Effects of breathing dense gas mixtures on cardiovascular function and EEG rhythms

Gas mixtures containing oxygen and nitrogen or dense inert gases (sulfur hexafluoride, SF6, or argon, Ar) were inhaled by anaesthetized, artificially ventilated rabbits and cats. SF6 and Ar were compared to nitrous oxide (N2O), a dense inert gas well known for its anaesthetic properties. Concentrations in these gases were 50% (SF6) and 60% (Ar or N2O). In cats, there was a significant increase in total lung resistance with SF6 or Ar associated with a slight but significant drop in arterial blood pressure and heart rate (-5% and -10% with SF6 and Ar, respectively), with no change in electrocardiogram activity. N2O induced in some cats a slower electroencephalographic (EEG) pattern constituted by delta waves of higher amplitude, whereas neither SF6 nor Ar changed the EEG rhythms in this species. In the rabbits, the unsteadiness of the EEG rhythms did not make it possible to assess the cortical effects observed with SF6 or N2O.