Abstract
The aim was to examine the drift in the measurements of fractional concentration of oxygen (FO2) and carbon dioxide (FCO2) of a Nafion-using metabolic cart during incremental maximal exercise in 18 young and 12 elderly males, and to propose a way in which the drift can be corrected. The drift was verified by comparing the pre-test calibration values with the immediate post-test verification values of the calibration gases. The system demonstrated an average downscale drift (P < 0.001) in FO2 and FCO2 of −0.18% and −0.05%, respectively. Compared with measured values, corrected average maximal oxygen uptakevalues were 5–6% lower (P < 0.001) whereas corrected maximal respiratory exchange ratio values were 8–9% higher (P < 0.001). The drift was not due to an electronic instability in the analyzers because it was reverted after 20 min of recovery from the end of the exercise. The drift may be related to an incomplete removal of water vapor from the expired gas during transit through the Nafion conducting tube. These data demonstrate the importance of checking FO2 and FCO2 values by regular pre-test calibrations and post-test verifications, and also the importance of correcting a possible shift immediately after exercise.
Highlights
Maximal oxygen uptake (Vo2max) is defined as the highest rate at which oxygen can be taken up and utilized by the body during exercise
One of the main potential sources of error in the calculation of Vo2max using automated systems is related to the stability of FEO2 and FECO2 measurements, because the electronic oxygen (O2) and carbon dioxide (CO2) analyzers are prone to drift over time (Winter, 2012; Gore et al, 2013)
There was no statistical difference (P = 0.08; 95% confidence intervals (CI): −0.00 to 0.01 L) in the registered air volumes between post-test verification (2.99 ± 0.01 L) and pre-test calibration values (2.99 ± 0.01 L)
Summary
Maximal oxygen uptake (Vo2max) is defined as the highest rate at which oxygen can be taken up and utilized by the body during exercise. 4 of these 8 studies reported the average numerical drift values in O2% and CO2% (Wilmore et al, 1976; Armstrong and Costill, 1985; Prieur et al, 1998; Rietjens et al, 2001), which ranged from 0.02 to 0.22% These reported drift values, according to the equations governing gas concentrations (Beaver et al, 1973; Wasserman et al, 1994a), would have caused an error in Vo2max up to 8–9% in standard laboratory conditions (∼20◦C of temperature, ∼40% of relative humidity and ∼720 mmHg of barometric pressure). It is unclear how the drift readings should be adjusted or corrected to overcome the inaccuracy due to the drift (Winter, 2012)
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