Personality and behavioural outcomes in diving: current status and recommendations for future research.

This paper provides a brief overview of the shift from studies describing the personality profiles of divers to studies exploring associations between personality variables and diving performance in terms of behavioural outcomes. The personality associations that were investigated include performance during training, panic proneness, diving injuries, susceptibility to inert gas narcosis, and the behaviour of tourist divers. The paper concludes with a number of suggested directions for further research on personality and diving that may provide tangible benefits in terms of both enhanced safety and improved performance underwater.

Objective vs. Subjective Evaluation of Cognitive Performance During 0.4-MPa Dives Breathing Air or Nitrox.

BACKGROUND: Divers try to limit risks associated with their sport, for instance by breathing enriched air nitrox (EANx) instead of air. This double blinded, randomized trial was designed to see if the use of EANx could effectively improve cognitive performance while diving. METHODS: Eight volunteers performed two no-decompression dry dives breathing air or EANx for 20 min at 0.4 MPa. Cognitive functions were assessed with a computerized test battery, including MathProc and Ptrail. Measurements were taken before the dive, upon arrival and after 15 min at depth, upon surfacing, and at 30 min postdive. After each dive subjects were asked to identify the gas they had just breathed. RESULTS: Identification of the breathing gas was not possible on subjective assessment alone, while cognitive assessments showed significantly better performance while breathing EANx. Before the dives, breathing air, mean time to complete the task was 1795 ms for MathProc and 1905 ms for Ptrail. When arriving at depth MathProc took 1616 ms on air and 1523 ms on EANx, and Ptrail took 1318 ms on air and and 1356 ms on EANx, followed 15 min later by significant performance inhibition while breathing air during the ascent and the postdive phase, supporting the concept of late dive/postdive impairment. DISCUSSION: The results suggest that EANx could protect against decreased neuro-cognitive performance induced by inert gas narcosis. It was not possible for blinded divers to identify which gas they were breathing and differences in postdive fatigue between air and EANx diving deserve further investigation.Germonpré P, Balestra C, Hemelryck W, Buzzacott P, Lafère P. Objective vs. subjective evaluation of cognitive performance during 0.4-MPa dives breathing air or nitrox. Aerosp Med Hum Perform. 2017; 88(5):469-475.

Diving under the influence: issues in researching personality and inert gas narcosis.

BACKGROUND: This paper considers the relationship between measures of personality and mood states, and susceptibility to inert gas narcosis. It briefly reviews the topics of inert gas narcosis affecting personality, and personality affecting the susceptibility to inert gas narcosis. There appears to be is a theoretical argument for a possible relationship between measures of personality, mood states, and susceptibility to narcosis. Practically, such a relationship may speak to issues in selection, training and preparation, risk assessments, and even accident investigation in the diving and/or hyperbaric environment. MATERIALS AND METHODS: Twenty one divers completed measures of personality and mood states, and were then compressed to 709 kPa (equivalent to 60 msw) in a dry compression chamber, where they completed a task measuring speed of information processing, and a scale measuring subjective narcosis. RESULTS AND CONCLUSIONS: The main finding was the absence of any significant correlations between measures of personality traits and mood, and susceptibility to inert gas narcosis. Although the study found no evidence of any major relationship, it is presented as a case study to highlight some of the issues and pitfalls involved in such research. The lessons learned - including the careful defining and describing of concepts, and choosing of samples and measurements - are used to discuss some of the methodological and conceptual issues and future directions for researchers to consider.

Inert gas narcosis disrupts encoding but not retrieval of long term memory.

