What's the difference?

General Discussion on any topic relating to CPAP and/or Sleep Apnea.
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Arizona-Willie
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What's the difference?

Post by Arizona-Willie » Wed Aug 13, 2008 4:26 pm

Bi-pap and Bi-level machines have two pressure levels, as I understand it, one for inhaling and one for exhaling.

Some CPAP machines have EPR where it lowers the pressure when you exhale.

So what's the difference?

Seems to me both types do the same thing.


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bdp522
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Re: What's the difference?

Post by bdp522 » Wed Aug 13, 2008 7:35 pm

C-flex and EPR only give momentary pressure relief so it's easier for you to start the exhale. The pressure is back to normal before you start to inhale. Bipap keeps the set exhalation pressure for the entire exhalation. Bipap also allows for a larger ramge of pressure relief. Bipap also comes with c-flex for those who need even more pressure relief at the start of exhale.

Brenda


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rested gal
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Re: What's the difference?

Post by rested gal » Thu Aug 14, 2008 8:11 am

bdp522 wrote:C-flex and EPR only give momentary pressure relief so it's easier for you to start the exhale. The pressure is back to normal before you start to inhale.
That's true of C-Flex (in Respironics machines), however EPR (in resmed machines) keeps the pressure down throughout the entire exhalation and until you start to breathe in again -- or until X number of seconds have gone by and you haven't started to inhale yet. In that respect (keeping the pressure down throughout the entire exhalation) EPR would be more like the way a bilevel machine works than C-Flex is, but neither feel exactly like the complete relief when exhaling that a bilevel gives. Nor does EPR's exhalation pressure relief work the way a bilevel's lower exhalation pressure does.

To me, EPR has more of a feeling of resistance in STARTING to breathe out than C-Flex has, and definitely more of a feeling of resistance in STARTING to breathe out than with any true bilevel machine. EPR brings the exact 1, 2, or 3 cms drop down as the exhalation progresses...not giving all of its drop at the beginning of the exhalation. A bilevel machine gives its full drop in exhale pressure right when you start to exhale, and keeps the pressure down until you start to breathe in again... no matter how long that takes.

Incidentally, that's one reason why it's important to have the EPAP (exhalation pressure) on a bilevel machine set high enough to keep the throat from collapsing completely. Gotta be able to draw at least a thread of air in again to trigger the bilevel machine to switch to the higher IPAP (inhale pressure) or it will just stay, and stay, and stay, and stay down at the EPAP pressure. So...EPAP should be set at a pressure high enough to prevent full apneas...to prevent total closure of the airway.

But back to C-Flex vs EPR:
EPR's drop happens as the exhalation progresses -- not a full drop at the beginning of the exhalation. I prefer C-flex in order to get the most drop each time I START to breathe out. C-Flex does not give exact 1, 2, or 3 cm drops that EPR can be set for, but C-Flex does give its drop in pressure at the beginning of the exhalation -- where most people need the most drop (imho), in order to get each exhalation started easily.
bdp522 wrote: Bipap keeps the set exhalation pressure for the entire exhalation. Bipap also allows for a larger ramge of pressure relief. Bipap also comes with c-flex for those who need even more pressure relief at the start of exhale.
Brenda describes that well. Just a small typo... Respironics' BiPAP comes with "Bi-Flex", not c-flex. Bi-flex does drop the beginning of the already lower exhale pressure setting in the Respironics bipap a bit more. Rounds out or "softens" the transitions between inhaling/exhaling pressures. As with any of the "Flex" comfort features in the Respironics' machines, Bi-Flex can be turned off if a person doesn't like or need it.

Last edited by rested gal on Thu Aug 14, 2008 8:24 am, edited 1 time in total.
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Arizona-Willie
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Re: What's the difference?

Post by Arizona-Willie » Thu Aug 14, 2008 8:20 am

Thanks for the replies and information.

I had been wondering about that. I dont' use the EPR on my Resmed but when I see bi-paps or bi-levels mentioned I always wondered what the difference was since EPR <appears> to have two pressure levels also.

Unless a person needed more than 3 cm difference in pressures, it doesn't seem that a bi-level machine would be worth the extra money. Not really all that much difference.

But then, I haven't experienced breathing via a bi-level so I guess it might make more of a difference than it seems.

Thanks again for the info.


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Re: What's the difference?

Post by rested gal » Thu Aug 14, 2008 8:53 am

Arizona-Willie wrote:But then, I haven't experienced breathing via a bi-level so I guess it might make more of a difference than it seems.
Right, it does make more of a difference. Even if only a 3 cm difference in IPAP (inhale) and EPAP (exhale) pressures is set on a bilevel (bipap) machine, getting an exhalation started is much, much easier with a bilevel machine than with EPR set for a 3 cm drop on another type of machine.

