VALIDITY OF OXYGEN-UPTAKE MEASUREMENTS DURING EXERCISE UNDER MODERATEHYPEROXIA

Purpose: The validity of oxygen uptake in hyperoxia (FIO2 = 30%) measu red by an automated system (MedGraphics, CPX/D system) was assessed du ring the simulation of gas exchanges during exercise with a mechanical system and during submaximal exercise by human subjects. Methods: The simulation system reproduced a stable and accurate (V) over dot O-2 f or 30 min (sim-test). This trial was repeated nine times in normoxia a nd nine rimes in hyperoxia. Ten subjects also performed two submaximal exercises (55% of normoxic (V) over dot O-2max) on a cycle ergometer at the same absolute power in normoxia and in hyperoxia (ex-test). Res ults: There was a significant downward drift of the oxygen fraction me asurement in hyperoxia (less than or equal to 0.10% for FIO2 and FEO2) during sim-test, but (V) over dot (O2) measurement remained stable in the two conditions. There was also a downward drift of the oxygen fra ction measurement in the two conditions (less than or equal to 0.07% f or FIO2) during ex-test. (V) over dot (O2) was significantly higher in hyperoxia (+4.6%), and this result was confirmed using a modified Dou glas bag method. Conclusions: These findings show that the CPX/D syste m is stable and valid for assessing (V) over dot (O2) in moderate hype roxia.