Regional cerebral blood flow measured by 133Xe inhalation in tracheostomized and laryngectomized men and women.

The question of contamination of cerebral clearance curves utilized for measuring regional cerebral blood flow by radioactivity derived from the nasopharyngeal air passages following inhalation of 133Xe was tested in patients with chronic tracheostomy. The peak counts for head curves were 5--9% higher when 133Xe was inhaled via a face mask than when inhaled via the tracheal stoma. Calculated flow values using standard recommended start-fit-times were not significantly different between these two different methods. Present results indicate that neither overestimation of fast flow values due to contamination from rapid 133Xe washout recorded from the air passages nor the underestimation of slow flow due to contamination from 133Xe trapped in the air sinuses produced significant measurement errors. However, if earlier start-fit-times were used, flow values were artificially high, particularly for brain stem/cerebellar probes because of an initial rapid decline in the head desaturation curves due to an arterial peak believed to be derived from the basilar artery.