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how do our machines know CA from OA?
#1
I'm just wondering how our machines know the difference between an obstructive apnea and a central apnea. It seems to me that all it would know is whether we are breathing or not, but not why. Also, can it always tell that we are asleep? What would it look like to the machine if we just held our breath? I only started my treatment yesterday, so I will wait a few days and then post some of my Sleepyhead data for some input on that. I'm sure I'll be having a lot of the typical newbie questions, so thanks in advance for your patience!

Thanks!

PS, I was looking at my Sleepyhead data again and a few of the large leak events correlate pretty closely with the central events. I was (naturally, for the first night) tossing and turning a lot. Could the thrashing about and adjusting of the mask be interpreted as an event?

Thanks again!
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#2
If you hold your breath with an open throat, after about ten seconds, you will experience a kind of pulsing of air, the machine is sensing whether you have an open or closed airway. In the case of an open throat, it will detect CA, or Clear Airway. If the throat is closed, it will sense an OA or Obstructive Apnea. If partially closed, it will sense a Hypopnea.

I have experimented a lot with what positions I am in and what I was doing, using a video running all night of myself. Many events are the result of my holding my breath while changing body positions, both in Clear Airways and also in Obstructive Airways and Hypopneas.

I find, when my Flow Rate is fairly erratic around those events, it is likely that my body is in some kind of motion. Likewise, if the Flow Rate is very regular around those events, those are the times I am likely fast asleep and my body is very still.

In realizing the above, I can see that a lot of my events are likely the result of my holding my breath while moving about while sleeping which ends up portraying my AHI higher than it really is.
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#3
Thanks Richard, that was very helpful. I suppose the AHIs really won't be very accurate until I get a little more used to the machine and am not moving so much. I'm sure that I would have been holding my breath while doing some of the readjusting I was involved in.
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#4
Resmed machines use a pulse reflection technique. After cessation of flow for 4 seconds, the pressure is modulated with a 4 Hertz, 1 cm-water amplitude waveform. The reflection is examined by the flow sensor; and scored as CA or OA. They call it their FOT algorithm.

PR machines have their own proprietary technique.

Your correlation of Large leak to CA, may indicate a time when pressure is higher. You may have some pressure induced CA that may abate with time.
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#5
Thanks for the info! I did some research on FOT and it's pretty interesting. I was really disappointed to find, however, that the people at my sleep clinic didn't know about that. They said that the machines are unable to detect the differences between the types of apnea and that even the doctor they work with says that. They also didn't know about Sleepyhead. The printout that they gave me, which goes to them wirelessly from my machine, has a pitiful amount of information. Seems like it's mainly to show compliance but not give any detailed data. I don't like to work with medical professionals that don't know everything I do, and much more, about the condition I'm being treated for, but I have found that to be the case.
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#6
(03-01-2017, 01:42 PM)Leemax Wrote: They said that the machines are unable to detect the differences between the types of apnea and that even the doctor they work with says that.

Well, it's sorta kinda true depending on what you mean by "difference".  Your machine cannot technically tell if an apnea is Central or not.  All they can do is determine that the apnea occurred while your airway was not blocked.  That does not prove that the apnea meets the clinical definition of "central apnea".  The machine also can't tell if you are awake or asleep, and if you are awake it's reports are pretty well meaningless so far as the severity of your sleep apnea is concerned.

But it can give you enough information for your own purposes.  If an apnea occurs while your airway is not closed, then it's pretty well got to be a central, but the technical definition requires an actual measurement of your brain waves, which your machine cannot do.
Ed Seedhouse
VA7SDH

Your brain is not the boss.

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#7
(03-01-2017, 01:42 PM)Leemax Wrote: They said that the machines are unable to detect the differences between the types of apnea and that even the doctor they work with says that.

Well ... technically they can't really tell. They make an educated guess. It takes the chest belt used in a sleep study to confirm no respiratory effort before a central apnea can be positively identified. CPAP machines determine what some call a clear-airway event.

The people who told you that likely know none of this, though.

Quote:They also didn't know about Sleepyhead.

For legal reasons they can't use it anyway. But often they've heard of it and have used for their own personal use. What you must do as a patient is, once SleepyHead identifies an issue, confirm it with the official software. That's the only way many professionals will even look at it.

Quote:I don't like to work with medical professionals that don't know everything I do, and much more, about the condition I'm being treated for, but I have found that to be the case.

That will be very much the case for almost all educated users. In that sense we really are no longer patients, but instead managers of our own health.

