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Information about Torr

For the standard botanical author abbreviation Torr., see John Torrey.


The torr (symbol: Torr) is a non-SI unit of pressure defined as 1/760 of an atmosphere. It was named after Evangelista Torricelli, an Italian physicist and mathematician who discovered the principle of the barometer in 1644.[1]

History

Torricelli attracted considerable attention when he demonstrated the first mercury barometer to the general public. He is credited with giving the first modern explanation of atmospheric pressure. Scientists at the time were familiar with small fluctuations in height that occurred in barometers. When these fluctuations were explained as a manifestation of changes in atmospheric pressure, the science of meteorology was born.

Over time, 760 millimeters of mercury came to be regarded as the “standard” atmospheric pressure. The unit of barometric pressure (one millimeter of mercury) was named in honor of Torricelli.

In 1954, the definition of atmosphere was revised by the 10th Conférence Générale des Poids et Mesures (10th CGPM)[2] to the currently accepted definition: one atmosphere is equal to 101325 pascals. The torr was then re-defined as 1/760 of one atmosphere. This change in the definition of “torr” has been a source of confusion ever since.

SI units of pressure

The SI unit of pressure is the pascal (symbol: Pa), defined as one newton per square meter. Other units of pressure are defined in terms of SI units.[3][4] These include:

* The bar (symbol: bar), defined as 105 Pa exactly.


* The atmosphere (symbol: atm), defined as 101,325 Pa exactly.


* The torr (symbol: Torr), defined as 1/760 atm exactly.


These four SI-related pressure units are used in different settings. For example, the bar is used in meteorology to report atmospheric pressures.[5] The torr, a more convenient unit for low pressures, is used in high-vacuum physics and engineering.

Manometric units of pressure

Manometric units are units such as millimeters of mercury or centimeters of water that depend on an assumed density of a fluid and an assumed acceleration of gravity. These units are now regarded as obsolete, and their use is discouraged.[6] Nevertheless, manometric units are used routinely in medicine and physiology, and they continue to be used in areas as diverse as weather reporting and scuba diving.

The millimeter of mercury (symbol: mmHg) is defined as the pressure exerted at the base of a column of fluid exactly 1 mm high, when the density of the fluid is exactly 13.5951 g/cm³, at a place where the acceleration of gravity is exactly 9.80665 m/s². [7]

There are several things to notice about this definition:

* A fluid density of 13.5951 g/cm2 was chosen for this definition because this is the approximate density of mercury at 0 °C. The definition, therefore, assumes a particular value for the density of mercury. This assumption limits the precision of any pressure measurement (in mmHg) to six significant digits.[8]


* The definition assumes a particular value for the acceleration of gravity: the standard acceleration gn = 9.80665 m/sec2. In practice, of course, measurements are made using local values.


These assumptions limit both the validity and the precision of the mmHg as a unit of pressure. No metrology laboratory measures or calibrates pressure directly in these terms. It would be extremely difficult to find a fluid with exactly this density, and a place where g was exactly 9.80665 m/s². According to the UK’s National Physical Laboratory (NPL):

:The need to assume fixed and exact but ultimately incorrect values of
:liquid density and acceleration due to gravity inherently limits knowledge
:of the relationship between [the millimeter of mercury] and the pascal.
:By contrast, the magnitude of pressure values expressed in the SI pressure
:unit, the pascal, can flex (albeit not by much) to take account of technological
:improvements in the underlying definitions of mass, length and time – the
:SI base quantities from which pressure is derived.[9]


The performance of modern transducers approaches the precision required to distinguish between the torr and the millimeter of mercury. The NPL concludes

:Thus, in the near future, the accuracy claims being made for otherwise
:state-of-the-art instruments scaled in manometric units will become
:inherently inferior. Even now, confusion and large errors abound through
:the use of differing definitions, including alternative values of ‘standard?
:gravity and varying assumptions about the density and temperature of the
:fluid. Misunderstandings about temperature assumptions alone can lead
:to errors of several tenths of a percent and there are many stories of this
:leading to major mistakes in pressure measurement.

