Percieved difference in pressures between two machines

MandoJohnny · Post by **MandoJohnny** » Sun May 25, 2008 12:32 pm

I also posted this on another forum, in case anyone is getting Deja Vu. I really would appreciate some advice on this.

I travel to the same place on business every week. Instead of lugging a CPAP through airports twice a week, with my doctor's encouragement, I got a second machine that I keep at the work city. At home, I have a Resmed S8. The remote machine is a GoodKnight 420G. Both have the associated humidifiers. I have Swift II masks with each machine, although I just got an Opus 360 I like and I have been transporting that city to city each week. Because of the problem I am going to describe, I recently had both machines professionally checked and they are putting out right at my prescribed pressure of 11. I backed up those checks with an inexpensive hand-held CPAP pressure checker that I got from a CPAP website. I wanted to make sure the addition of the humidfiers did not change things. With the humidifiers hooked up, I got the exact same reading on both machines. EPR is off on the S8 and ramp is off on both.

Here's the problem: With the S8 and either mask, I feel like I am getting good pressure and breathing is easy. With the 420G and either mask, I feel like I have to struggle to inhale. What could cause this? One DME supplier I talked to told me that different machines can have different levels of pressure required to exhale, depending the size of the blower motor, but inhalation should be the same on any two machines that are set at the same pressure. But that is not what I am experiencing. This is a real problem for me. Any help would be greatly appreciated.

Goofproof · Post by **Goofproof** » Sun May 25, 2008 12:56 pm

You are trying to compare the taste of a apple and a orange, news flash they don't taste the same. Pick which you like best get another one like it. E

Even with two apples, they wont taste the same. Any two manufactured items won't be the same either, most electronics have a spec of +or- ten %, out of ten items built 3 will be great, 5 will be fair, and 2 will be dogs, this applies to most products. If one could select a product made up of all plus parts, and made with plus labor that would be great , but in the real world that doesn't happen, if it does it would it would be a accident.

As far as a cheap blow manometer, trash it they are useless. The Factory spec for XPAP flow is .5 + or - 1 cm. So between two machines you could be 2 cm off and the machines still be in spec. Use APAPs correctly then they will give the treatment you need, and the numbers won't matter. Jim

Slinky · Post by **Slinky** » Sun May 25, 2008 7:02 pm

GoodProof, could it also be due to the different algorhythms of the two manufacturers and how and how fast they respond to the change in respiration between exhalation and inhalation??

I've only used a Respironics pre-M Series and the Resmeds and I never noticed any difference between them but I've often read references in the forums to some people not responding as well to the algorhythm of one manufacturer as to anothers.

MandoJohnny · Post by **MandoJohnny** » Sun May 25, 2008 7:45 pm

Well, as I said, my cheap manometer was just a double check. Both machines were professionally tested as being dead on at 11, within a week of each other, so the factory spec + or - argument is not the answer. Also, I am not prescribed for an auto and I am completely satisfied with CPAP treatment with the S8, so I have no plans to pursue getting one. All I want to do is get the 420G roughly approximating the performance of the S8, even though both are putting out 11. It would seem the obvious answer just to bump the 420G up until it feels the same, but I wonder if that is the right way to go. It seems to be guesswork, but that's what I will do absent a better answer.

The algorithm thing may be the cause, but I wonder. The percieved harder inhalation seems to be continuous, thoughout the inhalation, not just right at the changeover. In any case, even if that was the cause, what would the solution be?

roster · Post by **roster** » Sun May 25, 2008 7:52 pm

The bigger variable might be the difference between being at home in bed and being in a hotel on business in bed. Some people are under more stress at work. Then there is eating in restaurants which is typically heavier, greasier, spicier, saltier meals than at home.

Goofproof · Post by **Goofproof** » Sun May 25, 2008 8:06 pm

Slinky wrote:GoodProof, could it also be due to the different algorhythms of the two manufacturers and how and how fast they respond to the change in respiration between exhalation and inhalation??

I've only used a Respironics pre-M Series and the Resmeds and I never noticed any difference between them but I've often read references in the forums to some people not responding as well to the algorhythm of one manufacturer as to anothers.

Yes, that's why you can't expect a apple to taste like a orange, I also wouldn't choose a Resmed because of it's treatment. I wouldn't be concerned about using the 420G, i'm sure I could get it set to work for me.

Rooster has a point about different locations and meals, even coming off air travel, and maybe a change in ALT. I wouldn't trust professionals to set the machines up correctly, unless they were under factory conditions, you need a accroate guage and the calibrated orfice. Jim

MandoJohnny · Post by **MandoJohnny** » Sun May 25, 2008 8:12 pm

rooster:

Good thought. That may be part of it. While the heavy meals factor is all too true, I used to travel with the S8 before I got the 420G and never had this problem. In fact, I still travel with it anytime I am going to a city other than the one the 420G is in. What's more, due to a side trip I had to take, I had both machines side by side a couple of weeks ago. The S8 just does a better job no matter where I am.

