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This purpose of this study was to evaluate the contribution of post-dive peripheral tissue warming to the production of venous gas emboli (VGE) in divers. Inert gas elimination from the tissues is limited by both perfusion and diffusion. If changes in diffusion are matched by corresponding perfusion (vasoactive) changes, decompression should be asymptomatic (within allowable exposure limits). Under conditions when the diffusion of inert gas from the tissues is not matched by blood perfusion, VGE will ensue. Increasing tissue temperature will decrease inert gas solubility and thus diffusion into the blood. It has been demonstrated that problems may arise during rapid changes in peripheral temperature, as often occurs post-dive, when divers previously exposed to cold water actively rewarm themselves in showers or baths. The effect of moderate rewarming, however, may be to increase the rate of inert gas elimination without the formation of VGE since increased perfusion is encouraged. The effect of mild post-dive warming was investigated. Ten male subjects, between the ages of 21 and 29 years completed two dry chamber dives to 70 feet for 35 minutes (no decompression limit of the Canadian Forces Air Diving tables). Each dive was followed by a 30 minute head-out immersion in either a thermoneutral (28°C) or warm (38°C) bath. Non-invasive Doppler ultrasonic monitoring was then carried out at 30 minute intervals for the next 150 minutes to assess measurable VGE. Subjects did not display VGE formation in either the control or experimental conditions. Our findings suggest that: 1) the Canadian Forces table limits (for the profile employed) provide safe no-decompression limits not compromised by mild post-dive warming, and 2) mild peripheral warming, since not bubble generating, may be a useful adjunctive therapy in the management of decompression sickness by increasing the rate of inert gas elimination. / Education, Faculty of / Curriculum and Pedagogy (EDCP), Department of / Graduate

Thesis (MScMedSc)-- Stellenbosch University, 2014. / ENGLISH ABSTRACT: The commercial and military deep diving environment is typically a low visibility environment, where dependence on the visual senses often needs to be replaced by a reliance on tactile senses. This thesis reviewed the current knowledge regarding neuropsychological manifestations of nitrogen narcosis and exposed a number of shortcomings in the current body of knowledge. In particular, the human performance effects of hyperbaric exposure on tactile perception and memory have not been systematically studied. It is further not clear, how exactly psychological factors (e.g. anxiety, mood states) and biographical factors (e.g. age, education, technical exposure, experience) might influence tactile perception and memory performance under conditions of hyperbaric exposure. The correlation between subjective experiences of narcosis, tactile performance, and psychological and biographical variables is also unknown. This study thus set out to investigate certain neuropsychological aspects of nitrogen narcosis, with special reference to tactile perception and memory, and to examine the relationships of tactile performance with other psychological and biographical factors. The effects of experimental hyperbaric exposure (EHE) on tactile (form) perception and tactile shape memory were examined by testing these functions at 6 ATA and 1 ATA, using a cross-over design where two groups completed the same tasks, in opposite sequence. The psychological variables included trait anxiety, transient mood states, and subjective ratings of narcosis, while the biographical variables included age, education, and previous technical exposure. The results demonstrated the detrimental effect of nitrogen narcosis on tactile form perception and manipulation, irrespective of the sequence of testing. It also demonstrated this effect on tactile form memory, although the sequence of testing also played a role here. Higher trait anxiety was associated with poorer recall, and tension was associated with a larger decrement in recall performance, while fatigue was associated with poorer task completion. Subjective experiences also played a role, where feelings of physical anxiety (i.e. increased arousal) were associated with better recall, and feelings of cognitive suppression (decreased arousal) were associated with a larger decrement in recall performance. Lower academic attainment was associated