Reliability of gas exchange measurements from two different spiroergometry systems

Reliability of two different spiroergometric systems was investigated by comparing gas exchange measurements from two consecutive identical bicycle ergometer ramp exercise tests which were conducted after an initial habituation trial. Twenty-three healthy subjects (age: 25 +/- 5 years; weight: 71 +/- 10 kg; peak oxygen uptake: 55 +/- 9 ml x min(-1) x kg(-1)) took part in the study. One apparatus was a portable mixing chamber system (MetaMax I, Cortex, Leipzig, Germany), the other one a stationary spiroergometric device measuring in the breath-by-breath mode (MetaLyzer 3B, Cortex). There were no relevant systematic changes in gas exchange measurements and heart rate from test 1 to test 2. Intra-class reliability coefficients were 0.984 (oxygen uptake = VO2), 0.977 (carbon dioxide Output = VCO2), and 0.973 (minute ventilation = V-E) for the MetaMax I, and 0.969 (VO2), 0.964 (VCO2), and 0.953 (V-E) for the MetaLyzer 3B. Bland-Altman plots revealed a slightly smaller variability of MetaLyzer 3B measurements compared to those of MetaMax I. It is concluded that the spiroergometric devices MetaMax I and MetaLyzer 3B represent reliable instruments for exercise testing in sports medical routine and research. This is important to decide if longitudinal changes in gas exchange measurements represent clinically meaningful differences in performance or merely inconsistencies of the measuring tool.