Isn't Resmed's Expiratory Pressure Relief really Inspiratory Pressure Support??

[mhehe]

I,m afraid Reznik's thesis of Hypopneas causing in some way Central Apneas does not compute for me. In my particular case, I was diagnosed with severe OSA, Hypopnea by the legendary Christian Guilleminault, a pioneer in sleep disorders, in 1996. Iwas on fixed CPAP therapy for many years. Recently, almost 2 years ago, I went on a system one, model 560, APAP machine that showed very high AHIs, in the order of 15 or higher. In an effort to reduce this I am trying a Remed AirCurve 10 Vauto VPAP and was able to see an AHI value of 1.81. (The actual value is probably 1.5 since some of the CA events recorded by the machine were when I was awake but with a mask and machine on but swallowing from my mouth either saliva or other with the full face mask and low leaks). My event chart as recorded by the machine does not show a causal relationship between HA and CA as postulated by Reznik.

[Reznik]

I,m afraid Reznik's thesis of Hypopneas causing in some way Central Apneas does not compute for me. In my particular case, I was diagnosed with severe OSA, Hypopnea by the legendary Christian Guilleminault, a pioneer in sleep disorders, in 1996. Iwas on fixed CPAP therapy for many years. Recently, almost 2 years ago, I went on a system one, model 560, APAP machine that showed very high AHIs, in the order of 15 or higher. In an effort to reduce this I am trying a Remed AirCurve 10 Vauto VPAP and was able to see an AHI value of 1.81. (The actual value is probably 1.5 since some of the CA events recorded by the machine were when I was awake but with a mask and machine on but swallowing from my mouth either saliva or other with the full face mask and low leaks). My event chart as recorded by the machine does not show a causal relationship between HA and CA as postulated by Reznik.

Hi mhehe,

Thanks for jumping into the discussion.  

I've never suggested that hypopnea causes CA, that hypopnea always leads to CA, or that a IPAP always resolves CA.  It all depends upon the individual and the pressures involved.  In individuals who have hypopneas followed by CA, the Pressure Support/IPAP can help to break the cycle.  The wrong IPAP can make things worse.

Hypopnea leading to CA is very common for people who experience Cheyne Stokes Respirations.  CSR is a pattern of hypopnea, CA, hypopnea, hyperpnea, hypopnea, CA, etc.  Bi-level can break this pattern (in some people) by increasing tidal flow and leveling out the inspirations so that person inspires at a level rate.  In other people, ASV is required.  In other people, presumably nothing works.

Your event chart shows the result with your bi-level treatment, which includes an IPAP that is higher than your EPAP.  I think that its a bit unfair to suggest that my proposition is false because after you receive the very treatment that I suggest will help, you don't have the symptoms.  It is also possible that the treatment you're receiving is working so well that it prevents the patterns that I talked about, which is why you don't see them.  Or perhaps you're just not one of the people who have the condition I'm describing.

Suppose that I proposed that watching TV causes headaches in some people, and that taking aspirin before watching TV might help to prevent the headaches.  If you replied that you always take an aspirin before you watch TV, you never get headaches, and for that reason, watching TV must not cause headaches, I would respond the same way as I have here:  You might not be one of those people who get headaches when watching TV, and even if you were, the aspirin might be preventing it.

I do also want to conclude by pointing that my real thesis here is that EPR is a misnomer.  Since the Resmed machines with EPR activated actually increase the pressure only during inspiration (and always maintain the lower pressure both during expiration and during the period between inspiration and expiration - including apneas), it would seem that the machine doesn't so much relieve pressure during expiration as it does increase pressure during inspiration.  EPR is a misnomer and the value displayed on the screen of the machine is wrong because it never actually delivers that value except when you are actually breathing in.

[Sleepster]

I'm referring to someone who only needs (and uses) CPAP for the control of OSA, and who is using an Airsense 10 with the Expiratory Relief Feature.

The point I'm making applies to that situation. Someone who is titrated at a pressure of 12 cm can set their Airsense 10 to a pressure of 12 cm and be well-treated. If they then decide to turn on EPR to 3 it will provide them a greater level of comfort and they may still be well-treated with no significant changes in their indices. If they then raise their pressure to 15 cm it can elevate their CA index and cause discomfort.

