Temporal dynamics of the partial pressure of brain tissue oxygen during functional forepaw stimulation in rats

The partial pressure of tissue oxygen (pO₂) was measured in rat somatosensory cortex during periodic electrical forepaw stimulation of either 1 min or 4 s in duration, and correlated with simultaneous laser Doppler flowmetry. For both stimulus durations, a transient decrease in tissue pO₂ preceded blood flow changes, followed by a peak in blood flow and an overshoot in tissue pO₂. With protracted stimulation, tissue pO₂ remained only slightly above pre-stimulus baseline, while blood flow was maintained at a reduced plateau phase. A sustained post-stimulus undershoot in tissue pO₂ was observed only for the 1 min stimulus. These findings suggest a complex dynamic relationship between oxygen utilization and blood flow.