Comparative assessments of the COSMED adaptive mixing chamber vs. breath-by-breath methods for oxygen uptake measurements in recreationally active adults

Background: Respiratory gas exchange during cardiopulmonary exercise testing (CPET) is commonly measured using either a mixing chamber (MC) or a breath-by-breath (BxB) technique. MC measurements reduce the impact of erratic ventilatory patterns thereby improving the accuracy of oxygen uptake (V̇O 2 ) values, but often lack adequate temporal resolution for ventilatory thresholds (VTs) determination. Accordingly, BxB is preferred when both V̇O 2 and VTs determination are sought simultaneously. Recently, an adaptive MC (aMC) with high temporal resolution was developed. The aims of this study were to examine the concordance of aMC- and BxB-derived gas exchange data, and to determine if the aMC provides adequate temporal resolution for the assessment of VTs. Methods:Fourteen healthy, recreationally active individuals (7 females, 7 males; 23.6 ± 1.4 years; 171.8 ± 9.0 cm; 67.9 ± 11.1 kg) performed a maximal CPET on a treadmill with gas exchanges being measured simultaneously using BxB and aMC techniques. Results: Compared to BxB measurement, V̇O 2 values at peak effort were 5.0 ± 7.8% lower using the aMC (p = 0.0419). Similar bias was observed for V̇O 2 values obtained at submaximal workloads. Noteworthy, the aMC provided adequate temporal resolution to identify VTs among all participants in whom they could be measured with confidence using BxB (n=13/14). Conclusions: The aMC provides consistent and reproducibly lower V̇O 2 values compared to BxB acquisition and provides adequate temporal resolution to determine VTs during incremental effort CPET. This newly developed technology appears to integrate the well-established strengths of both conventional MC and BxB gas exchange measurement techniques.