Bias Flow Rate ?

Robbie · Post by **Robbie** » Fri Mar 14, 2008 9:31 am

Sorry to beat a dead horse here with repeated/related posts, but I'm having a hard time "connecting the dots". I switched from a mask my machine recognized to one that it didn't (different manufacturers). I've set the mask type on my CPAP (ResMed S8 Elite) to "Standard". I noticed the leak rate went up drmatically from my old mask (which was recognized by the machine - same manufacturer).

I've done some research based on some tips provided here and have learned that the "Bias Flow Rate" for my mask at my pressure is 31.5 L/min. I'm guessing this is the amount of air that is known to pass out of the diffuser (a leak by design?) at my pressure.

Am I correct in assuming that if I subtract the Bias Leak Rate (a constant) from the leak rate my machine displays at the end of the night, that I'll get the "real" leak rate? (which now appears to be minimal if the above is true). I'm guessing the "Standard Mask" setting means, among other things, that the S8 will make no attempt to factor in the known leak or Bias Flow Rate when it calculates my leak rate since it can't possibly know what that bias flow rate is.

Ami I getting warm? Do I at least have the correct understanding that the Bias Flow Rate is a known, calculated leak - meaning the air that blwosw through the diffuser on a mask?

Wulfman · Post by **Wulfman** » Fri Mar 14, 2008 10:53 am

Robbie,

I have a .jpg file that one of our members created a couple of years ago.....which has the S8 mask settings and their flow rates at different pressures.
If you'll PM me with your e-mail address, I'll send it to you. I'm a little busy to convert it to text at the moment.

You didn't say what your pressure was, but the "Standard" setting has an expected vent flow rate of 30 at a pressure of 8. A pressure of 10 is 33.

Den

Wulfman · Post by **Wulfman** » Fri Mar 14, 2008 10:56 am

I'll make it easier than that......

Here's the link to the chart that "Bob..." created.

viewtopic.php?t=13659&highlight=

This way, others can save it to their computers for further reference.

Den

DreamStalker · Post by **DreamStalker** » Fri Mar 14, 2008 2:13 pm

To get the true or actual or real leak rate ...

Add the leak value from the LED to the appropriate leak rate (based on the mask setting you have for your Elite machine) in Bob's table that Den provided a link to.

For example:

Your mask setting is set to "STANDARD"
Your pressure is set to 10 cm
Your LED value is 0.1 L/sec

"Real" leak rate = 33 L/min + (0.1 L/sec * 60 sec) = 39 L/min
...from Bob's table ^.........unit conversion ^

ResMed tried to take the math out of their equipment (I guess dumb DMEs are not that good at math ... perhaps why their stuff is over priced) but assumed only older ResMed masks would be used.

Bob's table -