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

Abstract

PH and K⁺ from the extracellular space, PO₂, 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. PO₂ fell rapidly to 30% of control levels at regional CBF (rCBF) of 30 ml 100 g⁻¹ min⁻¹. As CBF was further reduced, PO₂ 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.