HLTH2200 Lecture Notes - Lecture 3: Vasoconstriction, Arteriole, Hypothalamus
15 Jun 2018
School
Department
Course
Professor
Environmental Extremes
Exercise in the Cold +
Diving physiology
Outlines:
• Defence against cold
• Cold injury
• Cold water immersion
• Cold acclimation
• Diving physiology
• Decompression sickness
• SWB
Hypothalamus control in the cold
Lines of defence against cold
1st line of defence against the cold
• Vasoconstriction:
• Peripheral vasoconstriction occurs as a result of sympathetic stimulation to the
smooth muscle surrounding arterioles in the skin.
• Resulting in?
Lines of defence against cold
2nd line of defence against the cold
• Shivering
Cold injury
Can be divided into
• Cold-Wet injury
• Chilbain
• Trenchfoot
• Cold-Dry injury
• Frostnip
• Frostbite
• Difference is largely the depth of the freezing
• Early warning signs of cold injury include:
• tingling and numbness in the fingers and toes
• burning sensation in the nose and ears
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Wind Chill
• Adds cold stress by increasing the rate of heat loss via convection and conduction
• Warmer insulating layer surrounding the body continually exchanges with the
cooler ambient air
• Wind speed and forward velocity are additive
Heat loss in water
• Water has a thermal conductivity about 26 times greater than air
• At water temperatures below 32° C humans if inactive become hypothermic at a rate
proportional to either the duration of exposure or the thermal gradient
• Immersion in cool water of only 28 - 30° C often imposes a thermal stress invoking
shivering if people remain inactive because of a large conductive heat loss
Heat loss in water
• At 15° water temperature individuals immersed in water experience a decrease in
rectal temperature of about 2.1°C per hour
• At 4°C, 3.2°C per hour
Heat loss in water
• How does swimming affect heat loss?
Exercise in cold water
• Convective heat losses
• Can exercise offset heat losses?
Cold water immersion
• What is the key concern for falling into water <10C?
• Hypothermia?
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find more resources at oneclass.com
Cold water immersion
1-10-1 Rule
• Cold Shock Response (~1 min)
• Automatic gasp reflex
• Hyperventilation
• Cold Incapacitation (~10min)
• Vasoconstriction
• Loss of muscle function
• Hypothermia (~10 – 60min)
• Drop in Tc >35oC
• Circum-rescue Collapse
• Collapse just before, during or after rescue
Hypothermia
Hypothermia
• Below what temperature does the hypothalamus begin to lose its ability to regulate
body temperature?
• Hypothalamus regulation is completely lost when internal temperature decreases to
about 29.5°C
• Individuals who are immersed in near freezing water will die within a few minutes
when their rectal temperature decreases from normal (37°C) to 24 - 25°C
• Lethal lower limit of core temperature is usually between 23 - 25°C
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Outlines: defence against cold, cold injury, cold water immersion, cold acclimation, diving physiology, decompression sickness, swb. Wind chill: adds cold stress by increasing the rate of heat loss via convection and conduction, warmer insulating layer surrounding the body continually exchanges with the cooler ambient air, wind speed and forward velocity are additive. Immersion in cool water of only 28 - 30 c often imposes a thermal stress invoking shivering if people remain inactive because of a large conductive heat loss. Heat loss in water: at 15 water temperature individuals immersed in water experience a decrease in rectal temperature of about 2. 1 c per hour, at 4 c, 3. 2 c per hour. 1-10-1 rule: cold shock response (~1 min, automatic gasp reflex, hyperventilation, cold incapacitation (~10min, vasoconstriction. Loss of muscle function: hypothermia (~10 60min, drop in tc >35oc, circum-rescue collapse, collapse just before, during or after rescue.
