Torr

The Torr ( unit symbol: Torr) or millimeter of mercury, unit symbol: mmHg ( formerly and currently in Switzerland only millimeters of mercury ) is a unit of pressure. A Torr is the static pressure, which is generated by a mercury column of 1 mm height.

The mmHg is not an SI unit, but in the countries of EU and Switzerland is a legal entity permitted for the scope " Blood pressure and pressure of other body fluids ."

The torr is named after Evangelista Torricelli, an assistant of Galileo Galilei who invented the mercury barometer.

Definition

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Use and history

The millimeter of mercury - but not the Torr - is (written there without a hyphen ) in the European Union and Switzerland legal unit in the indication of pressures of body fluids, especially blood pressures. The World Meteorological Organization (WMO ) in 1954 set on their part, that the pressure ( 9.80665 m / s ² ) valid for 1 mmHg at the locations of the standard acceleration at 0 ° C. A blood pressure of " 120 over 80 " corresponds approximately to a systolic pressure of 16 kPa ( 160 mbar or hPa or ) and a diastolic of 10.6 kPa ( 106 mbar or hPa or ), where not the absolute but the relative pressure ( relative to the atmospheric pressure) is meant.

The unit was formerly among other things in physics and meteorology (air pressure ) are common; in Germany and Austria are the Torr and the conventional millimeter of mercury since January 1, 1978 no longer generally allowed. However, pressures of body fluids may be given in " mm Hg " in medicine continue. Only in thermodynamics it is otherwise partially still common pressure units " mm Hg " as appropriate.

In the U.S. Torr is next to the most common psi pressure unit.

The relationship 1 Torr = 1 mmHg is strictly valid only at a temperature of 0 ° C. and at standard gravity because the density of mercury is temperature-dependent and depends on the weight of the latitude and longitude. Taken even more stringent this does not apply in Germany; The official exchange relations are here namely 1 mmHg = 133.322 Pa and 1 Torr = ( 101325/760 ) Pa = 133.322368 ... Pa.

Today is For the conventional millimeter of mercury, only the unit symbol " Hg " in use, once called " mmHg" were, "mm Hg " ( only as yet in Switzerland) and used " mmQS " or " mmQS ".