How does S9 record mouth breathing when using nasal mask

[TooGroggy]

Does the S9 record mouth breathing as central events when you are using a nasal mask?

[SleepingUgly]

I don't see why it would. I would think that if it's significant enough, it would show up in the leak rate; however, I don't find that the S9's reporting of leaks is particularly sensitive. I would not be 100% confident that I am NOT mouth leaking with a nasal mask if I based it only on the S9's leak rate.

[TooGroggy]

I guess I was figuring that since I wasn't breathing any of the air from the machine, the machine would conclude that I wasn't breathing and thus record a central event.

But to get to the point of the question, I am trying to determine how much mouth breathing I am doing to decide whether or not I should continue to use a nasal mask. Any thoughts on how one goes about ferreting that out of the data?

[SleepingUgly]

Do you wake up with your mouth dry?

[Janknitz]

The machines can't distinguish mouth breathing per se. You have to put two and two together:
1. You will see big leaks on the data.
2. You will experience symptoms of mouth breathing like a very dry mouth.
3. A bed partner (if you have one) might report a lot of noise.

[SleepingUgly]

There are times that my mask is leaking quite a bit and nothing registered on my leak graph. I don't know how long, and to what extent, there needs to be a leak before it registers on the graph. Also, if you're running in APAP mode, it might just ramp up in an attempt to compensate for a mouth leak, so you might not know if you have some degree of a mouth leak. It's a good question: How sensitive is the S9 to detecting mouth leaks sufficient enough to effect therapy? I don't know.

[SleepingUgly]

Hmmm... Having said that, I just saw in an IntelliPap manual:

Autotitrating units do not increase pressure in response to leaks because higher pressures could
cause higher leak rates. (Example: mouth breathers or excessive mask leak) Reporting leaks is
valuable to therapy analysis however, because leaks may distort some algorithmic functions.

My doctor had said that we wouldn't know for sure if I were mouth breathing with a nasal mask because the autopap would try to compensate for leaks, so either she was wrong, or this info is specific to Intellipap and doesn't necessarily apply to other machines. Guess it would be good if we could get our hands on S9 info in this regard... I have a feeling it may be classified info, though.

[robysue]

Hmmm... Having said that, I just saw in an IntelliPap manual:

Autotitrating units do not increase pressure in response to leaks because higher pressures could
cause higher leak rates. (Example: mouth breathers or excessive mask leak) Reporting leaks is
valuable to therapy analysis however, because leaks may distort some algorithmic functions.

My doctor had said that we wouldn't know for sure if I were mouth breathing with a nasal mask because the autopap would try to compensate for leaks, so either she was wrong, or this info is specific to Intellipap and doesn't necessarily apply to other machines. Guess it would be good if we could get our hands on S9 info in this regard... I have a feeling it may be classified info, though.

I believe the way that a modern CPAP or APAP compensates for small-to-medium sized unintentional leaks is to increase the air flow through the mask just enough to keep the pressure at the desired level. So an APAP has no need to respond to leaks by increasing the pressure.

The idea is like trying to keep an intertube with a slow leak fully inflated: If you have a pump attached to the tire value, you can keep the tire inflated by pumping air into the system as the same rate that it's being lost through the leak. Same thing with a CPAP/APAP: If there's an unintentional leak at a rate of lets say 2 L/min (or 0.033 L/sec), then all the machine has to do to keep the pressure constant is to increase the air flow through the system by 2 L/min (or 0.033 L/sec).

Problems with large leaks occur because it's difficult to pump enough extra air through the system to properly compensate for the leak. Hence you lose some of the pressure.

[LoQ]

But to get to the point of the question, I am trying to determine how much mouth breathing I am doing to decide whether or not I should continue to use a nasal mask. Any thoughts on how one goes about ferreting that out of the data?

I believe there is an extremely simple answer to your question. Look at the flow graph. It will only measure what is going through the hose via the mask.

[-SWS]

Regarding the question about how Resmed responds to leaks: Resmed's flow chart shows an allowable pressure increase in response/compensation to leaks---but only as long as an upper leak limit has not been met:
http://www.google.com/patents?id=xVnSAA ... ak&f=false

In summary, Resmed will attempt to compensate a leak with more pressure. However, if the leak gets too bad, then Resmed will drop pressure in an attempt to reestablish a better mask seal. Also a reminder that the pneumotach flow sensor is inside the machine. So the algorithm can only estimate leaks at best. Here is Resmed's leak definition:

Leak is an estimate of the total rate of air escaping due to mouth and mask leaks. It is derived by analysing the inspiratory and expiratory airflows, together with the expected mask vent flows. High or changing leak rates may affect the accuracy of other measurements.

http://www.google.com/search?q=%22leak+ ... =p&pdl=300

That last sentence implies that even changing leak rates (not necessarily high) will result in flow variations that can, in turn, be misread by the SDB-event sensing algorithm.

