J Appl Physiol 119: 719–723, 2015.
First published July 2, 2015; doi:10.1152/japplphysiol.00421.2015.
Innovative Methodology
A strategy for oxygen conditioning at high altitude: comparison with air
conditioning
John B. West
Department of Medicine, University of California San Diego, La Jolla, California
Submitted 22 May 2015; accepted in final form 29 June 2015
equivalent altitude; cognitive ability; exercise tolerance; fire hazard;
work efficiency
LARGE NUMBERS OF PEOPLE live at high altitude. For example
some 140 million reside at altitudes exceeding 2,500 m (5), and
there are a number of towns and cities at altitudes above 3,000
m (Table 1). La Rinconada in southern Peru is at the extraordinary altitude of 5,100 m (7). It is well known that visitors to
high altitude are likely to suffer from the hypoxia. For example, lowlanders who ascend to altitudes above 2,500 m may
develop acute mountain sickness and occasionally develop
more serious illnesses such as high altitude pulmonary edema
and high altitude cerebral edema. Some negative effects are
seen at very moderate altitudes. For example, night vision may
be affected at 1,500 m altitude, changes in complex reaction
times have been described at 1,520 m, and sleep impairment is
often seen at 2,500 m.
A particularly important group at high altitude consists of
sojourners, that is, people who normally live at low altitude but
are required to work for months or even years at high altitude.
Some of these are people who work in large corporations,
embassies, or banks in high cities. Many others are employed
in high-altitude mines or telescopes. For example, some mines
in Peru and Chile have working and sleeping quarters as high
as 4,000 m, and there are telescopes on the Chajnantor Plateau
in north Chile at an altitude of 5,000 m. Sojourners have a
reduced exercise tolerance because of the hypoxia, and there is
Address for reprint requests and other correspondence: J. B. West, UCSD
Dept. of Medicine 0623A, 9500 Gilman Dr., La Jolla, California 92093-0623
(e-mail: [email protected]).
http://www.jappl.org
also cognitive impairment with difficulties of concentrating, a
tendency to make errors, and marked deficiencies in problem
solving.
A third group of people at high altitude are the permanent
residents who have been at altitude for generations. Many of
these live at altitudes over 4,000 m. The hypoxia causes a
reduced exercise capacity, and some people develop chronic
mountain sickness, especially in the South American Andes. In
addition, there is some evidence that the cognitive ability of
permanent residents may be improved in an oxygen-enriched
environment (see below).
Until recently it has generally been assumed that all these
people who live or work at high altitude are inevitably affected
by the hypoxia. However, about 20 years ago the technology of
oxygen enrichment of room air was introduced, and this is now
used in various dormitories, hotels, mines, and telescopes at
high altitudes. As technology has progressed, it has become
clear that large working places and indeed whole buildings can
be safely oxygen enriched with the result that the occupants
are, in effect, transported to a lower altitude where their
well-being and productivity are improved.
The purpose of this article is to explore the potential of what
can be called oxygen conditioning. This is similar in many
respects to air conditioning that has transformed the living and
working environment of people who live in hot climates. In the
same way it is now feasible for oxygen conditioning on a large
scale to be used at high altitude with the resulting major
improvement of well-being and work productivity.
OXYGEN ENRICHMENT OF ROOM AIR
This procedure was first described about 20 years ago (6),
and the basic principle is simple. Oxygen is obtained from
atmospheric air using synthetic zeolite by a pressure swing
adsorption technique. This only requires compressors run by
electrical power. An alternative process is vacuum swing
adsorption. Another possible source is cryogenic oxygen if
electrical power is not available. The oxygen that is generated
is added to the room ventilation, thus increasing the oxygen
concentration from 21 to as much as 30%. The procedure is
remarkably effective in reducing the equivalent altitude, that is,
the altitude that has the same inspired PO2 when ambient air is
breathed (Fig. 1). For each 1% increase in oxygen concentration, for example from 21 to 22%, the equivalent altitude is
reduced by ⬃300 m. Thus at an altitude of 4,000 m, increasing
the oxygen concentration by 7% will reduce the equivalent
altitude to ⬃1,800 m, which is only a little above the altitude
of Denver.