with poorer recall, while higher diving qualification was associated with better recall. Performance on the surface was a good predictor of performance at depth. Qualitative analysis rendered three themes, namely focus vs. distraction, following instructions, and shape memory. Psychometric properties of the subjective narcosis measure were also reported. Theoretical implications include support for the slowed information processing model when completing complex neuropsychological tasks, as well as support for the memory model, thus suggesting that this particular pattern of memory impairment occurs because encoding under narcosis produces a weaker memory trace than normal. Lastly, the study has a number of implications for industry. For example, divers need to compensate for slowed task completion by, firstly, planning more time to complete complex tasks, and secondly, by practicing those tasks prior to the actual deep dive (either on the surface or in shallow water). The need for using additional forms of recording of events or objects at depth, to aid memory encoding and subsequent recall at surface was also emphasised. / AFRIKAANSE OPSOMMING: Kommersieële en militêre duik vind dikwels plaas in ‘n omgewing met swak sig, waar duikers moet staatmaak op taktiele sintuie, eerder as op visuele sintuie. Die tesis begin met ‘n oorsig oor die huidige kennis rakende neurosielkundige verskynsels van stikstof narkose, en het ‘n aantal tekortkominge gevind. Meer spesifiek, die menslike faktor in die effek van hiperbariese druk op taktiese persepsie en geheue is nog nie sistematies bestudeer nie. Dit is verder nie duidelik presies hoe sielkundige faktore (angs, gemoedstoestande) en demografiese faktore (ouderdom, opvoeding, tegniese blootstelling, ondervinding) taktiele persepsie en geheue onder toestande van hiperbariese druk sou beïnvloed nie. The korrelasie tussen die subjektiewe ervaring van narkose, taktiele taakverigting, en sielkundige en biografiese veranderlikes is ook nie bekend nie. Die studie het verskeie neurosielkundige aspekte van stikstof narkose, met spesifieke verwysing na taktiele persepsie en geheue, sowel as die verhouding tussen taktiele prestasie en sielkundige en biografiese faktore ondersoek. Die effek van hiperbariese druk op taktiele persepsie en geheue is ondersoek deur hierdie funksies te toets by 6 en 1 ATA, deur middel van ‘n oorkruis studie ontwerp, waar twee groepe die take voltooi het, in teenoorgestelde volgorde. Die sielkundige veranderlikes het bestaan uit trek-angs, tydelike gemoedstoestande, en die subjektiewe evaluering van narkose, terwyl die biografiese veranderlikes ouderdom, opvoeding, en vorige tegniese blootstelling ingesluit het. Die resultate het die nadelige effek van stikstof narkose op taktiele vorm persepsie en manipulasie gedemonstreer, ongeag die rigting van toetsing. Dit het ook hierdie effek op taktiele vorm geheue gedemonstreer, hoewel die rigting van toetsing wel hier ‘n rol gespeel het. Hoër trek-angs was geassosieër met swakker herroeping, en spanning met ‘n groter agteruitgang in herroeping, terwyl matheid geassosieer was met swakker taakvoltooiing. Subjektiewe ervarings het ook ‘n rol gespeel, met ervarings van fisiese spanning (verhoogde opwekking) geassosieer met beter herroeping, en ervarings van kognitiewe onderdrukking (verlaagde opwekking) met groter agteruitgang in herroeping. Laer akademiese kwalifikasie was geassosieer met swakker herroeping, terwyl hoër duik kwalifikasie geassosieer was met beter herroeping. Taakverrigting op die oppervlak was ‘n goeie voorspeller van prestasie op diepte. Kwalitatiewe analiese het drie temas geidentifiseer, naamlik fokus vs. afleibaarheid, die volg van instruksies, en vorm geheue. Die psigometriese eienskappe van die subjektiewe narkose meetinstrument is ook gerapporteer. Teoretiese implikasies van die studie sluit in ondersteuning vir die vertraagde prosesseringsmodel, wanneer komplekse neurosielkundige take voltooi word, sowel as ondersteuning vir die model vir hierdie spesifieke herroepingspatroon wat ‘n swakker geheuespoor laat wanneer enkodering plaasvind onder toestande van narkose. Die studie het ook praktiese implikasies vir industrie. Dit is byvoorbeeld nodig om te kompenseer vir vertraagde taakvoltooïng deur, eerstens, die beplanning vir meer tyd om komplekse take te voltooi, en tweedens, deur daardie take te oefen voor die diep duik plaasvind. Die noodsaaklikheid vir additionele maniere om gebeure of voorwerpe op diepte vas te lê is ook beklemtoon.