Minimum pressure -- trying to understand the algorithm

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cathyf
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Minimum pressure -- trying to understand the algorithm

Post by cathyf » Mon Oct 20, 2014 8:58 pm

My A10 is set at 7-20. I am looking at my 10 days of cpap usage, and I have 32 separate mask-on time periods. For the first 5 days I had ramp turned on. Every one of those had a time at 4cm pressure, then when the machine decided I was asleep, it would immediately climb steeply to at least 8, and usually more like 9-10. Then until I hit stop, it would bounce up and down, but NEVER go below 8cm. Then I turned ramp off for the next 5 days, and now it stays at 7cm until the machine thinks that I'm asleep, and then climbs steeply, and then bounces around. Again, it NEVER goes below 8cm. Even when I wake up and you can tell by the respiration rate that I'm awake, it's still hanging out above 8, and spending lots of time over 9 and 10.

Because of what I have learned here, I would worry about the minimum pressure being too low. But watching the ResMed algorithm at work, it doesn't seem to feel any obligation to return to the minimum pressure once it goes through the min at the beginning of the session.

Is that the way everyone else understands the algorithm too?

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Wulfman...
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Re: Minimum pressure -- trying to understand the algorithm

Post by Wulfman... » Mon Oct 20, 2014 9:24 pm

cathyf wrote:My A10 is set at 7-20. I am looking at my 10 days of cpap usage, and I have 32 separate mask-on time periods. For the first 5 days I had ramp turned on. Every one of those had a time at 4cm pressure, then when the machine decided I was asleep, it would immediately climb steeply to at least 8, and usually more like 9-10. Then until I hit stop, it would bounce up and down, but NEVER go below 8cm. Then I turned ramp off for the next 5 days, and now it stays at 7cm until the machine thinks that I'm asleep, and then climbs steeply, and then bounces around. Again, it NEVER goes below 8cm. Even when I wake up and you can tell by the respiration rate that I'm awake, it's still hanging out above 8, and spending lots of time over 9 and 10.

Because of what I have learned here, I would worry about the minimum pressure being too low. But watching the ResMed algorithm at work, it doesn't seem to feel any obligation to return to the minimum pressure once it goes through the min at the beginning of the session.

Is that the way everyone else understands the algorithm too?
Without seeing any reports, I can't explain why it never seems to go below 8 when the minimum is 7. But, the minimum is important because having it high enough will head off most of the events it's going to have to "chase" during the night.
The APAPs primarily respond (with pressure increases) to Flow Limitations and Snores......as they're believed to be precursors to Apnea events.
If you're still having events that aren't being addressed, maybe moving your minimum up a bit may help.


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Re: Minimum pressure -- trying to understand the algorithm

Post by palerider » Mon Oct 20, 2014 9:38 pm

cathyf wrote:My A10 is set at 7-20. but NEVER go below 8cm. it's still hanging out above 8, and spending lots of time over 9 and 10.
..........
Is that the way everyone else understands the algorithm too?
read page 6 and 7 of the provider manual, specifically the section on 'autoset for her mode'.

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Re: Minimum pressure -- trying to understand the algorithm

Post by palerider » Mon Oct 20, 2014 9:39 pm

Wulfman... wrote: I can't explain why it never seems to go below 8 when the minimum is 7.
feature of 'autoset for her' mode.

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Re: Minimum pressure -- trying to understand the algorithm

Post by Wulfman... » Mon Oct 20, 2014 9:50 pm

palerider wrote:
Wulfman... wrote: I can't explain why it never seems to go below 8 when the minimum is 7.
feature of 'autoset for her' mode.
Okie, Dokie.


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Re: Minimum pressure -- trying to understand the algorithm

Post by Pugsy » Mon Oct 20, 2014 10:06 pm

For those that don't have the new AirSense for Her manual.

Minimum pressure (Min. Pressure) that adjusts according to the frequency of apneas:
If two apneas occur within a minute, the pressure reached in response to the second apnea will
become the new minimum treatment pressure until the next treatment session.

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Re: Minimum pressure -- trying to understand the algorithm

Post by Goofproof » Mon Oct 20, 2014 10:40 pm

Sounds like a good way to climb the letter until you reach the top. Don't think I'd want that. Jim

I'd also be spending more time keeping my AHI my number one project, rather that worrying how the program in the machine works.
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Re: Minimum pressure -- trying to understand the algorithm

Post by cathyf » Tue Oct 21, 2014 7:22 am

palerider wrote:
Wulfman... wrote: I can't explain why it never seems to go below 8 when the minimum is 7.
feature of 'autoset for her' mode.
Except I don't have the "ForHer" model! That's still on back order at my DME for another couple of weeks. (I "settled" for the black autoset because I didn't want to wait the extra time.)

