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Understanding leak numbers
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Dawei Offline

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Posts: 342
Joined: Feb 2012

Machine: ResMed S9 AutoSet
Mask Type: Other
Mask Make & Model: Respironics "FitLife"
Humidifier: H5i
CPAP Pressure: 10-20
CPAP Software: ResScan SleepyHead

Other Comments: Began CPAP in 2006; spent the first 6 years with a "brick"

Sex: Male
Location: Western North Carolina

Post: #1
Understanding leak numbers
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?
03-23-2012 08:01 AM
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jdireton Offline

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Posts: 149
Joined: Feb 2012

Machine: Resmed S9 Elite
Mask Type: Nasal mask
Mask Make & Model: Resmed Mirage FX
Humidifier: Resmed H5i
CPAP Pressure: 12
CPAP Software: ResScan

Other Comments: ClimateLine Hose

Sex: Male
Location: Florida

Post: #2
RE: Understanding leak numbers
(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!
03-23-2012 08:39 AM
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JumpStart Offline

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Posts: 297
Joined: Feb 2012

Machine: ResMed S9 Autoset
Mask Type: Full face mask
Mask Make & Model:
Humidifier: ResMed H5i
CPAP Pressure: 10 - 20 (auto range)
CPAP Software: ResScan SleepyHead

Other Comments: ResMed Mirage Quattro

Sex: Male
Location: Houston, Texas

Post: #3
RE: Understanding leak numbers
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!
03-23-2012 08:41 AM
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shanzlik Offline

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Posts: 22
Joined: Feb 2012

Machine: ResMed S9 Autoset
Mask Type: Nasal mask
Mask Make & Model:
Humidifier: ResMed H5i
CPAP Pressure: 12
CPAP Software: ResScan SleepyHead

Other Comments:

Sex: Male
Location: Texas

Post: #4
RE: Understanding leak numbers
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.
(This post was last modified: 03-23-2012 01:10 PM by shanzlik.)
03-23-2012 01:04 PM
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Dreamcatcher Offline

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Posts: 899
Joined: Mar 2012

Machine: Resmed Autoset Spirit II with Quattro F/F & FX Masks
Mask Type: Full face mask
Mask Make & Model:
Humidifier: H4i
CPAP Pressure: 10 - 18 cmH20 (auto range)
CPAP Software: ResScan SleepyHead Other Software

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Sex: Male
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Post: #5
RE: Understanding leak numbers
Wonder why they changed from L/s to L/m when the S9 came out Im still using L/s on my S8 Resmed
03-23-2012 03:31 PM
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Netskier Offline

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Posts: 125
Joined: Mar 2012

Machine: Resmed S9 Autoset, Mirage Quattro Full-Face Mask, Slimline tube.
Mask Type: Full face mask
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Humidifier: H5i, but not being used.
CPAP Pressure: 6-13 cm H20; Ramp OFF.
CPAP Software: SleepyHead

Other Comments: Currently studying Reversal of Aging.

Sex: Male
Location: Los Angeles South Bay, about 20 min South of Downtown LA.

Post: #6
RE: Understanding leak numbers
(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
03-23-2012 03:37 PM
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