VO2 and VCO2 variabilities through indirect calorimetry instrumentation

Area of Science:

• Physiology
• Metabolic Measurement
• Biomedical Engineering

Background:

• Resting energy expenditure (REE) estimation using indirect calorimetry (IC) exhibits significant inter-individual variability.
• This variability may stem from differences in how metabolic monitors measure oxygen (VO2) and carbon dioxide (VCO2) dynamics.
• Understanding VO2 and VCO2 variabilities is crucial for accurate REE assessment.

Purpose of the Study:

• To investigate and compare the measurement of VO2 and VCO2 variabilities using mixing chamber (MC) and breath-by-breath (BbB) techniques in IC.
• To determine how these variabilities influence REE estimation.
• To identify technological differences between MC and BbB methods in capturing metabolic data.

Main Methods:

• A hybrid calorimeter employing both MC and BbB techniques was used.
• Fifteen volunteers underwent a clino-orthostatic maneuver to induce steady and non-steady physiological states.
• Variances and power spectrum energies (0-0.5 Hz band) of VO2 and VCO2 were measured.

Main Results:

• MC technique showed negligible inter-individual VO2/VCO2 variabilities (as variances).
• BbB technique revealed significant increases in VO2 (71%) and VCO2 (56%) variabilities (as spectral energies, p < 0.05).
• An novel 0.025 Hz cyclic rhythm in VO2/VCO2 was observed during the orthostatic stage.

Conclusions:

• Metabolic monitors should integrate both MC and BbB techniques for accurate REE interpretation, accounting for steady/non-steady state variabilities.
• MC is suitable for average VO2/VCO2 computation (low-pass filter), while BbB excels at measuring variabilities (high-pass filter) for spectral analysis.
• New insights into VO2/VCO2 variabilities explain discrepancies in REE estimates from different IC techniques.