This is only one of several possibilities and it may be that some people will indeed need to raise their pressure to compensate for EPR, but to say that such a thing is true for all, or even most, people is a claim that may not be valid.

[Reznik]

I'm referring to someone who only needs (and uses) CPAP for the control of OSA, and who is using an Airsense 10 with the Expiratory Relief Feature.

The point I'm making applies to that situation. Someone who is titrated at a pressure of 12 cm can set their Airsense 10 to a pressure of 12 cm and be well-treated. If they then decide to turn on EPR to 3 it will provide them a greater level of comfort and they may still be well-treated with no significant changes in their indices. If they then raise their pressure to 15 cm it can elevate their CA index and cause discomfort.

This is only one of several possibilities and it may be that some people will indeed need to raise their pressure to compensate for EPR, but to say that such a thing is true for all, or even most, people is a claim that may not be valid.

I'm really glad you responded because you've touched on something that doesn't make sense to me. 

If the hypothetical person we're talking about was titrated to a pressure of 12 cm, that means that 11 cm, 10 cm, and 9 cm was insufficient to control their OSA.  Rather, they were prescribed EPAP and IPAP of 12 cm.  

If they are using a Resmed machine that is set at 12 cm, and they then enable EPR at level 3, now they're really only getting 9cm of EPAP while still getting IPAP of 12.  Since EPAP is what prevents their OSA, they are now at a level of EPAP that is inadequate - they need 12 but are getting 9.  It may be well be more comfortable, but it isn't what they need.  They need 12 cm, per their titration, and are getting 9 because of the EPR.  Even worse, they now have 3 cm of pressure support, which as you've noted, can induce CAs.

Based upon what you've said, it seems you disagree with me, but I cannot tell why.  Can you give more explanation as to why turning on EPR at 3 would not make a significant change in their indices?  If 9 cm EPAP was sufficient to control their OSA, wouldn't that have been the result after their sleep study (instead of 12)?  Or is it just the case that when you introduce bi-level therapy, you sometimes can find that lower EPAPs can be sufficient and nobody really knows why?

[Sleepster]

If the hypothetical person we're talking about was titrated to a pressure of 12 cm, that means that 11 cm, 10 cm, and 9 cm was insufficient to control their OSA. 

Well, what it means is that raising the pressure above 12 didn't cause a significant reduction in their OA and H indices, but raising it from 11 to 12 did. At least it did that one night in whatever sleeping positions and other conditions happened to be present. OSA is a statistical thing, it's not like it completely disappears at some magic level of pressure.

If they are using a Resmed machine that is set at 12 cm, and they then enable EPR at level 3, now they're really only getting 9cm of EPAP while still getting IPAP of 12.  Since EPAP is what prevents their OSA,

What makes you think that it's EPAP that prevents OSA? It may well be that with no CPAP therapy the airway rarely collapses during exhale, but instead after inhalation has begun. I don't know.

Even worse, they now have 3 cm of pressure support, which as you've noted, can induce CAs.

That seems to be a more prevalent opinion on this board than it used to be. I don't know that it's anywhere near as prevalent among patients. It takes a higher PS than 3 to elevate my CA index and perhaps that's true of a majority of us. It may be that raising PS has no effect at all on the CA index for a majority of people. It may also be true that the effect is entirely temporary for many of the people who do experience it, in that it tends to subside as the patient adapts.

Can you give more explanation as to why turning on EPR at 3 would not make a significant change in their indices? 

Before trying to understand why it happens, observe that for a lot of people turning on EPR makes no significant change in their indices.  

This reminds me of the old joke about theoretical and experimental physicists. The experimentalist has measured both A and B and found that A is larger. The theorist goes to work trying to prove that experimental result. Months later the experimentalist reports that new experiments indicate that B is larger. There's an audible sigh of relief from the theorist as he says that that will be even easier to prove.  

[ajack]

There seems to be a misunderstanding, that I also shared, if you read a recent post. It is common in groups to have a shared falsehood. I too took what was said for granted, that you raise the ipap when you add epr and passed it on.

