(08-03-2014, 10:03 PM)surferdude2 Wrote: Since the machine's pressure sensor is inside the machine and the pressure we want to subject our face to is downstream considerably, it would seem to follow that the number registered on the machine's LED is arrived at arbitrarily and was arrived at by taking into consideration several pressure drop factors which are affected by flow rate, such as the line length and the mask type. That's borne out by the fact that you must use a different setting on the machine when you change mask types.
Except for the amount being arbitrary, what you say is correct for ResMed S9 machines. With PRS1 you dial the amount in by selecting the System One Resistance. These are small pressure adjustments on the order of less than 1 cm H2O.
They don't matter much for the crude bathtub manometer measurement.
What does matter, though, is the IPAP pressure if you have a bi-level machine like Kate does. The bathtub manometer will measure only the EPAP pressure, not the higher IPAP pressure because no one's inhaling!
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