Circulatory bubble dynamics: from physical to biological aspects

Association between rat decompression sickness resistance, transthyretin single nucleotide polymorphism, and expression: A pilot study

Decompression sickness (DCS) is a systemic syndrome that can occur after an environmental pressure reduction. Previously, we showed that the plasmatic tetrameric form of transthyretin (TTR) nearly disappeared in rats suffering DCS but not in asymptomatic ones. In this pilot study, we assessed whether the resistance to DCS could be associated with polymorphism of the gene of TTR. For this study, Sanger sequencing was performed on purified PCR products from the liver of 14-week-old male and female standard and DCS-resistant rats (n = 5 per group). Hepatic TTR mRNA expression was assessed by RT-qPCR in 18-19 week-old male and female standard and resistant rats (n = 6 per group). There is a synonymous single nucleotide polymorphism (SNP) on the third base of codon 46 (c.138 C > T). The thymine allele was present in 90% and 100% of males and females standard, respectively. However, this allele is present in only 30% of DCS-resistant males and females (p = 0.0002301). In the liver, there is a significant effect of the resistance to DCS (p = 0.043) and sex (p = 0.047) on TTR expression. Levels of TTR mRNA were lower in DCS-resistant animals. To conclude, DCS resistance might be associated with a SNP and a lower expression of TTR.

Levitation and dynamics of bodies in supersaturated fluids

A body immersed in a supersaturated fluid like carbonated water can accumulate a dynamic field of bubbles upon its surface. If the body is mobile, the attached bubbles can lift it upward against gravity, but a fluid-air interface can clean the surface of these lifting agents and the body may plummet. The process then begins anew, and continues for as long as the concentration of gas in the fluid supports it. In this work, experiments using fixed and free immersed bodies reveal fundamental features of force development and gas escape. A continuum model which incorporates the dynamics of a surface buoyancy field is used to predict the ranges of body mass and size, and fluid properties, for which the system is most dynamic, and those for which body excursions are suppressed. Simulations are then used to probe systems which are dominated by a small number of large bubbles. Body rotations at the surface are critical for driving periodic vertical motions of large bodies, which in turn can produce body wobbling, rolling, and damped surface 'bouncing' dynamics.

Physiology of deep closed circuit rebreather mixed gas diving: vascular gas emboli and biological changes during a week-long liveaboard safari

Introduction: Diving decompression theory hypothesizes inflammatory processes as a source of micronuclei which could increase related risks. Therefore, we tested 10 healthy, male divers. They performed 6-8 dives with a maximum of two dives per day at depths ranging from 21 to 122 msw with CCR mixed gas diving. Methods: Post-dive VGE were counted by echocardiography. Saliva and urine samples were taken before and after each dive to evaluate inflammation: ROS production, lipid peroxidation (8-iso-PGF2), DNA damage (8-OH-dG), cytokines (TNF-α, IL-6, and neopterin). Results: VGE exhibits a progressive reduction followed by an increase (p < 0.0001) which parallels inflammation responses. Indeed, ROS, 8-iso-PGF2, IL-6 and neopterin increases from 0.19 ± 0.02 to 1.13 ± 0.09 μmol.min-1 (p < 0.001); 199.8 ± 55.9 to 632.7 ± 73.3 ng.mg-1 creatinine (p < 0.0001); 2.35 ± 0.54 to 19.5 ± 2.96 pg.mL-1 (p < 0.001); and 93.7 ± 11.2 to 299 ± 25.9 μmol·mol-1 creatinine (p = 0.005), respectively. The variation after each dive was held constant around 158.3% ± 6.9% (p = 0.021); 151.4% ± 5.7% (p < 0.0001); 176.3% ± 11.9% (p < 0.0001); and 160.1% ± 5.6% (p < 0.001), respectively. Discussion: When oxy-inflammation reaches a certain level, it exceeds hormetic coping mechanisms allowing second-generation micronuclei substantiated by an increase of VGE after an initial continuous decrease consistent with a depletion of "first generation" pre-existing micronuclei.

Iatrogenic air embolism: pathoanatomy, thromboinflammation, endotheliopathy, and therapies

Iatrogenic vascular air embolism is a relatively infrequent event but is associated with significant morbidity and mortality. These emboli can arise in many clinical settings such as neurosurgery, cardiac surgery, and liver transplantation, but more recently, endoscopy, hemodialysis, thoracentesis, tissue biopsy, angiography, and central and peripheral venous access and removal have overtaken surgery and trauma as significant causes of vascular air embolism. The true incidence may be greater since many of these air emboli are asymptomatic and frequently go undiagnosed or unreported. Due to the rarity of vascular air embolism and because of the many manifestations, diagnoses can be difficult and require immediate therapeutic intervention. An iatrogenic air embolism can result in both venous and arterial emboli whose anatomic locations dictate the clinical course. Most clinically significant iatrogenic air emboli are caused by arterial obstruction of small vessels because the pulmonary gas exchange filters the more frequent, smaller volume bubbles that gain access to the venous circulation. However, there is a subset of patients with venous air emboli caused by larger volumes of air who present with more protean manifestations. There have been significant gains in the understanding of the interactions of fluid dynamics, hemostasis, and inflammation caused by air emboli due to in vitro and in vivo studies on flow dynamics of bubbles in small vessels. Intensive research regarding the thromboinflammatory changes at the level of the endothelium has been described recently. The obstruction of vessels by air emboli causes immediate pathoanatomic and immunologic and thromboinflammatory responses at the level of the endothelium. In this review, we describe those immunologic and thromboinflammatory responses at the level of the endothelium as well as evaluate traditional and novel forms of therapy for this rare and often unrecognized clinical condition.

