dc.contributor.advisor |
Mitchell, Simon |
|
dc.contributor.advisor |
Sleigh, Jamie |
|
dc.contributor.advisor |
van Waart, Hanna |
|
dc.contributor.author |
Vrijdag, Xavier Cornelis Elisa |
|
dc.date.accessioned |
2022-04-26T02:28:00Z |
|
dc.date.available |
2022-04-26T02:28:00Z |
|
dc.date.issued |
2021 |
en |
dc.identifier.uri |
https://hdl.handle.net/2292/58779 |
|
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 |
https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm |
en |
dc.rights.uri |
http://creativecommons.org/licenses/by-nc-sa/3.0/nz/ |
|
dc.title |
Monitoring gas narcosis in hyperbaric environments |
|
dc.type |
Thesis |
en |
thesis.degree.discipline |
Anaesthesiology |
|
thesis.degree.grantor |
The University of Auckland |
en |
thesis.degree.level |
Doctoral |
en |
thesis.degree.name |
PhD |
en |
dc.date.updated |
2022-03-31T04:09:43Z |
|
dc.rights.holder |
Copyright: The author |
en |
dc.rights.accessrights |
http://purl.org/eprint/accessRights/OpenAccess |
en |