Ann. occup. Hyg., Vol. 47, No. 3, pp. 241–252, 2003
© 2003 British Occupational Hygiene Society
Published by Oxford University Press
DOI: 10.1093/annhyg/meg033
Occupational Health Conditions in Extreme
Environments
K. RODAHL
Maaltrostveien 40, 0786 Oslo, Norway
Received 17 May 2002; in final form 26 November 2002
The problems of work in extreme environments have been studied for many years. This paper
discusses various aspects of work in hot and cold environments and at high pressure.
Keywords: cold stress; heat stress; pressure
hobbling effect of bulky clothing and the slowing
down of ordinary simple functions because of snow
and ice. Heat, if intense, may greatly reduce endurance because of the need for more of the circulating
blood volume to be devoted to the transportation of
heat rather than to the transportation of oxygen, and
because of the effect of dehydration often accompanying heat exposure as a result of loss of body
fluids (sweating). High gas pressures, encountered in
underwater operations in connection with modern
offshore oil exploration, present new and rather
unique problems for work physiologists. The drastic
reduction in physical work capacity at high altitudes
is one of the best studied problems concerning
environmental effects on physical work capacity. In
fact, significant muscle fibre atrophy has been noted
after only 5 days in space (Booth and Criswell, 1997).
Finally, the nature of the work to be performed,
apart from work intensity and duration, is of decisive importance when considering an individual’s
capacity to endure prolonged work stress. Since all
life functions generally consist of rhythmic, dynamic
muscular work in which work and rest, muscle
contraction and relaxation are interspersed at more or
less regular, fairly short intervals, the ideal way to
perform physical work is to perform it dynamically,
with brief work periods interrupted by brief pauses.
This routine will provide some rest during the actual
work period, so the worker may avoid fatigue and
exhaustion. Similarly, the work position is also
important in that working in a standing position may
represent a greater circulatory strain than does
working in a sitting position. Conversely, working in
a standing position, which will permit the worker to
move about and thereby vary the load on individual
muscle groups and facilitate circulation, may at times
INTRODUCTION
The ability to perform physical work depends on the
ability of the muscle cell to transform chemically
bound energy in the food which we eat into mechanical energy for muscular work (Fig. 1). This in turn
depends on the capacity of the service functions that
deliver fuel and oxygen to the working muscle fibre,
i.e. on the nutritional state, nature and quality of the
food ingested, frequency of meals, oxygen uptake
including pulmonary ventilation, cardiac output and
oxygen extraction and the nervous and hormonal
mechanisms that regulate these functions.
Many of these functions depend on sex, age, body
dimensions and state of health. In addition, physical
performance is, to a significant extent, a function of
psychological factors, notably motivation, attitude to
work and the will to mobilize one’s resources for the
accomplishment of the task in question. Several of
these factors may be affected by training and adaptation.
Physical performance may also, directly or indirectly, be greatly influenced by factors in the external
environment. Thus, air pollution may affect physical
performance directly by increasing airway resistance
and thereby pulmonary ventilation and indirectly by
causing ill health. The same applies to cigarette
smoking. Alcohol may also have a negative effect
on performance (Price and Hicks, 1979; Kahn and
Cooper, 1990). Noise is a stress, which may not only
damage hearing but also cause an elevation of heart
rate and affect other physiological parameters that
reduce physical performance. Cold weather, if
severe, may in itself reduce physical performance
because of numbness of the hands or lowered body
temperature (the opposite effect of a warm-up prior to
an athletic competition). But it may also involve the
241
242
K. Rodahl
be preferable. The working technique may be of
major importance in conserving energy and in
providing varied use of different muscle groups. The
monotony of a working operation may be a stress for
some individuals but a relief for others who can carry
on the work more or less automatically while
thinking about something else. In any case, the tempo
of work performance may be extremely important
and impose stresses which, in some instances, may be
unbearable or harmful to the individual. Finally, the
work schedule, including shift work, is a problem
requiring increasing attention in modern industry.
For a review of military performance in hot, cold,
high altitude and hyperbaric conditions, see Pandolf
et al. (1988).
WORKING IN HEAT
The temperature of the environment is one of the
factors affecting human performance (see Fig. 1). At
body temperatures substantially higher than the
optimal levels (36.5–37.5°C), both physical and
mental performance may deteriorate due to the
complicated interplay of physiological and pathophysiological processes. Prolonged heat stress may
lead to loss of body fluid (hypohydration), which in
itself impairs performance, especially endurance. In
addition, prolonged heat strain may impair mental
and psychomotor functions, thereby affecting performance. It is, therefore, of considerable practical importance to be able to assess the magnitude of the thermal
stress in the working environment and the worker’s
physiological reaction to it, in order to ensure optimal
conditions for health and productivity.
A comprehensive review of the thermal effects on
occupational conditions was made by Parsons (1993).
