Technical, Mask Pressure and Inhale\Exhale flow rate

I started drifting of topic on some else's thread and get into more and more technical discussion which does not belong on that thread. So I have started a new thread for that side discussion and I would like if an admin could clear some of the off-topic posts from that thread and move them here, leaving just single line comment that was part of original discussion. I think it rude to yank someone else's posts from one thread to another so I will not ask for any other posts to be moved, but I would welcome them into this tread to piece together the discussion again. I have cataloged my posts that I request be moved and the occasional replacement sentence.


viewtopic.php?p=1279158#p1279158 ( replace with (What is the thickness of your hose?)
viewtopic.php?p=1279267#p1279267
viewtopic.php?p=1279279#p1279279 replace with:
("BCman, looks like it is not worth it to try and get a performance hose. But the sleep study is still very important.")
viewtopic.php?p=1279469#p1279469 (replace with "Thread moved.")

Moving posts isn't a smooth function with the forum software. I have tried to both combine and move posts and I ended up with nothing but a big mess...and moving means moving the entire post...not just the contents....I couldn't move the post and still add something in there.

What I suggest you do is go into those threads that you want to move the discussion to here ...and edit your own posts (you can do that)...and copy what you want to move here.. then paste that copied text into a post in this thread...then go back and edit the original post to reflect whatever you want to say.

Last time I tried to move something and combine things I ended up having to totally delete the thread involved and eat some crow with the person who started the thread because I messed things up so badly.
Moving isn't simple here but editing your own posts and use the copy function and paste in a new post here...would be easy for you to do and that way you get it exactly like you want it and won't risk my screwing it up.

See the little pencil thing upper right of your screen....that's the edit button...click on the pencil and you can edit all you want to.

Moved down below.

Pugsy wrote: ↑

Tue Dec 11, 2018 4:34 pm

Moving posts isn't a smooth function with the forum software. I have tried to both combine and move posts and I ended up with nothing but a big mess...and moving means moving the entire post...not just the contents....I couldn't move the post and still add something in there.

What I suggest you do is go into those threads that you want to move the discussion to here ...and edit your own posts (you can do that)...and copy what you want to move here.. then paste that copied text into a post in this thread...then go back and edit the original post to reflect whatever you want to say.

I was afraid it would come down to that. OK, cut paste:

I know that when I got a new machine, or was it a new set of consumables, I got a narrower hose than I had been using. These spiral wire, contracted plastic webbing between are horribly inefficient air flow hoses. They are lighter, cheaper, more flexible and virtually kink proof, but the air resistance inside is huge. I am also a big guy these days, 330 lbs, and I could not get enough air through the smaller hose. When I switched back to my old, fatter hose I was fine again. If they gave you the narrow hose you maybe having trouble getting enough airflow when inhaling. With the larger inhale airflow o a bigger man, you get a higher flow rate for each inhale and that causes a larger pressure drop at the mask. If you are trying to suck in more air than the hose is good for, then your body may be sensing that pressure drop and assuming there is a blockage and you have to breather hard, i.e. faster to make up for it. And breathing faster further increases the pressure drop. Since you can sleep much of the night this feedback loop must flatten out. But it might leave you with an unconscious feeling of limited air supply, which could slowly build to a panic attack. Or the oxygen levels in your blood drop too low and cause a panic attack. When you finally hit the panic attack your heart starts racing and your muscles go to 'fight-or-flight' mode, both increasing your oxygen demand. Deeper breathing to make up the oxygen shortage leads to even more pressure drop, confirms that you are in trouble and wakes you up, tearing the breathing obstruction off your face.

If the above is not just another of my fights of fancy, you would need a larger diameter and/or shorter hose and preferably supplemental oxygen. If you currently have the 15mm hose, I would try to get a 19mm, or a shorter one. If you already have a 19mm, try a 19mm Performance hose. You can get one for under $15 in the US, but it is not heated. I didn't see any heated hose with the smooth inner bore. The oxygen will likely have to wait until the sleep study is done.

