Language politics

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Language_politics 

 

The politics of language are evident in French-speaking Brussels, which is located in the Flanders region of Belgium, where people typically speak Flemish. Divisive preference of either language is avoided by using both French and Flemish on nearly all signs in Brussels.

Language politics is the way language and linguistic differences between peoples are dealt with in the political arena. This could manifest as government recognition, as well as how language is treated in official capacities.

The topic is a multi-faceted one. As such, this page serves as a nexus for some of the overall topics with easy access to relevant pages. Below are some categories in languages and the politics surrounding them, along with examples and links to other relevant pages.

Language planning and policy

Main article: Language planning

Language planning refers to concerted efforts to influence how and why languages are used in a community. It is usually associated with governmental policies which largely involve status planning, corpus planning and acquisition planning. There are often much interaction between the three areas. Status planning involves giving a language or languages a certain standing against other languages and is often associated with language prestige and language function. Corpus planning often involves linguistic prescription as decisions are made in graphization, standardization and modernization of a language. Acquisition planning fundamentally involves language policies to promote language learning.

Status planning

• Legal status of a language as an official language in a country, state, or other jurisdiction. This generally means that all official documents affecting a country or region are published in the official language(s), but not in those that are not. Evidence in a court of law may also be expected to be presented in an official language.
• In countries where there are more than one main language, there are often political implications in decisions that are seen to promote one group of speakers over another, and this is often referred to as language politics. An example of a country with this type of language politics is Belgium.
• In countries where there is one main language, immigrants seeking full citizenship may be expected to have a degree of fluency in that language ('language politics' then being a reference to the debate over the appropriateness of this). This has been a feature of Australian politics.
• At various times minority languages have either been promoted or banned in schools, as politicians have either sought to promote a minority language with an aim of strengthening the cultural identity of its speakers, or ban its use (either in teaching, or on occasion an entire ban on its use), with an aim of promoting a national identity based on the majority language. An example of recent promotion of a minority language is the promotion of Welsh or Leonese by the Leonese City Council and an example of official discouragement of a minority language is of Breton.
• Language politics also sometimes relate to dialect, where speakers of a particular dialect are perceived to speak a more culturally 'advanced' or 'correct' form of the language. Politicians may therefore try to use that dialect rather than their own when in the public eye. Alternatively, at times those speaking the dialect perceived as more 'correct' may try to use another dialect when in the public eye to be seen as a 'man/woman of the people'.

Corpus planning

Corpus planning consists of three traditionally recognised forms: graphization, standardization and modernization. Graphization involves the development of written scripts and orthography of languages. Standardization involves giving a selected variety of a language precedence over the other varieties as the "standard" form for others to emulate. Modernization often involves expanding the lexicon of a language as a result of language shift over time.

• To promote national identity, what are strictly dialects of the same language may be promoted as separate languages to promote a sense of national identity (examples include Danish and Norwegian, and Serbian and Croatian – the latter two also use different scripts for what is linguistically the same language – Cyrillic for Serbian and roman script for Croatian). Whether or not something is a language can also involve language politics, for instance, Macedonian.
• On the contrary, to unify the country, China worked towards a common national language with a standard written script (see: Standard Chinese). The efforts started as early as 1912 after the establishment of the Republic of China. Initial efforts tried to create a language that was phonologically hybridised from the existing languages but they later on settled on pronunciations based on the Beijing variety of Mandarin. Nonetheless, there were still influence from the other Chinese varieties in this standard language. All other language varieties are officially known as 方言 fāngyán which directly translates to regional speech or more well known as Chinese dialects despite being mutually unintelligible. However, the different speakers communicate via a common written script known as a unified Chinese script. After the Chinese Civil War, the People's Republic of China continued the efforts of a common national language, renaming the standard language from 国语 guóyǔ ("national language") to 普通话 pǔtōnghuà ("common speech") in 1955.
• 'Political correctness' describes the situation where language forms must be used (or not used) to comply with national (or group) ideology
• Co-existence of competing spelling systems for the same language, associated with different political camps. Examples:
  • Debate on traditional and simplified Chinese characters
  • Simplification of Russian orthography; proposals for such a reform were viewed as subversive in the late years of the Russian Empire and were implemented by the Bolsheviks in 1918, after which the "old orthography" became associated with the White movement.
  • The two spelling systems for the Belarusian language, one of which is associated with the country's political opposition.

Language is also utilised in political matters to unify, organise and criticise in order to unify a political group.

• The Moldovan Cyrillic alphabet preserved in Transnistria.

Acquisition planning (language in education)

Acquisition planning often manifests in education policies after the status and corpus planning policies have been introduced. These policies can take in the form of compulsory language education programmes, enforcing a specific language of instruction in schools or development of educational materials. In some countries, mainstream education is offered in one language: English in the United States, Italian in Italy, Russian in Russia, just to name a few. In some countries, mainstream education provide education in several languages. This is especially common in countries with more than one official languages. Some countries promote multilingualism in their policies: bilingual policy in Singapore, three-language formula in India, just to name a few.

Linguistic discrimination

Main article: Linguistic discrimination

 

Martin Luther King Jr. Elementary, Vancouver, Washington, building entrance, November, 2019

Linguistic discrimination, or linguicism, refers to unequal treatment of speakers of different languages or language varieties. It can be observed with regard to spoken language, where speakers may be discriminated against based on their regional dialect, their sociolect, their accent, or their vocabulary. In terms of language planning, linguistic discrimination can occur at different stages, such as the choice of one or more official languages, choosing the language of instruction, the availability of essential services such as health care in minority languages, and the protection or lack thereof of minority languages and dialects.