The effect of heat stress on heart rate
It is well known that heat stress may represent an
additional load on the cardiovascular system. This is
evidenced by an elevated heart rate at the same work
load in a hot environment versus a room temperature
environment. The explanation is that, in the case of
the heat stress, our circulating blood volume, in addition to having to transport oxygen, also has to serve
as a cooling fluid. It therefore transports heat from
the interior of the body to the skin where it is dissipated to the surrounding environment by conduction,
convection, radiation and sweat evaporation. This
requires an increase in speed of the blood circulation,
i.e. the cardiac output (minute volume) has to be
elevated. This can only be done by increasing the
stroke volume of the heart and/or increasing the heart
rate. Since the possibility of increasing the stroke
volume of the heart is limited, a major increase in the
minute volume can only be achieved by an increase
in the heart rate. Thus, the heart rate becomes an
expression of the magnitude of the additional load
exerted on the cardiovascular system when the body
is exposed to a certain heat stress.
It is, therefore, to be expected that the heart rate
increases with increasing body temperature. In turn,
Fig. 1. Factors affecting physical performance.
Extreme environments
this is affected by the temperature of the environment
as well as the work rate. It is, therefore, not surprising
that when recording the heart rate in workers operating in the Soderberg pot room in an aluminium
production plant, it was, in some cases, observed that
the heart rate emulated the environmental temperature expressed in terms of the Botsball temperature
measured with a wet globe thermometer (see Rodahl,
1989). In other words, they fluctuated synchronously (for a description of the Botsball, see
http://www.labour.gov.sk.ca/safety/thermal/hot/page
%207%20.htm).
The next step is to determine what part of the
increased heart rate is caused by the heat stress in the
workers operating in the pot room. In six subjects at
rest and at two different work loads on a cycle ergometer at room temperature, a systematic registration of
the heart rate was made in the laboratory (mean Botsball temperature 15.4–16.4°C) and at a selected location in front of a Soderberg pot in the pot room (mean
Botsball temperature 22.0–23.1°C). Each subject was
studied on two different days. The first day the subject
was studied at normal room temperature in the laboratory in the morning. The subject rested in a sitting
position for 15 min. This was followed by a 10 min
cycle ergometer exercise at a load of 300 kpm/min
(49 W), then a 5 min rest in a sitting position and,
finally, a 10 min cycle ergometer exercise at a load of
600 kpm/min (98 W) followed by a 60 min rest at
normal room temperature. The subject then went to a
selected place in front of a pot in the Soderberg pot
room, where he or she remained seated in a chair for
45 min in order for the body temperature to become
adjusted to the prevailing ambient temperature.
Following this, the programme was identical to that
followed at room temperature in the laboratory.
The second day, the same subject went through the
programme in reverse order, i.e. he or she started in
the pot room and finished in the laboratory. This was
done in order to adjust for the possible effects of
circadian rhythm changes in body temperatures and
heart rate as a consequence of the different time of
the day.
The mean difference in the heart rate in the laboratory (room temperature) and in the pot room (heat
stress) was as shown in Table 1.
The results of this study show that the heat stress
alone which faces the operator working at a rate of
Table 1. The mean difference in the heart rate in the laboratory
(room temperature) and in the pot room (heat stress)
Location
Rest
300 kpm/min 600 kpm/min
(49 W)
(98 W)
Pot room
79
119
140
Laboratory
74
100
115
Difference
5
19
25
243
300 and 600 kpm/min (49 and 98 W/min) in front of
a typical Soderberg pot, represents an additional load
on the cardiovascular system of the order of 20–25
beats/min, corresponding to an ∼20% increase in the
work load. This should be taken into account in order
to prevent undue fatigue in workers engaged in jobs
involving excessive heat exposure.
During a series logging the physiological effects of
intensive heat exposure in a glass factory (Rodahl
and Guthe, 1991; Rodahl and Guthe et al., 1991) it
was observed that the heart rate reacted surprisingly
quickly to the ambient temperature and, more or less,
oscillated synchronously with the temperature
surrounding the subject. This very rapid increase in
the heart rate was not caused by physical activity
since the subject was standing quietly in front of the
heat source. It can, therefore, only be caused by the
heat stress. This poses the question as to the physiological mechanism behind the elevated heart rate.
The answer to this would be essential in order to
counteract the effect.
There are a number of indications that the head,
and especially the face, plays a key role in the body’s
reaction to heat stress. Riggs et al. (1981) have shown
in laboratory experiments that cooling the face in
physically active subjects caused a drop in heart rate
without any changes in blood pressure or rectal
temperature.
In connection with a study of divers and the socalled diving reflex, it has been shown that cooling
the face causes a reduced heart rate (Kawakami et al.,
1967; Hurwitz and Furedy, 1986).The exact location
of the specific receptors in the face that elicit the
heart rate effect, however, is not clear.
In mammals, the diving reflex is elicited by
submerging the head. The sensory inputs are assumed
to be caused by neural signals from the face, causing
cessation of respiratory movements as well as vasoconstriction and reduced heart rate (Dykes, 1974).
In a study of cardiac stress in glass bangle workers
in India, exposed to radiant heat of ∼46°C and
ambient temperatures of ∼38°C, Rastogi et al. (1990)
observed a mean increase in pulse rate to 113
beats/min and a retarded recovery of the pulse rate
after work. The authors recommended a series of
revisions of the practices in the glass bangle industry
in order to reduce the level of environmental heat and
thermal radiation. In a study of subjects from the
same glass bangle factory, Kumar et al. (1991) found
impairment of the short-term memory. Extreme
thermal stress has also been recorded in boilermakers
during the repair of electrometallurgy furnaces
(Chaurel et al., 1993).
