Vol.:(0123456789) 1 3 European Journal of Applied Physiology https://doi.org/10.1007/s00421-018-4020-y ORIGINAL ARTICLE Inert gas narcosis in scuba diving, diferent gases diferent reactions Monica Rocco 1  · P. Pelaia 2  · P. Di Benedetto 3  · G. Conte 4  · L. Maggi 5  · S. Fiorelli 1  · M. Mercieri 1  · C. Balestra 6  · R. A. De Blasi 1  on behalf of ROAD Project Investigators Received: 18 May 2018 / Accepted: 13 October 2018 © Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract Purpose Underwater 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 ficker 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 efect on dopamine release. Methods Sixty experienced divers breathing Air, Trimix or Heliox, were studied during an open water dive to a depth of 6 ATA with a square profle testing CFFF measurement before (T 0 ), during the dive upon arriving at the bottom (6 ATA) (T 1 ), 20 min of bottom time (T 2 ), and at 5 m (1.5 ATA) (T 3 ). Results CFFF 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 difered among the three groups being lower in the air group than in the other groups. All CFFF values returned to basal values 5 min before the fnal ascent at 5 m (T 3 ), but the Trimix measurements were still slightly better than those at T 0 . Conclusions Our results highlight that nitrogen and oxygen alone and in combination can produce neuronal excitability or depression in a dose-related response. Keywords Nitrogen narcosis · Divers’ safety · Critical ficker fusion frequency · GABA receptors Abbreviations ATA Atmospheres of pressure absolute 1 ATA = 1.01325 bar, 760 mmHg, 10 m H 2 O CFFF Critical ficker fusion frequency DCS Decompression sickness EAN Enriched air nitrox GABA receptors Gamma aminobutyric acid receptors HELIOX Helium and oxygen HPNS High pressure nervous syndrome TRIMIX Mixture of nitrogen, helium and oxygen Communicated by Jean-René Lacour. The members of the ROAD Project Investigators are mentioned in Acknowledgments section. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00421-018-4020-y) contains supplementary material, which is available to authorized users. * Monica Rocco monica.rocco@uniroma1.it 1 Department of Surgical and Medical Science and Translational Medicine, Anesthesia and Intensive Care, Sapienza University, Rome, Italy 2 Department of Biomedical Sciences and Public Health, Anesthesia and Intensive Care, Università Politecnica delle Marche Torrette, Ancona, Italy 3 Azienda Ospedaliero, Universitaria Sant’Andrea, Rome, Italy 4 Department of Informatics Engineering, University Politecnica delle Marche, Ancona, Italy 5 Anesthesia and Intensive Care, Università Campus Biomedico, Rome, Italy 6 Environmental, Occupational and Ageing (Integrative) Physiology Lab, Haute Ecole Bruxelles-Brabant (HE2B), Brussels, Belgium