Reduction in regional cerebral metabolic rate of oxygen during human aging.

To investigate changes in cerebral circulation and oxygen metabolism during aging, regional cerebral blood flow (rCBF), regional oxygen extraction fraction (rOEF), regional cerebral metabolic rate of oxygen (rCMRO2) and regional cerebral blood volume (rCBV) were measured using the 15O labelled gas inhalation technique and a multi-slice positron emission tomograph (PET) in 22 healthy volunteers, aged from 26 to 64 years old. The measurements were performed with subjects at rest, without sensory deprivation. The values of rCBF, rOEF, rCMRO2 and rCBV in more than 40 anatomical structures of the brain were evaluated by studying a large series of scans in each region of interest after the functional PET image had been anatomically identified using x-ray computed tomographic images corresponding to the PET. In mean gray values, only CMRO2 showed significant reduction with age. rCMRO2 significantly decreased with age only in the supratentrium, and much more in the left hemisphere. Especially remarkable was rCMRO2 reduction in the left caudate region. Both CBF and OEF were variable and less age-dependent. It was concluded that CMRO2 could be reflecting healthy brain aging most properly.