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How does a CPAP machine identify CA events ?
#1
How does a CPAP machine identify CA events ?
Greetings from down under .

I'm a new CPAP user (just 1-month into this surreal journey). I've benefited greatly from reading various tips being generously shared in this forum.  My heart-felt thanks to all who have contributed to this wonderful community effort.

Truth be known, I almost gave up using CPAP devices before discovering this AB website. My sleep physician, and the hospital where I had my sleep-study, did not provide much information regarding my condition, except to say that I had severe OSA (averaging more than 30 events per hour), and that I must start treatment using a CPAP . During the titration night session at the hospital, I could not get into any deep sleep period. The nasal mask and the chin strap they used to stop my mouth-breathing were just too uncomfortable . At any rate, the hospital gave me a prescription to go and rent a CPAP machine (to be set at 14 cm H2O) , and a N20 nasal mask .  This combination did not work for me, and after a week of trying, I was a wreck. (The CPAP definitely removed my sleep apneas, so to speak, because I no longer slept ! Sad ) .

Reading through this forum, I learned how to change the settings in my rented CPAP from a fixed pressure of 14 to the APAP mode (8 and 14) . This gradually helped me pick a more personally suitable constant pressure of 9.5  . Instead of using a nasal mask, I've switched to a F&P Simplus full-face mask, which solved my problem of mouth-breathing. I now sleep in an elevated position (using a pile of carefully-packed pillows), and wore a soft cervical collar in bed . It's all rather uncomfortable at first but luckily my body adapted to this new nocturnal ritual, and I can now get around 6 to 7 hours of sleep each night with the CPAP .

I've also learned to use the OSCAR sofware, and through which found out that my AHI usually contained more CA's than OA's (roughly 60% CA and 40% OA) . In a way, this kind of  makes sense, since I'm a person of small-build, having hardly any excess fat, a non-smoker, and non-drinker . (Even my doctor said that he'd never guess that I have OSA problems. As a matter of fact, I suffered recurrent shortness-of-breath and heart-palpitation symptoms for over two years, going to hospitals and cardiologists several times for various tests on my heart and lung, without any clear diagnosis. One day, I mentioned to my family doctor that I noticed myself unconsciously holding my breath long and frequently whenever  absorbed in certain tasks which required some concentration. He looked up at me, then said I'd better go get a sleep-study !)

As I understand it, CA's (central apneas , or clear airway apneas) are events where no air flows into the lung, plus no chest or abdomen movements detected , implying there are no brain signals to trigger the body breathing actions . Without any sensors attached to the chest and the abdomen, like what is done in an in-lab sleep-study, how would  a CPAP machine identify CA events ?   This is truly a big puzzle to me . Can anyone help ?
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#2
RE: How does a CPAP machine identify CA events ?
G'day daviddm. Welcome to Apnea Board.

Yes, you're right - a central apnea occurs when the brain fails to send the "breathe now" signal to the lungs. It can be a pre-existing condition or it can emerge after you start treatment. It's important to know if you had pre-existing central apnea, so please post a copy of your sleep report to help us see what's going on. Unfortunately central apnea is often overlooked (or ignored) when diagnosing apnea - most docs think all apnea is obstructive. When you post the report please include the charts and tables, not just the written summary. Also make sure your name, address etc is deleted.

If you would like some input on your treatment, please post an Oscar daily chart, formatted according to the instructions here: http://www.apneaboard.com/wiki/index.php...ganization

Getting to your specific question, the machines diagnose central apneas indirectly. Resmed use the FOT (forced oscillation technique) which sends a series of tiny pulses through the mask and measures the return pulses. From this they can determine if the airway is open (central) or closed (obstructive). Philips do something similar but they use a single puff instead of a sequence. It's not a foolproof method and can give some false positives, but generally works quite well.
DeepBreathing
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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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#3
RE: How does a CPAP machine identify CA events ?
Welcome to the forum.
Please post your OSCAR dailies so we can work on reducing your Central Apneas.
The Sleep studies will provide a history as will a screenshot of your overview
Fred Bonjour - Project Manager and Lead Tester for OSCAR - Open Source CPAP Analysis Reporter 
OSCAR

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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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#4
RE: How does a CPAP machine identify CA events ?
Your device is not able to detect central apneas event because it can't detect if you woke up or not (arousal). You need an EEG for that.

