108 research outputs found

    Critical Flicker Fusion Frequency: A Marker of Cerebral Arousal During Modified Gravitational Conditions Related to Parabolic Flights

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    In situ evaluation of human brain performance and arousal remains challenging during operational circumstances, hence the need for a rapid, reliable and reproducible tool. Here we hypothesized that the Critical flicker fusion frequency (CFFF) reflecting/requiring visual integration, visuo-motor skills and decision-taking process might be a powerful, fast and simple tool in modified gravity environments. Therefore 11 male healthy volunteers were assessed for higher cognitive functions with CFFF during parabolic flights. They were assessed at different time points: upon arrival to the base, 30 min after subcutaneous scopolamine administration, before parabolas, during hypergravity and microgravity at break time (between the 16th and the 17th parabola), on the return flight and on the ground after landing. First, a stable, and consistent measurement of CFFF could be obtained within 12 s. Second, under modified gravitational conditions, the perceptual ability of participants is significantly modified. Compared to the baseline, evolution is characterized by a significant increase of CFFF when in microgravity (0g: 106.9 ± 5.5%), and a significant decrease of CFFF while in hypergravity (2g: 94.5 ± 3.8%). Other time-points were not statistically different from the baseline value. Although the underlying mechanism is still debated, we suggest that the CFFF test is a global marker of cerebral arousal as the result of visuo-motor and decision taking testing based on a simple visual stimulus with an uncomplicated set up that could be used under various environmental conditions. The authors express an opinion that it would be advisable to introduce CFFF measurement during spaceflights as it allows individual longitudinal assessment of individual ability even under conditions of incomplete physiological compensation, as shown here during parabolic flights

    Pre-dive Whole-Body Vibration Better Reduces Decompression-Induced Vascular Gas Emboli than Oxygenation or a Combination of Both

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    Purpose: Since non-provocative dive profiles are no guarantor of protection against decompression sickness, novel means including pre-dive “preconditioning” interventions, are proposed for its prevention. This study investigated and compared the effect of pre-dive oxygenation, pre-dive whole body vibration or a combination of both on post-dive bubble formation. Methods: Six healthy volunteers performed 6 no-decompression dives each, to a depth of 33 mfw for 20 min (3 control dives without preconditioning and 1 of each preconditioning protocol) with a minimum interval of 1 week between each dive. Post-dive bubbles were counted in the precordium by two-dimensional echocardiography, 30 and 90 min after the dive, with and without knee flexing. Each diver served as his own control. Results: Vascular gas emboli (VGE) were systematically observed before and after knee flexing at each post-dive measurement. Compared to the control dives, we observed a decrease in VGE count of 23.8 ± 7.4% after oxygen breathing (p < 0.05), 84.1 ± 5.6% after vibration (p < 0.001), and 55.1 ± 9.6% after vibration combined with oxygen (p < 0.001). The difference between all preconditioning methods was statistically significant. Conclusions: The precise mechanism that induces the decrease in post-dive VGE and thus makes the diver more resistant to decompression stress is still not known. However, it seems that a pre-dive mechanical reduction of existing gas nuclei might best explain the beneficial effects of this strategy. The apparent non-synergic effect of oxygen and vibration has probably to be understood because of different mechanisms involved

    Just say NO to decompression bubbles: is there a real link between nitric oxide and bubble production or reduction in humans?