BCman wrote: ↑Sun Dec 09, 2018 10:01 am
The hose is standard size. I'll look into a bigger one.
I'll definitely look into what you're saying.
I just remembered that there is a simple way, short of a sleep study to at least see if your hose is adequate. Disconnect the hose from your machine, put the mask on and try breathing through just the mask and hose. This will only look at the air resistance of the hose without the beneficial effect of the fan. Regardless of how high the fan pressure is in the static case you still have to move all that air down the hose.

Once you have the mask with hose on try several normal breaths, then as many shallow breaths as you feel comfortable with (they should closer to deep sleep breath) then go to deep breaths to catch back up. If the normal breathing feels restricted I would worry. I the shallow breathing felt resistance I would definitely and consider giving up on having a heated hose and buy a performance hose. If you only feel some restriction with the deep breathing, it may add to the anxiety once the anxiety has already started peaking on it;s on but will contribute to making it worse.

If any of the test cases above are positive try splitting the problem in half. Take the hose off the mask and do the same 3 tests with just the mask. Remember that the mask will likely work better with the forced air flow but if it feels fine without then it should do even better with. Then take the mask off and try breathing through just the hose. Since the hose has no moving parts it should be much like when attached to everything else (the mask might have a flapper valve to separate exhaled air from the next inhale). Try the same tests with the same suggestions for the results. If you have trouble breathing through the hose. strongly consider buying a performance hose and compare to see if it makes it easier for you to breath.

If the mask and hose together cause no trouble breathing, than the problem lies elsewhere and you can ignore all the rest of what I said.

palerider,
it would seem that my concern over hose types may be greater than justified. I am assuming that the 4cm and 12cm pressures were are the outlet side, going into a chamber with an adjustable outlet rate to the pressure desired when the fan was at maximum speed. I must admit I am surprised that the slim line did better than the regular instead of worse. I wonder just how high the inlet pressures were to get that high a flow rate.

Although those were static tests. If I understand my sleepyhead chart correctly, what it labels 'mask pressure' (I don't have a pressure sensor in my mask so I am not if that is an extrapolated value or the bi-pap chamber pressure) and the breathing flow rate show that the pressure changes are a quarter of a cycle behind, so that peak inhale flow rate has the pressure only halfway up, and peak pressure occurs just as inhale reverses very sharply to exhale, so peak exhale flow rate is against full inhale pressure. With 28 respirations per minute that is only 2 seconds for each cycle so not much time time to read the chamber pressure and flow rate, do the pressure feedback loop to keep the max and min pressures correct but also keep the positive feedback part of it stable, do a feed forward set the target pressure for the pressure feedback loop and also project tube pressure drop and then get the fan to speed up or slow down as needed. But if it is not even able to match inhale and exhale pressures with the patient's flow rates, I don't see how it can provide feedback correction for pressure drops across the hose unless it is more feed forward estimation from the flow rate. I didn't see anything in the 'mask pressure' chart so if the mask pressure was estimated then the tube air resistance correction had already been removed and if the value was actually the bi-pap chamber pressure the effect was too small to see. Then again my sleepyhead graph for for flow limit was so close to zero that it implies that no correction was needed.

I am glad you were able to find some good references on the maximum flow rates of the tubes, and yes, like BCman my tidal volume averaged around 300 ml and typical peak flow rate under 60Lm so much less than the limits you posted. I did however do something very unusual. I actually experimented to find the answers. I have replaced but still usable hoses in my emergency backup stash. It turns out that one is standard and the other slim line. I tried breathing through each one and it was definitely more difficult to breath through the slim line than the standard, but not too hard for either. I guess I am sensitive to less than 1cm pressure differences.

