Examination of the Moxus Modular Metabolic System by the Douglas-bag technique

The purpose of this study was to examine the performance of the Moxus Modular Metabolic System from AEI Technologies, Inc. using the Douglas-bag method as reference. To achieve this, eight moderately trained subjects cycled for 5 min at constant powers from 50 to 300 W in increments of 50 W. The O₂ uptake was measured simultaneously by both systems during the last minute of each stage. The O₂ uptake reported by the Moxus system was 83 ± 78 mL·min⁻¹ higher (mean ± SD; ≈3%, +62 µmol·s⁻¹, P < 0.001) than that reported by the Douglas-bag method; the bias varied by ≈2% between the subjects. The higher O₂ uptake of the Moxus system was a consequence of 1.4% ± 3.0% higher reported ventilation and 2% ± 3% higher reported O₂ extraction per volume of air breathed. The respiratory exchange ratio (R value) reported by the Moxus system rose proportionally to that of the Douglas-bag method and was 1% ± 2% higher for the range examined (0.75-1.10). Repeated tests of the maximal O₂ uptake showed a variability (coefficient of variation) of 2.5%. The study concluded that measurements by the Moxus system showed some bias and residual variation and, in addition, some systematic...