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Relationship of Pressure adj to CAs
Relationship of Pressure adj to CAs
This question comes from an earlier thread (Newbie's used unit arrived. Need some advice.) but I wanted to post a new thread so as not to hijack the earlier one on a tangent.

(05-22-2015, 01:28 PM)Sleeprider Wrote: Just want to add, you can basically subtract the CA from the total AHI. It won't respond to pressure and many times is inconsequential, and may just reflect a normal arousal.

I'm confused about the CA a little by Sleeprider's comment. I'm still new so I am probably combining separate ideas into a wrong conclusion, or maybe even made erroneous notes from previous threads.

Need some feedback on the following...

My prior understanding was that you crank up the pressure as needed to breakthrough the OAs. But if the pressure gets too high beyond what is needed to nail the OAs, then it might actually create new CAs and hypopneas because the pressure works against a natural exhale.

Based on that understanding I was doing a little study on opening up my S10 in auto mode to see what might happen to improve on my AHI which hadn't yet settled down under 5 in my first two weeks of therapy at a constant setting.

My CPAP Rx was 10. I turned it on auto 4-20 for a week or so and what I saw was pressures up around 14 would eliminate almost all the OAs. Most of the hypops and nearly all of the CAs were occuring at pressures above 14 (except for ones very early and very late which I think were transitional into and out of sleep).

With the drop from 10 to 4 initial pressure, I was uncomfortable breathing, so I reset the auto range to 8-14 and ran for another week. I started to notice that OAs were not all going away during that week, and so a couple of days ago I bumped the auto range to 9-14.6 and I'm watching now for a week to see what happens.

I am trying to goose the pressure up a little at a time if needed for OAs but also trying to not get above where the CAs crept in. That might be a flawed strategy based on Sleeprider's comment on OAs. There was also another comment on a different thread where someone said CAs are normal until your body gets used to the therapy. So I have a couple of question marks against my understanding of CAs caused by pressure.

My original plan was to get this as good as I can get based on what I have learned here, and then show you guys a typical report to ask for advice on next steps.

Sleeprider's comment about CAs generally not responding gave me a pause to stop and make sure I am not running down some wrong path with my own made-up strategy.

It might be that naturally occurring CAs don't respond to CPAP therapy but it's possible to cause some artificially by too much pressure. That would fit in with what I understand up to now, but I might also be all wet on CAs altogether.

Any feedback or thoughts?


Saldus Miegas
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RE: Relationship of Pressure adj to CAs
Most of my CA's are something I can ignore. They happen almost always when I am awake or semi-awake and typically when I am moving and adjusting position. The machine doesn't know if I am awake or not but you can see them in the charts plain as day.

Sometimes they are caused by pain related to CHF which my normal response when I am awake is to do a weird breathing thing (my cardiologist had never seen anyone do that before) and something I ended up evolving into over a period of 4 years of dealing with pain every day.

As for you, it really depends on when you are getting them, if they are happening when you are awake or if you have a real issue that needs to be looked at. If you have real CA's that are a result of an actual problem, you will need to use a different machine type to deal with them or have to back the upper pressure back until they subside.
[size=x-small]Current Settings PS 4.0 over 10.6-18.0 (cmH2O) BiLevel Auto
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RE: Relationship of Pressure adj to CAs

I think that your understanding of CAs are correct. One can not make CAs go away by raising the pressure. CAs can be temporarily brought on by changes to your therapy and some other things. For some people pressure above a certain point can cause CAs to show up and this can be temporary or more permanent. CAs that occur when you are awake or during the times that you are transitioning into or out of sleep are normal to everyone and can be ignored in terms of sleep apnea. As with OAs the length and periodicity of CAs can make them important.

Also as with OAs don't sweat the small stuff.

Best Regards,


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RE: Relationship of Pressure adj to CAs
Pressure reduces or abates OAs. Hypos, are usually mini OAs that don't grow up to be total OAs.
Pressure can induce CAs. In some folks this is a problem. In others they go away with time as the body adjusts.
CAs are induced by pressure because the lungs are being supercharged by positive pressure. The brain says -- hey I don't need to take a breath. Auto PAP machines do not raise pressure on a detected CA.

I think your pressure strategy is fine. You are dialing in a limited therapy window that the machine can work with.
For most people that works well. Also, you're giving time for changes to to work.

If I may attempt to clarify what Sleeprider said, CAs that appear as we are falling asleep or awaking are normal and don't really count.
The brain is in a state between sleep and wakefulness.

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RE: Relationship of Pressure adj to CAs
What are the duration times for your Ca's?
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RE: Relationship of Pressure adj to CAs
Saldus I think from what I read here you are experiencing is so common as to be expected. I am experiencing similar events. Currently trying to be patient and hope to find the Goldie Locks setting if you will. I'm using a bipap just because I can but getting similar results.
What drives me nuts is nocturia has me sleeping in 2.5 - 3 hr blocks and when I examine those blocks some are nearly 'perfect'. AHI of 0.0 during several of these blocks yet either side may be much higher. What's up with that? Anyway it seems like any other PLC loops the tighter you are able define your auto range the quicker it will learn to find the best solution within that range balancing the different events at any given circumstance. Side sleep, prone, sinus problems, whatever....
I use my PAP machine nightly and I feel great!
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Rise Time x3 Fixed Bi-Level EPAP 9.0 IPAP 11.5 (cmH2O)
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RE: Relationship of Pressure adj to CAs

Thanks everyone for the thoughtful feedback!

(05-25-2015, 08:33 PM)sgearhart Wrote: SaldusMiegas,
What are the duration times for your Ca's?


Here is a montage of sleepyhead screenshots of a typical night illustrating the CAs occurring above 15cm pressure.

btw, there must be a good way of adding in SH screen shots. I have seen them in other threads but a search for how-to came up empty. So I futzed around in GIMP for nearly an hour in the middle of the night combining graphics until I got one scaled below 500K max atch file size. Hope it is even readable. Any pointers to how this is properly done would be much appreciated.


Based on this report (and another day or two showing similar) I scaled back the auto upper limit from 20 to 14 which was below all of the CAs.

The left side of the graphics show the event detail for the CAs and hypops with durations and time stamps.

thanks for your interest and time,

Saldus Miegas

p.s. doing much better on reducing leaks since this snapshot was taken.
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RE: Relationship of Pressure adj to CAs
Looking at your left detailed picture, I'd like to add a bit: On my first night in the sleepLab I had an AHI above 50 without mask, quite evenly split between OAs and CAs. During the next (titration night), the AHI went down to 8, still fifty-fifty (nearly). ... The explanation of the sleepdoctor why CPAP therapy also removed a lot of the CAs (not just the OAs, as expected), including the question, whether those CAs have been true CAs, was: Sometimes true CAs are provoked by just happened OAs, kind of an echo, by a reflex of the nerves around the 4. neck vertebra, yet not really understood ... I followed a strategy similar to yours and 'they' went down to AHI around 1, hand in hand ... Smile
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RE: Relationship of Pressure adj to CAs
@SaldusMiegas - Welcome. Sounds like a good strategy. And, I see the CAs listed only lasted between 10 and low 20s, unlikely to cause much drop in blood oxygen.

@.... - Welcome to the forum. With that name, I was surprised your explanation did not go on and on. Interesting info on sympathetic CA after OAs. I will have to look back at my charts to see if there is a hint of this.

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RE: Relationship of Pressure adj to CAs
I was told by my DME that they really don't know what causes CAs. I'm not sure if that is true or not.
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