Heat strain in an aluminium plant
A systematic assessment of the heat stress to which
some of the pot room operators were exposed, and
the effect of the exposure on the operators, was made
244
K. Rodahl
in an aluminium production plant in Norway (Nes et
al., 1990).
The study was based on the combination of a 12-bit
Squirrel logger and standard temperature probes for
skin and rectal temperature in addition to Botsball
and black ball thermometers. The study was
performed in close collaboration with the engineers
of the plant laboratory. For a description of the
Squirrel logger and the Botsball and black ball thermometers, see Rodahl (1989).
A total of eight operators, of whom two were
women, took part in the study. Three of them were
engaged in gas manifold changing, three in burner
cleaning, one in jack raising and one working in the
foundry. They were studied during a total of 38 work
shifts, both during the winter and the summer. Each
subject was studied repeatedly during subsequent
days in order to determine the reproducibility of the
results.
The ambient heat stress was recorded by a Botsball
thermometer mounted on top of the worker’s helmet.
This made it possible to measure the ambient heat
stress at the place where the operator was actually
working. In addition, a small black ball thermometer,
measuring the radiant heat, was placed next to the
Botsball thermometer on the helmet.
The physiological reaction to the heat stress in
terms of body temperature was recorded, i.e. the skin
temperature on the middle of the thigh as an indication of mean skin temperature and the rectal temperature as an expression of core temperature. This was
done with the aid of temperature sensors (supplied by
Grant Instruments Ltd) plugged into the temperature
inputs of the 12-bit Squirrel logger. The logger was
shielded against the magnetic field in the pot room by
being kept in a fitted steel box and carried in a belt on
the subjects’ back. The stored data was transferred
to a personal computer and the results displayed
immediately after the observation period to those
involved in the study. One advantage with this immediate display of the results was that the subject could
see the effect of his different activities in terms of
specific heat stress and the direct relationship
between cause and effect. The fluid loss in terms of
sweating was determined by weighing the subject on
an accurate scale before and after the work shift. The
weight of food and fluid intake as well as the stool
and urine output were taken into consideration.
The results of this project showed convincingly
that heat stress was a major problem at this particular
aluminium plant. The results showed considerable
differences in heat stress at the different plant operations, as well as variations in the heat stress from one
day to the next and at different seasons of the year
(Nes et al., 1990). From the observations made, it
was evident that burner cleaning represented by far
the most severe heat stress. It had Botsball tempera-
tures as high as 35°C and radiant temperatures
exceeding 60°C. The rectal temperature exceeded
38°C in all the subjects studied, in some cases with
peaks >39°C. The skin temperature oscillated with
the radiant temperature, exceeding 40°C and, in some
cases, reached peaks close to the pain threshold.
Next in terms of heat stress was gas manifold
changing, where in one case the skin temperature
under the foot reached ∼42°C. Then came jack
raising on the pre-baked pots. In one case, this
involved continuous exposure for >2 h, causing a
gradual rise in the rectal temperature from 37 to
>38°C in spite of a moderate Botsball temperature
rise from 15 to ∼25°C.
The fluid loss and hypohydration due to sweating
reflected, on the whole, the magnitude of the heat
stress as evidenced by the Botsball and body temperatures. The mean values showed that those who were
most exposed to heat stress also had the greatest fluid
loss by sweating. The fluid loss in the same subjects
(examined both during summer and winter) showed a
significantly lower fluid loss during the winter (Nes
et al., 1990), but even in the winter the fluid loss
exceeded the level which, as a rule, may give symptoms of hypohydration with fatigue, reduced stamina
and reduced alertness.
In some of the subjects, a net deficiency in fluid
intake of 3.5 l during a work shift was recorded. This
represents a significant degree of hypohydration and
emphasizes the need of the operators to drink water
regularly during the work shift, regardless of whether
or not they feel thirsty. This is due to the feeling of
thirst being a slow reacting indicator of the body’s
state of fluid balance. In addition, sweat loss may be
significantly reduced by reducing each period of heat
exposure, to for example 20 min, interspersed by
frequent 10 min cooling-off periods in order to prevent
an excessive rise in the internal body temperature.
The heat strain could be significantly reduced by
using heat-resistant and heat-reflective clothing,
including reflective aprons. The need for effective
protective garments is particularly stressed by the
finding of the very high skin temperatures both on the
legs and under the foot soles. Some of our figures in
these areas approached the level of activating pain
sensors in the skin. These findings merely confirmed
the experience of the operators, and may easily be
remedied by using reflective shields in front of their
legs and heat-resistant insulating insoles and perhaps
even covering the boots with heat-reflective material,
as well as using heat-resistant gloves or mittens.
For a detailed discussion of industrial heat stress,
including industries producing steel, ferroalloys,
aluminium, magnesium and silicocarbide, as well as
studies of sailors on board ships operating in tropical
waters, see Rodahl (1989).