Here's another point of "difference" to consider... say that a person's prescribed pressure to prevent full apneas is 10. And say that any less than 10 does, indeed, allow that person's throat to collapse shut completely as their exhalation peters out or during the pause before inhaling again. Scenario: Pressure of 9 lets an apnea happen for that person. 10 prevents an apnea. If EPR is set at 1 (for a 1 cm drop) putting the pressure down at 9, that person's throat IS going to slam shut sometimes during the night -- especially during the pause at the end of exhaling...BEFORE he/she can start to breathe in again. Situation is worse if EPR is set for more relief, dropping that necessary prescribed pressure of 10 down to 8 or 7.

With a bilevel machine, ideally the person has had a "bilevel titration" in a sleep lab, and the absolute minimum pressure that will prevent full apneas has been chosen. The EPAP (exhale) pressure. In the same person we were talking about in the example above, that pressure might very well be 10...to prevent full apneas. So, the EPAP (exhale pressure) is set at 10. The IPAP (inhale) pressure is set higher...perhaps at 13.

Even without a formal bilevel titration, a person who wants to use a bilevel machine simply for more comfort exhaling, could set an effective EPAP pressure if they had the software to see what EPAP pressure they needed to prevent Obstructive Apneas from appearing on the data when they downloaded the machine.

Personally, if I were going to use a cpap machine that has EPR, and I were going to use EPR, I'd set the cpap's regular pressure one or two cms higher than I'd been prescribed. So that the drop I received during exhaling with EPR would not be as likely to allow my throat to close off with an apnea at the end of the exhalation and prevent getting another breathe STARTED in a timely fashion...a scenario which could happen over and over again if my prescribed pressure was right on the cusp, so to speak, of keeping my throat at least partially open (so that inhaling could be STARTED) during the pause before starting to breathe in again.

Using the example of the fellow who needs 10 to prevent full apneas at the end of exhaling, if I were him and were going to use a cpap machine with EPR, I'd set my pressure at 12 if I were going to use EPR 2 or 3. I'd set the pressure at 11 if I were going to use EPR 1.

But that's just me, and I'm not a doctor or anything in the health care field. I can (and have, in the past) gotten very good treatment with no exhalation relief of any kind. I don't need C-Flex, A-flex, or EPR. Nor do I even need to use a bilevel rather than a plain cpap. I just like using a bilevel for the comfort in exhaling right from the get-go. Like breathing out into an empty hose. Feels nice to have no feeling of pressure at the beginning of the exhalation or at any point throughout it.

As a side note: Since C-flex allows the "regular" pressure back in before the exhalation is completely finished, the therapeutic pressure is already in place and (presumably) keeping the throat open at least enough to get an inhalation started again. If EPR has let the throat close completely, it will remain closed despite the person's attempts to breathe in, until X number of seconds has passed and the machine realizes "it ain't gonna happen" ...and suspends EPR (lets the regular pressure back in) until breathing has normalized again.

Of course, even with straight cpap and no exhalation feature of any kind, many people do not feel resistance when breathing out, especially as the night progresses. Many have reported that what felt like "work" breathing out at the beginning of each night, feels so natural as the night goes on that they have to put their hand up to the mask exhaust vent to be sure the machine is still blowing air at 'em. That's been the case for me, too, when I use straight cpap with no exhalation relief feature at all. I prefer that comfort from the start, though.

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Re: What's the difference?

Post by Arizona-Willie » Sat Aug 16, 2008 8:54 am

Very interesting, rested gal.

Hadn't considered EPR letting the airway collapse.

But then I don't use it so didn't really think too much about it. It just seemed like the machine had two pressure levels available which didn't seem much different than a bi-pap.

I am also one of those who feels a slight effort in exhaling when I first put the mask on but it soon feels perfectly natural and I sometimes check to see if it is working. But I'm at relatively low pressure too ... only 9.6 last night. I had been at 9.4 but I'm slowly moving it up trying to eliminate hypopneas. I get a LOT of those and a few apneas almost every night.

Wish I could rent an auto for a week or two to let it find my ideal pressure(s).

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Re: What's the difference?

Post by Snoredog » Sat Aug 16, 2008 10:05 am

EPR suspends its relief in the presence of SDB:
Comfort without compromise
To ensure comfort without compromising therapy, EPR has an automatic time-out feature. After determining the baseline breathing average for each patient, the device suspends EPR if the patient’s breathing drops 75% below the baseline for 10 seconds or more. EPR restarts when the event is over and breathing is again within range.
So in the presence of events resembling that of hypopnea or apnea, EPR is suspended. That means that exhale relief stops in the presence of events.

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Re: What's the difference?

Post by echo » Sat Aug 16, 2008 5:00 pm

Arizona-Willie wrote:Wish I could rent an auto for a week or two to let it find my ideal pressure(s).
Willie - I wouldn't worry too much about that. I tried to do that with my APAP and durn if it couldn't find the right pressure. Using CPAP and upping the pressure by a little bit every week worked much better at finding my 'sweet spot' than the APAP. of course YMMV!

You are on the right track. Keep going until you eliminate the hypop's. Continue if you're still getting flow limitations & still feeling bad. Watch out for central's (sometimes you have to find the right balance between the number of obstructive and central events). (that's my non-medical advice )
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Detecting centrals

Post by Arizona-Willie » Sun Aug 17, 2008 10:38 am

How do you tell a central apnea from the " regular " kind?

