Monitoring gas narcosis in hyperbaric environments

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dc.contributor.advisor Mitchell, Simon
dc.contributor.advisor Sleigh, Jamie
dc.contributor.advisor van Waart, Hanna Vrijdag, Xavier Cornelis Elisa 2022-04-26T02:28:00Z 2022-04-26T02:28:00Z 2021 en
dc.description.abstract Divers may be subject to narcotic effects caused by hyperbaric gases (particularly nitrogen). The principal hazard of gas narcosis is the induction of euphoria, overconfidence and loss of judgment. This may cause the diver to become less alert, take extra risks, and start a chain of events culminating in a serious diving accident. No early warning signal is available. Therefore, an objective method for detecting narcosis could improve diver safety and prove useful in related research. In three experiments, divers were exposed to 1) three low-dose concentrations of nitrous oxide (20, 30 and 40%), 2) air and heliox at 2.8 and 6 atmospheres absolute (ATA) (284 and 608 kPa) and 3) oxygen at 1.0, 1.4 and 2.8 ATA (101, 142 and 284 kPa). The cerebral effects were measured with pupillometry, critical flicker fusion frequency (CFFF), psychometric tests and electroencephalogram (EEG). The complexity of the time course of the EEG was estimated using a novel metric – default mode network (DMN) complexity. The degree of spatial functional connectivity – estimated using mutual information – was summarised with the global efficiency network measure. Pupillometry and CFFF showed no differences between conditions. In the nitrous oxide EEG recording, the DMN complexity correlated with the psychometric test results in a mixed-effects model (r2=0.67; receiver operating characteristic area, 0.72 (95% CI 0.59 to 0.85), p<0.001). DMN complexity did not detect a difference with the hyperbaric air exposure. However, air-breathing at 6 ATA (608 kPa) (experienced as mild nitrogen narcosis) caused a significant increase in brain connectivity, compared to surface air-breathing (p=0.001). Air-breathing at 2.8 ATA (284 kPa) trended in a similar direction, showing the early signs of nitrogen narcosis. Hyperbaric oxygen did not increase global efficiency as hyperbaric nitrogen did, which could be interpreted as oxygen not being narcotic. Oxygen caused a decrease in DMN complexity, which might indicate oxygen hyperexcitability at 1 ATA (101 kPa) and higher. In conclusion, the results of these studies have provided two novel quantitative EEG analysis algorithms that quantify the distinct cerebral effects of nitrous oxide, nitrogen and oxygen, which might correlate with their different molecular mechanisms of action.
dc.publisher ResearchSpace@Auckland en
dc.relation.ispartof PhD Thesis - University of Auckland en
dc.relation.isreferencedby UoA en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated.
dc.rights.uri en
dc.title Monitoring gas narcosis in hyperbaric environments
dc.type Thesis en Anaesthesiology The University of Auckland en Doctoral en PhD en 2022-03-31T04:09:43Z
dc.rights.holder Copyright: The author en
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