Computing energy expenditure from indirect calorimetry data: a calculation exercise

Energy expenditure (Q) can be accurately derived from the volume of O2 consumed (VO2), and the volume of CO2 (VCO2) and CH4 (VCH4) produced. When the measurements are performed using a respiration chamber, VO2, VCO2 and VCH4 are calculated by the difference between the inflow (l/h) and outflow rates (l/h), plus the change in volume of gas in the chamber between successive measurements. There are many steps involved in the calculation of Q from raw data. These steps are rarely published in full detail, nor are they well documented for the training of students, researchers or technical staff. The objective of this chapter is to provide a complete calculation exercise for students at MSc level and researchers or technicians with little background in indirect calorimetry. Based on an example dataset and using a stepwise approach, the calculations used for calibrations, volumes of gas, Q, the respiratory quotient and activity related Q are explained and illustrated.