A Study of the Arterial Clearance of Xenon 133 in Man.

Arterial xenon 133 concentrations have been measured after inhalation of the isotope in anaesthetized and conscious human patients. The anaesthetized patients were ventilated by either a mechanical or a manual method. The arterial concentration of xenon 133 was compared with the pulmonary radioactivity measured by external scintillation counting during clearance of the gas. The rates of arterial clearance of xenon 133 were expressed as the length of time taken to fall to 10 per cent of the original level of radioactivity. In the control group this value was 3.5 minutes. Pulmonary external scintillation counting did not reflect the concentration of arterial xenon 133 accurately. The significance of these findings was discussed with particular reference to the determination of cerebral blood flow.