How accurate are readings off the Cpap machine?

Maple Leaf · Post by **Maple Leaf** » Sat May 22, 2010 12:45 pm

I don't have access to my EncorePro for awhile as my new PC is a bit stubborn. Anyway, I've been clearing the data off my unit each night to get a fresh overnight reading, rather than the 7 day or 30 day avg. I'm using the Activia LT and the manual indicates a leak rate of 34 l/m @ 12cm. This morning my unit showed a reading of 26 l/m. I know there is no restrictions as far as my mask venting properly (plugged vent holes, mask buried in pillow etc). Just wondering if maybe my mask is not allowing the proper vent rate, or, perhaps my unit is not providing an accurate reading? Any thought appreciated.

Regards,
Rick

Maple Leaf · Post by **Maple Leaf** » Sun May 23, 2010 4:09 pm

Anybody????? Still showing a leak rate this morning of 26 lpm and yet my mask should be venting at 34 lpm?

Nord · Post by **Nord** » Sun May 23, 2010 4:43 pm

Maple Leaf wrote:I don't have access to my EncorePro for awhile as my new PC is a bit stubborn. Anyway, I've been clearing the data off my unit each night to get a fresh overnight reading, rather than the 7 day or 30 day avg. I'm using the Activia LT and the manual indicates a leak rate of 34 l/m @ 12cm. This morning my unit showed a reading of 26 l/m. I know there is no restrictions as far as my mask venting properly (plugged vent holes, mask buried in pillow etc). Just wondering if maybe my mask is not allowing the proper vent rate, or, perhaps my unit is not providing an accurate reading? Any thought appreciated.

Regards,
Rick

Hi Rick...

I'm not sure what the variance is for your machine but I think you will find that the software allows for plus or minus a percentage.
The mask also has a manufacturing variation.
Still that would not account for a difference of 8 l/min...
I think Respironics might point to the phase that it is an estimate based on all other criteria.
Only other possibility is the math you're doing.

At the end... that is one great leak rate with the Activa.

Nord

Wulfman · Post by **Wulfman** » Sun May 23, 2010 4:44 pm

From what I've read, the LCD information does not always coincide with the information on the reports.
I can't speak from experience with the M Series, but I do know (from experience) that with the Legacy models, the numbers can vary according to which firmware level they have......or at least from the ones I have. With my fixed pressure of 12 cm. and the mask I use, my leak rate should be in the 39 - 40 range. I have one REMstar Auto with 2.8 firmware that consistently reports leak numbers in the low 30's and one REMstar Auto with 2.5 firmware that shows leak numbers several LPMs higher than 40.

Den

Maple Leaf · Post by **Maple Leaf** » Sun May 23, 2010 5:08 pm

Okay, thanks guys for your replies. I was just a bit worried that my Co2 exchange was not being met..... need my few brain cells that remain!

Thanks again,
Rick

Nord · Post by **Nord** » Sun May 23, 2010 5:11 pm

Maple Leaf wrote:Okay, thanks guys for your replies. I was just a bit worried that my Co2 exchange was not being met..... need my few brain cells that remain!

Thanks again,
Rick

If you still up to the math test... some of your cells seem to be left...

Nord

PST · Post by **PST** » Sun May 23, 2010 5:31 pm

What is the basis for using 12 cm as the reference pressure for the expected vent rate? If you are using your unit in fixed pressure mode at 12 cm, then the difference is hard to explain. I guess maybe expiration relief could result in pressure that averages a touch below 12 cm, but that seems minor. On the other hand, if the machine is in auto mode and 12 cm is only an average pressure as reported, maybe there is some deviation from the expected vent rate for that average because of different kinds of averaging, or because the change in expected vent rate as pressure changes is nonlinear. The latter could happen if a minute spent 1 cm above average increases the vent rate less than a minute spent 1 cm below average decreases it. If using auto, you might test the machine for a few hours at constant pressure to see if it matches the expected vent rate.

Maple Leaf · Post by **Maple Leaf** » Sun May 23, 2010 5:36 pm

PST wrote:What is the basis for using 12 cm as the reference pressure for the expected vent rate?

My titrated pressure 2 years ago was 11 cm. Since managing my own therapy with EncorePro, I have been able to reduce my AH1 down from 2.5 to 0.9. This has been achieved by running my unit in straight cpap @ 12 cm with no flex feature.

