Water Manometers

[Brett]

I am looking to purchase a water manometer to test pressure in my Auto-Bipap and have a couple of questions that I hope someone on here might be kind enough to answer.

1. I have seen a lot of link to a Fisher and Paykel manometer but in each image, it appears to be hooked up to an F&P humidification chamber. My current machine does not use that sort of humidifier. Can the F&P Manometer work with other systems?

2. What experience have you had with manometers and is there any particular one that is a "best value" in terms of quality and price?

3. While I understand how a manometer works, how can you get an Auto Bi-Pap machine to replicate IPAP and EPAP to make sure both pressure outputs are OK?

Thanks for all of your help.

[JeffH]

build one. I did, and they are easy enough to make.

http://www.cpap-supply.com/Articles.asp?ID=130

[6PtStar]

I bought the F&P. I guess it would work on any type of chamber if you could get the rubber stopper to fit the hole and a connection for the hose. The one from cpap.com comes with the chamber (some don't) and that is what they are designed around. I do know that the pressure tubes with the little ball in it are worthless. Someone posted that the one with the pressure gague worked OK but I have not tried it. As far as checking the IPAP and theEPAP pressures, I don't think you can do this. All they are designed to do is to check the output pressure so you would have to set each pressue and check it against the pressure standard. All they can do is check the output against what the screen says is that pressure to insure the readout is correct.

The F&P is the only one that I found that worked correctly IMHO. I started to try and make one but I had trouble finding all the parts so I took the easy route.

Jerry

[Velbor]

Complete agreement with JeffH. Build one. Two simple approaches:

-- U-Tube. Bend a piece of glass, or even simpler, a piece of plastic tubing. Adapters from standard CPAP tubing diameter down through a conical reducer are readily available. But simpler, I think, is:

-- Straight glass tubing. Use the F&P pictures as a model. The F&P chamber is inexpensive and makes connections easy, though you can use any closed, rigid reservoir. Mark a piece of glass tubing with "magic marker" at "zero" and each cm (accurate enough for most purposes) from 6 to 20 cm. A cork from a bottle of wine (the wine need not be wasted!) is about the right size, though it may need to be shaved down a bit. Drill a hole through the center of the cork to receive the glass tubing. Partially fill the reservior with water, and insert the cork / tubing into one opening so that the zero mark is at water level. Attach the machine to the other opening with a short length of standard tubing. Ready to go!

HOWEVER: Your question #3 about replicating inhalation & exhalation pressures raises more fundamental questions than just building (or buying) the manometer.

The first questions is: WHY (other than simple curiosity, which I understand fully) do you want to do this? What difference does it make if, for example, the pressure is "off" by half a cm, or even a full cm? What do you plan to do about any "discrepancies"? This is not an idle question, and there are some good answers (and some trivial answers), but you might want to carefully think through your own reasons and motivations before proceeding.

The second question is: measuring static head pressure is easy, but what does it tell you? Ideally, you would want a system thay measures dynamic pressure, while air is moving. Before even getting to your issues of inhalation & exhalation, how do you plan to replicate the conditions of air blowing through the vents of your mask? This may or may not be hard, depending on your mask, but it needs to be thought through. You need a way to hook up your mask vents (or an equivalent) while blocking off airflow that would otherwise go to the nose. And you need a T or Y adapter so that pressure can be measured through one arm while allowing airflow through the other. (And ideally, these measurements should be made at the far end of your main tubing, not right at the machine.)

Finally, only after addressing these issues, comes your question #3. To which I have no good answer. Good luck, and please let us know how you work all of this out.

[JeffH]

I just used an old 6' hose wire tied to a board. That really makes it simple.


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CPAPopedia Keywords Contained In This Post (Click For Definition): hose

[Brett]

Velbor:

Your questions are worth answering.

I want to do this because my gut is telling me that the pressure being outputted is not what the display is reading.

The simple thing to do of course would be to bring the unit into my DME for testing. That is sort of a hassle, both in terms of time and in terms of the fact that I have raised the pressure slightly from the original prescription as I got a little heavier and thought I might be needing a little more juice since I was not waking up refreshed. While my DME has been excellent and helpful, they are also pretty "by-the-book" and would probably complain that I had deviated the settings from the prescription and I don't need the headache if I can avoid it.

If I did see a discrepancy, I would try to adjust the setting to compensate or take it to the DME for a repair.

[tomjax]

I am a bit on the lazy side and prefer simplicity.

All the fancy U tubes and commercial models are fine,
But mine is very simple.

I simply disconnect the hose from the mask and dip it into a container of water about 6-8 inches deep and hold a ruler to the bottom of the hose. A metric one is even better.

Turn machine on and very slowly raise the tube. When air starts coming out the bottom of the hose, look at your ruler and you have your pressure.

works for moi.

