How does it know it's a Central?

[wardmiller]

SleepyHead classes the Events as Hypopnea, Apnea, Obstructive, and Clear Airway. ResScan says they are Obstructive, Central, Unknown and Hypopnea. Apparently SleepHead's Clear Airway is the same as ResScan's Central.

How do they determine an event is a Central/Clear Airway? Is it the hardware? The software? A combination? How do they know it is not an Apnea? Both events show a cessation of breathing.

Thanks for any help in my understanding.

[Nooblakahn]

Someone will correct me if I'm wrong.. but I believe the machine sends a "pulse" of air to see what the back pressure is. Lower pressure would be a central. Clear airways and centrals are the same thing.

Both a central and an obstructive are apneas... they are just different types.

[Pugsy]

The determination as to central vs obstructive is made by the machine.
With the Resmed machines it is by using the FOT. In Respironics they use something called pressure pulses. BTW...SleepyHead calls them Clear Airway because originally SleepyHead was designed for Respironics machines because that is what Mark had at the time. If he had been using a ResMed machine then they would likely be called Centrals.

http://www.resmed.com/uk/products/s9_se ... clinicians
CSA detection

Central Sleep Apnea (CSA) detection is now available in both the S9 AutoSet and S9 Elite. It uses the Forced Oscillation Technique (FOT) to determine whether the airway is open or closed during an apnea. Small oscillations in pressure are added to the current device pressure. The CSA algorithm uses the resulting flow and pressures to measure whether the airway is open or closed.

[jnk...]

How does it know . . .?

An executive military strategist once said something along the lines that there are known knowns, known unknowns, and unknown knowns. I have no idea what that means. But I believe it to be true.

Lab/center studies KNOW when there is a central apnea with near certainty, since belts around the patient do a pretty good job of allowing 'the effort of the patient to breathe' to be judged well.

On the other hand, home-treatment machines are designed to provide trending data, not diagnostic data, and so make educated guesses based on air movement and state of the airway.

It is important to understand that fact because even during an event that is in essence a central, a patient's airway can close from the lack of air movement. A lab will call it a central because it can tell the patient didn't try to breathe. A home-treatment machine will call it an obstructive, because the airway closed. Similarly, home-treatment machines can at times call an obstructive event central when the airway isn't completely closed when it tests the airway. It's a particularly fuzzy line between the two in the home-treatment-machine realm, since the call is made by using mostly nonmedical proprietary definitions and algorithms.

The point is, that's all OK. It is still VERY useful data, since the home-treatment-machine data can be used to notice long chains of many open-airway events and that is the only time to be concerned with them. Many healthy people have occasional perfectly-harmless "centrals" from time to time during the night--"centrals" that would be ignored during an actual lab sleep study.

All in all, a "central" on its own, as judged by a home-treatment machine, is generally something to feel relieved about, in the sense of "at least it wasn't an obstructive event" and "I'm glad it didn't start a cascade of repeating cycles of centrals, which might, if continuous, indicate the need to be tested for using a different kind of machine."

[grayghost4]

jnk wrote "known knowns, known unknowns, and unknown knowns"

I like that line.

Thanks for the dissertation on apnea's We all learn a little more reading through the threads on here.

[jnk...]

Oops. Sorry. Looks like I butchered Rumsfeld's words:

"There are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we know we don't know. But there are also unknown unknowns. There are things we don't know we don't know." -- Donald Rumsfeld. -- http://www.brainyquote.com/quotes/quote ... 48142.html

But that's OK. He's butchered more than a few words himself.

https://www.youtube.com/watch?v=GiPe1OiKQuk

https://www.youtube.com/watch?v=IsV-r1-8Jo8

[wardmiller]

First, many thanks to all of you who responded. I've learned some valuable information.

How does it know . . .?

All in all, a "central" on its own, as judged by a home-treatment machine, is generally something to feel relieved about, in the sense of "at least it wasn't an obstructive event" and "I'm glad it didn't start a cascade of repeating cycles of centrals, which might, if continuous, indicate the need to be tested for using a different kind of machine."

Now here is why I asked the question. I've been successfully using CPAP for about three years. My AHI has been around 2 and lower (untreated it was 68). Often below 1. Beginning June 30 I began having clusters of Centrals. Some nights AHI would spike as high as 10 to 15. Then a few days back down to AHI 1 or 2. The clusters would sometimes last for almost an hour, with an Event every minute or so. Sometimes two or three clusters a night. A lot of Central spikes on the AHI history graph for the past three months, AHI between 5 and 12, almost totally Centrals.

