Millimeter of Mercury (mmHg)
The millimeter of mercury (mmHg) is a unit of pressure commonly used in medicine and science. It is defined as the pressure exerted by a column of mercury one millimeter high.
Equivalencies
1 mmHg is equivalent to:
- 1 torr
- 0.001 atm (atmosphere)
- 133.322 Pa (Pascal)
History
The mmHg unit originated from the use of mercury barometers to measure atmospheric pressure. The height of the mercury column in the barometer was directly proportional to the atmospheric pressure.
Applications
mmHg is commonly used in:
- Medicine: Measuring blood pressure and other physiological pressures.
- Science: Measuring gas pressure, vacuum pressure, and other pressure-related phenomena.
Advantages
- Simplicity: mmHg is a simple and intuitive unit to understand, based on the height of a mercury column.
- Historical Significance: The mmHg unit has a long history of use and is well-established in many fields.
Disadvantages
- Toxicity: Mercury is a toxic substance, and the use of mercury barometers poses potential health risks.
- Inaccuracy: The mmHg unit is not a very precise unit of pressure, as it is dependent on the density of mercury, which can vary with temperature and other factors.
Alternatives
Other units of pressure are becoming more common, including:
- Pascal (Pa): The standard SI unit of pressure.
- Bar (bar): A unit of pressure commonly used in industry.
While the mmHg unit is still widely used, its use is gradually declining due to concerns about mercury toxicity and the availability of more precise and convenient units of pressure.