[JeffH]

[quote="tomjax"]I am a bit on the lazy side and prefer simplicity.

All the fancy U tubes and commercial models are fine,
But mine is very simple.

I simply disconnect the hose from the mask and dip it into a container of water about 6-8 inches deep and hold a ruler to the bottom of the hose. A metric one is even better.

Turn machine on and very slowly raise the tube. When air starts coming out the bottom of the hose, look at your ruler and you have your pressure.

works for moi.

[tomjax]

No need to double the number.

This is a direct measurement of the pressure that is preventing the air from escaping.
When the air begins to escape, this measurement of the column of air is correct anad is the pressure your nmachine is set to..

I have no idea why you think the number should be doubled.
Simiple physics.

tom

[JeffH]

No need to double the number.

This is a direct measurement of the pressure that is preventing the air from escaping.
When the air begins to escape, this measurement of the column of air is correct anad is the pressure your nmachine is set to..

I have no idea why you think the number should be doubled.
Simiple physics.

tom

OK, I see yours works different than mine.

[Velbor]

JeffH, that is one MONSTER manometer! I never would have thought of building something on that size scale. Interesting to see in your photo that you have a level immediately to the left!

tomjax, submerging the tube is elegant in its simplicity. And right, of course, no doubling necessary. In fact, this methodology was used in the early days of PEEP (Positive End-Expiratory Pressure, a close relative of CPAP) respiratory therapy: simply having the patient exhale against an exhaust tube submerged a fixed distance under the surface of water (with precautions that inhalation would not suck up the water!).

My own preference remains the single vertical tube. That allows for more easily observing variations in the pressure level, and is not as susceptible as a U tube to oscillation of the water between the tube arms.

Always a balance between simplicity, and the ability to see what you want to see. Thanks for the interesting ideas.

Brett, your response shows that you're aware of the important fact that from many (though not all) perspectives, the absolute pressure measurement is less important than how YOU are responding to whatever the pressure actually is, and that (within reason) you can "compensate" for some level of inaccuracy. Need to keep in mind that some machines may put out a "higher than displayed" static pressure, to insure against dynamic pressure drops at the end of the delivery tube. So the questions become, what is an "acceptable discrepancy" and what is a "significant discrepancy." I don't have simple answers. Good luck to you.

EDIT: JeffH, I see what you just posted, and now understand that when you talked about "doubling" you were speaking about the U-Tube system, not the simple submergence system. You are right - if you are measuring from the original baseline, to the height of the upper water level, that needs to be doubled. Most often with U-Tubes, readings are simply made from the lower level to the upper level, rather than with reference to the original level. That does the "doubling" automatically. And that's why I commented about the level: helps with the proper measurement from one water surface to the other!

[Goofproof]

Another thing to consider, if you are using it as APAP, and have the software to optomize your treatment. it doesn't matter if the machine is pressure correct, in that case treatment pressure will be correct. Pressure numbers won't matter as long as the machine is providing what you need.

The machines have a pretty wide error factor anyway. +or - 0.5 CM, that could be 1 CM and still be in spec. Jim

[JeffH]

[quote="Velbor"]JeffH, that is one MONSTER manometer! I never would have thought of building something on that size scale. Interesting to see in your photo that you have a level immediately to the left!

tomjax, submerging the tube is elegant in its simplicity. And right, of course, no doubling necessary. In fact, this methodology was used in the early days of PEEP (Positive End-Expiratory Pressure, a close relative of CPAP) respiratory therapy: simply having the patient exhale against an exhaust tube submerged a fixed distance under the surface of water (with precautions that inhalation would not suck up the water!).

My own preference remains the single vertical tube. That allows for more easily observing variations in the pressure level, and is not as susceptible as a U tube to oscillation of the water between the tube arms.

Always a balance between simplicity, and the ability to see what you want to see. Thanks for the interesting ideas.

Brett, your response shows that you're aware of the important fact that from many (though not all) perspectives, the absolute pressure measurement is less important than how YOU are responding to whatever the pressure actually is, and that (within reason) you can "compensate" for some level of inaccuracy. Need to keep in mind that some machines may put out a "higher than displayed" static pressure, to insure against dynamic pressure drops at the end of the delivery tube. So the questions become, what is an "acceptable discrepancy" and what is a "significant discrepancy." I don't have simple answers. Good luck to you.

EDIT: JeffH, I see what you just posted, and now understand that when you talked about "doubling" you were speaking about the U-Tube system, not the simple submergence system. You are right - if you are measuring from the original baseline, to the height of the upper water level, that needs to be doubled. Most often with U-Tubes, readings are simply made from the lower level to the upper level, rather than with reference to the original level. That does the "doubling" automatically. And that's why I commented about the level: helps with the proper measurement from one water surface to the other!