Cooperation of peripheral and central chemosensitive mechanisms in the control of the extracellular pH in brain in non-respiratory acidosis.

The mathematical model of the respiratory control system in man of Middendorf and Loeschcke (1976 a, b) opens the possibility to stimulate the constellation of parameters in non-respiratory acidosis. Several investigators agree that the pH in CSF or in the extracellular fluid of the brain stays remarkably constant in this situation and it can be shown that this is a result of a precise control rather than the consequence of a sluggishly reacting system. Application of the model assuming constant extracellular brain pH allowed to calculate the relative sensitivities to pH changes of the central and the peripheral sensory mechanisms generating respiratory drive. Assuming air breathing and a normal critical arterial O2-pressure and otherwise normal parameters of respiration, circulation and blood composition (except diminished buffer base) the central chemosensitivity to a pH change turned out to be 25 times the peripheral. This factor is critically dependent on the ratio of the bicarbonate change in extracellular brain fluid to that in arterial blood. The coinciding data of Fencl (1971) and of Kronenberg and Cain (1968) were used for the calculation.