1. Thermoregulation
1.1. balance between
1.1.1. heat gain
1.1.1.1. from metabolic heat production
1.1.1.1.1. nonshivering thermogenesis
1.1.1.1.2. shivering thermogenesis
1.1.2. heat loss
1.1.2.1. to the environment
1.1.2.1.1. countered by
1.2. periodic flutuation in blood flow
1.2.1. between
1.2.1.1. minimal
1.2.1.2. greater-than-normal flow
1.2.1.2.1. continues throughout the cold exposure
1.2.2. mechanisms
1.2.2.1. Cold induced vasodilation
1.2.2.1.1. mediated by the cessation of norepinephrine release after initial release
1.2.2.1.2. when the CIVD is absent
1.2.2.2. due to decrease tissue temperature
1.2.2.2.1. diminish SNS
2. Special concerns
2.1. Children
2.1.1. higher surface area to mass ratios
2.1.2. smaller adipose tissue deposits
2.2. Older individuals >50 yrs
2.2.1. higher risk
2.2.1.1. due to
2.2.1.1.1. diminished SNS mediated reflex vasoconstriction
2.3. spinal cord injuries
2.3.1. less sensitive to the sensation of cold on the skin surface
2.3.2. have diminished perception of skin temperature change
2.3.3. diminished capability to stabilize core temperature
3. Influence of wind, rain, and immersion
3.1. immersion
3.1.1. the heat transfer
3.1.1.1. 70:1
3.2. the best survival strategy for accidental, prolonged cold-weather immersion
3.2.1. 1. stay calm
3.2.1.1. unless you're wearing an immersion suit
3.2.1.2. cold shock
3.2.2. 2. make a plan
3.2.2.1. decide whether to swim or stay
3.2.2.1.1. in the present location
3.2.3. 3. swim
3.2.3.1. 800-1500m in cold water
3.2.3.2. 45 min
3.2.4. 4. stay
3.2.4.1. complete any tasks that require the use of hands
3.2.5. 5. stick to your decision
3.2.5.1. after 30 min in cold water
3.2.5.1.1. you may become hypothermic
3.2.5.1.2. you won't make the best decisions
4. Environmental risk factors
4.1. wind-chill temperature index
4.1.1. an index of cold stress
4.1.2. formula
4.1.2.1. wind chill
4.1.2.1.1. 35.74 + 0.6 T - 35.75V
4.1.2.1.2. where T = air temperature (F)
4.1.2.1.3. where V = wind speed (mph)
4.1.3. estimates the danger of extreme cooling of exposed skin
4.1.3.1. while walking 3 mph
4.1.3.2. the effect of air movement produced by the body should be taken into account when using the wind-chill recommendations
4.1.4. WCT <18F -27C
4.1.4.1. the risk of developing frostbite in exposed skin in less than
4.1.4.1.1. 30 min
4.1.4.2. warranting closer observation
5. Predisposing medical conditions
5.1. Exercise-induced bronchospasm
5.1.1. exacerbated by exposure to cold, dry air
5.1.2. predisposing factor
5.1.2.1. asthma
5.1.2.2. allergies
5.1.3. possible mechanisms
5.1.3.1. osmotic theory
5.1.3.1.1. airway drying due to increased breathing rates
5.1.3.1.2. this increased vasoconstrictor response
5.1.3.2. combination of cold air and increased breathing rate
5.1.3.2.1. cools airway
5.2. Raynaud syndrome
5.2.1. intermittent vasospasm of the digital vessels
5.2.2. appearance
5.2.2.1. white
5.2.2.2. then possibly
5.2.2.2.1. blue
5.2.2.3. red
5.2.2.3.1. upon rewarming
5.2.3. Predisposing factors
5.2.3.1. may be
5.2.3.1.1. thoracic outlet syndrome
5.2.3.1.2. collagen vascular disease
5.3. Anorexia nervosa
5.3.1. limits the ability to maintain a normal core temperature
5.4. Cold urticaria
5.4.1. primary acquired
5.4.1.1. onset within 24 hrs exposure
5.4.2. secondary acquired (hereditary)
5.4.2.1. onset within 48 hrs exposure
5.5. CV disease
5.5.1. sensitive to increased demands
6. Nonenvironmental risk factors
6.1. previous cold injuries
6.1.1. >2-4 times
6.2. low caloric intake, dehydration, and fatigue
6.2.1. negative effect
6.2.1.1. low caloric intake
6.2.1.1.1. 1200-1500 kcal
6.2.1.2. hypoglycemia
6.2.1.2.1. fatigue
6.2.2. not negatively affect
6.2.2.1. dehydration
6.3. race
6.3.1. black individual
6.3.1.1. >2-4 times
6.3.1.2. less pronounced CIVD
6.3.1.3. increased sympathetic response to cold
6.4. nicotine, alcohol, and drug use
