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

Purpose. To examine the performance of the MetaMax (R) 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 O-2 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 O-2 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 O-2 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 O-2 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 O-2 uptake and with moderate random error.