Know the Difference Between mmHg and cm H2O

Know the Difference Between mmHg and cm H2O

Anthony D. Slonim MD, DrPH

Pressure is defined as the force per unit area. It can be applied either to a solid or a liquid interface at a point perpendicular to the surface and is represented by the height of the column that exerts a pressure at its base. Depending on the fluid used, the height of a column of fluid will differ because its density and therefore the pressure it exerts will differ.

Mercury (Hg) is a very dense fluid (13.5951 g/cm3) and is often used to calibrate pressure gradients and differentials. Normal atmospheric pressure can support 760mmHg. One millimeter of Hg therefore represents approximately 1/760 of an atmosphere and is a useful measure for comparing pressures. This measure is often referred to as a Torr, after the Italian physicist Torricelli. The unit mmHg is very useful in measurements for biologic systems. It is the conventional unit used to measure blood pressure.

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Jul 1, 2016 | Posted by in ANESTHESIA | Comments Off on Know the Difference Between mmHg and cm H2O

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