Exposure to increased ambient pressure causes inert gas narcosis of which one symptom is long-term memory (LTM) impairment. Narcosis is posited to impair LTM by disrupting information encoding, retrieval (self-guided search), or both. The effect of narcosis on the encoding and retrieval of LTM was investigated by testing the effect of learning-recall pressure and levels of processing (LoP) on the free-recall of word lists in divers underwater. All participants (n=60) took part in four conditions in which words were learnt and then recalled at either low pressure (1.4-1.9atm/4-9msw) or high pressure (4.4-5.0atm/34-40msw), as manipulated by changes in depth underwater: low-low (LL), low-high(LH), high-high (HH), and high-low (HL). In addition, participants were assigned to either a deep or shallow processing condition, using LoP methodology. Free-recall memory ability was significantly impaired only when words were initially learned at high pressure (HH & HL conditions). When words were learned at low pressure and then recalled at low pressure (LL condition) or high pressure (LH condition) free-recall was not impaired. Although numerically superior in several conditions, deeper processing failed to significantly improve free-recall ability in any of the learning-recall conditions. This pattern of results support the hypothesis that narcosis disrupts encoding of information into LTM, while retrieval appears to be unaffected. These findings are discussed in relation to similar effects reported by some memory impairing drugs and the practical implications for workers in pressurised environments.

Memory and metacognition in dangerous situations: investigating cognitive impairment from gas narcosis in undersea divers.

OBJECTIVE: The current study tested whether undersea divers are able to accurately judge their level of memory impairment from inert gas narcosis. BACKGROUND: Inert gas narcosis causes a number of cognitive impairments, including a decrement in memory ability. Undersea divers may be unable to accurately judge their level of impairment, affecting safety and work performance. METHOD: In two underwater field experiments, performance decrements on tests of memory at 33 to 42 m were compared with self-ratings of impairment and resolution. The effect of depth (shallow [I-II m] vs. deep [33-42 m]) was measured on free-recall (Experiment I; n = 41) and cued-recall (Experiment 2; n = 39) performance, a visual-analogue self-assessment rating of narcotic impairment, and the accuracy of judgements-of-learning JOLs). RESULTS: Both free- and cued-recall were significantly reduced in deep, compared to shallow, conditions. This decrement was accompanied by an increase in self-assessed impairment. In contrast, resolution (based on JOLs) remained unaffected by depth. The dissociation of memory accuracy and resolution, coupled with a shift in a self-assessment of impairment, indicated that divers were able to accurately judge their decrease in memory performance at depth. CONCLUSION: These findings suggest that impaired self-assessment and resolution may not actually be a symptom of narcosis in the depth range of 33 to 42 m underwater and that the divers in this study were better equipped to manage narcosis than prior literature suggested. The results are discussed in relation to implications for diver safety and work performance.

Complex tactile performance in low visibility: the effect of nitrogen narcosis.

BACKGROUND: In a task-environment where visibility has deteriorated, individuals rely heavily on tactile performance (perception and manipulation) to complete complex tasks. When this happens under hyperbaric conditions, factors like nitrogen narcosis could influence a person's ability to successfully complete such tasks. OBJECTIVE: To examine the effect of nitrogen narcosis on a complex neuropsychological task measuring tactile performance at a pressure of 608 kPa (6 atm abs), in the absence of visual access to the task. METHODS: In a prospective cross-over study, 139 commercial divers were tested in a dry chamber at 101.3 kPa and 608 kPa. They completed the Tupperware Neuropsychological Task (TNT) of tactile performance without visual access to the task, and completed questionnaires to provide psychological and biographical data, which included trait anxiety and transient mood states, as well as formal qualifications and technical proficiency. RESULTS: A significant decrement (9.5%, P < 0.001) in performance on the TNT at depth was found, irrespective of the sequence of testing. Generally, neither the psychological nor biographical variables showed any significant effect on tactile performance. Tactile performance on the surface was a good indicator of performance at depth. CONCLUSION: These findings have practical implications for professional diving where conditions of low visibility during deeper diving occur. Recommendations are made towards managing potential impairments in tactile performance, such as pre-dive practical learning ('rehearsal') as an aid to successful completion of tasks.

Effects of hyperbaric nitrogen-induced narcosis on response-selection processes.

