Validity of oxygen uptake measurements during exercise under moderate hyperoxia.

PURPOSE

The validity of oxygen uptake in hyperoxia (FIO2 = 30%) measured by an automated system (MedGraphics, CPX/D system) was assessed during 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 VO2 for 30 min (sim-test). This trial was repeated nine times in normoxia and nine times in hyperoxia. Ten subjects also performed two submaximal exercises (55% of normoxic VO2max) on a cycle ergometer at the same absolute power in normoxia and in hyperoxia (ex-test).

RESULTS

There was a significant downward drift of the oxygen fraction measurement in hyperoxia (< or = 0.10% for FIO2 and FEO2) during sim-test, but VO2 measurement remained stable in the two conditions. There was also a downward drift of the oxygen fraction measurement in the two conditions (< or = 0.07% for FIO2) during ex-test. VO2 was significantly higher in hyperoxia (+4.6%), and this result was confirmed using a modified Douglas bag method.

CONCLUSIONS

These findings show that the CPX/D system is stable and valid for assessing VO2 in moderate hyperoxia.