Comparison of gas exchange measurements with a mouthpiece, face mask, and ventilated canopy.

This study compared gas exchange measurements obtained by using a mask, mouthpiece, and ventilated canopy in 30 normal, healthy volunteers. The ventilated canopy and its gas analyzers had an accuracy for oxygen consumption of 98.0 +/- 0.8% and for carbon dioxide production of 100.1 +/- 1.1%. The study indicates that the apparatus used for gas exchange measurement will significantly affect the measurements. The magnitude of the effect is a significant 7.9% increase for oxygen consumption with a mouthpiece and a significant 7.1% increase with a face mask. Carbon dioxide production was significantly increased 10.2% with a mouthpiece and 4.1% with a face mask. There were no differences in the respiratory quotient. The specific purpose for collecting gas exchange measurements will determine whether these differences are of practical significance.