Reported mask pressure 'capped' to 15.88 cmH20 by OSCAR?

[chrisj]

Hi all,

Just a quick one - my Dreamstation autoSV is set with an EPAP min of 9, ps 3.0 -> 21, yet no matter what happens OSCAR is showing 15.88 as being as high as the 'mask pressure' ever goes - I know it goes higher than that though as the machine itself says it does. If I stop breathing for a lengthy period eventually it'll max out at 30, but OSCAR only ever shows 15.88 max.

Is this a bug? or maybe I'm misinterpreting the information. Screenshot attached.

Thanks
Chris

[loggerhead12]

I believe the machine reports pressure, not mask pressure. They are not the same thing.

[Dog Slobber]

Oscar does not actually report the "Max" settings, it reports the 99% value. This way potential extreme outliers are not reported.

[chrisj]

I believe the machine reports pressure, not mask pressure. They are not the same thing.

They are the same thing as it's a closed loop system. If I test the output with a manometer it's exactly consistent no matter what level of additional pressure relief I add to the circuit.

To clarify, even if what you were saying were true, the pressure reported by the machine could only ever be higher than that actually at the mask due to leak rate. I've done tests where I deliverately let the machine push to 30cmH2O yet in OSCAR this is still reported as 15.88

[chrisj]

Oscar does not actually report the "Max" settings, it reports the 99% value. This way potential extreme outliers are not reported.

Pretty certain that's not it in this case, as much time is spent signifincantly over 15.88 - way more than could be considered outliers (sometimes over 30 mins in a night).

I also have a Resmed S9 VPAP Adapt and Oscar reports the exact correct figures for that machine (up to the full 25cm h2o)

Thanks

[loggerhead12]

They are the same thing as it's a closed loop system.

I don't think so. The two numbers are tracked separately by the machine and the software. Why do that if they are the same?

To clarify, even if what you were saying were true, the pressure reported by the machine could only ever be higher than that actually at the mask due to leak rate. I've done tests where I deliverately let the machine push to 30cmH2O yet in OSCAR this is still reported as 15.88

That is a whole other issue and might indicate a problem with your machine or the software.

[palerider]

I believe the machine reports pressure, not mask pressure. They are not the same thing.

They are the same thing as it's a closed loop system. If I test the output with a manometer it's exactly consistent no matter what level of additional pressure relief I add to the circuit.

To clarify, even if what you were saying were true, the pressure reported by the machine could only ever be higher than that actually at the mask due to leak rate. I've done tests where I deliverately let the machine push to 30cmH2O yet in OSCAR this is still reported as 15.88

Explain how you got the machine to "push to 30cmH2O"?

[ChicagoGranny]

chrisj wrote: ↑Mon Apr 05, 2021 1:37 pm
They are the same thing as it's a closed loop system.

I don't think so. The two numbers are tracked separately by the machine and the software. Why do that if they are the same?

The machine doesn't measure mask pressure. It can't - there are no pressure sensors on masks.

A factored number is programmed into the machine or OSCAR. Meaningless. I've always ignored it.

[palerider]

chrisj wrote: ↑Mon Apr 05, 2021 1:37 pm
They are the same thing as it's a closed loop system.

I don't think so. The two numbers are tracked separately by the machine and the software. Why do that if they are the same?

The machine doesn't measure mask pressure. It can't - there are no pressure sensors on masks.

A factored number is programmed into the machine or OSCAR. Meaningless. I've always ignored it.

*mask pressure* with a resmed machine (perhaps not applicable here) is a direct readout of *measured pressure* at the machine compensated for pressure drops caused by the humidifier, hose, antibacterial filters and the mask, whereas "pressure" is the *desired pressure*.

I'm not sure how Philips does "mask pressure" since the only machine that reports it (I think) is their AutoSV (and maybe AVAPS).

[ChicagoGranny]

..
compensated for pressure drops caused by the humidifier, hose, antibacterial filters and the mask,

... and cough drops.

[SleepGeek]

*mask pressure* with a resmed machine (perhaps not applicable here) is a direct readout of *measured pressure* at the machine compensated for pressure drops caused by the humidifier, hose, antibacterial filters and the mask, whereas "pressure" is the *desired pressure*.

antibacterial filters also affect (dampen) some events because of these drops across the filter.
IOW - your AHI may not read correctly with an *Inline Filter* - it can read lower.

I don't know of any way the cpap will know IF there is an antibacterial filter installed in order to compensate the reading.
https://www.philips.com/c-dam/b2bhc/mas ... NTQwOC42MA

[Pugsy]

I don't know of any way the cpap will know IF there is an antibacterial filter installed in order to compensate the reading.

ResMeds do
see page 16 of the manual
https://www.respshop.com/manuals/ResMed ... %20her.pdf
also mentioned on page 13 and what it can do to results and what they recommend to use in terms of resistance.
This is of course the AirSense 10 manual...but the S9 models had the same yes/no choice in their menu.
I assume that since there is a choice then they must compensate in some fashion but I have never seen it documented.

Of course maybe a moot point when talking about Respironics machines (which the OP here has) as I don't think there is a choice but my memory may have failed me.

To the OP here....about all you can do is use Encore Pro and see what it says for mask pressure. Maybe a bug in OSCAR software calculations for the DreamStation ASV for all I know. Encore Pro is available by request at the apneaboard forum but it is Windows only software and a real bitch to install and use.

[chunkyfrog]

Apples and oranges are hard to compare--they will both roll off a dodgy table,
and are too delectable to resist.

[chrisj]

chrisj wrote: ↑Mon Apr 05, 2021 1:37 pm
They are the same thing as it's a closed loop system.

I don't think so. The two numbers are tracked separately by the machine and the software. Why do that if they are the same?

The machine doesn't measure mask pressure. It can't - there are no pressure sensors on masks.

A factored number is programmed into the machine or OSCAR. Meaningless. I've always ignored it.

Of course it measures mask pressure - the measurement is taken at the machine itself... the air pressure within the hose, and within the machine body where the sensor is, is equal to that within the mask... it's how the machine compensates for mask leaks by increasing the pressure when it senses a drop.

Mask pressure is the only figure that matters, as that's what a physician's prescribed setting pertains to.

[chrisj]

I believe the machine reports pressure, not mask pressure. They are not the same thing.

They are the same thing as it's a closed loop system. If I test the output with a manometer it's exactly consistent no matter what level of additional pressure relief I add to the circuit.

To clarify, even if what you were saying were true, the pressure reported by the machine could only ever be higher than that actually at the mask due to leak rate. I've done tests where I deliverately let the machine push to 30cmH2O yet in OSCAR this is still reported as 15.88

Explain how you got the machine to "push to 30cmH2O"?

It's ASV, so if no breaths are taken it will progessively attempt to deliver them at increasing pressure levels until it tops out - hence by simply blocking the hose at the mask the machine will revert to it's backup rate, and progressively deliver stronger and stronger breaths at 12 BPM (iirc) until it hits 30cmH2O - the max output pressure of the DreamStation BiPAP autoSV.