I also thought about elevation being a variable, but the two cities are only a few hundred feet apart in elevation. Another variable might be humidification. While the S8 sems to put out more air volume, the humidifier is whimpy. It has to be turned all the way up to do much good. The 420G humidifier is a real "cooker" though, I can never get it past halfway or it rains out like crazy. But those are just guesses as to variables that might effect percieved pressure.

GumbyCT · Post by **GumbyCT** » Sun May 25, 2008 9:00 pm

MandoJohnny wrote:With the 420G and either mask, I feel like I have to struggle to inhale. What could cause this? One DME supplier I talked to told me that different machines can have different levels of pressure required to exhale, depending the size of the blower motor, but inhalation should be the same on any two machines that are set at the same pressure.

Did DME say how different exhale pressure affected the inhale difference you feel? Sounds like maybe DME doesn't know either.

To me it sounds more like a flow (volume) problem than a pressure problem. Have to tried switching hoses? Are they the same length hose? Maybe filters? How old are these units?

Good Luck,
GumbyCT

MandoJohnny · Post by **MandoJohnny** » Sun May 25, 2008 9:55 pm

The DME said that inhaled pressure/flow at a given setting should not change even if the exhaled effort is different. I guess its kind of like an EPR in reverse. He did relate an anecdote that one manufacturer (he did not say which one) had to pull a unit off the market some years back because they put too big a blower motor in it and people were complaining about the exhalation. They put a smaller motor in it and successfully re-released it.

I have not tried switching hoses, but I will look into that angle. The hoses are the same length, though. I have checked the filters. They are good on both machines. As to age, the S8 is about a year and a half old and has worked the same for the whole time. No change. The 420G is new, less than 2 months. And as I have said, I had them both professionally checked for function and pressure, although as someone said DMEs often make mistakes.

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CPAPopedia Keywords Contained In This Post (Click For Definition): 420G, DME

dllfo · Post by **dllfo** » Sun May 25, 2008 11:16 pm

I started to post on this same subject a few weeks ago.

My wife and I both used the Respironics BiPap Auto for over a year. Then I went to the Respironics BiPap Auto Servo Ventilator machine. 10cmH2O on the BiPap Auto vs the SV is night and day. The pressure off the SV feels much, much more powerful than the straight BiPap Auto. I am sure part of it is because the SV gets to the pressure much faster than the BiPap Auto.

I always felt like a really deep breath with my BiPap Auto was.... well, I was dragging it behind my lungs. With the SV, if I am at 4 and want 10, by the time I inhale it is at 10 waiting for me. My wife swears it is a miniture leaf
blower.

I have wondered if 10cmH2O on the BiPap Auto is the same as 10 on the SV. I don't know. I wish I knew.

Slinky · Post by **Slinky** » Mon May 26, 2008 6:42 am

Altho it doesn't answer your question as to WHY, I would be inclined to just adjust the pressure setting of the 420E to the comfort level of the Elite and see what type of data I got w/the 420E at that setting.

Ooops. Sorry. My mistake. I just noticed that it is the 420G you have, not the 420E. The G isn't fully data capable, is it? Or is it?

MandoJohnny · Post by **MandoJohnny** » Mon May 26, 2008 7:36 am

You are right, the "G" is not fully data capable. The only data it provides is usage, which is no help. So all I have to go on is a subjective comparison with my S8. I do know that with the S8 I am getting great results, both subjectively and according to the data. I have been on CPAP treatment for two years and had some ups and downs with it, and now I feel I can compare the subjective and objective reasonably well. Maybe I'm kidding myself, but I feel know what good sleep looks like and feels like. The sleep I am getting with the 420 seems pretty comparable to the S8. I sleep through the night, I wake feeling good and I don't get sleepy during the day. The only problem is this perception of not getting enough air when I am trying to fall asleep.

I'm going to ask my sleep doc about it. He is great about answering questions over the phone. Also, my main DME (NOT the one I got the 420 from) has a CPAP clinic once a week, where they will check out machines, answer questions, etc. I will see if they will do an independent check on my 420. If it has a problem, I will get it replaced under warranty. In the meantime, I think I will bump the 420 pressure up until I feel comfortable with it.

Slinky · Post by **Slinky** » Mon May 26, 2008 8:40 am

Trust your instincts!!

TerryB · Post by **TerryB** » Mon May 26, 2008 12:06 pm

Happily you are not flying an airplane but sucking on a hose. In flying you should always trust your instruments. My suggestion would be to get the two machines side by side in one city or the other and test with the same manometer.

Good luck,
TerryB

Percieved difference in pressures between two machines

Percieved difference in pressures between two machines

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