Man at High Altitudes

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

2. Physiological Responses to Cold Environments • Homeostasis- Warm-blooded mammals maintain a relatively constant body temperature regardless of ambient conditions- humans 37oC • 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

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

4. 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%

5. 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

6. Thermoregulation

7. 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

8. Wind Chill Science • http://windchill.ec.gc.ca/workshop/index_e.html? • http://windchill.ec.gc.ca/workshop/papers/html/session_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.

9. 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

10. 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)

11. 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

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

13. 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 30o; 593 mb (winter)-616 mb (summer) at 60o • Cyclone could drop pressure 10-20 mb; equivalent to several hundred meters in elevation • Grover (1974); Man living at high altitudes. Arctic and Alpine Environments.

14. Inspired Oxygen as a Function of Elevation 200mb 100mb

15. 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

16. Oxygen in the body • PIO2- inspired oxygen- oxygen available in the lungs • O2 transported in body by respiratory pigment haemoglobin in red blood cells • Lungs oxygenate blood • Heart pumps blood through body • High pressure of O2 in capillaries causes diffusion into tissue • Sea-level- 100 ml of blood contains 20 ml of O2

17. Physiological Adaptions to Hypoxia • Reduced PIO2 reduces pressure of O2 in blood: PaO2 • 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 • # O2 molecules taken into lungs per minute is nearly same as at sea level • However, while quantity of O2 available in lungs remains unchanged, PaO2 reduced as elevation increases • Reduced PaO2 haemoglobin binds less O2; less saturation of O2 in blood; reduces O2 in blood

18. Oxygen Saturation 70 116 mb

19. Haemoconcentration

20. 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

21. VO2 • Highest pressure in O2 transport system determines efficiency of system • VO2- aerobic working capacity- maximum amount of O2 that can be consumed per minute • 10% decrease in VO2 per 1000m increase in altitude above 1500 m • Humans can’t work as hard at high elevation as at lower ones

22. VO2

23. 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

24. Athletic Use of Hypoxia http://www.sltrib.com/2001/aug/08262001/sports/126267.htm