Multiple propane gas flow rates procedure to determine accuracy and linearity of indirect calorimetry systems : An experimental assessment of a method.

Objective: Indirect calorimetry (IC) systems measure the fractions of expired carbon dioxide (F E CO 2 ) and oxygen (F E O 2 ) recorded at the mouth in order to estimate whole body energy production (EP). The fundamental principal of IC relates to oxidative mechanisms, expressed as rate of oxygen uptake (V̇O 2 ) and carbon dioxide production (V̇CO 2 ). From these volumes we calculate energy production and respiratory exchange ratio which is used to estimate substrate utilization rates. The accuracy of IC systems is critical to detect small changes in respiratory gas exchanges. The aim of this technical report was to assess the accuracy and linearity of IC systems using multiple propane gas flow rates procedure. Approach: A series of propane gas with different flow rates and ventilation rates were run on three different IC systems. The actual experimental V̇O 2 and V̇CO 2 were calculated and compared to stoichiometry theoretical values. Results: showed a linear relationship between gas volumes (V̇O 2 and V̇CO 2 ) and propane gas flows (99.6%, 99.2%, 94.8% for the Sable, Moxus, and Jaeger metabolic carts, respectively). In terms of system error, Jaeger system had significantly ( p < 0.001) greater V̇O 2 ( M = -0.057, SE = 0.004), and V̇CO 2 ( M = -0.048, SE = 0.002) error compared to either the Sable (V̇O 2 , M = 0.044, SE = 0.004; V̇CO 2 , M = 0.024, SE = 0.002) or the Moxus (V̇O2, M = 0.046, SE = 0.004; V̇CO 2 , M = 0.025, SE = 0.002) metabolic carts. There were no significant differences between the Sable or Moxus metabolic carts. Conclusion: The multiple flow rates approach permitted the assessment of linearity of IC systems in addition to determining the accuracy of fractions of expired gases.