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^oC

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

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.

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

Slide 13

Slide 14

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_IO₂- 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

Physiological Adaptions to Hypoxia

Reduced P_IO₂ 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

Oxygen Saturation

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

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

VO₂

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


	Atmosphere controls ability to live at high altitudes
		Cold temperature
		Low humidity
		Low oxygen


	Homeostasis- Warm-blooded mammals maintain a relatively constant body temperature regardless of ambient conditions- humans 37^oC
	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


	To maintain temperature:
		Increase insulation
		Increase heat production
		Lower core temperature (hypothermia)


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%


	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


	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


	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.


	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


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


	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


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


	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


	P_IO₂- 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


	Reduced P_IO₂ 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


	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


	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


	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