CPAPtalk.com

For the same reason you'll find braille buttons on the keypad at your drive-up ATM. Or a lock on the door of your "WE NEVER CLOSE" 24-hour convenience store.

Usually such a convention comes about when someone defines a new instrument, or a way of using an existing one (e.g. a manometer) in a new application. Can't very well use mercury in a manometer connected to a human patient, so use water. Water is less dense than mercury so it would allow better resolution of pressure measurements than mercury. Anyway, someone probably published a paper, or wrote up the procedure in a chapter in a medical text, and everyone who read it simply adopted the methodology so they could compare their results with that of the author.

Science is full of very odd units, Physics, especially so. Particle physics even more so!

Why is pressure measured in cmH2O?

I agree with all the others above. I don't know either but I don't have a story and I know how to say "I don't know".
It is and it works, I do know that.

Different units AND specific gravity.

Well maybe better to use furlongs per fortnight?

Whatever the original reason, it is nice that measuring tools for cm/h2o
are fairly easy and cheap to McGyver.

macmermaid wrote: Why is pressure measured in cmH2O?

After all those wide-ranging answers, the Scottish mermaid left the forum and hasn't been seen in the last eight years.

Can't say I blame her.

phuqueutoo wrote:Well maybe better to use furlongs per fortnight?

That wouldn't be an appropriate measure, since it's a distance measurement, not a pressure measurement

How about furlongs per fortnight per elevation change...

chunkyfrog wrote:Whatever the original reason, it is nice that measuring tools for cm/h2o
are fairly easy and cheap to McGyver.

First combine one part Hydrogen and two parts oxygen, shake until mixed. Jim

Easy!

HoseCrusher wrote:How about furlongs per fortnight per elevation change...

yeah, I shoulda said a speed measurement, not a pressure measurement

To the OP. If you don't think that cmH2O is appropriate, how else would you suggest measuring?

D H. wrote:To the OP. If you don't think that cmH2O is appropriate, how else would you suggest measuring?

Impressive...you are funnin' wit us right? OP is

by macmermaid on Fri Dec 04, 2009 2:14 pm

scary maybe not
2017-2009= hmm try this

If I understand this unit of measure, I can take my cpap hose, hold it perfectly vertical into a bucket of water, turn on the machine and the water level in the hose should push down the indicated number of centimeters. It seems to be quite logical like this.

Doublev wrote:If I understand this unit of measure, I can take my cpap hose, hold it perfectly vertical into a bucket of water, turn on the machine and the water level in the hose should push down the indicated number of centimeters. It seems to be quite logical like this.

that's one way, yes.

One thing you people aren't getting, to test the pressure, it also must meet the requirement of flow at pressure. You can check the pressure deadheaded (Plugged), but it also needs to meet that pressure while your mask is venting.

The specs call for a hole (Leak) before the guage, to simulate the mask venting.

Their is a dia. size for the hole, but I have forgot what it is, it's in MM's. Checking the air pushing on the water isn't the correct way. The machine could make the correct pressure plugged, but not be able to with the mask leak. Jim