The machine can only detect that you didn't inhale and that there were no obstruction preventing you from doing so. That's it. If that condition happens for more than 10 seconds, a clear airways event is flagged. But be careful, this doesn't mean it was a real central event. Waking up and holding your breath for some times or tossing and turning can look like a central apnea event to your device but it's not because you were awake. Also, REM breathing is sometimes very irregular especially if you are dreaming and that can confuse the machine as well. So if you see lot of clear airways events, that may be central apnea but it doesn't mean it is.  Only a real sleep study can tell you if you are having central apneas. 

A quick way to determine if a central apnea event is possibly real or not is to take a look at your tidal volume chart. The tidal volume represents the amount of air moving in and out of your lungs during one breath. If the line is steady and your breath is regular before the event, it's probably a real central apnea. But if you see a big jump in the tidal volume in your chart right before the event, it probably means you woke up and took a deep breath and didn't have the need to breath again for a little while. That's not central apnea because you were awake but again your device can't tell if you are awake or not. 

So please take these results with a grain of salt. It's a good indication but don't diagnose yourself with central apneas based on Oscar results.
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#5
RE: How does a CPAP machine identify CA events ?
I'll point out that machine results are acceptable for the AASM professionally.
Fred Bonjour - Project Manager and Lead Tester for OSCAR - Open Source CPAP Analysis Reporter 
OSCAR

Download OSCAR
New to Apnea? Helpful tips to ensure success
Soft Cervical Collar
Mask Primer
Dealing with a DME
Organize Charts
Attaching Charts

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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#6
RE: How does a CPAP machine identify CA events ?
(11-07-2019, 09:12 AM)bonjour Wrote: I'll point out that machine results are acceptable for the AASM professionally.

How long did it takes the AASM to just consider RERAs? Most doctors still ignore them. The AHI is still the AASM gold standard if I remember correctly which is a joke. 

The fact is your device has no way to tell if you are sleeping or not. So based on that, draw your own conclusions. Just wear you CPAP while awake and see how many central apneas events your machine reports.
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#7
RE: How does a CPAP machine identify CA events ?
Hello daviddm, a sincere welcome to the Apnea Board.

You've been treated like lots of the rest of us with our apnea related issues. Unfortunate, but there it is. I think you'll be happy to have found the AB, as members can help you be successful. As was mentioned, ResMed machines use FOT or the Forced Oscillation Technique. For the DreamStation, it's similar but unique in their approach just a bit.

I'll suggest as did a few others, get OSCAR and post a few charts. We'll be able to see how effective the treatment is going and offer some setting edits to make it better. If not mentioned, you can also post redacted screenshots of the detailed sleep study as it may clue us in on whether or not central apnea is treatment emergent. It can signify approaching things differently.

Best wishes for success.
Dave

I'm not a doctor in real or fictional life. My posts include opinions based upon user experience regarding CPAP therapy and should not be considered medically professional direction or advice.


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#8
RE: How does a CPAP machine identify CA events ?
(11-07-2019, 10:16 AM)alexp Wrote:
(11-07-2019, 09:12 AM)bonjour Wrote: I'll point out that machine results are acceptable for the AASM professionally.

How long did it takes the AASM to just consider RERAs? Most doctors still ignore them. The AHI is still the AASM gold standard if I remember correctly which is a joke. 

The fact is your device has no way to tell if you are sleeping or not. So based on that, draw your own conclusions. Just wear you CPAP while awake and see how many central apneas events your machine reports.

daviddm asked for assistance regarding how centrals are detected and that's what others and myself have offered. Accuracy about how xPAP machines do that is off topic. If you want to debate accuracy, open your own thread on that. Thank you.
Dave

I'm not a doctor in real or fictional life. My posts include opinions based upon user experience regarding CPAP therapy and should not be considered medically professional direction or advice.


Wiki Info for Beginners
OSCAR Chart Organization
Mask Primer
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#9
RE: How does a CPAP machine identify CA events ?
Also, like to add since the OP is using a DreamStation and not a ResMed machine, that a Respironics machine uses Pressure Pulses to detect if the Airway is open or closed.

