Flow Limitation

Miss Emerita · Post by **Miss Emerita** » Wed Nov 03, 2021 12:01 pm

EPR can help with flow limitations because the pressure when you inhale is higher than the pressure when you exhale. The boost sometimes helps people complete their inhalations more easily and smoothly.

I don't follow the reasoning about exhaling through your mouth. If your exhale pressure is lower than your inhale pressure, wouldn't you be LESS likely to mouth-breath when you exhale? But maybe there's something I'm missing there.

The concept of reliance or dependence also seems out of place. We're all reliant or dependent on PAP to treat apnea; if EPR is not harmful, but instead helps us in our apnea treatment, why wouldn't we embrace it as a regular part of our treatment, same as we embrace PAP?

dataq1 · Post by **dataq1** » Wed Nov 03, 2021 1:18 pm

Miss Emerita wrote: ↑
Wed Nov 03, 2021 12:01 pm
... wouldn't you be LESS likely to mouth-breath when you exhale? But maybe there's something I'm missing there.

That would seem to be the most reasonable thought.

Then again, some may have it in mind that exhaling through the mouth is problematic ( but I don't know that it is).
Which, of course, leads me to ask if flow limitation "events " are ever graded during the expiration phase.

As to not preferentially not using EPR, it may be that the sleep tech is working on the theory that "if you can get acclimated to the most difficult, then a lesser challenge seems easier"
(aka force yourself to eat okra, then peas don't seem so bad !)

MMcG · Post by **MMcG** » Thu Nov 04, 2021 3:52 am

dataq1 wrote: ↑
Wed Nov 03, 2021 1:18 pm

Miss Emerita wrote: ↑
Wed Nov 03, 2021 12:01 pm
... wouldn't you be LESS likely to mouth-breath when you exhale? But maybe there's something I'm missing there.
That would seem to be the most reasonable thought.

Then again, some may have it in mind that exhaling through the mouth is problematic ( but I don't know that it is).
Which, of course, leads me to ask if flow limitation "events " are ever graded during the expiration phase.

As to not preferentially not using EPR, it may be that the sleep tech is working on the theory that "if you can get acclimated to the most difficult, then a lesser challenge seems easier"
(aka force yourself to eat okra, then peas don't seem so bad !)

I think that was his thought process in a nutshell!

ChicagoGranny · Post by **ChicagoGranny** » Thu Nov 04, 2021 6:50 am

dataq1 wrote: ↑
Wed Nov 03, 2021 1:18 pm
Then again, some may have it in mind that exhaling through the mouth is problematic ( but I don't know that it is).

It's an open mouth that is the problem. When the mouth opens, the mandible moves slightly backward due to universal human anatomy. This backward movement tends to narrow the airway.

dataq1 · Post by **dataq1** » Thu Nov 04, 2021 10:31 am

ChicagoGranny wrote: ↑
Thu Nov 04, 2021 6:50 am
It's an open mouth that is the problem. When the mouth opens, the mandible moves slightly backward due to universal human anatomy. This backward movement tends to narrow the airway.

So, you raise a good point.
Is the narrowing of the airway (by mandible movement) evidenced in all positions (prone, supine and upright)? Consider the track athlete, at the end of a race do they tend to exhale through their nose or mouth. Just a general question.

I am certainly no expert, but it would seem to me that flow limitations (due to narrowing of the airway) are largely problematic during the inhalation phase. But we were discussing the situation where a patient was inhaling thru their nasal pillow but exhaling (of at least some fraction) thru their mouth and that exhalation is not captured by a nasal mask.

