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How to survive in a raft An exercise in applied physiology
Mattijn Buwalda
anaesthesiologist-intensivist
Le Radeau De La Meduse Theodore Gericault
Ik ga op reis en neem mee….
Problems
• Cold
• Heat
• Dehydration • Starvation
• Mental condition
• Hostile marine animals
Thermoregulation
Fluid balance
Heat balance
Metabolism
•Resting state 100 watt
•Exercise 1500 watt
External heat
Heat loss
Core body
36-37o C
Hypothermia :
Mild 35o– 32o
Moderate 31o- 28o
Severe < 28o Heat exhaustion
Heat stroke
Heat exchange (in air)
External heat
•Radiation
•Conduction
•Convection
Heat loss
•Radiation
•Conduction
•Convection
•Evaporation
Conduction
In air
• direct contact between
skin and object
• 26 mW/M2/k
• standing human: minimal
conductive heat loss
In water
• 630 mW/M2/k
• Thermal conductivity x 24!
Radiation
• All heat objects emit or absorb
thermal radiation
• Difference between mean surface
temp of two objects
• Infra red spectrum
• No medium required (space)
• No radiation in water
• Radiating surface area 50-95%
Convection
Boundary layer
• Air or water layer close to the
skin
• Provides insulation when
stagnant
• The thicker the layer the more
insulation
In air:
• Wind chill factor!
• Max > 15 km/h
In water:
• Max > 1.8 km/h
• Max conductive heat loss
during swimming
Evaporation
• Each liter evaporated sweat
removes 576 kcal of heat!
• = 2419 J
• Droplets don’t cool!
• Sweating does not help in a fully humidified environment
Thermoneutral zone
In Air
• 26-30 o C
• naked person
• no sweating or
shivering
• still air (no wind)
In Water
• 35-35.5 o C
• naked person
• no sweating or shivering
• stagnant water
Water vs Air Thermal conductivity x 24
Volume specific heat capacity x 3500
Thermo
neutral zone
Thermoregulatory
zone
Thermoregulatory
zone
vasoconstriction
piloerection
shivering
vasodilation
sweating
26
C
30
C
Air temperature
core: 36o C
skin: 33o C
Thermoregulation
• Skin
– cold receptors > heat receptors
– very close to skin surface (fast
response)
• Hypothalamus (brain)
– more heat then cold receptors
– more sensitive to change
compared to skin receptors
Temperature receptors
•skin perfusion
•piloerection
•shivering
•sweating
Thermoregulation
• Peripheral shutdown (vasoconstriction)
– Max perfusion = 3 - 4 L/min
– Min perfussion = 0.02 L/min
– 99% shutdown!
• Subcutaneous fat insulation
• Unperfused muscle
• Skin temperature decreases and approximates
environmental temperature
vasoconstriction
Thermoregulation
• Skin blood flow regulation
• 3 functionally different regions
• Extremities (hands, feet, ears, lips, nose)
– Extreme vasoconstriction
• Trunk and upper limbs
– Moderate vasoconstriction
• Head and neck
– Scalp constant blood flow
– Heat loss!!
Vasoconstriction
Scalp > 50% body
heat loss in cold
environment
Core vs peripheral temperature
Thermoregulation
• “Goose bumps”
• Increased boundary layer
• Strongest on forearms
• Dysfunctional in hairless humans
• Pre-humans living in East Africa 4.4 million years ago inhabited savannas
piloerection
Thermoregulation
• Increased muscle tone (stiffness)
• Shivering
– Motor units 10-20/sec out of phase
– But alternating with opposing muscle
– No external work only heat production
– Can co exist with voluntary exercise (to a degree)
– Max heat production = basal x 5 = 500 watt
– Shivering stops when:
• Glucose runs out (starvation, alcohol)
• Hypoxia, hypercapnia
• < 30o C (spasticity)
Heat production
• We want an ambient thermoneutral temperature!
