What's the point?

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BleepingBeauty
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What's the point?

Post by BleepingBeauty » Fri Sep 19, 2014 3:44 pm

What's the point, exactly, of the 90% pressure number? Why is it even used? Wouldn't the *average* number be more helpful?

My new pulmonologist/sleep doc (I had a follow-up appointment with him recently re: my bout with pneumonia early this summer) was wrong about what it means, telling me that the 90% EPAP reported on my data of 15.8 is where my machine was for 90% of the night, and he advised that I should raise my EPAP (set for 10-17) accordingly. I corrected him about what the 90% number represents, but it left me wondering why the number is even reported. It seems to confuse everyone.

Anyone know?
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Pugsy
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Re: What's the point?

Post by Pugsy » Fri Sep 19, 2014 3:54 pm

You know I have wondered the same thing myself.
Long term the 90 % number might be useful for establishing something close to a fixed cpap pressure but that's long term as in months. I think that may have been behind the 90% classification.

Long term my 90 % apap pressure number was within 1 cm of my long term average pressure number...that's how it should be.
Short term the 90 % number is too easily skewed by whacko nights. I've see 90% numbers of 18 cm maybe 2 nights a week...maybe none in a week. But long term over 6 months my 90 % number was 12.4 and my average was 11.4 (this was with using 10 min and 20 maximum).
There's no way that I need 18 cm all night long on fixed cpap mode. Just sometimes I need it briefly during the night but it doesn't take very long to really skew the 90% number so that it is really much higher and people forget the "or below" part of the diagnosis.

So the 90% number in anything (95% in Resmed) can be useful but it isn't the holy grail of numbers like people tend to think of it as.

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Re: What's the point?

Post by SleepyEyes21 » Fri Sep 19, 2014 4:04 pm

BleepingBeauty wrote:What's the point, exactly, of the 90% pressure number? Why is it even used? Wouldn't the *average* number be more helpful?

My new pulmonologist/sleep doc (I had a follow-up appointment with him recently re: my bout with pneumonia early this summer) was wrong about what it means, telling me that the 90% EPAP reported on my data of 15.8 is where my machine was for 90% of the night, and he advised that I should raise my EPAP (set for 10-17) accordingly. I corrected him about what the 90% number represents, but it left me wondering why the number is even reported. It seems to confuse everyone.

Anyone know?
Hi Beauty- this 90% pressure number confused me also, so I read the manual with my machine, and it is described as you say your doc told you. What is your understanding of it?
Why would your doc want you to raise your EPAP level? Isn't it better for our 90% number to be lower than our recommended max pressure?

I would prefer to know what rate I used for a majority of the time, as opposed to just the average because if the pressure number is significantly high or low on any given day, it could be a signal for me to investigate how the mask/ machine are working.

What completely confuses me in the settings is the 'periodic breathing' number; isn't periodic breathing what we are doing in between apneas?

I'd appreciate what others can tell us about both of these features

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Re: What's the point?

Post by chunkyfrog » Fri Sep 19, 2014 4:11 pm

I believe the 90% figure tries to be sensitive to statistics by disregarding up to 10% of the extreme readings.
Your doctor may know something; wants to cover his butt, or just be sure you have not shorted yourself on pressure.
It can't hurt to try his advice, observe your data and use whatever pressure that works best.
If you intend to share your actions with the doctor, save documentation to support your decision;
--or you can just be quiet and not rock your boat.

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Re: What's the point?

Post by SleepyEyes21 » Fri Sep 19, 2014 4:12 pm

Pugsy wrote:You know I have wondered the same thing myself.
Long term the 90 % number might be useful for establishing something close to a fixed cpap pressure but that's long term as in months. I think that may have been behind the 90% classification.

Long term my 90 % apap pressure number was within 1 cm of my long term average pressure number...that's how it should be.
Short term the 90 % number is too easily skewed by whacko nights. I've see 90% numbers of 18 cm maybe 2 nights a week...maybe none in a week. But long term over 6 months my 90 % number was 12.4 and my average was 11.4 (this was with using 10 min and 20 maximum).
There's no way that I need 18 cm all night long on fixed cpap mode. Just sometimes I need it briefly during the night but it doesn't take very long to really skew the 90% number so that it is really much higher and people forget the "or below" part of the diagnosis.

So the 90% number in anything (95% in Resmed) can be useful but it isn't the holy grail of numbers like people tend to think of it as.
Hi Pugsy - are you saying that once the machine records your pressure at a certain number, it stays there (for that night/ time period), although the user may not have been at that number for the majority of the time?

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Re: What's the point?

Post by SleepyEyes21 » Fri Sep 19, 2014 4:17 pm

chunkyfrog wrote:I believe the 90% figure tries to be sensitive to statistics by disregarding up to 10% of the extreme readings.
Your doctor may know something; wants to cover his butt, or just be sure you have not shorted yourself on pressure.
It can't hurt to try his advice, observe your data and use whatever pressure that works best.
If you intend to share your actions with the doctor, save documentation to support your decision;
--or you can just be quiet and not rock your boat.
Hi CF - wouldn't the user want to know the extreme readings so they can have a record of how well the set max pressure is working for them? (this is totally confusing me )

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Re: What's the point?

