Update on the mask leak rates data

As some folk will already know, I have posted at the
http://www.internetage.com/cpapinfo/
link, a menu item called 'Mask Leak Rates'

The input to this table came from a number of the regulars here (see the last column ).

What I am pleased to announce, is that I now have worked out a formula that will now allow me to plug in 3 good (accurate) values for any three known CMS settings and the formula accurately calculates all other values.

e.g. If we want to see the predicted leak rates for all CMS settings from 4 to 20 with 0.5 increments (i.e. CMS = 4.0, 4.5, 5.0, 5,5, 6.0 etc: etc:)
Then all I need is 3 of the known values (i.e. known data for the Resmed UMFF at 10,15&20cms: 10cms=29 lpm, 15cms=36 lpm, 20cms=43 lpm (lpm meaning litres of air per minute). This is published by Resmed.

When I take any 3 cms values & have the accurate lpm for those 3 cms values, the formula can calculate all the values in the range wanted, and quite accurately thus it can fill the tables out in full (some mask manufacturers only provide a few values - hybrid being a good example of sparse data) .

The problem with this though is that some masks aren't expected to operate at all the values the formula can calculate for that mask. e.g. some nasal prongs masks might blow apart at 25cms so the manufacturer never shows that as a valid value on their published charts. Some mfgr's just don't provide much data of any sort.

Additional info required ...
What many of us would really like to add as well is the deadspace volume for each mask (a hot topic among some of us here). Deadspace (IIRC ) is the volume of expired air that remains in the mask & gets re-breathed on the next inhalation. This air can make a difference to the benefit some people get from cpap therapy.

So, anyone who has any such data, or at least 3 accurate values for cms vs lpm for any mask not shown, please PM it to me or post it here.

DSM

Hey DSM,

Saw your post and realized you didn't have a dead space number for the Activa. Per the tech specs in the owners manual that number would be 127 ml.

On a sidenote, would you happen to have any mask leakage data on the Mirage Vista? Thanks, Ken

full (some mask manufacturers only provide a few values - hybrid being a good example of sparse data) .

The Hybrid comes with a graph. The graph line passes through all known CPAP pressures. It is linear above 10 cm/H2O. I thought you only needed 3 points? How many do you want?

Ken,

No the Mirage Vista is one I don't think I have - also thanks for the deadspace data for the Activa - I plan to add that tonight.

DSM

deadspace for the Hybrid is "less than 125 cm3".

Are you planning on filling in the table for all the pressures for the Hybrid?

Maryb

dsm, I've added (scanned charts) for a couple more masks:

http://www.tnlc.com/Lara/laura/osa/Mask ... sure-flow/

There are also charts up there for some of the masks others had already contacted you about, in case you want to fill in some more numbers.

Who's "RG"?

rested gal

Again thanks - I hope to do some more work on the chart tonight.

I can usually do the calc with just 3 points as the leak curve should be predictable & have no kinks in it (the cms increase is linear). It may be that I need lpm values from one low point (somewhere in the 4-8 cms range) + one medium (10-15 cms range) + one high (15-290 cms range) then calc everything between.

I need to double check the formula I did as I got some strange results
with some of the data for a few of the masks. Most come out as per mfg spec. I was even able to produce a curved line that matches some of the masks published curve lines.

Cheers DSM

(ps - RG will also get updated to rested gal )

DSM,

I was able to find the Mirage Vista curve at the Resmed web site, which is as follows:

http://www.myresmed.com/MyResMedUS/page ... 0210acRCRD

They have owners manuals/curves there for the Swift, Ultra Mirage II (nasal), the Vista, the Kidsta (pediatric use?), and the UMFF.

Here's my interpretation of the Vista curve:

Mask Brand = Resmed
Mask Model = Mirage Vista
Mask Type = (nasal)
CMS vs Leak Rate Table

CMS Leak Rate (lpm)
=== ==========
8.0------30.0
9.0------31.5
10.0----33.5
11.0----35.5
12.0----36.5
13.0----38.0
14.0----39.0
15.0----41.0
16.0----42.0
17.0----43.5
18.0----45.0
19.0----47.0
20.0----47.5

Dead Space for both the standard and deep is listed as 84 ml

Ken