Acid-Base Relations Between Spinal Fluid and Arterial Blood With Special Reference to Control of Ventilation

Abstract

Simultaneous determinations of arterial blood and spinal fluid pH, CO₂ tension and bicarbonate concentration have been made in dogs under various experimental conditions. The following results were obtained: a) under control conditions spinal fluid pH is significantly lower than arterial pH; spinal fluid CO₂ tension is significantly higher than arterial CO₂ tension; bicarbonate concentrations are essentially the same in both compartments. b) Ammonium chloride administration produces acidosis in arterial blood and a simultaneous shift of spinal fluid pH in an alkaline direction; sodium bicarbonate administration produces arterial alkalosis and a simultaneous shift of spinal fluid pH in an acid direction. c) These ‘paradoxical ’ shifts of spinal fluid pH are dependent on the fact that the spinal fluid compartment is permeable to CO₂ and that changes in bicarbonate concentration take place slowly. d) Spinal fluid pH is determined by the CO₂ tension of the spinal fluid; at a given moment CO₂ tension is usually related to the level of ventilation. e) The acid-base relations of spinal fluid differ from those of extracellular fluid generally and probably do not reflect the acid-base balance of the respiratory center. Submitted on April 24, 1958