Post by Wulfman... » Fri Sep 19, 2014 4:19 pm

I don't know either.
In the past, when trying to determine a fixed pressure off of a range of pressures, I've suggested that a number somewhere between the "Average" and the "90%" (or 95%) number seemed to work pretty good.

But, trying to apply that to Auto Bi-Level or ASV data seems like a different ballgame to me.


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palerider
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Re: What's the point?

Post by palerider » Fri Sep 19, 2014 4:33 pm

SleepyEyes21 wrote:What completely confuses me in the settings is the 'periodic breathing' number; isn't periodic breathing what we are doing in between apneas?

I'd appreciate what others can tell us about both of these features
I could try and explain the 90 or 95% numbers, but robysue does a much better job explaining what they mean.

as to the periodic breathing, the online medical dictionary defines it thusly: periodic breathing - abnormal respiration in which periods of shallow and deep breathing alternate.

as opposed to regular breathing where your breaths are pretty regular.

make sense?

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Re: What's the point?

Post by Pugsy » Fri Sep 19, 2014 6:44 pm

For the newbies....the 90/95 % numbers just means that for 90/95% of the time you were at OR BELOW that number whether it is pressure or leak numbers.
It's NOT where you spent 90/95% of the night...but people tend to forget the "or below" part of the definition.

Here's one of my old reports where my pressure didn't change much at all and the 90% pressure is barely above my minimum of 10 cm.

Image

And here's one where the 90% pressure climbs on up there. This wasn't extremely rare for me......but then not horribly common either...maybe once or twice a week. Usually in what appears to be the time frame for REM stage sleep where my OSA is worse.

Image

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Re: What's the point?

Post by palerider » Fri Sep 19, 2014 7:22 pm

as to what the point of the 90/95% number... I guess it's a statistics kind of thing.

your max may have been a brief spike, so it's more of an anomoly and best ignored, whereas the 95% is a better representation of your high end values.

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Re: What's the point?

Post by sleepy1235 » Fri Sep 19, 2014 7:53 pm

A 90% number or 95% number is a very useful number in many cases and communicates very different information than the mean or median.

This is because distributions can be non-gaussian. Defects, errors, failures, etc. tend to have very non-gaussian behaviors.

As a hypothetical example in applying it to leaks. It might be that a few times during the night you had some high leaks for short periods of time, but overall you didn't have any leaks of consequence.

The mean would give you a value suggesting that you don't have a leak problem. The 95% value would indicate if you had occasional leaks.

Let's lay about 94% of the time the leak was from 9 to 10, and 6% of the time it was 20. The leaks would contribute only 1.2 to the average figure and the mean would say you were about 10 to 11. the 95% value would be 20.

So it would flag you that you had something going on.

It would be much better if the software actually gave you a histogram of your results. Or some better binning of the data. It wouldn't take a lot of programming to give both the mean and median as well as a typical distribution data, 5%, 10%, 25%, 50% (median), 75%, 90%, and 95%. It is just a few lines of code and not much computing problem. The stats for sleep software are like something out of the 1980s.

I use statistics in my job analyzing data and Resmed is like the stone age.

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Re: What's the point?

Post by SleepyEyes21 » Sun Sep 21, 2014 4:12 pm

palerider wrote:
SleepyEyes21 wrote:What completely confuses me in the settings is the 'periodic breathing' number; isn't periodic breathing what we are doing in between apneas?

I'd appreciate what others can tell us about both of these features
I could try and explain the 90 or 95% numbers, but robysue does a much better job explaining what they mean.

as to the periodic breathing, the online medical dictionary defines it thusly: periodic breathing - abnormal respiration in which periods of shallow and deep breathing alternate.

as opposed to regular breathing where your breaths are pretty regular.

make sense?
Thanks for the info and link, PR.. lots to digest and will have to read and re-read to remember and make sense of it all

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Re: What's the point?

Post by SleepyEyes21 » Sun Sep 21, 2014 4:19 pm

Pugsy wrote:For the newbies....the 90/95 % numbers just means that for 90/95% of the time you were at OR BELOW that number whether it is pressure or leak numbers.
It's NOT where you spent 90/95% of the night...but people tend to forget the "or below" part of the definition.

Here's one of my old reports where my pressure didn't change much at all and the 90% pressure is barely above my minimum of 10 cm.

Image

And here's one where the 90% pressure climbs on up there. This wasn't extremely rare for me......but then not horribly common either...maybe once or twice a week. Usually in what appears to be the time frame for REM stage sleep where my OSA is worse.

Image
Hi Pugsy - thanks for your input. Your explanation is completely opposite of how the manual explains it.. which now leads me also to ask 'what's the point?'

(sorry for the delay in response - dealing with a migraine this weekend )

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Re: What's the point?

Post by raftergirl » Sun Sep 21, 2014 7:38 pm

My user manual for the PR REMStar System One Auto explains 90% the same as how Pugsy explained it.

"90% pressure is defined as the pressure at which the device spent 90% of the session time at or below."

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Re: What's the point?

Post by SleepyEyes21 » Sun Sep 21, 2014 8:08 pm

raftergirl wrote:My user manual for the PR REMStar System One Auto explains 90% the same as how Pugsy explained it.

"90% pressure is defined as the pressure at which the device spent 90% of the session time at or below."
Hi raftergirl - maybe I should say ' the way I understand it from how it is explained in the manual.'
Thanks for the clarification!

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