Extreme environments
Failure to tolerate heat
The vastly increasing number of participants in
long distance running races under hot conditions has
led to a marked increase in heat casualties and heat
illnesses, such as heat exhaustion, heat syncope and
heat stroke; often in combination with dehydration,
especially in the case of marathon runners (Sutton,
1984). It should be noted that brain function is particularly vulnerable to heat (Baker, 1982). Tolerance to
elevated deep body temperature is extended if the
brain is kept cool (Carithers and Seagrave, 1976).
The most serious consequence of exposure to
intense heat is heat stroke, which may be fatal. It is
caused by a sudden collapse of temperature regulation leading to a marked rise in body heat. The rectal
temperature may be 41°C or higher. The skin is hot
and dry. There is tachycardia and hypotension, metabolic acidosis, disseminated intravascular coagulation and occasionally renal failure. The victim is
confused or unconscious. This form of temperature
regulatory failure is rare. The risk is higher in nonacclimatized than in acclimatized individuals. Obese
persons and older individuals are most susceptible.
The treatment is rapid cooling (for instance by
pouring cold water over the victim, the application of
ice packs, etc.) until the rectal temperature has
dropped below 39°C.
Since heat stroke is often associated with peripheral circulatory collapse, the oral temperature of
the victim may not necessarily be very high, while
the rectal temperature always is. This emphasizes the
importance of measuring rectal temperature in long
distance runners who collapse (Sutton, 1984).
Another type of temperature regulation failure is
the so-called anhidrotic heat exhaustion. The victim
may have a body temperature of 38–40°C and may
sweat very little or not at all. He or she feels very
tired, may be out of breath and has tachycardia. The
main trouble is reduced sweat production. When the
patient stops exercising and is removed to a cool
place, this condition rapidly improves.
A third type of serious disturbance due to heat
exposure is excessive loss of fluid and salt, usually
because of failure to replace fluid and salts lost
through sweating. After several weeks’ exposure, the
patient may eventually experience cramps, the socalled miner’s cramps, which in rare cases may be
fatal. Intravenous administration of NaCl will
promptly relieve the cramps.
Heat syncope is a less serious affliction due to heat
exposure. This is primarily caused by an unfavourable blood distribution. A large proportion of the
blood volume is distributed to the peripheral vessels,
especially in the lower extremities, as the result of
prolonged standing, or by a reduction in blood
volume due to dehydration. The result is a fall in
blood pressure and inadequate oxygen supply to the
245
brain, which may lead to unconsciousness. If the
victim is placed in a horizontal position, preferably
with the legs elevated, he or she will quickly regain
consciousness. This type of heat collapse is one of the
body’s built-in safety mechanisms.
Literature on acute and chronic occupational heat
illness and the usefulness of the various heat stress
standards recommended by occupational health
authorities have been reviewed by Dukes-Dobos
(1981). Parsons (1999) has described the available
international standards for the assessment of the risk
of thermal strain on clothed workers in hot environments. For advice about keeping athletes safe in hot
weather see Sandor (1997) and Sparling and MillardStafford (1999).
Age
Davies (1981) has shown that thermal responses of
children are quantitatively different from young
adults, evaporative sweat loss being lower in children
and skin temperature higher for the same environmental conditions than in young adults. It is generally
believed that children cannot tolerate hot environments as well as adults and that the greatest risk of
heat sickness for children is heat exhaustion, i.e.
cardiovascular instability (Armstrong and Maresh,
1995).
Although the experimental data are limited, earlier
evidence suggests that heat tolerance is reduced in
older individuals (Robinson, 1963; Leithead and
Lind, 1964; Lind et al., 1970). They start to sweat
later than do young individuals. Following heat
exposure, it takes longer for their body temperature to
return to normal levels. Older people react with a
higher peripheral blood f1ow, but their maximal
capacity is probably lower. In one study, it was found
that 70% of all individuals who suffered heat stroke
were over 60 yr of age (Minard and Copman, 1963).
On the other hand, Davies (1979) observed no
evidence for differences in thermoregulatory function which could be ascribed to sex or age in his 1 h
treadmill exercise experiments on subjects 18–65 yr
of age in a moderate environment. Furthermore,
studies by Drinkwater et al. (1982) revealed that in
healthy older women, ageing does not diminish the
functional capacity of the sweating mechanism to
cope with heat stress while resting.
On the basis of a review of the literature on heat
tolerance, Pandolf (1997) concluded that the work
heat tolerance of habitually active and aerobically
trained middle-aged men is the same as, or better
than, younger individuals. On the other hand, the
elderly may be more susceptible to hypo- or hyperthermia than young adults (Anderson et al., 1996).
For a discussion of ageing and heat tolerance, see
Pandolf (1991).
246
K. Rodahl
Sex
The available evidence shows that women require
evaporative cooling in both hot wet and hot dry environments (Shapiro et al., 1981). Women have a lower
tissue conductance in the cold and a higher tissue
conductance in heat than do men. This fact indicates
a greater variation in the peripheral reaction to
climatic stress in women. It appears that this fact is of
no importance for the performance of work, however.
From studies of active men versus active women
during acclimatization to dry heat, Horstman and
Christensen (1982) concluded that active women
performed exercise of equal relative intensity in dry
heat as well as active men. Ventilatory, metabolic
and cardiovascular differences between the sexes
were minimal. Frye and Kamon (1983) observed no
differences in sweating efficiency between the sexes
in dry heat, but the women maintained a significantly
higher sweating efficiency than the men in humid
heat. In both environments, the men recruited a significantly lower percentage of their available sweat
glands than did the women.