I now think I was wrong. we aren't working from the epap end and adding PS to increase ipap. you already have the ipap right. So adding epr just gives you, what could be called an epap setting. It shouldn't affect the treatment pressure, be it EPR 1,2 or 3

[Sleepster]

It is common in groups to have a shared falsehood.

Yup, it even has a name. Group-think.

I'm not saying that's necessarily the case here, though. I think that raising the pressure to compensate for EPR might be the right thing to do in some cases, but it's not true in all cases, and I doubt that it's true in the majority or even vast majority of cases.

I remember, it was December 2011, shortly after my CPAP therapy began, when I was switched from CPAP at the titration pressure of 13 cm to BiPAP at 13 over 8 to treat aerophagia. It made my CA index shoot up to around 15 or 20. No one here on this board had a clue as to why that might happen. Now it seems to be common knowledge that it's a result of blowing off too much CO2. My doctor and my DME had no clue, either. They lowered the pressure thinking it was induced by high pressure. When they lowered it to 11 over 8 my CA index went down and the aerophagia abated. After that I took over my own treatment.

Anyway, getting back to the group-think thing, I think there's another area where that might apply to some of us around here. We hear so much about clueless doctors and DME's that we think they're all lame and we can do so much better. But the thing is, there are a lot of medical professionals out there who do know exactly what they're doing. Some of them are researchers, but all of them are using the results of clinical research to advise and treat patients. On the other hand, we are not professionals, we don't have the same knowledge base as some of these doctors and researchers, and we instead rely on what we read and on the anecdotal evidence we gather by talking to and advising people here. Yes, we can do a lot better than the lame professionals out there offering treatment, but our knowledge level is and always will be poor compared to the genuinely competent professionals.

[Reznik]

There seems to be a misunderstanding, that I also shared, if you read a recent post. It is common in groups to have a shared falsehood. I too took what was said for granted, that you raise the ipap when you add epr and passed it on.

I now think I was wrong. we aren't working from the epap end and adding PS to increase ipap. you already have the ipap right. So adding epr just gives you, what could be called an epap setting. It shouldn't affect the treatment pressure, be it EPR 1,2 or 3

I'm afraid I don't quite understand what you're saying here.  

EPAP is the pressure that the machine gives during expiration, during any transition from expiration to inspiration (or the other way around), and during any apnea.  In CPAP therapy, EPAP is the same as IPAP.  In Bi-Level Therapy, EPAP is always LOWER than IPAP.

IPAP is the pressure that the machine gives during inspiration.  In machines that are spontaneous, the IPAP is only delivered after the patient initiates inhalation and stops as soon as the patient stops inhalation.  In machines that are timed (or timed backup), the IPAP will be delivered at the programmed time interval to force inspiration even when it has not happened.  In CPAP therapy, IPAP is the same as EPAP.  In Bi-Level Therapy, IPAP is always HIGHER than EPAP.

Pressure Support is IPAP minus EPAP.

When we speak of "increasing Pressure Support," we are increasing the difference between IPAP and EPAP.  So, if IPAP = 8 and EPAP = 5, you have a Pressure Support of 3.  If you increase IPAP to 9, pressure support increases to 4.  But, if you increase IPAP to 9 and EPAP to 6, then Pressure Support remains at 3.

When a ResMed AirSense 10 model is in AutoSet mode, enabling Expiratory Pressure Relief converts the machine to a spontaneous (non-timed) BiPap Mode, where the displayed pressure on the screen is the IPAP, the EPR level (1, 2, or 3) is the amount of Pressure Support, and the EPAP is the displayed pressure minus the EPR level.

So, if a ResMed Airsense 10 is set for 10.0 without EPR enabled, then the patient is receiving EPAP at 10, IPAP at 10, and Pressure Support is 0.  If the patient enables EPR at 3, then his EPAP lowers to 7 (3 below the machine's stated pressure), his IPAP remains at 10 (the machine's stated pressure), and his Pressure Support increases to 3 (IPAP of 10 minus EPAP of 7 = 3).  

