Resmed S9 Auto vs. Respironics System One REMstar Auto

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Resmed S9 Auto vs. Respironics System One REMstar Auto

Postby after0darkthirty » Sun Mar 25, 2012 2:19 am

Between these two auto cpap machines, which one has a better algorithm?
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Re: Resmed S9 Auto vs. Respironics System One REMstar Auto

Postby robysue » Wed Mar 28, 2012 5:34 pm

Between these two auto cpap machines, which one has a better algorithm?


They are both fine machines with auto algorithms that have been thoroughly tested. And both machines can provide top-notch therapy to a patient. But, while the algorithms are not the same, it's impossible to say one is somehow better than the other. It's rather like debating whether Coke or Pepsi tastes better: It all depends on who you ask. And rather like Coke vs. Pepsi, some folks have very, very strong preferences, but for the most part, most people can't really tell enough of a difference to for it to matter.

Still there are some real differences in the algorithms and for a small minority of patients, the subjective way the two machines feel will make a difference in their comfort while using the machines.

Both machines will respond to snoring, flow limitations, and clusters of OAs and Hs by increasing the pressure. Both machines will attempt to determine whether a given apnea is a clear airway apnea or an obstructive apnea. Both machines will lower the pressure back down after the algorithm is satisfied that your breathing is now stable.

The S9 algorithm tends to respond to events by rapidly increasing pressure and then, once it is happy with the shape of the wave flow, it immediately starts to slowly decrease the pressure back down. And it will keep decreasing the pressure until the machine detects snoring, flow limitations, OAs, or Hs. If more events occur, the machine once again will rapidly increase the pressure. This gives the S9's pressure curve a characteristic "wave" appearance where the fronts of the waves are steep and the back sides of the waves are much more gently sloped.

The System One algorithm is slower to respond to events and is slower to start decreasing the pressure back down once it is happy with your breathing. The System One also uses a "hunt-and-peck" algorithm for determining the optimal pressure: About every ten minutes or so, the System One will increase the pressure by 2cm over something like a two minute period while checking for improvements in the wave flow pattern. If improvements are found, the baseline pressure is reset to the pressure that gave the optimal wave flow. If no improvements are found, the pressure is then dropped back to the baseline setting over the course of a minute or so. And the machine waits for about 5-6 more minutes before starting the new hunt-and-peck cycle. To decrease the pressure, the System One does a reverse "hunt-and-peck": It temporarily decreases the pressure slightly looking for any deterioration in the shape of the wave flow. If it sees any deterioration, no matter how minor, it bumps the pressure back up to the current setting. But if no deterioration is seen, then the baseline pressure setting is reset at the lower level. And the machine then waits for about 5-6 minutes before testing whether the pressure can be decreased again. The "hunt-and-peck" algorithm used on the Respironics machines gives the pressure curve a characteristic saw tooth appearance.

The net result of both algorithms is that the machine can gracefully respond to a need for a modest increase in pressure and hence improve patient comfort by reducing the overall pressure needed to splint the airway open. Both machines have some problems providing high quality therapy if the minimum pressure setting is way, way below what the person needs. (Hence running the machine wide open with a pressure range of 4--20cm usually does not improve patient comfort.)

But each has its own strengths and weaknesses in terms of therapy:

The S9 can respond very quickly to a nasty cluster of events (in an effort to "bust the cluster up" as it's often put around here). And that quick response to events is a real strength of the S9 algorithm. But it can be very slow to lower the pressure back down. And if the min pressure is set far too low, it can lower the pressure back down to a pressure level that is clearly not high enough, which can then trigger another cluster of events. The fact that the S9 increases pressure only in response to snoring, flow limitations, OAs, and Hs also means that it always waits until something happens to increase the pressure and it always tries to lower the pressure all the way back down the minimum pressure setting.

The System One is much slower to respond to clusters of events. Judging from the pressure curves I've seen it appears that the System One will raise the pressure in 1-2 cm increments once a minute in response to snoring, flow limitations, OAs, and Hs. And then it waits to see if things clear up before it increases the pressure again by a 1--2 cm increase. So that can make it less effective at "busting up" clusters of events. But the System One is less likely to lower the pressure too much after the events are over. And theoretically that "hunt-and-peck" algorithm proactively raises the pressure before the flow wave deteriorates to the point of where snoring, flow limitations, OAs, and Hs can take place. In other words, the "hunt-and-peck" algorithm is supposed to help the machine figure out the appropriate pressure level even in the absence of event clusters.