Certain underwater circumstances carry risk of inert gas narcosis. Impairment of sensorimotor information processing due to narcosis, induced by normobaric nitrous oxide or high partial nitrogen pressure, has been broadly evidenced, by a lengthening of the reaction time (RT). However, the locus of this effect remains a matter of debate. We examined whether inert gas narcosis affects the response-selection stage of sensorimotor information processing. We compared an air normobaric condition with a hyperbaric condition in which 10 subjects were subjected to 6 absolute atmospheres of 8.33% O2 Nitrox. In both conditions, subjects performed a between-hand choice-RT task in which we explicitly manipulated the stimulus-response association rule. The effect of this manipulation (which is supposed to affect response-selection processes) was modified by inert gas narcosis. It is concluded, therefore, that response selection processes are among the loci involved in the effect of inert gas narcosis on information processing.

Subjective Narcosis Assessment Scale: measuring the subjective experience of nitrogen narcosis.

BACKGROUND: The interaction of subjective experiences and objective measures of neuropsychological performance during hyperbaric exposure has received less attention in the literature, in part due to the shortage of available and appropriately standardized measures. OBJECTIVE: This study aimed to describe the psychometric properties of a modified version of the Subjective High Assessment Scale when used in the hyperbaric context, by exploring internal reliability, factor structure, associations with psychological variables and simple cognitive delayed recall, and the effect of task focus on the recall of subjective experience. METHOD: Seventy qualified divers completed dry hyperbaric chamber dives to 607.95 kPa, and completed ratings of their subjective experiences. Some also completed a delayed recall task and psychological measures prior to their dives. RESULTS: The scale displayed good internal consistency, with four meaningful factors emerging. It showed some significant but small associations with trait anxiety and transient mood states, and a small to moderate correlation with recall performance. There was no significant effect of task focus on self-report of subjective experiences. CONCLUSION: The modified scale, renamed the Subjective Narcosis Assessment Scale here, has useful psychometric properties, and promising potential for future use.

Nitrogen narcosis and tactile shape memory in low visibility.

OBJECTIVE: Commercial diving often occurs in low visibility, where divers are reliant on their tactile senses. This study examined the effect of nitrogen narcosis on tactile memory for shapes as well as the influence of psychological and biographical factors on this relationship. METHOD: This crossover study tested 139 commercial divers in a dry hyperbaric chamber at 101.325 and 607.95 kPa (1 and 6 atmospheres absolute/atm abs). Divers memorized shapes while blindfolded, using their tactile senses only. Delayed recall was measured at the surface after each dive. Psychological and biographical data were also collected. RESULTS: A significant effect of hyperbaric pressure on tactile memory was demonstrated, and a further effect of sequence of testing found. Thus, divers' delayed shape recall deteriorated by 8% after learning material at depth, compared to learning on the surface. There were also significant but small effects of psychological and biographical markers on tactile memory performance, with lower trait anxiety associated with better recall, and lower education associated with poorer recall. CONCLUSION: The findings emphasize the importance of utilizing other forms of recording of events or objects at depth, particularly in conditions of low visibility during deeper diving, to aid memory encoding and subsequent recall at the surface.

The levels of processing effect under nitrogen narcosis.

Previous research has consistently demonstrated that inert gas (nitrogen) narcosis affects free recall but not recognition memory in the depth range of 30 to 50 meters of sea water (msw), possibly as a result of narcosis preventing processing when learned material is encoded. The aim of the current research was to test this hypothesis by applying a levels of processing approach to the measurement of free recall under narcosis. Experiment 1 investigated the effect of depth (0-2 msw vs. 37-39 msw) and level of processing (shallow vs. deep) on free recall memory performance in 67 divers. When age was included as a covariate, recall was significantly worse in deep water (i.e., under narcosis), compared to shallow water, and was significantly higher in the deep processing compared to shallow processing conditions in both depth conditions. Experiment 2 demonstrated that this effect was not simply due to the different underwater environments used for the depth conditions in Experiment 1. It was concluded memory performance can be altered by processing under narcosis and supports the contention that narcosis affects the encoding stage of memory as opposed to self-guided search (retrieval).

