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We report a rare case of syndrome of inappropriate antidiuretic hormone secretion (SIADH) associated with amyotrophic lateral sclerosis (ALS). A 69-year-old man was admitted to our hospital with sustained hyponatremia. Hyposmolality with elevated urinary osmolality and sodium excretion was observed, which indicated SIADH. The treatment for SIADH was challenging; the patient developed carbon dioxide narcosis, which led to the diagnosis of ALS. After the initiation of noninvasive positive-pressure ventilation, the patient's serum sodium concentration normalized and became stable. Thus, ALS should be recognized as a possible cause of SIADH in the clinical setting.

Introduction Gas narcosis impairs divers when diving deeper. Pupillometry is sensitive to alcohol intoxication and it has been used in anaesthesia to assess nitrous oxide narcosis. It is a potential novel method to quantify narcosis in diving. The aim of this study was to evaluate pupillometry for objective measurement of narcosis during exposure to hyperbaric air or nitrous oxide. Method Pupil size in 16 subjects was recorded directly at surface pressure and during air breathing at 608 kPa (equivalent to 50 metres' seawater depth) in a hyperbaric chamber. Another 12 subjects were exposed to nitrous oxide at end-tidal percentages of 20, 30 and 40% in random order at surface pressure. Pupil size and pupil light reflex were recorded at baseline and at each level of nitrous oxide exposure. Results Pupil size did not significantly change during exposure to hyperbaric air or nitrous oxide. The pupil light reflex, evaluated using percentage constriction and minimum diameter after exposure to a light stimulus, was affected significantly only during the highest nitrous oxide exposure - an end-tidal level of 40%. Conclusion Pupillometry is insensitive to the narcotic effect of air at 608 kPa in the dry hyperbaric environment and to the effects of low dose nitrous oxide. Pupillometry is not suitable as a monitoring method for gas narcosis in diving.

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., info:eu-repo/semantics/published

Although many factors contributing to inert gas narcosis onset and severity have been put forward, the available evidence is not particularly strong. Using objective criteria, we have assessed brain impairment associated with narcosis under various environmental diving conditions. 40 volunteers performed a no-decompression dive (33 m for 20 min) either in a dry chamber, a pool or open sea. They were assessed by critical flicker fusion frequency before the dive, upon arriving at depth, 5 min before ascent, on surfacing and 30 min post-dive. Compared to the pre-dive value, the mean value of each measurement was significantly different. An increase of flicker fusion to 105.00±0.69% when arriving at depth is followed by a decrease to 94.05±0.65%. This impairment persists when surfacing and 30 min post-dive, decreasing further to 96.36±0.73% and 96.24±0.73%, respectively. Intragroup comparison failed to demonstrate any statistical difference. When objectively measured narcosis may not be influenced by external factors other than pressure and gas. This might be of importance for training to avoid any over- or underestimation of the severity of narcosis based only on subjective symptoms.

Diving narcosis results from the complex interaction of gases, activities, and environmental conditions. We hypothesized that these interactions could be separated into their component parts. Where previous studies have tested single cognitive tasks sequentially, we varied inspired partial pressures of CO2, N2, and O2 in immersed, exercising subjects while assessing multitasking performance with the Multi-Attribute Task Battery II (MATB-II) flight simulator. Cognitive performance was tested under 20 conditions of gas partial pressure and exercise in 42 male subjects meeting U.S. Navy age and fitness profiles. Inspired nitrogen (N2) and oxygen (O2) partial pressures were 0, 4.5, and 5.6 ATA and 0.21, 1.0, and 1.22 ATA, respectively, at rest and during 100-W immersed exercise with and without 0.075-ATA CO2. Linear regression modeled the association of gas partial pressure with task performance while controlling for exercise, hypercapnic ventilatory response, dive training, video game frequency, and age. Subjects served as their own controls. Impairment of memory, attention, and planning, but not motor tasks, was associated with N2 partial pressures >4.5 ATA. Sea level O2 at 0.925 ATA partially rescued motor and memory reaction time impaired by 0.075-ATA CO2; however, at hyperbaric pressures an unexpectedly strong interaction between CO2, N2, and exercise caused incapacitating narcosis with amnesia, which was augmented by O2. Perception of narcosis was not correlated with actual scores. The relative contributions of factors associated with diving narcosis will be useful to predict the effects of gas mixtures and exercise conditions on the cognitive performance of divers. The O2 effects are consistent with O2 narcosis or enhanced O2 toxicity.

Human beings are exposed to compressed air or a nitrogen-oxygen mixture, they will produce signs and symptoms of nitrogen narcosis such as amnesia or even loss of memory, which may be disappeared once back to the normobaric environment. This study was designed to investigate the effect of nitrogen narcosis induced by repetitive hyperbaric nitrogen-oxygen mixture exposure on long-term cognitive function in newborn mice and the underlying mechanisms. The electroencephalogram frequency was decreased while the amplitude was increased in a pressure-dependent manner during 0.6, 1.2, 1.8 MPa (million pascal) nitrogen-oxygen mixture exposures in adult mice. Nitrogen narcosis in postnatal days 7-9 mice but not in adult mice induced by repetitive hyperbaric exposure prolonged the latency to find the platform and decreased the number of platform-site crossovers during Morris water maze tests, and reduced the time in the center during the open field tests. An increase in the expression of cleaved caspase-3 in the hippocampus and cortex were observed immediately on the first day after hyperbaric exposure, and this lasted for seven days. Additionally, nitrogen narcosis induced loss of the dendritic spines but not of the neurons, which may mainly account for the cognitive dysfunction. Nitrogen narcosis induced long-term cognitive and emotional dysfunction in the postnatal mice but not in the adult mice, which may result from neuronal apoptosis and especially reduction of dendritic spines of neurons.

