ORIGINAL ARTICLE Inter-unit variability in two ParvoMedics TrueOne 2400 automated metabolic gas analysis systems

Abstract Knowing the inter-unit variability, especially the technological error, is important when using many physiological measurement systems, yet no such inter-unit analysis has been undertaken on duplicate automated gas analysis systems. This study investigated the inter-unit performance of two identical ParvoMedics TrueOne 2400 automated gas analysis systems during a range of sub-maximal steady-state exercises performed on an electro-magnetic cycle ergometer. Fifteen adult males were tested on two separate days a rest, 30, 60, 90, and 120 Watts with the duplicate gas analysis units arranged (1) collaterally (2 min of steady-state expired gas was alternately passed through each system), and (2) simultaneously (identical steady-state expired gas was passed simultaneously through both systems). Total within-subject variation (biologi-cal? technological) was determined from the collateral tests, but the unique inter-unit variability (technological error between identical systems) was shown by the simul-taneous tests. Absolute percentage errors (APE), coefficient of variations (CV), effect sizes and Bland–Altman analyses were undertaken on the metabolic data, including expired ventilation (VE), oxygen consumption (VO2) and carbon dioxide production (VCO2). The few statistically significant differences detected between the two duplicate systems were determined to have small or trivial effect sizes, and their magnitudes to be of little physiological importance. The total within-subject variations for VO2, VCO2 and VE each equated to a mean CV and mean APE value of*4 and *6 %, whilst the respective inter-unit technological errors equated to *1.5 and *2.1 %. The two ParvoMedics TrueOne 2400 systems demonstrated excellent inter-unit agreement