Tropicaldiver, I support what you said. From what I understand they not only regulate the flow, and thus pressure of the air supplied to the diver but also us the air pressure to control diaphragms and valves and were not designed to work with a compressed air feed. So I not surprised that it was very difficult to breath through. So if the regulator functions more like the cpap, which also allows any flow rate at a controlled pressure relative to ambient, and closer analogy might be to remove the regulator too and try breathing through just the mouth piece. But since a little extra pressure from the regulator an make up for a lot of resistance in the mouth piece it is probably even less useful a test.

palerider wrote: ↑Mon Dec 10, 2018 4:21 pm
mbushroe wrote: ↑Mon Dec 10, 2018 2:37 am
But if it is not even able to match inhale and exhale pressures with the patient's flow rates, I don't see how it can provide feedback correction for pressure drops across the hose .
It can, easily... Computers are fast, people are slow. I don't know for sure what the Air10 machines have in them, but the S9 machines had an ARM® 32-bit Cortex®-M3 CPU with MPU, ( 72 MHz maximum frequency, 1.25 DMIPS/MHz (Dhrystone 2.1) performance at 0 wait state memory access) If the Air10 machines aren't using the same CPU, I can only imagine what's inside is even more powerful.
Yes I know the microcontrollers can be faster than humans. I normally work with 8 bit micros for my under water robots, and even they can take up to 100,000 analog measurements per second. Where the speed limit comes is doing complex math functions. But the 32 bit ARMs are much faster at math, too. Having not worked with the ARMs I was more likely to worry about the processing as well as the ability of the fan to change speed/flow rate by that big a delta and that short a time period. It is after all a mechanical device without the benefit of electrons switching at tens of millions of times per second. But it is clear from my chart that they can at least start making changes in less than a 1/2 second.

I was talking with our corporate nurse who used to work respiratory in the hospital, and then also while googling I saw vague mention of it using bi-paps in particular to regulate respiration rate as well as airway pressure. And if I looked at those two charts of mine as an electrical system with the flow rate comparable to the rotation rate of an electric motor and the mask pressure as part of its drive power then the 1/4 cycle offset would be correct for trying to slow the motor down, as if it were in a car going down hill or an elevator going to a lower floor. And if the desired respiration rate is somewhere around 12 to 15 then the bi-pap would be trying hard to slow down my breathing to get deeper breaths to clear more stale air from the fringes of my lungs and improve CO2 elimination. My chart shows that I take lots of brief, shallow breaths. The delayed timing causing the wrong pressure may be deliberate to try to convince my body to breath more slowly.

BCman has nearly the same respiration rate that I do and about the same median tidal volume. If BCman were to post a plot zoomed in as far possible of the flow rate and mask pressure graphs we might see it is also doing the same thing to him. I am not sure what we could do to stop or fix that, and he already meditates before going to bed which should keep his breathing rate down for as long as possible. But seeing if his is also offset would at least be some extra information about his sleep and how his machine interacts with his sleep.

palerider wrote: ↑Mon Dec 10, 2018 4:21 pm
[
Did you remember to change the tube tupe settings when swapping hoses?
Not possible!

Mine is currently configured to not allow almost any user changes. I can set mask to full, nasal, or pillow but there is no option for hose type, length, or diameter.

Here is the tightest zoom in I can do. I have used the left and right arrow keys at this zoom level to look at a fair chunk of this data and the timing between them appears to be within a tenth of a cycle so this is not cherry picked data to support my prior posts.

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image goes here sleepyhead-off-phase-pressure-flow-2018-12-10.png
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sleepyhead-off-phase-pressure-flow-2018-12-10.png (251.06 KiB) Viewed 66 times
Palerider, it looks to me like your graph shows much the same phase shift. The mask pressure peak just before the cursor lines up with peak exhale flow rate the peak inhale just before that is only halfway up the ramp from low to high. The mask pressure does drop faster than exhale flow rate, but by the time mask pressure hits minimum most of the exhale is done there is not much benefit to the lower pressure when you aren't exhaling anymore. It makes sense that the start of the inhale flow rate precedes the ramp up to inhale pressure but the ramp up looks more like 2 seconds than 1/4 of a second. Most of the inhale is at less than max positive pressure and the much of the exhale is against more than the minimum pressure. I guess some of what I a seeing is inherent delay when doing breathing triggered control but much of the flow rate in each direction is at the wrong pressure and the inhale only gets peak positive airway pressure in the tip of the spike just before the inhale ceases. If that last fraction of a second of peak pressure is enough to prevent apnea then that is all that is important. But I would have guessed that maximum positive airway pressure would be desired to the beginning or at least middle of the inhale.

