NP13 Heat balance, body temperature, calorimetry

12 important questions on NP13 Heat balance, body temperature, calorimetry

Energy balance in humans; energy input, energy output

energy input
  • Diet

energy output
  • Heat
  • Work

How/where do you gain heat from and heat loss?

Heat gain
  • BMR
  • Muscular activity
  • Hormones
  • Thermic effect of food
  • Postural changes
  • Environment


Heat loss
  • Radiation
  • Conduction
  • Convection
  • Evaporation

What is the drive of the heat balance: heat load of heat loss?

Compare environmental temp 20*C, 19*C, or 10*C


At 20
At 19
At 10 you will shiver
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How does the body release heat (via skin)

  • The body releases heat via radiation, conduction, convection and evaporation
  • This is a physical mechanism, but skin temp is a physiological basis
  • clearly, the capacity of these processes to release heat is related to the environmental temperature

In what ways do pigs loss body heat ranging from 5 to 35 *C

At 5*C
  • radiation and convention are large,
  • evaporation and conduction are low/the same

at 35 *C
  • evaporation is mostly the heat loss
  • little of convection, radiation and conduction

What are the consequences for young vs. Adults with respect to their ability to maintain their body temperature?

What behaviour is related to this ratio?

For babies it is harder to stay warm, so they need more layers of clothes


Constantly moving, to stay warm

How to establish the level of heat production (kJ/day or kJ/min)

Estimation by a formula
  • Brody (maintenance) H(kJ/day) = 400 * W^0.75
  • Harris Benedict BMR; weight, length, age, gender

Measurements
  • direct calorimetry heat produced
  • indirect calorimeter H (kJ/day) = 16 O2 + 5 CO2
    • 1 liter O2 = 20 kJ, 1 liter CO2 = 25 kJ

What is the kJ/g for carbohydrate, protein and fat?

carbohydrate 17.6
protein 18.4
fat 39.8

Heat production (kJ): 16.18 O2 + 5.02 CO2 - 5.99 Nurine

Humans
  • 500 liter O2
  • 400 liter CO2
  • 100 gram porties (16 grams N)


Calculate the ME that is utilised by the body from its: O2 consumption and CO2 production

Heat production (kJ) = 10002 kJ 

--> protein contribution is only ca. 1%

Heat (kJ) = 16 O2 + 4 O2 ± 20 x O2 (L)

(in)direct calorimetry
  • Both methods can give different results, why?
  • What is measured by direct calorimetry? -->
  • What is measured by indirect calorimetry? -->
  • What can be the difference?

Both methods can give different results, why?
What is measured by direct calorimetry?
  • Heat
What is measured by indirect calorimetry?
  • O2 and CO2
What can be the difference?

Measurement of energy expenditure can besides looking at O2 and CO2 also be done by ...

Indirect calorimetry using dual-labelled water, 2H218O


Look at the difference between the lines

It is very expencive

How fast do we run into problems? (fever)
  • Calculate the time needed to raise the body temperature from 37 to 40 *C
  • Assume
    • complete insulation of the body ( 70kg)
    • maintenance heat production (7kJ/min)
    • Heat capacity ??? (kJ/kg *C)
    • Athletes stop exercising at a core temperature of ±40.1 *C

1 cal = 1 gr H2O 1*C; 1 cal = 4.186 J --> 4.18 kJ/kg *C

(3.5 kJ * 70) * 3 = 750

metabolic rate: 7 kJ/min --> 100min
marathon: 10-12 MJ; 80 kJ/min --> 10 min
solar radiation: 1000 W/m2; 17 kJ/min M2 --> 45 min

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