So, a reasonable question might be: Are flow limitations (as reported by Resmed and others) captured and graded during inhalation phase only? By the way, the graphic of flow limitations that you presented the other day seemed to be only during inhalation.

dataq1 · Post by **dataq1** » Thu Nov 04, 2021 12:24 pm

ChicagoGranny wrote: ↑
Thu Nov 04, 2021 6:50 am

So sorry Granny, it was Miss Emerita that posted the inhalation graphic. My error

palerider · Post by **palerider** » Thu Nov 04, 2021 1:49 pm

Miss Emerita wrote: ↑
Wed Nov 03, 2021 12:01 pm
EPR can help with flow limitations because the pressure when you inhale is higher than the pressure when you exhale. The boost sometimes helps people complete their inhalations more easily and smoothly.

I don't follow the reasoning about exhaling through your mouth. If your exhale pressure is lower than your inhale pressure, wouldn't you be LESS likely to mouth-breath when you exhale? But maybe there's something I'm missing there.

Exhaling through the mouth when wearing a nasal mask is a thing that happens, or, 'excessive mouth leaks' is another way to think about it.

ChicagoGranny · Post by **ChicagoGranny** » Thu Nov 04, 2021 3:09 pm

dataq1 wrote: ↑
Thu Nov 04, 2021 10:31 am
But we were discussing the situation where a patient was inhaling thru their nasal pillow but exhaling (of at least some fraction) thru their mouth and that exhalation is not captured by a nasal mask.

What evidence is there that the patient is inhaling through the nose and exhaling through the mouth? Eyewitness accounts are notoriously unreliable. To make matters more doubtful, this eyewitness account comes from a person who was sleeping.

dataq1 · Post by **dataq1** » Thu Nov 04, 2021 4:15 pm

ChicagoGranny wrote: ↑
Thu Nov 04, 2021 3:09 pm
What evidence is there that the patient is inhaling through the nose and exhaling through the mouth? Eyewitness accounts are notoriously unreliable. To make matters more doubtful, this eyewitness account comes from a person who was sleeping.

"Eyewitness accounts" notoriously unreliable, very true but this eyewitness has suggested exhale puffing through the mouth a conclusion that his sleep technician had as well. In any event, his original question had to do with a comparing his flowrate time curve with the flowrate-time model suggested by the Resmed video as characteristic of a flow limitation.

In the OSCAR discussion of flow limitation http://www.apneaboard.com/wiki/index.ph ... Limitation includes a graphic that is interesting:

: Expiratory mouth breathing.jpg (15.88 KiB) Viewed 1023 times

Notice that the inhalation phase seems fairly normal in morphology and the volume per inhalation seems consistent breath to breath. On the other hand, the exhalation phase seems very short and does not seem to accommodate the volume of air that was just recently inspired. Assuming that the patient did not blow up like a balloon (or explode) the air must have escaped without being measured by the device. The most logical way I could imagine that is if the patient were using a nasal mask and was exhaling (or at least partially) through their mouth (thereby avoiding the device from realizing the volume of exhaled air.

At least this seems like a reasonable explanation to me.

While we are about it, I would propose that the area under the flowrate-time curve (from zero flowrate to zero flowrate) as shown in red here is representative of the tidal volume.

: Tidal Volume.jpg (6.6 KiB) Viewed 1023 times

I'm open to opinions to the contrary.....

BlueDragon · Post by **BlueDragon** » Thu Nov 04, 2021 5:39 pm

fwiw, for ResMed and DeVilbiss machines, tidal volume shown by OSCAR is as reported by the CPAP machine. We don't really know exactly what the machine is doing but report what the machine says.

For F&P SleepStyle, tidal volume is calculated by OSCAR. OSCAR looks at the the inhalation on the flow graph (i.e., the "upper half" of the flow graph). However, the machine reports flow in an unusual way that OSCAR has to compensate for, and OSCAR then calculates tidal volume by examining that compensated flow graph. So quirks in the flow data can result in some unusual calculated tidal volume values. This usually shows up as unexpected peaks in the tidal volume graph and a ridiculously high maximum value in the statistics panel on the Daily page.

dataq1 · Post by **dataq1** » Thu Nov 04, 2021 8:57 pm

BlueDragon wrote: ↑
Thu Nov 04, 2021 5:39 pm
for ResMed and DeVilbiss machines, tidal volume shown by OSCAR is as reported by the CPAP machine. We don't really know exactly what the machine is doing but report what the machine says.

