2 Methods Flashcards
Discuss how the thermal environment can be monitored and the thermal indices that have been developed, Critically evaluate the methods used to measure the thermal responses of individuals in different environments
Heat Balance Equation 1:
Heat Storage (S)= M - W ± R ± C ± K – E
K= Conduction C= Convection R= Radiation M= Metabolism (VO2) E= Evaporation (water vapour) W= Power output S= Change in mean body temp (heat storage)
Heat balance equation 2:
Heat gain:
- Environment (K) (C) (R)
- Metabolism (M)- Basal metabolism, muscular activity
- Thermogenic hormones and thermogenic effect of food.
Heat loss: -(K) -(C) passive & forced (R) (E)
Core Temp (Tcore) Measurement
- Oesophageal: Good but invasive, thin wire up nose and swallow until level with heart
- Aural & tympanic: Radiation of heat from vessels in ear, can be influenced by ambient temp which causes vasoconstriction
- Rectal: Safer than oesophageal, effective
- Gastrointestinal: swallow a pill that emits a frequency related to temperature. Need to make sure it goes through stomach before testing (at least 1 hour)
- Oral
- Forehead: Only in stable environment
- Urine
Skin Temp (Tsk) Measurement
-Thermistor / thermocouple
calibration check required
-Infrared thermography
surface distortions
Evaporation 1
- Evaporation of fluid from surface of skin
- Latent heat of vaporisation = 2430 kJ.l-1
Evaporation 2
-Sweat loss:
total sweat loss = change in naked mass
evaporated sweat loss = change in clothed mass
account for fluid & food; urine & faeces; respiratory & substrate losses
-Sweat capsule: sweating thresholds in specific areas
Muscle temperature
Thermistor / thermocouple inserted or implanted into muscle
Muscles: vastus lateralis; sartorius; gastrocnemius; brachioradialis
Depth: 25.3 mm; 30-33 mm; 4-5 cm; 4 cm then withdrawn at 1 cm intervals
Measuring environmental temperature
Wet bulb globe temperature (WBGT)
WBGT and work rates
Level of work:
- Low: Acclimatised no limit, un-acclimatised 32 (c)
- Medium: acclimatised 30 (c), un-acclimatised 26 (c)
- High: acclimatised 27 (c), un-acclimatised 24 (c)
- Extreme- 20 and 20 (max 30 mins) (c)
Heat stress index (HIS)
HSI = Ereq x 100%
Emax
0- no thermal strain
100- max strain tolerated by fit acclimatised young men
