Supraorbital transcutaneous neurostimulation has sedative effects in healthy subjects

Transcutaneous neurostimulation (TNS) at extracephalic sites is a well known treatment of pain. Thanks to recent technical progress, the Cefaly® device now also allows supraorbital TNS. During observational clinical studies, several patients reported decreased vigilance or even sleepiness during a session of supraorbital TNS. We decided therefore to explore in more detail the potential sedative effect of supraorbital TNS, using standardized psychophysical tests in healthy volunteers.Clinical TrialJournal Articleinfo:eu-repo/semantics/publishe

Field study of anthropomorphic and muscle performance changes among elite skippers following a transoceanic race

Background: Ocean racing has become increasingly demanding, both physically and psychologically. The aim of the study was to assess global changes after a transoceanic race. Materials and methods: Eight male sailors were evaluated pre- and post-race through anthropometric measurements (weight, skinfold, girth at different level and estimated body fat percentage), multifrequency tetrapolar bioelectrical impedance, muscular performance, visual analogic scale for perceived fatigue and Critical Flicker Fusion Frequencies for cerebral arousal. Results: Compared to pre-race values, a significant decrease in body weight (–3.6 ± 1.4%, p = 0.0002) and body composition with reduction of body fat percentage (–15.1 ± 3.5%, p < 0.0001) and fat mass (–36.4 ± 31.4%, p = 0.022) was observed. Muscle performance of the upper limb was preserved. In the lower limb, monohulls skippers showed a significant reduction of jump height (–6.6 ± 4.8%, p = 0.022), power (–11.7 ± 7.3%, p = 0.011) and speed (–14.6 ± 7.4%, p = 0.0006) while a multihulls skipper showed a gain in speed (+0.87%), power (+8.52%), force (+11%) resulting in a higher jump height (+1.12%). These changes were inversely correlated with sea days (Pearson r of –0.81, –0.96 and –0.90, respectively, p < 0.01). Conclusions: Changes in body weight and composition are consistent with previous data indicating a probable negative energy balance. The main finding demonstrates a difference in muscular conditioning between upper and lower limbs that might be explained by differential workload related to boat architecture (trampolines) or handling

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

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

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

Is there a need for more diving science for divers?

Decompression illness (DCI)/dysbaric disorders represent a complex spectrum of pathophysiological conditions with a wide variety of signs and symptoms related to dissolved gas and its subsequent phase change. Any significant organic or functional decrement in individuals who have recently been exposed to a reduction in environmental pressure (i.e. decompression) must be considered as evidence of DCI until proven otherwise. However, apart from the more obvious acute manifestations, individuals who have experienced repetitive exposures (e.g. commercial or professional divers and active recreational divers) may also develop sub-acute or chronic manifestations sub-clinically - insidious, even if subtle, and almost symptomless. It is, in fact, generally accepted that sub-clinical forms of DCI exist, with little or no reported symptoms, and that these may cause changes in the bones, the central nervous system and the lungs. All this has led us to analysing 'decompression stress', the actual way of understanding decompression. Current research into decompression sickness (DCS) is focused on biological markers that can be detected in the blood. Investigators are exploring the potential association between decompression stress and the presence of membrane microparticles (membrane-bound vesicles shed from a variety of cell types) in the blood. Microparticle levels increase in association with many physiological disease states as well as with the shearing stress caused by bubbles in the blood. The working hypothesis is that certain microparticles (possibly induced by inert gas bubbles) may initiate, be a marker of or contribute to the inflammatory response that leads to DCS. This investigation goes beyond the pure bubble model. While bubbles in the blood certainly play a key role in the development of DCS, their presence or absence does not reliably predict DCS symptom onset. Investigating this process at the molecular level may teach us a great deal more about DCS, providing insights that we hope will improve the effectiveness of both prevention and treatment. Approaches to evaluating decompression stress have considered a wide range of 'markers': different physiological changes after the dive (flow mediated dilatation reduction, blood pressure); personal susceptibility (VO2max, age); environmental factors (altitude, temperature); various physiological states (dehydration, increased vascular resistance as well as bubble counts, predictive decompression models, etc. etc. All this shows how far today's approach to decompression is removed from 'traditional' understanding. It reflects both the need to consider the phenomenon of decompression in a different way than previously and the advances in knowledge over the past 20 years of diving science research. The 14 researchers who have been working for three years under the PHYPODE European Project reached a point where they felt the need to publish a new book in English to allow divers to learn more about the modern approaches to understanding decompression and its problems. Almost every young scientist participating in the PHYPODE project had the responsibility of writing a chapter. This was by no means a simple job considering the different linguistic origins of this group of young researchers, many of whom had their own doctoral theses or research programmes to complete in parallel. Authors also include renowned and established scientists and diving medicine specialists. The intended readership is divers, as well as medically or scientifically educated individuals, interested in increasing their knowledge of the science behind diving and decompression. One may question this project considering the huge amount of information available on the internet on such a topic. Let us illustrate our motivation by means of a story from Japan where one of the major cosmetic companies received a customer complaint because he received an empty soap box. They launched a huge investigation and discovered that the defect arose in the packaging department. The plan was to develop a robust and reliable system ensuring zero defects in the process of product packaging and the company invested heavily in the design and implementation of a solution. A few weeks later, a similar problem occurred in a small soap-manufacturing company in India. This time the approach was very different. The manufacturer bought a big industrial fan and placed it facing the soap box chain. Boxes that were empty simply blew off the chain and the rest moved ahead to the storage house! Our aim was to keep the concepts as clear as possible but maintain the scientific integrity of the subject. References are limited and proposed as further reading. As many of those conceiving some of the new approaches are authors, this is our opportunity to be the "fan that blows empty boxes". As the PHYPODE Project has no means to receive profits from book sales or rights, the book will be published under the name of EUBS/PHYPODE, with EUBS being the beneficiary. The tentative title could be "Diving science for divers - What your diving instructor never told you". The final editor has to be decided during the Excom meeting in Wiesbaden and the book will then be published shortly after.Editorialinfo:eu-repo/semantics/publishe

Contribution à l'étude des mécanismes neurophysiologiques de la fatigue chez le sujet humain.

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

Coeur et Plongée

info:eu-repo/semantics/publishe

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

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

An Introduction to Clinical Aspect of Decompression Illness (DCI)

info:eu-repo/semantics/publishe

Oxygen: A Stimulus, Not “Only” a Drug

Depending on the oxygen partial pressure in a tissue, the therapeutic effect of oxygenation can vary from simple substance substitution up to hyperbaric oxygenation when breathing hyperbaric oxygen at 2.5–3.0 ATA. Surprisingly, new data showed that it is not only the oxygen supply that matters as even a minimal increase in the partial pressure of oxygen is efficient in triggering cellular reactions by eliciting the production of hypoxia-inducible factors and heat-shock proteins. Moreover, it was shown that extreme environments could also interact with the genome; in fact, epigenetics appears to play a major role in extreme environments and exercise, especially when changes in oxygen partial pressure are involved. Hyperbaric oxygen therapy is, essentially, “intermittent oxygen” exposure. We must investigate hyperbaric oxygen with a new paradigm of treating oxygen as a potent stimulus of the molecular network of reactions