Simulated High Altitude Helium-Oxygen Diving.

BACKGROUND: Experience with commercial heliox diving at high altitude is limited. The purpose of this study was to evaluate the effects of acute high-altitude exposure on fitness to dive and the safety of decompression after heliox diving while using U.S. Navy heliox decompression tables with Cross correction. METHOD: Four professional male divers were consecutively decompressed in a hypo- and hyperbaric chamber to altitudes of 3000 m (9842.5 ft), 4000 m (13,123.4 ft), and 5200 m (17,060.4 ft) during the 8-d study. The dive profiles tested were to 30 m (98.4 ft) for 60 min at all three altitudes and, in addition, a dive to 50 m (164 ft) for 60 min at 5200 m altitude. The decompression followed the U.S. Navy heliox decompression table. The safety of decompression was evaluated by precordial Doppler venous gas emboli (VGE) monitoring during the decompression stages and postdive monitoring of the divers for symptoms of decompression sickness (DCS). Effects of altitude exposure were measured as subjective rating and EEG signs of sleepiness and fatigue, clinical symptoms of high altitude disease, and fitness to dive. RESULTS: A total of 24 person-dives were conducted. There were no VGE detected during the decompression and no postdive symptoms of decompression illness. Both the EEG findings and subjective evaluation indicated increased sleepiness and fatigue at 3000 m, 4000 m, and 5200 m, all compared with the sea level baseline. During the diving phase, both the EEG findings and subjective evaluation scores returned to the baseline and the divers successfully completed diving. DISCUSSION: Diving at high altitude with a short acclimatization period appears safe despite divers exhibiting clinical symptoms and EEG signs of impairment by hypoxia at high altitude. Despite a small number of dives, the results of this study indicate that our application of U.S. Navy standard heliox decompression tables with Cross correction is effective and could be used for underwater constructions up to 5200 m altitude, with due caution.Shi L, Zhang Y, Tetsuo K, Shi Z, Fang Y, Denoble PJ, Li Y. Simulated high altitude helium-oxygen diving. Aerosp Med Hum Perform. 2017; 88(12):1088-1093.

[Prevention of Rhodiola-astragalus membranaceus compounds against simulated plateau hypoxia brain injury in rat].

OBJECTIVE: To observe the protective effects of Rhodiola-astragalus membranaceus mixture against brain damage during hypoxia under simulated plateau environment and the mechanisms maybe involved in. METHOD: Adult SD rats were randomly divided into 3 groups, which were normoxic control, simulated plateau hypoxia, and Rhodiola-astragalus membranaceus mixture pretreatment group. Rats in the latter two groups were exposed to simulated 8000 m altitude in a hypobaric chamber for 7 h. Water content, Na+, K(+)-ATPase activity and SOD activity in cerebral tissue, malondialdehyde (MDA) and lactic acid content in cerebral homogenate and serum were measured. RESULT: As compared with control group, cerebral water content was significantly higher in hypoxia group, while it was obviously lower in pretreatment group. MDA contents of hypoxia group both in cerebral homogenate and serum were higher than that of control group, while the pretreatment group they were both decreased obviously. Lactic acid content of hypoxia group in cerebral and in serum increased markedly and decreased drastically in pretreatment group compared to that of hypoxic group. CONCLUSION: Rhodiola-astragalus membranaceus mixture has preventive effects on hypoxic damage induced by simulated plateau environment. This prevention may be related to the antagonistic effect on membrane lipid peroxidation and the inhibition on the accumulation of lactic acid in brain tissue and serum.