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Most central apneas across the patient population entail an open airway. However, some central apneas also entail a closed airway. In that latter case there is no brain signal to breath and thus no respiratory effort. Those will correctly score as central during PSG because there is no respiratory effort...

Additionally, the PSG can't easily differentiate a closed-airway central apnea from an open-airway central apnea. Rather, those tend to be differentiated in clinical research versus clinical practice. If I recall correctly research methodology has relied on endoscopy to observe closed-airway central apneas versus open-airway central apneas. FOT represents open-airway central apneas (only) with excellent specificity and sensitivity.

But because a good percentage of central apneas entail a closed airway, FOT cannot detect those as the central apneas they are by PSG definition. FOT instead identifies those as obstructive apneas. The S9 machine raises the pressure to begin clearing that central apnea's concomitant obstruction---which is the correct pressure response.

ozij wrote:For most people, when an obstruction blocks the flow there's a great struggle to breathe - so I don't understand your quetion.

True, but what we're discussing is the machine's ability to distinguish between centrals and obstructives. The machine can't sense a struggle, or lack of, to breathe. All the S9 can sense is a stop in flow, so then it does the FOT thing. If FOT determines a blockage exists in the airway then the apnea is scored as OA. If it does not detect an obstruction then the only other choice is CA. You could say the CAs, i.e., lack of brain signal, are scored by process of elimination, not by active determination as are OAs. I don't see how a machine malfunction can cause you to not breathe, but it could falsely score apneas, I suppose.

idamtnboy wrote:

ozij wrote:For most people, when an obstruction blocks the flow there's a great struggle to breathe - so I don't understand your quetion.

True, but what we're discussing is the machine's ability to distinguish between centrals and obstructives.
[question]
True.

I don't see how a machine malfunction can cause you to not breathe, but it could falsely score apneas, I suppose.

That's what I meant. Since we're discussing the machines and not the breathing person.

-SWS wrote:Most central apneas across the patient population entail an open airway. However, some central apneas also entail a closed airway. In that latter case there is no brain signal to breath and thus no respiratory effort. Those will correctly score as central during PSG because there is no respiratory effort...

But because a good percentage of central apneas entail a closed airway, FOT cannot detect those as the central apneas they are by PSG definition. FOT instead identifies those as obstructive apneas.

So our conclusion is that when the S9 scores a CA, there is a very high probability it is in fact a CA, except if we are awake. But, when it scores an OA the probability of a correct score is lower, but is still fairly high. There's probably no practical way to assign a meaningful number to those probabilities.

ozij wrote:

JohnBFisher wrote: 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. ...

As I understand it ... and I'm willing to learn, since I can be wrong ... during a sleep study that the two are true (obstruction is deduced from those two factors). With just a xPAP device, most of the current machines measure the length of the airway (or listen for the heartbeat). And this in an of itself is fascinating technology!! If the apnea occurs and the airway is clear (not obstructed), then it assumes a CA event. As I've noted, that should really be termed a Clear Airway event, not a Central Apnea event.

idamtnboy wrote: So our conclusion is that when the S9 scores a CA, there is a very high probability it is in fact a CA, except if we are awake.

That's my take, idamtnboy. Many of us should expect to see a slight discrepancy between S9 scored CA's and PSG scored CA's---with the PSG having correctly discarded all waked-based phenomena.

But, when it scores an OA the probability of a correct score is lower, but is still fairly high. There's probably no practical way to assign a meaningful number to those probabilities.

I think epidemiological research assigns a meaning ratio of those two types across the SDB population. If I recall correctly (and I so often don't! ) some central SDB patients are significantly more inclined toward closed-airway central apneas than others. So I don't think there's a way to assign a meaningful probability to an individual---short of endoscopic observation as in the case of research methodology.

idamtnboy wrote:... So our conclusion is that when the S9 scores a CA, there is a very high probability it is in fact a CA, except if we are awake. But, when it scores an OA the probability of a correct score is lower, but is still fairly high. There's probably no practical way to assign a meaningful number to those probabilities. ...

Yes. Except that the S9 will score "CA" events that occurs during wake/sleep and sleep/wake transition that a PSG will exclude. We sometimes see people who worry about a high CA score on their machine, but when you LOOK at their data, it becomes obvious that those CA events were transition events. They all cluster at the same time. When we probe about the sleep that night you find out that sure enough the person woke up, went to the bathroom (or the like), and then went back to bed.

In other words, think of the data gathered from the machine as windsock data. You can actually, and safely land a plane with just a windsock. It's not "accurate", but it is enough to get the job done.

But don't try to tell your doctor what is going on in your sleep assuming your machine measured everything to the Nth degree. It's just a windsock. Certainly that windsock has gotten more accurate over the years. But it's definitely not a PSG.

Well said.

Went to my sleep doctor today and when she read my S9 card it did not indicate I was having the high "centrals" readings that I got with the software download from here. For some reason, the report only spit out the past two months and the "centrals" number was .1 for the two months. The report did indicate I had high apneas for the past few nights, but she said that could be from a leak which seemed to line up with the apneas.

Any suggestions why I'm seeing high numbers on my machine and on my reports and the docs don't show that?

Thanks,

Bob

bob007 wrote: Any suggestions why I'm seeing high numbers on my machine and on my reports and the docs don't show that?

I am betting they just looked at the summary statistics.

Why not post one of your night's daily details along with the summary page....

Hi Pugsy,

My summary stats show the centrals too while her's didn't.

I'll look into posting something.

Thanks,

Bob

bob007 wrote:My summary stats show the centrals too while her's didn't.

Did she give you a copy of what she had on the report she was basing her comments on?
If she got the data from your card then she either did something weird with software or was looking at something else.
That makes no sense whatsoever...
Hmm, wonder if her software was older software???? Just thought of that. I wouldn't think that the data would be backwards compatible but never know I guess.