Regional cerebral blood flow and oxygen consumption in human aging.

The oxygen-15 continuous inhalation technique and PET were used to study the age-related changes in regional CBF and CMRO2. Twenty-seven patients, aged 19 to 76 years, free of any history of cerebral disease and vascular risk factors were examined in "resting state." CBF, CMRO2 and oxygen extraction fraction (OEF) values were calculated in seven different brain structures as well as in mean gray matter. Left-right ratios were also computed for all symmetrical structures analyzed. Mean gray CBF, but not mean gray CMRO2, decreased linearly with age (p less than 0.02). However, when younger subjects (less than or equal to 50 yrs) were compared to older subjects (greater than 50 yrs), an age-related matched decrease in CBF and CMRO2 was observed in mean gray matter (18% and 17%, p less than 0.05) and in all gray matter regions analyzed, particularly in frontal, temporo-sylvian and parieto-occipital cortex. White matter CBF and CMRO2 remained remarkably stable with advancing age. Although the possibility of methodological artifacts was considered, we favor progressive loss of cortical neurones and/or diminished activity of those remaining to explain our findings. In addition, age-related changes in cognitive activities might also be involved.