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

Abstract

The aimof 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 ( ) and carbon dioxide (CO2 ) production ( ). A precision gas blender infused nitrogen (N2 ) and CO2 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 CO2 concentration was compared based on errors between measured versus expected values for respiratory exchange ratio, and metabolic rate. 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 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. PID control in a whole-room indirect calorimeter system leads to more accurate measurements of substrate oxidation during dynamic metabolic studies.