As for comfort? Again there are strengths and weaknesses of both algorithms:

The S9's rapid pressure increases disturb some folks and wakes them up. Those rapid pressure increases can also trigger leaks. But except for when the machine is actively increasing the pressure in response to clear events (including snores and flow limitations as well as OAs and Hs), the machine is running at a stable or slowly decreasing pressure. And if the min pressure is pretty much set to what you need for at least 50%-60% of the night, you'll have nice long periods where the pressure is not changing at all.

The System One's pressure increases are not dramatically fast. And that means they are less likely to wake you up. And they're less likely to trigger a leak. But that hunt-and-peck algorithm is constantly kicking in. And so every 10 minutes or so there is a pressure increase. And that's enough to bother some people. But that hunt-and-peck algorithm is also going to help keep the machine from decreasing the pressure below a therapeutic level when the min pressure setting is set too low: Once the pressure is suboptimal, the subtle differences in the wave flow combined with the hunt-and-peck algorithm will prevent the machine from further decreasing the pressure much of the time.

Overall, there is some evidence that the System One's algorithm provides less overall variation in pressure and a quicker return to the baseline pressure after a series of "events" and attempts to locate a meaningful baseline pressure through the hunt-and-peck algorithm. The S9's algorithm provides a quicker response to clusters of events, a gentler decrease in pressure going back down to baseline, and a stronger effort to use the min pressure setting as the target baseline pressure.

Finally, Robert McCoy and Ryan Diesem have written a scholarly paper that discusses the Resmed and Respironics auto algorithms, along with auto algorithms from several other manufacturers. The paper is a bit dated: The machines being looked at are the Resmed S8 and the Repironics M-Series. This generation of machine was not capable of distinguishing between CAs and OAs. But the two companies overall choices in the design of their auto algorithm have not changed and so the stuff in the paper about how and when pressure is increased and decreased pretty much applies to the current S9 AutoSet and the PR System One Auto. The link to this paper is given below.

Link to A Bench Comparison of Five Auto-Adjusting Positive Airway Pressure Devices, Response to Apnea, Hypopnea and Flow Limitation, by Robert McCoy BS RRT FAARC, Ryan Diesem BA, Valley Inspired Products Inc. (December 1, 2008)
current settings Min EPAP = 4, Max IPAP = 8 and Rise time = 3

8/1/2010 sleep study results:
AHI = 3.9 [AHI = (#OA +#CA + #H w/desat) per hour]
RDI = 23.4 [RDI = (#OA +CA + #H w/desat + #H w/arousal) per hour]
Dx: Moderate OSA
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Re: Resmed S9 Auto vs. Respironics System One REMstar Auto

Postby Daniel » Wed Mar 28, 2012 8:48 pm

Excellent post Robysue.

Daniel.
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Re: Resmed S9 Auto vs. Respironics System One REMstar Auto

Postby robysue » Thu Mar 29, 2012 9:32 pm

Daniel,

Thank you for the complement!
current settings Min EPAP = 4, Max IPAP = 8 and Rise time = 3

8/1/2010 sleep study results:
AHI = 3.9 [AHI = (#OA +#CA + #H w/desat) per hour]
RDI = 23.4 [RDI = (#OA +CA + #H w/desat + #H w/arousal) per hour]
Dx: Moderate OSA
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Posts: 1330
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Location: Buffalo, NY
Machine: PR System One BiPAP Auto
Mask: Swift FX for Her
Humidifier: System One Heated Humidif
Year Diagnosed: 2010

Re: Resmed S9 Auto vs. Respironics System One REMstar Auto

Postby hannah » Mon Oct 01, 2012 8:05 pm

That was a great response and had a bunch of stuff I didn't know.

It looked like it was all about what the algorithm does when you are truly asleep, and so it would be hard to test out how you feel about those differences in your DME's office. But there is another difference between the 2 algorithms that you CAN test out while you are awake.

The difference is in the way the machines reduce air pressure while you are EXHALING (breathing out). This is called EPR on the Resmed and C-Flex on the Respironics.

