Simultaneous ResMed & Respironics Blowers: A Failed Experime

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Velbor
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Simultaneous ResMed & Respironics Blowers: A Failed Experime

Post by Velbor » Thu Jan 14, 2010 3:22 pm

Simultaneous ResMed & Respironics Blowers: A Failed Experiment

The pharmaceutical industry has been sternly criticized for only publishing research studies which produce the desired results. Failed studies, or studies which produce unfavorable results, are rarely made public. Not wanting to be accused of such behavior, I here report on a failed experiment.

I have presented data here in the past, comparing and contrasting ResMed S8 and Respironics M-Series units used at different times but under essentially identical conditions. There is much discussion on this forum regarding the differences in reporting of respiratory events by each of these machines.

It occurred to me that it might be interesting to run both machines, together, simultaneously, in parallel, to view their reporting under the SAME conditions at the SAME time.

It occurred to me that this could only be done under constant pressure conditions, with each machine producing the same pressure, or else a continuous "pull-me push-you" situation would occur, with each machine trying to "correct" the other machine’s attempts at maintaining a "wrong" pressure.

Uncertain of the accuracy of either machine’s pressure setting, I used a single-calibrated-tube water manometer to measure the dynamic output pressure of each machine set at 10 cmH2O. (By dynamic, rather than static pressure, I mean that a Y connector was used to allow "leak" through the venting port of an otherwise blocked-off Activa mask, while the pressure measurements were being taken.) Somewhat surprisingly, the ResMed indicated 11.8, and the Respironics indicated 11.2 cmH2O.

[img]http://velbor.home.comcast.net/cpap/cpa ... 1_2529.jpg[/img]

I then attached each machine to opposite ends of the same U-tube water manometer, to balance their static pressure outputs against each other. Somewhat surprisingly, in view of the 0.6 cmH2O difference in individual pressure noted above, the same 10.0 pressure setting on each machine did result in equal water levels in each arm. There were no observable oscillations or fluctuations in the water levels over time.

[img]http://velbor.home.comcast.net/cpap/cpa ... 1_2534.jpg[/img]

Since the Respironics machine provides more data in AutoPAP mode than in CPAP mode, I set it to auto, with minimum pressure = maximum pressure = 10.0 cmH2O. The ResMed machine was set to CPAP mode, fixed pressure = 10.0 cmH2O. The continued equivalent pressure with these settings was confirmed with the U-tube manometer.

With a Y adapter and short lengths of tubing, I connected the two blower outputs, before running the combined output into my stand-alone humidifier.

[img]http://velbor.home.comcast.net/cpap/cpa ... 1_2540.jpg[/img]

My expectation was that each machine would contribute an equal half of the total airflow required to maintain the 10.0 cmH2O pressure. I anticipated that this would result in each machine reporting half the leak. I also expected that the leak patterns would be helpful in synchronizing the time scales of the two machines.

I selected 10.0 cmH2O despite my usual use of 11.0 when using fixed-mode CPAP. I wanted to try to assure that there would be adequate apneas and hypopneas for each machine to assess.

At bed time, difficulties began immediately. The system produced a great deal of noise, which I was unable to localize. Soon, the ResMed machine’s leak alert alarm triggered, indicating over 0.70 lps leak for over 20 seconds. I examined the overall system for leaks, but found none. My assumption, since no similar leak alert was reported by the Respironics machine, was that, despite my efforts to balance pressure, the ResMed machine (which did register a higher actual pressure when measured individually) was blowing excess air out through the Respironics machine. I also assumed that this was the source of the loud noise.

Based on this assumption, I began lowering the ResMed pressure in 0.2 cmH2O steps. (I had earlier decided that all setting changes would be made with the ResMed machine, since it's pressure is adjustable in 0.2 increments whereas the Respironics is adjustable in only 0.5 increments. Further, the ResMed Clinical Menu is easily accessed for modification "on the fly," while Respironics needs a "power-down power-up" cycle to get to its Clinical Menu.) After reducing the ResMed pressure stepwise by 0.2 increments from 10.0 to 9.0 cmH2O, the high leak warnings stopped, though the loud system noise continued. I further reduced the Respironics pressure stepwise down to 8.0, with no change in the noise. I finally settled on a ResMed pressure of 8.6 cmH2O. The system was noisy, but seemed stable, and I slept for about 8 hours using this configuration, hoping that I was not damaging either machine.

In the morning, I eagerly looked at both data cards, and was greatly disappointed. Neither contained any usable data. ResMed software reflected only 11 minutes of use at the beginning of the night. Respironics software showed only the first 26 minutes of use, out of almost 8 hours blower on time. Even during these limited periods, no useful information was recorded.

