Harmonica effect

[permabear]

Hi folks,

I've been on xPAP therapy for 6 months now. Although I do notice some positive effects, I still suffer from fatigue. My Oscar charts look pretty good. But there's one thing I don't quite grab yet. I see some periods with changing amplitudes. Some kind of a harmonica effect so to say.
Could you please elaborate on this topic? What does it have to say? Is it a kind of FL (and should I adjust pressure) or is it otherwise a sign of therapy insufficiency? 
It happens for an hour or so, followed by an hour with a nearly perfect chart. So it might have something to do with sleep position. 

Thanks a lot for your comments!

   
   
   

[Sleeprider]

I think your settings are far less than ideal, with PS too high, EPAP too low and no opportunity for the Vauto to adjust pressure. I have not seen a history of how you got here, but it is pretty unusual to see an EPAP set to essentially the minimum and PS over 4 with no room to move on IPAP. The oscillations in respiration suggest you are near an apneic threshold and as a result respiratory volume is periodically suppressed by cycling into hypercapnia and back. Your AHI seems well controlled, but it would be interesting to compare settings of EPAP min 5.0, PS 4 and IPAP max 11.0 just to see what the machine does with it and how your respiration responds.

[permabear]

Thank you. I figured out that an EPAP of 4 is sufficient while I don't have any obstructive apneas at all.
Furhtermore the PS of 5.6 is the result of a search for elimination FL. I did not use auto mode because it gave me a dizzy head in the morning. But maybe that is someting that will become better over time.
So you think I need more EPAP even though the complete absence of obstructive apneas? And could this changing of amplitude be the culprit that I still don't feel any better?

[Sleeprider]

With no OA, a low EPAP is fine. I think the PS is a balancing act and you may need to bring it down a bit to 5.0 to avoid the respiratory oscillations, and it's fine to limit the machine pressure range if that is disruptive to sleep. Without history, I was looking to observe what a wider range would bring, but you seem to have put some good thought into these settings, and may have just over-shot the PS a bit.

[permabear]

Thanks for the input. Much appreciated!
I'll give the algorithm another chance, allbeit within a restricted range.
Just one more question if you don't mind. You wrote the following: "The oscillations in respiration suggest you are near an apneic threshold and as a result respiratory volume is periodically suppressed by cycling into hypercapnia and back."
If I am close to an apneic event, I would expect that even more PS is needed at that time. But you suggest to lower PS a bit (and give some more room to the EPAP algorithm).
How does this make sense? Or do you mean that the high PS blows off the Carbon Dioxide (CO2) resulting in a lower drive to breathe (and maybe also a lower breathing volume?).

[Sleeprider]

First, I mis-spoke, the effect of too much PS is hypocapnea not hypercapnea. The effect is to ventilate more than you actually need and reduce CO2. In your case it does not reach the point where CA events occur, but you react with reduced respiratory effort and that leads into the oscillating feedback loop. Your tidal volume and minute vent are relatively high, so there is no problem with getting enough air. I think if really want to see what is contributing to the oscillations, you have to show the flow rate with the tidal volume, respiration rate and minute vent to see if they all move in unison or if it is just a tidal volume.

It's a significant objective among many members to minimize flow limitation, but that doesn't mean every breath needs to be perfectly formed. Boy, I'm in trouble if that's the case. If we can avoid respiratory arousals from flow limitation that is plenty.

[permabear]

Thanks again, Sleeprider. I think I've been a bit too keen on eliminating FL.
However I'm still wondering how this oscillating feedback loop can lead to arousals or sleepfragmentation.

Tomorrow I'll try to get flow rate with the tidal volume, respiration rate and minute vent together in one picture.
And tonight I'll be sleeping with EPAP min 4.0, PS 5 and IPAP max 11. Let's see what it does!

[permabear]

Please find attached the charts with tidal volume, respiration rate and minute vent included.
Thank you in advance for your comments.

   
   
   

[permabear]

BTW last night I gave some more room to the Resmed Algorithm with EPAP min 4.0, PS 5 and IPAP max 11.
However, pressure hardly moved: IPAP reached 9.26 at maximum. Apparently the algorithm did not detect any relevant events.
Could this have something to do with TiControl’s Ti Max and Ti Min parameters? For maximum comfort I have set Ti Max at 4.0s and Ti Min at 0.2s (Trigger/Cycle=med).

[Sleeprider]

Results look the same. If you feel good, it's good enough. Inspiration time has no effect on your therapy as you are 100% spontaneous trigger and cycle. Your maximum Ti is 2.36, and you clearly don't need Ti max of 4 seconds, but it doesn't affect anything. A ti max of 3.0 would be the same. Ti min 0.2 is default.