Far from getting expiration relief, the patient is actually getting LESS than his prescribed EPAP pressure (7 instead of 10) and a healthy dose of pressure support (3.0) that he may not need and which may actually cause him problems.  The patient may even complain that the machine feels as if it is inflating his lungs when he breathes in.  That's why I say EPR is really Inspiratory Pressure Support, and not Expiratory Pressure Relief.

On the other hand, if a patient is titrated to BiPap therapy at EPAP of 8 and IPAP of 10 and given a $1,700 AirCurve 10 S or VAUTO, that patient could get the same therapy with a cheaper $800 AirSense 10 CPAP or Autoset or an AirMini set to 10 with EPR set a 2.0.  A machine so configured would deliver EPAP 8.0 and IPAP 10.0, just like the more expensive AirCurve 10 when set to those settings.

I'll post in another message (in reponse to Sleepster's question) why EPAP is what matters when it comes to preventing obstructions.

I hope this clarifies things.

[Crimson Nape]

This post was deleted because my laptop jumped to this thread while I was trying to post in another one.

[Reznik]

If they are using a Resmed machine that is set at 12 cm, and they then enable EPR at level 3, now they're really only getting 9cm of EPAP while still getting IPAP of 12.  Since EPAP is what prevents their OSA,

What makes you think that it's EPAP that prevents OSA? It may well be that with no CPAP therapy the airway rarely collapses during exhale, but instead after inhalation has begun. I don't know.

Hi Sleepster,

Thanks again for responding!

Every resource that I've read indicates that EPAP is what prevents OSA, and Pressure Support (the difference between EPAP and IPAP) affects tidal volume and can be used to treat central apneas.  Too much pressure support can create too large a tidal volume and too little Pressure Support can create too little tidal volume.  The right amount of EPAP and Pressure Support is, of course, variable from person to person, and may even vary during the night.  That's why Auto Bi-Level machines and ASV machines will adjust EPAP and IPAP independently.

For example, I've read titration guides from Resmed & Respironics, titration guides from several sleep clinics around the country, published articles in Sleep and Chest, a sleep technologists guide to titration, and clinical manuals for all the Resmed machines sold in the U.S.  They all say the same thing, i.e. EPAP is what prevents obstructions by splinting the airway during expiration and during the pauses between inspiration and expiration.  IPAP affects tidal volume.

I've also read the details (in both the clinical guides and published studies) about how Auto BiPAP machines and Bi-Level Auto ASV machines work, and those guides indicate that EPAP is adjusted to respond to flow restrictions and obstructive apneas, while Pressure Support (via IPAP) is adjusted to either increase or decrease tidal volume as appropriate to help prevent central apneas.  The fact that both ResMed and Respironics program their Auto bi-level machines to do so suggests that they believe that EPAP is what prevents obstructions, while Pressure Support (via IPAP) is what affects tidal volumes and central apneas.

If you're looking for a quick and dirty way to confirm what I've said here, I recommend looking at page 4 of the Clinical Guide for the ResMed AirCurve 10 ASV.  

It explains that EPAP is adjusted to respond to obstructions and inspiratory flow limitations:

"In addition to the functionality of the ASV mode, the device in ASVAuto mode automatically adjusts the expiratory pressure in order to provide only the amount of pressure (EPAP) required to maintain upper airway patency. The device analyzes the state of the patient’s upper airway on a breath-by-breath basis and delivers expiratory pressure within the allowed range (Min EPAP and Max EPAP) according to the degree of obstruction. EPAP is automatically adjusted depending on three parameters: inspiratory flow limitation, snore, and obstructive apnea."

It explains that Pressure Support is used to treat central apneas:

"[the machine] treats central sleep apnea and/or mixed apnea and periodic breathing by automatically adjusting the pressure support (PS) in a defined pressure range to maintain Minute Ventilation at the target."

Since EPAP is the lower number (IPAP is always equal to or higher than EPAP) and since IPAP is only present during actual inspiration (and not during apneas or the transition between inhalation/expiration), it makes sense that EPAP is the number that matters when it comes to preventing obstructions.  It also makes sense that increasing IPAP will cause an increased tidal volume, since it essentially gives a boost only while you're actually breathing in.