Sex Differences and Age-Related Decline in Absolute Cerebral Metabolic Rate of Oxygen (CMRO2) Consumption

Motivation: Resting CMRO2 is a marker of brain health that may inform typical and pathological brain aging. However, there is conflicting literature describing how CMRO2 changes across the lifespan, which may be influenced by extraneous variables such as sex and end-tidal partial pressure of carbon dioxide (PETCO2). Goal(s): This study aimed to evaluate CMRO2 changes across the lifespan, after considering these possible confounding variables. Approach: Dual-calibrated BOLD fMRI quantified grey matter absolute CMRO2 in 83 participants. Results: Sex and age significantly predicted CMRO2. Females had higher CMRO2 than males, and CMRO2 decreased with increasing age for females. Impact: Grey matter CMRO2 decreases in normal healthy aging. Considering both sexes, the CMRO2 decline rate was -0.88 per year, after accounting for PETCO2 and sex. When males and females were analysed separately, females only showed a significant decline with age.