Simultaneous measurements of brain tissue pO2 and cerebral blood flow during functional stimulation

Simultaneous partial pressure of tissue oxygen (pO(2)) and laser Doppler (LD) flowmetry measurements of cerebral blood flow (CBF) were obtained from the rat somatosensory cortex during periodic electrical forepaw stimulation of either 1-min or 4-s duration. For both stimulus durations, a transient significant decrease or "initial dip" in tissue pO(2) preceded blood flow changes, followed by a peak in blood flow and an overshoot in tissue pO(2). A sustained poststimulus undershoot in tissue pO(2) was observed only for the 1-min stimulus. The magnitude of this poststimulus tissue pO(2) decrease was significantly greater than the "initial dip" observed after stimulus onset, suggesting that relative tissue hypoxia alone does not mediate blood flow changes observed with functional stimulation. Our results suggest a complex dynamic relationship between oxygen utilization and blood flow exists during functional stimulation. (C) 2002 Elsevier Science B.V. All rights reserved.