Sodium valproate interactions with the HPNS: EEG and behavioral observations.

A new baboon model was used to investigate the therapuetic effect of sodium valproate on the high pressure neurologic syndrome (HPNS). A hyperbaric chamber was used to achieve environmental pressures of 61 ATA, over a 5-h period. Eight animals underwent two compressions, a control and a valproate-treated compression (half the animals had valproate on the first compression). Mild signs of HPNS (e.g., paw and limb tremor) were first observed at approximately 20 ATA. More severe signs (e.g., whole body tremor, myoclonus, and vomiting) were observed above 40 ATA. Sodium valproate was administered during the compression phase and for 2 wk previously. It was effective at the higher pressures above 41 ATA in reducing the severity of the signs of HPNS. The major effect of pressure on the EEG was to increase alpha and theta wave amplitude in a linear manner. Alpha wave amplitude was reduced by sodium valproate.