Inert gas narcosis in scuba diving, different gases different reactions

PurposeUnderwater divers face several potential neurological hazards when breathing compressed gas mixtures including nitrogen narcosis which can impact diver's safety. Various human studies have clearly demonstrated brain impairment due to nitrogen narcosis in divers at 4 ATA using critical flicker fusion frequency (CFFF) as a cortical performance indicator. However, recently some authors have proposed a probable adaptive phenomenon during repetitive exposure to high nitrogen pressure in rats, where they found a reversal effect on dopamine release.MethodsSixty experienced divers breathing Air, Trimix or Heliox, were studied during an open water dive to a depth of 6 ATA with a square profile testing CFFF measurement before (T-0), during the dive upon arriving at the bottom (6 ATA) (T-1), 20min of bottom time (T-2), and at 5m (1.5 ATA) (T-3).ResultsCFFF results showed a slight increase in alertness and arousal during the deep dive regardless of the gas mixture breathed. The percent change in CFFF values at T-1 and T-2 differed among the three groups being lower in the air group than in the other groups. All CFFF values returned to basal values 5min before the final ascent at 5m (T-3), but the Trimix measurements were still slightly better than those at T-0.ConclusionsOur results highlight that nitrogen and oxygen alone and in combination can produce neuronal excitability or depression in a dose-related response.