Regards,
Rick

SleepingUgly · Post by **SleepingUgly** » Tue May 25, 2010 7:42 am

Not to hijack, but along the same lines... Last night my maximum leak rate was 2.4 (yes, I got the decimal in the right place!) with the Activa-LT at Auto 9-13, with a median pressure of 9.7 and a maximum pressure of 11.7. How could I have a median leak rate of 0, a 95% leak rate of 0, and a maximum leak rate of 2.4?!!

Nord · Post by **Nord** » Tue May 25, 2010 7:59 am

SleepingUgly wrote:Not to hijack, but along the same lines... Last night my maximum leak rate was 2.4 (yes, I got the decimal in the right place!) with the Activa-LT at Auto 9-13, with a median pressure of 9.7 and a maximum pressure of 11.7. How could I have a median leak rate of 0, a 95% leak rate of 0, and a maximum leak rate of 2.4?!!

Hi sleeping...

You can. You leaks are excellent as the 0.0's indicate.
You just either took the mask off before shutting down the machine or made some quick adjustments at one point during the night.
For a very short period of time the leak rate was very high... for 95% of the night it was perfect.

Nord

SleepingUgly · Post by **SleepingUgly** » Tue May 25, 2010 8:13 am

Nord wrote:
SleepingUgly wrote:Not to hijack, but along the same lines... Last night my maximum leak rate was 2.4 (yes, I got the decimal in the right place!) with the Activa-LT at Auto 9-13, with a median pressure of 9.7 and a maximum pressure of 11.7. How could I have a median leak rate of 0, a 95% leak rate of 0, and a maximum leak rate of 2.4?!!
Hi sleeping...

You can. You leaks are excellent as the 0.0's indicate.
You just either took the mask off before shutting down the machine or made some quick adjustments at one point during the night.
For a very short period of time the leak rate was very high... for 95% of the night it was perfect.

Nord

I'm totally confused... My leak rate was HIGH? At a pressure of 10, the intentional leak rate is 31. My maximum was 2.4.

see chart: http://www.resmed.com/au/assets/documen ... nz_eng.pdf

What am I confused about? Is my machine suddenly deciding to subtract out the intentional leak rate? It wasn't doing that the day before!

Nord · Post by **Nord** » Tue May 25, 2010 8:21 am

SleepingUgly wrote:
Nord wrote:
SleepingUgly wrote:Not to hijack, but along the same lines... Last night my maximum leak rate was 2.4 (yes, I got the decimal in the right place!) with the Activa-LT at Auto 9-13, with a median pressure of 9.7 and a maximum pressure of 11.7. How could I have a median leak rate of 0, a 95% leak rate of 0, and a maximum leak rate of 2.4?!!
Hi sleeping...

You can. You leaks are excellent as the 0.0's indicate.
You just either took the mask off before shutting down the machine or made some quick adjustments at one point during the night.
For a very short period of time the leak rate was very high... for 95% of the night it was perfect.

Nord
I'm totally confused... My leak rate was HIGH? At a pressure of 10, the intentional leak rate is 31. My maximum was 2.4.

see chart: http://www.resmed.com/au/assets/documen ... nz_eng.pdf

What am I confused about? Is my machine suddenly deciding to subtract out the intentional leak rate? It wasn't doing that the day before!

Well... you don't state whether its l/min or l/sec or which machine you use... so I assumed you were stating l/sec because you sounded worried...
Your confusion... led to mine.

SleepingUgly · Post by **SleepingUgly** » Tue May 25, 2010 9:34 am

Nord wrote:Well... you don't state whether its l/min or l/sec or which machine you use... so I assumed you were stating l/sec because you sounded worried...
Your confusion... led to mine.

I just checked and it's l/min. Does that change anything?

Nord · Post by **Nord** » Tue May 25, 2010 10:39 am

Yes... it changes me thinking that it was a large leak range.
I assume you have a ResMed machine which takes into account the type of Mask you have and subtracts it from the overall leak.
That means since you have an Activa LT and the leak rate that you have selected is correct for Nasal (example??) then...
you should expect that a perfect night in a perfect world... your leak rate should be Median 0.0; 95 Percentile 0.0; and Maximum 0.0.
Since you have most of a perfect world and 2.4 l/min leak for only your maximum...
because you adjusted the mask once or twice... or had a small facial leak briefly and you corrected it.

IMHO... I never worry about maximum leaks at all... I want 95% to be 0.0 and I'm happy (so is the therapy)

Nord

edited for spelling...

How accurate are readings off the Cpap machine?

How accurate are readings off the Cpap machine?

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