Topic 65 - Calorimetryc methods, the definition and importance of the respiratory quotient

Question 1

Words to include in calorimetryc methods

Answer 1

• Direct calorimetry
  
  • Method of Lavoiser and Laplace
  • Complex direct caloirmetry
  • Compensation calorimetry
  • Gradient calorimetry
• Indirect calorimetry
  
  • Open system
  • Closed system

Direct calorimetry

• Method of Lavoiser and Laplace
  
  • Chamber
    
    • Animal
    • Surrounded by ice
  • Heat generation
    
    • Amount of melted ice
  • Expired air and evaporation (ø measured)
• Complex direct calorimetry
  
  • Emission of water vapor
  • Heat isolated chamber
  • Adiabatic calorimeter
  • Total heat production
    
    • Water evaporated
      
      • Increase in weight (calculated)
    • Water absorbing substances
• Compensation calorimeter
  
  • 2 chambers of identical thermal capacity
    
    • Constant temperature
    • 1 chamber: animal
    • 1 chamber: electric bulb of known output
  • Animal heats up chamber = bulb warms up the other chamber for equal temperatur
  • 1J = 1Ws (Watt-secundum)
• Gradient calorimeter
  
  • Double walled chamber
    
    • Inner wall: heat conducter
    • Outer wall: constant temperature
  • Heat difference between wall
    
    • Amount of heat dissipated

Indirect calorimetry

• Open system
  
  • Environmental / atmospheric O₂ inspired
  • Expired air measured
  • Douglas bag
    
    • Gas-storing bag
    • Exhalation
    • Inhalation
• Closed system
  
  • No atmospheric O₂ inhaled
  • Oxygen added to system
  • Amount of consumed O₂

Complex indirect and direct calorimetry

• Atwar-Rose Respiratory Calorimetry
• Closed, heat-isolated chamber
  
  • Measure water temperature ↑
  • Velocity of water outflow

Question 2

Words to include in respiratory quotient (RQ)

Answer 2

• RQ = CO₂ [vol./time] / O₂ [vol./time]
• Respiratory quotient = respiratory exchange rate
• Range of RQ: 0.7-1.0
  
  • Hyperventilation: RQ ↑ (2.0)
  • Metabolic acidosis: RQ ↑
  • After exercise: RQ ↓ (0.5)
  • Fattening: RQ > 1
  • Starving RQ < 0.5
• Oxidized carbohydrate, protein and fat:
  
  • Expired CO₂
  • Inspired O₂
• Qualitiative composition of energy sources
• Chemical reaction of metabolism
  
  • Stoichiometric

Question 3

Calorimetryc methods

Name the different calorimetryc methods

Answer 3

1. Direct calorimetry
   
   • Method of Lavoiser and Laplace
   • Complex direct calorimetry
   • Compensation calorimetry
   • Gradient calorimetry
2. Indirect calorimetry
   
   • Open system
   • Closed system
3. Complex indirect and direct calorimetry (Atwater-Rose respiratory calorimeter)

Question 4

Calorimetryc methods

Direct calorimetry

Answer 4

​Method of Lavoiser & Laplace

• Chamber containing the animal surrounded by ice
  
  • ​The amount of melting ice and the water being produced was used to estimate heat generation
• Disadvatages:__​
  
  • ​Expired air and evaporation off the body are not measured
  • High humidity in the chamber

Complex direct calorimetry

• Emission of water vapor from the body
• Water of known temperature enters the outer casing of the heat isolated chamber (containing the animal)​
• Heat emitted from the animal heats up the water
  
  • Temperature of the water leaving the casing is measured
  • From this value and velocity of flow, heat production can be calculated (adiabatic calorimeter)

Compensation calorimeter

• 2 chambers of identical thermal capacity are connected
  
  • Chamber 1: animal inside
  • Chamber 2: electric bulb of known output inside
• Animal heats up tis chamger → the bulb will warm up its chamber to keep the temperature equal in both chambers
• Energy used by the bulb = output of heat produced by animal
• 1 J = 1 Ws (watt-secundum)

Gradient calorimeter

• Double walled chamber
  
  • ​Inner wall: good heat conduction
  • Outer wall: constant temperature
• The heat difference between the two walls is measured to calculate the amount of heat dissipated
• It detects the heat loss occuring by means of:
  
  • Radiation
  • Conduction
  • Convection

Question 5

Calorimetryc methods

Indirect calorimetry

Answer 5

Open system

• Environmental / atmospheric O₂ inspired
• Expired air is measured
• Douglas bag
  
  • ​Gas storing bag
  • Exhalation
  • Inhalation

Closed system

1. ​On atmospheric O₂ inhaled
2. Oxygen is added to the system
3. Indicator directly shows amount of consumed O₂

• Advantage of indirect calorimetry:
  
  • Animal can move freely in its natural environment
• Disadvantage of indirect calorimetry:
  
  • Restricted ability to measure the O₂-dependant energy production only

Question 6

Calorimetryc methods

Complex indirect and direct calorimetry

Answer 6

• Atwar-Rose respiratory calorimeter
• The experimental animal is placed into a closed, heat-isolated chamber. The degree of heat production of the animal can be calculated from data collected by measuring:
  
  • Water temperature ↑
  • Velocityof thewater outflow
• O₂ consumption and CO₂ production of the animal can also be determined

Question 7

Respiratory quotient

Answer 7

• Respiratory quotient = respiratory exchange rate
• Definition: the volume of production of CO₂ within a time unit divided by the volume of consumed O₂ during the same period
• Range of RQ: 0.7 - 1.0
  
  • ​Hyperventilation: RQ ↑ (2.0)
  • Metabolic acidosis: RQ ↑
  • After exercise: RQ ↓ (0.5) - paying back of O₂ debt
  • Fattening: RQ > 1
  • Starving: RQ < 0.5
• The amount of oxidized carbohydrate, protein and fat can be approximated from the amounts of:
  
  • Expired CO₂
  • Inspired O₂
  • Nitrogen excretedin theurine
• RQ values can provide information about the qualitative composition of energy sources (carbohydrate, protein & fat)
• Chemical reactions of metabolism are stoichiometric