Multiparameter monitoring of the awake brain under hyperbaric oxygenation

To elucidate the mechanism of brain toxicity developed under hyperbaric oxygenation, a multiparameter monitoring approach was adopted. In the awake brain exposed to hyperbaric conditions we were able to measure the following parameters continuously and simultaneously: 1) tissue O₂ partial pressure (P(O₂)) and intramitochondrial NADH redox state for energy metabolism evaluation, 2) extracellular K⁺ activity for the evaluation of the functional state of cellular membranes, 3) electrocorticography (ECoG) and DC steady potential as electrical signals, 4) brain surface temperature in correlation with core temperature. The typical results obtained under hyperbaric oxygenation presented in the paper were analyzed and divided into three periods, i.e., preconvulsive, convulsive, and the postconvulsive. The main events occurring during the preconvulsive stage are activation of the ECoG, oxidation of NADH, and a small increase in extracellular K⁺. During the convulsive period tonic-clonic seizures were accompanied by waves of spreading depression, as identified by the various parameters monitored. During this phase, the high extracellular K⁺ was pumped back into the cells indicating that the ATPase system was activated rather than inhibited. During the postconvulsive period, cessation of respiration led to a decrease in P(O₂) and in available energy, resulting in an increase in extracellular K⁺ and in a general depolarization.