Calorimetry

 Calorimetry 

Calorimetry is the method of measuring changes in state variables of a body for the purpose of deriving the heat transfer associated with changes of its state due, for example, to chemical reactions, physical changes, or phase transitions under specified constraints. Calorimetry is performed with a calorimeter. The word calorimetry is derived from the Latin word calor meaning heat and the Greek word metron meaning to measure. Scottish physician and scientist Joseph Black, who was the first to recognize the distinction between heat and temperature is said to be the founder of the science of calorimetry.

Types of Calorimetry

It may be Direct or Indirect calorimetry-

1.     Direct Calorimetry- This is done by putting the subject inside a specially prepared heat proof chamber (Atwater-Benedict’s respiration calorimeter). Heat produced is measured by changes in circulating water. This method gives accurate results but can hardly be used in clinical setting due to elaborate apparatus and time constraints.

2.     Indirect calorimetry- Indirect calorimetry calculates heat that living organisms produce by measuring either their production of carbon dioxide or from their consumption of oxygen. Lavoisier noted in 1780 that heat production can be predicted from oxygen consumption this way, using multiple regressions. The dynamic energy budget theory explains why this procedure is correct. There are two methods for this a

a.      Closed circuit method-Different instruments are used for this purpose like Benedict Roth apparatus to calculate heat production and O2 consumption.

b.     Open circuit method- Here different types of respirometers are used to calculate O2 consumed and CO2 produced to calculate heat production.