It was hypothesized that normoxic 30% nitrous oxide (N2O) would suppress and hyperthermia would increase exercise ventilation during short duration, high intensity exercise. Thirteen males (24.2±0.8y; mean±SE), of normal physique (BMI, 23.8±1.0kgm(-2)), performed 4 separate 30s Wingate tests on a cycle ergometer. Exercise ventilation and its components, as well as mean skin and esophageal temperature (TES), were assessed in 2 way experimental design with factors of Thermal State (Normothermia or Hyperthermia) and Gas Type (Air or 30% Normomoxic N2O). In the 2 hyperthermic tests TES was elevated to ∼38.5°C in a 40°C bath. The main results indicated a significant interaction (F=7.14, P=0.02) between Gas Type and Thermal state for the exercise-induced increase in ventilation (ΔV˙E). During both the normothermia and hyperthermia conditions with AIR breathing, the exercise ΔV˙E was ∼80Lmin(-1) and it was significantly decreased to 73.1±24.1Lmin(-1) in the normothermia condition with N2O breathing relative to that of 92.0±25.0Lmin(-1) in the hyperthermia condition with N2O breathing. In conclusion, normoxic N2O breathing suppressed high intensity exercise ventilation during normothermia relative to that during hyperthermia on account of decreases in the tidal volume and this led CO2 retention.

BACKGROUND Nitrogen (N2) in air causes cognitive impairment from gas narcosis when breathed at increased ambient pressures. This impairment might be reduced by using enriched air nitrox (EANx) mixtures, which have a higher oxygen and lower N2 content compared to air. This study aimed to investigate if divers differed in memory ability and self-assessment when breathing air and EANx30. METHODS The effect of depth (shallow vs. deep) and breathing gas (air vs. EANx30) on memory ability and subjective ratings of impairment was compared in 20 divers. RESULTS Memory performance was significantly worse in deep water (Air: M = 22.1%, SD = 21.7%; EANx30: M = 22.1%, SD = 17.2%) compared to shallow water (Air: M = 29.2%, SD = 18.3%; EANx30: M = 33.3%, SD = 18.2%), but this impairment did not differ significantly between air and EANx30. Subjective ratings of impairment increased significantly from shallow water (Air: M = 5.2, SD = 5.9; EANx30: M = 3.0, SD = 4.4) to deep water (Air: M = 36.8, SD = 25.3; EANx30: M = 24.8, SD = 16.1) when breathing both air and EANx30. However, ratings were significantly lower when breathing EANx30 compared to air when in the deep water. DISCUSSION It was concluded EANx30 does not reduce narcotic impairment over air. Additionally, divers were able to make a correct global self-assessment they were impaired by narcosis, but were unable to make a finer assessment, leading them to erroneously believe that EANx30 was less narcotic than air.

Recreational scuba diving is no longer reserved for young healthy individuals, and as a result, medical drug consumption is on the rise in the diving population. Due to the possible potentiation of nitrogen narcosis by psychotropic drugs, the latter are hence discouraged and are subject to contraindications for practice. However, there are no available experimental data to support this theoretical assumption. The objective of this study is to investigate whether psychotropic drug users are more at risk of severe narcosis. An online survey was sent to the licensed divers from the East of France registered with the French Underwater Federation. Divers were surveyed regarding their consumption of psychotropic drugs, the occurrence of nitrogen narcosis as well as their respective diver’s curriculum vitae.1 608 divers responded to the survey of which 15.2% confirmed having used psychotropic drugs and 7.8% since they became divers. Overall, 40.0% and 5.5% experienced severe and critical narcosis. In multivariate analysis, neither severe nor critical narcosis was associated with psychotropic drug use (OR 0.97 [0.59–1.57] and 0.76 [0.29–2.00], respectively).In conclusion, despite the recommendations, a significant proportion of divers use psychotropic drugs but do not seem to be more prone to severe narcosis.

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 [1-11 m] vs. deep [33-42 m]) was measured on free-recall (Experiment 1; 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.

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.

Decompression injuries occur on account of the special hyperbaric effects during the emerge phase and require superior therapeutic knowledge. Vitally important is emergency treatment with high concentrated oxygen at an early stage. Sever decompression injuries require oxygenation in a hyperbaric treatment chamber.

Inert gas narcosis (IGN) impairs cognitive performance and some divers are more susceptible to IGN than others. We compared the sensitivity of two reaction time tests to detect changes in performance at pressure and compared these results with critical flicker fusion frequency (CFF) changes at the same ambient pressures.The study assessed simple reaction time (RT), mean time correct of the discrimination reaction time (MTC) and CFF in 30 professional divers breathing air at 101 kPa and 608 kPa in a hyperbaric chamber.RT and MTC increased at 608 kPa by 5.1 ± 9.4% (P = 0.04) and 7.3 ± 12.3% (P = 0.01) respectively. RT decreased to pre-compression level after decompression and MTC decreased to a level lower than pre-compression (P0.001) values. CFF increased by 2.5 ± 2.8% (P0.001) at 608 kPa. CFF decreased to pre-compression level after decompression. An increase in CFF was inversely correlated with a decrease in RT (r = 0.38, P = 0.04) and in MTC (r = 0.43, P = 0.02) at 608 kPa.Response speeds of the same subjects were impaired in both reaction time tasks at 608 kPa, whereas CFF increased at depth. An association between changes in response times and changes in CFF suggests that divers susceptible to IGN may also be susceptible to the effects of elevated oxygen partial pressure. If this holds true, the future selection of professional divers could be improved by the use of simple cognitive tests.

