on the S9 might not have been scored as centrals in your sleep study.

Hence, some "clear airway" apnea events that score as centrals on the S9 might not have been scored as centrals in your sleep study.

The S9 does not monitor sleep or wake states, and does not monitor chest or abdominal effort.

On this we agree. I have wondered, though, whether some people have lower AHI's with the S9 than another machine, with both set to deliver true CPAP at the same pressure, because the s9 has an algorithm which attempts to eliminate events associated with wakefulness. But that's another thread.

An open airway apnea means you're airway is open (not obstructed), you're supposed to be breathing, and yet there is no airflow because your brain in not giving your muscle the commands to start breathing.

Actually, that's the definition of a central, isn't it? Or, accounting for all pickable nits, an open airway central. I'm sure most open airway apneas are centrals, but open airway would include apneas caused by something interfering with the peripheral nervous system or the muscles themselves. I would guess that most people who experience non-central open airway apneas probably either die or get better when the curare wears off, but it's one of the questions I haven't thoroughly explored yet. That fact that Philips has made a point of not claiming to detect central apnea makes me wonder if there are non-obstructive apneas that are not centrals.

There can be many reason's for the brain behaving like that.
In a sleep lab, the scoring is based on your sleep / wake status.

A good point, and the most likely reason why the S9 would score more centrals than the sleep lab.

If there is no airflow, and no chest/abdominal effort, that's a central apnea -- open airway or not.

Yes, ignoring curare, etc.

The APAP tries to figure out if the airway is open -- in order not raise the pressure should that be the case.

True. But I'm afraid, ozij, you have misunderstood my post. My point was that the S9 can't know for sure whether or not someone is trying to breathe because it doesn't have any sensors for muscular activity. Instead, it has to guess based on FOT. In one of Resmed's white papers, they mention that leaks and incorrect/unknown circuit impedance can make FOT less accurate. And though when the leak rate goes above a certain threshold, the S9 will class apnea events as "unknown", I suspect that it does score some centrals that are actually obstructive, and it wouldn't surprise me if there are a few users who regularly fool the machine for one reason or another. In a sleep study, OTOH, there are sensors that reliably monitor your respiratory muscles, and it's obvious whether or not you are trying to breathe.

Now that you mention it, I agree that sleep/wake state is more likely to be the answer than blowgun darts or the limitations of FOT. But though I may have confused you, I don't believe I confused any of the terms I used. It will happen now and then, though. I have much to learn, and while I've been sleeping better recently, I'm still a bit foggy sometimes.

[ozij]

My point is that it doesn't really matter that much whether we call the apnea "open airway" or "central". And I'm pretty sure a sleep lab, diagnosing a "central" apnea is not making a diagnosis of problems in the CNS.

An open airway apnea means you're airway is open (not obstructed), you're supposed to be breathing, and yet there is no airflow because your brain in not giving your muscle the commands to start breathing.

Actually, that's the definition of a central, isn't it?

No. Because in the sleep lab, they watch the flow and the effort -- and if you make no effort to breathe when you're supposed to be breathing, they call it a central apnea. A sleep lab doesn't directly observe the state of the airway. It looks at flow and effort, and if there's a lot of effort and now flow, it knows there's an obstruction. No flow +no effort = central apnea.
APAP's try to figure out things based on flow alone.
I think we agree on this: APAP's try to circumvent to lack of information about effort by guessing at the state of the airway. Intelligent guessing, but still, only guessing. "Open airway apneas" as far as I know is a term invented by APAP manufacturers to indicate a type of apnea they won't (shouldn't) respond to.
In Respironics' older algorithm, their ability to detect central apneas was so bad that they invented a "non-responsive" apnea -- apneas that keep returning despite raised pressure. And Resmed simply ignored all apnea's above 10 cm h2o and responded to all apneas below 10. No fun if some of your centrals happen beneath 10...

