Environmental physiology: Cold

Question 1

Mechanisms of heat loss

Answer 1

1. Radiation - the exchange of electromagnetic energy waves emitted from one object and absorbed by another
2. Conduction - occurs when two surfaces with different temps. are in direct contact
3. Convection - require that one of the media be moving as occurs with a fluid and gaseous medium
4. Evaporation - heat transferred from body surface through change in liquid water on skin to gaseous water vapour in the environment

Question 2

Wind chill index

Answer 2

gives equivalent still air temperature for a particular ambient temperature at different wind velocities

Question 3

Physiological responses to cold environement

Answer 3

1. Increase in metabolic rate
   - voluntary - exercise: increase in heat production 10-20 times the basal rate
   - involuntary - shivering: increases basal rate 3-4 times basal rate
2. Increased tissue insulation
   - vasoconstriction of peripheral blood vessels and shunting of blood flow in deeper vessels

Question 4

Factors affecting responses to cold

Answer 4

1. skinfold thickness - the thicker the layer of fat, the greater the insulation
2. gender - women on avg. tend to have more subcutaneous fat that avg. men –> better insulation. However, women have greater SA to mass ration (the greater the ratio = more heat loss)
3. Clothing - effective insulation since air is trapped between layers of clothing…BUT wet clothes do not insulate

Question 5

Hypothermia

Answer 5

a condition characterized by a body core (brain, heart, lungs, liver blood and kidneys) temperature below 35C

Question 6

What are critical areas of heat loss

Answer 6

• head
• neck
• sides of chest
• groin

Question 7

Factors associated with hypothermia

Answer 7

• immersion in cold water or wet clothing
• wind
• physical exhaustion
• low percent body fat
• inadequate clothing for conditions
• hypoglycemia
• alcohol (decreases shivering, increases blood flow to skin, impairs judgement)

Question 8

Frostbite

Answer 8

freezing of superficial tissue which occurs when skin temperature is between -2C to -6C

• many people are unaware of frostbite bc sensory nerves are blocked and skin is numb

Question 9

Cold exposure and respiratory tract

Answer 9

Inhaled air is conditioned as it enters the upper respiratory passageways- warmed to 37C and saturated with water vapour.
Therefore you can’t “freeze” your lungs when exercising in very cold weather.

Question 10

All the following are decreased because of the cold:

Answer 10

• strength and power
• nerve conduction velocity
• reaction time
• manual dexterity
• flexibility

Question 11

Cold exposure

Answer 11

• immersion in cold water can cause more dramatic and rapid heat loss
• water is 25 times more conductive than air

Question 12

Pressure of air at:
a) sea level (0 ft)
b) 33 ft.
c) 66 ft.

Answer 12

a) 1 atmosphere or 760 mm Hg
b) 2.0 atmosphere
c) 3.0 atmosphere
pressure increases by 1 atm with every addition 33ft or 10m of depth

Question 13

Boyles law

Answer 13

The volume of any gas in inversely proportional to the pressure

Question 14

Limits to snorkel size

Answer 14

1. Pressure effect
   - compressive force of water against chest cavity is so large that inspiratory muscles are usually unable to overcome external pressure and expand thoracic cavity
2. Increase in pulmonary dead space

Question 15

Breath hold diving

Answer 15

When skin diver descends, the air in lungs is compressed –> lungs are squeezed

When lung volume is compressed below residual volume –> lung damage occurs as the blood is being suck from pulmonary capillaries into the alveoli

Question 16

paradoxical drowning

Answer 16

• diver hyperventilates
• holds breath and dives down to a certain breath
• gases in the lungs are compressed and partial pressure increases
• diver holds breath as long as possible and then starts to ascend
• partial pressure of gases in the lungs decrease on ascent
• PaO2 decreases below critical point
• diver looses consciousness and drowns

Question 17

Scuba

Answer 17

Self contained underwater breathing apparatus

Question 18

embolus

Answer 18

any material that enters and obstructs a blood vessel

Question 19

Air embolism

Answer 19

• diver inflate lungs as he begins ascent from depth
• diver doesn’t exhale
• pressure decreases
• air in alveoli expand to the point where alveoli rupture
• air bubbles enter blood vessels
• blocked artery in heart/ brain (stroke or heart attack)
• possibility of death (16%)

Question 20

Pneumothorax

Answer 20

Lung collapse
- rupture of alveoli
- air pocket forms outside of lung between chest wall and lung tissue
- continued expansion of trapped air during ascent causes ruptured lung to collapse

Question 21

Nitrogen narcosis

Answer 21

at depths over 30m the increased partial pressure and quantity of dissolved nitrogen produce anesthetic effects on the CNS - similar to alcohol intoxication

• decrease attentiveness, awareness of cold hallucinations and increase in reckless behaviour

Question 22

The bends (the decompression sickness)

Answer 22

• if the diver ascend to rapidly from prolonged dive, dissolved nitrogen moves out of solution and forms bubbles in body tissues and fluids
• pain is felt in joints within 4 - 6 hours after dive. If bubbles lodge in artery –> result in permanent damage or death
• treatment: recompression in hyperbaric chamber to force nitrogen gas into solution and then slow decompression

prevention: ascend to the surface in stages

Question 23

Eustachian tube

Answer 23

a small membrane lined passage from the middle ear cavity to the back of the throat

Question 24

Oxygen poisining

Answer 24

occurs when inspired PO2 exceeds 1520mm Hg for more than 30 - 60 minutes

• irritation to respiratory passages which progresses to pneumonia is exposure continues