Contribution of skin thermal sensors under inert gas narcosis to the raising hypothermia is not known. Such information is vital for understanding the impact of narcosis on behavioural thermoregulation, diver safety and judgment of thermal (dis)comfort in the hyperbaric environment. So this study aimed at establishing the effects of normoxic concentration of 30% nitrous oxide (N(2)O) on thermo-tactile threshold sensation by studying 16 subjects [eight females and eight males; eight sensitive (S) and eight non-sensitive (NS) to N(2)O]. Their mean (SD) age was 22.1 (1.8) years, weight 72.8 (15.3) kg, height 1.75 (0.10) m and body mass index 23.8 (3.8) kg m(-2). Quantitative thermo-tactile sensory testing was performed on forearm, upper arm and thigh under two experimental conditions: breathing air (air trial) and breathing normoxic mixture of 30% N(2)O (N(2)O trial) in the mixed sequence. Difference in thermo-tactile sensitivity thresholds between two groups of subjects in two experimental conditions was analysed by 3-way mixed-model analysis of covariance. There were no statistically significant differences in thermo-tactile thresholds either between the Air and N(2)O trials, or between S and NS groups, or between females and males, or with respect to body mass index. Some clinically insignificant lowering of thermo-tactile thresholds occurred only for warm thermo-tactile thresholds on upper arm and thigh. The results indicated that normoxic mixture of 30% N(2)O had no influence on thermo-tactile sensation in normothermia.

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. Language: en

Previous microdialysis studies performed in rats have revealed a decrease of striatal dopamine and glutamate induced by nitrogen narcosis. We sought to establish the hypothetical role of the glutamatergic corticostriatal pathway because of the glutamate deficiency which occurs in the basal ganglia in this hyperbaric syndrome. Retrodialysis with 1 mM of Saclofen and 100 mM of KCl in the prefrontal cortex under normobaric conditions led to an increase in striatal levels of glutamate by 95.2% and no changes in dopamine levels. Under 3 MPa of nitrogen and with the infusion, the rate of striatal glutamate decreased by 51.3%, to a greater extent than under pressurised nitrogen alone (-23.8%). The rate of dopamine decreased, which also occurred under pressurised nitrogen (-36.9 and -31.4%, respectively). In conclusion, the function of the corticostriatal pathway is affected by nitrogen under pressure. This suggests that the nitrogen-induced break point seems to be located at the glutamatergic striatopetal neurons.

Exposure to nitrogen-oxygen mixture at high pressure induces narcosis, which can be considered as a first step toward general anaesthesia. Narcotic potencies of inert gases are attributed to their lipid solubility. Nitrogen narcosis induces cognitive and motor disturbances that occur from 0.3 MPa in man and from 1 MPa in rats. Neurochemical studies performed in rats up to 3 MPa have shown that nitrogen pressure decreases striatal dopamine release like argon, another inert gas, or nitrous oxide, an anaesthetic gas. Striatal dopamine release is under glutamatergic and other amino acid neurotransmission regulations. The aim of this work was to study the effects of nitrogen at 3 MPa on striatal amino acid levels and to compare to those of 3 MPa of helium which is not narcotic at this pressure, by using a new technique of microdialysis samples extraction under hyperbaric conditions, in freely moving rats. Amino acids were analysed by HPLC coupled to fluorimetric detection in order to appreciate glutamate, aspartate, glutamine and asparagine levels. Nitrogen-oxygen mixture exposure at 3 MPa decreased glutamate, glutamine and asparagine concentrations. In contrast, with helium-oxygen mixture, glutamate and aspartate levels were increased during the compression phase but not during the stay at maximal pressure. Comparison between nitrogen and helium highlighted the narcotic effects of nitrogen at pressure. As a matter of fact, nitrogen induces a reduction in glutamate and in other amino acids that could partly explain the decrease in striatal dopamine level as well as the motor and cognitive disturbances reported in nitrogen narcosis.

Nitrogen pressure exposure in rats results in decreased dopamine (DA) release at the striatal terminals of the substantia nigra pars compacta (SNc) dopaminergic neurons, demonstrating the narcotic potency of nitrogen. This effect is attributed to decreased excitatory and increased inhibitory inputs to dopaminergic neurons, involving a change in NMDA and GABA(A) receptor function. We investigated whether repetitive exposures to nitrogen modify the excitatory and inhibitory control of the dopaminergic nigro-striatal pathway. We used voltammetry to measure dopamine levels in freely-moving rats, implanted with dopamine-sensitive electrodes in the striatum. NMDA/GABA(A) receptor agonists (NMDA/muscimol) and antagonists (AP7/gabazine) were administered through a guide-cannula into the SNc, and their effects on striatal dopamine levels were measured under normobaric conditions, before and after five repetitive exposures to 1 MPa nitrogen. NMDA-mediated dopamine release was greater following repetitive exposures, AP7-mediated inhibition of glutamatergic input was blocked, suggesting that NMDA receptor sensitivity was increased and glutamate release reduced. Muscimol did not modify dopamine levels following repetitive exposures, whereas the effect of gabazine was greater after exposures than before. This suggested that interneuronal GABA(A) receptors were desensitized, leading to an increased GABAergic input at dopaminergic cells. Thus, repetitive nitrogen exposure induced persistent changes in glutamatergic and GABAergic control of dopaminergic neurons, resulting in decreased activity of the nigrostriatal pathway.