Moved from somewhere else...

mbushroe wrote: ↑

Tue Dec 11, 2018 3:10 am

palerider wrote: ↑

Mon Dec 10, 2018 5:21 pm

Did you remember to change the tube type settings when swapping hoses?

Not possible!

Mine is currently configured to not allow almost any user changes. I can set mask to full, nasal, or pillow but there is no option for hose type, length, or diameter.

Of course it's possible, in fact, it's mandatory for proper operation.

If nothing else, go into the clinical menu.

If you put a slim hose on while the machine was set to regular, you'll have abnormally low pressure at the mask.
If you put a regular hose on while the machine is set to slim, then you'll have abnormally high pressure at the mask.

If your tube type wasn't set right, your whole experiment is faulty, and the data gained spurious.
I thought my machine was broken the first time I turned it on, because I had a regular hose and it was set to slimline.

mbushroe wrote: ↑

Tue Dec 11, 2018 3:10 am

Here is the tightest zoom in I can do.

You can highlight a section with the mouse and it'll zoom in to that section, so you can zoom in tighter for more detail.

mbushroe wrote: ↑

Tue Dec 11, 2018 3:10 am

Palerider, it looks to me like your graph shows much the same phase shift.

There is no phase shift.

mbushroe wrote: ↑

Tue Dec 11, 2018 3:10 am

The mask pressure peak just before the cursor lines up with peak exhale flow rate the peak inhale just before that is only halfway up the ramp from low to high.

That's not what Sleepyhead is showing you. On the flow rate chart "up" is not simply "inhale" and "down" isn't "exhale", rather, anything above the zero line is inhaling, and anything below the zero line is exhale. (it helps if you right click the 'flow rate' label, and turn on the zero dotted line, as below):


*everything* above the red line is inhalation, that is the *rate* of airflow, both positive and negative, so the higher the peak, the higher the inhalation rate, even as the line starts coming back down, you're still inhaling, right up until the line crosses the zero and goes into negative flow, that's the start of the exhale phase.

You can see, the top arrow shows exactly where the inhalation ends and the exhalation begins, then if you follow down you'll see that pressure peaked a split second *before* the zero crossing, and started to drop, just before exhalation begins.

No "phase shift".

mbushroe wrote: ↑

Tue Dec 11, 2018 3:10 am

The mask pressure does drop faster than exhale flow rate, but by the time mask pressure hits minimum most of the exhale is done there is not much benefit to the lower pressure when you aren't exhaling anymore.

It makes sense that the start of the inhale flow rate precedes the ramp up to inhale pressure but the ramp up looks more like 2 seconds than 1/4 of a second.

That's because EasyBreathe(tm) increases pressure gently, timed with your breathing, so that it feels natural and easy.

If you want to see "what the machine can do", then flip it over to S mode, turn Easy-Breathe off, set the Rise time to 150 (that's 150 milliseconds), epap 4 and ipap 25.

strap in and hit the 'go' button. Ok, I'm being mean, set the EPAP to 14 and IPAP to 18., you're used to those pressures.

You'll get a square wave pressure instead of the ramps, like the bottom trace here:

mbushroe wrote: ↑

Tue Dec 11, 2018 3:10 am

Most of the inhale is at less than max positive pressure

True, with EasyBreathe turned on.

mbushroe wrote: ↑

Tue Dec 11, 2018 3:10 am

and the much of the exhale is against more than the minimum pressure.