Or, accounting for all pickable nits, an open airway central. I'm sure most open airway apneas are centrals, but open airway would include apneas caused by something interfering with the peripheral nervous system or the muscles themselves. I would guess that most people who experience non-central open airway apneas probably either die or get better when the curare wears off, but it's one of the questions I haven't thoroughly explored yet.

Neither have I.

[Otter]

An open airway apnea means you're airway is open (not obstructed), you're supposed to be breathing, and yet there is no airflow because your brain in not giving your muscle the commands to start breathing.

Actually, that's the definition of a central, isn't it?

No. Because in the sleep lab, they watch the flow and the effort -- and if you make no effort to breathe when you're supposed to be breathing, they call it a central apnea.

See the nit below

Or, accounting for all pickable nits, an open airway central.

A sleep lab doesn't directly observe the state of the airway.

Hence the above nit.

[idamtnboy]

No. Because in the sleep lab, they watch the flow and the effort -- and if you make no effort to breathe when you're supposed to be breathing, they call it a central apnea. A sleep lab doesn't directly observe the state of the airway. It looks at flow and effort, and if there's a lot of effort and now flow, it knows there's an obstruction. No flow +no effort = central apnea.

Are there any other reasons for no flow besides no breathing effort, i.e., lack of signal from the brain, or an obstruction that blocks the flow? If not, then the FOT of the S9 pretty much has to be correct because if there is no flow, and there is no obstruction, the only other choice is no brain signal, i.e., a central. That's why it looks like a central when we simply pause in our breathing while awake.

NotMuffy, am I on or off base?

[JohnBFisher]

No. Because in the sleep lab, they watch the flow and the effort -- and if you make no effort to breathe when you're supposed to be breathing, they call it a central apnea. A sleep lab doesn't directly observe the state of the airway. It looks at flow and effort, and if there's a lot of effort and now flow, it knows there's an obstruction. No flow +no effort = central apnea.

Almost. No flow + No obstruction + No effort + Asleep + Not during transition (from wake to sleep or from sleep to wake) = Central Apnea.

The S9 machine can check two things:

Flow
Airway

It can not measure effort (but assumes if the airway is clear then it is not obstructed). It can not determine if you are asleep. It can not determine if you are transitioning from wakefulness to sleep or from sleep to wakefulness. Those transition times often result in central apneas. But those are (usually) normal and are excluded.

So, the best (and what ResMed and Respironics SHOULD say) is that it detected a Clear airway Apnea (CA), not a central apnea.

... Are there any other reasons for no flow besides no breathing effort, i.e., lack of signal from the brain, or an obstruction that blocks the flow? If not, then the FOT of the S9 pretty much has to be correct because if there is no flow, and there is no obstruction, the only other choice is no brain signal, i.e., a central. That's why it looks like a central when we simply pause in our breathing while awake.

NotMuffy, am I on or off base?

Hmmm... Again, it has to be all those things above. As you note, if we are awake and simply pause breathing, the machine registers it as a CA event, but as I note, it SHOULD mean "Clear Airway" not "Central Apnea".

Now, if someone has LOTS of CA events throughout the night (and not just clustered), then it is probably an indication that the patient should discuss the data with their doctor during their next visit. Untreated central apneas are as bad as untreated obstructive apneas.

Hope that makes sense and adds to the discussion.

[ozij]

Almost. No flow + No obstruction + No effort + Asleep + Not during transition (from wake to sleep or from sleep to wake) = Central Apnea.

John, you're implying an obstruction is observed. I think the obstruction is deduced from no flow and the struggle to breathe.

... Are there any other reasons for no flow besides no breathing effort, i.e., lack of signal from the brain, or an obstruction that blocks the flow?

Machine malfunction?
If you're not breathing, you're not breathing. "Lack of signal from the brain" does mean you're not breathing - and not making an effort to breathe. For most people, when an obstruction blocks the flow there's a great struggle to breathe - so I don't understand your question.

Maybe its time to take another look at this excellent Resmed video:
http://www.resmed.com/us/multimedia/und ... 40x380.swf