Hyperbaric stress in divers and non-divers: neuroendocrine and psychomotor responses

This study compared neuroendocrine and psychomotor responses in divers (D, n = 11) and non-divers (ND, n = 9) following 30-minute hyperbaric and decompression stress to 180, 300 and 450 kPa. Venous blood was drawn pre-dive and at 20 and 60 minutes post-dive and analyzed for norepinephrine (NE), epinephrine (E), tryptophan (TRP), cortisol (COR), growth hormone (GH), adrenocorticotrophic hormone (ACTH) and prolactin (PRL). Reaction time was assessed using a psychomotor vigilance task. There was no difference between groups, across time or among levels of hyperbaric stress, for NE, E, TRP or GH. Small decreases over time in COR were noted. ACTH was significantly higher for ND at 20 minutes following 180 kPa and after 60 minutes for 450 kPa exposure. PRL increased significantly more for ND, and changes from baseline following 450 kPa exposure were moderately related (r = 0.52) to the significant slowing of reaction time at 20 minutes (296 +/- 55 msec) and 60 minutes (277 +/- 35 msec) compared with baseline (247 +/- 22 msec), although PRL returned to baseline levels faster than reaction time. It was concluded that for the stress hormones measured, PRL may provide some indication of the adaptation involved with repeated hyperbaric stress, but its relationship to changes in reaction time was weak.