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.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.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.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.The modified scale, renamed the Subjective Narcosis Assessment Scale here, has useful psychometric properties, and promising potential for future use.

Previous studies have demonstrated opposite effects of high-pressure helium and nitrogen on extracellular dopamine (DA) levels, which may reflect disturbances on the synthesis, release or metabolic mechanisms. Intrastriatal microdialysis was used to measure the precursor (tyrosine), DA and its metabolites (DOPAC, HVA) levels under nitrogen- or helium- at pressure up to 3 MPa. Under 3 MPa of helium–oxygen breathing mixtures, the extracellular concentration of tyrosine is decreased while the extracellular concentration of DA is increased. On the contrary, nitrogen–oxygen breathing mixture at the same pressure increased extracellular tyrosine concentration and decreased DA release. Under both conditions, an increment of the DOPAC and HVA levels could be noted. Our results suggest that changes in DA release and metabolism during high-pressure helium exposure reflect the effect of the pressure per se, whereas the intrinsic effects of narcotic gases, although sensitive to pressure, would be revealed by hyperbaric nitrogen exposure.

Inert gas narcosis is a neurological syndrome appearing when humans or animals are exposed to hyperbaric inert gases (nitrogen, argon) composed by motor and cognitive impairments. Inert gas narcosis induces a decrease of the dopamine release at the striatum level, structure involved in the regulation of the extrapyramidal motricity. We have investigated, in freely moving rats exposed to different narcotic conditions, the relationship between the locomotor and motor activity and the striatal dopamine release, using respectively a computerized device that enables a quantitative analysis of this behavioural disturbance and voltammetry. The use of 3 MPa of nitrogen, 2 MPa of argon and 0.1 MPa of nitrous oxide, revealed after a transient phase of hyperactivity, a lower level of the locomotor and motor activity, in relation with the decrease of the striatal dopamine release. It is concluded that the striatal dopamine decrease could be related to the decrease of the locomotor and motor hyperactivity, but that other(s) neurotransmitter(s) could be primarily involved in the behavioural motor disturbances induced by narcotics. This biphasic effect could be of major importance for future pharmacological investigations, and motor categorization, on the basic mechanisms of inert gas at pressure.

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.

Previous findings of a narcosis-induced reduction in heat production during cold water immersion, as reflected in oxygen uptake (VO2), have been attributed to the attenuation of the shivering response. The possibility of reduced oxygen utilization (VO2) by the muscles could not, however, be excluded. Accordingly, the present study tested the hypothesis that mild narcosis, induced by inhalation of a normoxic gas mixture containing 30% nitrous oxide (N2O), would affect VO2. Nine male subjects participated in both maximal and submaximal exercise trials, inspiring either room air (AIR) or a normoxic mixture containing 30% N2O. In the submaximal trials, the subjects exercised at 50% of maximal exercise intensity (Wmax) as determined in the maximal AIR trial. Though the subjects attained the same Wmax in the AIR and N2O trials, maximal VO2 was significantly higher (P < 0.05) during the N2O condition [58.9 (SEM 3.1) ml x kg(-1) x min(-1)] compared to the AIR condition [55.0 (SEM 2.4) ml x kg(-1) x min(-1)]. However, the VO2-relative exercise intensity relationship was similar during both maximal AIR and maximal N2O at submaximal exercise intensities. There were no significant differences in the responses of oesophageal temperature, sweating rate, heart rate and ventilation between AIR and N2O in the maximal and submaximal tests. It was concluded that the previously reported narcosis-induced reductions in VO2 observed during cold water immersion can be attributed solely to a reduction in the shivering response rather than to decreased oxygen utilization by the muscles.

Inert gases at raised pressure exert anaesthetic effects. It is assumed that anaesthesia by the inert gases is fundamentally similar to anaesthesia produced by general anaesthetics. However, do general anaesthetics bind directly to proteins or influence activity by indirectly perturbing membrane lipids still remains a major question. Although the pressure required to achieve anaesthesia with inert gases has been suggested to exert potentially some pressure antagonism per se, this has not been studied yet to our knowledge. We investigated this possibility using nitrogen, argon, and nitrous oxide. Whatever the narcotic agent used, our results showed that the pressure of narcotic required to induce anaesthetic effects increased, as compression rate increased, in a sigmoid fashion rather than in a linear fashion. Evidence for sigmoidal responses vs. linear responses depended of the narcotic potency of the anaesthetic agent used (nitrogen: r2=0.973 vs. r2=0.941; argon: r2=0.971 vs. r2=0.866; nitrous oxide: r2=0.995 vs. r2=0.879). Since a linear antagonism is predicted by lipid theories, we think it likely that these findings indicate that inert gases bind to a modulatory site of a protein receptor and act as allosteric modulators. Since other workers provided evidence for binding processes using volatile anaesthetics, the present findings could indicate that all classes of general anaesthetics, including inert gases, could act by binding directly to proteins rather than by dissolving in some lipids of the cellular membrane.

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.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.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.A significant decrement (9.5%, P0.001) 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.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.

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).

We investigated the effect of narcosis induced by subanesthetic concentrations of nitrous oxide (N2O), a behavioral analogue for hyperbaric nitrogen, on psychomotor performance. In particular, we assessed individual susceptibility to narcosis.The participants were 12 female and 12 male undergraduate students. Psychomotor assessment was conducted with a computerized Visual Simple Reaction Time (VSRT) test, and Trail Making Tests Part A (TMTA) and Part B (TMT-B). The tests were conducted on two separate occasions in the following order: VSRT, TMT-A, TMT-B. On the first occasion participants conducted the tests breathing room air (air trial), and during the second test they conducted the tests while breathing a normoxic mixture containing 30% N2O (N2O trial).Males had significantly (p = 0.036) shorter VSRT in the air trials. There was no effect of gender on psychomotor performance in the N2O trials. Overall, mean performance in the N2O trials degraded significantly (p = 0.004) only in VSRT. Performance of individual participants exhibited different and inconsistent direction of change in the N2O trials.N2O-induced alterations in psychomotor function are primarily dependent on individual susceptibility to narcosis (i.e., concentration threshold).