Manometric units in medicine and physiology

In medicine, the mmHg (measured with a sphygmomanometer) is the gold standard for blood pressure measurement. In physiology, manometric units are used to measure Starling forces. Other applications include:

* Intraocular pressure (tonometry)
* CSF pressure
* Intracranial pressure
* Intramuscular pressure (compartment syndrome)
* Central venous pressure
* Pulmonary artery catheterization
* Mechanical ventilation
* Pulmonary gas pressure
* Esophageal motility studies


Manometric results in medicine are sometimes given in torr. This is usually incorrect, since the Torr and the mmHg are not the same thing. Pressures obtained with a manometer (or its transducer equivalent) should be reported in mmHg.

Conversion factors

The mmHg is defined as 13.5951 x 9.80665 = 133.322387415 Pa. This is an exact number, although it is too long to be of any practical use.

The torr is defined as 1/760 of one atmosphere, while the atmosphere is defined as 101,325 Pa. Therefore, one Torr is equal to 101325/760 of one Pa. The decimal form of this fraction (133.322368421...) is, unfortunately, an infinitely long, periodically repeating decimal.

The relationship between the Torr and the mmHg is: 1 Torr = 0.999 999 857 533 699... mmHg 1 mmHg = 1.000 000 142 466 321... Torr The mmHg and the Torr differ from one another by less than 2 x 10-7 Torr. The difference between one atmosphere (101325 Pa) and 760 mmHg (101325.0144354 Pa) less than 0.2 μPa/Pa (less than 0.00002%). This small difference is negligible for most applications outside of the research laboratory.

Notes

1. ^ Devices similar to the modern barometer, using water instead of mercury, were studied by a number of scientists in the early 1640s ([1] Torricelli’s explanation of the principle of the barometer appears in a letter to Michelangelo Ricci ([2] dated June 11, 1644.
2. ^ [3]
3. ^ Cohen ER et. al. Quantities, Units and Symbols in Physical Chemistry, 3rd ed. Royal Society of Chemistry, 2007.
4. ^ DeVoe H. Thermodynamics and Chemistry. Prentice-Hall, Inc. 2001.
5. ^ Note that a pressure of 1 bar (100,000 Pa) is slightly less than a pressure of 1 atmosphere (101.325 Pa).
6. ^ National Physical Laboratory: Pressure units. [4]
7. ^ Conventional millimeters of mercury. [5]
8. ^ The density of mercury is now known to 6 decimal places (8 significant digits). See, for example, [6]
9. ^ National Physical Laboratory: Pressure and vacuum. [7]

See also

External links

John Torrey (August 15, 1796 – March 10, 1873) was an American botanist.

Torrey was born in New York. When he was 15 or 16 years of age his father received a prison appointment at Greenwich, and there he made the acquaintance of Amos Eaton, a pioneer of natural history
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Pressure (symbol: p) is the force per unit area applied on a surface in a direction perpendicular to that surface.

Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.
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Standard atmosphere is a pressure defined as 101 325 Pa and used as unit of pressure (symbol: atm). Standard atmosphere is a non-SI unit that is internationally recognized.
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Torricelli can refer to the following:
  • Evangelista Torricelli, Italian physicist
  • Robert Torricelli former American politician
  • Moreno Torricelli, former Italian football player
  • Torricelli languages, a subgroup of the Papuan languages

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A barometer is an instrument used to measure atmospheric pressure. It can measure the pressure exerted by the atmosphere by using water, air, or mercury. Pressure tendency can forecast short term changes in the weather.
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2, 1
(mildly basic oxide)
Electronegativity 2.00 (scale Pauling)
Ionization energies 1st: 1007.1 kJ/mol
2nd: 1810 kJ/mol
3rd: 3300 kJ/mol
Atomic radius 150 pm
Atomic radius (calc.
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Meteorology (from Greek: μετέωρον, meteoron, "high in the sky"; and λόγος, logos, "knowledge") is the interdisciplinary scientific study of the atmosphere that focuses on weather processes and
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The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Young's modulus and tensile strength). It is a measure of perpendicular force per unit area i.e. equivalent to one newton per square meter or one Joule per cubic meter.
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Si, si, or SI may refer to (all SI unless otherwise stated):

In language:
  • One of two Italian words:
  • sì (accented) for "yes"
  • si

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The newton (symbol: N) is the SI derived unit of force, named after Sir Isaac Newton in recognition of his work on classical mechanics.

