How does ResMed determine the intentional leak rate?

Followup of discussion here:

viewtopic.php?f=1&t=98205&p=916968#p916968

How does ResMed S9 determine the intentional leak rate?

We got into this discussion because ResMed S9 machines throw away any leak date below what it thinks the "intentional" leak rate is.

The question is how do they set this level?

I've always assumed the S9 machines assume a standard leak rate vs. pressure rate for all masks, perhaps based on the mask type you tell it. (FFM, nasal, pillows.)

It's been suggested that the machine does some sort of averaging operation.

What do you folks think?

Arch, one enters the type of mask used into the machine. ResMed assumes you are using a ResMed mask and the flow rates for their masks are known to them. The difference between the actual rate and the known rate for the mask selected is the leak rate. For a non-ResMed mask the user should choose a mask setting which has a flow rate close to that of the mask to be used (flow rates for most masks are published by the manufactures).
For example, if I choose Full Face on a Resmed machine and use a Simplus mask, the leak rate will appear to be lower than if I use a Quattro FFM because the Simplus has a lower static flow rate than the Quattro. They are subtracting or "throwing away" as you put it the higher flow rate of the Quattro making the Simplus look better.

Jay Aitchsee wrote:Arch, one enters the type of mask used into the machine. ResMed assumes you are using a ResMed mask and the flow rates for their masks are known to them. The difference between the actual rate and the known rate for the mask selected is the leak rate. For a non-ResMed mask the user should choose a mask setting which has a flow rate close to that of the mask to be used.

if one assumes that, then why does the leak rate on the treatment detail screen bounce around for the first few breaths, before stabilizing? (page 16 of the vpap auto clinician manual to see the screen I'm talking about, for example)

I'm sorry, Palerider, my comments were based on my experience with ResMed CPAP and APAP only and probably should have been so qualified. VPAP may well use a different methodology. But, if it does, why bother to enter the type of mask (pp 20 VPAP manual)? I would assume it takes some breaths to compute the actual net outflow from the machine and ResMed does say it is a 5 breath moving average (pp 17 VPAP manual).

Jay Aitchsee wrote:Arch, one enters the type of mask used into the machine.

Mine seems to only list mask choices as "full face, nasal, nasal ultra, and pillows."

I did a little googling last night and it looked to me like many of the ResMed masks had the nearly same leak rates. In particular I thought it showed the same graphs for Swift FX and the Quattro FFM, which seems counter intuitive. It was late, so I went to bed.

However, in the light of day, they're still pretty close.


Mask type leak at 4 20


Swift FX 20 49
P10 airfit for her 20 49
Mirage softgel 19 45
Mirage FX 19 45
Quattro Air 22 54
Mirage Quattro 22 54
Quattro FX 22 54

(Grumble, grumble, lousy proportional fonts with no fixed font choice. grumble grumble)

Philips masks vary considerably more. Makes sense. Without the crippled data the S9 records, Philips can design the flow rate for what works best, not having to artificially limit themselves to a fixed rate per mask type.

http://www.healthcare.philips.com/pwc_h ... 111027.pdf

archangle wrote:Mine seems to only list mask choices as "full face, nasal, nasal ultra, and pillows."

Yes, I think those are the standard choices now, although I believe my S8 was a little different, and I think they are based on ResMed masks only. Like you say, if you look at the published numbers or flow rate graphs, they are pretty close ranging from a low for the swift to highest for the Quattro family. And it does seem to be on purpose, shape not withstanding, it looks all ResMed FFM are going to have a leak rate of 22 - 54. I'm not sure if that's a good or bad thing, but it does seem it would limit design somewhat.
My Simplus, on the other hand, is rated at 22 - 50. Not much different than the Quattro, but the curve is a little flatter and I can tell which mask I'm wearing by looking at the leak line in ResScan. Overall, the Simplus line will be lower with a minimums of 0. The Quattro minimums, however, will be about 1.

archangle wrote:

Jay Aitchsee wrote:Arch, one enters the type of mask used into the machine.

However, in the light of day, they're still pretty close.
Mask type leak at 4 20
Swift FX 20 49
P10 airfit for her 20 49
Mirage softgel 19 45
Mirage FX 19 45
Quattro Air 22 54
Mirage Quattro 22 54
Quattro FX 22 54

(Grumble, grumble, lousy proportional fonts with no fixed font choice. grumble grumble)

why would different masks necessariliy have different vent rates? you can design the vent rate to be anything.

I don't have anything to cite at present, but I have a vague memory that the different mask settings were so the machine could factor in the dead space of the mask into it's calculations, which, if you think about it, makes far more sense, since full face, nasal, nasal ultra, and pillows will all have different relative volumes, yet will all be fairly close to each other.

palerider wrote:

archangle wrote:
why would different masks necessariliy have different vent rates? you can design the vent rate to be anything.

I don't have anything to site at present, but I have a vague memory that the different mask settings were so the machine could factor in the dead space of the mask into it's calculations, which, if you think about it, makes far more sense, since full face, nasal, nasal ultra, and pillows will all have different relative volumes, yet will all be fairly close to each other.

The higher the vent rate, the more air is "wasted." This increases the amount of water used by the humidifier, probably causes more noise, uses more power if you're using a battery, clogs the filters faster, makes it harder to heat the air if you want a heated hose, etc. It probably makes it more difficult to sense mask pressure and detect apneas, since more of the airflow is being vented instead of going to the patient.

The effect is multiplied because you have to design the vent to give adequate venting at the lowest pressure.