Understood, but do you know what the ResMed machine actually measures (that is, what transducers are present)? Is there a flow (liters) sensor or a Flowrate(liters/min) sensor? Alternatively, are flow and/or flowrate computed from pressure readings?

Regardless, do you agree that the area under the positive flowrate vs. time curve should represent the total flow during that inhale? (and the converse ought be true as well ). The net effect being that the inhale volume should be equal to the exhale volume, providing there are no extraordinary leaks.

palerider · Post by **palerider** » Thu Nov 04, 2021 9:21 pm

dataq1 wrote: ↑
Thu Nov 04, 2021 8:57 pm

BlueDragon wrote: ↑
Thu Nov 04, 2021 5:39 pm
for ResMed and DeVilbiss machines, tidal volume shown by OSCAR is as reported by the CPAP machine. We don't really know exactly what the machine is doing but report what the machine says.
Understood, but do you know what the ResMed machine actually measures (that is, what transducers are present)? Is there a flow (liters) sensor or a Flowrate(liters/min) sensor?

I posted the actual part numbers for the sensors in response to one of your other endless questions, go back, find the post, look up the part numbers, and learn something.

BlueDragon · Post by **BlueDragon** » Thu Nov 04, 2021 9:39 pm

dataq1 wrote: ↑
Thu Nov 04, 2021 8:57 pm
Understood, but do you know what the ResMed machine actually measures (that is, what transducers are present)? Is there a flow (liters) sensor or a Flowrate(liters/min) sensor? Alternatively, are flow and/or flowrate computed from pressure readings?

No, I do not know the innards of the machine.

dataq1 wrote: ↑
Thu Nov 04, 2021 8:57 pm
Regardless, do you agree that the area under the positive flowrate vs. time curve should represent the total flow during that inhale? (and the converse ought be true as well ). The net effect being that the inhale volume should be equal to the exhale volume, providing there are no extraordinary leaks.

It would certainly seem to be the case that inhale volume must equal exhale volume overall, but not on a breath-by-breath basis. There are, after all, few other places for the air to go! Some could be swallowed (aerophagia) but that volume is surely low. One could, for example, have a series of short intake breaths followed by a large exhale, and vice versa. Or several breaths with incomplete exhale followed by a complete exhale. Deep breathing alternating with shallow breathing, etc.

dataq1 · Post by **dataq1** » Thu Nov 04, 2021 9:49 pm

palerider wrote: ↑
Thu Nov 04, 2021 9:21 pm

So I looked at your parts list and realized that you were mis-identifying parts. Sensirion SDP is NOT a flow meter.
Inaccuracy plus snark is not a contributor I want to deal with or respond to in the future

dataq1 · Post by **dataq1** » Thu Nov 04, 2021 10:23 pm

BlueDragon wrote: ↑
Thu Nov 04, 2021 9:39 pm

It would certainly seem to be the case that inhale volume must equal exhale volume overall, but not on a breath-by-breath basis. There are, after all, few other places for the air to go! Some could be swallowed (aerophagia) but that volume is surely low. One could, for example, have a series of short intake breaths followed by a large exhale, and vice versa. Or several breaths with incomplete exhale followed by a complete exhale. Deep breathing alternating with shallow breathing, etc.

While I quite agree that there are exceptions; in the ideal case (as represented by the normal flow morphology graphic from the OSCAR reference) inhale volume tends to equal exhale volume at least over a series of breaths. However, flow limitations or abnormalities (such as that displayed by the apneaboard wiki (shown above) suggest that a significant volume that has to exhaled eventually is not being captured by the device (at least not within scope of the graphics time scale).

What concerns me is that a flow pattern, like that shown in the apneaboard wiki graphic, would be graded as a flow limitation and subsequently an increase in pressure would be ordered in a APAP machine.

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