Weird (?) question. Normal on exhale?

[nudave]

So I've been using my S1 now for 2 weeks now. Avg AHI is 2.08 and I have it down to minimum leaks. All is well, except for one thing..explained below:

One night last week, I woke up and I could sense the machine breathing for me. My breathing was off of the machines breathing timing. I would exhale and could hear the noise/air flow increase out of the mask, and then inhale the noise/air flow would decrease. I would actually have to reset my breathing to match the S1. It happened again last night as well. My experience so far (when awake, falling asleep, and waking up in the middle of night) the pressure has been steady and couldn't hear an increase/decrease in air flow.

[Alshain]

It shouldn't breath FOR you. It's not a respirator. It should maintain a constant pressure unless you have C-Flex turned on, in which case it will decrease it's pressure when you exhale. This decrease is not a 'timed' event, it detects when you are exhaling so it can't get out of sync. I'm not sure what would cause it to increase when you exhale, that doesn't sound right. The only thing that comes to mind is if your mistaking the venting of CO2 on exhale for an increase in pressure. Naturally when you exhale, the entire pressure under the mask will be higher because you and the machine are putting force against it. When you inhale, you create a vacuum so only the machine is putting force against the mask.

[Pugsy]

Sounds like Flex setting is not suited to your breathing rhythm. Perhaps you are/were just now more aware of it.
I would suggest you try other Flex settings to try to find something more compatible. I find AFlex of 3 is simply to fast, I can't keep up. Setting of 1 pretty much is perfect match to my normal rhythm. Everyone breathes a little differently while awake and it can even change during sleep.

There is a choice to test each setting in the menu. Do you have the clinical manual that shows how to get to it?

Flex settings (either CFlex or AFlex) is not the same per cm pressure drop that ResMed machines do. It is a much smaller decrease and works more with respiration rhythms.

http://cflexplus.respironics.com/ CFlex plus description. Others have links in upper right.

[nudave]

Great! Thanks Pugsy and Alshain. I'll try X1 tonight. I've been using X2 since the night after I started. I started on X3.

I'll follow up with you tomorrow.

Edit: I was also thinking it may have been the pressure pulses, but I think that its unlikely.

[Alshain]

Sounds like Flex setting is not suited to your breathing rhythm. Perhaps you are/were just now more aware of it.
I would suggest you try other Flex settings to try to find something more compatible. I find AFlex of 3 is simply to fast, I can't keep up. Setting of 1 pretty much is perfect match to my normal rhythm. Everyone breathes a little differently while awake and it can even change during sleep.

There is a choice to test each setting in the menu. Do you have the clinical manual that shows how to get to it?

Flex settings (either CFlex or AFlex) is not the same per cm pressure drop that ResMed machines do. It is a much smaller decrease and works more with respiration rhythms.

http://cflexplus.respironics.com/ CFlex plus description. Others have links in upper right.

Well maybe I don't understand the Flex settings like I thought I did. Sounds like maybe there is a rhythm. Sorry for the bad info.

[Pugsy]

Well maybe I don't understand the Flex settings like I thought I did. Sounds like maybe there is a rhythm. Sorry for the bad info.

Don't worry about it. There is a slight reduction but just not like the EPR feature on your machine. I have never used a ResMed machine. So I can't adequately explain how the difference in the 2 machines feels. I have played with the various settings though. AFlex mimics my own breathing to the point it feels just like I am breathing normally. CFlex I couldn't really feel any difference at any settings. My first machine was M series APAP with only CFlex as a choice. I ended up turning it off. Next was M series APAP with both AFlex and CFlex choices. Aflex of 2 was a perfect match to my respiration rate. With the new PR S1 APAP, I find that Aflex of 1 is better match. When I try 3 it simply rushes me to breathe. Makes me feel like I am breathing too fast, like hyperventilating, though I know I am not.

It is hard to explain. Since it is strictly a comfort feature I just tell people to play with the choices till they find something that is the most comfortable.

I have never noticed the pressure pulses so I don't know how much this might impact how a person feels on exhale.

[robysue]

Chiming in as someone who has used both a S9 Autoset with EPR turned on (for several months) and a S1 BiPAP Auto with Bi-Flex turned on for a few 30 minute experiments here and there.

Pugsy is right, the two systems don't work the same way. I think for most people, the difference in feel may be so subtle that it's hard to tell the difference. But for some people, the differences between the systems are significant enough to detect real, meaningful differences in how the machines feel in use.

To understand the differences it helps to look at the idealized wave forms illustrating what's going on in each system.

Resmed EPR
Here's the picture for the EPR system on the Resmed machines:

The top curve is the graph of the pressure the machine is providing. The bottom is the wave form of the patient's breathing. Note that the change from "exhale" to "inhale" occurs somewhere on that flat part of the wave form. And different folks have different perceptions of when they "quit exhaling" and "start inhaling".

