I need Help Understanding how a ResMed VPAP Auto 25 Works

I've got a call out to the group that provided the Machine. I should be hearing from them today.

I'd like to see something like this .... to start

MAX IPAP: 16.0
MIN EPAP: 8.0
Pressure Support: 4

I think this would mean that the lowest it would go is 12.0 ..... if a Higher IPAP was needed it could go up to 16.0 .... and as it went up it would drag the Min EPAP along .. always 4 behind ....

That would in effect get that pressure down 20% ..... I think that's correct anyway

Fred

jnk wrote:I
Although you are running in VAUTO mode, which is autobilevel mode, there isn't much room for pressure variation at those settings. With 4 cm of PS and only 5 cm difference between minimum EPAP and maximum IPAP, there is only 1 cm of play for the auto to work with, because of the way that machine works, which is very different from the other brand.

Thanks much for pointing this out----I knew I was shooting in the dark so to speak.

Now educate me on the differences cause I actually do want to know them.

Here's how I know my PR S1 behaves in AUTO mode:

1) Events that cause pressure increases:

• IPAP increases in response to hyponeas, flow limitations, and PR's RERAs.
  EPAP increases in response to vibratory snores (VS) and OAs.

In addition there's that (somewhat silly) hunt and peck algorithm that affects IPAP: In the same way the PR System One APAP increases CPAP pressure periodically to experimentally test if a modest (2cm?) increase in pressure improves the inspiratory part of the wave form in terms of roundness indicating a nice open airway, the PR S1 BiPAP does the same thing with the IPAP pressure. And this results in the characteristic saw-toothed IPAP graph you get when your breathing is nice and steady with a good clear airway for an hour or more.

2) When you turn the machine on (with NO ramp), the pressure will be at:

• EPAP = MIN EPAP
  IPAP = MIN EPAP + 2

3) And for pressure INCREASES, this happens:

• Need to increase IPAP:
  • * If IPAP - EPAP = PS, then increase both IPAP and EPAP together until IPAP = MAX IPAP is reached.
    * If IPAP - EPAP < PS, then increase IPAP until IPAP-EPAP = PS and then increase both IPAP and EPAP until IPAP = MAX IPAP is reached.
  Need to increase EPAP:
  • * If IPAP - EPAP = 2, then increase both IPAP and EPAP together until IPAP = MAX IPAP is reached
    * If IPAP - EPAP > 2, then increase EPAP alone until IPAP-EPAP = 2 and then increase both IPAP and EPAP together until IPAP = MAX IPAP is reached

4) And for pressure DECREASES, this happens:

• Need to decrease IPAP:
  • * If IPAP - EPAP = 2, then decrease both IPAP and EPAP together until EPAP = MIN EPAP is reached.
    * If IPAP - EPAP > 2, then decrease IPAP until IPAP-EPAP = 2 and then decrease both IPAP and EPAP together until EPAP = MIN EPAP is reached
  Need to decrease EPAP:
  • * If IPAP - EPAP = PS, then decrease both IPAP and EPAP together until EPAP = MIN EPAP is reached
    * If IPAP - EPAP < PS, then decrease EPAP until IPAP-EPAP = PS and then decrease both IPAP and EPAP together until EPAP = MIN EPAP is reached

jnk, can you give me a similar rundown on how the pressures are adjusted on the Resmed VPAP Autos when running in VAUTO mode?

fredn wrote:I'm not super thrilled with the level of communications that has been going on since we've had the CPAP Machine .... it seems like they expect us to know what to do and come to them when we need something and tell them what the solution is ..... rather than them really knowing all of the options to try and make this thing more comfortable for her.

I do Computer Problem Determination for a living ..... these guys fail at PD

As long as they have thier $$$$ ....... ooops .... did I say that.

Fred

Sounds to me like you know EXACTLY how that part works!

Was the diagnosis OSA or other? And what was the Rx exactly?

robysue I'm with you on wanting to know ..... this is where the rubber meets the road

Fred

fredn wrote:I've got a call out to the group that provided the Machine. I should be hearing from them today.

I'd like to see something like this .... to start

MAX IPAP: 16.0
MIN EPAP: 8.0
Pressure Support: 4

I think this would mean that the lowest it would go is 12.0 ..... if a Higher IPAP was needed it could go up to 16.0 .... and as it went up it would drag the Min EPAP along .. always 4 behind ....

That would in effect get that pressure down 20% ..... I think that's correct anyway

Fred

Sounds reasonable to me. And yes, that is how it works, as I understand it.

fredn wrote:I went back over maybe 60 or so detailed reports ...... everyone is flat-lined at 15.0 ..... except for 3 instances where it did go up to 16.0. There were no apneas or hypopneas when it went up to 16.0 though .... so I don't know what's going on.

ResMeds react to indications of obstruction. If it doesn't sense any, it doesn't react. Shape of flow curve can make the pressure go up, even when the change in flow does not result in hypopnea or apnea. It is the way it tries to be preemptive, as I understand it.

jnk wrote:

fredn wrote:I've got a call out to the group that provided the Machine. I should be hearing from them today.

I'd like to see something like this .... to start

MAX IPAP: 16.0
MIN EPAP: 8.0
Pressure Support: 4

I think this would mean that the lowest it would go is 12.0 ..... if a Higher IPAP was needed it could go up to 16.0 .... and as it went up it would drag the Min EPAP along .. always 4 behind ....

That would in effect get that pressure down 20% ..... I think that's correct anyway

Fred

Sounds reasonable to me. And yes, that is how it works, as I understand it.

jnk,

Correct me if I'm wrong:

Are both you and Fred saying that on the VPAP Auto set to Auto mode, IPAP = EPAP + PS at all times? In other words, IPAP and EPAP are not allowed to independently increase or decrease (within certain bounds)?

