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

Abstract

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 (O 2) fractions was investigated. Methods: Eight male volunteers performed, in random order, two dry chamber dives breathing either air or EANx40 (40% O 2 −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 (HbO 2) 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, HbO 2 and HHb values indicate a significant, O 2-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.

Evaluation of Divers’ Neuropsychometric Effectiveness and High-Pressure Neurological Syndrome via Computerized Test Battery Package and Questionnaires in Operational Setting

“…The device was described previously (Balestra et al, 2018). Correlation between cognitive performance with physiological index using CFFF in both normobaric and hyperbaric condition was demonstrated in previous studies (Hemelryck et al, 2013; Lafere et al, 2019). Subjects were instructed to hold the Flicker device at an arm’s length at eye level, to look straight at the LED light and press the button when the flickering light changes to constant fusion, read the fusion number, defined as a frequency (HZ) on the back of the device, and enter it in the related section in Physiopad software.…”

“…In recent years, several studies were published introducing Flicker as a reliable method to monitor changes in brain function and cortical arousal (Ortiz et al, 2005; Sharma et al, 2011). Flicker was used earlier to measure alertness and cognitive function in divers (Lafere et al, 2010, 2019; Germonpre et al, 2017). Decreased cognitive function was reported to be associated with a decrease in Flicker test and vice versa (Balestra et al, 2018; Lafere et al, 2019).…”

“…Flicker was used earlier to measure alertness and cognitive function in divers (Lafere et al, 2010, 2019; Germonpre et al, 2017). Decreased cognitive function was reported to be associated with a decrease in Flicker test and vice versa (Balestra et al, 2018; Lafere et al, 2019). Flicker has several limitations and the results would change due to the distance from the eyes, vision, and average brightness (Lafere et al, 2010).…”

“…The Psychology Experiment Building Language (PEBL) battery is a free software consisting of approximately 50 different validated experimental psychology and behavioral neurology tests to evaluate cognitive function in subjects (Piper et al, 2012). Several studies have previously used selected tests of PEBL package to study cognitive function such as visual motor coordination and visual memory in divers (Germonpre et al, 2017; Lafere et al, 2019). A collection of these psychomotor tests, as well as different questionnaires, was gathered in a computerized test battery (Physiopad package, rev 2.0, Divetech, Biot, France & I-Phy, Belgium) to monitor diver cognitive function and HPNS-related symptoms.…”

Assessment of Alertness and Cognitive Performance of Closed Circuit Rebreather Divers With the Critical Flicker Fusion Frequency Test in Arctic Diving Conditions

“…Most of the studies conducted in diving medicine in regard to CFFF have been conducted in pressure chambers or by breathing normobaric oxygen (NBO; Seki and Hugon, 1976 ; Hemelryck et al, 2013 ; Kot et al, 2015 ; Tikkinen et al, 2016 ; Lafère et al, 2019 ; Vrijdag et al, 2020 ) and only a select handful of studies have been done in pools or open water environments ( Balestra et al, 2012 ; Lafère et al, 2016 ; Rocco et al, 2019 ). The results in these studies have varied or even been contradictory, most likely due to differences in the study set ups.…”