Millimetre of mercury

Millimetre of mercury (mmHg) is a unit of pressure, formerly defined as the extra pressure generated by a column of mercury one millimetre high. It is now defined more precisely as exactly 133.322387415 pascals. It is used as a standard unit of pressure measurement, particularly in the field of medicine and meteorology. The use of mmHg in medicine is widespread for measuring blood pressure, where it is a critical value for diagnosing and monitoring the health conditions related to the cardiovascular system.

History

The concept of using mercury to measure pressure was developed in the early 17th century by Evangelista Torricelli, an Italian physicist and mathematician. Torricelli's experiment demonstrated that air pressure could be measured by the height of a mercury column, leading to the development of the mercury barometer. The millimetre of mercury unit derives from this principle, applying it on a smaller scale.

Medical Use

In the medical field, mmHg is most commonly associated with the measurement of blood pressure. Blood pressure is recorded as two measurements: systolic (the pressure when the heart beats) and diastolic (the pressure when the heart is at rest between beats). These measurements are expressed in mmHg, such as 120/80 mmHg, where 120 represents the systolic pressure, and 80 represents the diastolic pressure.

The mmHg measurement is crucial for diagnosing conditions such as hypertension (high blood pressure) and hypotension (low blood pressure), which can lead to more serious health issues like heart disease, stroke, and kidney failure. Regular monitoring of blood pressure and maintaining it within a healthy range is vital for preventing these conditions.

Meteorological Use

In meteorology, mmHg is used to measure atmospheric pressure. The standard atmospheric pressure at sea level is defined as 760 mmHg, which is equivalent to 1013.25 hPa (hectopascals). Changes in atmospheric pressure are important for weather forecasting, as they can indicate the approach of different weather systems.

Conversion

The conversion between mmHg and other units of pressure is important for scientific calculations and applications. One mmHg is exactly equivalent to 133.322387415 pascals. To convert mmHg to pascals, multiply the number of mmHg by 133.322387415. Conversely, to convert pascals to mmHg, divide the number of pascals by 133.322387415.

Safety and Environmental Considerations

While mercury is useful for measuring pressure due to its high density and low vapor pressure, it is also toxic. The use of mercury in devices, including traditional blood pressure monitors and barometers, poses health and environmental risks if the mercury is released. As a result, alternatives such as aneroid and digital devices are increasingly used for measuring pressure.

See Also

• Blood pressure
• Hypertension
• Hypotension
• Heart disease
• Stroke
• Kidney failure
• Atmospheric pressure
• Barometer

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  Barometer by Charles Frodsham, view 1, London, date unknown, mahogany, mercury, metal, glass - Shugborough Hall - Staffordshire, England