This technology is now used in many places. One of the first
applications was in the dormitories of a high-altitude mine in
Chile where some miners had difficulties sleeping because of
the altitude. Another early application was in a small radio
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West JB. A strategy for oxygen conditioning at high altitude: comparison with air conditioning. J Appl Physiol 119: 719 –723, 2015. First
published July 2, 2015; doi:10.1152/japplphysiol.00421.2015.—Large
numbers of people live or work at high altitude, and many visit to trek or
ski. The inevitable hypoxia impairs physical working capacity, and at
higher altitudes there is also cognitive impairment. Twenty years ago
oxygen enrichment of room air was introduced to reduce the hypoxia,
and this is now used in dormitories, hotels, mines, and telescopes.
However, recent advances in technology now allow large amounts of
oxygen to be obtained from air or cryogenic oxygen sources. As a
result it is now feasible to oxygenate large buildings and even
institutions such as hospitals. An analogy can be drawn between air
conditioning that has improved the living and working conditions of
millions of people who live in hot climates and oxygen conditioning
that can do the same at high altitude. Oxygen conditioning is similar
to air conditioning except that instead of cooling the air, the oxygen
concentration is raised, thus reducing the equivalent altitude. Oxygen
conditioning on a large scale could transform living and working
conditions at high altitude, where it could be valuable in homes,
hospitals, schools, dormitories, company headquarters, banks, and
legislative settings.
Innovative Methodology
720
Oxygen Conditioning
•
West JB
A COMPARISON OF OXYGEN CONDITIONING AND AIR
CONDITIONING
Table 1. Cities or towns over 3,000 m altitude
Name
Country
Altitude, m
Approximate Population
La Rinconada
Morococha
Toromocho
Cerro de Pasco
El Alto
Potosí
Litang
Shigatse
Juliaca
Puno
La Oroya
Oruro
Lhasa
La Paz
Cusco
Huancayo
Leadville
Huaraz
Peru
Peru
Peru
Peru
Bolivia
Bolivia
China
China
Peru
Peru
Peru
Bolivia
China
Bolivia
Peru
Peru
USA
Peru
5,100
4,540
4,550
4,300
4,150
4,060
4,000
3,800
3,800
3,800
3,750
3,700
3,650
3,650
3,400
3,250
3,094
3,050
7,000
?5,000
5,000
75,000
1,000,000
150,000
50,000
100,000
225,000
150,000
33,000
265,000
370,000
850,000
435,000
425,000
2,580
135,000
Fig. 1. Oxygen conditioning diagram. Equivalent altitudes are shown for actual
altitudes and the oxygen concentration in the air. For example, at an actual
altitude of 4 km, increasing the oxygen concentration in the air from 21 to 28%
results in a reduction of the equivalent altitude to 1.78 km. (Equivalent altitude
is that which gives the same inspired PO2 for air breathing.) Note that the
bottom section of the diagram is not available because oxygen concentrations
here would result in a fire hazard according to the National Fire Protection
Agency guidelines.
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telescope installation in Chile where the personnel lived in an
atmosphere of 28% oxygen that reduced the equivalent altitude
from 5,000 m to less than 3,000 m (8). The largest facility
using oxygen enrichment at the present time is the Atacama
Large Millimeter Array, an enormous radio telescope with
some 60 antennas, at an altitude of 5,000 m in north Chile.
There are ⬃400 workers on the site at the present time.
Another remarkable application of the technology is in the train
from Golmud in Qinghai province, China to Lhasa. The train
ascends to over 5,000 m and each passenger car is equipped
with an oxygen generator that raises the oxygen concentration
in the air to ⬃24-25%. In this situation where the passengers
are seated at rest, the equivalent altitude does not have to be
reduced as much as in a facility where the occupants are doing
manual work.
An issue that is sometimes raised is whether moving from an
oxygen-enriched room to the outside might cause serious
problems such as fainting. However, this is not the case in
practice. The best way to approach this is by referring to the
equivalent altitude. People move up and down a mountain
without serious consequences, and the same is true of oxygenenriched rooms. In fact most people are not initially aware of
moving either into or out of an oxygen-enriched environment.
There is a fire hazard if the oxygen concentration is raised
too high. People who hear about the procedure for the first time
often raise this issue, but it turns out not to be a limiting factor.