Incorrect.

mbushroe wrote: ↑

Tue Dec 11, 2018 3:10 am

I guess some of what I a seeing is inherent delay when doing breathing triggered control but much of the flow rate in each direction is at the wrong pressure

I don't know why you think it's "the wrong pressure", it's not.

mbushroe wrote: ↑

Tue Dec 11, 2018 3:10 am

and the inhale only gets peak positive airway pressure in the tip of the spike just before the inhale ceases.

Yes.

mbushroe wrote: ↑

Tue Dec 11, 2018 3:10 am

If that last fraction of a second of peak pressure is enough to prevent apnea then that is all that is important.

That has nothing at all to do with preventing apnea. Apnea is prevented at *EPAP*, not IPAP. The airway has to be held open by EPAP, because if your airway closes, then you'll never inhale to trigger the machine to switch to IPAP in the first place.

mbushroe wrote: ↑

Tue Dec 11, 2018 3:10 am

But I would have guessed that maximum positive airway pressure would be desired to the beginning or at least middle of the inhale.

You can program your machine to do that. I've experimented with it, I don't like it, it's like being thumped every breath.

Frankly, getting the pressure spot on at the right instant is only a small part of what the machine is constantly calculating...

https://patents.google.com/patent/US6152129

There's plenty more patents out there if you want to dig around a little.

palerider wrote: ↑

Tue Dec 11, 2018 5:34 pm

Moved from somewhere else...

mbushroe wrote: ↑

Tue Dec 11, 2018 3:10 am

palerider wrote: ↑

Mon Dec 10, 2018 5:21 pm

Did you remember to change the tube type settings when swapping hoses?

Not possible!

Mine is currently configured to not allow almost any user changes. I can set mask to full, nasal, or pillow but there is no option for hose type, length, or diameter.

Of course it's possible, in fact, it's mandatory for proper operation.

If nothing else, go into the clinical menu.

Sorry I got a bit snippish with this response. I was not happy with the very limited controls for the user and I have not yet researched how to break into the clinical menu or what extra options are available there. Right now I have a heated hose on the machine so it knows that only one heated hose is approved for use on that machine so it already knows the length, diameter, and type and so there is no need for options to mess that up, at least on the user menu. Since I assume that it has correctly configured itself for the hose, I don't a need to get into the clinician menu for that.


On the flow rate and mask pressure charts, you I know that inhale is only above the zero line and exhale only below. The initiation of inhale is followed by a short time delay than a gradual slope up from the minimum pressure. And I can see that the saw tooth peak in the pressure waveform lines up very well with the zero crossing going from inhale to exhale.

But if you eye ball integrate the inhale times the pressure and the exhale times the pressure at each instant of time, it comes out not being inhale at the inhale pressure or exhale at the exhale pressure, on average. On the inhale, the time delay before the ramp starts gives about a tenth of the inhale volume being breathed in at the lowest pressure, about a third more reaching about the peak flow rate is at or below the midpoint of the ramp up, giving an integrated average of less than 1/3 of PS, the remaining inhale at or just after max flow rate is about half the total volume is between the mid point and the peak so averaging around 3/4 PS, and just as the inhale stops so the final 7% get the full PS. The overall integral, by eye ball, is around 0.5 PS. So unless the timing of when the inhale is getting a weak push and when it is getting a strong push is much more important than the overall average pressure, it would seem that the inhale would work as well with a constant pressure half way between.

For the exhale, the saw tooth drops off much faster than it went up, but not as fast as the exhale comes out. The peak exhale is against about the middle of the ramp down. About the first 1/4 of the exhale volume chases the pressure down giving slightly more than 3/4 PS against 1/4 exhale, then next 1/2 covers the lower half of the ramp down, and the remaining 1/4 sees the exhale pressure. Once the eye ball integration gives the exhale against an average of a 1/3 PS higher than the lower pressure, but with the initial and highest flow rate part being against nearly inhale pressure.

