Room Indirect Calorimetry Operating and Reporting Standards (RICORS 1.0): A Guide to Conducting and Reporting Human Whole-Room Calorimeter Studies

Abstract

Whole-room indirect calorimeters have been used to study human metabolism for more than a century. These studies have contributed substantial knowledge to the assessment of nutritional needs and the regulation of energy expenditure and substrate oxidation in humans. However, comparing results from studies conducted at different sites is challenging because of a lack of consistency in reporting technical performance, study design, and results. In May 2019, an expert panel was convened to consider minimal requirements for conducting and reporting the results of human whole-room indirect calorimeter studies. We propose Room Indirect Calorimetry Operating and Reporting Standards, version 1.0 (RICORS 1.0) to provide guidance to ensure consistency and facilitate meaningful comparisons of human energy metabolism studies across publications, laboratories, and clinical sites.

Figure 1.

The first human open-circuit calorimeter built by Pettenkofer.

Figure 2.. (A)

Schematic layout of a room calorimeter. (B) Calorimeters located at the University of Colorado Anschutz Medical Campus (upper left), Pennington Biomedical Research Center (upper right), Maastricht University (lower left), and National Institutes of Health, Bethesda (lower right).

Figure 3.

Room calorimeter validation methods. Combustion of propane (A) and alcohol (B) are well-established validation approaches that provide relatively constant rates of CO₂ production (VCO₂) and O₂ consumption (VO₂), verified by weight. The ratio of VCO₂/VO₂ is constant and stoichiometrically-derived for each fuel source (0.6 for propane and 0.67 for alcohol). (C) Gas blenders infuse N₂ and CO₂ at user-defined rates governed by mass-flow controllers to mimic variable, independent rates of VO₂ (via oxygen dilution) and VCO₂. Gas blender images provided by MEI Research Ltd.

Figure 4.

Components of total daily energy expenditure. Physical activity energy expenditure (PAEE) has a linear relationship with concurrent activity measured by radar. The energy expenditure at zero activity, i.e. the y-intercept, represents the sum of the resting metabolic rate (RMR) and thermic effect of feeding (TEF). The RMR is comprised of the sleeping metabolic rate (SMR) and the energy expenditure from arousal. Adapted from Ravussin, et. al., 1986 (17).

Figure 5.

Body composition adjustments for energy expenditure. (A) Plotting resting metabolic rate (RMR) as a function of fat-free mass for 17 women (closed symbols) and 20 men (open symbols) results in a shared linear regression (RMR (MJ/d) = 2.27 + 0.091 fat-free mass (kg), r² = 0.78) suggesting a sex-independent relationship between RMR and fat-free mass. (B) Dividing RMR by fat-free mass, however, yields a greater “normalized” RMR for women due to the non-zero intercept in (A). Adapted from Westerterp, 2000 (61).

Figure 6.

Repeated 23h participant measurements to assess biological intra-individual variability. Bland-Altman plots of the difference between day 1 and day 2 versus their average for oxygen consumption (VO₂, A), carbon dioxide production (VCO₂, B), energy expenditure (EE, C), and respiratory exchange ratio (RER, D) for 10 participants fed a eucaloric, energy balanced diet and instructed to approximate their same daily routine both days. Average differences for the group are VO₂: 11.2±13.3 L/day (2.6±2.9%); VCO₂: 5.6±12.8 L/day (1.5±3.4%); EE: 50.4±62.7 kcal/day (2.4±2.9%); RQ: −0.01±0.02 (−1.3±2.4%). (E) Minute-by-minute tracings over 23 hours for EE (solid lines, left y-axis) and RER (broken lines, right y-axis) on day 1 (black) and day 2 (red) for the subject with the lowest daily EE and activity. Data provided by KYC (unpublished).