First it should be emphasized that although the PO2 in the air is
increased by oxygen enrichment, it is always below the value
at sea level because the altitude is so high. For example, in the
example given above where 28% oxygen is used at an altitude
of 4,000 m, the PO2 is only 130 mmHg, which is much less than
the sea level value of 159 mmHg. Note that the PO2 is not the
only important variable because the PN2 also plays a role in
flammability. The safe levels for oxygen enrichment have been
worked out by the National Fire Protection Agency, who state
that the maximal oxygen concentration that can be used without a fire hazard is equal to 23.45 divided by the square root of
the fractional barometric pressure. In practice it is always
possible to reduce the equivalent altitude to a useful level while
using a safe oxygen concentration.
Oxygen conditioning and air conditioning have many similar
features. Both process the air that ventilates a room or a
building. In essence, the only difference is that whereas air
conditioning reduces the temperature of the air and then circulates it, oxygen conditioning increases the oxygen concentration. In both instances compressors are used that are normally powered by the electric supply. For air conditioning, a
refrigerant gas is compressed and then allowed to expand so
that air that is passed over coils has heat removed. For oxygen
conditioning, outside air is compressed, allowing nitrogen to be
preferentially adsorbed, and the effluent oxygen-enriched gas
is added to the ventilation.
In both instances the volume of fresh air must be sufficient
to ensure adequate ventilation of the rooms. For oxygen conditioning, the ventilation is maintained at a safe but minimal
level to reduce the expense of generating unnecessary amounts
of oxygen. Typically a carbon dioxide meter in the room is
used to ensure that the CO2 level does not rise unduly. The
appropriate guidelines for room ventilation are set by the
American Society of Heating, Refrigerating and Air Conditioning Engineers. Because of the cost of producing oxygen, the
ventilation of rooms is maintained at the lowest acceptable
level and windows and doors are closed to keep the ventilating
flow rate to a minimum.
The volume of oxygen that needs to be produced can be
reduced by limiting the delivery only to rooms that are occupied by people. Modern technology can include sensors that
determine whether a room is occupied. If not, a valve is closed
to cut off the airflow until someone enters the room. Sometimes the lighting is dimmed as well. This ventilation-saving
procedure is now employed in some modern air conditioning
systems.
Innovative Methodology
Oxygen Conditioning
It is common knowledge that air conditioning has transformed the living and working conditions of people in hot
climates of developed countries. On a personal note, I briefly
worked at the NASA Johnson Space Center near Houston,
Texas during the summer, and it is inconceivable that efficient
work could be done in the absence of air conditioning. Indeed
we now take air conditioning for granted in hot environments.
In principle, the same attitude can be taken to oxygen
conditioning. In many areas of the world at high altitude,
oxygen conditioning would increase well-being and working
efficiency. The only difference is we are dealing with a hypoxic rather than a hot environment. Although this has not
previously been emphasized, the potential is enormous.
It is useful to consider three groups of people at high altitude
in the context of oxygen conditioning. These are visitors to
high altitude, sojourners, that is, lowlanders who are temporarily living or working at high altitude for some reason, and
high-altitude permanent residents.
This group will clearly benefit from oxygen conditioning.
Visitors who ascend to altitudes above 2,500 m will certainly
notice a reduction in exercise capacity, and this will be associated with increasing shortness of breath. In addition they will
probably have difficulty sleeping with frequent arousals probably associated with periods of apnea. Finally they may be
aware of impairment of cognitive function if they go high
enough. They may feel disoriented, they will tend to make
arithmetical errors, and they will find it difficult to choose the
right course if a problem arises.
Newcomers to high altitude may also develop acute mountain sickness, although in most cases this will resolve after 2 or
3 days. However, in some people the problem may persist and
be so severe that they need to descend. Occasionally visitors to
high altitude may develop high-altitude pulmonary edema or
even high-altitude cerebral edema, although these conditions
are uncommon. Oxygen conditioning reduces the risk of developing these diseases, but if they do occur, descent is
essential. Some pilgrims in Southeast Asia ascend rapidly to
very high altitudes, and oxygen conditioning of their dormitories would clearly be beneficial if this was practicable.