Physical fitness is an important factor to be considered when men and women are compared in the
heat. When fitness levels are similar, the previously
reported sex-related differences in response to an
acute heat exposure seem to disappear (Avellini et
al., 1980; Nielsen, 1980).
For a review of the effect of chemical protective
clothing on work tolerance in the heat, see White et
al. (1991).
Mental work capacity
An evaluation of mental or intellectual performance during exposure to heat or cold is hampered by
subjective variations and lack of suitable objective
testing methods. As a rule, a deterioration is observed
when the room temperature exceeds 30–35°C if the
individual is acclimatized to heat. For the unacclimatized, clothed individual, the upper limit for optimal
function is ∼25°C. The observed deterioration in
performance capacity refers to precise manipulation
requiring dexterity and coordination, ability to
observe irregular, faint optical signs, the ability to
remain alert during prolonged, monotonous tasks and
the ability to make quick decisions. During a 3 h
drilling operation, the best results were achieved at
29°C, but at a room temperature of 33°C the performance was reduced to 75%, at 35.5°C to 50% and at
37°C to 25%. A high level of motivation may to some
extent counteract the detrimental effect of the climate
(Pepler, 1963). For a review of task performance in
the heat, see Ramsey (1995).
Wyon et al. (1979) examined the effect of moderate
heat stress (up to 29°C) on mental performance in 17yr-old boys and girls. They were subject to rising air
temperature conditions, typical of occupied classrooms, in the range 20–29°C. Sentence comprehen-
sion was significantly reduced by intermediate levels
of heat stress in the third hour. A multiplication task
was performed significantly more slowly in the heat
by male subjects, showing a minimum of 28°C.
Recognition memory showed a maximum at 26°C,
decreasing significantly at temperatures below and
above.
WORKING IN THE COLD
Physiologically speaking, working in the cold is
primarily a matter of maintaining thermal balance,
since both energy metabolism and neuromuscular
functions are temperature dependent. Body temperature is also subject to variations due to circadian
rhythms. While local acclimatization to cold is well
established, and may be of considerable practical
benefit, general acclimatization to cold, if in fact a
reality, is at best of limited practical value compared
to know-how, experience and environmental protection.
In a study in Finland, Anttonen and Virokannas
(1994) showed that in outdoor work in the winter,
cold stress frequently reduced working ability by
some 70%, at least for a short period. Virokannas
(1996) has shown that the most common problem
during light outdoor work in the cold is cooling of the
extremities and the face.
Some of the major problems associated with the
performance of physical work in the cold are consequences of the hobbling effect of the protective
clothing, as well as the obstructive effects of snow
and ice and the chilling effect of wind.
Contrary to coal mines in the rest of the world, the
temperature in the Spitsbergen coal mines is quite
low, due to the permafrost. Because of the geological
conditions (almost horizontal sedimentary layers and
coal seams only 70–110 cm thick) the miners have to
work lying on the ground. In order to get to the coal
face, the workers have to crawl several hundred
yards. The work is performed in a lying, half-sitting
or squatting position for two sessions of ∼3 h each in
each shift period. The temperature in the mine is 2 to
–4°C all the year round, and the workers have always
complained of finding it difficult to keep their feet
warm.
In collaboration with the health department of the
mining company, the actual work stress was assessed
in four of the miners (Alm and Rodahl, 1979). They
were studied for 24 h periods, both during work in the
mine and during time off and sleep. The study
included: (i) assessment of maximal work capacity
based on the recording of the heart rate during
submaximal cycle ergometer exercise; (ii) assessment of physical work load based on the continuous
recording of heart rate with the aid of a shielded
Oxford Medilog miniature portable magnetic tape
recorder; (iii) assessment of thermal stress based on
Extreme environments
continuous recording of rectal and skin temperature
by the same Medilog recorder; (iv) assessment of the
general stress response, based on the analysis of
urinary catecholamine elimination.
The estimated physical work load in the mine,
which was quite similar for all four subjects, corresponded, on average, to ∼30–40% of their maximal
work capacity. This is considerably higher than work
loads commonly encountered in most industries,
where they seldom exceed 25% of the maximal work
capacity. It is evident that this type of mining operation may impose some rather unique types of stress,
as in the case when, at the onset of the work shift, the
miner crawls along the narrow passage, dragging a
box containing 50 kg of dynamite tied to his leg,
causing his heart rate to approach 165 beat/min. The
work load of these coalminers is comparable to that
of coastal fishermen. The levels of urinary catecholamine elimination of the fishermen equalled those
observed in the coal miners.
The rectal temperature ranged from 37.5 to 38.5°C
during work. In spite of the high rectal temperature,
the skin temperature of the thigh dropped in two of
the subjects to ∼28°C. Thus, our observation supported
the miner’s complaints of cold feet, a problem which
under existing circumstances could only be remedied
by using properly insulated trousers and boots.
For a review of different methods to evaluate the
need for occupational cold protective clothing and the
thermal insulation of textile materials and clothing, see
Anttonen (1993).
