Assessing the Validity and Reliability of the PNOE¯ for Measuring Cardiometabolic Outcomes During Walking Exercise

Background: The accuracy of measurement of cardiometabolic outcomes in terms of gaseous exchange and energy expenditure of individuals is crucial. The objective of this study was to compare the validity and reliability of the PNOE¯ in measuring cardiometabolic outcomes from the respiratory gaseous exchange of healthy individuals during treadmill walking exercise. Methods: A total of 21 healthy subjects (15 male and 6 female) aged 22.76 ± 3.85 years took part in this study. Oxygen uptake (VO₂), carbon dioxide production (VCO₂), respiratory exchange ratio (RER), metabolic equivalents (METs), tidal volume (VT), and energy expenditure (EE) were measured using the PNOE¯ and COSMED K5 portable systems during a twenty-eight-minute, four-stage incremental protocol, where speed increased from 1.7 mph to 4.2 mph with a 2% incline on a treadmill. Test-retest reliability was tested on separate days with trail repetition. Validity was evaluated by Bland-Altman plots, intraclass correlation coefficients (ICCs) and mean percentage difference. Results: ICCs showed that VCO₂ was in the good range (0.75-0.90). The ICC of the RER from stages 1 to 3 of the incremental protocol and the VT from stages 2 to 4 of the incremental protocol showed good to excellent reliability. No clear trend was seen for VO₂, VCO₂, and EE datapoints with variations in speed. Pearson's correlation coefficients were moderately high (r = 0.60-0.79) between VO₂, VCO₂, RER, METs, VT, and EE measured by the PNOE¯ and K5 systems. All subjects, except for a few cases in VT, were within the upper and lower 95% confidence intervals of the acceptable range of the Bland-Altman plots. Conclusions: The PNOE¯ system is a valid and reliable measure of cardiometabolic outcomes and is comparable to the COSMED K5 system.