Previous studies on nitrogen narcosis have focused on how it affects behavior, performance, and cognitive function. However, little is known about the effects of nitrogen narcosis on the emotional processing of external stimuli.We presented 20 volunteers with images from the International Affective Picture System (IAPS) and categorized as unpleasant, neutral, or pleasant, while sitting in a hyperbaric chamber at the surface (101,3kPa) and at 39 m equivalent depth (496.4 kPa). The participants rated the images along three affective dimensions: valence (intrinsic attractiveness or aversiveness of a stimuli), arousal, and dominance.In the valence dimension there was no significant effect of increased pressure or interaction between increased pressure and image category. There was a significant interaction between image category and the pressure at which the images were viewed in the arousal dimension. The mean arousal rating score for unpleasant stimuli was 0.5 point (on a 9-point scale) lower at hyperbaric conditions and equal arousal rating score for neutral stimuli in general.The absence of any effect of pressure in the valence dimension suggests that divers have no impairment in their ability to determine the pleasantness or unpleasantness of different stimuli. Furthermore, this study suggests that the effects of nitrogen narcosis on the emotional processing of external stimuli are primarily evident in the arousal dimension. Although differences in arousal ratings were relatively small in magnitude, even a small alteration in emotional response to external stimuli might be important in the context of deep diving.

Measurement of inert gas narcosis and its degree is difficult during operational circumstances, hence the need for a reliable, reproducible and adaptable tool. Although being an indirect measure of brain function, if reliable, critical flicker fusion frequency (CFFF) could address this need and be used for longitudinal studies on cortical arousal in humans.To test the reliability of this method, the comparison between CFFF and three tests (Math-Processing Task, Trail-Making Task, and Perceptual Vigilance Task) from the Psychology Experiment Building Language battery (PEBL) were used to evaluate the effect of 10 minutes of 100% normobaric oxygen breathing on mental performance in 20 healthy male volunteers.Breathing normobaric oxygen significantly improved all but one of the measured parameters, with an increase of CFFF (117.3 ± 10.04% of baseline, P0.0001) and a significant reduction of time to complete in both the math-processing (2,103 ± 432.1 ms to 1,879 ± 417.5 ms, P = 0.0091) and trail-making tasks (1,992 ± 715.3 to 1,524 ± 527.8 ms, P = 0.0241). The magnitude of CFFF change and time to completion of both tests were inversely correlated (Pearson r = -0.9695 and -0.8731 respectively, P0.0001). The perceptual vigilance task did not show a difference between air and O₂ (P0.4).The CFFF test provides an assessment of cognitive function that is similar to some tests from PEBL, but requires a less complicated set up and could be used under various environmental conditions including diving. Further research is needed to assess the combined effects of increased pressure and variations in inspired gas mixtures during diving.

The effect of an increased nitrogen partial pressure under hyperbaric conditions is known as nitrogen narcosis (NN). At an ambient pressure of about 4 bar, reduced cognitive performance as well as euphoric effects are reported. We examined the effect of NN on pain perception. 22 subjects completed an experimental (50 meters = 6 bar) and a simulated control dive (0 m = 1 bar) in a hyperbaric chamber. Before and during each dive a standardized cold pressure test was performed. The intensity of pain perceived was assessed with the help of a visual analogue scale; additionally, subjects assessed the subjective effect of NN. The study showed that the perceived pain intensity is significantly reduced under nitrogen narcosis conditions (F1.21 = 5.167, p0.034) when compared to the perceived pain intensity under the control dive conditions (F1.21 = 0.836, p = 0.371). A connection between perceived pain intensity and subjects experience of the NN was not found under the experimental dive condition (r = 0.287, p = 0.195). We could show that even relatively moderate hyperbaric conditions may have an influence on the perception of pain. The results are highly relevant since nitrogen narcosis occurs in divers as well as in medical personnel or construction workers, working under hyperbaric conditions.

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 5 52.8; SD 5 12.1) water compared to the shallow water (mean 5 46.9; SD 5 8.4). In addition, anxious subjects took significantly longer to complete the task in the deep water (mean 5 48.6; SD 5 6.8) compared to non-anxious subjects (mean 5 53.2; SD 5 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 man- ual dexterity was sensitive to the effects of depth and will be a useful tool in future research

In man, nitrogen narcosis is characterized by euphoria, impaired cognitive function, neuromuscular incoordination and, ultimately, loss of consciousness. Because of the motor movement disorders, we chose to study the nigrostriatal system, whose major function is to regulate the extrapyramidal nervous system. The purpose of this investigation was to monitor changes in extracellular levels of dopamine (DA), 3, 4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the striatum of conscious rats, using intracerebral microdialysis. Results show a 40% decrease in extracellular DA concentration, a 59% increase in extracellular DOPAC and an increase in HVA starting with exposure to the nitrogen mixture. Thirty minutes after the beginning of the exposure, a compensation phase took place. HVA returns to its initial basal value, and levels of DOPAC and DA returned towards normal but never reached their initial values. These results contrast with those observed during the High Pressure Neurological Syndrome (HPNS, 5.1 MPa of helium pressure) in which there is a significant increase in extracellular DA. Therefore, some of the symptoms of nitrogen narcosis may be linked with the decrease in the extracellular DA levels.

