Hello Guest, Welcome to Apnea Board !
As a guest, you are limited to certain areas of the board and there are some features you can't use.
To post a message, you must create a free account using a valid email address.

or Create an Account

New Posts   Today's Posts

[CPAP] ResMed - Unclassified Apneas
I am a recent (30 days) CPAP user and finally got around to uploading my data to SleepyHead. The treatment has brought my overall AHI down from 60 to 10 on average but I am confused by the 10 remaining. On Sleepyhead I show as having 0 CA and 0 OA but all my events show up as Unclassified Apneas. I do have periods of high leaks but they do not match when the Unclassified Apneas occur, high leaks are when I turn on my side and knock the mask off a little.

So I have a quandary. If the UAs are Obstructive increasing pressure may be a solution, if they are Central then reducing pressure may be a solution. How should I go about solving this? I've attached a screen shot of what a period of these apneas look like on SleepHead and my overall stats for a night.

Thanks for any help

Post Reply Post Reply

Donate to Apnea Board  
Well, hang in here until some of our bi-pap experts show up, but your results look to me like your doing pretty well, and just need to modify things a little to get to your sweet spot.

For openers, I think the range between min and max is a little large for you (5). I think you might see better results if you drop that to 4. Also, since you're spending all your inhale time at the top of the range (15), I think moving the bottom end up to about 12 might be a good thing. That would give you a top of 16 which might just be the thing to knock down those unknowns.

Post Reply Post Reply
What is your back-up rate set to?

Setting your EPAP up to 12 will not move your IPAP. In order to get to 16/12 you will need to set the IPAP to 16 also assuming that this works the same as my VPAP does.

Best Regards,


Admin Note:
PaytonA passed away in September 2017
Click HERE to read his Memorial Thread

~ Rest in Peace ~
Post Reply Post Reply
Your VPAP ST machine has a timed backup rate. You can see that it switches to IPAP pressure twice during your apnea events.
I don't see the 1 cm-H2O 4 Hz pressure wave called the FOT algorithm in either your pressure or flow waveform. That's how it classifies apnea as CA or OA. Sort of like sonar. Try unplugging the power to your machine for a few minutes, then plugging it back in. This may reset the processor to get the FOT to work. Or, perhaps, the S9 VPAP ST does not have FOT -- but, I think it does.

Frankly, they look like central apnea; and you may need to be on an ASV type machine.

Admin Note:
JustMongo passed away in August 2017
Click HERE to read his Memorial Thread

~ Rest in Peace ~
Post Reply Post Reply
Hi MR-ab,
WELCOME! to the forum.!
Hang in there for more answers to your question and much success to you as you continue and finetune your CPAP therapy.
Post Reply Post Reply

Donate to Apnea Board  
G'day MR-ab, welcome to Apnea Board.

I can't add to what the others have said about adjustments. However my VPAP Adapt also reports everything as an unclassified apnea, so your VPAP ST may just do the same.
Apnea Board Moderator


Post Reply Post Reply
Thank you all for your comments and suggestions. I have taken them into consideration and am going to take the following course of actions.

a) Reduce the IPAP and EPAP a little and close the gap between them to 4. This is based on a hypothesis that these are central apneas and my centrals went up with increased pressure during my initial titration sleep study. I will let this run for a week and see if there is a change.

b) I'm going to do some more research on the FOT algorithm which I had never heard of before (thanks justMongo). It should be helping but I also see no evidence of it working with my machine on the ST setting. For reference I found a good paper on the FOT algorithm at


Two follow up question if I may:
a) How long would you suggest I run with new setting before I could expect a change in my AHI if the apneas are central (days, weeks, months)? I know this is most likely person specific but would like to be as scientific with the tests as possible so I don't have to repeat them.

b) Are there tell tail signs I should look for in the pressure waveforms that would indicate if the apneas are central or obstructive? .... Or do I really need a respiratory effort sensor in parallel with the Sleepyhead software output to figure this out? I'm assuming with a central there would be no respiratory effort while the apnea is underway... with obstructive there should be significant effort.

Thanks again for all your assistance.


Post Reply Post Reply
Don't change too many things at once. It's like adjusting a carburetor, turn too many screws and you'll not know what made the difference.
Make small changes and run about a week.

The FOT in action -- here's two consecutive obstructive events -- you can see the FOT pressure oscillation and its reflection in the flow waveform.
My machine is an auto bilevel, you can see the machine up the pressure after the event.
[Image: 12Jan_Page_07.jpg]

Admin Note:
JustMongo passed away in August 2017
Click HERE to read his Memorial Thread

~ Rest in Peace ~
Post Reply Post Reply
(01-15-2015, 10:31 AM)MR-ab Wrote: So I have a quandary. If the UAs are Obstructive increasing pressure may be a solution, if they are Central then reducing pressure may be a solution. How should I go about solving this?

Hi MR-ab, welcome to Apnea Board.

