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EPAPmin and minimum EPAP
#11
(04-21-2016, 10:05 AM)tmoody Wrote: I thought I saw a thread on this very question, but now I can't find it, so...

If my EPAPmin is set to 8.5 (it's never been lower than 8), how is it that SH often reports nightly EPAP minimums lower than 8, sometimes lower than 7?

My flex setting is 1, if that's relevant.
Flex is the relevant thing. Flex totally explains what's going on.

Regardless of flex setting, flex reduces the pressure to below the EPAP setting at the beginning of each exhalation. The EPAP data is just the pressure on exhalation, so the EPAP data picks up that little bit of "extra" pressure relief created by the Flex system.

It's also worth noting that regardless of the Flex setting, it is possible for the Flex system to reduce the pressure by as much as 2 cm on a very strong exhalation. The Flex setting does more to control the "rounding" of the IPAP-to-EPAP and EPAP-to-IPAP transitions than it does the actual pressure relief in terms of cmH2O.

JediMark has said (in a different place) that the "granularity" of the PR exhalation pressure data is not as fine as it is on the Resmed machines, so the EPAP curve is not going to pick up the individual breath-by-breath variations caused by Flex. But if the EPAP data was sampled at the beginning of a strong exhalation when EPAP = 8.5, that could easily result in the EPAP curve dropping below 7 since 7cm is only 1.5cm less than your min EPAP.
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#12
[quote='palerider' pid='158841' dateline='1461265879']
what I think you're missing here is that the machines are very sophisticated.

they measure the pressure and flow many times per second, 25 per in the case of resmed, respironics is probably similar.
[quote]

This is what I mentioned as potential lag, and I didn't know how fast the machines were or how fast they can adjust pressure.

[quote]
besides, your idea of the pressure going up too high on exhale and resulting in a higher epap wouldn't coincide with the original question.... which was why is my epap being reported lower than the minimum set. [/quote]


Well, here is an example of what I was looking at while typing before, as you can see it displays exactly what I am referring to - the flow rate reverses causing a spike downward in pressure, which is then corrected by the machine bringing the pressure back up to the 10 line which is the setting (in my case). What I see is that there is a positive spike is at the end of the inhalation, and a negative spike at the beginning of the exhalation - which is what I described. I don't know if they are intentional or do to lag or even potentially a "fluid hammer" effect (inertia).

Describing the positive spike was simply to setup the entire scenario, i.e. that this happened in both directions.

Pressure at Mask vs Flow Rate

Well darn, leave it to robysue to come up with the correct solution as opposed to my overly complex attempt Smile
I am not a Medical professional and I don't play one on the internet.
Started CPAP Therapy April 5, 2016
I'd Rather Be Sleeping
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#13
(04-21-2016, 01:59 PM)palerider Wrote:
(04-21-2016, 10:05 AM)tmoody Wrote: I thought I saw a thread on this very question, but now I can't find it, so...

If my EPAPmin is set to 8.5 (it's never been lower than 8), how is it that SH often reports nightly EPAP minimums lower than 8, sometimes lower than 7?

My flex setting is 1, if that's relevant.

flex lowers your epap.

I thought 1 was the "off" setting for flex.
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#14
(04-21-2016, 03:03 PM)tmoody Wrote: I thought 1 was the "off" setting for flex.
Nope. The Off setting for BiFlex is "Rise Time" on a PR BiPAP.

Seriously: In the clinical set up menu you have to choose between "BiFlex" and "Rise Time".

If you pick "BiFlex", the Flex algorithm is used and the setting controls the transitions from EPAP-to-IPAP and IPAP-to-EPAP and also provides a bit of extra pressure relief at the beginning of each exhalation. The amount of the relief varies based on both the flex setting and the forcefulness of the exhalation. But it's never more than about 2 or 2.5 cm of extra relief than that created by the drop from IPAP to EPAP. The Flex system brings the pressure back to full EPAP during the second half of the exhalation.

