Development of xenongas as an inhalational anesthetic.

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1. The effects of xenon and nitrous oxide on pulmonary resistance : Xenon causes an increase in airway resistance due to its high density and viscosity. In normal dpgs, pulmonary resistance breathing 70% xenon, but not 50% xenon, was greater than that with 70% nitrous oxide, 50% nitrous oxide or control gas. In methacholine-treated dogs, however, the pulmonary resistance breathing 50% xenon was not greater than that during 50% nitrous oxide or control. The results suggest that inhalation of high concentrations of xenon increases airway resistance, but only to a modest extent in dogs with normal or bronchoconstricted airways.2. The effects of xenon on cardiovascular system : The effects of 50% xenon on cardiovascular system were examined in comparison with 80% nitrous oxide in dogs with or without pharmacological blockade of the autonomic nervous system (ANSB) during halothane anesthesia. Xenon significantly decreased mean arterial pressure and dp/dt in both dogs with and without ANSB.In dogs with ANSB,however, these depressions with xenon were significantly less than those with nitrous oxide. The results indicate that the direct depressive effect of xenon on cardiovascular system is smaller than that of nitrous oxide.3. The EGG and EMG changes during xenon and nitrous oxide anesthesia in humans : The EEG changes were similar with xenon and nitrous oxide. The attenuation pf alpha wave and slight decrease in frequency of basic rhythm were observed at 0.33 and 0.5 MACs and slow alpha and theta waves at the higher MAC of 0.66 with both anesthetics. An appearance of laughing, which was evaluated with the EMG changes, was observed in 2/7 wiht xenon and 5/7 with nitrous oxide at 0.66 MAC.