A method to determine energy use by the body by measuring heat that emanates from the body
The relation between energy output and oxygen consumed has been determined using the human respiration calorimeter.
Reliable data regarding the energy output and oxygen consumed in human beings could be obtained only after Atwater –Rosa – Benedict perfected the human respiration calorimeter. This equipment consists of an air-light copper chamber insulated by wooden walls with air spaces in between. A folding bed, chair and table are provided in the chamber. A man can comfortably stay in the calorimeter for a few days and do some work such as reading, writing etc. A small opening is provided at the two ends for passing food and drink and removing the excreta. The chamber is ventilated by a current of air; the co2 and water given off are removed by soda lime and sulphuric acid respectively. Oxygen utilized by the subject replaced by introducing known amounts of oxygen through gas meter into the chamber with the air current. From the above, the quantity of oxygen consumed and co2 produced can be calculated. The heat produced is measured accurately by circulating a current of water through copper pipes and measuring the quantity of water that has been circulated through the chamber and also the difference between the temperature of the water entering and leaving the chamber.
Example:
Adult weighing 65 kgs. Amount of heat output in 24 hours = 2,400 KCal. Amount of oxygen consumed in 24 hours = 500 litres. Heat output per litre of oxygen consumed = 4.8 KCal.
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