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Query on higher pressure
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mdh235 Offline

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Post: #11
RE: Query on higher pressure
Yes, my CAs go up with the higher pressure, as do my hypos. I measure mask leakage purely by the annoyance factor, i.e. does air blowing in my eyes or by my cheeks wake me up. My measured leaks are still way beneath the Resmed threshold.

Perhaps I'm unclear about what the 95% number means. I thought it was the pressure that I spend 95% of the time at or below. It just seems strange to me that even with very low AHI numbers that number equals my maximum pressure, even on nights when I have zero events.
07-17-2014 09:52 PM
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diamaunt Offline

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Post: #12
RE: Query on higher pressure
Quote:
(07-17-2014 06:57 PM)mdh235 Wrote:  However, my machine seems to think the maximum pressure should be higher because my 95% number always equals my maximum pressure number,

I don't understand. To me all this means is that you're spending 5% of the time at your maximum pressure, and that's successfully treating your apneas and hypopneas.

if the 95% pressure = max pressure, how do you get only 5% of the night at max?
07-17-2014 10:15 PM
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PaytonA Offline
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Post: #13
RE: Query on higher pressure
Good question
07-17-2014 10:20 PM
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diamaunt Offline

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Post: #14
RE: Query on higher pressure
(07-17-2014 09:52 PM)mdh235 Wrote:  Yes, my CAs go up with the higher pressure, as do my hypos. I measure mask leakage purely by the annoyance factor, i.e. does air blowing in my eyes or by my cheeks wake me up. My measured leaks are still way beneath the Resmed threshold.

Perhaps I'm unclear about what the 95% number means. I thought it was the pressure that I spend 95% of the time at or below. It just seems strange to me that even with very low AHI numbers that number equals my maximum pressure, even on nights when I have zero events.

robysue, our resident math professor, wrote up a good "so you slept through basic statistics class" for those of us that forgot, or never knew, what it all means.

yes, it means you spent 95% or the night at or below that pressure, but, depending on how the actual numbers worked out, you could have spent most of the night at that pressure.... or only a little bit of it.

that one number, alone, or even with 95% and max doesn't tell the story... you have to look at the chart to see what it means.

more on the 95% here: http://adventures-in-hosehead-land.blogs...de-to.html
07-17-2014 11:57 PM
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Sleepster Offline
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Post: #15
RE: Query on higher pressure
(07-17-2014 09:52 PM)mdh235 Wrote:  Yes, my CAs go up with the higher pressure, as do my hypos.

Sometimes raising the pressure can raise the CA index. Your rise is so small that it's not significant anyway.

Quote:I measure mask leakage purely by the annoyance factor, i.e. does air blowing in my eyes or by my cheeks wake me up. My measured leaks are still way beneath the Resmed threshold.

So they don't interfere with your therapy but they do interfere with your sleep. I suppose you've tried a variety masks.

Quote:Perhaps I'm unclear about what the 95% number means. I thought it was the pressure that I spend 95% of the time at or below.

Right, so you spend 5% of the time above that pressure. But as you said the 95% pressure equals the maximum pressure, so you are spending 5% of the time at your maximum pressure.

And it's working well for you because your AHI is less than one. So, no worries. You said that raising the pressure increases the leaks so you may want to lower the pressure.

Quote:It just seems strange to me that even with very low AHI numbers that number equals my maximum pressure, even on nights when I have zero events.

Think of it this way. As your airway goes through the process of collapsing it first limits the flow of air, but not enough to be scored as a hypopnea. As it continues to collapse it would be a hypopnea then an apnea, provided it stayed there for at least 10 seconds. But what can happen is that you never get past the flow limitation stage because the machine raises your pressure.

That's why diamaunt mentioned flow limitation and snoring. They cause the machine to raise the pressure. If you look at the flow limitation graph and see spikes, then you can look at the simultaneous portion of the flow graph and you'll see misshapen waves, or simply waves with a slightly lower amplitude. Look at the snore graph, too. You should be able to see places where the pressure rose in response to these things that are not apneas or hypopneas so they don't count in the AHI.

Even though they don't count in the AHI they can be indicators that a apnea or hypopnea is about to occur. They can also interfere with sleep quality by causing arousals. They can also cause oxygen desats.

Sleepster
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07-18-2014 12:20 AM
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readyforsleep Offline

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Post: #16
RE: Query on higher pressure
I have a similar situation, my 95% pressure = my max pressure. I am slowly
lowering my high pressure- 20, then 19 and now 18.5. I'm going to see how low
I can go. My ahi remains the same - just under 5

2010 sleep study 63 AHI, 2014 3.0
07-18-2014 09:10 AM
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robysue Online
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Post: #17
RE: Query on higher pressure
Folks,

In this thread the following statements have been made about mdh235's 95% pressure levels:

(07-17-2014 06:57 PM)mdh235 Wrote:  My apnea is totally controlled with a maximum pressure of around 12.6 (typical nights AHI .2 to .6). However, my machine seems to think the maximum pressure should be higher because my 95% number always equals my maximum pressure number, so I've been experimenting by raising the upper limit until my 95% value is always below it. For me, that's a setting of 14.

