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      Static Metabolic Bubbles as Precursors of Vascular Gas Emboli During Divers’ Decompression: A Hypothesis Explaining Bubbling Variability

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          Abstract

          Introduction

          The risk for decompression sickness (DCS) after hyperbaric exposures (such as SCUBA diving) has been linked to the presence and quantity of vascular gas emboli (VGE) after surfacing from the dive. These VGE can be semi-quantified by ultrasound Doppler and quantified via precordial echocardiography. However, for an identical dive, VGE monitoring of divers shows variations related to individual susceptibility, and, for a same diver, dive-to-dive variations which may be influenced by pre-dive pre-conditioning. These variations are not explained by currently used algorithms. In this paper, we present a new hypothesis: individual metabolic processes, through the oxygen window (OW) or Inherent Unsaturation of tissues, modulate the presence and volume of static metabolic bubbles (SMB) that in turn act as precursors of circulating VGE after a dive.

          Methods

          We derive a coherent system of assumptions to describe static gas bubbles, located on the vessel endothelium at hydrophobic sites, that would be activated during decompression and become the source of VGE. We first refer to the OW and show that it creates a local tissue unsaturation that can generate and stabilize static gas phases in the diver at the surface. We then use Non-extensive thermodynamics to derive an equilibrium equation that avoids any geometrical description. The final equation links the SMB volume directly to the metabolism.

          Results and Discussion

          Our model introduces a stable population of small gas pockets of an intermediate size between the nanobubbles nucleating on the active sites and the VGE detected in the venous blood. The resulting equation, when checked against our own previously published data and the relevant scientific literature, supports both individual variation and the induced differences observed in pre-conditioning experiments. It also explains the variability in VGE counts based on age, fitness, type and frequency of physical activities. Finally, it fits into the general scheme of the arterial bubble assumption for the description of the DCS risk.

          Conclusion

          Metabolism characterization of the pre-dive SMB population opens new possibilities for decompression algorithms by considering the diver’s individual susceptibility and recent history (life style, exercise) to predict the level of VGE during and after decompression.

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          Most cited references88

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          Physicochemical approach to nanobubble solutions

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            Association of microparticles and neutrophil activation with decompression sickness.

            Decompression sickness (DCS) is a systemic disorder, assumed due to gas bubbles, but additional factors are likely to play a role. Circulating microparticles (MPs)--vesicular structures with diameters of 0.1-1.0 μm--have been implicated, but data in human divers have been lacking. We hypothesized that the number of blood-borne, Annexin V-positive MPs and neutrophil activation, assessed as surface MPO staining, would differ between self-contained underwater breathing-apparatus divers suffering from DCS vs. asymptomatic divers. Blood was analyzed from 280 divers who had been exposed to maximum depths from 7 to 105 meters; 185 were control/asymptomatic divers, and 90 were diagnosed with DCS. Elevations of MPs and neutrophil activation occurred in all divers but normalized within 24 h in those who were asymptomatic. MPs, bearing the following proteins: CD66b, CD41, CD31, CD142, CD235, and von Willebrand factor, were between 2.4- and 11.7-fold higher in blood from divers with DCS vs. asymptomatic divers, matched for time of sample acquisition, maximum diving depth, and breathing gas. Multiple logistic regression analysis documented significant associations (P < 0.001) between DCS and MPs and for neutrophil MPO staining. Effect estimates were not altered by gender, body mass index, use of nonsteroidal anti-inflammatory agents, or emergency oxygen treatment and were modestly influenced by divers' age, choice of breathing gas during diving, maximum diving depth, and whether repetitive diving had been performed. There were no significant associations between DCS and number of MPs without surface proteins listed above. We conclude that MP production and neutrophil activation exhibit strong associations with DCS.
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              Microparticles initiate decompression-induced neutrophil activation and subsequent vascular injuries.

              Progressive elevations in circulating annexin V-coated microparticles (MPs) derived from leukocytes, erythrocytes, platelets, and endothelial cells are found in mice subjected to increasing decompression stresses. Individual MPs exhibit surface markers from multiple cells. MPs expressing platelet surface markers, in particular, interact with circulating neutrophils, causing them to degranulate and leading to further MP production. MPs can be lysed by incubation with polyethylene glycol (PEG) telomere B surfactant, and the number of circulating MPs is reduced by infusion of mice with PEG or antibody to annexin V. Myeloperoxidase deposition and neutrophil sequestration in tissues occur in response to decompression, and the pattern differs among brain, omentum, psoas, and leg skeletal muscle. Both MP abatement strategies reduce decompression-induced intravascular neutrophil activation, neutrophil sequestration, and tissue injury documented as elevations of vascular permeability and activated caspase-3. We conclude that MPs generated by decompression stresses precipitate neutrophil activation and vascular damage.
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                Author and article information

                Contributors
                Journal
                Front Physiol
                Front Physiol
                Front. Physiol.
                Frontiers in Physiology
                Frontiers Media S.A.
                1664-042X
                11 July 2019
                2019
                : 10
                : 807
                Affiliations
                [1] 1Divetech , Biot, France
                [2] 2Department of Computer Engineering, Galatasaray University , Istanbul, Turkey
                [3] 3DAN Europe Research Division, Divers Alert Network (DAN) , Roseto, Italy
                [4] 4Centre for Hyperbaric Oxygen Therapy, Military Hospital Brussels , Brussels, Belgium
                [5] 5Environmental, Occupational and Ageing Physiology Laboratory, Haute Ecole Bruxelles-Brabant (HE2B) , Brussels, Belgium
                Author notes

                Edited by: Richard D. Boyle, National Aeronautics and Space Administration (NASA), United States

                Reviewed by: Danilo Cialoni, Dan Europe Foundation, Italy; Jacek Kot, Medical University of Gdańsk, Poland; Rodrigue Pignel, Université de Genève, Switzerland

                *Correspondence: Salih Murat Egi, smegi@ 123456daneurope.org

                This article was submitted to Environmental, Aviation and Space Physiology, a section of the journal Frontiers in Physiology

                Article
                10.3389/fphys.2019.00807
                6638188
                4f9f9375-ea08-4cde-a513-9c6dcc3e5e2b
                Copyright © 2019 Imbert, Egi, Germonpré and Balestra.

                This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

                History
                : 03 February 2019
                : 06 June 2019
                Page count
                Figures: 2, Tables: 1, Equations: 8, References: 95, Pages: 12, Words: 0
                Categories
                Physiology
                Hypothesis and Theory

                Anatomy & Physiology
                diving,decompression sickness,desaturation,oxygen window,pre-conditioning
                Anatomy & Physiology
                diving, decompression sickness, desaturation, oxygen window, pre-conditioning

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