Inert gas narcosis and the encoding and retrieval of long-term memory.

BACKGROUND: Prior research has indicated that inert gas narcosis (IGN) causes decrements in free recall memory performance and that these result from disruption of either encoding or self-guided search in the retrieval process. In a recent study we provided evidence, using a Levels of Processing approach, for the hypothesis that IGN affects the encoding of new information. The current study sought to replicate these results with an improved methodology. METHODS: The effect of ambient pressure (111.5-212.8 kPa/1-11 msw vs. 456-516.8 kPa/35-41 msw) and level of processing (shallow vs. deep) on free recall memory performance was measured in 34 divers in the context of an underwater field experiment. RESULTS: Free recall was significantly worse at high ambient pressure compared to low ambient pressure in the deep processing condition (low pressure: M = 5.6; SD = 2.7; high pressure: M = 3.3; SD = 1.4), but not in the shallow processing condition (low pressure: M = 3.9; SD = 1.7; high pressure: M = 3.1; SD = 1.8), indicating IGN impaired memory ability in the deep processing condition. In the shallow water, deep processing improved recall over shallow processing but, significantly, this effect was eliminated in the deep water. DISCUSSION: In contrast to our earlier study this supported the hypothesis that IGN affects the self-guided search of information and not encoding. It is suggested that IGN may affect both encoding and self-guided search and further research is recommended.

Measuring manual dexterity and anxiety in divers using a novel task at 35-41 m.

BACKGROUND: Nitrogen narcosis has a detrimental impact on the manual dexterity of divers and prior research has suggested that this impairment may be magnified by anxiety. Preliminary findings of the effects of depth (i.e., narcosis) and subjective anxiety on a novel test of manual dexterity are presented. METHODS: There were 45 subjects who were given a test of manual dexterity once in shallow water (1-10 m/3-33 ft) and once in deep water (35-41 m/115-135 ft). Subjective anxiety was concurrently measured in 33 subjects who were split into 'non-anxious' and 'anxious' groups for each depth condition. RESULTS: Subjects took significantly longer (seconds) to complete the manual dexterity task in the deep (mean = 52.8; SD = 12.1) water compared to the shallow water (mean = 46.9; SD = 8.4). In addition, anxious subjects took significantly longer to complete the task in the deep water (mean = 48.6; SD = 6.8) compared to non-anxious subjects (mean = 53.2; SD = 9.9), but this was not the case in the shallow water. DISCUSSION: This selective effect of anxiety in deep water was taken as evidence that anxiety may magnify narcotic impairments underwater. It was concluded that the test of manual dexterity was sensitive to the effects of depth and will be a useful tool in future research.

Anxiety and psychomotor performance in divers on the surface and underwater at 40 m.

INTRODUCTION: Performance impairments attributed to the effects of nitrogen narcosis have been reported to be significantly larger in studies conducted underwater compared to in hyperbaric chambers. One suggestion is that the larger impairment results from higher levels of anxiety in the underwater environment. The current study aimed to investigate the impact of anxiety and narcosis, in isolation and in combination, on a measure of psychomotor performance. METHODS: The effects of self-reported anxiety (anxious vs. not anxious) and depth (surface vs. underwater) on performance on the digit letter substitution test (DLST) were measured in 125 divers. RESULTS: Change from baseline scores indicated that divers performed significantly worse on the DLST underwater (mean = 3.35; SD = 4.2) compared to the surface (mean = 0.45-0.73; SD = 4.0-4.2). This decrement was increased when divers reported they were also anxious (mean = 7.11; SD = 6.1). There was no difference on DLST performance at the surface between divers reporting they were anxious and those reporting they were not anxious. DISCUSSION: The greater decrement in performance at depth in divers reporting anxiety compared to those not reporting anxiety and the lack of this effect on the surface suggested that anxiety may magnify performance deficits presumed to be caused by narcosis.