Or are you saying that MAX (IPAP - EPAP) = PS at all times? (which is just like the PR S1 BiPAP Auto).

And what does MIN (IPAP - EPAP) equal on the VPAP in Auto mode? Because I don't see how PS = 4 automatically says IPAP can't decrease below 12cm given the proposed settings---unless MIN (IPAP - EPAP) = 4 as well as PS = 4.

robysue wrote:. . . educate me on the differences . . .

RR uses a maximum PS, RM uses a fixed PS.

Here was one of my stranger attempts at explaining that:

viewtopic.php?f=1&t=56581&p=531326#p531326

ResMed made the VPAP Auto algorithm by basically taking it's regular AutoSet algorithm then piggybacking a PS onto it, it seems to me. Since the IPAP and EPAP are joined in unison, the VPAP Auto algorithm mostly ignores the fact that it is delivering two different pressure and basically reacts to breathing exactly as the ResMed AutoSet II does, best I can tell. It does so by interpreting the IPAP and EPAP into a theoretical pressure midway between IPAP and EPAP (or, PS divided by two, which it calls "AutoSet P") and the algorithm thinks it is delivering that one pressure midway between IPAP and EPAP, if that makes sense. But that is all hidden from the user inside the algorithm. The point is that it doesn't have a separate approach for determining IPAP and EPAP adjustments, since they are joined together.

Or as ResMed puts it in my manual:

The AutoSet pressure will vary across the session according to the patient’s needs. It responds to apneas, snoring and flattening of the patient’s flow curve. . . . Note: The device will stay at Min EPAP (with the selected amount of pressure support) during the Settling time (if selected) at the beginning of a session.

. . . Note that the actual delivered pressures will be AutoSet pressure ± 0.5 x pressure support (as set by the clinician).

robysue wrote: . . . Are both you and Fred saying that on the VPAP Auto set to Auto mode, IPAP = EPAP + PS at all times?

Yes.

RR made their approach before the AASM standardized what PS should be in a bilevel for treating OSA. A PS of 4 is the standard, but there is no way to enfore a PS of at least 4 in a RR autobilevel, since the minimum PS is built in as 2, I think. You can only set a maximum PS for the PS in that brand; you can't change the minimum.

In a RM autobilevel, you set the PS and PS never varies. The pressures are locked together in tandem, but are able to roam together between the max and min allowed, called IPAP Max and EPAP Min. But there is no PS Max or or PS Min--PS is always the same, even if IPAP hits the ceiling OR EPAP hits the floor.

fred, Jeff (jnk) is modest, but he understands thoroughly how the ResMed VPAP Auto 25 works. You're in good hands taking his advice.

I'm using the same machine. Very good machine.

Jeff's explanation of how the "PS" (pressure support) works in the ResMed VPAP Auto is a classic. He mentioned the link to his post. Here it is again...must reading for anyone who wants to understand the difference in how the two major brands use the "PS" setting:


Jeff's (jnk) great explanation about the difference in how the ResMed VPAP Auto (and "25") and the Respironics BiPAP Auto handle the "PS" (Pressure Support) setting:
topic: ResMed VPAP Auto 25 Clinician's manual
viewtopic.php?p=376749#p376749


___________________

Jeff (jnk) answering IFLEW's questions:
topic: ResMed Pressure Support
viewtopic.php?p=428022#p428022

Well the plot thickens as they say ......

In response to Jeff's question about the type of apnea that my wife has I asked her to dig out her sleep study.

I know more now than the 1st time that I read it .... and I see that during her study she had 41 events.

3 Apneas and 38 Hypopneas .... here's what I missed the first time ... the 3 apneas were CSA (Central Apnea) not OSA (Obstructive Apnea) ... so that raises another bunch of questions for the doctors .... and more reading on my part.

I guess there's some machines that are better for CSA than others .... the one that seems to be favored is "Adaptive servo-ventilation (ASV)" machines.

Like I said .... more to read. Got any thoughts?

There should be a specific diagnosis from the doc somewhere on the diagnostic study, or the diagnostic portion. Did the doc diagnose her as CSA or as OSA? A few central apneas isn't usually enough to get a CSA diagnosis, as I understand it. There should be a statement from the doc saying what was concluded about the specific condition, or conditions, to be treated.

Also, from the titration study, or titration portion of the study, what was the prescribed pressure, or set of pressures? That should be on the Rx, too.

If the centrals happened during the titration, for example, a lot of us have a few in reaction to the pressure at first.

And even if the centrals happened during the diagnostic study, or portion of the study, they still may be no big deal.

The key is what the diagnosis was, not what a few of the events were, as I understand it.

At another apnea board:
http://www.apneasupport.org/viewtopic.php?p=24677

In a reply titled "Nope" sleepydave (RRT, RPSGT and manager of an accredited sleep center) responds to honda's question:

honda wrote:
"Thanks for the comments, one other question though, do the 4 central apneas have any significance ?"

"None whatsoever.
sleepydave"

sleepydave's nicknames on cpaptalk are "deltadave" "StillAnotherGuest"(SAG) "Muffy" and "NotMuffy"

I'm not sure if we got all of the paperwork ..... we found the sleep study. We need to look somemore for the titration (if I have this right, that was the followup sleep study where she wears headgear and uses a cpap and they see what works?) Plus I have no idea if we ever got a formal Rx ....

Like everything else to do with doctors, medicines, and all else, you never know what should be happening, what you should be getting, what you should be doing, and even if you do get something what the heck it means.

I'm a reasonably intelligent guy .... and I find it a huge undertaking .... what about those that have if even harder.

Really a shame .....

Fred