Attempts have been made to develop a simple
index to describe and predict cold strain (Moran et
al., 1999; Castellani et al., 2001). The IREQ method
(insulation required), which is generally used for the
calculation of clothing insulation in the cold, has
been descibed by Holmèr (1992) and evaluated by
Griefahn (2000). For further reading on the subject of
assessment of cold exposure, see Holmèr (2001). For
a review of mental performance in cold environments, see Palinkas (2001). For further reading on the
effect of ageing on human cold tolerance, see Young
(1991) and the reviews from a symposium on the
different aspects of ageing in the International
Journal of Circumpolar Health; 59(3–4): 149–284,
2000.
Cold injury
Cold injury may be inflicted in common winter
sports such as skiing and skating and in long distance
runners competing in cold, windy conditions. Local
cold injury may occur in the exposed parts of the
body such as the face, hands and feet, either due to
the freezing of tissue and formation of ice crystals,
i.e. frostbite, or by vasoconstriction causing deprivation of the blood circulation to the exposed parts,
leading to ischemic cold injury. The pathological
consequences of the freezing may, to some extent,
247
depend on the speed of the cooling. In rapid cooling,
the ice crystals formed may break the cells and cause
tissue destruction and necrosis. In slow cooling, ice
crystals are formed in the tissues, but since solutes
are excluded in the freezing process, the osmotic
pressure in the extracellular fluid increases, pulling
fluid out of the cell, with exudate formation as a
result. This in itself will cause cell damage, augmented
by the concomitant vasoconstriction with increased
venous pressure, reduced capillary blood flow, blood
cell aggregation, thrombosis and necrosis.
The treatment of local cold injury consists of local
re-warming in the case of first degree frostbite, blisters (second degree frostbite) should be left intact,
and third degree frostbite requires hospitalization. At
any rate, the patient should be brought into shelter,
tight clothing should be loosened and the patient should
be kept warm, given hot drinks and, if possible, made
to be active in order to produce internal heat. The
treatment should be kept up until the return of normal
colour and feeling in the affected parts, and the
patient should be kept under surveillance. If normal
functions are not restored within 30 min the patient
should be hospitalized.
Local cold injury to the eyes, i.e. transitory
epithelial damage to the cornea with the formation of
corneal edema and blurred vision, has been observed
in cross-country skiers competing at very low
temperatures (Kolstad and Opsahl, 1969). Similar
afflictions have been reported among early aviators,
racing cyclists, speed skaters and natives of the
Arctic. (for references see Kolstad and Opsahl,
1969). In skiers, this particular type of injury is
usually seen only during competitive ski races, not
during training. It is especially apt to occur during
long distance races at temperatures below –15°C
combined with wind. The symptoms usually develop
toward the end of the race and consist of impaired or
blurred vision evidently caused by pathological
changes in the lower segment of the cornea.
According to Kolstad and Opsahl (1969), who first
described this phenomenon, the cause may be an
impaired blinking reflex and an incomplete closure of
the eyelids during blinking due to a lowering of the
surface temperature of the cornea. As a result of the
reduced blinking, the thin tear film, covering the
cornea and nourishing it, will not be maintained. This
may explain the observed degeneration of the epithelium of the unprotected part of the cornea. The
damage is transitory, however, and will usually heal
completely within 24 h. A possible prevention may
be achieved by protecting the eyelids and the cornea
by wearing suitable headgear, perhaps in combination with the use of contact lenses.
For a comprehensive review of cold injuries, see
the various articles in the International Journal of
Circumpolar Health; 59(2): 2000.
248
K. Rodahl
Hypothermia
Clinically speaking, hypothermia is a condition
usually characterized by body temperatures below
35°C.
During the initial stages of hypothermia, the
patient shivers, then gradually he or she becomes
disoriented, apathetic, hallucinatory or may become
aggressive, excited or even euphoric. As the rectal
temperature gradually drops below 34°C, the patient
may appear distant and stuperous, he or she may be
unconscious, respiration is shallow and the pulse is
weak. Cardiac arythmia may develop. There is loss of
reflexes and the pupils are dilated. Finally, the patient
reaches the paralytic stage as the rectal temperature
drops below 30°C. The skin is cold, no pulse can be
detected, the pupils are dilated, there are no reflexes
and no heart sounds.
If the patient cannot be brought to hospital safely
and the treatment must be performed under field
conditions, slow re-warming should be applied
(0.5°C/h). The danger of rapid re-warming in the
field is a further drop in deep body temperature due to
the return of cool venous blood from the skin and
extremities to the core. This temperature drop may be
fatal due to cardiac arythmia (ventricular fibrillation),
which requires defibrillation.
It should be kept in mind that even at more
moderate degrees of body cooling, the muscle
temperature may be significantly lowered, causing
muscular weakness, impaired neuromuscular function and reduced endurance. This may be the underlying cause of some of the fatal accidents among
climbers and cross-country skiers.
For an extensive study on cold and muscle
performance, see Oksa (1998).