(Fair warning, I'm also comparing the previous generations, Resmed S8 vs the Repironics M-Series. The algorithms may have changed on the current generation, but my point remains: try them both to see whether you love one and hate the other.)

I had no idea about this difference until my wonderful DME pointed it out. All I knew is that I couldn't stand the Respironics's EPR, it made me feel like it was "forcing me to breath in before I was ready". I routinely turned it off and my sleep doctor routinely told me it couldn't possibly be more comfortable turned off, and he would turn it back on again (fortunately it is user-controllable.)

What my DME did was have me lie down (if a DME fits masks or machines to you while you are sitting up, run don't walk to a different DME!) and try first one machine and then the other, with EPR and C-Flex turned on. It is important to note that he turned off Auto on both machines, as well as turning off ramping. And of course setting each machine to the same pressure. (Just to make sure, he actually repeated it a few times, with different pressures (the same on each machine) and different levels of EPR/C-Flex.)

For me the difference was night and day. For me, the Resmed feels like natural breathing. The Respironics feels like it thinks it knows better than me, and it's wrong. (And Coke beats Pepsi by a mile :-) )

Insist that your DME do this test for you on any machines your are considering.

I've talked with people who like the Respironics better, others who like the Resmed better, and plenty of people who don't feel a difference. I also talked with a different DME (at an A.W.A.K.E. meeting) who'd done a little informal experiment with the staff in his office, testing for the same EPR/C-Flex preference. He told me people were pretty much split right down the middle. But they definitely felt the difference, it's not just me!

Until then I just went around telling people "EPR is better." Now I've learned my lesson and tell people "there's a difference, you need to try it for yourself!"
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Re: Resmed S9 Auto vs. Respironics System One REMstar Auto

Postby robysue » Tue Oct 02, 2012 12:37 pm

Yep, I forgot to make much mention of EPR vs. Flex.

When I used an S9 Autoset, I had to have EPR set to 2 or 3 just to be able to exhale. I didn't particularly like the way it tickled the back of my throat just at the end of each exhalation and it also made me feel like the machine was rushing me to inhale.

But I also cannot stand Bi-Flex on my current machine. The increase in pressure during the second half of the exhale is much more noticeable and makes me feel even more like the machine is trying to rush me to inhale. Fortunately for me, the fact that I've got a BiPAP lets me turn Flex off altogether, but I still get pressure relief from the drop from IPAP to EPAP. The great thing about the BiPAP (with BiFlex turned OFF) is that the pressure remains at EPAP all the way through my whole exhalation. The machine does not raise the pressure back up at all until it detects the beginning of an inhalation.
current settings Min EPAP = 4, Max IPAP = 8 and Rise time = 3

8/1/2010 sleep study results:
AHI = 3.9 [AHI = (#OA +#CA + #H w/desat) per hour]
RDI = 23.4 [RDI = (#OA +CA + #H w/desat + #H w/arousal) per hour]
Dx: Moderate OSA
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Humidifier: System One Heated Humidif
Year Diagnosed: 2010

Re: Resmed S9 Auto vs. Respironics System One REMstar Auto

Postby trebons » Sat Oct 06, 2012 2:00 am

after0darkthirty wrote:Between these two auto cpap machines, which one has a better algorithm?

ResMed would say the S9 is better and Respironcis would say their machine is better and both don,t publish much info
I would go with the S9 AutoSet. the S9 win the popularity contest almost by 2 to 1
better data display on the machine LCD, user friendly and supported by two readily available free software

the PRS1 60 series is not supported by SleepyHead at this stage
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Re: Resmed S9 Auto vs. Respironics System One REMstar Auto

Postby pamsyflower1 » Tue Oct 23, 2012 4:05 pm

What fabulous posts! Thankyou - to all of you who have contributed. I'm a newbie and am informed and comforted by all of it.
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Humidifier: heated humidifier
Year Diagnosed: 2012

Re: Resmed S9 Auto vs. Respironics System One REMstar Auto

Postby BTW » Wed May 01, 2013 2:51 pm

I just got a ResMed S9 and it's driving me crazy. My old machine delivered a steady stream of air pressure. The S9 keeps blasting me with air and waking me up - all night long. Is there any way to prevent this machine from increasing air pressure?
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