Multiple propane gas burn 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 (FeCO2), and oxygen (FeO2) recorded at the mouth to estimate whole-body energy production. The fundamental principle of IC relates to the catabolism of high-energy substrates such as carbohydrates and lipids to meet the body's energy needs through the oxidative process, which are reflected in the measured oxygen uptake rates ((V) over dotO(2)) and carbon dioxide production rates ((V) over dotCO(2)). Accordingly, it is important to know the accuracy and validity of(V) over dotO(2) and (V) over dotCO(2) measurements when estimating energy production and substrate partitioning for research and clinical purposes. Although several techniques are readily available to assess the accuracy of IC systems at a single point for (V) over dotCO(2) and (V) over dotO(2), the validity of such procedures is limited when used in testing protocols that incorporate a wide range of energy production (e.g., basal metabolic rate and maximal exercise testing). Accordingly, we built an apparatus that allowed us to manipulate propane burn rates in such a way as to assess the linearity of IC systems. This technical report aimed to assess the accuracy and linearity of three IC systems using our in-house built validation procedure. Approach. A series of trials at different propane burn rates (PBR) (i.e., 200, 300, 400, 500, and 600 mL min(-1)) were run on three IC systems: Sable, Moxus, and Oxycon Pro. The experimental values for (V) over dotO(2) and (V) over dotCO(2) measured on the three IC systems were compared to theoretical stoichiometry values. Results. A linear relationship was observed between increasing PBR and measured values for (V) over dotO(2 )and (V) over dotCO(2) (99.6%, 99.2%, 94.8% for the Sable, Moxus, and Jaeger IC systems, respectively). In terms of system error, the Jaeger system had significantly (p < 0.001) greater (V) over dotO(2) (mean difference (M) = -0.057, standard error (SE) = 0.004), and (V) over dotCO(2) (M = -0.048, SE = 0.002) error compared to either the Sable ((V) over dotO(2), M = 0.044, SE = 0.004; (V) over dotCO(2), M = 0.024, SE = 0.002) or the Moxus ((V) over dotO(2), M = 0.046, SE = 0.004; (V) over dotCO(2), M = 0.025, SE = 0.002) IC systems. There were no significant differences between the Sable or Moxus IC systems. Conclusion. The multiple PBR approach permitted the assessment of linearity of IC systems in addition to determining the accuracy of fractions of expired gases.