If you pick "Rise Time", the Flex algorithm is turned off and the Rise Time setting controls how quickly the pressure is increased from EPAP to IPAP at the beginning of each inhalation. When using Rise Time, the transition from IPAP-to-EPAP is abrupt--the pressure is suddenly reduced to EPAP as soon as the beginning of the exhalation starts. There's no rounding at all. The increase in pressure from EPAP-to-IPAP is sharp and linear. How steep the linear increase is depends on the Rise Time setting. The higher the Rise Time setting, the longer it takes to increase the pressure from EPAP-to-IPAP.

I have my PR BiPAP set to Rise Time = 3 because Flex drove be crazy: I could feel that small increase from "EPAP-FLEX" to "EPAP" during the second half of my exhalations when I was a newbie and it felt like the machine was trying to force me to inhale before I'd finished exhaling. Rise Time = 3 keeps the increase back to IPAP from feeling like I've hit a brick wall with each inhalation.
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#15
(04-21-2016, 03:22 PM)robysue Wrote: I have my PR BiPAP set to Rise Time = 3 because Flex drove be crazy: I could feel that small increase from "EPAP-FLEX" to "EPAP" during the second half of my exhalations when I was a newbie and it felt like the machine was trying to force me to inhale before I'd finished exhaling. Rise Time = 3 keeps the increase back to IPAP from feeling like I've hit a brick wall with each inhalation.

That is exactly what I was trying to describe to my sleep doctor about how I felt during one part of the sleep study. I am pretty sure it was during BiPAP tests and I am pretty sure they were using a PR machine with remote control?
I am not a Medical professional and I don't play one on the internet.
Started CPAP Therapy April 5, 2016
I'd Rather Be Sleeping
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#16
(04-21-2016, 03:27 PM)FrankNichols Wrote:
(04-21-2016, 03:22 PM)robysue Wrote: I have my PR BiPAP set to Rise Time = 3 because Flex drove be crazy: I could feel that small increase from "EPAP-FLEX" to "EPAP" during the second half of my exhalations when I was a newbie and it felt like the machine was trying to force me to inhale before I'd finished exhaling. Rise Time = 3 keeps the increase back to IPAP from feeling like I've hit a brick wall with each inhalation.

That is exactly what I was trying to describe to my sleep doctor about how I felt during one part of the sleep study. I am pretty sure it was during BiPAP tests and I am pretty sure they were using a PR machine with remote control?
Could be. The last titration test I had was a couple of years back. I remember specifically telling the tech I used a PR machine and I hated flex and to make sure that Rise Time was set to 3. I think she honored my requests because I didn't get that nagging tickle in my throat with the sensation that the machine was trying to encourage me to inhale while lying in bed for over an hour during my first WASO period.

I'll add that when I was a newbie I was so sensitive to the increase in pressure during exhalation that my original Resmed S9 AutoSet's EPR + EasyBreathe also drove me nuts. The Resmed EPR+EasyBreathe starts to raise the pressure during the last 1/5 or so of the exhalation. The EasyBreathe on the Remsed S8/S9 VPAPs waits until the inhalation is detected before starting to increase the pressure.

I had a very long winded discussion about this with two different RTs who were regular posters on the other board during my first year of PAPing. At first they didn't want to believe me that EPR+EasyBreathe felt distinctly different from what I was then calling "real bilevel", but then one of them found the appropriate graphic buried deep on the Resmed web pages that showed definitively that EasyBreathe on the VPAP cycles subtly differently than EPR+EasyBreathe on the S8s and S9s.

I would assume that difference is still present in today's AirSense and AirCurve machines.
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#17
(04-21-2016, 02:43 PM)FrankNichols Wrote: Well, here is an example of what I was looking at while typing before, as you can see it displays exactly what I am referring to - the flow rate reverses causing a spike downward in pressure, which is then corrected by the machine bringing the pressure back up to the 10 line which is the setting (in my case). What I see is that there is a positive spike is at the end of the inhalation, and a negative spike at the beginning of the exhalation - which is what I described. I don't know if they are intentional or do to lag or even potentially a "fluid hammer" effect (inertia).

