Behavior of microflow and local PO2 of the brain cortex during and after direct electrical stimulation. A contribution to the problem of metabolic regulation of microcirculation in the brain.

Microflow was continuously recorded at four sites of the brain cortex (cat) during and after direct electrical stimulation of the brain. In some experiments local oxygen partial pressure (PO2) was additionally measured with a new combined element in the same capillary area where microflow was determined. This simultaneous measurement of both microflow and local PO2 in the tissue enabled us to analyze the kinetics of microflow and its dependence on local PO2 during activation. Microflow increased at all sites measured, in most cases within 1-2 s after the beginning of stimulation, reached the maximum of hyperemia after the end of stimulation and then gradually returned to the initial level within 30 s up to several minutes according to the intensity of the stimulation. The reaction pattern of microflow was uniform. As local PO2 normally did not decrease and did not even show an initial decrease after the onset of stimulation, the hyperemia could not be caused by local hypoxia. On the contrary, local PO2 always increased with the increase of microflow. This PO2 increase is necessary, because the tissue which consumes more oxygen needs higher PO2 gradients to transport the oxygen to the mitochondria.