Notice that the EPR algorithm on the Resmed machines reduces the pressure by a fixed amount at the start of every exhalation. At the start of the exhalation, the rate of drop in pressure is a bit steeper than it is during the middle part of the exhalation. The minimum pressure level, which equals SET PRESSURE - EPR Setting, is reached sometime during the middle to late part of the exhalation and pressure starts to very gradually increase until you start to inhale, at which point the pressure is increased (rather rapidly) back up to the SET PRESSURE.


Reprionics Flex Systems
The various Flexes in the PR family of machines work differently than EPR. The most basic of the Flexes is C-Flex. It's curve looks like this:

The dotted line on the patient's wave form is the zero line---i.e. no air moving in or out of the lungs. And some folks (and the EPR algorithm) seem to feel that's the point where "exhale" turns to "inhale." But other folks (and the Resprionics BiPAP algorithm for switching to IPAP) seem to define the beginning of "inhale" later---where there's clear movement of air into the lungs as marked by the vertical lines on this graph.

Now notice that C-Flex reduces the pressure by a small (non-constant) drop in pressure at the start of each exhalation---i.e. the pressure drops below the current CPAP pressure setting by just a bit, and the pressure increases back up to the full pressure level starting about half-way through the exhalation.

The next step "up" in the Flex family is C-Flex+. It's wave form looks like this:

Notice that as with C-Flex, there's a bit of non-constant pressure relief right at the start of the exhale. But C-Flex+ does the increase back up to full pressure in two stages: Halfway through the exhale, C-Flex+ increases the pressure part-way back to the full pressure setting and then as soon as the inhalation proper starts, it quickly (as in instantly) jumps the pressure back to the full setting.

A-Flex is basically C-Flex+ for the Resprionics Auto machines and it looks like this:

The main difference is that as the pressure is increased, A-Flex also increases that middle-level target line for the first stage of pressure increase that takes place during the second half of each exhalation.

The Flex on my machine is Bi-Flex and it looks like this:

Note that Bi-Flex is similar to A-Flex and C-Flex+ in that it provides an additional small (non-constant) drop in pressure at the start of each exhalation---i.e. the pressure drops below the EPAP setting by just a bit. And then approximately half-way through the exhalation, the pressure is increased back up to the full EPAP setting. And as soon as the inhale starts, the pressure (instantly) jumps up to the IPAP setting.


Notes about both systems
It's important to realize that both EPR and all the various Flexs depend on the machine's ability to accurately track and interpret the actual transition from inhale to exhale and back to inhale. And whether the person using the machine has the same idea as the machine does about where their exhales stop and their inhales start. If a particular machine's algorithm for tracking your breaths doesn't do a good job or if it's job doesn't match up with your brain's notion of what's going on, it's not a surprise that you might feel the machine is "breathing for you" or "rushing your breaths" or simply "out of sync with your breathing".

And for the Flex family members: There is a definite, distinct rise in pressure during the active exhalation part of each breath cycle. And for some folks that definite rise in pressure can be detected and it can be highly irritating in the sense of making you feel like the machine is rushing your inhales.


And my own personal experience with the two systems?
The short version is: I could tolerate EPR, but it did feel like it was rushing my inhales much of the time. And I can't stand Bi-Flex at all. Even at Bi-Flex = 1, the pressure increase before I'm done exhaling is deeply irritating and quickly becomes intolerable.

On the S9 AutoSet with EPR turned on, I couldn't tell that much difference between EPR = 2 and EPR =3. I couldn't exhale against my (not very high) pressure without EPR turned on and set to at least 2 or 3. But breathing never felt completely normal. Sure, there would be a steady drop in pressure at the start of each exhale, but I could detect a very slight increase in pressure just before I felt like I was genuinely inhaling. So I felt that the S9 was rushing my inhales just a bit. Not enough to make it impossible to breath or exceptionally uncomfortable, but just enough to make it feel like it was always tickling the back of my throat.

When I got my BiPAP, the tech had set Bi-Flex to 3. Having read about the Flex family and also having read about the "test" feature on the System One that lets you try out the various Flex settings in real time at your prescribed pressure, I spent about 30 minutes or so playing around with Bi-Flex and quickly discovered I couldn't stand any of them: Even at Bi-Flex = 1, I felt that increase in pressure occurring (much) sooner than the increase in pressure on the S9. And the sensation went from "annoying and irritating" to "can't imagine ever sleeping with this" Fortunately the whole point of putting me on BiPAP in the first place was to give me a very low EPAP---much lower than my titrated straight CPAP pressure. And turning BiPAP completely OFF fixed the problem for me. The System One does a good job of detecting my inhales/exhales and I hardly ever feel the pressure go up from EPAP to IPAP since without Bi-Flex, the entire jump occurs at the start of my inhales.

[nudave]

Well..reporting back in this morning. I changed the CFlex+ setting from 2 to 1. I think it worked great! I woke up once during the night, didn't notice my mask and thought I flinged it off during my sleep. However, it was still there. I guess I'm getting used to the mask.

