Man at High Altitudes Atmosphere controls ability to live at high altitudes –Cold temperature –Low humidity –Low oxygen

Physiological Responses to Cold Environments Homeostasis- Warm-blooded mammals maintain a relatively constant body temperature regardless of ambient conditions- humans 37 o C Homeostasis achieved by control mechanisms that regulate heat production and loss Core body temperature drop of a few degrees reduces enzymatic activity, coma, death Core body temperature increases of a few degrees may irreversibly damage the central nervous system C Van Wie (1974) Physiological response to cold environments. Arctic & Alpine Enviornments

Adaptation to Cold Environments To maintain temperature: –Increase insulation –Increase heat production –Lower core temperature (hypothermia)

Thermoregulation Heat produced by metabolic processes and muscular exertion –Inactive Brain 16% Chest and abdomen 56% Skin and muscles 18% –Active Brain 3% Chest and abdomen 22% Skin and muscles 73%

Thermoregulation Heat lost from body core to muscle and skin by conduction and convection Blood circulating through body carries heat from core to outer body –Some lost to air –Much of the heat transferred to cooler veinous blood returning from extremities –Enables body to maintain extremities at lower temperature

Thermoregulation

Skin layer heat losses As air flow increases, convective heat loss from skin increases- windchill Evaporation Predominant heat loss from skin in cold environments is radiation –Nude, with skin temp 31C, radiates 116 Watts to room with walls of 21C –At rest, total heat production is 84 Watts –Better put some clothes on

Wind Chill Science sion_2_paper_1_e.htmlhttp://windchill.ec.gc.ca/workshop/papers/html/ses sion_2_paper_1_e.html 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.

Pathologic Effects of Excessive Heat Loss If skin temperature < freezing for extended period: –Chilblains- red, swollen itching lesions between joints of fingers –Trench foot- similar to chilblains except on foot If skin freezes –Frostbite- local burning and stinging followed by numbness Exposure- condition when body is not able to maintain a normal temperature –Core temp < 30C lose consciousness –Core temp < 27C heart ceases

Physiological Response to Cold Stress Autonomic control measures respond to cold by: –Increasing heat production –Increasing insulation layers –Permit moderate hypothermia (lower core body temperature)

Heat Generation At rest, muscles provide 18% of total heat Voluntary exercise- heat production increased 10 times Involuntary exercise- shivering –heat production increased 4-5 times –but 90% of heat produced by shivering lost by convection because of body movements Non-shivering thermogenesis –Metabolism/hormones of body adjust and increase heat production

Insulation Initial reaction to cold –Blood vessels in extremities contract rapidly –Increases insulation of body Long term- more fat

Physiological Factors of Altitude: Oxygen Deficiency Proportion of Oxygen in atmosphere- 21% Partial pressure of Oxygen decreases with height in proportion to other gases Lungs saturated with water vapor; reduces available oxygen Oxygen in lungs: (ambient pressure – saturation water vapor pressure at body temp (37C) (63 mb)) *.21 Sea level (1013 – 63 ) *.21 = 200 mb; 5000 m (540 – 63 ) *.21 = 100 mb Hypoxia- intolerance to oxygen deficiency –Humans can tolerate half sea level value indefinitely –Symptoms significant above 3000 m (133 mb of Oxygen) Standard Atmosphere varies with latitude (4000 m roughly 630 mb equatorward of 30 o ; 593 mb (winter)-616 mb (summer) at 60 o Cyclone could drop pressure mb; equivalent to several hundred meters in elevation Grover (1974); Man living at high altitudes. Arctic and Alpine Environments.

Inspired Oxygen as a Function of Elevation 200mb 100mb

Supplemental Oxygen Mt. Everest (8848 m/29,028 ft) –Mean pressure near 314 mb –Most climbers use bottled oxygen above 7300 m (24,000 ft) Pilots required to use supplemental oxygen above 3810 m (12,500 ft) for flights lasting more than 30 minutes

Oxygen in the body P I O 2 - inspired oxygen- oxygen available in the lungs O 2 transported in body by respiratory pigment haemoglobin in red blood cells –Lungs oxygenate blood –Heart pumps blood through body –High pressure of O 2 in capillaries causes diffusion into tissue Sea-level- 100 ml of blood contains 20 ml of O 2

Physiological Adaptions to Hypoxia Reduced P I O 2 reduces pressure of O 2 in blood: PaO 2 Brain triggers respiratory muscles to bring greater volume of air into lungs with each breath Hyperventilation- increase volume of air inspired per minute offsets decrease in air density # O 2 molecules taken into lungs per minute is nearly same as at sea level However, while quantity of O 2 available in lungs remains unchanged, PaO 2 reduced as elevation increases Reduced PaO 2 haemoglobin binds less O 2 ; less saturation of O 2 in blood; reduces O 2 in blood

Oxygen Saturation mb

Haemoconcentration

Other physiological changes Decrease in Oxygen in blood causes heart rate to increase initially in order to maintain Oxygen transport Amount of water in blood plasma decreases after about a week –Decreases plasma volume without changing volume of red blood cells –Blood can carry greater quantity of Oxygen –Prolonged hypoxia stimulates bone marrow to produce more red blood cells After a week, heart rate normalizes but stroke volume (volume pumped by left ventricle) decreases, leading to net drop in cardiac oxygen output

VO 2 Highest pressure in O 2 transport system determines efficiency of system VO 2 - aerobic working capacity- maximum amount of O 2 that can be consumed per minute 10% decrease in VO 2 per 1000m increase in altitude above 1500 m Humans can’t work as hard at high elevation as at lower ones

VO 2

Problems at High Altitude Humans can adapt to altitudes of 3-4 km and remain healthy indefinitely Acute mountain sickness- initial response to rapid ascent to high elevation –Poor sleep; headaches; nausea; vomiting; apathetic; irritable; little appetite Chronic mountain sickness- develops in people who have lived at high elevation for years; lose adaptation to hypoxia Pulmonary Oedema –Accumulation of fluids in the lungs interrupts transfer of oxygen from air to blood

Athletic Use of Hypoxia