• Preferably with as little clothes as possible
• We lost most of our insulation and body hair
• Heat thermoregulation >>> cold thermoregulation
• We are still naked apes living in the African savanna’s
Behavioral thermoregulation
• Naked body thermoneutral temperature
– in air: 26-30o C
– in water: 35o C
• Physiological thermoregulation is limited and time
dependent
• Proper clothing can get you anywhere on the planet!
Behavioral thermoregulation
• Goal = thermoneutral inner temp 26-30 C
• Clothing reduces:
– Radiant heat loss (proportional to layers of clothing)
– Conductive heat loss (boundary layer of air)
– Convective heat loss is minimized (proper size)
• More layers > more trapped air
• Avoid draught (neck, arms and legs)
• Avoid moisture or getting wet
• How much clothes?
Behavioral thermoregulation
ambient temperature: 21 C
relative humidity: < 50%
Wind speed: < 0.9 km/h
no exertion
Behavioral thermoregulation
Old sayings….
• “If you want to stay warm in the mountains, stay
slightly cold”
– Minimize sweating to preserve clothing insolation
• “If you want to keep your hands warm in the cold
wear a hat”
– > 50% heat loss through the head
– A normal core temperature provides warm blood to
perfuse the extremities
Behavioral thermoregulation
Cold environment
• Multiple layers
• Wear a hat
• Protect hands and feet
• Avoid draught
• If dry: vapour permeable
clothing
• Splash: waterproof outer
garment
• Windproof outer garment
• Dark coloured (absorption)
Hot environment
• Loose fitting
• Promote draught
• Light +flexible
• Light coloured (reflection)
What shall I wear?
When thermo regulation fails…
Sea temperature and death rate
Aboard raft < 5o C 5-10o C 10-20o C 20-31o C
% died 50 36 6 6
Man at risk 306 1240 7894 6101
McCance RA, et al. The hazards to men in ships lost at sea, 1940-44. Medical Research
Council, Special Report Series No. 291. HMSO. London
Hypothermia prevention in a raft
• Stay dry
• Put on as much clothing
as possible
• Stay out of the wind
• Prevent conductive heat
loss (raft floor)
• Minimize body surface
ara
• Remove wet clothing
during sun shine
• Use a saturation bag
when shivering and
during the night
Saturation bag
Heat preservation in water
Survival time in cold water
Barnett PW field tests of two anti exposure assemblies. 1962 Arctic arospace laboratories report No AAL-TDR-61-56
Survival prediction
• SAR time 3-6 x predicted
50% survival time
• 5 C >> 6 h search time
• 20-30o C >> 24 h search
time
• Relevant factors:
– Fat or slim
– Physical fitness
– Naked or immersion suit
Stay in your raft!
Cold water immersion
Drowning
Wave splash:
•cooling of head
•frequent micro aspirations
•exhaustion
Cold shock:
•intense vasoconstriction
and tachycardia
•gasp reflex and
hyperventilation
Swim failure
Fast loss of
manual dexterity
Hypothermia
Dehydration
Cold environment
1. Hypothermia
2. Dehydration
3. Starvation
Dessert environment
1. Dehydration
2. Hyperthermia
3. Or nocturnal
hypothermia
4. Starvation
Popular survival literature:
3-3-3 rule: "3 minutes without air, 3 days without water,
and 3 weeks without food.
Fluid balance
Water balance
In 2250 ml
• Metabolism: 500 ml
• Intake: 1750 ml
Out 2250 ml
• Feces: 100 ml
• Skin 500 ml
• Lungs: 500 ml
• Urine: 1150 ml
• Thermoneutral environment
• Resting person
• Healthy person! C6H12O6 + 6 O2 = 6 CO2 + 6 H2O
Insensible
loss
What happens if you drink:
More then 1150 ml?