As for worrying about my AHI first before thinking about the algorithm -- my AHI is 0.36 and has only been above 1 on one day (yesterday when it was 1.14) when I had a cluster of 5 events when I was awake and really annoyed about being awake at 3:30am. (I think that bitter sarcastic sighing gets scored as central apneas.) So I'm indulging in my techie side! This cpap thing is working so amazingly well for me that I seriously have wondered if I really have apnea -- but it's this little stuff here where I can see the machine is actually working very hard and very smart to keep me out of trouble.

What I think I am seeing is that this machine works in such a way that you can't have the maximum pressure too high or the minimum pressure too low (which could very well be by design, since as we all know there are stupid providers out there handing out machines set at 4-20.) When I had ramp set at AUTO and fell asleep quickly, I stayed at 4cm as long as the machine thought I was awake, but then when I fell asleep the machine dialed up to 10 within a couple of minutes. The minimum setting of 7cm didn't seem to have any effect on the machine's behavior. Since I turned ramp OFF what happens is that the 7cm is my ramp-time pressure -- until I fall asleep the machine stays at 7, but then when I fall asleep it quickly climbs to 10 and then hangs out in the 9-10 range except that sometimes it drops all the way to 8 and sometimes climbs to 13 or 14.

Given what people are saying about how the S9 ResMed algorithm works, it really does return to the minimum setting between "eventful activity". And if the minimum is set too low, it could mean it has too far to go to get to a pressure sufficient to prevent an obstructive event in time when your breathing starts getting wonky. The documentation implies that the A10 "classic" algorithm isn't different from the S9 algorithm, but my data makes it sound like it is.

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Re: Minimum pressure -- trying to understand the algorithm

Post by Pugsy » Tue Oct 21, 2014 7:36 am

I forgot that you didn't get the for Her model.
The only thing I can think of is that maybe the machine senses some sort of flow limitation that is keeping the machine at wanting to offer 8 cm all the time instead of dropping down to the minimum of 7. Odd that it would happen all night though...but I suppose not impossible.

I just went back and looked at the manual again to see if maybe I missed something but that "new higher minimum" thing is definitely listed under the "for Her" new algorithm.
If they had changed the original algorithm I would have thought they would have included that description for the regular apap mode but it's definitely under the new "for Her" apap mode.

So I dunno what is going on.

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Re: Minimum pressure -- trying to understand the algorithm

Post by palerider » Tue Oct 21, 2014 8:33 am

Pugsy wrote:ISo I dunno what is going on.
without charts, we're just guessing.

I'd guess snores or flow limits, that's what usually causes pressure to spike like she's describing.

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Re: Minimum pressure -- trying to understand the algorithm

Post by Pugsy » Tue Oct 21, 2014 8:43 am

palerider wrote:I'd guess snores or flow limits, that's what usually causes pressure to spike like she's describing.
Yeah...my thoughts but for it never go below 8 to the minimum of 7 ...all night long...most snores and FLs aren't that constant all night long. They sort of come and go and if they didn't come and go and were constant enough to do that to the apap...I might be re evaluating my minimum pressure ...maybe.
Would indeed be interesting to see the pressure graph and maybe the FL graph and snore graph.

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Re: Minimum pressure -- trying to understand the algorithm

Post by cathyf » Tue Oct 21, 2014 2:16 pm

Ok, I gotta figure out a better way to link to pictures -- using Shutterfly is way too convoluted!

Here are the flow graphs between Oct 10-20. First four days are ramp set to AUTO. Fifth day is ramp set to 45 minutes (that was a mistake). Then the remaining six days are with ramp turned to OFF. The dotted line is the median pressure.

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Re: Minimum pressure -- trying to understand the algorithm

Post by Pugsy » Tue Oct 21, 2014 2:27 pm

Those are pressure graphs and not the flow limitation graph...can you do just a couple of flow limitation graphs with pressure graph right next to it? Like this?
You can move the graphs around so that Flow limitation graph is right next to pressure graph.


Image

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Re: Minimum pressure -- trying to understand the algorithm

Post by palerider » Tue Oct 21, 2014 2:47 pm

cathyf wrote:Ok, I gotta figure out a better way to link to pictures -- using Shutterfly is way too convoluted!
\
upload to imgur.com

post the 'linked bbcode' link here.

also, it's just a lot easier all around if you just hit f12 and upload the screenshot, make it look something like this:

Image

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Re: Minimum pressure -- trying to understand the algorithm

Post by cathyf » Tue Oct 21, 2014 2:56 pm

Pugsy wrote:Those are pressure graphs and not the flow limitation graph...can you do just a couple of flow limitation graphs with pressure graph right next to it?
Ah... dropbox is much less trouble... Same order as before:

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