Optimization of VO 2 and VCO 2 outputs for the calculation of resting metabolic rate using a portable indirect calorimeter.

This study aimed to compare the Cosmed K5 portable indirect calorimeter, using the mixing chamber mode and face mask, with a stationary metabolic cart when measuring the resting metabolic rate (RMR) and to derive fitting equations if discrepancies are observed. Forty-three adults (18-84 years) were assessed for their RMR for two 30-min consecutive and counterbalanced periods using a Cosmed K5 and an Oxycon Pro. Differences among devices were tested using paired sample Student's t-tests, and correlation and agreement were assessed using Pearson's correlation coefficients, intraclass correlation coefficient and Bland-Altman plots. Forward stepwise multiple linear regression models were performed to develop fitting equations for estimating differences among devices when assessing oxygen uptake (VO 2 diff , mL·min -1 ) and carbon dioxide production (VCO 2 diff , mL·min -1 ). Furthermore, the Oxycon Pro was tested before being confirmed as a reference device. Significant differences between devices were found in most metabolic and ventilatory parameters, including the primary outcomes of VO 2 and VCO 2 . These differences showed an overestimation of the Cosmed K5 in all metabolic outcomes, except for Fat, when compared to the Oxycon Pro. When derived fitting equations were applied (VO 2 diff  - 139.210 + 0.786 [weight, kg] + 1.761 [height, cm] - 0.941 [Cosmed K5 VO 2 , mL·min -1 ]; VCO 2 diff  - 86.569 + 0.548 [weight, kg] + 0.915 [height, cm] - 0.728 [Cosmed K5 VCO 2 , mL·min -1 ]), differences were minimized, and agreement was maximized. This study provides fitting equations which allow the use of the Cosmed K5 for reasonably optimal RMR determinations.