• Osmolality ↓
• n= 280 mosm/kg
• 1% decrease triggers
osmoreceptors
• Down regulation ADH output
• Collecting ducts less permeable
to H2O
• More diluted urine
Less then 1150 ml
• Osmolality ↑
• 1% increase triggers
osmoreceptors
• Thirst sensation
• More ADH
• More H20 reabsorption
• Less and more concentrated
urine
Dehydration
Max ADH secretion
• Assuming GFR 125 ml/min
• Urine osmolality 1200 mosm/L
• Urine composition:
– Urea 600 mmol/L
– Non urea electrolytes 600 mmol/L
• Urine production 500 ml/day
Renal failure
• Oliguria < 400 ml/day
• Anuria < 100 ml/day
• Hyperosmolality
• ↑Na
• ↑ Urea
• And many more disurbances
• Urea and electrolytes need H2O to be excreted
• Max urinary salt excretion = 20 gram/ liter H2O
Human long nephron
The spinifex hopping-mouse
• It does not need to drink. The seeds, insects and
roots that it eats provide enough water to live on.
• It has no sweat glands.
• Its droppings are almost completely dry.
• Its kidneys waste very little water. 9400 mosm/l
• Mothers produce very concentrated milk (and drink
the urine of their young).
Dehydration Continued insensible H20 loss 1000 ml/day
Or more in a tropical climate
Circulation:
•Hemoconcentration
•Tachycardia
•Hypotension
Kidney:
•Needs H2O to excrete Na+
•Renal failure
•Hyper Na+ > 170 mmol/l
CNS:
•Hyperactive deep tendon reflexes
•Muscular weakness
•Seizures
•Lethargy
•Confusion/ delirium
•Coma
Water restriction and survival
Daily H2O
ration
Men at risk Men who died % of men who
died
“none” 143 57 40
“some” 896 135 15
“0-110 ml 684 165 24
110-220 ml 1314 96 7
220-330 ml 523 7 1
“plenty” 56 1 2
121 life-craft voyages involving 3616 men
Critical volume of potable
water = 100 - 200 ml/dag McCance RA, et al. The hazards to men in ships lost at sea, 1940-44. Medical Research
Council, Special Report Series No. 291. HMSO. London
Water management
• Don’t drink in the first 24 hours!
– Use your body’s reserve
– Much of the water drunk will be excreted!
• Restrict intake to 500 ml/day
• Optimize the use of shade and convective cooling
• Wetting clothing and exposed skin with seawater
• Don’t eat protein if low on water
• Stay horizontal when cooling off in the sea!
Conservation
Urea excretion:
3 ml water for
every gram prot.
The great temptation
Day after day, day after day,
We stuck, nor breath nor motion;
As idle as a painted ship
Upon a painted ocean.
Water, water, everywhere,
And all the boards did shrink;
Water, water, everywhere,
Nor any drop to drink.
The Rime of the Ancient Mariner
Samuel Taylor Coleridge (1772 - 1834)
Seawater
Seawater
Drinking seawater
No. of Life
craft
No. Of men
at risk
No. Men
who died
Seawater
group
29 997 387 = 38.8 %
Non seawater 134 3994 133 = 3.3 %
McCance RA, et al. The hazards to men in ships lost at sea, 1940-44. Medical Research
Council, Special Report Series No. 291. HMSO. London
Seawater enemas
• “busted myth”
• Causes osmotic diarrhea
• Ascelerates dehydration
• Colon is incapable of concentrating seawater!
• What could help is an enema with unpalatable
fresh water
Other trics
• Fish lymph
– same salinity as plasma
– Squeezing fish takes a lot of energy
• Fish eyes and spinal fluid
• Turtle blood
– Same salinity
– 50 ml blood per kg
Solar still
Reverse Osmosis
Katadyn Survivor 35 Desalinator
The most widely-used emergency desalinator
•Produces up to 4.5 litres per hour.
•20 strokes/ minute
•Produces enough water for multiple person liferafts.
•Widely used by US and international military forces,
voyagers, sea kayakers, and other adventurers.
$1,995.00 - Survivor 35 Desalinator
Osmotic desalination
• 500 ml in 5 hours
• Filters 97% of the
salt in seawater
Starvation…….
Is not the main concern!
Thank you for listening!
mattijnb@gmail.com
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