during in vitro gas flow studies ( helium ; oxygen ; helium/oxygen mixtures ; or 70 % nitrous oxide/30 % oxygen with 0 , 1 , 2 , or 3 % isoflurane ) , air boluses ( 0.01 to 5.0 ml ) were injected into a gas flow circuit and outlet nitrogen levels were measured by a collins 21232 emission spectrometer .
C0018880
helium
C1875235
helium/oxygen