In the United States, speakers of African-American Vernacular English (AAVE) often experience linguistic discrimination. A study, published in 1982, of attitudes towards AAVE at Martin Luther King Junior Elementary school in Ann Arbor, Michigan, revealed that black students who primarily spoke AAVE received less help from their teachers in comparison to their white peers. One social worker observed that these AAVE-speaking students faced a significant linguistic barrier to academic achievement and success in the predominantly White American society at that time. This is one example of a larger controversy surrounding African-American Vernacular English in education.

Colonialism

Main article: Colonialism

 

Guerillas rugendas

Colonialism is a significant context in which linguistic discrimination takes place. When territories were colonized for the purpose of settlement buildling, indigenous languages became gravely endangered because the native speaker groups were either destroyed by war and disease, or had undergone a partial language shift to speak their master's language. In exploitation colonies however, colonizers would usually only teach their language to a select group of locals. In postcolonial states like India, it was observed that the difference in language education had widened the socioeconomic class divide. Thus, access to education, social mobility, and economic opportunities were deprived of the locals who had not learnt the colonial language of before.

Approximately 1.35 billion people in the world now speak English, with about 360 million native English speakers. As of 2015, more than 75% of all scientific papers were published in English. English is also the most commonly studied foreign language in the world. This global prevalence of English can be attributed to many developments that have occurred in recent history, namely, the expansion of the British Empire, which has resulted in the establishment of English as an official language in at least 75 countries. David Crystal gives a detailed explanation about the spread of English worldwide in Chapter 9 of A History of the English Language (ed. Richard M. Hogg). Robert Phillipson has posited this is an example of linguistic imperialism. However, this notion is contested in the field of applied linguistics.

Linguistic Imperialism

Main article: Linguistic imperialism

Linguistic imperialism refers to the dominance of one language over another on a national (and sometimes international) scale as a result of language policy and planning. According to Robert Phillipson, it is a variant of linguicism and is enacted through systemic changes and language attitudes, resulting in unfair treatment of non-dominant language groups. This form of discrimination works in ways similar to racism, sexism, and classism, on a national administrative scale.

As an example, a case study on the usage of Irish Sign Language (ISL) in Ireland revealed unfair treatment of a deaf community in Ireland. The study observed the enforcement of English over ISL in the educational system, as well as the prohibition of ISL among deaf children who were deemed capable enough to learn oral language (oralism). The study also highlighted anti-ISL language attitudes among school officials, unequal pay of ISL teachers, unequal status given to ISL in the education system, and the systemic marginalisation of ISL users. Efforts to elevate the usage of English over ISL also entailed the teaching of Manually Coded English (MCE) to deaf students, a signed language based on the grammatical structure of English. Unfortunately, MCE and other manually coded languages are often difficult and slow to use for communication among signers. Despite this, such language policies have influenced members of the deaf community (especially older members) to internalise the belief that ISL is inferior to spoken language.

Names and politics

See also: Toponymy and Critical toponymy

Critical toponymies

Toponymy is the study of place names (from Ancient Greek: τόπος / tópos, 'place', and ὄνομα / onoma, 'name'). According to Lawrence D. Berg and Jani Vuolteenaho, traditional research into place names has focused more on describing their origins in an empirical way. However, they note that there are 'power relations inherent in geographical naming', because to have the power to name something is to have the 'power of "making places"'. Their book, Critical Toponymies, is, according to them, the 'first interdisciplinary collection published in English that tackles explicitly place naming as "a political practice par excellence of power over space"', and gathers research from various scholars about the politics inherent in the naming of places.

Choice of language

Road signs in Karasjok (Kárášjohka), northern Norway. The top and bottom names are Northern Sámi; the second-from-bottom is Finnish; the rest are Norwegian.

As an example, the powers-that-were in Norway began strictly regulating Sámi place names in the 1870s, replacing them with Norwegian names in official documents, even suggesting that if no Norwegian name had yet been made for a certain place, a Norwegian translation ought of the name ought to be used on maps. This 'toponymic silence' gave the impression that Norwegians had settled in places where the Sámi historically lived; and the silence lives on till the present -- Norwegians may believe that Sámi place names which have not been recorded on maps etc. are not in common use (even though they are); alternatively, since Sámi names for natural features have remained but not names for settlements, Norwegians may believe that Sámi people only reside in otherwise uninhabited areas. Now, even though Sámi place names can be restored to official status, they must still be proven to actually be in use among the community. This is not the case for Norwegian names, which will remain official even if few people in the locality use that name. With these observations, it can be concluded that the Sámi have not received full 'decolonisation' yet - the colonisation being in the Norwegian power to rename Sámi places.

Choice of pronunciation

In places where native names have been reclaimed in writing, there is a secondary issue of pronunciation. With reference to New Zealand, Robin Kearns and Lawrence Berg note that how a place name is pronounced also has a political meaning. Letters to the editors of New Zealand newspapers sometimes complain about newscasters' choice to pronounce place names in a more Māori-like way. Even if Lake Taupo maintains an ostensibly Māori-derived name, some argued against a Member of Parliament telling others to read it 'toe-po' ([ˈtoʊpɔː]; see Taupo). Kearns and Berg note that the written forms of Māori place names give no hints as to how they should be pronounced, and so even some Māori speakers might not know the 'true' pronunciation. These people might not be trying to make any political statement by reading the names their own way. Even so, their utterance of the name becomes situated in a wider political context of 'a resurgence of Maori cultural forms, and increasing calls for self-determination', which 'presents a threatening and uncertain environment for members of the status quo'. In this way, language in the form of place names becomes part of politics - part of the 'contest over the symbolic ownership of place' in New Zealand.

