Spontaneous Fluctuations of PO₂ in the Rabbit Somatosensory Cortex

Abstract

In many tissues, PO₂ fluctuates spontaneously with amplitudes of a few mmHg. Here we further characterized these oscillations. PO₂ recordings were made from the whisker barrel cortex of six rabbits with acutely or chronically placed polarographic electrodes. Measurements were made while rabbits were awake and while anesthetized with isoflurane, during air breathing, and during 100 % oxygen inspiration. In awake rabbits, 90 % of the power was between 0 and 20 cycles per minute (cpm), not uniformly distributed over this range, but with a peak frequently near 10 cpm. This was much slower than heart or respiratory rhythms and is similar to the frequency content observed in other tissues. During hyperoxia, total power was higher than during air-breathing, and the dominant frequencies tended to shift toward lower values (0–10 cpm). These observations suggest that at least the lower frequency fluctuations represent efforts by the circulation to regulate local PO₂. There were no consistent changes in total power during 0.5 or 1.5 % isoflurane anesthesia, but the power shifted to lower frequencies. Thus, both hyperoxia and anesthesia cause characteristic, but distinct, changes in spontaneous fluctuations. These PO₂ fluctuations may be caused by vasomotion, but other factors cannot be ruled out.