Inert gas narcosis in scuba diving, different gases different reactions

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 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. 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 profile 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 differed 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 final 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 flicker fusion frequency • GABA receptors Abbreviations ATA Atmospheres of pressure absolute 1 ATA = 1.01325 bar, 760 mmHg, 10 m H 2 O CFFF Critical flicker 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.

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

“…Indeed, shortterm normobaric O 2 (maximum 101 kPa O 2 ) influenced cognitive abilities such as memory, visuospatial and verbal abilities in a positive manner, 28 whilst functional MRI studies have demonstrated that normobaric hyperoxia (30 kPa O 2 ) during verbal or visual tasks increases the activation of brain areas associated with cognitive processing. 29 In divers, an association between changes in response times and changes in CFFF suggest that divers susceptible to IGN may also be susceptible to the effects of elevated PO 2 . 30 Also, even a small reduction in PN 2 , associated with a conservative dive profile, resulted in a modest beneficial effect of EANx28 (28% O 2 -72% N 2 ) on performance that may contribute to diving safety.…”

A Single Simulated Heliox Dive Modifies Endothelial Function in the Vascular Wall of ApoE Knockout Male Rats More Than Females

“…However, we found no indication of increased ROS production that could explain the differences between diving and non-diving rats. It may be worth noting that ventilation with helium has been reported to have an anti-inflammatory effect (Brubakk et al, 2014; Rocco et al, 2019), which may have reduced any side effect of potential O 2 toxicity.…”

Variation of Cognitive Function During a Short Stay at Hypobaric Hypoxia Chamber (Altitude: 3842 M)

“…When the subject saw a change in LED light from flicker to fusion, the subject acknowledged it to the investigator (through a sign without leaving sight of the LED) and the test was stopped. This noninvasive test has been validated to measure awareness (Hemelryck et al, 2013; Balestra et al, 2018; Rocco et al, 2019), mental fatigue (Ma et al, 2014), or executive dysfunction (Mewborn et al, 2015). It has already been demonstrated that CFFF could follow the recovery of cognitive function after propofol sedation earlier than psychometric testing (Sharma et al, 2011).…”