New examination of the performance of the MetaMax I metabolic analyser with the Douglas-bag technique

Abstract

Purpose. To examine the performance of the MetaMax® I metabolic analyser of Cortex Biophysik, running a recent version of the software (MetaSoft v. 1.11.05), using the Douglas-bag method as reference. Experiments. First, 182 measurements of the maximal O₂ uptake on school children were analysed both by a former version of the software (MetaMax Analysis) and by a recent version (MetaSoft). In further experiments, seven grown-up subjects of different fitness levels cycled for 5 min at constant powers between 50 and 350 W while the O₂ uptake was measured simultaneously by the MetaMax I and the Douglas-bag method during the last minute of altogether 39 exercises. Results. The calculated maximal O₂ uptake of the 182 school children was on average 3% lower when the data were reanalysed by MetaSoft than when analysed by the former version of the software. There was in addition a 2% variation. In further experiments on grown-up subjects the O₂ uptake reported by the MetaMax I did not differ from that reported by the Douglas-bag system when data for all subjects were pooled, and the random error was 4%. However, the relationships differed slightly between the subjects (p = 0.005), and consequently the random error within each subject was 2–3%. The respiratory exchange ratio (R-value) reported by the MetaMax I differed systematically from that of the control method. However, a reliable R-value could be calculated from the instrument's raw data. Conclusions. Our data suggest that the MetaMax I running MetaSoft reports unbiased values of the O₂ uptake and with moderate random error.

Key Words::

• Douglas-bag technique
• measurement
• metabolic analyser/metabolic cart
• MetaMax I instrument
• MetaSoft
• oxygen consumption/uptake
• pulmonary gas exchange
• respiratory exchange ratio

Acknowledgements

We thank engineer Steinar Messel at the National Institute of Occupational Health for making the connector used to connect the breathing valves and for taking the photos. We are grateful to Sylvi Rørvik who improved the English language in the manuscript.

Ethical standards: The experiments comply with current Norwegian laws on studies on healthy humans.

Declaration of interest: The authors declare that they have no conflict of interest. The authors alone are responsible for the content and writing of the paper.