I would naively assume that the sparse saw tooth should really be a square wave, which you said would be much more uncomfortable, and begin at least a quarter earlier, and possibly end it just before the zero crossing by measuring the first stage of flow rate drop. But I guess there must be considerably more complexities to what it going on so that what seems counter productive is actually better.

Very CLASSY, mbushroe and Palerider!

You two are more than just the smart kids.
You've got CLASS!

Thanks from the peanut gallery for letting us try to follow along.

Hopefully others will add their two cents here too~~~

mbushroe wrote: ↑

Tue Dec 11, 2018 8:33 pm

palerider wrote: ↑

Tue Dec 11, 2018 5:34 pm

mbushroe wrote: ↑

Tue Dec 11, 2018 3:10 am

palerider wrote: ↑

Mon Dec 10, 2018 5:21 pm

Did you remember to change the tube type settings when swapping hoses?

Not possible!

Mine is currently configured to not allow almost any user changes. I can set mask to full, nasal, or pillow but there is no option for hose type, length, or diameter.

Of course it's possible, in fact, it's mandatory for proper operation.

If nothing else, go into the clinical menu.

Sorry I got a bit snippish with this response. I was not happy with the very limited controls for the user and I have not yet researched how to break into the clinical menu or what extra options are available there.

No worries. Head over to the link at the top of apneaboard.com, and follow the instructions on how to request, and receive, the clinical manual via email. I strongly urge you to do that instead of looking on youtube for the 'secret handshake', as Pugsy puts it... because there's a lot of good information in the clinical manual that you won't get on youtube. If you have trouble with them, let me know and I'll get you a copy.

mbushroe wrote: ↑

Tue Dec 11, 2018 8:33 pm

On the flow rate and mask pressure charts, you I know that inhale is only above the zero line and exhale only below. The initiation of inhale is followed by a short time delay than a gradual slope up from the minimum pressure.

It's not a short delay, per se, rather it's the issue that you have to make enough of an inhale for the machine to say "ok, now it's time to move to IPAP", and that value, the amount of inhalation you have to do before the machine triggers to IPAP is configured by the Trigger setting in the clinical menu. You can modify the sensitivity from very low to very high, meaning you have to take more, or less of a breath before the machine springs into action.

I can see where, not knowing this detail, it would look like the machine is slow, or there's a delay... but that's not the case.

mbushroe wrote: ↑

Tue Dec 11, 2018 8:33 pm

But if you eye ball integrate the inhale times the pressure and the exhale times the pressure at each instant of time, it comes out not being inhale at the inhale pressure or exhale at the exhale pressure, on average. On the inhale, the time delay before the ramp starts gives about a tenth of the inhale volume being breathed in at the lowest pressure, about a third more reaching about the peak flow rate is at or below the midpoint of the ramp up, giving an integrated average of less than 1/3 of PS, the remaining inhale at or just after max flow rate is about half the total volume is between the mid point and the peak so averaging around 3/4 PS, and just as the inhale stops so the final 7% get the full PS. The overall integral, by eye ball, is around 0.5 PS. So unless the timing of when the inhale is getting a weak push and when it is getting a strong push is much more important than the overall average pressure, it would seem that the inhale would work as well with a constant pressure half way between.

Not clear on what you're getting at.

mbushroe wrote: ↑

Tue Dec 11, 2018 8:33 pm

For the exhale, the saw tooth drops off much faster than it went up, but not as fast as the exhale comes out. The peak exhale is against about the middle of the ramp down. About the first 1/4 of the exhale volume chases the pressure down giving slightly more than 3/4 PS against 1/4 exhale, then next 1/2 covers the lower half of the ramp down, and the remaining 1/4 sees the exhale pressure. Once the eye ball integration gives the exhale against an average of a 1/3 PS higher than the lower pressure, but with the initial and highest flow rate part being against nearly inhale pressure.

