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Atmosphere controls ability to live at high
altitudes |
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Cold temperature |
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Low humidity |
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Low oxygen |
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Homeostasis- Warm-blooded mammals maintain a
relatively constant body temperature regardless of ambient conditions-
humans 37oC |
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Homeostasis achieved by control mechanisms that
regulate heat production and loss |
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Core body temperature drop of a few degrees
reduces enzymatic activity, coma, death |
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Core body temperature increases of a few degrees
may irreversibly damage the central nervous system |
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C Van Wie (1974) Physiological response to cold
environments. Arctic & Alpine Enviornments |
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To maintain temperature: |
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Increase insulation |
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Increase heat production |
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Lower core temperature (hypothermia) |
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Heat produced by metabolic processes and
muscular exertion |
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Inactive |
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Brain 16% |
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Chest and abdomen 56% |
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Skin and muscles 18% |
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Active |
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Brain 3% |
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Chest and abdomen 22% |
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Skin and muscles 73% |
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Heat lost from body core to muscle and skin by
conduction and convection |
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Blood circulating through body carries heat from
core to outer body |
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Some lost to air |
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Much of the heat transferred to cooler veinous
blood returning from extremities |
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Enables body to maintain extremities at lower
temperature |
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As air flow increases, convective heat loss from
skin increases- windchill |
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Evaporation |
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Predominant heat loss from skin in cold
environments is radiation |
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Nude, with skin temp 31C, radiates 116 Watts to
room with walls of 21C |
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At rest, total heat production is 84 Watts |
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Better put some clothes on |
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http://windchill.ec.gc.ca/workshop/index_e.html? |
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http://windchill.ec.gc.ca/workshop/papers/html/session_2_paper_1_e.html |
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Bluestein, Maurice, Jack Zecher, 1999: A New
Approach to an Accurate Wind Chill Factor. Bulletin of the American
Meteorological Society: Vol. 80, No. 9, pp. 1893–1900. |
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If skin temperature < freezing for extended
period: |
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Chilblains- red, swollen itching lesions between
joints of fingers |
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Trench foot- similar to chilblains except on
foot |
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If skin freezes |
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Frostbite- local burning and stinging followed
by numbness |
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Exposure- condition when body is not able to
maintain a normal temperature |
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Core temp < 30C lose consciousness |
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Core temp < 27C heart ceases |
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Autonomic control measures respond to cold by: |
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Increasing heat production |
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Increasing insulation layers |
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Permit moderate hypothermia (lower core body
temperature) |
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At rest, muscles provide 18% of total heat |
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Voluntary exercise- heat production increased 10
times |
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Involuntary exercise- shivering |
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heat production increased 4-5 times |
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but 90% of heat produced by shivering lost by
convection because of body movements |
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Non-shivering thermogenesis |
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Metabolism/hormones of body adjust and increase
heat production |
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Initial reaction to cold |
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Blood vessels in extremities contract rapidly |
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Increases insulation of body |
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Long term- more fat |
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Mt. Everest (8848 m/29,028 ft) |
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Mean pressure near 314 mb |
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Most climbers use bottled oxygen above 7300 m
(24,000 ft) |
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Pilots required to use supplemental oxygen above
3810 m (12,500 ft) for flights lasting more than 30 minutes |
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PIO2- inspired oxygen-
oxygen available in the lungs |
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O2 transported in body by respiratory
pigment haemoglobin in red blood cells |
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Lungs oxygenate blood |
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Heart pumps blood through body |
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High pressure of O2 in capillaries
causes diffusion into tissue |
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Sea-level- 100 ml of blood contains 20 ml of O2 |
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Reduced PIO2 reduces
pressure of O2 in blood: PaO2 |
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Brain triggers respiratory muscles to bring
greater volume of air into lungs with each breath |
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Hyperventilation- increase volume of air
inspired per minute offsets decrease in air density |
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# O2 molecules taken into lungs per
minute is nearly same as at sea level |
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However, while quantity of O2
available in lungs remains unchanged, PaO2 reduced as elevation
increases |
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Reduced PaO2 haemoglobin binds less O2;
less saturation of O2 in blood; reduces O2 in blood |
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Decrease in Oxygen in blood causes heart rate to
increase initially in order to maintain Oxygen transport |
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Amount of water in blood plasma decreases after
about a week |
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Decreases plasma volume without changing volume
of red blood cells |
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Blood can carry greater quantity of Oxygen |
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Prolonged hypoxia stimulates bone marrow to
produce more red blood cells |
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After a week, heart rate normalizes but stroke
volume (volume pumped by left ventricle) decreases, leading to net drop in
cardiac oxygen output |
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Highest pressure in O2 transport
system determines efficiency of system |
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VO2- aerobic working capacity-
maximum amount of O2 that can be consumed per minute |
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10% decrease in VO2 per 1000m
increase in altitude above 1500 m |
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Humans can’t work as hard at high elevation as
at lower ones |
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Humans can adapt to altitudes of 3-4 km and
remain healthy indefinitely |
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Acute mountain sickness- initial response to
rapid ascent to high elevation |
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Poor sleep; headaches; nausea; vomiting;
apathetic; irritable; little appetite |
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Chronic mountain sickness- develops in people
who have lived at high elevation for years; lose adaptation to hypoxia |
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Pulmonary Oedema |
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Accumulation of fluids in the lungs interrupts
transfer of oxygen from air to blood |
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