Curious about pressure numbers.

[sonadams1]

Being the nosy individual that I am, I'm wondering what units the xPAP pressure numbers are in.

I have heard they are in cm H2O, but this raises a few other questions in my mind:

Does the machine put out a specific pressure, or a specific pressure difference from the local atmospheric?

If it is a specific pressure, it cannot just be cm H2O, as for example 16 cm H2O is about 0.016 atm, which is less than sea level atmospheric pressure (1 atm). Then again, the number might assume 1atm + pressure #, so at 16 the pressure would be 1.016 atm, for a fixed pressure output.

On the other hand, if it is saying 16 cm H2O difference, then at sea level the pressure output would be 1.016 atm, but at 7000 feet elevation the pressure would be .8 atm + .016 = 0.816 atm, though the airflow and "cheek bulge" effect would be the same as at sea level, as those depend on the pressure difference.

Anecdotal evidence regarding the airflow being lower at sea level implies a fixed pressure output, as the lower flow speed implies smaller pressure difference (inside machine - local atmospheric), which would be accounted for by the higher sea level atmospheric pressure, assuming the machine pressure stayed constant.

[ozij]

Being the nosy individual that I am, I'm wondering what units the xPAP pressure numbers are in.

I have heard they are in cm H2O, but this raises a few other questions in my mind:

Does the machine put out a specific pressure, or a specific pressure difference from the local atmospheric?

That depends on the machine. Some machines have automatic altitude adjustmetn, and some (the simpler, cheaper ones) don't. For those that don't the adjustment is done by the user, by telling the machine at which altitude it is now functioning.

16 cm h2o is the amount of air pressure needed to raise a column of water to the height of 16 cm. Admitedly not much - but certainly more than whatever the pressure is wherever you are.

O.

[sleepie]

cheek buldge-----ahhaha i get that sometimes---happy sleepin---pat

[billbolton]

Anecdotal evidence regarding the airflow being lower at sea level implies a fixed pressure output, as the lower flow speed implies smaller pressure difference (inside machine - local atmospheric), which would be accounted for by the higher sea level atmospheric pressure, assuming the machine pressure stayed constant.

In general, xPAPs generators are concerned with flow rather than pressure. The name of the game is to keep the air flow rate resonably constant (in relation to whatever mode they are operating in) over a range of altitudes, usually 0m to 2400m.

Setting a machine located at sea level to a higher altitude range and operating it while it is still at sea level will result in a higher flow, but operating it at the correct altitude it would give the same flow as at sea level.

Cheers,

Bill