Heterogeneity and Stability of Local PO2 Distribution within the Brain Tissue
Heterogeneity of tissue pO2 is a necessary consequence of the fact that in order to supply living tissue with O2, molecular oxygen has to be transported from the arterial blood to the intracellularly situated mitochondria. The O2 delivery of the blood towards the tissue and the diffusional O2 transport within the tissue produce an oxygen pressure field the heterogeneity of which characterizes quantitatively the tissue O2 supply. On the basis of theoretical analyses it could be predicted1,2 that for monitoring this heterogeneity small pO2 sensors having diameters of only a few microns would be necessary. In 1948 using small needle-shaped pO2 electrodes as developed by Davies and Brink3 Rémond could measure directly such pO2, profiles between two adjacent small vessels on the brain surface4,5. In a footnote6 it was reported that G. Millikan suggested to use this electrode for intracerebral measurements. Distributions of parameters can be quantitatively presented by a frequency histogram. To our knowlegde Jamieson and van den Brenk7 were the first who used in 1963 pO2 frequency histograms of different organs (included brain tissue) to characterize tissue O2 supply. pO2 histograms are now widely used to describe the O2 supply of the brain under normal and pathological conditions8, but it is still difficult to decide by which means a histogram is measurable which can be considered as representative for the tissue O2 supply. To answer this question a set of pO2 profiles were measured under steady state conditions puncturing the brain cortex with small needle electrodes. It was found that there is a strong local heterogeneity which can be quite different in different punctures, but that by increasing the number of punctures it is possible to obtain a pO2 histogram by which the O2 supply of the brain tissue is characterized.
KeywordsBrain Cortex Frequency Histogram Cumulative Histogram Single Puncture Torr Oxygen
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