Cross-state conflicts

Even across states, agreement on a single name is difficult. This can apply to places which a state does not own: for example, see the Sea of Japan naming dispute or the Persian Gulf naming dispute. Mapmakers often acquiesce by creating two versions of the same map, but with the names of geographical features swapped out depending on which state the maps are sold in. Notably, Greece objected to the use of the name 'Macedonia' by the then newly-independent Republic of North Macedonia. According to Naftalie Kadmon, the Greek government was worried that '[c]laims of the South Yugoslavians to the name Macedonia might in time lead to political demands towards Greece, and finally to military aggression.' The case was escalated to the UN, and it was decided that the new state should be named the Former Yugoslav Republic of Macedonia (FYROM).

A view of Piran from Savudrija. The Bay of Piran/Savudrija separates these two settlements.

These conflicts between states regarding names still nevertheless indicate a conflict over ownership or belonging. For example, the Bay of Piran between Croatia and Slovenia began being referred to by Croatian official sources as the Bay of Savudrija (Savudrijska vala) around the early 2000s. In both cases, the names of the bay are taken from towns (Piran is in Slovenia, and Savudrija is in Croatia). This recent Croatian insistence on a new name linked to Croatia 'represents a transfer of the identity of the bay elsewhere - to another place far from Piran', and stakes 'Croatia's ownership of this part of the bay'.

Recognition of importance of names

The United Nations Economic and Social Council (ECOSOC) set up the United Nations Group of Experts on Geographical Names (UNGEGN) and the United Nations Conferences on the Standardization of Geographical Names (UNCSGN). The UNCSGN has three main objectives:

• 'encourage national and international geographical names standardization;
• 'promote the international dissemination of nationally standardized geographical names information; and
• 'adopt single romanization systems for the conversion of each non-Roman writing system to the Roman alphabet.'

The UNCSGN occurs every five years, and the UNGEGN 'meets between the Conferences to follow up the implementation of resolutions adopted by the Conferences and to ensure continuity of activities between Conferences'.

Other names

The politics applied to naming places can also applies to naming ethnic groups. For example, it is generally offensive to use words which are considered by some to have negative implications (pejorative exonyms) to describe a group of people: e.g. 'Gypsies' (or even more negatively, 'Gypos') instead of 'Romani', or indeed using the term 'Gypsies' to cover Traveller peoples as well as Romani people.

As another example, the Haudenosaunee Confederacy writes that although they have been 'called the Iroquois Confederacy by the French, and the League of Five Nations by the English, the confederacy is properly called the Haudenosaunee Confederacy meaning People of the long house.' The rejection of the exonym 'Iroqouis' (which is still the name used in, for example, the Wikipedia page) is inherent in the statement that the confederacy (and the people) are properly called 'Haudenosaunee'.

Angular momentum of light

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Angular_momentum_of_light 

The angular momentum of light is a vector quantity that expresses the amount of dynamical rotation present in the electromagnetic field of the light. While traveling approximately in a straight line, a beam of light can also be rotating (or "spinning", or "twisting") around its own axis. This rotation, while not visible to the naked eye, can be revealed by the interaction of the light beam with matter.

There are two distinct forms of rotation of a light beam, one involving its polarization and the other its wavefront shape. These two forms of rotation are therefore associated with two distinct forms of angular momentum, respectively named light spin angular momentum (SAM) and light orbital angular momentum (OAM).

The total angular momentum of light (or, more generally, of the electromagnetic field and the other force fields) and matter is conserved in time.

Introduction

Light, or more generally an electromagnetic wave, carries not only energy but also momentum, which is a characteristic property of all objects in translational motion. The existence of this momentum becomes apparent in the "radiation pressure" phenomenon, in which a light beam transfers its momentum to an absorbing or scattering object, generating a mechanical pressure on it in the process.

Light may also carry angular momentum, which is a property of all objects in rotational motion. For example, a light beam can be rotating around its own axis while it propagates forward. Again, the existence of this angular momentum can be made evident by transferring it to small absorbing or scattering particles, which are thus subject to an optical torque.

For a light beam, one can usually distinguish two "forms of rotation", the first associated with the dynamical rotation of the electric and magnetic fields around the propagation direction, and the second with the dynamical rotation of light rays around the main beam axis. These two rotations are associated with two forms of angular momentum, namely SAM and OAM. However this distinction becomes blurred for strongly focused or diverging beams, and in the general case only the total angular momentum of a light field can be defined. An important limiting case in which the distinction is instead clear and unambiguous is that of a "paraxial" light beam, that is a well collimated beam in which all light rays (or, more precisely, all Fourier components of the optical field) only form small angles with the beam axis.

For such a beam, SAM is strictly related with the optical polarization, and in particular with the so-called circular polarization. OAM is related with the spatial field distribution, and in particular with the wavefront helical shape.

In addition to these two terms, if the origin of coordinates is located outside the beam axis, there is a third angular momentum contribution obtained as the cross-product of the beam position and its total momentum. This third term is also called "orbital", because it depends on the spatial distribution of the field. However, since its value is dependent from the choice of the origin, it is termed "external" orbital angular momentum, as opposed to the "internal" OAM appearing for helical beams.

Mathematical expressions for the angular momentum of light

One commonly used expression for the total angular momentum of an electromagnetic field is the following one, in which there is no explicit distinction between the two forms of rotation:

$${\displaystyle \mathbf {J} =\varepsilon _{0}\int \mathbf {r} \times \left(\mathbf {E} \times \mathbf {B} \right)d^{3}\mathbf {r} ,}$$

where ${\displaystyle \mathbf {E} }$ and ${\displaystyle \mathbf {B} }$ are the electric and magnetic fields, respectively, ${\displaystyle \epsilon _{0}}$ is the vacuum permittivity and we are using SI units.

