Tissue PO2 was measured in the primary visual cortex of anesthetized, artificially ventilated normovolemic cats to examine tissue oxygenation with respect to depth. The method utilized 1) a chamber designed to maintain cerebrospinal fluid pressure and prevent ambient PO2 from influencing the brain, 2) a microelectrode capable of recording electrical activity as well as local PO2, and 3) recordings primarily during electrode withdrawal from the cortex rather than during penetrations. Local peaks in the PO2 profiles were consistent with the presence of numerous vessels. Excluding the superficial 200 microm of the cortex, in which the ambient PO2 may have influenced tissue PO2, there was a slight decrease (4.9 Torr/mm cortex) in PO2 as a function of depth. After all depths and cats were weighted equally, the average PO2 in six cats was 12.8 Torr, with approximately one-half of the values being

The flash visual evoked potential (F-VEP), elicited by a 100 ms diffuse light flash presented at 2 Hz, was examined in the cat primary visual cortex (Area 17). Intracortical F-VEP depth profiles were recorded to characterize waveform changes with electrode depth. A positive surface component, with a latency of 200 ms, was the dominant waveform feature within the cortex, reversing in polarity and increasing in magnitude as the cortex was penetrated. Other prominent components with latencies of 30, 50, 100, and 125 ms were also observed. Changes in the waveform with stimulus duration and illumination were examined and revealed the sensitivity of prominent components to stimulus parameters.

Tissue PO2 was measured in the primary visual cortex of anesthetized, artificially ventilated, normovolemic cats to evaluate the effect of small doses [1 g perfluorocarbon (PFC)/kg] of a PFC emulsion (1 g PFC/1.1 ml emulsion; Alliance Pharmaceutical, San Diego, CA) on brain oxygenation. The change in tissue PO2 (DeltaPO2), resulting from briefly changing the respiratory gas from room air to 100% oxygen, was measured before and after intravenous infusion of the emulsion. Before emulsion, DeltaPO2 was 51.1 +/- 45.6 Torr (n = 8 cats). Increases in DeltaPO2 of 34.0 +/- 26.1 (SD) % (n = 8) and 16. 3 +/- 8.4% (n = 6) were observed after the first and second emulsion infusions, respectively. The further increase in DeltaPO2 after the third dose (7.9 +/- 10.5%; n = 7) was not statistically significant. The observed increases in tissue oxygenation as a result of the PFC infusions appear to be the result of enhanced oxygen transport to the tissue.