wk1 thermal balance and pathophysiology Flashcards
what is the formula for heat storage
S = M - W +- E +- C +- R +- K (all in ‘W. m^-2’ watts per square meter)
M - metabolic energy production
w - work done
e - evaporative heat transfer
c - convective heat transfer
r - radiative heat transfer
k - conductive heat transfer
what is the formula of heat storage also referred to as
the 1st law of thermodynamics
what are the 4 main environmental parameters affecting heat balance
ambient temp
humidity - diffusion gradient reduced when it’s very humid
air velocity
solar radiation
what personal factors affect heat balance
age
biological sex
body surface area
aerobic fitness
what are the task dependant factors affecting heat balance
rate of metabolic heat production
clothing
what measures the total heat generation and exchange
whole body calorimeters
what is another example of how we can measure body heat storage and exchange
thermometry
on a graph depicting heat loss and production how would you find the ‘whole body heat storage’
it’s the shaded area between the two values
what are the efferent responses to cold temps
blood vessels constrict
shivering
what is the efferent response to high temps
blood vessels dilate to produce sweat
what locations do we measure body core temp
oesophageal - mouth (most accurate)
rectal - anus
gastro intestinal - from mouth to anus (moving blood away from gut during exercise so is slow)
tympnic - ear canal
what is the thermoeffector response during heat stress
body temp spikes
effector output increases proportionally to body temp (plateaus at max value)
body temp change is needed to cause effector output
how is skin (cutaneous) temp different to core
skin can vary around the body core is always the same, it is not regulated
how do we measure skin temp
Has to be at a min of 4 sites
infared thermography - measures radiating energy released from the body
thermocouples - connected wires attached to the body
ibuttons - small metallic buttons placed on the body
what is the sweating response across time
steep rise to own plateau - no uniformity in sweat rates
decline local - due to hidromeiosis (reduction of sweating occurring when sweat glands are blocked)
decline central - osmoregulatory and baroreceptive
what is vital about sweat loss through evaporation
humans can only dissipate heat from skin if environmental temp > skin temp
how do we measure sweat rate
body mass change - respiratory loss and metabolic change
patch collection - Na loss
ventilated capsules - measure of thermoregulation
what happens to muscle temp during exercise
rapidly increases, non active muscles have a slower rate of change
what happens to intramuscular temps as exercise goes on
become more uniformed (blood = coolant and warmant)
what is the heat stress index for
to predict the physiological strain from a stressful environment
what are the two types of heat stroke
classic and exertional
how to deal with heat related illness
remove from heat
rehydration
rest in ‘supine’ position
how can heat stress impair performance
lower brain and muscle blood flow
increased perception of effort and exertion
higher cho oxidation
CNS disorder
what is hypernatremia
plasma sodium conc of 145mmoL
What is hyponatermia
plasma sodium conc of 135mmoL or less
normally due to lots of water intke and no sodium intake
what is heat storage governed by
biophysical properties
what are the biophysical of the environment
radiation (out)
convection (out)
wind
evaporation (out)
conduction
direct and diffused radiation
reflected radiation
how does our thermoeffector responses change during heat stress
increases effector output
higher change in mean body temp to initiate activation of effector response
lower maximal values
what can inhibit sweating process
hidromeiotic effect of skin pressure
what drives heat related illness
heat exposure
driven by ambient heat stress and internal metabolic energy production
what is heat stroke characterized by
40c temp and CNS dysfunction
what are the characteristics of heat exhaustion
profound fatigue, weakness, nausea, headache or dizziness
moderate-serve dehydration
elevated core temp
what is heat syncope
fainting due to pooled blood, caused by peripheral vasodilation
what is heat edema
swelling of the limbs, caused by peripheral vasodilation and intestinal pooling
definition of heat cramps
painful muscle spasms during/after exercise in heat
individual susceptibility risk factors heat related illness
age
existing conditions
pregnancy
medication
cognitive impairments
disabled
immobilisation
social isolation
sociocultural factors affecting heat illness
poverty
racism
social cohesion
housing status
literacy
worker protections
consequences of exertional strokes
CNS disorder
high core temp
tissue/organ damage
endotoxaemia
how can sweat loss be counteracted
fluid consumption and activation of the RAAS
what are the two types of hyponatremia
asymptomatic and symptomatic
what is the capacity of the environment to absorb heat dependent on
water vapour pressure
air movement
resistance to heat transfer - posture/clothing
ambient temp