However, another expression of the angular momentum naturally arising from Noether’s theorem is the following one, in which there are two separate terms that may be associated with SAM (${\displaystyle \mathbf {S} }$) and OAM (${\displaystyle \mathbf {L} }$):

$${\displaystyle \mathbf {J} =\varepsilon _{0}\int \left(\mathbf {E} \times \mathbf {A} \right)d^{3}\mathbf {r} +\varepsilon _{0}\sum _{i=x,y,z}\int \left(E^{i}\left(\mathbf {r} \times {\boldsymbol {\nabla }}\right)A^{i}\right)d^{3}\mathbf {r} =\mathbf {S} +\mathbf {L} ,}$$

where ${\displaystyle \mathbf {A} }$ is the vector potential of the magnetic field, and the i-superscripted symbols denote the cartesian components of the corresponding vectors.

These two expressions can be proved to be equivalent to each other for any electromagnetic field that vanishes fast enough outside a finite region of space. The two terms in the second expression however are physically ambiguous, as they are not gauge-invariant. A gauge-invariant version can be obtained by replacing the vector potential A and the electric field E with their “transverse” or radiative component ${\displaystyle \mathbf {A} _{\perp }}$ and ${\displaystyle \mathbf {E} _{\perp }}$, thus obtaining the following expression:

$${\displaystyle \mathbf {J} _{\perp }=\varepsilon _{0}\int \left(\mathbf {E} _{\perp }\times \mathbf {A} _{\perp }\right)d^{3}\mathbf {r} +\varepsilon _{0}\sum _{i=x,y}\int \left({E^{i}}_{\perp }\left(\mathbf {r} \times {\boldsymbol {\nabla }}\right)A_{\perp }^{i}\right)d^{3}\mathbf {r} .}$$

A justification for taking this step is yet to be provided. The latter expression has further problems, as it can be shown that the two terms are not true angular momenta as they do not obey the correct quantum commutation rules. Their sum, that is the total angular momentum, instead does.^{[citation needed]}

An equivalent but simpler expression for a monochromatic wave of frequency ω, using the complex notation for the fields, is the following:

$${\displaystyle \mathbf {J} ={\frac {\varepsilon _{0}}{2i\omega }}\int \left(\mathbf {E} ^{\ast }\times \mathbf {E} \right)d^{3}\mathbf {r} +{\frac {\varepsilon _{0}}{2i\omega }}\sum _{i=x,y,z}\int \left({E^{i}}^{\ast }\left(\mathbf {r} \times {\boldsymbol {\nabla }}\right)E^{i}\right)d^{3}\mathbf {r} .}$$

Let us now consider the paraxial limit, with the beam axis assumed to coincide with the z axis of the coordinate system. In this limit the only significant component of the angular momentum is the z one, that is the angular momentum measuring the light beam rotation around its own axis, while the other two components are negligible.

$${\displaystyle \mathbf {J} \approx {\frac {{\hat {z}}\epsilon _{0}}{2\omega }}\int \left(\left|E_{\text{L}}\right|^{2}-\left|E_{\text{R}}\right|^{2}\right)d^{3}\mathbf {r} +{\frac {{\hat {z}}\varepsilon _{0}}{2i\omega }}\int \sum _{i=x,y,z}\left({E^{i}}^{\ast }{\frac {\partial }{\partial \phi }}E^{i}\right)d^{3}\mathbf {r} .}$$

where ${\displaystyle E_{\text{L}}}$ and ${\displaystyle E_{\text{R}}}$ denote the left and right circular polarization components, respectively.

Exchange of spin and orbital angular momentum with matter

Spin and orbital angular momentum interaction with matter

When a light beam carrying nonzero angular momentum impinges on an absorbing particle, its angular momentum can be transferred on the particle, thus setting it in rotational motion. This occurs both with SAM and OAM. However, if the particle is not at the beam center the two angular momenta will give rise to different kinds of rotation of the particle. SAM will give rise to a rotation of the particle around its own center, i.e., to a particle spinning. OAM, instead, will generate a revolution of the particle around the beam axis. These phenomena are schematically illustrated in the figure.

In the case of transparent media, in the paraxial limit, the optical SAM is mainly exchanged with anisotropic systems, for example birefringent crystals. Indeed, thin slabs of birefringent crystals are commonly used to manipulate the light polarization. Whenever the polarization ellipticity is changed, in the process, there is an exchange of SAM between light and the crystal. If the crystal is free to rotate, it will do so. Otherwise, the SAM is finally transferred to the holder and to the Earth.

Spiral Phase Plate (SPP)

Schematic of generating light orbital angular momentum with spiral phase plate.

In the paraxial limit, the OAM of a light beam can be exchanged with material media that have a transverse spatial inhomogeneity. For example, a light beam can acquire OAM by crossing a spiral phase plate, with an inhomogeneous thickness (see figure).

Pitch-Fork Hologram

Schematic showing generation of orbital angular momentum of light in a Gaussian beam.

A more convenient approach for generating OAM is based on using diffraction on a fork-like or pitchfork hologram (see figure). Holograms can be also generated dynamically under the control of a computer by using a spatial light modulator.

Q-Plate

The q-plate effect for left and right-hand circular polarizations.

