Reversal of oxygen difference between arterial blood and cerebrospinal fluid in the rabbit

The experiments were carried out in rabbits under general anaesthesia with muscle relaxation and artificial ventilation with atmospheric air. Samples of arterial blood and cerebrospinal fluid were obtained. Of particular interest was reversal of the oxygen gradient, that is PaO2 less than PCSFO2 at arterial blood hypoxia below 65 Torr. The animals were given then acetazolamide intravenously which was followed by acidification and increased partial oxygen pressure in the arterial blood. At the same time the oxygen gradient between the arterial blood and cerebrospinal fluid (CSF) practically disappeared. Administration of a hypoxic breathing mixture reversed again the oxygen gradient. It is worth stressing that the pH of the arterial blood showed no statistically significant fall. In view of this it is postulated that Bohr's effect is not responsible for the reversal of the oxygen gradient although it has been suggested by Jankowska and Grieb [13]. We put forward the hypothesis that the rate of oxygen passage on the arterial side of the blood-brain barrier is not identical in both directions, and its passage from the blood into the CSF decreases with increasing arterial hypoxia. This mechanism of "oxygen trap" may be the cause of reversal of the oxygen gradient between the arterial blood and CSF in hypoxia.