One of the possible risks incurred while diving is inert gas narcosis (IGN), yet its mechanism of action remains a matter of controversy. Although providing insights in the basic mechanisms of IGN, research has been primarily limited to animal studies. A human study, in real diving conditions, was needed. Twenty volunteers within strict biometrical criteria (male, age 30-40 years, BMI 20-23, non smoker) were selected. They performed a no-decompression dive to a depth of 33 mfw for 20 min and were assessed by the means of critical flicker fusion frequency (CFFF) measurement before the dive, during the dive upon arriving at the bottom, 5 min before the ascent, and 30 min after surfacing. After this late measurement, divers breathed oxygen for 15 min and were assessed a final time. Compared to the pre-dive value the mean value of each measurement was significantly different (p, JOURNAL ARTICLE, info:eu-repo/semantics/published

In this study, we investigated the influence of mild narcosis on temperature perception, thermal comfort, and behavioral temperature regulation in humans. Twelve subjects (six males and six females) participated in two trials, during which they wore a water-perfused suit (WPS). The temperature of the WPS (TWPS) fluctuated sinusoidally from 27 degrees to 42 degrees C, at a heating and cooling rate of 1.2 degrees C x min(-1). In the first trial, the subjects had no control over TWPS: They determined their thermal comfort zone (TCZ) by providing a subjective response whenever they perceived the temperature changing from a comfortable to an uncomfortable level and vice versa; in addition, they provided subjective ratings of temperature perception and thermal comfort on a 7-point and 4-point scale, respectively, at each 3 degrees C change in TWPS. In the second trial, subjects could change the direction of TWPS whenever it became uncomfortable by depressing a button on a manual control. The protocols were conducted with subjects breathing either room air (AIR), or a normoxic breathing mixture containing 30% N2O. Subjects perceived increasing TWPS as equally warm and the decreasing TWPS as equally cold with AIR or N2O. However, equal changes in TWPS were perceived as significantly less discomforting (P0.05) during N2O, and the magnitude of the TCZ significantly (P0.01) increased. Thus, narcosis did not alter thermal sensation, but it significantly changed the perception of comfort. These changes were not reflected in the behavioral response. Subjects produced similar TWPS damped-oscillation patterns in the AIR and N2O trials. We conclude that the narcosis-induced alteration in the perception of thermal comfort does not change the preferred temperature, or the ability to behaviorally maintain thermal comfort.

Photopic contrast sensitivity of air-breathing scuba divers was measured with a translucent test pattern at depths up to 40 m. The pattern was composed of sine wave gratings with spatial frequency and contrast changing logarithmically. The spatial transfer characteristics were measured at various depths under controlled optical conditions in seawater and in fresh water. Analysis indicates that the visual contrast sensitivity, and therefore probably also acuity, of sport divers is not affected up to depths of 40 m. This holds under ideal as well as poor diving conditions.

Previous neurochemical studies performed in rats have revealed a decrease of striatal dopamine and glutamate induced by inert gas narcosis. We sought to establish the hypothetical role of glutamate and its main receptor, the N-methyl-d-aspartate (NMDA) receptor, in this syndrome. We aimed to counteract the nitrogen narcosis-induced glutamate and dopamine decreases by stimulating the NMDA receptor in the striatum. We used bilateral retrodialysis on awake rats, submitted to nitrogen under pressure (3 MPa). Continuous infusion of 2 mM of NMDA under normobaric conditions (0.01 MPa) ( n = 8) significantly increased extracellular average levels of glutamate, aspartate, glutamine, and asparagine by 241.8%, 292.5%, 108.3%, and 195.3%, respectively. The same infusion conducted under nitrogen at 3 MPa ( n = 6) revealed significant lower levels of these amino acids ( n = 8/6, P > 0.001). In opposition, the NMDA-induced effects on dopamine, dihydrophenylacetic acid (DOPAC), and homovanillic acid (HVA) levels were statistically not affected by the nitrogen at 3 MPa exposure ( n = 8/6, P > 0.05). Dopamine was increased by >240% on average. HVA was decreased (down to 40%), and there was no change in DOPAC levels, in both conditions. Results highlight that the NMDA receptor is not directly affected by nitrogen under pressure as indicated by the elevation in NMDA-induced dopamine release under hyperbaric nitrogen. On the other hand, the NMDA-evoked glutamate increase is counteracted by nitrogen narcosis. No improvement in motor and locomotor disturbances was observed with high striatal concentration in dopamine. Further experiments have to be done to specify why the striatal glutamate pathways, in association with the inhibition of its metabolism, only are affected by nitrogen narcosis in this study.

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.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.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.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.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.

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.The current study aimed to test this assumption by comparing subjective (ratings) and behavioural (Digit Letter Substitution Test) responses to nitrogen narcosis and alcohol.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.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.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.

The spontaneous motor activity and pose reflexes of male adult rats (Wistar) were observed in the course of high pressure nitrogen compression up to 4,1 MPa. The experiments were carried out under normoxic and hypoxic conditions. Stabile rat motor cortex oxygen tension was recording during the nitrogen compression up to 7,1 MPa under normoxic condition. Sensitivity to nitrogen high pressure to be on the increase under hypoxic conditions. In its turn, resistibility to nitrogen high pressure to be on the decrease under hypoxic conditions (oxygen partial pressure from 0,012 to 0,004 MPa). Quantity of high dencity heat shock proteins (Hsp70) rats motor cortex neurons was 3,44 times higher after course of high pressure nitrogen compression up to 4,1 MPa. For hypoxic exposure (6% O2) the difference was less pronounced - 2,2 times. Data about rat motor cortex neurons Hsp70 concentration under high nitrogen pressure and low oxygen pressure may turn to be a clear base for explanation hypoxic influence on processes of nitrogen narcosis.

