Abstract 63: Age-related Changes In Gray Matter Cerebral Metabolism And Vascular Reactivity In Children

Introduction: Metabolic demand changes throughout childhood as the brain develops, peaking in the 2 nd decade of life. Cerebral blood flow (CBF) is dynamic throughout childhood, likely in response to the increased metabolic demand of brain development. Cerebrovascular reactivity (CVR) reflects the ability to further increase CBF in response to a stimulus, such as carbon dioxide (CO 2 ). We hypothesized that gray matter oxygen metabolism (GM CMRO 2 ) is increased in younger children, corresponding to higher GM CBF and lower GM CVR. Methods: CVR was calculated as the proportional change of a subject’s MRI-measured blood oxygen level dependent signal in response to an increase in end-tidal CO 2 administered by the RespirAct® RA-MR™ device. GM CMRO 2 was calculated voxel-by-voxel as the product of GM CBF (arterial spin labeling), GM oxygen extraction fraction (asymmetric spin echo), and arterial oxygen content (= Hb х (oxygen saturation)х1.34). Univariate relationships were tested using Spearman’s correlation coefficient, and corrected for multiple comparisons. Results: GM CVR, CBF, and CMRO 2 were calculated for 15 healthy participants (ages 8-19, 7 male). GM CMRO 2 was highest in young children and decreased with age (ρ=-0.68, P=0.005), as did CBF (ρ =-0.67, P=0.006). CVR was lower in young children, increasing with age (ρ=0.58, P=0.02). However, while GM CVR correlated with CBF (ρ=-0.64, P=0.01) it did not significantly associate with CMRO 2 (ρ=-0.43, P=0.114). Conclusion: Although GM CMRO 2 and CVR both have age-related changes, CVR does not directly correlate with CMRO 2 . Rather, their relationship may be moderated through other influences on CBF, as further study will investigate. Figure: Linear fits and 95% confidence intervals of subject data, including age, GM CBF, and GM CMRO 2 , versus GM CVR. P-values are from Spearman’s test for monotonic correlation.