CIRCADIAN RHYTHMS AND PERFORMANCE
In human beings, a variety of physiological functions, such as heart rate, oxygen uptake, rectal
temperature and urinary excretion of potassium and
catecholamines, show distinct rhythmic changes in
the course of a 24 h period, with the values falling to
their lowest during the night (low dip around 4 a.m.)
and rising during the day, reaching their peak in the
afternoon (Smolander et al., 1993). This phenomenon is known as circadian rhythms, and is thought to
be regulated by several separately operating biological clocks. It occurs in most individuals, although
there are apparently a few exceptions; some individuals show reversed rhythms, the rectal temperature,
for example, being highest at night (Folk, 1974). For
a review of the basic aspects of mammalian circadian
rhythms, see Illnerova (1991).
These rhythmic changes in physiological functions
have been found to be associated with changes in
performance. This relationship appears to exist
especially in the case of rectal temperature and
performance. In general, the lowest performance is
observed early in the morning (about 4 a.m.). Thus,
the delay in answering calls by switchboard operators
on night shift was twice as long between 2 and 4 a.m.
as during the daytime (Colquhoun, 1971). A similar
relationship may exist also in the case of athletic
performance. Thus, Rodahl et al. (1976), studying the
performance of top swimmers who competed under
comparable conditions early in the morning and late
in the evening, found that the swimmers performed
significantly better in the evening than in the morning
(P < 0.001).
These findings show that circadian rhythms must
be considered when interpreting the results from
prolonged physiological experiments and when
performing fitness tests in athletes at different times
of the day.
Shift work
The fact that human beings are ‘day animals’ and
that some of their basic physiological functions
which are associated with their performance capacities are subject to circadian rhythm changes suggests
that humans may not ideally be suited for night work.
Nonetheless, shift work has been practiced for generations in one form or another. Yet, little precise information is available as to what effect shift work has on
physiological functions or physical performance, and
there is no general agreement as to what type of shift
work or work schedule is to be preferred. Most of the
available information refers to clinical, social or
psychological aspects of shift work.
A review of the literature indicates that the health
of shift workers in general is good in spite of such
complaints as loss of sleep, disturbance of appetite
and digestion and a high rate of stomach ulcers
(Fujita et al., 1993). The social and domestic effects
of shift work represent greater problems than do the
physiological effects (Alward and Monk, 1990). The
results of studies pertaining to the effects on productivity are conflicting, as are results concerning accident rates. Absenteeism because of illness appears to
be lower among shift workers than among day
workers. It has been suggested that the physiological
and biological effects are probably related to circadian rhythms rather than to work schedule. To what
extent such circadian rhythms are related to health,
performance and a feeling of well-being is still undetermined. According to Harma et al. (1990), physiological adjustment to night work is not influenced by
age.
Systematic studies of men engaged in rotating shift
work and in continuous night work (Vokac and
Rodahl, 1974; Vokac et al., 1975) indicate that shift
work does represent a physiological strain on the
organism. It causes a desynchronization between
functions such as body temperature and the biological clocks governing these functions. These
Extreme environments
studies show that there are considerable individual
differences in the reaction to shift work, supporting
the general experience that not everyone is equally
suited for such work (some individuals consistently
show relatively high values for urinary catecholamine elimination during shift work, whereas others
have consistently low values). As judged by the
catecholamine excretion, the greatest strain occurs
when the worker, after several free days, starts work
on night shift. The results of these studies indicate
that it is preferable, from a physiological standpoint,
to distribute the free days more evenly throughout the
entire shift cycle, i.e. alternate between work and free
time regularly instead of assigning several consecutive free days.
The study of continuous night work shows that at
the onset, body temperature and work pulse fell in the
course of the night as if the subject was sleeping,
although he was working. It takes several weeks for
this normal rhythm to revert (i.e. for an increase in
body temperature in the course of night work). In
view of this, it would appear unrealistic to keep shift
workers on continuous night work for prolonged
periods in order to obtain the benefit of the reverted
physiological reactions, since such a reversion takes
too long to occur and is lost when interrupted by a
single day.
Recently bright light has been used to adjust the
biological clock following changes of circadian
rhythms during shift work (Wetterberg, 1994;
Eastman et al., 1995).
Disturbances in circadian rhythms may give rise to
considerable problems for those who have to travel
by air from one continent to another in order to
conduct business, to take part in political negotiations
or to participate in athletic competitions. It is an open
question whether the indisposition or functional
disturbances experienced after such intercontinental
flights are in fact due to disturbed circadian rhythms,
to loss of sleep or to both. It is a common experience,
however, that by being able to sleep during such
travel, if necessary by using sleep-inducing drugs, the
individual can maintain a reasonable functional
capacity in spite of the rapid shifts from one time to
another. (For further references see Rutenfranz and
Colquhoun, 1978, 1979.) According to Shinkai et al.
(1993), salivary cortisol appears to be an excellent
measure for monitoring circadian rhythm variation in
adrenal activity in healthy individuals during shift
work.
HIGH GAS PRESSURES
Although humans can become acclimatized to low
air pressures, there is no way to become biologically
acclimatized to high air pressures, such as those
encountered in deep sea diving or when a submarine
crew tries to escape from inside the craft, where the
249
pressure is normal, to the surface through sea where
the air pressure is higher. For a more comprehensive
review of the subject, see Lambertsen (1967), Behnke
(1971, 1978), Fagraeus (1974), Halsey (1982) and
Ross et al. (1997).