[robysue]

-SWS,

Thanks for providing the links.

The links refer to two kinds of pressure:

Treatment pressure at the patient interface and flow generator pressure.

After reading the links, my take on what they say is this:

A unintentional leak leads to the treatment pressure at the patient interface being below the desired level. And the algorithm says the machine increases the flow generator pressure in an attempt to bring the treatment pressure back up to where it is supposed to be. And the article further notes that if the increase in flow generator pressure winds up increasing the leak rate, then the flow generator pressure is lowered in an attempt to see if that results in a better seal at the patient interface and a reduction in the leak rate.

And my take on this is that the flow generator pressure is a measure of how much air the machine is pushing through the system---i.e. a measure of air flow and not a measure of the delivered treatment pressure at the patient interface. And so in the presence of a leak, the machine is increasing the amount of air being blown into the system (i.e. increasing the flow generator pressure) in order to bring the treatment pressure at the patient interface back to the desired setting---which is not the same as what most folks think of when we use the phrase, "the APAP increased the pressure"---since that conveys the machine deciding to pump enough additional air into the system to raise the desired setting for the treatment pressure at the patient interface.

[Big Daddy RRT,RPSGT]

I think one of the points is that the data, the AHI and such, are much less reliable if there are lots of leak and this might lead to various problems with the data and the ability of an auto to properly titrate.

[robysue]

I think one of the points is that the data, the AHI and such, are much less reliable if there are lots of leak and this might lead to various problems with the data and the ability of an auto to properly titrate.

Clearly that's the main issue when looking at leaks and their impact on therapy. But related questions include: How big do the leaks have to be before it causes problems with the data and the ability of an auto to properly titrate? And what does an xPAP machine actually do to compensate for "small" leaks?

With the Resmed machines, there's Resmed's own literature that indicates they (the company's engineers) believe the machine can gracefully handle unintentional leak rates below the RedLine value of 24 L/min and that unless the leaks at this level are lasting at least 25% of the night, therapy should be "ok" and the data numbers shouldn't be too inaccurate. Mr. Red Frowny Face shows up when the 75% leak rate is AT or ABOVE 24 L/min to indicate that leaks are an issue that need to be addressed.

I haven't found anything this clear about the PR machines in the documentation that I've been able to locate. Heck, I can't even find any information on how a PR xPAP machine "determines" when to flag a Large Leak. And even the worst of my leaks, which would be above the RedLine in ResScan, have not triggered any Large Leak flags showing up in either Encore or on the System One's LCD. Fortunately for me, my leak lines are usually very flat and my worst leaks only show up on the very occasional very bad night.

[-SWS]

After reading the links, my take on what they say is this:

A unintentional leak leads to the treatment pressure at the patient interface being below the desired level. And the algorithm says the machine increases the flow generator pressure in an attempt to bring the treatment pressure back up to where it is supposed to be. And the article further notes that if the increase in flow generator pressure winds up increasing the leak rate, then the flow generator pressure is lowered in an attempt to see if that results in a better seal at the patient interface and a reduction in the leak rate.

That's my take above as well.

And my take on this is that the flow generator pressure is a measure of how much air the machine is pushing through the system---i.e. a measure of air flow and not a measure of the delivered treatment pressure at the patient interface.

Okay... However, there's a single pneumotach sensor inside the machine used for both pressure and flow calculations. The overall algorithm continuously calculates both.

And so in the presence of a leak, the machine is increasing the amount of air being blown into the system (i.e. increasing the flow generator pressure) in order to bring the treatment pressure at the patient interface back to the desired setting---which is not the same as what most folks think of when we use the phrase, "the APAP increased the pressure"---since that conveys the machine deciding to pump enough additional air into the system to raise the desired setting for the treatment pressure at the patient interface.

I'll take slight semantic issue on a couple bases, Robysue: 1) This machine stents/targets static pressure (flow is not a primary target, but an input signal for control logic toward pressure delivery), but more importantly 2) sum-total flow is the resultant of: a) patient-sourced flow to the mouth, and b) all admittances at the various designed and unintentional leak points...

Back to algorithmically grappling with a single sensor inside the machine: when proximal leak ("far-end leak") becomes excessive, then the pressure difference at the internal sensor and that proximal leak also becomes greater. That far-end pressure loss is algorithmically compensated by increasing pressure back at the sensor---to maintain target mask/proximal pressure with which to stent upper airway obstructions closer to that proximal leak-point.

[avi123]

Does the S9 record mouth breathing as central events when you are using a nasal mask?

I am almost certain that a CPAP can't distinguish mouth leaks from other leaks even when there is a dedicated mask- air- pressure feed back to the CPAP controller such as in some Puritan Bennett's systems. The S9 measures the air flow and pressure at the outlet of the flow generator and decides if to raise or lower the pressure upon these data.

So, my reply is, NO, and the S9 needs to rely on other methods to detect Central Apneas.