When a physician quotes a blood pressure, to what does this relate?

1 Answer
Nov 6, 2016

Blood pressure is measured in #"gauge pressure"#. The given values are over (or below) atmospheric pressure, i.e. over and below #"760 mm Hg"#.


Historically, columns of mercury (or even water) were used for pressure measurement. The difference in heights of the columns represented the difference in pressure. A dense liquid such as mercury gives measurements convenient to the experimentalist (#"1 atmosphere"# will support a column of water approx. 10 m high, which would be a rather inconvenient measurement to make). You are possibly too young to remember the old blood pressure monitors, but these were filled with (short) columns of mercury.

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