Effect of nitrogen narcosis on free recall and recognition memory in open water.

RATIONALE: Previous research has demonstrated that nitrogen narcosis causes decrements in memory performance but the precise aspect of memory impaired is not clear in the literature. OBJECTIVE: The present research investigated the effect of narcosis on free recall and recognition memory by appling signal detection theory (SDT) to the analysis of the recognition data. METHODS: Using a repeated measures design, the free recall and recognition memory of 20 divers was tested in four learning-recall conditions: shallow-shallow (SS), deep-deep (DD), shallow-deep (SD) and deep-shallow (DS). The data was collected in the ocean offDahab, Egypt with shallow water representing a depth of 0-10m (33ft) and deep water 37-40m (121-131ft). The presence of narcosis was independently indexed with subjective ratings. RESULTS: In comparison to the SS condition there was a clear impairment of free recall in the DD and DS conditions, but not the SD condition. Recognition memory remained unaffected by narcosis. CONCLUSIONS: It was concluded narcosis-induced memory decrements cannot be explained as simply an impairment of input into long term memory or of self-guided search and it is suggested instead that narcosis acts to reduce the level of processing/encoding of information.

Subjective and behavioural responses to nitrogen narcosis and alcohol.

RATIONALE: There is a widespread assumption that nitrogen narcosis is comparable to alcohol intoxication, a similarity that may extend to patterns of tolerance. It has been suggested this indicates evidence of a shared biological mechanism but there is a paucity of experimental data to support these claims. OBJECTIVE: The current study aimed to test this assumption by comparing subjective (ratings) and behavioural (Digit Letter Substitution Test) responses to nitrogen narcosis and alcohol. METHODS: Experiment 1 compared responses to narcosis in 39 participants posited to differ in tolerance based on prior exposure to alcohol (heavy/light drinkers) and narcosis (novice/experienced divers). Experiment 2 compared responses to narcosis and after a 0.5 g/kg dose of alcohol in 23 participants. In both experiments narcosis was measured at depths between 40 and 45m in the ocean off Port Vila, Vanuatu. RESULTS: Experiment 1 measured a significant decrement in the behavioural measure underwater, compared to baseline but failed to find any differential responding to narcosis between drinker or diving experience groups. In contrast, Experiment 2 found positive correlations between alcohol and narcosis on both subjective and behavioural measures, indicating those affected to a greater degree by alcohol were also affected to a greater degree by narcosis. CONCLUSIONS: These results support the contention of a relationship between nitrogen narcosis and alcohol, although the role of diving and drinking history, if any, remains obscure.

Change in strategy of solving psychological tests: evidence of nitrogen narcosis in shallow air-diving.

The depths from 10 to 30 m are usually not considered narcotic in scuba air-diving, and evidence of psychomotor disturbances attributable to nitrogen narcosis at these depths is weak and contradictory. 15 experienced male divers were tested in a chamber at 1, 2, 3, and 4 bars over five consecutive days using a battery of computer generated psychological tests-Computerized Reactionmeter Drenovac (CRD-series). Total test solving time, minimal single task solving time, total "ballast" time, and total number of errors were recorded. Nitrogen narcosis effects were evident at all hyperbaric pressures with marked performance differences among subjects. MANOVA revealed significant effects of nitrogen partial pressure for groups of the same variables as follows: total test solving time (p < 0.001), total "ballast" time (p < 0.001), and total number of errors (p = 0.038), but not for minimal single task solving time. ANOVA showed significant effects of pressure only on tests of visual discrimination of signal location (total test solving time: p = 0.012, total "ballast" time: p < 0.001), simple convergent visual orientation (total test solving time: p = 0.012), and convergent thinking (total test solving time: p = 0.002, total number of errors: p = 0.049). The order of the pressure exposures had no influence on subject performance. Impaired psychomotor processing found during air exposures from 2 to 4 bars suggests that nitrogen narcosis at depths usually considered safe from its effects might be a problem in underwater operations that require accuracy, speed, limited time of performance, and complex psychomotor skills.

