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Design Handbook on Animal Research Facilities Using Static Microisolators 
jacket. Ice melted by animal heat yielded water, which dripped out. A requirement for all direct 
calorimeters is that heat from the general environment must be excluded from the measurement 
of animal heat production. In Lavoisier’s device, heat entering from the air surrounding the 
calorimeter was intercepted by a second ice-filled jacket that enclosed the first jacket that 
immediately surrounded the animal. Heat entering the animal area melted ice. Lavoisier was able 
to calculate the rate of heat output from the animal by collecting the water produced over 
measured periods of time, and by knowing the amount of heat required to melt each gram. 
3.1.3 Indirect Measurement of Metabolic Rate - Indirect Calorimetry 
Another method for measuring metabolic rates is an indirect method that has two advantages: 
relatively low cost and technical simplicity. An indirect calorimeter determines energy 
expenditure from the amounts of oxygen consumed and carbon dioxide produced in the chemical 
reactions that produce the energy expenditure. Heat production is based on using a mixed 
respiratory quotient (RQ). In indirect calorimetry, the gas analyzers take direct measurements of 
gas concentration in the calorimeter air stream. Thus the calculation of both oxygen consumption 
and carbon dioxide production can be determined by using the following relationships: 
O 2 (L/min) = ACL percent x Flow Rate of Exhaust Air From Calorimeter (L/min) x {(Barometric 
Pressure (mmHg) x 273))/(760 x (273+C)} 
CO 2 (L/min) = ACCL percent x Flow Rate of Exhaust Air From Calorimeter (L/min) x 
{(Barometric Pressure (mmHg) x 273))/(760 x (273+C)} 
Where: 
A O 2 (L/min) = percent CL entering calorimeter minus percent CL leaving calorimeter 
A CO 2 (L/min) = percent CCL leaving calorimeter minus percent CCL entering 
calorimeter 
C = Calorimeter inside temperature (°C) 
The respiration quotient is defined as: 
RQ = CO 2 (carbon dioxide production L/min )/ O 2 (oxygen consumption L/min) 
Calculation of heat production is based on CO 2 and CL production and a fixed RQ value of 0.82. 
The heat production is calculated based on CL consumption calculated from a mixed RQ =0.82 
which is for a caloric equivalent of 4.825 Kcal/LCL. This is generally accurate within a 3 percent 
range regardless of actual RQ (R=0.7 with caloric equivalent of 4.686 Kcal/L CL and R= 1.0 with 
caloric equivalent of 5.047 Kcal/L CL). 
