Closed-loop control of air supply to whole-room indirect calorimeters to improve accuracy and standardize measurements during 24-hour dynamic metabolic studies.

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 (O ) consumption ( ) and carbon dioxide (CO ) production ( ).

Methods: A precision gas blender infused nitrogen (N ) and CO into the calorimeter over 24 hours based on static and dynamic infusion profiles mimicking and patterns during resting and non-resting conditions. Constant (60 L/min) versus time-variant flow set by a PID controller based on the CO concentration was compared based on errors between measured versus expected values for 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 CO concentration inside the calorimeter, resulting in more accurate 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 (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 (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.