Incidentally, I've recently worn my pulse-oximeter several nights and even when I've had a cluster of Centrals lasting an hour, my O2 saturation has been remained above 90%, mostly 92% to 96%, during the Centrals.

As I understand it, a Central occurs when the brain does not send a "breath" signal to the diaphragm. Same effect as OSA Event, but totally different cause. I have not found much info on the "why" except one cause can be a stroke. So I have wondered, at my age it would be easy to have had a mini-stroke and not recognize its occurrence.

I went to see my Pulmonologist yesterday. Doctors knowledgeable on OSA are in short supply around here and he is the best I've been able to find, but I think I know more about CPAP machines and their output than he does. When I showed him the graphs with all the Centrals, he obviously was concerned about what was causing them. When I mentioned an undiagnosed mini-stroke, he agreed that certainly was a possibility. And that was when he asked, "How does the machine know it is a Central and not an Apnia?" Hence, my question to this forum.

BTW, he said he would consult with a couple of friends who are hotshots on OSA. In the meantime, I'll let him know what I have learned here from this thread. Thanks again for your comments.

[jnk...]

. . . The clusters would sometimes last for almost an hour, with an Event every minute or so. Sometimes two or three clusters a night. . . .

Good job speaking to a doc about it. Especially a pulmo.

. . . even when I've had a cluster of Centrals lasting an hour, my O2 saturation has been remained above 90%, mostly 92% to 96%, during the Centrals. . . .

Clusters can involve alternating overbreathing and underbreathing. It is the regulation of the breathing that gets out of whack, and it doesn't always show up as desats.

. . . As I understand it, a Central occurs when the brain does not send a "breath" signal to the diaphragm. Same effect as OSA Event, but totally different cause.

Well, yes and no. It isn't exactly the same effect as an OSA event, since the OSA event generally involves the combined trauma of disturbed sleep and struggles to breathe. A lone central may not disturb sleep at all, and there is usually no panic-juice released to jump-start the breathing. On the other hand, it is always good to look for causes of strings of central events, because that search can sometimes reveal useful info on, for example, heart or nerve status. Other times, no cause is found, but it is still always worth the search, just in case.

I have not found much info on the "why" except one cause can be a stroke. So I have wondered, at my age it would be easy to have had a mini-stroke and not recognize its occurrence.

Sometimes meds cause the problem. Sometimes change in altitude can be a factor if someone is on the edge. Sometimes the damage from years of untreated obstructive apneas appears to affect the blood-gas sensors in the body over time. And then the CPAP pressure (or especially, bilevel) needed to treat the OSA can even become a factor in the centrals. Regardless, if there is no known cause of the centrals (such as meds), a doc might want to do some cardiac workup stuff and run a few other tests.

I went to see my Pulmonologist yesterday. Doctors knowledgeable on OSA are in short supply around here and he is the best I've been able to find, but I think I know more about CPAP machines and their output than he does. When I showed him the graphs with all the Centrals, he obviously was concerned about what was causing them. When I mentioned an undiagnosed mini-stroke, he agreed that certainly was a possibility. And that was when he asked, "How does the machine know it is a Central and not an Apnia?" Hence, my question to this forum.

I always deeply respect any doc willing to ask a patient a question like that. Humble docs are rare in my neck of the non-woods in the state (NYC), seems to me. By the way, how come nobody calls this Lowstate New York? I guess some do call it Downstate, but Lowstate sounds better to me.

BTW, he said he would consult with a couple of friends who are hotshots on OSA.

I like this doc, based on what you say. Sounds like a keeper to me.

Even if the search for the cause of the centrals doesn't pan out, remember that some with strings of centrals get better sleep using an ASV machine rather than regular CPAP or, in your case, rather than autobilevel. You and your doc may find that to be the case for you. But don't just jump to ASV without getting yourself checked out. Centrals differ from OSA in that they are more a symptom of something else--sometimes a significant symptom, sometimes an ignorable symptom, but not a symptom to be assumed to be meaningless and just treated with ASV without a little digging around first.

Meantime, I understand that a few have found that it helps to take the PAP machine off of auto and not to use pressure relief such as EPR, or in your case not to have too much distance between IPAP and EPAP. Changes in pressure can occasionally be enough to start a string of centrals for someone on the edge with breathing-regulation issues. Bilevel lessens the work of breathing, and that, for some, tips the balance toward overbreathing and then underbreathing over and over. Bilevel and EPR causing that is relatively rare, I think, but it is still at least possible for those things to be factors. It is more common for auto mode to cause it or the combination of auto mode and bilevel. ASV solves all those issues in its own way.