Oxygenation of the cat primary visual cortex

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 μm 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 ≤10 Torr. The kurtosis of the PO₂ histogram, with all depths and cats weighted equally, was 3.61, and the skewness was 1.70.