Causes of Unknown Apnoea events?

[Ratchick]

Hi everyone.

So I usually get anywhere from one or two to a dozen or more apneas marked as UAs. My understanding is generally that these are apneas in the presence of a leak? But (apart from a couple of them early on when I was adjusting my mask a lot at the start of my therapy) mine are occurring at times where I have zero leaks measured, I'm fast asleep, not moving, not talking or coughing or anything weird. Any idea what might be causing those?

I can post a close up of the apnea (and the surrounding ones) if needed, but to me, it doesn't overtly look that different. That said, I'm still pretty bad at reading the charts too.

Thanks in advance if you have any ideas.

[Sleeprider]

UA is unknown apnea or mixed apnea. The machine is unable to determine if the airway is open or obstructed. This can happen with leaks, but it is sometimes flagged when apnea type cannot be determined with the FOT pulses.

[Geer1]

Not related to leaks although leaks can sometimes cause them. Resmed has some sort of algorithm for determining if an apnea is obstructive, central or unknown based on the results of the pressure wave signal it imparts after it appears that an apnea has started.

Here is an example of an obstructive apnea. You can see how the mask pressure graph shows the oscillating pressure wave Resmed imparts to check for airway patency and the flow rate returning a weak signal. The flatter the flow rate graph the more obvious an obstructive apnea is (and in theory closer to the machine). 

   

Here is an example of an unknown apnea right before a central apnea. This is interesting and reviewing the data close indicates a couple things and imo confirms that the first "unknown" apnea was probably an obstructive apnea and then the central apnea was probably me changing position after arousal. First of all you can see that the sine wave pattern on flow rate is lower amplitude for the UA. The reason for this is because during obstructive apnea less of your internal air space is open so less air flow occurs due to the increased/decreased pressure. You can also see that the amplitude of pressure graph sine wave is higher because the blower is deadheading against an obstruction so the pressure increases and decreases more because it is creating pressure rather than flow.

   

My guess is that Resmed's algorithm imparts a frequency oscillation on power to blower and then it determines obstructive vs central apnea based on some combination of measuring the resulting pressure amplitudes and perhaps takes into account the flow rate (which also takes into account leak rate). I think the unknown apnea example I posted was flagged as unknown apnea because it had a few lower amplitude pulses/higher amplitude flow rate periods, probably because it was an obstructive apnea that almost cleared itself. 

Leaks can result in UA apneas because of the obvious effect they can have on interpreting these pressure measurements. It is actually pretty impressive how well they are able to calculate/monitor these flow rates and pressure when leaks are present although when large leaks are present you see a lot more UA events. 

This is also why Resmed doesn't flag OA or CA on ASV because they variable PS and backup rate make it impossible to interpret a sine wave pulse like this.

[Ratchick]

Thanks... that's what I was thinking, that it might be a mixed apnea or just not cleanly falling into one or the other categories.

Most of the UAs are popping up in a string of CAs and honestly, they don't look significantly different from the CAs around them. But I'll keep an eye on them, and make sure they don't increase for any reason.

[jaswilliams]

Ratchick I was just wondering how your progressing I have mixed apnoea as well and ended up buying my own ASV as after the second sleep study I was offered a Resmed ST machine which was not great, my trust supports my usage of my own ASV machine I bought used in the USA and imported sometimes on Dotmed you can find a Resmed Vpap Adapt S9 I bought one of these for $150 but I needed to use a shipping service to get it to the uk I don’t use a humidifier. Mt trudt provides masks and the required reporting to the DVLA as sleep apnoea is a reportable disease once you are diagnosed I see elsewhere on this forum you have other health issues is it possible your medication or other health issues are contributing to your central apnoea

[Ratchick]

Ratchick I was just wondering how your progressing I have mixed apnoea as well and ended up buying my own ASV as after the second sleep study I was offered a Resmed ST machine which was not great, my trust supports my usage of my own ASV machine I bought used in the USA and imported sometimes on Dotmed you can find a Resmed Vpap Adapt S9 I bought one of these for $150 but I needed to use a shipping service to get it to the uk I don’t use a humidifier. Mt trudt provides masks and the required reporting to the DVLA as sleep apnoea is a reportable disease once you are diagnosed I see elsewhere on this forum you have other health issues is it possible your medication or other health issues are contributing to your central apnoea

Still waiting for my consultant to actually call me. Will be chasing them AGAIN tomorrow. And again. And again. 

I will definitely have a look if this continues but considering how crappy my sats are, I really need this managed by an actual doctor who gives a damn. Money is tight (because disabled, housebound, and limited income from ESA and PIP) but I guess I'll have to make it work somehow.

My other problems could very well be contributing - I have a type of dysautonomia that causes all manner of issues, plus I am using pain meds for severe pain, although my doctor has confirmed that is NOT the cause of my apnea, and my own data via OSCAR has confirmed this. There is zero correlation between when I use those pain meds and my AHI or sats which is always a comfort because I effectively live with pain from peritonitis 24/7/365. That said, I do try to minimise my pain med usage just to be sure.