The last time I saw my doctor I told her which machine I wanted and which settings I wanted. After telling me I hadn't waited five years yet i told her I wanted it anyway because the auto-adjusting bi-level machine I had bought on craigslist was treating my aerophagia and PS-induced central apnea better. She concurred and wrote it all out in the prescription so that the DME had no room to try and screw me out of a good machine. Despite that they still tried to overcharge me after delivery and luckily they caved when I objected and gave it to me for the price they'd quoted at the time of the sale.
Sleepster
Apnea Board Moderator
www.ApneaBoard.com


INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
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#8
(03-01-2017, 09:19 PM)Sleepster Wrote: That will be very much the case for almost all educated users. In that sense we really are no longer patients, but instead managers of our own health.

The last time I saw my doctor I told her which machine I wanted and which settings I wanted. After telling me I hadn't waited five years yet i told her I wanted it anyway because the auto-adjusting bi-level machine I had bought on craigslist was treating my aerophagia and PS-induced central apnea better. She concurred and wrote it all out in the prescription so that the DME had no room to try and screw me out of a good machine. Despite that they still tried to overcharge me after delivery and luckily they caved when I objected and gave it to me for the price they'd quoted at the time of the sale.

That's very true about being managers of our own health. I've had refractory epilepsy for almost 35 years, and had roughly 350 complex partial seizures a year for all that time. On many occasions I've needed to independently check out what my neurologists wanted me to do , and then decide if it was right for me. Sometimes it was, sometimes it wasn't. In the end I found, through a member of an epilepsy forum, a website (seizuretracker.com) that let's you track your seizures and then produces graphs and charts so you can really see patterns. Sort of like Sleepyhead for epilepsy. After using that I saw a pattern that made me realize I am a particularly fast metabolizer and that I needed to take my meds four times a day instead of twice. That allowed me to get into a therapeutic range without intolerable side-effects. Neither my neurologist nor epileptologist had heard of that website and did not really care to know about it, nor did they seem to think much of spreading out the dosage. I asked one of them why not, since it made a real difference for me and I am sure it would for others, and the reaction was that a lot of people would not want to take meds four times a day! That attitude is disappointing, but they didn't argue with what I wanted to do and I've been seizure-free for almost three years now. At this point if I need any med tweaks I pretty much tell them what I want and they go ahead and do it.

Oh well, onward and upward! It seems like there is a great group of people here!
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#9
(03-01-2017, 08:44 PM)eseedhouse Wrote: Well, it's sorta kinda true depending on what you mean by "difference".  Your machine cannot technically tell if an apnea is Central or not.  All they can do is determine that the apnea occurred while your airway was not blocked.  That does not prove that the apnea meets the clinical definition of "central apnea".  The machine also can't tell if you are awake or asleep, and if you are awake it's reports are pretty well meaningless so far as the severity of your sleep apnea is concerned.

But it can give you enough information for your own purposes.  If an apnea occurs while your airway is not closed, then it's pretty well got to be a central, but the technical definition requires an actual measurement of your brain waves, which your machine cannot do.

I had some time to think about this for over an hour this morning (starting about 2:00). When I came back to bed after getting up to go to the bathroom, I would start drifting off to sleep and have a transitional clear airway event, which happens a lot to me. What woke me more than the apnea, which I might have passed through and gone to sleep, were the "forced oscillations" of my machine to see if my airway was open or closed. Anyhow, while it's true that our machines can't tell if we're actually asleep, if we look at our analysis in the morning and see that we had, say, 13 seconds of no breathing, an open airway, and no big inhalation right before the apnea, we were almost certainly asleep (or heading that way) and not just holding our breath as we turned around in bed. When we have fifteen events of over 10 seconds duration, in the space of about 26 minutes, ( as I did on the 27th between 0406 and 0432), it seems that it's a pretty safe bet that sleep, or an attempt thereof, is happening. Is that an accurate analysis or just something that my 0200 brain came up with? Shy

Aside from all that it's pretty frustrating to be awakened by the FOT every few minutes. I wish there were a way to temporarily bypass that feature.

(I would have uploaded the screenshot, but I haven't really learned how to do that. I was looking at the tutorial that's reference here on the board, and it's too early to try to follow all of those instructions. I confess that I'm somewhat of a Luddite when it comes to doing stuff like that.)
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#10
You are not alone when it comes to understanding 'technical' things. I rely on other people who are more gifted in the area of technology than I am and I appreciate the fact that they are willing to share their knowledge with others - like me....Smile
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