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[Equipment] Mask Flow Rate Question
#1
Mask Flow Rate Question
Does anyone know how the mask manufacturers decide how much air to purposely vent out their masks?  I am not talkng about mask leaks.  In a former life I worked as an engineer and can kind of see how this would be tricky.  Too little venting and you suffocate or cause a mask leak or too much and you make your masks noisy and cause the motor to work harder to maintan high pressure settings.

There has been a lot of duscussion on the ResMed Quiet Air elbow and whether that change started causing user problems and whether the sound dampening collar they added was being contaminated.  I started using the Quiet Air elbow unknowingly about four months ago.  I only noticed that it was different when I couldn't feel the air exiting.  Resmed announced the change publicly over a year ago but it appears they are touting the fact that it is quieter.  Canuckguy posted photos of the old elbow and the Quiet Air elbow with the diffuser removed.  It's pretty obvious that the old standard elbow had larger holes.

I would like to find a full face mask with the higher vent rate, beacuase I think the new quiet air elbow is causing problems.  Last night I went back to an old Ultra Mirage mask with silicone seals and the adjustable forehead bar.  It is now obsolete but it has a healthy flow that I can feel and hear.  I thought I found the flow settings for the mask in the F20 written manual.  They had a specifications page with a presssure comparison between the "standard" elbow and the Qiuiet Air elbow.  They were different but after looking up the units (dBa) I think they were only talking about sound levels.

I have seen much decreased sound levels in the machines I have had over the years.  There being commercial competition between manufacturers I am beginning to suspect that quiet outweighs performance.  Anybody know where to get these specifications?  They must be proprietary if they don't show up directly in the manufacturers data sheets.
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#2
RE: Mask Flow Rate Question
I may have answered my own question.  I was looking at the user manual again and missed the flow rate chart on page 11.  I don't know how old this manual is but it's old enough to show both the Quiet Air elbow and the Standard elbow on the back cover.  It has the flow rate chart I was looking for:

Pressure              Flow Rate
(cm H20)               (liter/minute)

10                             37
16                             48
24                              60

It's odd that it doesn't distinguish between the two elbows.  It makes me think what I had assumed originally that the hole patterns for the two are the same.  That doesn't explain the comparison photos that Canuckguy made.

If I could only get the comparison data on the FFM from Philips.  I'll try that online.
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#3
RE: Mask Flow Rate Question
That's ok,  now read about Treatment-Emergent Central Apnea http://www.apneaboard.com/wiki/index.php...tral_Apnea
then about EERS modification which actually blocks those holes to minimize Treatment_Emergent Central Apnea.
Fred Bonjour - Project Manager and Lead Tester for OSCAR - Open Source CPAP Analysis Reporter 
OSCAR

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#4
RE: Mask Flow Rate Question
Thanks again Bonjour.  I found the Philips data online as well as another chart with all the masks that ResMed makes on one chart.  The manufacturers pretty much use the same flow rates for all their masks.  The difference between Philips and ResMed is pretty small.  For example Philips masks vary between 22 and 30 liter/minute at 10 cm-H20 of pressure.
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