SOJOURNERS
700
1
680
0.98
**
660
640
620
600
580
560
This is the largest group and also most interesting in the
context of oxygen conditioning. Some people argue that because these people have been born and bred at high altitude for
generations, they must be completely adapted and would not
benefit by going to a lower altitude, which is what oxygen
conditioning does. Again many people are impressed by the
physical ability of permanent residents and cite the fact that
Sherpas, for example, have shown extraordinary climbing
ability on Mt. Everest.
However, there is strong evidence that permanent highaltitude residents show improvements in physiological function when they move to a lower altitude. For example, their
maximal work rate increases. Thus Elsner et al. (1) reported
that Andean highlanders reduced their maximal oxygen consumption as the altitude increased from near sea level to 4,540
m and then to 6,400 m. Furthermore, in two subjects at an
altitude of 4,540 m who breathed gas with the same PO2 as sea
**
0.9
0.88
0.86
0.84
0.82
SL
Fig. 2. Reaction times and response accuracy
from a verbal working memory task in 2
groups of college students who lived at high
altitude (2,616 – 4,200 m) or near sea level.
Students were matched for ethnic background,
age, sex, and socioeconomic status. Differences were significant at the P ⬍ 0.05 level
(**). [Borrowed with permission from (10)].
0.92
520
HA
PERMANENT RESIDENTS OF HIGH ALTITUDE
0.94
540
500
mally live at or near sea level but are spending months or even
2 or 3 years at high altitude. Examples include personnel
associated with high-altitude mines who sleep at high altitude.
Sometimes the dormitories are somewhat lower than the mine.
For example, in the Collahuasi mine in Chile, the ore is at
4,400 to 4,600 m but the sleeping quarters are at the lower
altitude of 3,800 m. Even so, some of the miners sleep so badly
that oxygen enrichment of the bedrooms is essential. A new
mine in Peru called Toromocho is at much higher altitudes.
The ore is at an altitude of 4,700 to 4,900 m and the town with
the sleeping quarters is at an altitude of ⬃4,400 m. People who
come from near sea level such as engineers, scientists, truck
drivers, and operators of the enormous loaders are almost
certain to have very uncomfortable nights in the absence of
oxygen conditioning.
Another group of sojourners are those that work in high
cities such as El Alto, La Paz, and Lhasa. Although the altitude
of La Paz is given as 3,650 m in Table 1, the city extends up
the valley and merges with El Alto that has an altitude of 4,150
m. People who normally live near sea level but are employed
in banks, corporate headquarters, embassies, and the like
would benefit from oxygen conditioning in these buildings.
Even after several years at high altitude, these sojourners will
certainly notice exercise limitations, increased breathlessness,
and probably some cognitive impairment, although few measurements have been done on this population.
0.96
Accuracy (%)
Reaction Time (ms)
This is an important group who are likely to benefit substantially from oxygen conditioning. They are people who nor-
0.8
721
West JB
HA
SL
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VISITORS TO HIGH ALTITUDE
•
Innovative Methodology
722
Oxygen Conditioning
ADVANCES IN TECHNOLOGY RELEVANT TO OXYGEN
CONDITIONING
Oxygen conditioning on a large scale, for example, for a
multistory building, hospital, or school requires the generation of large amounts of oxygen. However, there are many
industries where this is now done. One example is paper
pulp mills where large volumes of oxygen are needed to
oxidize the pulp to produce very white paper. Chlorine was
previously frequently used for this but has gone out of favor
because of environmental concerns. Other industries that
require large amounts of oxygen include the commercial
production of various chemicals, mining and mineral processing, glass manufacturing, oil refining, and water purification. The associated technological advances in oxygen
West JB
production help make oxygen conditioning of large volumes
of buildings feasible.
It is interesting to look briefly at the changes in the technology of oxygen production from the initial studies of oxygen
enrichment of room air and the present proposal. In the first
experiments, the oxygen was obtained from a commercial unit
that produced 5 l/min of 90 –95% oxygen, and this was sufficient to maintain an oxygen concentration in a room of 24%
(6). By contrast off-the-shelf oxygen concentrators that provide
5,000 l/min of 90 ⫾ 5% oxygen are now available (PCI Gases,
Riverside, CA).
