Changing topographic patterns of human cerebral blood flow with age measured by xenon CT.

Changes in cerebral blood flow with age have been of long-standing interest. A study of 20 normal, healthy, right-handed volunteers 20-100 years old using a noninvasive method is reported. Local cerebral blood flow (LCBF) and partition coefficients (L lambda) were measured during inhalation of 35% stable xenon gas and serial computed tomographic (CT) scanning (CT-CBF). Throughout CT-CBF measurements, subjects lay comfortably at rest, with eyes closed and ears unplugged. Environmental stimulation was limited to ambient light and only those sounds unavoidable during CT scanning. LCBF values were correlated with advancing age by cross-sectional analysis. Relatively higher LCBF values were measured bilaterally in the cortex of occipital and frontal lobes; no significant differences were noted between left and right hemispheres. Significant age-related declines in LCBF values were observed for all cortical and subcortical gray and white matter regions of interest examined (p less than 0.001 for all three regions). Age-related declines were steepest in the cortex of the frontal lobes, particularly prefrontal cortex, caudate, putamen, and lentiform nuclei. Speech and visual cortical regions, functionally active throughout the normal life span, showed less age-related decline compared with all other regions, particularly prefrontal. So-called "hyperfrontality," ratio of mean flow values for frontal cortex to mean pooled values for total cortex, became progressively reduced with age (p less than 0.01).