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Understanding leak numbers
#1
S9 machines use 24L/min as a defining point between OK and not OK leakage (Green vs. Red face icons), as we know. That 24 L/min point is also displayed on the ResScan graphs. Yet, the stats that are reported for Leak are the three figures: Median, 95th percentile, and Max.
How does one relate these two leak measurements? Is one more important than another?
Here's an example. For the past 7 nights, I've met the Green face 24L/min goal on all but one night. Meanwhile, for this same period, the Leak Median was 4.8; 95th percentile was 48 and the Max. was 68.4.
Put together, does this indicate leak is controlled to an acceptable level, or not? With numbers like these, can one feel that leakage is not affecting AHI readings to any significant level?
What say you, fellow hoseheads?

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#2
(03-23-2012, 08:01 AM)Dawei Wrote: Leak Median was 4.8
95th percentile was 48
Max. was 68.4

The median is where 50% of the number of readings are above it and 50% are below it. It is different than a mathematical average (mean) in that a small number of very high (or low) readings don't affect it much where they might impact an average.

95% is the same, 95% of the number of readings are below it and 5% are above it. 95% is a good estimate of a real maximum leak because events like mask dislocation due to movement, getting up at night, etc. do not change it dramatically. This is what I use.

The maximum leak, IMHO, is fairly useless. High maximums may tell you that you have dislocated your mask or even taken it off! Rescan has shown me that I occasionally go off therapy for an hour or more on some nights and I don't remember a thing. I've got my machine set up for auto ON/OFF, so my mask is falling off, or I'm taking it off, then putting it back on later. The machine just starts and stops automatically.

So, at least half the time you're doing great (median). Rescan can show you exactly whats going on minute by minute. With a 95% percentile of 48, I'd look at your mask, headgear, and even your sleeping movement habits. I think most of would agree lower leakage is better from an AHI standpoint!

Good Luck!
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#3
I am uncertain about some of the leak figures as well, but my take on one of them, Max, is that this figure is largely irrelevant IF you have to reseat your mask during the night. I have nothing to support my thought, but it seems that if you allow air to flow freely (as when you lift the mask to reseat), then you will undoubtedly increase the Max figure dramatically but with no real consequence. After all, you are awake when fiddling with the mask and OSA is when you are sleeping. And the more times you do this, the greater the increase in Max will be. As to the median, I would think that 4.8 is a wonderful figure - that means that exactly half the night your leaks were at that number or below. Anybody else with a more scientific idea, or one supported with more thought?
Breathing keeps you alive. And PAP helps keep you breathing!
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#4
My goal is to have the 95th percentile be no higher than the 24L/min as an average over time. If one or two days every so often don't meet that, no big deal. That way I know I am getting the best possible effects the vast majority of the time I am using it.

I like for the median to be around 5L/min, but I don't stress about it since the machine can adjust up to the 24L/min leak rate. I like it to be low because I have noticed that I feel like I have slept better on nights with lower leak readings. If my median crept back up to 10L/min or higher, I'd start adjusting things to try to get it back down.

It took a couple of weeks of experimenting and checking leak data daily until I found the sweet spot on mask strap tightness. I only check now about once a week.
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#5
Wonder why they changed from L/s to L/m when the S9 came out Im still using L/s on my S8 Resmed
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#6
(03-23-2012, 08:41 AM)JumpStart Wrote: I am uncertain about some of the leak figures as well, but my take on one of them, Max, is that this figure is largely irrelevant IF you have to reseat your mask during the night. I have nothing to support my thought, but it seems that if you allow air to flow freely (as when you lift the mask to reseat), then you will undoubtedly increase the Max figure dramatically but with no real consequence. After all, you are awake when fiddling with the mask and OSA is when you are sleeping. And the more times you do this, the greater the increase in Max will be. As to the median, I would think that 4.8 is a wonderful figure - that means that exactly half the night your leaks were at that number or below. Anybody else with a more scientific idea, or one supported with more thought?

Mask reseating is a pain while sleepy. Because of this, I have taken to pushing the start/stop button to stop the pressure, then pulling the hose off of the mask, going to pee, coming back, pushing the power button to repower, reconnecting the hose, and inhaling hard to restart the pressure. Never taking off the mask saves a lot of time.
My age is none of my mind's business. --- Netskier
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