pH, K+, and PO2 of the Extracellular Space during Ischaemia of Primate Cerebral Cortex

pH and K + from the extracellular space, PO 2 , and CBF have been measured in the same region during progressive ischaemia of primate cerebral cortex. As blood flow was reduced, the other changes had the following sequence. PO 2 fell rapidly to 30% of control levels at regional CBF (rCBF) of 30 ml 100 g −1 min −1 . As CBF was further reduced, PO 2 continued to fall. pH remained stable until around 20 ml 100 g −1 min −1 , below which pH fell rapidly, with an exponential increase in H + concentration. K + showed the well-known relationship to CBF, remaining normal until around 10 ml 100 g −1 min −1 , below which K + rose rapidly. pH e and log K + were linearly related and confirmed that pH fell by 0.3 U before K + rose significantly, and fell by 0.6 U before the massive rise in K + . The mechanisms involved in this sequence of events and the role of pH changes in the development of the so-called “ischaemic penumbra” are discussed.