Describing the positive spike was simply to setup the entire scenario, i.e. that this happened in both directions.

Pressure at Mask vs Flow Rate


without knowing what type of machine it is (likely a resmed) AND what the settings are... the chart is meaningless... also, you don't normally see that behavior on a flow/mask pressure chart.

for what it's worth, here's a trace from a lab machine showing the recorded pressure wave:
[Image: GcI9IZdl.png]
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#18
(04-21-2016, 03:50 PM)palerider Wrote:
(04-21-2016, 02:43 PM)FrankNichols Wrote: Well, here is an example of what I was looking at while typing before, as you can see it displays exactly what I am referring to - the flow rate reverses causing a spike downward in pressure, which is then corrected by the machine bringing the pressure back up to the 10 line which is the setting (in my case). What I see is that there is a positive spike is at the end of the inhalation, and a negative spike at the beginning of the exhalation - which is what I described. I don't know if they are intentional or do to lag or even potentially a "fluid hammer" effect (inertia).

Describing the positive spike was simply to setup the entire scenario, i.e. that this happened in both directions.

Pressure at Mask vs Flow Rate


without knowing what type of machine it is (likely a resmed) AND what the settings are... the chart is meaningless... also, you don't normally see that behavior on a flow/mask pressure chart.

for what it's worth, here's a trace from a lab machine showing the recorded pressure wave:
[Image: GcI9IZdl.png]

It's a ResMed CPAP mode no EPR, no RAMP, nothing. Just CPAP. And Imgur is overload - lol...
I am not a Medical professional and I don't play one on the internet.
Started CPAP Therapy April 5, 2016
I'd Rather Be Sleeping
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#19
(04-21-2016, 04:02 PM)FrankNichols Wrote:
Quote:[Image: GcI9IZdl.png]
It's a ResMed CPAP mode no EPR, no RAMP, nothing. Just CPAP. And Imgur is overload - lol...
That machine is NOT a CPAP: It's got to be a ResMed VPAP running in straight VPAP mode with IPAP = 18 cm and EPAP = 13 and a PS = 5. And here's why:

From top to bottom the graphs in this image are:
  • Flow rate (or wave flow): The rate air is going into or out of the lungs measured in L/min
  • Mask pressure: The actual pressure delivered at the mask itself, measured in cmH2O
  • Expiration Set Pressure: The fixed EPAP pressure the machine is set to use, measured in cmH20
  • Inspiration Set Pressure: The fixed IPAP pressure the machine is set to use, measured in cmH2O.
  • Leak: The excess leak recorded by the machine
  • Minute Ventilation: The (estimated) total amount of air inhaled by the patient in a one minute period measured in L/min obviously.
  • Tidal Volume: The amount of air inhaled in one inhalation measured in Liters.

We know this is a NOT a Resmed CPAP because the set EPAP is NOT equal to the set IPAP: Look at those two curves closely: The IPAP is about 18cm. The EPAP is about 13cm. (The trick is to look at the scales on these two graphs--they're not the same.) So is machine is NOT a CPAP: It's got to be a ResMed VPAP running in straight VPAP mode with IPAP = 18 cm and EPAP = 13 and PS = 5.


The Mask Pressure curve lets us see how bilevel really works. Here's a marked up version of the relevant graph from the original image:

[Image: wdibnOO.png?1]

The part of the Mask Pressure curve before EasyBreathe is turned on shows how bilevel works in its most primitive form: If you look at the inhalations and exhalations that are trapped between the added vertical lines, you can easily see that when the flow rate graph is above 0, the mask pressure is at 18, and when the flow rate graph is below 0, the mask pressure is at 13. There is a sharp sudden drop in the pressure at the end of each inhalation and an equally sharp jump in pressure at the beginning of each inhalation. That's basically what my PR System One's transitions look like since I have Flex turned off: When I'm inhaling, the pressure is constant at my (current) IPAP setting and when I'm exhaling, the pressure is constant at my (current) EPAP setting. And there are sharp transitions between the two pressure settings.

