The effect of stable xenon on the regional cerebral blood flow (rCBF) was studied in 12 adult cats. Xenon in concentrations 17%, 33%, 50%, and 60% was mixed with oxygen, and inhaled by a semi-closed rebreathing system. Cortical rCBF was continuously measured by a heat clearance probe which had been calibrated using the hydrogen clearance method. Cortical rCBF decreased to 96%, 92%, 88%, and 88% of the control after inhalation of 17%, 33%, 50%, and 60% xenon, respectively, and these decreases in rCBFs were statistically significant (p<0.01, Student's paired t-test) under the high concentrations of xenon of 33% or more. No significant changes were seen in arterial carbon dioxide tension and the mean arterial blood pressure during xenon inhalation, whereas diffuse electroencephalographic slowing was observed during 50% xenon inhalation. The mechanism of the decrease of rCBF by xenon gas remains to be solved. The direct effect of xenon on rCBF should be considered when high concentrations of xenon are used for stable xenon-enhanced computed tomography.
