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Thermal Balance Core temperature declines in the cold when heat loss exceeds heat production Core temperature rises if heat gain exceeds heat loss Humans.

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Presentation on theme: "Thermal Balance Core temperature declines in the cold when heat loss exceeds heat production Core temperature rises if heat gain exceeds heat loss Humans."— Presentation transcript:

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3 Thermal Balance Core temperature declines in the cold when heat loss exceeds heat production Core temperature rises if heat gain exceeds heat loss Humans can tolerate a decline in deep body temperature of 10°C but only an increase of 5°C (88F or 103F)

4 Long-term Cold Exposure Hypothalamus acts as a thermostat Initiates the bodys heat-regulating mechanisms: Thermal receptors in the skin Direct stimulation (detect change in blood temp) Increases BMR, HR, respirations

5 Thermoregulation in Cold Stress: Heat Conservation & Production Stimulation of cutaneous cold receptors constricts peripheral blood vessels, reducing the flow of warm blood to the bodys surface and redirecting it to the core Epinephrine and norepinephrine increase heat production during cold exposure Prolonged cold stress stimulates release of thyroxine (increases resting metabolism)

6 Heat loss Circulation: At rest in the heat, heart rate and cardiac output increase while superficial arterial and venous blood vessels dilate to divert warm blood to the body shell Evaporation: An effective thermal defense exists when evaporative cooling combines with a large cutaneous blood flow Hormonal Adjustments: Sweating produces loss of water and electrolytes

7 Heat loss (cont.) Why is it important to keep your head covered when out in the cold? No vasoconstrictor fibers to the head; therefore the head always remains unaltered

8 Temperature Regulation Shivering Autonomic response to falling core temperature Metabolic heat No work is done, almost all energy contributes to generation of heat Physical activity provides the greatest contribution in defending against cold

9 Core Temperature During Exercise Heat generated by active muscles can raise core temperature to fever levels that would incapacitate a person if caused by external heat stress alone Fatigue generally coincides with core temperatures between 100.4F/38C and 104/40°C, which impairs muscle activation directly from a high brain temperature that decreases the central drive to exercise

10 Exercise in the Cold Core temperature becomes further compromised during chronic exertional fatigue and sleep loss, inadequate nourishment, reduced tissue insulation, and a depressed shivering heat production Exercise energy metabolism sustains a constant core temperature in air as cold as -22°F

11 Exercise in the Cold Wear several thin layers of clothing Add or remove during exercise as needed CLO units = measure of insulation of clothing 1.0 clothing is ordinary business dress Should be comfortable at 70F N & S poles need 12 CLO Sweating becomes an issue, especially when exercise is finished

12 Body Fat, Exercise, & Cold Stress Differences in body fat content among individuals influence physiologic function in the cold during rest and exercise Successful ocean swimmers possess a larger amount of subcutaneous fat than highly trained non-ocean swimmers; additional fat = insulation

13 Water Immersion Water has 25% greater thermal conductivity than air & 350 times greater heat capacity than air Greater the swimming intensity the colder the water. Sensory deprivation tank: 92 F Learning to swim: 86 F Actively swimming: 80 F Competitive swimmers: 77F

14 Body Fat, Exercise, & Cold Stress The physiologic strain from cold- water and cold-land environments depends on ones level of metabolism and body fats resistance to heat flow

15 Muscular Performance in Cold Every 2 degrees drop in F temp = 3% drop in muscle power Normal skin temp: 91.4F Extreme thermal discomfort < 77F Extremity temp: 73F = clumsiness 68F = impact on skin has to be 6x greater than normal for usual sensation to be registered 59F = loss fine manipulative performance

16 Muscular Performance in Cold (cont.) Joint synovium becomes more viscous creating stiffness Joints are needed in order to survive If you are stranded, its not a bad idea to start walking to stay warm. When fatigued, stopping to rest or eat/drink is detrimental Unable to generate enough heat & losses are greater

17 Optimal Exercise Temps Endurance on stationary bike = 52F Distance runners = 57F Climbers = anything above 0F

18 Cold Stress and Children Large ratio of body surface area-to-mass is a liability during cold stress body heat dissipates rapidly During exercise in the less stressful cold-air environment, children rely on: Augmented energy metabolism More effective peripheral vasoconstriction in the limbs Brown fat = thermogenesis Why more in kids?

19 Cold Stress and Children A childs distinctly large ratio of body surface area-to-mass facilitates heat loss in a warm environment but becomes a liability during cold stress because body heat dissipates rapidly During exercise in the less stressful cold-air environment, children rely on: Augmented energy metabolism More effective peripheral vasoconstriction in the limbs Brown fat = thermogenesis Why more in kids?

20 Injuries from Cold Frostbite Ice crystals form in skin Temp below 30.2F Recent studies suggest not to be too aggressive in cuttin goff the black tissue Once bit, reoccurrence is easy Tissue is painful and hard, difficult to heal Hypothermia Cold Shock

21 Frostbite Predisposing factors to frostbite: Alcohol use vasodilator = accelerated heat loss Low physical fitness Fatigue Dehydration Poor peripheral circulation Susceptible areas: Face, ears, fingers/hands, feet/toes Tingling, numbness, burning

22 Injuries from Cold Frostbite Hypothermia Cold, water, wind Occur during any season Sense of cold & shivering numbness & uncontrollable shivering speech slurs, thought process slows erratic mvmts, skin swells/blue unconsciousness death Cold Shock

23 Injuries from Cold Frostbite Hypothermia Cold Shock Ice cold water, fatal within 5-10 minutes 7 steps: 1.Peripheral vasoconstriction 2. HR, CO 3. systolic pressure 4.Immediate hyperventilation 5. muscular activity, inability to swim 100m 6. breath/hold time 7.Drowning, death by hypothermia uncommon

24 Survival times in water Naked 30 min 1.0 CLO min 5mm wet suit min Dry suit 300 min

25 Acclimatization to Cold Humans possess much less capacity for adaptation to long-term cold exposure than to prolonged heat exposure

26 Acclimatization to Cold (cont) Cold adaptation occurs with regular, prolonged exposure Body regulates at a lower core temperature Repeated cold exposure of hands/feet increases blood flow through these tissues Shivering occurs at a lower body temperature Improved ability to sleep in the cold Changes in peripheral blood flow distribution 5 – 2 minute cold immersions will reduce cold shock response by half

27 Wind-Chill Index Air currents on a windy day magnify heat loss because the warmer insulating air layer surrounding the body continually exchanges with cooler ambient air The wind-chill temperature index provides a useful way to understand the dangers from winter winds and freezing temperatures and provides frostbite threshold values

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