WHAT FACILITIES WOULD PARTICULARLY BENEFIT FROM
OXYGEN CONDITIONING?
All the evidence suggests that oxygen conditioning will
improve well-being and cognitive function in visitors to high
altitude and sojourners. In the case of permanent residents,
physical work capacity will be enhanced, but whether neuropsychological function will improve is unclear. Hospitals are
high on the list for institutions that would benefit. It is reasonable that essentially all sick patients would benefit from an
improvement in their tissue hypoxia. Neonatal wards are particularly interesting. There is strong evidence that neonatal
mortality increases with altitude. For example, the neonatal
mortality in the highlands of Peru has been shown to be about
double that of the lowlands (4). It has been known since the
Spanish conquest that mothers prefer to have their babies at
low altitude rather than high, but generally economic restrictions prevent this. Oxygen conditioning of the ward where
neonates are looked after offers obvious advantages. Although babies can be placed in an incubator with an oxygenenriched atmosphere, it is better to have the mother and
baby together, because this improves bonding and lactation.
Another place in a hospital where oxygen conditioning
would be an improvement is the operating rooms, where we
can expect the cognitive function and motor skills of the
surgeons to be improved.
Schools are another institution that would benefit from
oxygen conditioning. All children would have enhanced
physical ability, and in many instances improvement in
cognitive function can be expected. In fact, anywhere where
neuropsychometric function is important would be a candidate. The boardrooms of corporations, legislative chambers,
banks, and in fact anywhere where important decisions are
being taken.
In summary, air conditioning has transformed the living and
working conditions of people who live in hot climates. The
thesis here is that oxygen conditioning could do the same for
people who are required to live or work at high altitude.
Advances in technology have made oxygen conditioning feasible and it will be of great interest to see how effective it is.
DISCLOSURES
No conflicts of interest, financial or otherwise, are declared by the author(s).
AUTHOR CONTRIBUTIONS
Author contributions: J.B.W. conception and design of research; J.B.W.
prepared figures; J.B.W. drafted manuscript; J.B.W. edited and revised manuscript; J.B.W. approved final version of manuscript.
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level, the V̇O2 max max increased by ⬃30%. Also Favier et al.
(2) showed that Bolivians living at an altitude of 3,600 m had
a significantly higher maximum oxygen consumption when
they breathed sea level air. Having said this, it is also true that
Andean highlanders at a given altitude often have a higher
V̇O2 max than acclimatized lowlanders.
A particularly fascinating topic is whether neuropsychological function of these permanent residents of high altitude will be improved if they go to a lower altitude. There
is some evidence to suggest this, as reviewed by Yan (11).
For example, Hogan et al. (3) studied what were believed to
be comparable groups of infants, children, and adolescents
who lived at altitudes of ⬃500, 2,500, and 3,700 m in
Bolivia. The measurements were made at the altitude of
residence of the subjects. It was found that motor speed,
cognitive processing speed, and cerebral blood velocity fell
with increasing altitude.
In another pair of studies by Yan et al. (9, 10), neuropsychological function was measured in young adults who were
third or fourth generation descendants of immigrants to high
altitude, and the results were compared with those of a
control group who were born and raised at low altitude. The
measurements were made at the same low altitude. The
investigators reported that original high-altitude residents
had reduced accuracy in a verbal memory task and that there
were longer reaction times in both verbal and spatial working memory tasks (Fig. 2). Furthermore blood oxygen leveldependent functional magnetic resonance imaging showed
that the high-altitude subjects had decreased activation of
some brain regions compared with the low-altitude controls.
These results on third or fourth generation descendants may
not apply to people who have been living at high altitude for
longer periods.
These provocative data comparing comparable groups
living at different altitudes are of great interest but do not
necessarily mean that an acute reduction in altitude will
improve neuropsychometric function. The definitive experiment of giving an oxygen-enriched mixture to permanent
residents of high altitude and measuring neuropsychometric
function has apparently never been carried out. On general
biological grounds it would not be surprising if moving to a
lower altitude improved cognitive function, because presumably the PO2 of all tissues in the body increases as a
result, and it is well known that the central nervous system
is exquisitely sensitive to oxygen lack.
•
Innovative Methodology
Oxygen Conditioning
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