For every 10 m (33 ft) of seawater the diver
descends, an additional pressure of 1 atm is acting
upon his or her body. Small changes in sea depth thus
bring about great pressure changes. The body may
tolerate high pressures as long as the pressure is the
same inside and outside the body. When diving with
a snorkel connected to the mouth, one maintains the
atmospheric pressure in the lungs, while the surface
of the thorax, in addition, is exposed to the pressure
of the water. At a depth of about 1 m the pressure
difference becomes so great that the inspiratory
muscles no longer have the strength to overcome the
external pressure, and normal breathing becomes
impossible. For this reason, a snorkel system does not
permit diving to depths exceeding ∼1 m. At greater
depths, a breathing apparatus has to be used in which
the pressure in the system corresponds to that
prevailing at the depth in question. If there is overpressure in the system, the lung tissues may be
damaged, with haemorrhaging as a consequence.
As the pressure increases, more gases can be taken
up by the diver’s body and dissolved in the various
tissues. At a depth of 10 m, twice as much gas will be
dissolved in the blood and tissues as at the sea
surface. This is apt to give the diver trouble, mainly
because of the nitrogen.
The problem with nitrogen is that it diffuses into
various tissues of the body very slowly, and once
dissolved, it also leaves the body very slowly when
the pressure is once more reduced to normal atmospheric pressure. This is especially bad when the pressure is suddenly reduced from several atmospheres,
as may be the case during submarine escape or deep
sea diving. Then the nitrogen is released from the
tissues in the form of insoluble gas bubbles. These
bubbles congregate in the small blood vessels, where
they obstruct the flow of blood. This, then, gives rise
to symptoms such as pains in the muscles and joints,
and even paralysis may develop if the bubbles
become trapped in the brain. These symptoms are
known as the bends. Obviously, the severity of the
symptoms depends on the magnitude of the pressure,
which relates to the depth to which the person has
descended under water, the length of time spent at
that depth and the speed of ascent to the surface.
The bends can be avoided to a large extent by a
slow return to normal pressure so as to allow time for
the tissues to get rid of their excess nitrogen without
the formation of bubbles. Another way to avoid the
bends is to prevent the formation of nitrogen bubbles
by replacing atmospheric nitrogen by helium, which
is less easily dissolved in the body. This is done by
having the diver breathe a helium–oxygen gas
250
K. Rodahl
mixture. Another advantage of this method is that it is
more apt to prevent so-called nitrogen narcosis,
which occurs when air is breathed at 3 atm or more,
when there is an onset of euphoria and impaired
mental activity with lack of ability to concentrate.
With increasing pressures, the individual is progressively handicapped and may be rendered helpless at
10 atm. Diving to depths exceeding 100 m while
breathing ordinary atmospheric air may thus be fatal.
Prolonged breathing of 100% oxygen at 1 atm may
be harmful (Lambertsen, 1965; Gilbert, 1981); irritation of the respiratory tract may occur after 12 h and
frank bronchopneumonia after 24 h, and the peripheral blood flow (the flow through the brain) may be
reduced. In most individuals, no harmful effects
result from breathing mixtures with <60% oxygen,
but newborn infants are particularly susceptible to
oxygen poisoning and may suffer harmful effects
with oxygen concentrations >40%. The remarkable
thing is that oxygen poisoning is apparently no
problem when breathing 100% oxygen at altitudes
>6000 m, no matter for how long. Oxygen poisoning,
therefore, is not such a problem in aviation medicine,
but it is indeed an important problem in deep sea
diving, where it may even affect brain function when
pure oxygen is breathed under increased pressure.
This latter form of oxygen toxicity is apt to occur in
divers at depths >10 m, but there are great individual
variations in sensitivity to 100% oxygen. The onset
of symptoms may be hastened by vigorous physical
activity at great depths; it starts with muscular
twitching and a jerky type of breathing and ends in
unconsciousness and convulsions. The exact cause of
this is unknown, but it is assumed that it is a matter of
interference with certain enzyme systems in the
tissues.
When a person breathes pure oxygen at a pressure
of 3 atm or higher, the dissolved oxygen covers the
oxygen need of the body at rest. No oxygen would be
removed from oxy-haemoglobin during its passage
through the capillary bed. Therefore, the haemoglobin in the venous blood would still be saturated
with oxygen, which would interfere with the amount
of H+ ions taken up by haemoglobin, a weaker acid
than oxy-haemoglobin. Thus, CO2 entering the blood
from metabolizing cells would raise the blood pCO2
and the H+ concentration would be higher than under
normoxic conditions when the desaturation of oxyhaemoglobin simultaneously favours the removal of
H+ ions. The end result would be CO2 retention in the
tissues and acidosis.
When breathing air at a hyperbaric pressure during
heavy exercise, the increased air density reduces the
pulmonary ventilation. Depletion of energy stores in
the inspiratory muscles may contribute to limiting
pulmonary ventilation during maximal exercise at
raised air pressure (Hesser et al., 1981). Secondarily,
the maximal oxygen uptake may be reduced. By
substituting helium, with a lower density, for
nitrogen, pulmonary ventilation increases and oxygen
uptake may be higher than the maximum measured
under normal atmospheric conditions (Fagraeus,
1974).
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