The frustrating thing is that I was diagnosed with CSA over a decade ago - and was told nothing needed to be done. I spent the last decade telling everyone this and shouldn't I be treated for my sats dropping at night and how it MUST be contributing to how crappy I feel day-to-day (to the extent where I'm now bedbound between everything combined), but nope, every time it was written off or ignored. My new cardio finally referred me to have a second sleep study redone to see if it might show up anything and boom. Turns out I'm walking around with a CAI of 80+. So frustrating

[Geer1]

I just read some of your other threads for more detail. The opiods could definitely be causing your central sleep apnea and with your sats could be the cause of numerous current health issues. I was on Tramacet after recent nasal surgery and noticed respiratory depression in my OSCAR data. It shows up as a central apnea like phenomenon. I posted about it here.

http://www.apneaboard.com/forums/Thread-...Depression

Opioid induced respiratory depression is well known and your situation screams that this needs to be investigated if it hasn't already been done. I haven't researched it a lot but unfortunately if it is the cause I don't think there is any easy treatment, perhaps trying to find a different medication that doesn't cause the apnea or at least try reducing dose before sleep to see if that has any effect. I know your pain is probably through the roof but I personally would try a trial off the medication (use whatever you can that isn't known to cause respiratory depression and provide you with some help) to see how it affects your PAP data. I notice the change immediately the night after discontinuing Tramacet.

If you absolutely need opioids and there is not other option that works for you then you are probably stuck trying off label treatments like ASV. Here is an example article about using ASV for treating Opioid induced apnea. I would research this stuff and try to find some good info to convince any doctor to use ASV. If consultant is useless try to convince doctor or just start knocking on other doctors doors until you find one that feels like doing his job...

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3459205/

Frankly in my opinion your APAP treatment is utterly ridiculous. Why high pressure? Pressure treats obstruction which you don't have. Why no EPR? EPR treats flow issues which you have. Unfortunately your flow issues are central which means that increasing flow will probably just decrease respiratory drive further doing nothing but still if I was a doctor and going to try APAP it would be at lower pressures and max EPR (say 8 pressure, 3 epr) hoping that it helps (all your doctors appear to be doing is hoping rather than using common sense and medical knowledge). The only way to improve your specific apnea/sleep breathing issue is by either getting rid of/treating the problem (potentially removal of opioids), forcing you to breath (machine with backup rate and ability to treat central apnea such as ASV or in this case an ST-A with IVAPS or even a more dedicated ventilator may even be warranted since hypoventilation is your real issue), or at a very minimum trying to increase oxygen levels (maybe an oxygen bleed into APAP). Any steps less than this are arguably negligent and I wouldn't be afraid to tell doctor that if he refuses to acknowledge and act on your sats dropping into 70s each night... Heck if he refuses to take any responsibility he can at least order a titration study so a registered technician can try different machines to try and control CSA and maintain sats...

Again if at all possible I would first try at least a trial off of opioids to see if that fixes/improves CSA/O2 levels as that could very well be your main issue. I don't know exactly what your cause of pain is but there are other ways to deal with pain in some cases (nerve blocks etc) and almost dying from opiod induced respiratory depression would be a pretty good argument for doctors to take different steps on your pain treatment...

[Ratchick]

As I said above, opioids have been considered and ruled out as the primary cause (as proven by the fact that even when I went two months without taking any opioids at the start of using APAP, I still had exactly the same levels of central apneas). So while it's probably not ideal to be on them, it's also not the primary cause and - as I said - my data clearly demonstrates that my numbers remain unchanged (overall, because CA is nothing if not consistently inconsistent) regardless of my opioid usage. That said, even if my CSA was secondary to opioid use, ASV has been demonstrated to be appropriate management if opioids can't be stopped. 

Second, I know that the CPAP/APAP isn't helping (much - though at the end of the day an average of ~30 AHI is way better than 80-90AHI, IMO, and my oxygen sats are definitely better for it). This is WHY I am chasing my doctors about it, but it takes time, I'm afraid, when you don't have the money to pay for private healthcare and everything is backed up like hell because of the pandemic. The pressure was selected because I do get a few obstructive events at lower pressures, and these are pretty much eradicated (aside from sleep-wake junk) at this stage, based on my 95% pressure values when on APAP up to max pressure of 20.

And as cruddy as I feel every day, I feel already SO much better than I did before in terms of not having to nape every single day, and the constant headaches are gone and the rampant migraines are under control, and the memory fog and taking two hours to fully come around after waking up is gone. So yeah. I still feel like hot garbage, but right now, it's so much better than when I was spending pretty much the entire night with my sats below 90% barring a few minutes. 

The point is that nothing I do is going to make it much better at this point, and at least this is cutting my AHI by half or even two thirds - and occasionally even lower on a particularly low event night. And that's all I can do until my doctor finally deigns to honour me with his presence. It's frustrating, but I understand that CPAP/APAP isn't what I need and that this isn't helping, and as I'm living on disability benefits, I don't HAVE that kind of money to just cut the queues or buy out of pocket right now.

[Geer1]

I read the part about opioids ruled out but then forgot it when looking through your other thread, CSA must be because of other health issues then. ASV or potentially IVAPS would be your main chances of treatment. ASV would probably be more comfortable but with your hypoventilation IVAPS may be required. I would be reaching out to every sleep clinic I could if I was in a similar situation, imo you should already be scheduled for a titration study. Doctors will p*** around trying all the easy things first, you need to try and force them to understand this isn't a typical SDB case and that they need to take the next steps (then contact other doctors/clinics as necessary to do so if they won't). It sounds like you have the data to support this treatment is not sufficient (AHI is not acceptable and sounds like your sats aren't either) and that should be all you need, the key is just assembling that data and getting it into the hands of someone willing to help you.

It is promising that you feel better on APAP. Do you have a sample report to show what your sats look like on APAP?

Have you ever tried using EPR? It could make things better or worse, hard to say.

[Maskman888]

Most of the time unknown events are also caused by leaks that's too excessive