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Cold Environments and Human Performance -- Fill in the blanks style lecture notes with occasional extras about what was especailly important to remember and some further explanations.

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Simon Fraser University
Biomedical Physio & Kines
BPK 142
Paul Lee

COLD ENVIRONMENTS AND HUMAN PERFORMANCE I. HEAT BALANCE A. Mechanisms of Heat Loss 1. Radiation - the exchange of ____electromagnetic______ energy waves emitted from one object and absorbed by another 2. Conduction - occurs whenever two surfaces with differing temperatures are in direct ___contact______. Insulators - do not conduct __heat__ readily. Still _air__ is an excellent insulator, while __water__ is an excellent conductor. Heat conduction in water is about 25 times greater than in air. The rate of conductive heat exchange is inversely related to the __thickness____ of the insulating substance - air trapped in goose down clothing, body fat, layer principle of dressing for the cold 3. Convection - requires that one of the __media__ be moving as occurs with a fluid or gaseous medium. For example, heat transfer from skin to moving air or water. Wind Chill Index - gives the equivalent still air temperature for a particular ambient temperature at different wind velocities. The temperature gradient between the skin and air and the air velocity are important factors in determining convective heat loss. Convective heat loss during swimming is more than twice that during rest in still water. 4. Evaporation - the transfer of heat from the body surface through the change of ___liquid__ water on the skin to a __gaseous___ water vapour in the environment. II. PHYSIOLOGICAL RESPONSES TO A COLD ENVIRONMENT There are two primary physiological responses used by humans to defend against a cold environment: 1. Increase in ___metabolic__ rate a) voluntary - __exercise__ - can increase heat production 10-20 times the basal rate b) involuntary - __shivering___ - can increase basal rate 3-4 X 2. Increased tissue ___insulation____ - vasoconstriction of ___peripheral___ blood vessels and shunting of blood flow into deeper vessels. Because the superficial blood vessels in the __head__ do not constrict in the cold, the __head___ is an important source of heat loss - accounts for 30 - 35% of total heat loss at rest. Behavioural responses to the cold are important - clothing, seeking shelter, starting a fire, etc. [There are receptors all over the body. On our skin and important organs, that can increase the metabolic rate or insulation of the body [over time]. III. FACTORS AFFECTING RESPONSES TO COLD A. Skinfold Thickness The thicker the _fat_ layer, the greater the insulation. B. Gender The average female has more subcutaneous _fat___ than the average male  more insulation. However, women generally have __larger___ surface area to mass ratios than men. Children have even higher surface area to mass ratios. When men and women with similar skinfold thicknesses are compared, women lose heat more __rapidly__ than men during immersion in cold water. C. Clothing The effective insulation afforded by clothing is a function of the air layer next to the skin, the __thickness___ of the clothing, and the__air__ trapped between the layers of clothing. More clothing insulation is needed during rest than during __exercise__. Clothing insulation is __reduced___ if the clothing becomes wet. __Multiple__ layers of clothing are advisable during exercise in cold weather. The outer layer should be __water__ repellent and _wind__ resistant. Middle layers should provide __insulation__. The innermost clothing layer should not only provide insulation but also wick ___moisture__ away from the skin to reduce evaporative heat loss – polyester or polypropylene thermal underwear. Clothing insulation is reduced if wind penetrates the outer garments. IV. COLD INJURIES A. Hypothermia Hypothermia - a condition characterized by a body core temperature below __35 degrees Celsius_. Body core - refers to brain, heart ,lungs, blood, liver, kidneys. Critical areas for heat loss - head and neck, sides of chest, groin Shivering will __cease__ when core temperature (T c falls below 32-34 C. Death occurs when T drops to __24-28 degrees Celsius__ c Factors associated with hypothermia: 1. Immersion in cold water or wet clothing 2. Wind 3. Physical exhaustion 4. Inadequate clothing for conditions 5. Low percent body fat 6. Hypoglycemia 7. Alcohol consumption - causes a decrease in __shivering__, increased blood flow to skin, impairs _judgment__ *************Know this for exam!!!************* Hypothermia causes the oxyhemoglobin dissociation curve to shift to the _left_  __greater___ hemoglobin affinity for O2 __Less__ O is 2eleased to the tissues  body tissues shift to __anaerobic__ metabolism  hypoxia of heart and brain plus metabolic acidosis  ___depressed___ brain function and cardiac output  ventricular fibrillation and death B. Frostbite Freezing of superficial tissues which occurs when skin temperature reaches between __-2 C to -6 degree C______. Many people are unaware of frostbite because the sensory nerves are __blocked__ and the skin is __numb___ C. Cold Exposure and the Respiratory Tract Inhaled air is conditioned as it enters the upper respiratory passageways - warmed to _37 C__ and saturated with _waer__ vapor. Therefore you can’t “__freeze__” your lungs when exercising in very cold weather. Since cold air is very __dry___  cells lining the respiratory passageways become ___dry__  possibility of __throat__ irritation. V. EFFECTS OF COLD ON PERFORMANCE A. Cardiovascular Endurance When T cs decreased, VO m2x. is decreased due to __decreased___ maximum heart rate and shift of the oxyhemoglobin dissociation curve to the __left___. VO = Q x (a - vO ) diff. 2 2 For a given exercise intensity, a person is working at a higher percentage2of VO max. when core temperature is __decreased__  use glycogen stores at a faster rate  earlier onset of __fatique___ Reduced blood flow to muscle when body is cooled  more anaerobic metabolism B. Strength, Power & Flexibility All of the following are __decreased in a cold environment__: • strength and power • nerve conduction velocity • reaction time • manual dexterity • flexibility SPORT DIVING I. PRESSURE EFFECTS Pressure of air at sea level = _1.0_ atmosphere or 760 mm Hg The weight of a column of water directly above a diver's body (hydrostatic pressure) increases directly with increasing depth. The pressure increases by one atmosphere for each additional _33_ ft. of depth. 33 ft. = _2.0__ atmosphere 66 ft. = _3.0__ atmosphere Because the tissues of the body are largely water, they are non- compressible. However, the body contains __air__ cavities - lungs, respiratory passages, sinus and middle ear spaces - where volume and pressure will __change__ with increases or decreases in diving depth. Boyle's Law - the __volume__ of any gas varies inversely with the __pressure___ on it (ie) if the pressure is doubled, volume is __halved__. II.
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