Back to the CFlex, it seemed easier for me to go to sleep and not thinking about going to sleep which ends up in the vicious insomnia cycle. I found the pressure to feel more constant...which I liked. I'll keep the setting of 1 until something weird happens, if it does.

Looking at my stats from last night, my AHI has been progressively been higher and higher each day. The past 5 days - 1.59, 2.45, 2.00, 3.18, and last night 3.88. I think its the ramp function, as the majority of the hypopnea's are during the 45 minutes immediately after falling sleep.

Finally, I wanted to thank my fellow WNY'er robysue for her in depth write up on the differences between EPR and the S1 Flexes. It helped me understand (and hopefully future visitors) what's really going on..

[archangle]

I think ramp should only be used by newbies.

I'm beginning to believe that EPR should probably be dropped by most people once they get used to CPAP, too. I really can't feel a pressure of 12 anymore. EPR "pumps" the mask with every breath, probably making leaks more likely. I think it also pumps more air into my stomach.

[Pugsy]

Looking at my stats from last night, my AHI has been progressively been higher and higher each day. The past 5 days - 1.59, 2.45, 2.00, 3.18, and last night 3.88. I think its the ramp function, as the majority of the hypopnea's are during the 45 minutes immediately after falling sleep.

If you have to use ramp perhaps decrease time?? Or just mentally toss out any events that occur during that 45 minutes at the lower ineffective pressure? Sort of mentally re-figure the AHI?

[Mike6977]

Great explanation, robysue.

I wish there was a place on this board where in-depth posts (with illustrations!) like the one you just created could be stored and organized in an easy to access manner.

A living, evolving Sleep Wikipedia, or CPAP for Dummies section.

.................................................................


For what it's worth:

Comparative Efficacy of Two Expiratory Pressure Reduction Systems in the Treatment of OSA

Sleep Diagnosis and Therapy 2009

http://www.sleepdt.com/_journal/v4n1/pdf/SDT-20-25.pdf

[archangle]

Well maybe I don't understand the Flex settings like I thought I did. Sounds like maybe there is a rhythm. Sorry for the bad info.

I think you had it right to start with. I don't think there's a "rhythm" in any CPAP machine. When you exhale, the pressure drops at the start of the exhale, but as you taper off, the pressure comes back up to the inhalation pressure. If you exhale and stop, you may get the feeling it's trying to make you inhale again.

Some bilevel machines do have a rhythm and want you to take a certain number of breaths per minute.

[nudave]

Looking at my stats from last night, my AHI has been progressively been higher and higher each day. The past 5 days - 1.59, 2.45, 2.00, 3.18, and last night 3.88. I think its the ramp function, as the majority of the hypopnea's are during the 45 minutes immediately after falling sleep.

If you have to use ramp perhaps decrease time?? Or just mentally toss out any events that occur during that 45 minutes at the lower ineffective pressure? Sort of mentally re-figure the AHI?

Same issue the past two nights. The ramp is skewing my stats. I'll see about lowering it. I think I have the Clinician's Manual, will have to check.

[robysue]

Some bilevel machines do have a rhythm and want you to take a certain number of breaths per minute.

These are the PR BiPAP S/T and Resmedn VPAP S/T machines. When run in T mode, these machines will have a back up breathing rate and if the user is not breathing enough times per minute, the machine will attempt to trigger breaths. They are a definite step up in complexity from the more common BiPAP/BiPAP Auto and VPAP/VPAP Auto machines used by many.

The regular, plain bi-levels (PR System On BiPAP/BiPAP Auto and Resmed S9 VPAP/VPAP Auto) do NOT have a backup rate and cannot attempt to trigger a patient to breathe. And they have no more "rhythm" to follow than the PR System One Auto or the Resmed S9 AutoSet do.

A prescription for bi-level is enough to get either a PR BiPAP/BiPAP Auto or a Resmed VPAP/VPAP Auto. But it won't allow you to get the more sophisticated BiPAP S/T or VPAP S/T machines, which are really closer in many ways to the ASV (adaptive servo-ventilator) machines than they are to the plain-jane bi-levels.

[fiberfan]

Some bilevel machines do have a rhythm and want you to take a certain number of breaths per minute.

The regular, plain bi-levels (PR System On BiPAP/BiPAP Auto and Resmed S9 VPAP/VPAP Auto) do NOT have a backup rate and cannot attempt to trigger a patient to breathe. And they have no more "rhythm" to follow than the PR System One Auto or the Resmed S9 AutoSet do.

The Resmed S9 VPAP Auto and VPAP S don't have a backup rate. They do, however, have a min and max setting for inspiratory time. I have a S9 VPAP auto and the max inspiratory time setting was too short so the machine would switch to epap and sometimes back to ipap before I had finished inhaling. An increase in the max inspiratory time setting and the machine now stays at ipap until I start to exhale.