Evidence for inert gas narcosis mechanisms in the occurrence of psychotic-like episodes at pressure environment.

Psychotic-like episodes in divers exposed to high pressure have been attributed to either the high-pressure neurological syndrome, confinement in pressure chamber, the subject's personality, or the addition of nitrogen or hydrogen to the basic helium-oxygen breathing mixture used for deep diving. Alternatively, it is suggested that these disorders are in fact paroxysmal narcotic symptoms that result from the sum of the individual narcotic potencies of each inert gas in the breathing mixture. This hypothesis is tested against a variety of lipid solubility theories of narcosis. The results clearly support the hypothesis and provide new information about the cellular interactions between inert gases at raised pressure and pressure itself.

Evidence for inert gas narcosis mechanisms in the occurrence of psychotic-like episodes at pressure environment.

Psychotic-like episodes in divers exposed to high pressure have been attributed to either the high-pressure neurological syndrome, confinement in pressure chamber, the subject's personality, or the addition of nitrogen or hydrogen to the basic helium-oxygen breathing mixture used for deep diving. Alternatively, it is suggested that these disorders are in fact paroxysmal narcotic symptoms that result from the sum of the individual narcotic potencies of each inert gas in the breathing mixture. This hypothesis is tested against a variety of lipid solubility theories of narcosis. The results clearly support the hypothesis and provide new information about the cellular interactions between inert gases at raised pressure and pressure itself.

Relative narcotic potency and mode of action of sulfur hexafluoride and nitrogen in humans.

Impairments of psychomotor, perceptual, and cognitive abilities were determined in nine male subjects exposed to inhaled SF6 partial pressures of 0, 52, 104, and 156 kPa and to inhaled N2 partial pressures of 103, 575, 825, and 1,075 kPa. Also data from a previous study with inhaled N2O partial pressures of 0, 13, 26, and 39 kPa were included. With the highest gas concentrations, performances were reduced by 41-57%. Effective doses for a 20% performance impairment were 830, 97, and 21.5 kPa for N2, SF6, and N2O, respectively, yielding relative narcotic potencies of 1.0:8.5:39. The order of narcotic potencies is the same as for the lipid solubility of the three gases. In contrast, the order of increasing tendency for hydrate formation (decreasing hydrate dissociation pressure) for the three gases is N2, N2O, and SF6. Thus, mild to moderate inert gas narcosis in humans shows the same positive relationship to lipid solubility as was shown in previous animal models that utilized much deeper levels of anesthesia.

Subjective and behavioral effects associated with repeated exposure to narcosis.

Below 30 m, nitrogen narcosis can severely degrade the performance of air breathing divers. Within the diving community it is generally thought that this effect can be reduced by repeating deep air dives on successive days but laboratory studies have found no strong evidence to support the notion of adaptation to narcosis. One possible explanation for this discrepancy is that one's subjective impression or perception of narcosis may decrease during repeated exposure to hyperbaric air without parallel improvement on task performance. To examine this possibility, symptoms and performance were examined over the course of 5 days of repeated exposure to 30% nitrous oxide at 1 ATA. While the results revealed no clear cut changes in global perceptions of narcosis across days, several symptoms from an adjective checklist showed unequivocal signs of adaptation. With respect to performance effects, reaction time yielded no indications of improvement over days relative to the control. These findings suggest that subjective adaptation can occur without parallel performance improvement, an effect which could compromise safety and which may be of concern in other operational settings that involve repeated exposure to stimulus conditions which impact on performance and symptoms.