The BOLD-Specific Flow-Volume Relationship During Hypercapnia and Hypocapnia

Jean J. Chen¹, G. Bruce Pike¹

Grubbs power-law (with α =0.38) has been extensively used in fMRI, and the equivalence of this flow-volume relationship observed under neuronal activation and hypercapnia is instrumental in CMRo₂ estimation using calibrated BOLD. However, Grubbs α was based on measurements of total δCBV instead of the BOLD-specific venous δCBV. Moreover, the comparability of the venous flow-volume relationship under focal and CO₂-induced hyperemia has not been established. We used the venous refocusing for volume estimation (VERVE) technique to measure the venous flow-volume relationship in humans under graded hypercapnia and hypocapnia, and found α to be 0.190.04, equivalent to findings for neuronal activation.