Examining the system more closely in the morning, I found that air was blowing OUT OF the filtered intake port on the ResMed machine. This surprised me; I had concluded that, even with lower pressures, the ResMed machine was continuing to "leak" through the Respironics machine, and that my lowering the ResMed pressure had simply reduced the leak to manageable levels. It appears, however, that in fact the reverse was occurring.

I attempted RAISING the ResMed pressure in the expectation that it would at some point balance the Respironics pressure and eliminate the abnormal airflow OUT OF the ResMed filtered air intake port. Even with a ResMed pressure of 12.0, the Respironics at 10.0 still resulted in backwards airflow through the ResMed.

Also interestingly, while I was able to replicate in the morning the ResMed high leak alert (both machines reset at 10.0 cmH2O) while using a full face mask with no seal leak, the leak alert was NOT produced when I used a simple mechanical airflow constrictor.
These findings, for which I have no good explanation, indicate that my experimental model for the use of two machines simultaneously in parallel is flawed and unworkable. I am deeply disappointed, and more than slightly humbled.

Velbor
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Velbor
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Re: Simultaneous ResMed & Respironics Blowers: A Failed Experime

Post by Velbor » Thu Jan 14, 2010 10:17 pm

I have been experiencing technical difficulties with the above posting. Attempting to post, I received Server Error messages when I tried to save, preview or submit. The post was made for me through a back door by the system administrator at cpap.com, and he is trying to determine the cause of the problem. I am also currently unable to edit the above post.

There is an erroneous statement which requires correction. Where I stated that:
"I further reduced the Respironics pressure stepwise down to 8.0,"
that should have read ResMed, as is hopefully clear from the context.

The system does not appear to be linking to the photos of my setup in the above post.

The single-calibrated-tube manometer with dynamic venting:
Image

The U-tube manometer for balancing pressures on the two machines:
Image

The actual double-parallel machine setup:
Image

Thank you for your patience. Velbor

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Re: Simultaneous ResMed & Respironics Blowers: A Failed Experime

Post by TWW » Thu Jan 14, 2010 10:33 pm

Woo-hoo, that's good science!

In such situations, I like to declare "The experiment was a success -- we now know not to try that again."

You ever watch Red Green? It could be that you just needed a little duct tape.

Thanks for a wonderful post. Made my day, with 30 minutes to spare.

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dsm
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Re: Simultaneous ResMed & Respironics Blowers: A Failed Experime

Post by dsm » Thu Jan 14, 2010 10:52 pm

Velbor

Loved that experimenting - not sure what you really hoped to prove but it looked like a load of fun.

DSM
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ozij
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Re: Simultaneous ResMed & Respironics Blowers: A Failed Experime

Post by ozij » Fri Jan 15, 2010 7:29 am


I'm sure you had alot of fun creating that experiment, Velbor. At least as much as I had reading it.

My very very layperson's assumption is that turbulence created at the Y connector created wave forms neither machine could interpret as "this machine is functioning normally".

As for the leak through the Resmed: Prehaps it has to do with the Resmed's response to flow changes, when faced with Respironics' default up and down 0.5cm poke as it challenges the system in its search for optimal pressure -- it may be doing that pressure challenge simply because the mode is auto, even when it's on min=max =10

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carbonman
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Re: Simultaneous ResMed & Respironics Blowers: A Failed Experime

Post by carbonman » Fri Jan 15, 2010 8:02 am

Velbor wrote:Simultaneous ResMed & Respironics Blowers: A Failed Experiment
Velbor



Please! Remain in your seats, I beg you!
We are not children here, we are scientists!
I assure you there is nothing to fear!

LIFE! DO YOU HEAR ME? GIVE MY CREATION... LIFE!

It lives! It Lives! IT LIVES!
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to see or feel those changes, you'll never know what you're capable of."
I said that.

Velbor
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Re: Simultaneous ResMed & Respironics Blowers: A Failed Experime

Post by Velbor » Fri Jan 15, 2010 10:29 am

dsm wrote: Loved that experimenting - not sure what you really hoped to prove but it looked like a load of fun.
Doug, my goal was to be able to compare the reporting of apneas and hypopneas: since each machine uses different rules for identifying events, to what extent are they in agreement about my specific event pattern? If one machine reports "more" events, do those fully include all of the events reported by the "lower number" machine? I had hoped to synchronize the "clocks" of the raw data, and determine the extent of overlap of the two event datasets.