Nitrogen at pressure produces a neurological syndrome called nitrogen narcosis. Neurochemical experiments indicated that a single exposure to 3 MPa of nitrogen reduced the concentration of dopamine by 20% in the striatum, a structure involved in the control of extrapyramidal motor activity. This effect of nitrogen was explained by enhanced GABAergic neurotransmission through GABAA receptors and, to a lesser extent, by a decreased glutamatergic input to DA cells through NMDA receptors. The aim of this study was to study, under normobaric conditions, possible alterations of NMDA receptor activity in the substantia nigra pars compacta (SNc) induced by repetitive exposures to nitrogen pressure. Under general anesthesia, male Sprague-Dawley rats were implanted in the striatum with multifiber carbon dopamine-sensitive electrodes and in the SNc with guide cannulae for drug injections. After recovery from surgery, the striatal dopamine level was recorded by voltammetry in freely-moving rats, in normobaric conditions, before and after 5 repetitive exposures to 1MPa of nitrogen (threshold of nitrogen narcosis occurrence in rat). The effect of NMDA receptor activity on DA concentration was investigated using agonist (NMDA) and specific antagonist (AP7) SNc administration. Following repetitive nitrogen exposures, the ability of NMDA to elevate DA concentrations was enhanced. In contrast, after nitrogen exposure AP7 produced a paradoxical increase in DA concentration compared to its inhibitory effect before any exposure. Similar responses were obtained after a single exposure to 3MPa nitrogen. Thus, repetitive exposures to nitrogen narcosis produced a sensitization of postsynaptic NMDA receptors on DA cells, related to a decreased glutamatergic input in SNc. Consequently, successive nitrogen narcosis exposures disrupted ion-channel receptor activity revealing a persistent nitrogen-induced neurochemical change underlying the pathologic process.

This experiment investigated the effects of nitrogen narcosis on reaction time (RT) and P300 latency and amplitude. Ten subjects breathed either air or a non-narcotic 20% oxygen-80% helium (heliox) mixture in a hyperbaric chamber at 6.5, 8.3 and 10 atmospheres absolute (ATA). The subjects responded under controlled accuracy conditions to visually presented male or female names in an oddball paradigm. Single-trial analysis revealed a strong relationship between RT and P300 latency, both of which were slowed in a dose-related manner by hyperbaric air but not by heliox. A clear-cut dose-response relationship could not be established for P300 amplitude. These results indicate that P300 latency indexes nitrogen narcosis and are interpreted as support for the slowed processing model of inert gas narcosis.

The precise action of the immunological effects associated with hyperbaric exposure is poorly understood. This study's goal was to clarify the effects and etiology of deep air dives on the immune response.Sprague-Dawley rats were exposed to 7-ATA air for 60 min twice daily for 3 consecutive days. Several markers of immune function, the degree of stress, and oxidative stress following or during the exposures were determined. Rats exposed to 1.47-ATA oxygen or 7-ATA nitrox (0.21-ATA oxygen + 6.79-ATA nitrogen) were taken as controls.Peripheral lymphocytes and CD3+ and CD4+CD3+ subsets in peripheral blood and spleen, plasma interleukin-2 level, and the responses of splenic lymphocytes to concanavalin A all decreased, antioxidant enzyme activities and the concentration of reduced glutathione both decreased, while the level of malondialdehyde increased following hyperbaric air exposures. All changes returned to normal in 3-5 d. Similar changes were observed following exposures to 1.47-ATA oxygen, but not to normoxic nitrox. Plasma levels of adrenocorticotropic hormone and corticosterone increased after one exposure and recovered to normal levels after three exposures in rats treated with either hyperbaric or normobaric air. Pretreatment of the animals with N-acetylcysteine, a potent free radical scavenger and antioxidant attenuated the effects of hyperbaric air on immune and antioxidant systems.These results are consistent with the hypothesis that repetitive exposure to 7-ATA air has a temporary immunosuppressive effect on rats, which is related to oxidative stress induced by the high partial pressure of oxygen in breathing gas.

Hyperbaric nitrogen-oxygen exposure developed in rats a decrement of the striatal dopamine release, which was reversed by repetitive exposures. This dopamine decrease could be the result of the antagonistic effect of nitrogen on NMDA receptors. The increment of the dopamine release, following repetitive exposures to nitrogen, could be attributed to a desensitisation of NMDA receptors to the effects of nitrogen. To test these hypotheses, male Sprague-Dawley rats were implanted with electrodes in the striatum to measure dopamine release by voltammetry and cannula in the substantia nigra pars compacta for NMDA injection. Free-moving rats were exposed up to 3MPa of nitrogen-oxygen mixture before and after 5 exposures to 1MPa. At the first exposure to 3MPa, the dopamine level decreased (-15%) but is counteracted by NMDA administration. In contrast, after repetitive exposure, the second exposure to 3MPa, induces a 10% dopamine increase. NMDA administration significantly potentiated this increase. Our results neither support the hypothesis of an antagonist effect of nitrogen on NMDA receptors at the first exposure, nor that of a NMDA receptor desensitization following repetitive exposures to hyperbaric nitrogen.

