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Physiology of Performance in Extreme Environments (PPEE)College 1
Hyperthermia → body temperature increases
Hypothermia → body temperature decreases
2 types of sweat
- Thermal sweat
- Hormonal sweat
Sweat changes when acclimatizing to heat → Less salt when acclimatized
100W produce in rest (90W for females)/65Wper squared meter body surface
- Digestive organs (especially liver) and brains produce most heat
- Body constitution is different for females
Losing 100W
- 10degree gradient between environment and face
- Clothing reduced heat loss
Main heat loss in rest is dry heat loss by conduction/convection/radiation
Mechanisms to cope with thermal extremes
Heat
- Vasodilation
- Sweat loss (max. 3L/h = 2458W)
POWERFUL ACCLIMATIZATION
Cold
- Vasoconstriction
- Shivering
- Fur coat
- Brown fat
POOR ACCLIMATIZATION
Bloodflow in the skin is under sympathetic control
- When its heat/cold the sympathetic system is activated vasocontraction/vasodilatation or
sweating
- Shivering is 400W, the more you are trained, the higher this production
Sympathetic nerve innervation
Sympathetic action:
- Alpha 2 receptors: skin vasoconstriction
o In the fingers mainly alpha receptors
- Beta 2 receptors: dilation of blood vessels in muscles
Sensors are dominantly present in the peripheral places
Evolution
Left Africa 40.000 years ago
Clothing allows extending the habitat behind physiological limits
,Heat balance
Metabolism ± Radiation ± Convection/Conduction - Evaporation = Storage
M = total production (generally expressed in Watt)
R = radion transported by waves
C = stroming(convection) /fixed material-fixed material (conduction)
- Based on difference in skin temperature and environment
- Dry heat loss
Wet heat loss
Evaporation = measure by weighing people before and after exercise
Difference between heat production and heat loss is storage
- Measure by rectal temperature and skin temperature
- Limits to storage → above 41, or below 35 (hypothermia)
Heat balance in rest and exercise
Rest
- Equilibrium between heat production and heat loss
- Much slower compared to exercise
- Diet induced thermogenesis
Exercise
- Heat production exceeds heat loss
- Core temperature increase (immediately)
- Performance decrement
- Until there is an increase in storage
Thermal balance during exercise – 8km run
Lower ambient temperature → lower sweat loss
Due to running 100W of storage
Heat loss
- Wet heat loss increases in warmer whether
- 35deg → skin temp is almost the same, so no dry heat loss, only loss
by evaporation and sweat
Wet and dry heat loss
Thermal heat balance calculation
Needs to perform → energy = m*g*h
Mass = 82(body)+14(bike) = 96; g = 10; h = 1500 → 1.440.000 J
Power = (joule/seconds → 2hours = 7200s) 1440000/7200 = 200W
,Efficiency = 20% → 800W heat loss (the more efficient, the more you put into the bike and the less
heat loss)
Ambient temp = 35deg
Normal evaporation is 1L/1h = 650W
800/650 = 1.23L/h evaporation
Heat balance factors
Climate
- Higher temp, higher humidity gets it to the warm side
- Solar radiation
- Wind increases convection cooling → lowers heat balance
Individual factors
- Body shape, heat acclimation status
Clothing
- Barrier against evaporation/sweat
- Isolation
Metabolism (100W in rest)
We can quantify everything
Required clothing for thermal neutrality
Mortality and heat balance
Minimal mortality degrees → 17deg, higher or lower temp causes more deaths
- Most deaths in NL are below
- Children and elderly are more sensitive to the temp
Weather related mortality
23 years database of daily mortality (1995-2018)
Cold-related mortality exceeds heat-related mortality!
In the cold people die more instantly
- Cold more invective ziektes
- Heat more cardiovascular diseases
- In the cold it takes longer
‘typical’ associations between ambient temperature and mortality →
Effect of month → higher mortality in cold months
, Etiology heat/cold
Time series data on weather related mortality in The Netherlands
- Daily all-cause deaths 1Jan 1995-31ded 2017 (N=3.209.811) obtained from Statistics
Netherlands
o Stratified by gender and age (‘young’: <65yrs, ‘elderly’: 65-80yrs; ‘old’: >80yrs)
- Corresponding meteorological data (mean daily temperature, …) from temporally and spatially
averaged hourly readings of weather stations
- Important questions: - when to warn for heat wave (criteria)
What makes elderly more vulnerable to the heat
Physiological differences
- Delayed core temperature onset threshold for sweating → core temp has to be higher to start
sweating
- Reduced sweat output per gland
o Half of the sweat rate of the younger → cool less and have higher risk
- Attenuated increases in SkBF for a given change in core temperature
o Decreased sensitivity active vasodilator system
o Capillary density in aged skin is reduced
o Lower cardiac output
o Reduced bloodflow redistribution
▪ Latter 2 → fluid status
- Physical fitness
- Illness and diseases
Behavioral aspects
- Inadequate thermal behavior
o Sleep under a duvet
o Wear insulative clothing
o No ventilation
- Less willing to use adaptive cooling strategies
o Do not want to be seen as ‘old’ and ‘vulnerable’
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