Another method for generating OAM is based on the SAM-OAM coupling that may occur in a medium which is both anisotropic and inhomogeneous. In particular, the so-called q-plate is a device, currently realized using liquid crystals, polymers or sub-wavelength gratings, which can generate OAM by exploiting a SAM sign-change. In this case, the OAM sign is controlled by the input polarization.

Cylindrical Mode Converters

pi/2-cylindrical mode converter transforms HG mode into a proper LG mode.

OAM can also be generated by converting a Hermite-Gaussian beam into a Laguerre-Gaussian one by using an astigmatic system with two well-aligned cylindrical lenses placed at a specific distance (see figure) in order to introduce a well-defined relative phase between horizontal and vertical Hermite-Gaussian beams.

Possible applications of the orbital angular momentum of light

The applications of the spin angular momentum of light are undistinguishable from the innumerable applications of the light polarization and will not be discussed here. The possible applications of the orbital angular momentum of light are instead currently the subject of research. In particular, the following applications have been already demonstrated in research laboratories, although they have not yet reached the stage of commercialization:

1. Orientational manipulation of particles or particle aggregates in optical tweezers
2. High-bandwidth information encoding in free-space optical communication
3. Higher-dimensional quantum information encoding, for possible future quantum cryptography or quantum computation applications
4. Sensitive optical detection

Altitude sickness

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Altitude_sickness 

 

Altitude sickness
Other names	High-altitude sickness, altitude illness, hypobaropathy, altitude bends, soroche
Altitude sickness warning – Indian Army
Specialty	Emergency medicine
Symptoms	Headache, vomiting, feeling tired, trouble sleeping, dizziness
Complications	High-altitude pulmonary edema (HAPE), high-altitude cerebral edema (HACE)
Usual onset	Within 24 hours
Types	Acute mountain sickness, high-altitude pulmonary edema, high-altitude cerebral edema, chronic mountain sickness
Causes	Low amounts of oxygen at high elevation
Risk factors	Prior episode, high degree of activity, rapid increase in elevation
Diagnostic method	Based on symptoms
Differential diagnosis	Exhaustion, viral infection, hangover, dehydration, carbon monoxide poisoning
Prevention	Gradual ascent
Treatment	Descent to lower altitude, sufficient fluids
Medication	Ibuprofen, acetazolamide, dexamethasone, oxygen therapy
Frequency	20% at 2,500 metres (8,000 ft) 40% at 3,000 metres (10,000 ft)

Altitude sickness, the mildest form being acute mountain sickness (AMS), is the harmful effect of high altitude, caused by rapid exposure to low amounts of oxygen at high elevation. People can respond to high altitude in different ways. Symptoms may include headaches, vomiting, tiredness, confusion, trouble sleeping, and dizziness. Acute mountain sickness can progress to high-altitude pulmonary edema (HAPE) with associated shortness of breath or high-altitude cerebral edema (HACE) with associated confusion. Chronic mountain sickness may occur after long-term exposure to high altitude.

Altitude sickness typically occurs only above 2,500 metres (8,000 ft), though some are affected at lower altitudes. Risk factors include a prior episode of altitude sickness, a high degree of activity, and a rapid increase in elevation. Diagnosis is based on symptoms and is supported in those who have more than a minor reduction in activities. It is recommended that at high altitude any symptoms of headache, nausea, shortness of breath, or vomiting be assumed to be altitude sickness.

Prevention is by gradually increasing elevation by no more than 300 metres (1,000 ft) per day. Being physically fit does not decrease the risk. Treatment is generally by descending and sufficient fluids. Mild cases may be helped by ibuprofen, acetazolamide, or dexamethasone. Severe cases may benefit from oxygen therapy and a portable hyperbaric bag may be used if descent is not possible. Treatment efforts, however, have not been well studied.

AMS occurs in about 20% of people after rapidly going to 2,500 metres (8,000 ft) and 40% of people going to 3,000 metres (10,000 ft). While AMS and HACE occurs equally frequently in males and females, HAPE occurs more often in males. The earliest description of altitude sickness is attributed to a Chinese text from around 30 BCE which describes "Big Headache Mountains", possibly referring to the Karakoram Mountains around Kilik Pass.

Signs and symptoms

Left: A woman at normal altitude. Right: The same woman with a swollen face while trekking at high altitude (Annapurna Base Camp, Nepal; 4130 m).

People have different susceptibilities to altitude sickness; for some otherwise healthy people, acute altitude sickness can begin to appear at around 2,000 metres (6,600 ft) above sea level, such as at many mountain ski resorts, equivalent to a pressure of 80 kilopascals (0.79 atm). This is the most frequent type of altitude sickness encountered. Symptoms often manifest within ten hours of ascent and generally subside within two days, though they occasionally develop into the more serious conditions. Symptoms include headache, confusion, fatigue, stomach illness, dizziness, and sleep disturbance. Exertion may aggravate the symptoms.

Those individuals with the lowest initial partial pressure of end-tidal pCO₂ (the lowest concentration of carbon dioxide at the end of the respiratory cycle, a measure of a higher alveolar ventilation) and corresponding high oxygen saturation levels tend to have a lower incidence of acute mountain sickness than those with high end-tidal pCO₂ and low oxygen saturation levels.

