Evoked potential and other CNS reactions during a heliox dive to 360 msw

Six divers were compressed to 360 msw on heliox. Visual and cognitive evoked responses were performed repeatedly predive, during the dive, and postdive. The evoked response changes were compared with other neuropsychological and neurophysiological results from the dive. The individual diver analysis revealed normal visual evoked responses (P100) for 5 out of 6 divers. The diver with significant increase in P100-latency had more marked HPNS than the others. On the cognitive evoked responses, the P300-waves were not obtainable at the deepest depths (for 4 out of 6 divers) even if the shorter wave forms were normal. The P300-wave was obtainable at 354 msw and 215 msw for 4 divers, and 3 of them had increase in the P300-latency compared with their predive average. There was a significant correlation between P100 change and the sign-index on the other CNS-tests. In conclusion, valid results on the visual and cognitive evoked responses were obtained at pressure. Mild symptoms and signs of HPNS led to normal visual evoked responses, while more marked effects gave significant increases in the visual evoked latency. The more major changes in cognitive evoked responses at pressure, even on minor HPNS-affected divers, indicated that higher cortical functions are affected at high pressures (greater than 300 msw).