Cerebral hemodynamic response to acute
hyperoxia was investigated in awake mice. Using
laser-Doppler flowmetry (LDF), baseline cerebral blood flow (CBF) and the cerebrovascular responses to whisker stimulation were measured in awake mice during normoxia and
hyperoxia. Using two-photon
laser scanning microscopy (TPLSM), the changes in cortical microvasculature were measured during normoxia and
hyperoxia. During
hyperoxia (PaO2=482.3±19.7mmHg), baseline CBF was 6.8% lower than normoxia (PaO2=97.3±6.0mmHg). The degree of increase in CBF evoked by whisker stimulation was greater during
hyperoxia (18.1±5.0%) than normoxia (13.1±3.5%) (P<0.05). TPLSM imaging of the somatosensory cortex showed vasconstriction in arterioles and capillaries during
hyperoxia. Since the effective diffusivity for
oxygen in the capillary bed might decrease by
hyperoxia due to a decrease in capillary blood volume according to Hyder׳s model, an increase in the cerebral metabolic rate of
oxygen utilization by neural activation during
hyperoxia might need a greater increase in CBF as compared with normoxia. The hemodynamic response to neural activation could be modified by acute
hyperoxia due to modification of the relation between changes in CBF and oxygen consumption by neural activation.