(07-17-2014 09:40 PM)Sleepster Wrote:  I don't understand. To me all this means is that you're spending 5% of the time at your maximum pressure, and that's successfully treating your apneas and hypopneas.

Is there an issue with your sleep quality? Like are you waking frequently or feeling tired during the day?

(07-17-2014 09:52 PM)mdh235 Wrote:  Perhaps I'm unclear about what the 95% number means. I thought it was the pressure that I spend 95% of the time at or below.

(07-17-2014 10:15 PM)diamaunt Wrote:  
Quote:I don't understand. To me all this means is that you're spending 5% of the time at your maximum pressure, and that's successfully treating your apneas and hypopneas.

if the 95% pressure = max pressure, how do you get only 5% of the night at max?

(07-18-2014 12:20 AM)Sleepster Wrote:  
Quote:Perhaps I'm unclear about what the 95% number means. I thought it was the pressure that I spend 95% of the time at or below.

Right, so you spend 5% of the time above that pressure. But as you said the 95% pressure equals the maximum pressure, so you are spending 5% of the time at your maximum pressure.

It's time for a basic statistics lesson folks.

First let's review of the statistical definition of 95% for a set of data: When we say the 95% of a data set is 10, that means that 95% of the data points are LESS THAN or EQUAL TO the number 10. And this also means that remaining 5% of the data points are GREATER THAN or EQUAL TO the number 10. But we can't conclude how many data points are equal to 10.

Consider the following sets of data, all of which have twenty points and all of which have a 95% equal to 10. In each list, the bold, italicized 10 is the 19th number on our list of numbers and since 0.95*20 = 19, this bold italicized 10 is the 95% for the set of data.

Data set 1:
    6, 6, 6, 6, 7, 7, 7, 7, 8, 8, 8, 8, 8, 9, 9, 9, 9, 9, 10, 11
Note that 95% of the data points are AT or BELOW the value 10. The remaining 5% of the data (the 20th data point) happens to be strictly GREATER THAN 10 in this particular case.

Note that we're AT the value 10 for exactly 5% of the night, we're BELOW 10 for 90% of the night, and we're ABOVE 10 for 5% of the night.

Data set 2:
    6, 6, 6, 6, 7, 7, 7, 7, 8, 8, 8, 9, 9, 9, 9, 10, 10, 10, 10, 11
Note that 95% of the data points are AT or BELOW the value 10. The remaining 5% of the data (the 20th data point) happens to be strictly GREATER THAN 10 in this particular case.

Note that we're AT the value 10 for exactly 20% of the night, we're BELOW 10 for 75% of the night, and we're ABOVE 10 for 5% of the night.

Data set 3:
    6, 6, 6, 6, 7, 7, 7, 7, 7, 8, 8, 8, 8, 9, 9, 9, 9, 9, 10, 10
Note that 95% of the data points are AT or BELOW the value 10. The remaining 5% of the data (the 20th data point) happens to be EQUAL to 10 in this particular case. So the remaining 5% of the data are GREATER THAN or EQUAL TO the 95% value.

Note that we're AT the value 10 for exactly 10% of the night, we're BELOW 10 for 90% of the night, and we're ABOVE 10 for 0% of the night.

Data set 4
    6, 6, 6, 6, 7, 7, 7, 8, 8, 8, 8, 9, 9, 9, 9, 10, 10, 10, 10, 10
Note that 95% of the data points are AT or BELOW the value 10. The remaining 5% of the data (the 20th data point) happens to be EQUAL to 10 in this particular case. So the remaining 5% of the data are GREATER THAN or EQUAL TO the 95% value.

Note that we're AT the value 10 for exactly 25% of the night, we're BELOW 10 for 75% of the night, and we're ABOVE 10 for 0% of the night.

Data set 5
    6, 7, 8, 9, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 11
Note that 95% of the data points are AT or BELOW the value 10. The remaining 5% of the data (the 20th data point) happens to be strictly GREATER THAN 10 in this particular case.

Note that we're AT the value 10 for exactly 75% of the night, we're BELOW 10 for 20% of the night, and we're ABOVE 10 for 5% of the night.

Data set 5
    6, 7, 8, 9, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10
Since the bold, italicized 10 is the 19th number on our list of numbers and 0.95*20 = 19, this bold italicized 10 is the 95% for the set of data. 95% of the data points are AT or BELOW the value 10. The remaining 5% of the data (the 20th data point) happens to be EQUAL to 10 in this particular case. So the remaining 5% of the data are GREATER THAN or EQUAL TO the 95% value.

Note that we're AT the value 10 for exactly 80% of the night, we're BELOW 10 for 20% of the night, and we're ABOVE 10 for 0% of the night.

