Analysis of reproducibility of the 133xenon inhalation method, 1

The reproducibility of the values of cerebral blood flow (CBF) was measured by the 133Xe inhalation method. Two measurements of regional CBF were made at 13 locations in each hemisphere in 19 subjects with an age range of 19 to 83 years (mean age 51), with an interval of 10 to 70 minutes. The blood flow of the fast compartment (gray matter) of the brain (F1) was calculated as well as the initial slope index (ISI), the relative weight (W1) and the fractional flow (FF1) of the fast compartment. The mean value of hemispheric F1 of the second measurement was significantly smaller (-7.6 ml) than that of the first measurement (79.3 +- 18.4 ml per 100 gm brain per minute). The mean value of ISI of the second measurement was also significantly smaller (-5.7) than that of the first measurement (57.3 +- 13.8). This decrease of the mean hemispheric F1 or ISI was especially large in young subjects or subjects with high flow values. There was actually no difference of W1 and FF1 between the two measurements. There was no significant difference in PaCO2 or mean arterial blood pressure in the serial measurements. The reasons why F1 and ISI decreased are discussed. The values of variation coefficient (V.C.) of the change of mean hemispheric value from the first to the second measurement were 7.6% (F1), 13.9% (ISI), 4.1% (FF1), and 6.4% (W1). The V.C. of the changes of regional values were 13.8% (F1), 14.6% (ISI), 5.4% (FF1), and 9.3% (W1). The intermeasurement correlation coefficients of mean hemispheric F1 and ISI were 0.95 and 0.85, respectively. Analysis of the intermeasurement correlations of regional F1 and ISI also revealed significant correlations, though the degrees of correlation (F1 0.82, ISI 0.78) were less than those of the mean hemispheric values. (J.P.N.)