If the pulses determine the airway is open with no effort to breathe, it will be flagged as a Clear Airway event. If the pulses determine that the Airway is collapsing, but there is an effort to breathe, it is flagged as Obstructive.

You can see this easily on OSCAR by looking at the charts, and flow rate. You can also see on the events graph where the pressure pulses are flagged.
OpalRose
Apnea Board Administrator
www.ApneaBoard.com
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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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#10
RE: How does a CPAP machine identify CA events ?
Thank you all for your input . It's much appreciated .

I now have a better understanding about how my PR machine derives its number of CA events . The pressure-pulse method seems quite clever, reasonable and acceptable to me .  

With a background training in science and a lifetime of work dealing with computers, I'm no stranger to technology and know pretty well how one should view scientific data . I often thought to myself: "There is not much difference between arts and science. Just like beauty, accuracy is also in the eyes of the beholder" .

My sleep-study took place in July 2019. As a pensioner I had to rely on public hospitals for medical treatment, and the public system is generally not very forthcoming with information. As already mentioned, I was given no other details  apart from the verbal description of my condition . Knowing next to nothing about OSA at the time I did not know what to ask, and was not even sure whether to take it seriously or not . I had to wait for 3 months to have the sleep study done, then another month before I could see the specialist to get the result . He did not receive my report when I saw him, and had to ring the hospital to have it read to him. After advising me of my serious OSA problem, he recommended I start CPAP treatment . When I asked how to proceed, he said I'd be placed on a waiting list for an in-lab CPAP titration, which may be another 2 or 3 months . By a stroke of luck, the hospital called me in just a few weeks later, after a late cancellation by some other patient . I don't feel inclined to push my luck further by requesting charts and tables showing my sleep-study results .

In his response, DeepBreathing mentioned that  "...a central apnea occurs when the brain fails to send the "breathe now" signal to the lungs. It can be a pre-existing condition or it can emerge after you start treatment. It's important to know if you had pre-existing central apnea, ..." ,   which really struck a chord with me . As it happens, I generally have a lot of anxiety . Life circumstances have instilled a high degree tension and made me an anxious person from a young age . For many years I tried to counter anxiety attacks by meditation, slow and deep breathing, which may have messed up my body's natural rhythm, resulting in shallow and inadequate breathing instead . With this consideration in mind, it's quite reasonable to assume that my CA events are a pre-existing condition. As previously mentioned, I noticed myself doing long breath-holds unconsciously even during waking hours, so it would not be surprising if my body continues this pattern in its sleep .

Deep down I guess I have not quite come to terms with my OSA condition . I've spent the past 2 months researching and digging deep for a better understanding of the problem, but now a certain reluctance has emerged.  I don't want to become obsessed with it. The prospect of having to sleep with a device for the rest of one's life is rather depressing to me . I don't wish to think about it anymore than necessary . Simply noting and recording my daily AHI, my therapy hours from the machine display, plus any other worthwhile details about medication, dreams, mood, external weather etc, should be sufficient to keep track of my progress . No inclination to dig into chart details at present .

In the short time using the machine, I've already observed that my AHI can readily change from one day to the next (on the same machine settings), going from 1.3 to 7.5 for instance, corresponds to a drop in temperature due to unsettled weather . My mood, how much exercise I had during the day, how many pillows I used, also seemed to affect the AHI . Having seen how the condition of my sleep can be easily affected by these various factors, I'm no longer surprised by the high event count recorded in my sleep-study . With a spider web of wires on my head and chest, straps across my ribs and belly, it was amazing that I got any sleep at all .

My basic health problem was shortness of breath, low energy, and the occasional heart palpitations . The various hospital and cardiologist visits had not showed any obvious structural defects with my heart and lungs. I've learned to counter my shortness of breath by doing two or more daily workouts, and practice diaphragm breathing . After watching some Youtube videos of a cardiologist from York, I was reassured that my heart ectopics count of 300 is just a number, and no longer feel anxious about it . I was getting along OK until I inadvertently stepped on the OSA path . I'm glad to have found the most likely underlying cause  of my physical problems . This gives me a direction to focus my therapy effort . Meanwhile my gut feeling tells me : like the count of ectopics, AHI is just another number.
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