Early detection of diving-related cognitive impairment of different nitrogen-oxygen gas mixtures using critical flicker fusion frequency

Diving Hyperb Med. 2019 Jun 30;49(2):119-126. doi: 10.28920/dhm49.2.119-126.


Introduction: Cognitive impairment related to inert gas narcosis (IGN) is a threat to diving safety and operations at depth that might be reduced by using enriched air nitrox (EANx) mixtures. Using critical flicker fusion frequency (CFFF), a possible early detection of cognitive abilities/cerebral arousal impairment when breathing different oxygen (O2) fractions was investigated.

Methods: Eight male volunteers performed, in random order, two dry chamber dives breathing either air or EANx40 (40% O₂-60% nitrogen) for 20 minutes (min) at 0.4 MPa. Cognition and arousal were assessed before the dive; upon arrival at 0.4 MPa; after 15 min exposure at 0.4 MPa; on surfacing and 30 min post-dive using behavioural computer-based testing psychology experiment building language (PEBL) and by CFFF while continuously recording brain oxygenation with near-infrared spectroscopy.

Results: In both breathing conditions, CFFF and PEBL demonstrated a significant inverse correlation (Pearson r of -0.90, P < 0.0001), improved cognitive abilities/cerebral arousal occurred upon arrival at 0.4 MPa followed by a progressive deterioration. Initial brain activation was associated with a significant increase in oxyhaemoglobin (HbO2) and a simultaneous decrease of deoxyhaemoglobin (HHb). The magnitude of the changes was significantly greater under EANx (P = 0.038).

Conclusions: Since changes were not related to haemodynamic variables, HbO₂ and HHb values indicate a significant, O₂-dependent activation in the prefrontal cortex. Owing to the correlation with some tests from the PEBL, CFFF could be a convenient measure of cognitive performance/ability in extreme environments, likely under the direct influence of oxygen partial pressure, a potent modulator of IGN symptoms.

Keywords: Enriched air – nitrox; Narcosis; Near-infrared spectroscopy; Oxygen; Risk management.

MeSH terms

  • Cognitive Dysfunction* / chemically induced
  • Diving* / adverse effects
  • Flicker Fusion
  • Humans
  • Nitrogen / administration & dosage
  • Nitrogen / adverse effects*
  • Oxygen / administration & dosage
  • Oxygen / adverse effects*


  • Nitrogen
  • Oxygen