Summary
The extracellular hydrogen ion concentration of the brain cannot be determined by direct measurement. For experiments, in which the composition of the cerebrospinal fluid is varied independently of the composition of the blood, a mathematical model is proposed which allows approximate calculation of the extracellular pH from acid-base parameters of the blood and the cerebrospinal fluid. The model is based on former investigations regarding the diffusion of CO2 and bicarbonate in brain tissue. Cerebral blood flow is considered as a function of the arterial CO2 tension. For simplification homogenous perfusion has been assumed. The theoretical model is valid for stationary conditions only. Solutions of the model indicate that under the conditions specified above the extracellular pH is a function of the distance from the brain surface. The cerebrospinal fluid composition influences the extracellular hydrogen ion concentration not farther than 400–500 μm below the surface. It has been concluded that structures reacting to variations of the hydrogen ion concentration in the cerebrospinal fluid must be located within this distance from the surface. The central chemoreceptors of the respiratory system which in the cat respond to changes in cerebrospinal fluid pH locally limited to the ventral surface of the medulla, are thus very probably not identical with the medullary respiratory centres which have to be assumed as being located at a greater depth.
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Berndt, J., Berger, W. & Mückenhoff, K. Untersuchungen zum zentralen chemosensiblen Mechanismus der Atmung. Pflugers Arch. 332, 127–145 (1972). https://doi.org/10.1007/BF00589089
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DOI: https://doi.org/10.1007/BF00589089