trialing masks - pressure requirements, What's happening?

[SarcasticDave94]

That is probably the same thing the 10 series has, it's intended to blow CPAP pressure to test the mask fit. I personally always got the green but had major leaks overnight reported in OSCAR. My last machine was the ASV and it sometimes went up IPAP 25, so I had a leak control issue due to that and I couldn't use the much less invasive nasal pillows.

[TecFive]

To Wondering:
The criterion you are using, % of time above the 24 l/min threshold, may set an overly conservative "red line".
On the other cpap forum, the moderator there suggests that 24 l/min might be too low, she sets her threshold at approx 35 l/min, and says that accuracy of the system begins to degrade at 24 and becomes progressively worse. *

An interesting experiment...
see what your data tells you if you use (say) 35 l/min as the threshold for % of time above threshold.

* no one seems to have an answer as to how quickly things fall apart above 24 l/min

[SarcasticDave94]

The problem with resetting the 24 L/min red line threshold is the 24 redline is ResMed's set threshold. What I'm getting from that is ResMed is saying over the 24 L/Min unintentional leak threshold, the blower cannot keep up with that amount of leaks.

If one looks at Philips Respironics machines in OSCAR, you'll probably still see 2 leak rate lines in the leak chart. The lower will indicate intentional (expected) leaks, with the higher value trace line indicating unintentional leak. With the ResMed, it doesn't report intentional leaks, only unintentional leaks, labeled large leak.

Yes I'm aware ResMed and PR are completely different machines, just making mention these machines do have intentional and unintentional leak values. Even the PR has its own leak redline which means its blower motor cannot keep up with the high leaks.

Here's a silly illustration: think of your car tire, imagine it needs air added so you hook up a pump, the pump's value to inflate is X on a tire without puncture, but with a big hole in the sidewall your pump cannot inflate the tire due to the fact that pump isn't strong enough to inflate the tire with a hole in it.

With a CPAP that is attempting to blow into your lungs with very high unintentional leaks, that's akin to the tire with the hole.

[TecFive]

@ Dave,
Not such a silly analogy, the size of the hole (corresponding to the leak of the mask) will influence the ability of the tire pump to achieve the desired  pressure, and if the hole (mask leak) is sufficiently large, the tire will never pump up and possibly deflate to near zero regardless of the  blower (tire pump) ability to supply air.
I would concur.

However actual Oscar plots seem to show that large leaks (within reason) are accommodated by the Resmed blower. 
In the following plot, the pressure is in the 13+/- 1 range Prior to large leak However the large leak (topping out at approx 70 l/m) occurs, but the pressure range is still 13+/- 1cm . 
I would appear that the blower is capable of maintaining pressure, despite the significant leak.



   

[Wondering2]

To Tec5,
At your suggestion I've updated the excel page and added the % of time above 35 l/m.


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While working on leaks ( appointment pending with DME to check fitting), what I'm perplexed about is why the shift in pressures between the two masks? 

Both the F20 and the F30 masks have similar large leaks, so I would have expected similar pressure requirements.

The other thing that is troubling is that when the F30 leaked, I really knew it from the loud noise ( either putt-putting or a loud buzzing/humming - like a kazoo)
But I'm not hearing anything at all from the F20 mask. 

(last night I purposely got up every hour to check on my wife and any possible sounds from her mask - then compared my observations with her OSCAR report for leak at the time I was checking.  Nothing her mask was completely silent each and every time I checked.  But her OSCAR report showed she was above the leak threshold 90% of the night, and most significantly 4 of the five times I checked for any noise at all - and found none.