Regulation of local tissue PO2 of the brain cortex at different arterial O2 pressures.

Local tissue oxygen pressure (PO2) was recorded with a platinum multiwire surface electrode at adjacent sites of the cat cortex under steady-state conditions and with different arterial oxygen supply. Simultaneously PO2 in the sinus sagittalis was continuously recorded through the vascular wall in some experiments. Under normoxic and steady-state conditions local PO2 values varied between 0 Torr and almost arterial levels of 90 Torr. This was in accordance with the assumption of a diffusive transport of oxygen in tissue. With increased arterial oxygen supply local tissue PO2 reacted quite differently at adjacent sites. Linear increases in local tissue PO2 as compared to arterial PO2 as well as constant levels, very small increases and even small decreases were recorded. Constancy or small changes, respectively, of local PO2 (= local PO2 regulation) may be caused by changes in microflow, but changes in oxygen consumption cannot be excluded completely. The regulation of local PO2 could be abolished by adding CO2 to the gas mixture or by producing tissue anoxia. With severely reduced arterial oxygen supply local tissue PO2 dropped down to hypoxic or anoxic levels at all sites measured.