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Re: Detecting centrals

Post by Wulfman » Sun Aug 17, 2008 10:58 am

Arizona-Willie wrote:How do you tell a central apnea from the " regular " kind?
Probably no "true" way of telling without being wired up in a sleep study.
However......
They might appear at pressures over 10 cm. (pressure induced centrals)
They might appear in "clusters" on the reports (detailed data)......particularly using some APAPs with wider pressure settings where the pressure increases are still trying to resolve the events. ResMeds aren't suppose to respond to apneas over 10 cm and Respironics machines are suppose to back off of pressure increases after three attempts to resolve it. However, if there are snores and leaks, all bets are off concerning the pressure increases from APAPs.

If they were pressure induced and/or if your CPAP pressure was too high, there may still be some evidence in the detailed reports if clusters show up.

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Re: What's the difference?

Post by Arizona-Willie » Sun Aug 17, 2008 1:09 pm

Ah, sometimes I have clusters ... sometimes not.

I've noticed I usually do have a cluster after I first wake up and am laying there half asleep, sometimes going back for a few minutes and then awake again.
Just kinda waiting for the clock to chime for 6 am and then I go ahead and get up.

Sometimes I'm even aware I had an apnea while drowsing along like that. I realize I hadn't taken a breath and when I look at the data, sure enough there is one or more apneas.
This morning I believe there were 3 apneas and a bunch of hypops shown and only 3 apneas and 12 marked hypops all during the rest of the night.

And 1.3% of the night my SO2 was below 90% ... not real good.

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Re: What's the difference?

Post by RafterRattler » Sun Aug 17, 2008 1:30 pm

rested gal wrote:Here's another point of "difference" to consider... say that a person's prescribed pressure to prevent full apneas is 10. And say that any less than 10 does, indeed, allow that person's throat to collapse shut completely as their exhalation peters out or during the pause before inhaling again. Scenario: Pressure of 9 lets an apnea happen for that person. 10 prevents an apnea. If EPR is set at 1 (for a 1 cm drop) putting the pressure down at 9, that person's throat IS going to slam shut sometimes during the night -- especially during the pause at the end of exhaling...BEFORE he/she can start to breathe in again. Situation is worse if EPR is set for more relief, dropping that necessary prescribed pressure of 10 down to 8 or 7.

...

Personally, if I were going to use a cpap machine that has EPR, and I were going to use EPR, I'd set the cpap's regular pressure one or two cms higher than I'd been prescribed. So that the drop I received during exhaling with EPR would not be as likely to allow my throat to close off with an apnea at the end of the exhalation and prevent getting another breathe STARTED in a timely fashion...a scenario which could happen over and over again if my prescribed pressure was right on the cusp, so to speak, of keeping my throat at least partially open (so that inhaling could be STARTED) during the pause before starting to breathe in again.

Using the example of the fellow who needs 10 to prevent full apneas at the end of exhaling, if I were him and were going to use a cpap machine with EPR, I'd set my pressure at 12 if I were going to use EPR 2 or 3. I'd set the pressure at 11 if I were going to use EPR 1.
VERY interesting. This seems like it also explains what I see with my new Resmed Autoset II - and the question I posted in 'New to APAP'. When I use EPR, it seems that the machine CHOOSES a pressure 1-2cm higher then my sleep study titrated value. When I turn off EPR, it seems to drop back down. I'm hoping this means my machine is doing the right thing!

Mike

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Re: What's the difference?

Post by billbolton » Sun Aug 17, 2008 8:15 pm

Arizona-Willie wrote:Hadn't considered EPR letting the airway collapse.
It seems to me that is a somewhat "constructed" scenario, at best. There doesn't appear to be much evidence that I can discover in the literature of instances where a 1cm difference in flow rate is likely to cause a throat to "slam shut".

Cheers,

Bill

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Re: What's the difference?

Post by billbolton » Sun Aug 17, 2008 8:28 pm

Arizona-Willie wrote:I've noticed I usually do have a cluster after I first wake up and am laying there half asleep, sometimes going back for a few minutes and then awake again.
Any data scored when you are not fully autonomously breathing (that is fully asleep and breathing entirely unconsciously) is essentially meaningless. The flow generatrors are only able to score automomous breathing behaviour, but have no means of knowing whether you are in autonomous sleep or not..... so you need to discount any events scored when you know you weren't fully asleep.

Most APAPs have a "settling time" function that can be enabled to supress event scoring ove the time taken to initially fall asleep, but any semi-conscious breathing surrounding awakening in the morning will have to be manually be discounted by you in the assessing your sleep data from the flow generator (which is yet another good reason for having access to graphical representations of nightly data).

There are many artefacts of semi-conscious or conscious breathing behaviour that may be scored as apneas by flow generators but have nothing to do with obstructed or disordered sleep berating.

Cheers,

Bill

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