MmHg means millimetres of mercury (Hg = mercury) and is used in EU member states and Switzerland to measure the pressure of body fluids, such as eg blood pressure. ... The unit mmHg (millimeter mercury column) is also used to measure blood pressure.

Why do we use mmHg to measure pressure?

Because most barometers employ mercury as the liquid (since it is dense and has a low vapor pressure) the height of the liquid is often used as a measure of pressure. Thus millimeters of mercury (mmHg) or centimeters of mercury (cmHg) are sometimes used as units for pressure.

Why do doctors use mmHg?

As mercury is so much denser than water or blood, even very elevated blood pressures result in it rising no more than about a foot. This quirk of medical history gives us the modern measurement unit for blood pressure: millimetres of mercury (mmHg).