RÉSUMÉ
OBJECTIVE: The aim of this study was to test proportional-integral-derivative (PID) control of air inflow rate in a whole-room indirect calorimeter to improve accuracy in measuring oxygen (O2 ) consumption ( V Ì O 2 ) and carbon dioxide (CO2 ) production ( V Ì CO 2 ). METHODS: A precision gas blender infused nitrogen (N2 ) and CO2 into the calorimeter over 24 hours based on static and dynamic infusion profiles mimicking V Ì O 2 and V Ì CO 2 patterns during resting and non-resting conditions. Constant (60 L/min) versus time-variant flow set by a PID controller based on the CO2 concentration was compared based on errors between measured versus expected values for V Ì O 2 , V Ì CO 2 , respiratory exchange ratio, and metabolic rate. RESULTS: Compared with constant inflow, the PID controller allowed both a faster rise time and long-term maintenance of a stable CO2 concentration inside the calorimeter, resulting in more accurate V Ì CO 2 estimates (mean hourly error, PID: -0.9%, 60 L/min = -2.3%, p < 0.05) during static infusions. During dynamic infusions mimicking exercise sessions, the PID controller achieved smaller errors for V Ì CO 2 (mean: -0.6% vs. -2.7%, p = 0.02) and respiratory exchange ratio (mean: 0.5% vs. -3.1%, p = 0.02) compared with constant inflow conditions, with similar V Ì O 2 (p = 0.97) and metabolic rate (p = 0.76) errors. CONCLUSIONS: PID control in a whole-room indirect calorimeter system leads to more accurate measurements of substrate oxidation during dynamic metabolic studies.