The bioassay guided fractionation of the dried aerial part of Indigofera tinctoria Linn. led to the identification of an active fraction labelled as indigotin. On further chemical analysis, a compound isolated from indigotin was identified and characterized as trans-tetracos-15-enoic acid (TCA). The chemical structure of this compound was established on the basis of physical properties and spectral data, including NMR. It afforded significant hepatoprotection against carbon tetrachloride and paracetamol induced hepatotoxicity in experimental models. Silymarin, a well known plant based hepatoprotective agent, and N-acetylcysteine, which has proven efficacy as a replenisher of sulfhydryls, were used for relative efficacy. TCA was found to reverse the altered hepatic parameters in experimental liver damage. In the safety evaluation study the oral LD50 was found to be more than 2000 mg/kg, with no signs of abnormalities or any mortality for the 15 day period of observation after administration of a single dose of drug in mice. The studies revealed significant and concentration dependent hepatoprotective potential of TCA as it reversed the majority of the altered hepatic parameters in experimental liver damage in rats and mice and may be useful in the management of liver disorders.

Nitrogen at high pressures and anesthetics increase lipid monolayer surface pressure and in turn modulates monolayer associated lipolytic enzyme activity that could alter membrane lipids. We tested the hypothesis that nitrogen at pressures of 5 and 10 megapascals (MPa) and pentobarbital induce alterations in synaptosomal membrane phospholipid and free fatty acid (FFA). Rat cortical synaptosomes in Krebs-Henseleit buffer were placed in steel chambers and incubated for four hours at 37 degrees C: at 5 or 10 MPa of O2/balance N2; at one 0.1 MPa on room air, and with 10 mg pentobarbital. Free fatty acids (FFA) were quantified by thin-layer and gas chromatography, and neutral and acidic lipids by high-pressure thin layer chromatography and protein by Biorad colorimetric assay. Statistical analyses were by ANOVA and posthoc analysis by Neuman-Keuls and Kruskal-Wallis tests at p0.05. Sphyngomyelin, phosphatidylcholine, phosphatidylethanolamine, cerebroside and cholesterol were unchanged by 5 and 10 MPa nitrogen and pentobarbital. Free fatty acids (16:00, 18:00, 18:01, 20:00, 22:0, 22:01 and 24:01) at 10 MPa were reduced compared to 5 MPa (p0.05) but unaffected by pentobarbital. The decrease in synaptosomal membrane FFA at 10 MPa suggests attenuated hydrolysis of membrane phospholipids without detectable alterations in membrane phospholipid composition.

Brain auditory evoked potential (BAEP) in mice exposed to hyperbaric H2O2 pressure was monitored to reveal the correlation between altered synaptic transmission and hydrogen narcosis or isobaric HPNS. Inter peak latencies and wave amplitudes were selected as indices of assessment. The animals were exposed either to He-O2 or H2-O2 at 2.1 MPa and 4.1 MPa. Results showed that synaptic transmission was inhibited to various extents. The inhibition was partly due to the narcotic effect of hydrogen, which was added to the effect caused by hydrostatic pressure. On the other hand, asymmetrical reaction of each segment in the neuro-network might be responsible for the occurrence of HPNS.

The narcotic effect of nitrogen impairs diver performance and limits dive profiles, especially for deep dives using compressed air. It would be helpful to establish measurable correlates of nitrogen narcosis.The authors observed the electroencephalogram (EEG) of 10 subjects, ages 22-27 yr, who breathed air during a 3-min compression to a simulated depth of 80 msw (9 ATA). The EEG from a 19-electrode cap was recorded for 20 min while the subject reclined on a cot with eyes closed, first at 1 ATA before the dive and again at 9 ATA. Signals were analyzed using Fast Fourier Transform and brain mapping for frequency domains 0-4 Hz, 4-7 Hz, 7-12 Hz, and 12-15 Hz. Student's paired t-test and correlation tests were used to compare results for the two conditions.Two EEG patterns were observed. The first was an increase in delta and theta activity in all cortical regions that appeared in the first 2 min at depth and was related to exposure time. The second was an increase in delta and theta activity and shifting of alpha activity to the frontal regions at minute 6 of breathing air at 9 ATA and was related to the narcotic effects of nitrogen.If confirmed by studies with larger case series, this EEG pattern could be used to identify nitrogen narcosis for various gas mixtures and prevent the dangerous impact of nitrogen on diver performance.

The contribution of inert gases to the risk of central nervous system (CNS) oxygen toxicity is a matter of controversy. Therefore, diving regulations apply strict rules regarding permissible oxygen pressures (Po2). We studied the effects of nitrogen and helium (0, 15, 25, 40, 50, and 60%) and different levels of Po2 (507, 557, 608, and 658 kPa) on the latency to the first electrical discharge (FED) in the EEG in rats, with repeated measurements in each animal. Latency as a function of the nitrogen pressure was not homogeneous for each rat. The prolongation of latency observed in some rats at certain nitrogen pressures, mostly in the range 100 to 500 kPa, was superimposed on the general trend for a reduction in latency as nitrogen pressure increased. This pattern was an individual trait. In contrast with nitrogen, no prolongation of latency to CNS oxygen toxicity was observed with helium, where an increase in helium pressure caused a reduction in latency. This bimodal response and the variation in the response between rats, together with a possible effect of ambient temperature on metabolic rate, may explain the conflicting findings reported in the literature. The difference between the two inert gases may be related to the difference in the narcotic effect of nitrogen. Proof through further research of a correlation between individual sensitivity to nitrogen narcosis and protection by N2 against CNS oxygen toxicity in rat may lead to a personal O2 limit in mixed-gas diving based on the diver sensitivity to N2 narcosis.