My wife asked me exactly what does cm H2o mean? Can we compare it to Pounds per Square Inch (PSI) ?
I can read the words, but do not work with any other systems using it, so it is some nebulious term tossed out by an engineer with a propensity for accuracy.
It is a "relative term" to me, meaning...20 cm H2o is more than 10 cm H2o.
BUT is the scale linear or logarithmic?
Does 20 cm H2o roughly equal 20 PSI?
For those whose minds are clear and functioning within warranty specs, does it really matter for most of us?
Should it be construed as a simple scale for our use, not of any real importance to us?
Sometimes I like to "just know" what something means. Is there a simple explanation? BTW, one word answers don't get credit on today's exam
The short answers to your questions are as follows:
A cm of h2o means the amount of pressure needed to raise any column of h2o a height specified in centimeters.
The unit of cm of h2o can be converted to units of mm of Mercury, bars, pascals, atmospheres, as well as pounds per square inch.
The measurement scale is linear and absolute.
1 cm h2o = 0.014 lbs per square inch.
For whatever reason, the CPAP industry has chosen this unit of measure … perhaps it has to do with what units are used for other medical devices?
It is a very simple scale for us to use with our treatment.
Yes, it is a very simple explanation … do I pass the test?
For a more detailed definition of pressure in the context used for CPAP, continue below:
Pressure, in particular hydrostatic pressure (also referred to as head pressure), is measured as the force per unit area needed to raise a column of fluid to a specified height referenced from sea level … it is based on Pascal’s Law (Blaise Pascal, 1600’s) which states that:
Pressure = gravity * density of column of fluid * height of the fluid column
So basically, the pressure of your CPAP machine exerts a force distributed equally and perpendicularly outward against the entire surface area of your respiratory system that is equivalent to raising a column of water to the setting of your CPAP machine in centimeters.
That is all for today’s lesson on hydrostatic pressure ... tomorrow's lesson ... how to build a CPAP system with advice from your friendly cpaptalk members.