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    Vascular gas emboli (VGE) start forming during the degassing of tissues in the decompression (ascent) phase of the dive when bubble precursors (micronuclei) are triggered to growth. The precise formation mechanism of micronuclei is still debated, with formation sites in facilitating regions with surfactants, hydrophobic surfaces or crevices. Ho wever, significant inter-subject variability to VGE exists for the same diving exposure and VGE may even be reduced with a single pre-dive intervention. The precise link between VGE and endothelial dysfunction observed post dive remains unclear and a nitric oxide (NO) mechanism has been hypothesized. Subjects in good physical condition are at lesser risk of VGE and DCS observed post dive. More surprisingly, single pre-dive interventions or 'preconditioning' can influence the VGE observed post dive. Studies in rats have shown that a single bout of exercise 20 h pre dive can reduce post-dive VGE and mortality. In humans, the role of exercise has been debated and depending on its timing and intensity may increase or decrease bubbles. A NO-mediated change in the surface properties of the vascular endothelium favouring the elimination of gas micronuclei has been suggested to explain this protection against bubble formation.¹¹ NO synthase activity increases following 45 minutes of exercise and NO administration immediately before a dive reduces VGE. Nevertheless, bubble production is increased by NO blockade in sedentary but not in exercised rats, suggesting other biochemical pathways such as heat-sensitive proteins, antioxidant defenses or blood rheology may be involved. The first link between NO and DCS protection was shown by chance. In an experiment using explosive decompression of sedentary rats resulting in >80% mortality, some additional rats were needed to complete the experiment but only trained (treadmill-exercised) rats were available instead of sedentary ones. After the decompression, 80% of the trained rats survived. The explanation given for this observation was that the presence of NO in the trained rats resulted in fewer bubbles and less DCS. However, a French study showed that human volunteers had fewer bubbles post decompression after a treadmill exercise compared to the same exercise (same VO₂) after a cycle-ergometer stress test. If this was related to NO production, the number of bubbles should be more or less the same. There are some mechanical differences between the two forms of exercise, namely more impacts and vibrations during the treadmill test. It is hypothesized that micronuclei are reduced by a mechanical effect as shown by an experiment with vibration applied before diving, which reduced decompression bubbling. In conclusion, more investigations are needed to further ascertain the link between NO and post-decompression VGE modulation. Such studies should be directed more on high-intensity training (less NO-related), since aerobic efforts have already been extensively studied in relation to the reduction of decompression stress, this will probably allow more understanding of the subtle mechanisms for DCS protection. The variable effect of oxygen on bubble decay, with transient increase of volume in some cases, also requires further investigation.Editorialinfo:eu-repo/semantics/publishe

    Is the patency of the cardiac foramen ovale a risk factor for disbaric pathologies: contribution to diving research and fostering diving safety

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    Doctorat en kinésithérapie et réadaptationinfo:eu-repo/semantics/nonPublishe

    Dive Risk Factors, Gas Bubble Formation, and Decompression Illness in Recreational SCUBA Diving: Analysis of DAN Europe DSL Data Base.

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    Introduction: The popularity of SCUBA diving is steadily increasing together with the number of dives and correlated diseases per year. The rules that govern correct decompression procedures are considered well known even if the majority of Decompression Sickness (DCS) cases are considered unexpected confirming a bias in the "mathematical ability" to predict DCS by the current algorithms. Furthermore, little is still known about diving risk factors and any individual predisposition to DCS. This study provides an in-depth epidemiological analysis of the diving community, to include additional risk factors correlated with the development of circulating bubbles and DCS. Materials and Methods: An originally developed database (DAN DB) including specific questionnaires for data collection allowed the statistical analysis of 39,099 electronically recorded open circuit dives made by 2,629 European divers (2,189 males 83.3%, 440 females 16.7%) over 5 years. The same dive parameters and risk factors were investigated also in 970 out of the 39,099 collected dives investigated for bubble formation, by 1-min precordial Doppler, and in 320 sea-level dives followed by DCS symptoms. Results: Mean depth and GF high of all the recorded dives were 27.1 m, and 0.66, respectively; the average ascent speed was lower than the currently recommended "safe" one (9-10 m/min). We found statistically significant relationships between higher bubble grades and BMI, fat mass, age, and diving exposure. Regarding incidence of DCS, we identified additional non-bubble related risk factors, which appear significantly related to a higher DCS incidence, namely: gender, strong current, heavy exercise, and workload during diving. We found that the majority of the recorded DCS cases were not predicted by the adopted decompression algorithm and would have therefore been defined as "undeserved." Conclusion: The DAN DB analysis shows that most dives were made in a "safe zone," even if data show an evident "gray area" in the "mathematical" ability to predict DCS by the current algorithms. Some other risk factors seem to influence the possibility to develop DCS, irrespective of their effect on bubble formation, thus suggesting the existence of some factors influencing or enhancing the effects of bubbles.info:eu-repo/semantics/publishe
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