Evaluation of the cosmed K2 portable telemetric oxygen uptake analyzer

The purpose of this study was to determine the validity and evaluate the accuracy of a portable telemetric oxygen uptake analyzer (K2). Two experiments were carried out: a) using a mechanical lung, the accuracy of the K2 to measure oxygen fractions and minute ventilation following 10 and 60 min of warm-up was determined; and b) two maximal graded exercise tests (GXT) on 15 subjects, one with the K2 system and the other with a standardized breath-by-breath (BBB) system, while heart rate (HR), minute ventilation (V_E), and oxygen uptake (VO₂) were compared. Following 10-min warm-up prior to calibration, the K2 underestimated the true oxygen fraction as early as 5 min into the test, and this value continued to decrease throughout the 30-min test. After 60 min of warm-up prior to calibration, the K2 accurately measured the true oxygen fraction for the first 15 min; at minute 20, and on to minute 30, the K2 underestimated the oxygen fraction. Ventilation volumes were not affected by warm-up time. Minute ventilation during the K2 GXT was significantly higher than V_E for the BBB test. No significant differences were found between the HRs obtained with the BBB or K2 systems. No differences in VO₂ for any stage of the GXT were identified between the K2 device, BBB device or when a respiratory exchange ratio (RER) correction factor was applied to the K2 derived values. However, the RER correction factor did minimize the VO₂ differences between the BBB and K2 systems. Therefore, we conclude that the K2 accurately measures VO₂ during a GXT; however, its accuracy can be compromised by limitations inherent to the system.