Critical appraisal of cerebral blood flow measured from brain stem and cerebellar regions after 133 Xe inhalation in humans.

Validity of regional blood flow (rCBF) measurements recorded over the human posterior fossa after 133Xe inhalation was tested. Recording of counts from both brain stem and cerebellum (BSC) was reproducible and contamination by counts derived from surrounding anatomical structures was low and no greater than that found over hemispheres. BSC values were F1 = 99 +/- 19 ml/100g brain/min, F2 = 17 +/- 4 in reasonable agreement with data reported from experimental animals. BSC flow values showed significant correlation with the state of awareness as judged by clinical and EEG evaluation with lowest F1 values in semicoma and step increases in stupor, non-REM sleep, drowsiness, rest, activation, REM sleep and highest values during focal and generalized epileptic seizures.