Changes in Cerebral Arterial, Tissue and Venous Oxygenation with Evoked Neural Stimulation: Implications for Hemoglobin-Based Functional Neuroimaging

Abstract

Little is known regarding the changes in blood oxygen tension (PO2) with changes in brain function. This work aimed to measure the blood PO2 in surface arteries and veins as well as tissue with evoked somato-sensory stimulation in the anesthetized rat. Electrical stimulation of the forepaw induced average increases in blood flow of 44% as well as increases in the tissue PO2 of 28%. More importantly, increases in PO2 throughout pial arteries (resting diameters=59 to 129 μm) and pial veins (resting diameters=62 to 361 μm) were observed. The largest increases in vascular PO2 were observed in the small veins (from 33 to 40 mm Hg) and small arteries (from 78 to 88 mm Hg). The changes in oxygen saturation (SO2) were calculated and the largest increases were observed in small veins (Δ=+11%) while its increase in small arteries was small (Δ=+4%). The average diameter of arterial vessels was observed to increase by 4 to 6% while that of veins was not observed to change with evoked stimulation. These findings show that the increases in arterial PO2 contribute to the hyper-oxygenation of tissue and, mostly likely, also to the signal changes in hemoglobin-based functional imaging methods (e.g. BOLD fMRI).