A lot of thinking time and set-up time. Would have been more fun if it had worked! At least it gave a workout to my collection of assorted parts, tubes and connectors.
ozij wrote: .... Respironics' default up and down 0.5cm poke as it challenges the system in its search for optimal pressure -- it may be doing that pressure challenge simply because the mode is auto, even when it's on min=max ....
Sounds like another experiment to be done! But I may be the wrong person to do it; I sometimes have so much "Variable Breathing", which overrides the "chair-shaped poke", that my data wouldn't really settle the question.
(see perhaps the VB discussion at viewtopic.php?f=1&t=44325)
But my recollection is that the Respironics "poking" occurrs at about 6-minute intervals, whereas the backflow through the ResMed appeared to be continuous.

Thanks to all for reading my ravings. Velbor

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Re: Simultaneous ResMed & Respironics Blowers: A Failed Experime

Post by jnk » Fri Jan 15, 2010 10:48 am

Any experiment that does not end in an explosion is a success. That is not my personal definition, but it IS the reason I am not allowed to conduct experiments within the confines of my living area--at least, not as long as my wife chooses to retain her veto-power in such matters.

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Re: Simultaneous ResMed & Respironics Blowers: A Failed Experime

Post by Muse-Inc » Fri Jan 15, 2010 10:50 am

Oh Velbor, what fun you must have had with this! When I read what you were trying to do, I kept thinking that the ResMed machine was gonna freak with the odd feedback it was gonna be getting (feedback up from the Y connector) from Respironics tiny pulses that resemble no human's breathing...but then what the heck do I know about engineering
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Re: Simultaneous ResMed & Respironics Blowers: A Failed Experime

Post by kwikwater » Fri Jan 15, 2010 10:53 am

And to think that it's been asked in a poll whether we like technical discussions!!! LOL!!!!!
Yes we do!!!! Thansk for doing the work for us! Per the note above about duct tape, LOVE the use of your credit card!!!!
Kelvin

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Re: Simultaneous ResMed & Respironics Blowers: A Failed Experime

Post by kteague » Fri Jan 15, 2010 10:03 pm

Velbor, you may not have got the answers you sought but you learned something. I'm about as impressed with the experiment itself as I would have been with the results. I tip my hat to all the technical types on here. Feels like I rub shoulders with the cpap elite. Maybe just a little bit will rub off on me.

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Re: Simultaneous ResMed & Respironics Blowers: A Failed Experime

Post by dsm » Fri Jan 15, 2010 10:46 pm

Velbor

I can't resist offering an analysis

If both machines are fed into a common end point and in cpap mode and the pressures adjusted using the manometer. The end point should be stable (should). My guess at what would then happen is that as soon as the end point (perhaps you) changed the pressure by breathing, the two machines would each have their exit port sensing a change in the delivered pressure & each machine would seek to adjust the pressure to maintain the committed static delivery. The best hope is each machine delivers the adjustments to keep the 'perceived' delivered pressure stable. But in reality they would start competing with each other. I would expect possible instability in bursts (but mild) based on that eventually the delivered pressures would settle.

In Auto mode I would expect all hell to break loose. If for example you chose to snore, the Resmed would likely raise pressure faster than the Respironics which also would be merrily doing its 'steps & stairs' probing. My guess is that the two machines would start fighting each other as they each try to figure out what was going on. The worry is one machine might try to blow the other one's insides out (you kind of hinted at this with the comment re reverse airflow out the Resmed).

Now it would be really sad to learn that any one brand was actually a predator, but I am worried that your experiment has shown this to be the case.

This is scary

I am not sure I can trust keeping one of each brand in the same room anymore ?

DSM
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Re: Simultaneous ResMed & Respironics Blowers: A Failed Experime

Post by timbalionguy » Fri Jan 15, 2010 11:51 pm

If I had caught this early enough, I was going to joke that the two machines would catch fire from being forced to compete with each other!

The result you got was not a surprising one-- one machine dominated the other.

I wonder if the blower was turning backwards in the ResMed machine, or if the air was simply escaping around the blower. If the blower was really spinning backwards, the machine was hopelessly confused. If the blower was spinning backwards, you may have been lucky in not daamaging the motor driver circuit from the back EMF this would create.

Nevertheless, a fascinating experiment!
Lions can and do snore....

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Re: Simultaneous ResMed & Respironics Blowers: A Failed Experime

Post by Linus » Sat Jan 16, 2010 12:05 am

I love it. It is an interesting experiment. You could offer a fully redundant CPAP system someday.

Actually I got an image in my head. A humidifier and a de-humidifier in the same room battling each other.

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ozij
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Re: Simultaneous ResMed & Respironics Blowers: A Failed Experime

Post by ozij » Sat Jan 16, 2010 4:20 am

The interesting point is that neither machine recorded anything -- it the airflow patterns that enabled identification of events, and both were hoplessly confused about that.

O.

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