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Brain blood flow and mean transit time as related to aging.

Brain blood flow and mean transit time were measured in 41 normotensive control subjects aged from 21 to 76 years by using the intravenous 131I-RISA external counting method. The results showed a significant prolongation of mean transit time and a tendency to increase in brain blood volume relating to advancing age but no change in the blood flow. This indicates that prolonged transit time in the aged is probably due to the increased brain blood volume.