Primary symptoms

Headaches are the primary symptom used to diagnose altitude sickness, although a headache is also a symptom of dehydration. A headache occurring at an altitude above 2,400 metres (7,900 ft) – a pressure of 76 kilopascals (0.75 atm) – combined with any one or more of the following symptoms, may indicate altitude sickness:

Disordered system	Symptoms
Gastrointestinal	Loss of appetite, nausea, vomiting, excessive flatulation
Nervous	Fatigue or weakness, headache with or without dizziness or lightheadedness, insomnia, "pins and needles" sensation
Locomotory	Peripheral edema (swelling of hands, feet, and face)
Respiratory	Nose bleeding, shortness of breath upon exertion
Cardiovascular	Persistent rapid pulse
Other	General malaise

Severe symptoms

Symptoms that may indicate life-threatening altitude sickness include:

Pulmonary edema (fluid in the lungs)

Symptoms similar to bronchitis

Persistent dry cough

Fever

Shortness of breath even when resting

Cerebral edema (swelling of the brain)

Headache that does not respond to analgesics

Unsteady gait

Gradual loss of consciousness

Increased nausea and vomiting

Retinal hemorrhage

The most serious symptoms of altitude sickness arise from edema (fluid accumulation in the tissues of the body). At very high altitude, humans can get either high-altitude pulmonary edema (HAPE), or high-altitude cerebral edema (HACE). The physiological cause of altitude-induced edema is not conclusively established. It is currently believed, however, that HACE is caused by local vasodilation of cerebral blood vessels in response to hypoxia, resulting in greater blood flow and, consequently, greater capillary pressures. On the other hand, HAPE may be due to general vasoconstriction in the pulmonary circulation (normally a response to regional ventilation-perfusion mismatches) which, with constant or increased cardiac output, also leads to increases in capillary pressures. For those with HACE, dexamethasone may provide temporary relief from symptoms in order to keep descending under their own power.

HAPE can progress rapidly and is often fatal. Symptoms include fatigue, severe dyspnea at rest, and cough that is initially dry but may progress to produce pink, frothy sputum. Descent to lower altitudes alleviates the symptoms of HAPE.

HACE is a life-threatening condition that can lead to coma or death. Symptoms include headache, fatigue, visual impairment, bladder dysfunction, bowel dysfunction, loss of coordination, paralysis on one side of the body, and confusion. Descent to lower altitudes may save those affected by HACE.

Cause

See also: Breathing § Breathing at altitude, and Effects of high altitude on humans

 

Climbers on Mount Everest often experience altitude sickness.

Altitude sickness can first occur at 1,500 metres, with the effects becoming severe at extreme altitudes (greater than 5,500 metres). Only brief trips above 6,000 metres are possible and supplemental oxygen is needed to avert sickness.

As altitude increases, the available amount of oxygen to sustain mental and physical alertness decreases with the overall air pressure, though the relative percentage of oxygen in air, at about 21%, remains practically unchanged up to 21,000 metres (70,000 ft). The RMS velocities of diatomic nitrogen and oxygen are very similar and thus no change occurs in the ratio of oxygen to nitrogen until stratospheric heights.

Dehydration due to the higher rate of water vapor lost from the lungs at higher altitudes may contribute to the symptoms of altitude sickness.

The rate of ascent, altitude attained, amount of physical activity at high altitude, as well as individual susceptibility, are contributing factors to the onset and severity of high-altitude illness.

Altitude sickness usually occurs following a rapid ascent and can usually be prevented by ascending slowly. In most of these cases, the symptoms are temporary and usually abate as altitude acclimatization occurs. However, in extreme cases, altitude sickness can be fatal.

High altitude illness can be classified according to the altitude: high (1500-3500m), very high (3500-5500m) and extreme (above 5500m).

High altitude

At high altitude, 1,500 to 3,500 metres (4,900 to 11,500 ft), the onset of physiological effects of diminished inspiratory oxygen pressure (PiO₂) includes decreased exercise performance and increased ventilation (lower arterial partial pressure of carbon dioxide: PCO₂). While arterial oxygen transport may be only slightly impaired the arterial oxygen saturation (SaO₂) generally stays above 90%. Altitude sickness is common between 2,400 and 4,000 m because of the large number of people who ascend rapidly to these altitudes.

Very high altitude

At very high altitude, 3,500 to 5,500 metres (11,500 to 18,000 ft), maximum SaO₂ falls below 90% as the arterial PO₂ falls below 60mmHg. Extreme hypoxemia may occur during exercise, during sleep, and in the presence of high altitude pulmonary edema or other acute lung conditions. Severe altitude illness occurs most commonly in this range.

Extreme altitude

Above 5,500 metres (18,000 ft), marked hypoxemia, hypocapnia, and alkalosis are characteristic of extreme altitudes. Progressive deterioration of physiologic function eventually outstrips acclimatization. As a result, no permanent human habitation occurs above 6,000 metres (20,000 ft). A period of acclimatization is necessary when ascending to extreme altitude; abrupt ascent without supplemental oxygen for other than brief exposures invites severe altitude sickness.

Mechanism

The physiology of altitude sickness centres around the alveolar gas equation; the atmospheric pressure is low, but there is still 20.9% oxygen. Water vapour still occupies the same pressure too—this means that there is less oxygen pressure available in the lungs and blood. Compare these two equations comparing the amount of oxygen in blood at altitude:

	At Sea Level	At 8400 m (The Balcony of Everest)	Formula
Pressure of oxygen in the alveolus	${\textstyle 21\%\times (101.3{\text{ kPa}}-6.3{\text{ kPa}})-\left({\frac {5.3{\text{ kPa}}}{0.8}}\right)=13.3{\text{ kPa O}}_{2}}$	${\textstyle 21\%\times (36.3{\text{ kPa}}-6.3{\text{ kPa}})-\left({\frac {1.8{\text{ kPa}}}{0.74}}\right)=3.9{\text{ kPa O}}_{2}}$	${\textstyle F_{I}{\text{O}}_{2}\times (P_{\text{B}}-P_{{\text{H}}_{2}{\text{O}}})-\left({\frac {P_{{\text{CO}}_{2}}}{\text{RQ}}}\right)}$
Oxygen Carriage in the blood	${\textstyle \left(0.98\times 1.34\times 14{\frac {\text{g}}{\text{dL}}}\right)+(0.023\times 12{\text{ kPa}})={\frac {17.3{\text{ mL O}}_{2}}{100{\text{ mL blood}}}}}$	${\textstyle \left(0.54\times 1.34\times 19.3{\frac {\text{g}}{\text{dL}}}\right)+(0.023\times 3.3{\text{ kPa}})={\frac {14.0{\text{ mL O}}_{2}}{100{\text{ mL blood}}}}}$	${\textstyle ({\text{Sa}}_{{\text{O}}_{2}}\times 1.34{\tfrac {\text{mL}}{\text{g Hb}}}\times {\text{Hb}})+({\text{O}}_{2}{\text{ carriage in blood}}\times {\text{Pa}}_{{\text{O}}_{2}})}$

The hypoxia leads to an increase in minute ventilation (hence both low CO₂, and subsequently bicarbonate), Hb increases through haemoconcentration and erythrogenesis. Alkalosis shifts the haemoglobin dissociation constant to the left, 2,3-BPG increases to counter this. Cardiac output increases through an increase in heart rate.

The body's response to high altitude includes the following:

• ↑ Erythropoietin → ↑ hematocrit and haemoglobin
• ↑ 2,3-BPG (allows ↑ release of O₂ and a right shift on the Hb-O₂ disassociation curve)
• ↑ kidney excretion of bicarbonate (use of acetazolamide can augment for treatment)
• Chronic hypoxic pulmonary vasoconstriction (can cause right ventricular hypertrophy)

People with high-altitude sickness generally have reduced hyperventilator response, impaired gas exchange, fluid retention or increased sympathetic drive. There is thought to be an increase in cerebral venous volume because of an increase in cerebral blood flow and hypocapnic cerebral vasoconstriction causing oedema.

Diagnosis

Altitude sickness is typically self-diagnosed since symptoms are consistent: nausea, vomiting, headache, and can generally be deduced from a rapid change in altitude or oxygen levels. However, some symptoms may be confused with dehydration. Some severe cases may require professional diagnosis which can be assisted with multiple different methods such as using an MRI or CT scan to check for abnormal buildup of fluids in the lung or brain.

Prevention

Ascending slowly is the best way to avoid altitude sickness. Avoiding strenuous activity such as skiing, hiking, etc. in the first 24 hours at high altitude may reduce the symptoms of AMS. Alcohol and sleeping pills are respiratory depressants, and thus slow down the acclimatization process and should be avoided. Alcohol also tends to cause dehydration and exacerbates AMS. Thus, avoiding alcohol consumption in the first 24–48 hours at a higher altitude is optimal.

Pre-acclimatization

Pre-acclimatization is when the body develops tolerance to low oxygen concentrations before ascending to an altitude. It significantly reduces risk because less time has to be spent at altitude to acclimatize in the traditional way. Additionally, because less time has to be spent on the mountain, less food and supplies have to be taken up. Several commercial systems exist that use altitude tents, so called because they mimic altitude by reducing the percentage of oxygen in the air while keeping air pressure constant to the surroundings. Examples of pre-acclimation measures include remote ischaemic preconditioning, using hypobaric air breathing in order to simulate altitude, and positive end-expiratory pressure.

Altitude acclimatization

Altitude acclimatization is the process of adjusting to decreasing oxygen levels at higher elevations, in order to avoid altitude sickness. Once above approximately 3,000 metres (10,000 ft) – a pressure of 70 kilopascals (0.69 atm) – most climbers and high-altitude trekkers take the "climb-high, sleep-low" approach. For high-altitude climbers, a typical acclimatization regimen might be to stay a few days at a base camp, climb up to a higher camp (slowly), and then return to base camp. A subsequent climb to the higher camp then includes an overnight stay. This process is then repeated a few times, each time extending the time spent at higher altitudes to let the body adjust to the oxygen level there, a process that involves the production of additional red blood cells. Once the climber has acclimatized to a given altitude, the process is repeated with camps placed at progressively higher elevations. The rule of thumb is to ascend no more than 300 m (1,000 ft) per day to sleep. That is, one can climb from 3,000 m (9,800 ft) (70 kPa or 0.69 atm) to 4,500 m (15,000 ft) (58 kPa or 0.57 atm) in one day, but one should then descend back to 3,300 m (10,800 ft) (67.5 kPa or 0.666 atm) to sleep. This process cannot safely be rushed, and this is why climbers need to spend days (or even weeks at times) acclimatizing before attempting to climb a high peak. Simulated altitude equipment such as altitude tents provide hypoxic (reduced oxygen) air, and are designed to allow partial pre-acclimation to high altitude, reducing the total time required on the mountain itself.

Altitude acclimatization is necessary for some people who move rapidly from lower altitudes to higher altitudes .

