Extracellular pH in the Brain and Cerebral Blood Flow

Abstract

The present paper consists of two parts. In the first part, the regulation of extracellular pH in respiratory and non respiratory acid-base changes will be reviewed and related to known data on cerebral blood flow. In the second part, preliminary experiments will be reported which for the first time directly establishes the dependence of CBF upon extracellular pH. During the first minutes of an acute hypercapnia the increased COz tension will be associated with increased concentrations of COz, H2CO3 and H+, but not of HCO3- since the CSF lacks efficient buffers against COz. Due to the low buffer capacity a given increase in pCOz will give a relatively large decrease in pH. In sustained hypercapnia, however, pH is slowly regulated toward intermediate values due to a slow increase in the bicarbonate concentration. The facts indicate that there is a parallelism between extracellular H+ and CBF. The experiments have so far unequivocally shown that CBF varies directly with the extracellular H+ at constant CO2 tension. These findings, which will be reported in full elsewhere, have corroborated the unique importance of CSF for the homoeostasis of the brain and ought to stimulate to an even more intense study of the CSF composition in neurology and neurosurgery.