Definition

A newton
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Standard gravity, usually denoted by g0 or gn, is the nominal acceleration due to gravity at the Earth's surface at sea level. By definition it is equal to exactly 9.80665  m·s−2 (approx. 32.174 ft·s−2).
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A sphygmomanometer (often condensed to sphygmometer [1] ) or blood pressure meter is a device used to measure blood pressure, comprising an inflatable cuff to restrict blood flow, and a mercury or mechanical manometer to measure the pressure.
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Blood pressure (strictly speaking: vascular pressure) refers to the force exerted by circulating blood on the walls of blood vessels, and constitutes one of the principal vital signs.
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Formulated in 1896 by the British physiologist Ernest Starling, the Starling equation illustrates the role of hydrostatic and oncotic forces (the so-called Starling forces) in the movement of fluid across capillary membranes.
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Tonometry is the measurement of tension or pressure [1] . A tonometer is an instrument for measuring tension or pressure [2] .

In ophthalmology, tonometry is the procedure eye care professionals perform to determine the intraocular pressure (IOP),
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CSF may refer to:
  • Caesium fluoride (cesium fluoride), a chemical compound
  • California Scholarship Federation
  • California State University, Fullerton, a university in Southern California
  • Caltech Satanic Fellowship

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Intracranial pressure, (ICP), is the pressure exerted by the cranium on the brain tissue, cerebrospinal fluid (CSF), and the brain's circulating blood volume. ICP is a dynamic phenomenon constantly fluctuating in response to activities such as exercise, coughing, straining,
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Compartment syndrome
Classification & external resources

ICD-10 T 79.6
ICD-9 729.9 , 958.8

DiseasesDB 3028
MedlinePlus 001224
eMedicine emerg/739   pmr/33 sports/26

MeSH C05.651.
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Central venous pressure (CVP) describes the pressure of blood in the thoracic vena cava, near the right atrium of the heart. CVP reflects the amount of blood returning to the heart and the ability of the heart to pump the blood into the arterial system.
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In medicine pulmonary artery catheterization is the insertion of a catheter into a pulmonary artery. Its purpose is diagnostic; it is used to detect heart failure or sepsis, monitor therapy, and evaluate the effects of drugs.
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mechanical ventilation is a method to mechanically assist or replace spontaneous breathing when patients cannot do so on their own, and must be done so after invasive intubation with an endotracheal or tracheostomy tube through which air is directly delivered (in contrast to
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Following is a list of average partial pressures (in torr) for a human at rest:

Location pO2
(Torr) pCO2
(Torr)
Outside air - dry air at sea level 160 0.
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An esophageal motility study (EMS) or esophageal manometry is a study performed to evaluate the pressure of the esophagus in various stages along its length.

Indications


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Inches of mercury, inHg or "Hg is a non-SI unit for pressure. It is still widely used for barometric pressure in weather reports and aviation in the United States, but is considered somewhat outdated elsewhere.
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Pressure (symbol: p) is the force per unit area applied on a surface in a direction perpendicular to that surface.

Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.
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Standard atmosphere is a pressure defined as 101 325 Pa and used as unit of pressure (symbol: atm). Standard atmosphere is a non-SI unit that is internationally recognized.
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Conversion of units refers to conversion factors between different units of measurement for the same quantity.

Techniques

The simplest way to convert from one unit to another is to carry through the units themselves in the mathematical operation.
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A centimeter (centimetre) of water or cm H2O is a less commonly used unit of pressure. It is used to measure the central venous pressure, the intracranial pressure while sampling cerebrospinal fluid, as well as determining pressures during mechanical ventilation
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