Cognitive and emotional changes during a simulated 686-m deep dive.

Three experienced divers were subjected simultaneously to world record hyperbaric pressures using an oxygen-helium-10% nitrogen breathing mixture. The simulated depth reached by these divers was 686 m (2250 ft). Cognitive and emotional state measures were obtained predive, during compression, decompression, and postdive. Although the divers showed no overt signs of nitrogen narcosis or HPNS, declines in memory, adaptive, and spatial functions were seen at 670 m. These performance deficits were reversed when the divers returned to surface pressures. The observed declines in performance are discussed in light of their implications for future dives.