In ResMed machines like the S9 Elite, S9 AutoSet, S9 VPAP S and S9 VPAP Auto, which do perform the FOT to distinguish between obstructive apneas versus central apneas, whenever Leak is above 30 L/minute the ResMed machines do not attempt to perform the FOT, and all apneas are marked as being of Unknown type. To fix this, reduce Leak.

But on your machine, it looks to me like there was not excessive leak and all apneas are always of flagged as Unknown type.

This makes sense because the FOT takes about 6 to 10 seconds to work its magic, and ResMed machines with a back-up rate never take the time to perform the FOT. The machines jump right in without delay, treating the central event by automatically cycling between EPAP and IPAP.

Looks to me like the apneas in the data you posted might possibly be central apneas (these do look slightly similar to Cheyne-Stokes Respiration) but I think it much more likely that they are obstructive apneas, because the IPAP pressure pulses result in almost no Flow response, which is similar to the Flow during obstructive apneas. Therefore, I think a fix would likely be to increase both EPAP and IPAP equally, keeping Pressure Support (PS) unchanged, or perhaps it may help to increase both EPAP and PS.

(01-16-2015, 12:39 PM)MR-ab Wrote: b) Are there tell tail signs I should look for in the pressure waveforms that would indicate if the apneas are central or obstructive?

If no Flow results from an IPAP pressure pulse, the apnea is clearly obstructive.

If there is small Flow (non-zero) during IPAP and the IPAP pulses are being machine triggered (if the IPAP/EPAP pressure changes are occurring at the back-up rate), the apnea/hypopnea is likely central in type.

If the PS is 10 or higher, this usually would be high enough to do for us all the work of breathing during what would have become a central apnea. But a PS of 8 or 10 or higher would likely be excessive if used all the time, perhaps worsening unstable breathing or perhaps raising the amount of O2 in the blood to dangerously high levels. (Long periods of SpO2 of 98% or above are potentially dangerous, I think.)

So ST machines usually use values of PS which are too low to fully keep us ventilated if we stop all breathing effort, and therefore are usually only able to change central apneas into central hypopneas, unless the action of the machine cycling into IPAP manages to trigger some breathing effort by us.

In ASV machines, PS will automatically adjust only as high as needed to maintain an adequate amount of ventilation. Thus, during normal breathing PS may be small, but if we stop making effort to breathe PS will jump up high enough do for us all the work of breathing, keeping us ventilated adequately with no effort on our part. (Or at least, that's the concept.)

However, some patients with ASV machines are not able to handle high pressures (because of excessive and painful air-swallowing, or because of various problems with lungs or eyes or ears or jaw), so the ASV machine's Max Pressure setting has been severely limited until, like an ST machine, sometimes the ASV machine might only be able to change what would have become an apnea into an hypopnea, or change what would have become an hypopnea into a RERA event.

Take care,
--- Vaughn
Membership in the Advisory Member group should not be understood as in any way implying medical expertise or qualification for advising Sleep Apnea patients concerning their treatment. The Advisory Member group provides advice and suggestions to Apnea Board administrators and staff on matters concerning Apnea Board operation and administrative policies - not on matters concerning treatment for Sleep Apnea. I think it is now too late to change the name of the group but I think Voting Member group would perhaps have been a more descriptive name for the group.
Post Reply Post Reply

Donate to Apnea Board  
Thank you for the charts at least now I know what FOT should look like if it worked on my machine.

Thanks for the detailed explanation, this is finally beginning to make some sense to me. Selecting appropriate pressure settings looks like it will be a trial and error process in my case. I know for certain that increasing pressure triggered 3x the number of central apneas during my titration measurments , yet I may still have residual obstructive apneas to address that will require increased pressure. I'm doing much better than my 50-60 AHI per hour before CPAP, but would love to get it below 10 on average as a mid-term goal.


Post Reply Post Reply

Possibly Related Threads...
Thread Author Replies Views Last Post
  Leaks, Mask Change... now increased obstructive apneas MAPnea 7 195 06-20-2018, 02:15 PM
Last Post: Sleeprider
  Updates on Central Apneas KCFLY 22 906 05-09-2018, 02:07 PM
Last Post: Spy Car
  Apneas just as falling asleep? Nancy S 15 778 04-10-2018, 09:02 PM
Last Post: Mogy
Exclaimation Am I having Central Apneas? dk2011 11 520 03-29-2018, 05:13 PM
Last Post: Apnea Infant
  Can ammonia or VOC's cause apneas? MyronH 2 208 03-25-2018, 04:11 PM
Last Post: car54
  Sudden Central Apneas?? whats going on. fitmart 5 500 01-31-2018, 06:51 PM
Last Post: Sleeprider
  Sudden increase in Clear Airway apneas? tstburn 7 805 01-22-2018, 12:52 PM
Last Post: Sleep2Snore

Forum Jump:

New Posts   Today's Posts

About Apnea Board

Apnea Board is an educational web site designed to empower Sleep Apnea patients.