Medications

The drug acetazolamide (trade name Diamox) may help some people making a rapid ascent to sleeping altitude above 2,700 metres (9,000 ft), and it may also be effective if started early in the course of AMS. Acetazolamide can be taken before symptoms appear as a preventive measure at a dose of 125 mg twice daily. The Everest Base Camp Medical Centre cautions against its routine use as a substitute for a reasonable ascent schedule, except where rapid ascent is forced by flying into high altitude locations or due to terrain considerations. The Centre suggests a dosage of 125 mg twice daily for prophylaxis, starting from 24 hours before ascending until a few days at the highest altitude or on descending; with 250 mg twice daily recommended for treatment of AMS.^[21] The Centers for Disease Control and Prevention (CDC) suggest the same dose for prevention of 125 mg acetazolamide every 12 hours. Acetazolamide, a mild diuretic, works by stimulating the kidneys to secrete more bicarbonate in the urine, thereby acidifying the blood. This change in pH stimulates the respiratory center to increase the depth and frequency of respiration, thus speeding the natural acclimatization process. An undesirable side-effect of acetazolamide is a reduction in aerobic endurance performance. Other minor side effects include a tingle-sensation in hands and feet. Although a sulfonamide; acetazolamide is a non-antibiotic and has not been shown to cause life-threatening allergic cross-reactivity in those with a self-reported sulfonamide allergy. Dosage of 1000 mg/day will produce a 25% decrease in performance, on top of the reduction due to high-altitude exposure. The CDC advises that Dexamethasone be reserved for treatment of severe AMS and HACE during descents, and notes that Nifedipine may prevent HAPE.

There is insufficient evidence to determine the safety of sumatriptan and if it may help prevent altitude sickness. Despite their popularity, antioxidant treatments have not been found to be effective medications for prevention of AMS. Interest in phosphodiesterase inhibitors such as sildenafil has been limited by the possibility that these drugs might worsen the headache of mountain sickness. A promising possible preventive for altitude sickness is myo-inositol trispyrophosphate (ITPP), which increases the amount of oxygen released by hemoglobin.

Prior to the onset of altitude sickness, ibuprofen is a suggested non-steroidal anti-inflammatory and painkiller that can help alleviate both the headache and nausea associated with AMS. It has not been studied for the prevention of cerebral edema (swelling of the brain) associated with extreme symptoms of AMS.

Over-the-counter herbal supplements and traditional medicines

Herbal supplements and traditional medicines are sometimes suggested to prevent high altitude sickness including ginkgo biloba, R crenulata, minerals such as iron, antacids, and hormonal-based supplements such as medroxyprogesterone and erythropoietin. Medical evidence to support the effectiveness and safety of these approaches is often contradictory or lacking. Indigenous peoples of the Americas, such as the Aymaras of the Altiplano, have for centuries chewed coca leaves to try to alleviate the symptoms of mild altitude sickness. This therapy has not yet been proven effective in a clinical study.^[31] In Chinese and Tibetan traditional medicine, an extract of the root tissue of Radix rhodiola is often taken in order to prevent the symptoms of high altitude sickness, however, no clear medical studies have confirmed the effectiveness or safety of this extract.

Oxygen enrichment

In high-altitude conditions, oxygen enrichment can counteract the hypoxia related effects of altitude sickness. A small amount of supplemental oxygen reduces the equivalent altitude in climate-controlled rooms. At 3,400 metres (11,200 ft) (67 kPa or 0.66 atm), raising the oxygen concentration level by 5% via an oxygen concentrator and an existing ventilation system provides an effective altitude of 3,000 m (10,000 ft) (70 kPa or 0.69 atm), which is more tolerable for those unaccustomed to high altitudes.

Oxygen from gas bottles or liquid containers can be applied directly via a nasal cannula or mask. Oxygen concentrators based upon pressure swing adsorption (PSA), VSA, or vacuum-pressure swing adsorption (VPSA) can be used to generate the oxygen if electricity is available. Stationary oxygen concentrators typically use PSA technology, which has performance degradations at the lower barometric pressures at high altitudes. One way to compensate for the performance degradation is to use a concentrator with more flow capacity. There are also portable oxygen concentrators that can be used on vehicular DC power or on internal batteries, and at least one system commercially available measures and compensates for the altitude effect on its performance up to 4,000 m (13,000 ft). The application of high-purity oxygen from one of these methods increases the partial pressure of oxygen by raising the FiO₂ (fraction of inspired oxygen).

Other methods

Increased water intake may also help in acclimatization to replace the fluids lost through heavier breathing in the thin, dry air found at altitude, although consuming excessive quantities ("over-hydration") has no benefits and may cause dangerous hyponatremia.

Treatment

The only reliable treatment, and in many cases the only option available, is to descend. Attempts to treat or stabilize the patient in situ (at altitude) are dangerous unless highly controlled and with good medical facilities. However, the following treatments have been used when the patient's location and circumstances permit:

• Oxygen may be used for mild to moderate AMS below 3,700 metres (12,000 ft) and is commonly provided by physicians at mountain resorts. Symptoms abate in 12 to 36 hours without the need to descend.
• For more serious cases of AMS, or where rapid descent is impractical, a Gamow bag, a portable plastic hyperbaric chamber inflated with a foot pump, can be used to reduce the effective altitude by as much as 1,500 m (5,000 ft). A Gamow bag is generally used only as an aid to evacuate severe AMS patients, not to treat them at altitude.
• Acetazolamide 250 mg twice daily dosing assists in AMS treatment by quickening altitude acclimatization. A study by the Denali Medical Research Project concluded: "In established cases of acute mountain sickness, treatment with acetazolamide relieves symptoms, improves arterial oxygenation, and prevents further impairment of pulmonary gas exchange."
• The folk remedy for altitude sickness in Ecuador, Peru and Bolivia is a tea made from the coca plant. See mate de coca.
• Steroids can be used to treat the symptoms of pulmonary or cerebral edema, but do not treat the underlying AMS.
• Two studies in 2012 showed that Ibuprofen 600 milligrams three times daily was effective at decreasing the severity and incidence of AMS; it was not clear if HAPE or HACE was affected.
• Paracetamol (acetaminophen) has also shown to be as good as ibuprofen for altitude sickness when tested on climbers ascending Everest.