ISSN:
1432-2013
Keywords:
Brain cortex
;
Blood-free perfusion
;
$$P_{O_2 }$$ needle electrodes
;
Oxygen supply
;
Hypothermia
;
$$P_{O_2 }$$ histogram of brain tissue
;
$$P_{O_2 }$$ histogram of pial surface
;
Mean local tissue $$P_{O_2 }$$
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract The O2 supply of the blood-free perfused brain cortex of the guinea pig was investigated by measuring polarographically the local distribution of tissue $$P_{O_2 }$$ at 18°C, 24°C, and 37°C. The perfusion was performed in situ, using a medium equilibrated by a gas mixture of 95% O2 and 5% CO2. Papaverine was added to prevent vasoconstriction during hypothermia. To avoid measuring artefacts thin micro electrodes with a small sharpened tip of ca. 4 μm in diameter were used and a special puncturing technique was applied. The experimental results indicate the presence of a large variation of local tissue $$P_{O_2 }$$ . Local mean $$P_{O_2 }$$ increased up to a depth of 1000 μm, reached a plateau, and then decreased towards 3000 μm. This demonstrates that the O2 supply changes in dependence of the distance of the brain surface. This may partly becaused by the special vascularization pattern of the brain cortex. As it follows from the $$P_{O_2 }$$ histograms, at 24°C the tissue layer between 0–2000 μm (layer I) was well supplied with oxygen, whereas at the same time the layer between 2001–3000 μm (layer II) was hypoxic. At 37°C, both layers were hypoxic, but layer III showed the more pronounced tissue hypoxia. To obtain a sufficient oxygen supply the temperature had to be reduced below 24°C to sufficiently decrease tissue O2 consumption: at 18°C, there was no sign of hypoxia any more. In comparison with the $$P_{O_2 }$$ histogram of the tissue the $$P_{O_2 }$$ histogram of the pial surface was shifted to higher $$P_{O_2 }$$ values. The experiments show that in the blood-free perfused guinea-pig brain the $$P_{O_2 }$$ histogram of the surface or of the upper tissue layer were not representative for the deeper layers. This has to be taken into account, when comparing results of tissue $$P_{O_2 }$$ measurements with results of biochemical or photometric brain tissue investigations.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00580968
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