You don't want pressure to just drop off, for comfort sake... try putting your machine on, then turn it off, or pop the hose off towards the end of your breath, it's like someone just sat on you, having the pressure suddenly disappear.

mbushroe wrote: ↑

Tue Dec 11, 2018 8:33 pm

I would naively assume that the sparse saw tooth should really be a square wave,

I don't know what you're trying to say... If you mean the pressure transitions should be a square wave, that would be a very unnatural way of breathing.

mbushroe wrote: ↑

Tue Dec 11, 2018 8:33 pm

and begin at least a quarter earlier, and possibly end it just before the zero crossing by measuring the first stage of flow rate drop. But I guess there must be considerably more complexities to what it going on so that what seems counter productive is actually better.

Well, you'll never have cpap or bilevel begin much earlier, since they're spontaneously triggered by your initiating a breath. You don't want it to trigger too easily for the average person, since that can lead to having the machine switch to IPAP before you're actually ready. The only ones that will start earlier are timed machines, like an ASV or ST, where the machine increases pressure to force you to breathe when you're having a central apnea.

If you don't have some lung issues that necessitate pressure delivery like that, you don't want it.

I think, what it all comes down to, is that you're looking at a *comfort* pressure delivery algorithm, and thinking that it looks like that because the machines are too slow to do anything else... that's not the case at all, they're just doing it that way because it *feels natural* and easy to breathe with those pressure transitions.

Alright, I think I am beginning to see the comfort versus driving for full effect.

The section you are not clear on was trying to asses the effective average pressure or level of effort for inhale and exhale. I was describing multiplying sections of the volume by the pressure when that volume went through. Technically that should be instantaneous pressure times the flow rate integrated over time an then divided by total volume to get the average pressure. But that would either mean pasting a single cycle into a program to curve fit and approximate the data then integrate the curves or trying to decipher the raw data to get the numbers to do a discrete integral. Instead I broke the total volume into chunks of volumes that had much the same pressure and or much the same flow rate so that the flow rate integrated over time would already be done. In the case of the square wave that is too uncomfortable to use, the result would be a constant pressure integrated over flow rate to get volume, then divide by volume to get back the constant pressure, max for inhale and min for exhale. With the flat, spike, flat, spike mask pressure even though the pressure is at minimum most of the time, a lot of the exhale is against higher pressures and with maximum pressure only being there for an instant as the inhale stops means that most of the inhale is not supported by anywhere near as much as the maximum pressure. So the maximum and minimum pressures shape the waveform but have very little relationship to the effective pressures for inhale and exhale.

I am also confused as to why the spike comes at the end of the inhale instead of the beginning. The exhale does not need any extra pressure, it can just the soft tissue out of the way go out. But if the soft tissue even starts to block the inhale, the negative pressure against the back of the tongue pulls it even tighter blocking the flow even more. It would seem that the inhale needs the most help at the start, not the end. Although that probably would make the control and feedback loops in the machine quite a bit harder stay stable. And also why such a narrow spike. Surely the inhale could use the extra pressure throughout the inhale, unless leads to over pressuring or over filling the lungs.

I had not thought of the trigger value being a separate parameter to change. Any zero crossing detector would have to have some amount passed the zero point to be sure that the zero point had actually been crossed, not merely reached. And yes I have once or twice started then stopped an inhale and felt the machine lock into one mode then take a moment to switch back again. And there ae times when I first put the mask on that I feel like my lungs and the machine are 'negotiating' a mutually agreeable breathing patter, and then waking up in the middle of the night and noticing how natural my breathing felt. I have not notice the negotiating for some time now. I guess my body has developed a 'setting' for breathing with a bipap and as soon as I put it on automatically switches over.

Grace~~~ wrote: ↑

Tue Dec 11, 2018 10:40 pm

Very CLASSY, mbushroe and Palerider!

You two are more than just the smart kids.
You've got CLASS!

Thanks from the peanut gallery for letting us try to follow along.

Hopefully others will add their two cents here too~~~

Thanks! I am still learning all this myself as I go along. I do like it when discussions can be educational as well. And I try not to let mine devolve into shouting and name calling matches, but I am no more a saint than the next fellow.