Dynamic changes in cerebral blood flow, O-2 tension, and calculated cerebral metabolic rate of O-2 during functional activation using oxygen phosphorescence quenching

Changes in cerebral blood flow (CBF) using laser-Doppler and microvascular O-2 oxygen tension using oxygen-dependent phosphorescence quenching in the rat somatosensory cortex were obtained during electrical forepaw stimulatio n. The signal-averaged CBF response resulting from electrical forepaw stimu lation consisted of an initial peak (t = 3.1 +/- 0.8 seconds after onset of stimulation), followed by a plateau phase that was maintained throughout t he length of the stimulus. In contrast, microvascular O-2 tension changes w ere delayed, reached a plateau level (t = 23.5 +/- 1.7 seconds after the on set of stimulation) that remained for the length of the stimulus and for se veral seconds after stimulus termination, and then returned to baseline. Us ing Fick's equation and these dynamic measurements, changes in the calculat ed cerebral metabolic rate of oxygen (CMRO2) during functional stimulation were determined. The calculated CMRO2 response initially was comparable wit h the CBF, bur with protracted stimulation, CMRO2 changes were approximatel y one-third that of CBF changes. These results suggest that a complex relat ion exists, with comparable changes in CBF and CMRO2 initially occurring af ter stimulation but excessive changes in CBF compared with CMRO2 arising wi th protracted stimulation.