I don't know important this is in the real world, but there must be some importance to it, or they would just put a large standard size vent in all the masks. As it is, quite a few people find the air feels stale at pressures of 4. I presume this is because not enough air gets flushed out at low pressures to feel fresh. I've often thought there ought to be an optional extra hole or different mask for low pressure users to get better air flow. Or some sort of vent that has a more constant vent rate, but that sounds impractical.

How much venting is needed is probably a complicated question. There's a physiological question in terms of CO2/O2, and an issue of perceived staleness. Location of the vent, air inlet, and mask shape probably have a complicated effect as well.

Then there's this: viewtopic.php?f=1&t=98368&p=915020#p915022

Sludge wrote:

Jay Aitchsee wrote:

Sludge wrote:Note to self:

• F&P Simplus full face mask promotes CO2 washout when mouth breathing because of design;

Sludge, is this compared to other masks? That is, does the Simplus promote more CO2 washout when mouth breathing than other FFM? If so, does that mean mouth breathing Simplus users could be inclined to experience more Central Apneas than mouth breathing users of other types of FFM? Is this a result of purposeful design or happenstance?

With the exhalation ports at the top of the mask, if one has their mouth open, then the dead space of the oropharynx may be continually purged of CO2 (there's always ~30 LPM flow through there depending on pressure, see leak rate chart), thus creating a fertile ground for CompSAS.

ResScan Report Interpretation Guide, page 32

DEFINITIONS
Leak: This refers to unintentional leak,
which is the leak value after deduction
of the intentional mask leak.

ResScan Report Interpretation Guide, page 56

ResMed devices calculate unintentional leak:
Unintentional leak = Total leak – Intentional leak from mask CO2 washout
You have to set the mask type (default is nasal).

Jay Aitchsee wrote:ResScan Report Interpretation Guide, page 32

DEFINITIONS
Leak: This refers to unintentional leak,
which is the leak value after deduction
of the intentional mask leak.

The question is "do they use a table of leak vs. pressure or do they calculate the intentional leak rate by observing the airflow and/or pressure somehow."

Sorry Arch, I edited that while you were posting. I think it's pretty clear from the page 56 quote that they use the leak rate of the type of mask entered to obtain an intentional leak rate.

Jay Aitchsee wrote:Sorry Arch, I edited that while you were posting. I think it's pretty clear from the page 56 quote that they use the leak rate of the type of mask entered to obtain an intentional leak rate.

why would they use the phrase "deduction of the intentional mask leak" if they were simply doing a table lookup?

and, also, why does the treatment screen on the vpap adapt and vpap auto (at least) show the current leak rate jumping around for the first few breaths if they're looking it up in a table?

palerider wrote:why would they use the phrase "deduction of the intentional mask leak" if they were simply doing a table lookup?and, also, why does the treatment screen on the vpap adapt and vpap auto (at least) show the current leak rate jumping around for the first few breaths if they're looking it up in a table?

Nobody's looking anything up. I'm saying the values are part of the device's software. You tell the device what mask you have (set the mask type). The device uses preprogrammed values of intentional leak appropriate for that mask type. Each ResMed mask user guide states what mask setting to use for ResMed machines.
I said earlier that the unintentional leak rate is calculated over a 5 breath moving average, at least for VPAP machines, so I think it would be natural that it "jumped around" a little at the start.
See below.

Jay Aitchsee wrote:ResScan Report Interpretation Guide, page 32

DEFINITIONS
Leak: This refers to unintentional leak,
which is the leak value after deduction
of the intentional mask leak.

ResScan Report Interpretation Guide, page 56

ResMed devices calculate unintentional leak:
Unintentional leak = Total leak – Intentional leak from mask CO2 washout
You have to set the mask type (default is nasal).

Jay Aitchsee wrote: I would assume it takes some breaths to compute the actual net outflow from the machine and ResMed does say it is a 5 breath moving average (pp 17 VPAP manual).

Jay Aitchsee wrote:

palerider wrote:why would they use the phrase "deduction of the intentional mask leak" if they were simply doing a table lookup?and, also, why does the treatment screen on the vpap adapt and vpap auto (at least) show the current leak rate jumping around for the first few breaths if they're looking it up in a table?

Nobody's looking anything up. I'm saying the values are part of the device's software. You tell the device what mask you have (set the mask type). The device uses preprogrammed values of intentional leak appropriate for that mask type

that would be a lookup table, in the software, ie, looking it up. however, as archangel pointed out, most all the resmed masks have approximatly the same vent rate, so why would it matter what setting you used, if they all had the same vent rate?

Jay Aitchsee wrote: Each ResMed mask user guide states what mask setting to use for ResMed machines
I said earlier that the unintentional leak rate is calculated over a 5 breath moving average, at least for VPAP machines, so I think it would be natural that it "jumped around" a little at the start.
See below.

Jay Aitchsee wrote:ResScan Report Interpretation Guide, page 32

DEFINITIONS
Leak: This refers to unintentional leak,
which is the leak value after deduction
of the intentional mask leak.

ResScan Report Interpretation Guide, page 56

ResMed devices calculate unintentional leak:
Unintentional leak = Total leak – Intentional leak from mask CO2 washout
You have to set the mask type (default is nasal).

Jay Aitchsee wrote: I would assume it takes some breaths to compute the actual net outflow from the machine and ResMed does say it is a 5 breath moving average (pp 17 VPAP manual).

several other things are a 5 breath moving average when reported too, mv, rr, I:E

watching the treatment screen, it certainly LOOKS like it's homing in on a baseline, and, if it *DID* look up a value in a table in software, why wouldn't it already know what the leak rate would be, and not need to seek it out, or fluctuate the reading, when first starting up?