As these examples show, when the 95% = max value for a set of data, we can't conclude that we're at that max value for only 5% of the night.

A better way of thinking about 95% percentiles may be this:

You are AT or BELOW the 95% number for 95% of the time. And you are ABOVE the 95% for NO MORE THAN 5% of the time.

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(This post was last modified: 07-18-2014 11:20 AM by robysue.)
07-18-2014 09:47 AM
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robysue Online
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Post: #18
RE: Query on higher pressure
(07-17-2014 06:57 PM)mdh235 Wrote:  My apnea is totally controlled with a maximum pressure of around 12.6 (typical nights AHI .2 to .6). However, my machine seems to think the maximum pressure should be higher because my 95% number always equals my maximum pressure number, so I've been experimenting by raising the upper limit until my 95% value is always below it. For me, that's a setting of 14.

However, at the higher pressure my AHI goes up to over 1 and I have more leaks. Now I know that AHI is not bad, but it's odd that my machine thinks my pressure needs to be higher even though that results in more apneas.

I'm going to stick with it for a few days, but unless something changes I see no reason to keep my pressure so high.
You are right: There is no good reason to allow your pressure to go higher than you really need it to go to control your apneas. If you are MORE comfortable with a max pressure of 12.6, your AHI is well under 5.0 with a max pressure of 12.6, and you are FEELING GOOD in the daytime, there's really no good reason to increase the max pressure setting just because the machine is running at or near max pressure a lot of the time.

Think of it this way: If you were using fixed pressure, the fixed pressure has to be (just) high enough to properly control the apnea. And at fixed pressure, you're running at "max pressure" for 100% of the time.

mdh235 Wrote:However, my machine seems to think the maximum pressure should be higher because my 95% number always equals my maximum pressure number, so I've been experimenting by raising the upper limit until my 95% value is always below it. For me, that's a setting of 14.
and
(07-17-2014 09:52 PM)mdh235 Wrote:  It just seems strange to me that even with very low AHI numbers that number equals my maximum pressure, even on nights when I have zero events.
I usually have my max IPAP = 8, and on most nights both my 90% and median IPAP = 8. In other words, I'm running at max IPAP for at least 50% of the night most nights. Most people would say (in a knee jerk way): Your machine obviously needs to go higher. You need to increase the IPAP so you're not hitting the max setting so often.

And yet, with a max IPAP = 8, my apnea is controlled (AHI usually below 2.0, almost always below 3.0). And my stomach can tolerate this much pressure. And I'm feeling about as well as I ever feel in the daytime. (I have sleep issues other than my OSA to deal with, along with chronic migraines and vertigo.) And on three different titration tests my titrated IPAP was 7-8 cm.

I too have noticed that whenever I have experiment with increasing my max IPAP, the 90% (tracked by my machine) increases to the new setting until my max IPAP is up around 10 or 11cm. The AHI is no better with the higher max IPAP (and sometimes it's worse) and I feel WORSE with the higher max IPAP because aerophagia tends to set in and aggravates my sleep problems as well as makes me feel pretty miserable during the daytime.

In my case, what drives the continuing increase in IPAP pressures when I set my max IPAP above 8cm are flow limitations. Machines can respond pretty aggressively to minor flow limitations. And while some people are greatly bothered flow limitations, no matter how minor, other people are not. So if you're curious about why your S9 seems to keep the pressure at 12.6 for 5% or more of the typical night in spite of scoring no events, look at the flow limitation and snoring graphs. One or both of these probably explains what's going on.

And again: If you are MORE comfortable with a max pressure of 12.6, your AHI is well under 5.0 with a max pressure of 12.6, and you are FEELING GOOD in the daytime, there really is no good reason to increase the max pressure setting just because the machine is running at or near max pressure a lot of the time.

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(This post was last modified: 07-18-2014 11:29 AM by robysue.)
07-18-2014 10:22 AM
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diamaunt Offline

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Post: #19
RE: Query on higher pressure
(07-18-2014 09:47 AM)robysue Wrote:  Folks,

It's time for a basic statistics lesson folks.

Thank you for that, robysue, hopefully, some folks who've been making incorrect statements about the 95% will read your post, and stop spreading misinformation.

btw, you almost make math fun Smile
07-18-2014 06:15 PM
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zonk Offline

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Post: #20
RE: Query on higher pressure
(07-18-2014 06:15 PM)diamaunt Wrote:  Thank you for that, robysue, hopefully, some folks who've been making incorrect statements about the 95% will read your post, and stop spreading misinformation.
Others said the same thing about 95th percentile pressure in other threads but what RobySue say does carry more weight than the rest of us uneducated lots Coffee

Now about "S9 Sleep Quality", that was misinformation on my part but unintentionally, actually its not misinformation because misinformation when you say something knowingly to be untrue. That was what people were saying here and other forums by topnotch posters until you came along and said something different and debunked the myth
07-18-2014 07:20 PM
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