Turning EasyBreathe on controls the transition between IPAP and EPAP. That's all it does, but it controls the transition in a major way. Now look at the inhalations and exhalations in the "EasyBreathe" part of the graph: When the beginning of the inhalation is detected, the machine gradually increases the pressure until the IPAP setting is reached and ideally the IPAP pressure is reached just as the inhalation is finishing and the exhalation is starting. Once the exhalation starts, the pressure is dropped down more quickly than it was increased, but more slowly than the sudden drop from IPAP to EPAP that occurs without EasyBreathe. Once the pressure has dropped all the way to EPAP, it stays there until the beginning of the next inhalation starts.

It's also worth noting that on a Resmed VPAP there is no "EPR" because the "EPR" is built into the IPAP and EPAP settings. (EPR = IPAP - EPAP). The Resmed CPAP/APAPs need an EPR setting in order to use a slightly modified EasyBreathe algorithm. Here's a (old) image that I stole once upon a time for another post several years ago that shows the affect of EPR/EasyBreathe on the pressure curve for an S9 CPAP:

[Image: Screen%20Shot%202015-04-29%20at%2011.39....1278411991]

As this image shows, on a Resmed CPAP/APAP with EPR and EasyBreathe turned on, the therapeutic pressure setting is reached only at the end of every inhalation. At the beginning of the exhalation, the pressure then drops by a fixed amount that corresponds to the EPR setting. The drop in pressure looks sort of like the EasyBreathe drop on a VPAP. But on the CPAP/APAPs, as soon as "minimum" pressure is reached, the machine starts to slowly increase the pressure until the next inhalation is detected. At that point the rate of the pressure increased becomes more rapid and looks similar to the pressure increase on the VPAP. The difference, however, is that there is no "corner" in the mask pressure graph on a Resmed CPAP/APAP at the end of each exhalation. On the VPAP there is a small, but distinct corner at the end of each exhalation.

I'm not sure anybody ever uses EPR without EasyBreath on a Resmed CPAP, but for those who are interested, this is what it looks like:

[Image: 106094b01118e8b18e8f24e6c28a4360.jpg]
The dotted pressure curve is EPR without EasyBreathe. The transition to the therapeutic pressure setting is "faster" and happens earlier in the inhalation than the traditional EPR+EasyBreathe combo. The EPR+EasyBreathe combo is the default setting if you use EPR on a Resmed machine.

Finally it's worth noting that BiFlex affects the EPAP-IPAP transitions in different way than EasyBreathe does. Unfortunately we don't have the ability to get Mask Pressure graphs off the PR machines because they don't record it. From an ancient post on another forum we can look at this figure however, that provides a snapshot of Flex vs EPR+EasyBreathe:

[Image: 732976896c4b25d279984b3ca9f9575e.jpg]
The three vertical lines were added by a poster on the other forum. They are relevant to the discussion however.

All Flexes increase the pressure at the blue line, which is when exhalation has dropped significantly, but well before the next inhalation actually starts. The EPR+Easybreathe used on the Resmed APAPs and CPAPs start increasing the pressure at the red line: Later in the exhalation, but still before the inhalation really starts. VPAPs and BiPAPs increase the pressure at the green line---at the start of the inhalation proper. Even with BiFlex turned on, the BiPAPs increase the pressure "faster" than the VPAPs with EasyBreathe turned on.
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#20
I am sorry, I was not clear... oops. pale rider said that nothing could be determined about my graphs because he didn't know what machine it was or the settings, I was answering him. I could not see the graphs above because when I tried, imager said it was over loaded.
I am not a Medical professional and I don't play one on the internet.
Started CPAP Therapy April 5, 2016
I'd Rather Be Sleeping
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