6.4.1. nicotine
6.4.1.1. causes a reflex peripheral vasoconstriction
6.4.1.1.1. negating CIVD
6.4.1.1.2. enhancing the cold-induced vasoconstriction to maintain core temperature
6.4.2. alcohol
6.4.2.1. decrease the glucose concentration in the blood
6.4.2.1.1. tends to decrease the shivering response
6.4.3. drugs
6.5. body size and composition
6.5.1. larger body fat
6.5.1.1. >25% good insulator
6.5.2. larger muscle mass
6.5.2.1. shivering thermogenesis
6.6. aerobic fitness level and training
6.6.1. minor influence
6.7. sex
6.7.1. female > male
6.7.1.1. 2:1
6.7.1.2. due to less muscle mass
6.8. clothing
6.8.1. internal layer
6.8.1.1. allows evaporation of sweat w/o absorption
6.8.1.1.1. polyester
6.8.1.1.2. polypropylene
6.8.2. middle layer
6.8.2.1. provides insulation
6.8.2.1.1. fleece
6.8.2.1.2. wool
6.8.3. outer layer
6.8.3.1. wind & water resistant
6.8.3.2. evaporation of moisture
7. Pathophysiology of cold injury
7.1. hypothermia
7.1.1. definition
7.1.1.1. decrease in core body temperature
7.1.1.1.1. <95F 35C
7.1.2. S&S
7.1.2.1. changes in motor function
7.1.2.1.1. clumsiness
7.1.2.1.2. slurred speech
7.1.2.2. changes in cognition
7.1.2.2.1. confusion
7.1.2.2.2. poor decision making
7.1.2.2.3. memory loss
7.1.2.3. significant CNS changes
7.1.2.3.1. brain function becomes abnormal
7.1.2.3.2. ceases at
7.1.2.4. CV system
7.1.2.4.1. initial
7.1.2.4.2. and then
7.1.2.4.3. pathophysi
7.1.2.4.4. conduction system
7.1.2.4.5. atrial fibrillation
7.1.2.4.6. Ventricular fibrillation & arrhythmias
7.1.2.5. renal system
7.1.2.5.1. excreting large amounts of glomerular filtrate
7.1.2.5.2. cold-induced diuresis
7.1.2.6. respiratory system
7.1.2.6.1. initial
7.1.2.6.2. and then
7.1.2.6.3. CO2 production decreases by up to 50%
7.2. frostbite
7.2.1. definition
7.2.1.1. actual freezing of body tissues
7.2.2. mechanism
7.2.2.1. blood flow to the skin of the extremities is under
7.2.2.1.1. much stronger
7.2.2.1.2. than
7.2.2.1.3. independent of the CNS
7.2.2.2. differences in control of blood flow
7.2.2.2.1. produce the scenario of potential freezing injury to acral skin without a significant drop in core body temperatures
7.2.3. 3 phases
7.2.3.1. frostnip
7.2.3.1.1. occurs with
7.2.3.1.2. resulting in
7.2.3.2. mild frostbite
7.2.3.2.1. occur with
7.2.3.3. deep frostbite
7.2.3.3.1. what occurs
7.3. chilblain and immersion foot
7.3.1. definition
7.3.1.1. non-freezing cold injuries
7.3.1.2. cellular damage without ice crystal formation
7.3.2. pathophysi
7.3.2.1. abnormal inflammatory response
7.3.2.1.1. leads to build up intracellular
7.3.2.1.2. swelling
7.3.2.1.3. numbness
8. Heat loss mechanisms
8.1. 4 mechanisms
8.1.1. radiation
8.1.1.1. definition
8.1.1.1.1. directly to the environment by long-wave radiation
8.1.1.1.2. wind, wetness, and other factors do not affect it
8.1.1.2. greatest
8.1.1.2.1. at night
8.1.1.3. heat loss from
8.1.1.3.1. uncovered
8.1.1.3.2. 50-65% of all heat losses from the human body
8.1.2. convection
8.1.2.1. definition
8.1.2.1.1. the movement of air or water across the skin
8.1.2.2. air movement
8.1.2.2.1. running
8.1.2.2.2. skiing
8.1.2.2.3. cycling
8.1.2.3. wind-chill factor
8.1.3. conduction
8.1.3.1. direct contact with a cold surface
8.1.3.2. exacerbated by moisture
8.1.3.2.1. heat loss by up to 5 times
8.1.3.2.2. up to 25 times
8.1.3.3. reduce heat loss of by conduction
8.1.3.3.1. subcutaneous fat stores
8.1.3.4. with convection
8.1.3.4.1. 15% of all heat losses
8.1.4. evaporation
8.1.4.1. definition
8.1.4.1.1. through respiration and exposed skin
8.1.4.2. 15-25% of all heat loss
8.1.4.3. --
8.1.5. S=M-R-C-K-E
8.1.5.1. S
8.1.5.1.1. heat gain / loss
8.1.5.2. M
8.1.5.2.1. metabolic heat production
8.1.5.3. R
8.1.5.3.1. radiative heat loss
8.1.5.4. C
8.1.5.4.1. convective heat loss
8.1.5.5. K
8.1.5.5.1. conductive heat loss
8.1.5.6. E
8.1.5.6.1. evaporative heat loss