Can someone please explain pressure?

I'm looking at "Patient Circuit Accessory Pressure / Flow Characteristics in section 4.3.2 of the Remstar LX CPAP Systems Service Manual.

It lists different items (masks, tubing, valves, etc) with a "Pressure Drop @ 30 lpm (cm H2O)"

The 6ft Reusuable Flexible Tubing has 0.11 listed.

Is that saying that at 30cm or pressure (which the machine can only do 20 anyway, so I'm confused) that the pressure will drop .11 cm or .11 (11%)?

If it means neither, what does it mean?

ractar28 wrote: It lists different items (masks, tubing, valves, etc) with a "Pressure Drop @ 30 lpm (cm H2O)"

The 6ft Reusuable Flexible Tubing has 0.11 listed.

LPM is a flow rate (Liter per minute)
cm H20 is a pressure

My guess is that they are saying the tube has a .11 cm H20 pressure drop when air is flowing through it at 30 LPM. Which .11 cm H20 is basically negligible.

-craig

you are being confused . pressure by definitionis a force being applied .for there to be pressure there must be a resistance to FLOW. in your example the flow rate is 30 litres /minute. yes your machine is capable of only 20 cm-h20. at the 20 cm-h20, a pressure drop of .11 would result in a pressure reading at the end of the hose of 19.89cm-h20. pnuematics or hydraulics either one,pressure pushing creates movement of the media to overcome the resistance to flow. the pressure pushing against the tissues in your airways moves those tissues allowwing room for the air to flow- thus the theory of cpap. lung volume is meaured in litres. pressure is measured (for cpap purposes) in centimeters of water. we are all used to psi for our tires.10cm h20 basically is enough pressure to raise a column of water 10 cm higher than if no pressure was applied. and to really confuse you there is a correction depending on how high above sea level the measurement is take

There are three states of matter, Matter, Anti-Matter, and Don't Matter. Check, when your book was printed, it's for a very old system, if it says the manuel was hand printed by Ben Franklin, keep it it's worth money. With a modern machine nothing in that book will apply. Jim

Goofproof wrote:There are three states of matter, Matter, Anti-Matter, and Don't Matter. Check, when your book was printed, it's for a very old system, if it says the manuel was hand printed by Ben Franklin, keep it it's worth money. With a modern machine nothing in that book will apply. Jim

I work for a scientific company; will have to remember that for meetings.

Sure it matters. If my titration was at 12cm, then was that 12cm at the machine or at the end of a "standard" circuit? I checked my old machine and it was at 12, so obviously, it was the measure of the complete circuit. But I started with no humidifier. I've moved to a heated humidifier and a bacteria filter (and may change masks). Since different masks have different leak rates, if I were on a CPAP, I'd want to do some math and make sure the "final pressure" is correct. Even on an APAP, I still want to keep the starting pressure "somewhat in line".

My Ultra Mirage 2 has a flow of 38 at a pressure of 12. If I move to an Activa, the flow is about 34 at 12. Now all I have to figure out is what the bleeping leak rate is (and if that's a percentage or what).

Yep, I try hard to make this harder than it is.

All machines have a pressure spec of .5cm +/_ your set pressure, nothing normally used will make much difference in your treatment pressure, Except for the "Bacterial filter", which is extra and not needed, as long as your machine isn't contaminated. If it was, I wouldn't be using it in the first place. The air the machine breaths, is the same air you breath all day, do you wear a filter all day.

What is really needed is a machine that collects data and the software to see how your treatment is doing. One of those would have auto alt comp, and leak compensation to some degree. Jim

Can someone please explain pressure?

Pressure is like a fart....


It seeks the path of least resistance

ractar28 wrote:If it means neither, what does it mean?

It sounds like the service manual you are looking at is indeed giving the exact loss in pressure (in cm H20) for each accessory added to the patient circuit, but I don't think it's meaningful information for us. The xPAP is set to provide 12 cm H20 of pressure, meaning that if you take your mask off and the machine doesn't have anything to blow AGAINST, it will blow like crazy, trying to find some resistance to flow so it can do its job of creating 12 cm of pressure again. Put it back on, it has something to blow against, the blower slows down. So what if someone at Respironics hooked up some sensors to either end of a 6ft hose, set up a table fan blowing air through it at a rate of 30 lpm, and discovered that the hose has .11 cm H20 less pressure coming out the far end than going in? Does the table fan detect that loss of pressure and increase its speed to make up for it? No, but your xPAP does.

Same thing for the vent flow rates for masks. Vent flow rate (aka leak rate) is only useful when you have something to compare it to, for example, a leak rate reported by your xPAP. Say your machine displays last night's leak rate as 45 lpm. The user guide to your mask says that its vent flow rate, at the pressure your machine is set to, is 38 lpm. Then you know that you have a leak on the order of (45-38) or 7 lpm. That's useful information.

Things aren't always what they seem.

I did a series of tests about 18-24 months ago that showed across a variety of machines, that on a 6ft hose whith air flowing and pressure on the LCD or at the machine end saying say 12 CMs that only 11 CMs will show on a dial manometer at the mask UNLESS, the machine is one that uses an auxiliary pressure sensing line (like the PB330 or PB42x models in which case the pressures always matched the machine end. A 10ft hose had about 1.3 CMs of loss.

Cheers

DSM

#2 viewtopic.php?f=1&t=29035&hilit=pressur ... +6%27+tube

I can't seem to locate the original thread

D

Here we go again. So much for keeping it non-technical.

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mth712 wrote:........ You know what a fart is? Clearing the way for the main event!

That's clever. Could you also say, "Clearing the room so the main event can be enjoyed in private"?

rooster wrote:

mth712 wrote:........ You know what a fart is? Clearing the way for the main event!

That's clever. Could you also say, "Clearing the room so the main event can be enjoyed in private"?

Nature's way of telling you The Party's Over. Jim