Does Decreased Diffusing Capacity of the Lungs for Carbon Monoxide Constitute a Risk of Decompression Sickness in Occupational Divers?

Long-term alterations of pulmonary function (mainly decreased airway conductance and capacity of the lungs to diffuse carbon monoxide (DLCO)) have been described after hyperbaric exposures. However, whether these alterations convey a higher risk for divers' safety has never been investigated before. The purpose of the present pilot study was to assess whether decreased DLCO is associated with modifications of the physiological response to diving. In this case-control observational study, 15 "fit-to-dive" occupational divers were split into two groups according to their DLCO measurements compared to references values, either normal (control) or reduced (DLCO group). After a standardized 20 m/40 min dive in a sea water pool, the peak-flow, vascular gas emboli (VGE) grade, micro-circulatory reactivity, inflammatory biomarkers, thrombotic factors, and plasmatic aldosterone concentration were assessed at different times post-dive. Although VGE were recorded in all divers, no cases of decompression sickness (DCS) occurred. Compared to the control, the latency to VGE peak was increased in the DLCO group (60 vs. 30 min) along with a higher maximal VGE grade (p < 0.0001). P-selectin was higher in the DLCO group, both pre- and post-dive. The plasmatic aldosterone concentration was significantly decreased in the control group (-30.4 ± 24.6%) but not in the DLCO group. Apart from a state of hypocoagulability in all divers, other measured parameters remained unchanged. Our results suggest that divers with decreased DLCO might have a higher risk of DCS. Further studies are required to confirm these preliminary results.

Hyperbaric exposure in rodents with non-invasive imaging assessment of decompression bubbles: A scoping review protocol

Hyperbaric pressure experiments have provided researchers with valuable insights into the effects of pressure changes, using various species as subjects. Notably, extensive work has been done to observe rodents subjected to hyperbaric pressure, with differing imaging modalities used as an analytical tool. Decompression puts subjects at a greater risk for injury, which often justifies conducting such experiments using animal models. Therefore, it is important to provide a broad view of previously utilized methods for decompression research to describe imaging tools available for researchers to conduct rodent decompression experiments, to prevent duplicate experimentation, and to identify significant gaps in the literature for future researchers. Through a scoping review of published literature, we will provide an overview of decompression bubble information collected from rodent experiments using various non-invasive methods of ultrasound for decompression bubble assessment. This review will adhere to methods outlined by the Joanna Briggs Institute Manual for Evidence Synthesis and be reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses for Scoping Reviews (PRISMA-ScR). Literature will be obtained from the PubMed, Embase, and Scopus databases. Extracted sources will first be sorted to a list for inclusion based on title and abstract. Two independent researchers will then conduct full-text screening to further refine included papers to those relevant to the scope. The final review manuscript will cover methods, data, and findings for each included publication relevant to non-invasive in vivo bubble imaging.

Comparison of Newer Hand-Held Ultrasound Devices for Post-Dive Venous gas Emboli Quantification to Standard Echocardiography

Decompression sickness (DCS) can result from the growth of bubbles in tissues and blood during or after a reduction in ambient pressure, for example in scuba divers, compressed air workers or astronauts. In scuba diving research, post-dive bubbles are detectable in the venous circulation using ultrasound. These venous gas emboli (VGE) are a marker of decompression stress, and larger amounts of VGE are associated with an increased probability of DCS. VGE are often observed for hours post-dive and differences in their evolution over time have been reported between individuals, but also for the same individual, undergoing a same controlled exposure. Thus, there is a need for small, portable devices with long battery lives to obtain more ultrasonic data in the field to better assess this inter- and intra-subject variability. We compared two new handheld ultrasound devices against a standard device that is currently used to monitor post-dive VGE in the field. We conclude that neither device is currently an adequate replacement for research studies where precise VGE grading is necessary.

Mini Trampoline, a New and Promising Way of SCUBA Diving Preconditioning to Reduce Vascular Gas Emboli?

Background: Despite evolution in decompression algorithms, decompression illness is still an issue nowadays. Reducing vascular gas emboli (VGE) production or preserving endothelial function by other means such as diving preconditioning is of great interest. Several methods have been tried, either mechanical, cardiovascular, desaturation aimed or biochemical, with encouraging results. In this study, we tested mini trampoline (MT) as a preconditioning strategy. Methods: In total, eight (five females, three males; mean age 36 ± 16 years; body mass index 27.5 ± 7.1 kg/m2) healthy, non-smoking, divers participated. Each diver performed two standardized air dives 1 week apart with and without preconditioning, which consisted of ±2 min of MT jumping. All dives were carried out in a pool (NEMO 33, Brussels, Belgium) at a depth of 25 m for 25 min. VGE counting 30 and 60 min post-dive was recorded by echocardiography together with an assessment of endothelial function by flow-mediated dilation (FMD). Results: VGE were significantly reduced after MT (control: 3.1 ± 4.9 VGE per heartbeat vs. MT: 0.6 ± 1.1 VGE per heartbeat, p = 0.031). Post-dive FMD exhibited a significant decrease in the absence of preconditioning (92.9% ± 7.4 of pre-dive values, p = 0.03), as already described. MT preconditioning prevented this FMD decrease (103.3% ± 7.1 of pre-dive values, p = 0.30). FMD difference is significant (p = 0.03). Conclusions: In our experience, MT seems to be a very good preconditioning method to reduce VGE and endothelial changes. It may become the easiest, cheapest and more efficient preconditioning for SCUBA diving.

Full-Face Mask Use during SCUBA Diving Counters Related Oxidative Stress and Endothelial Dysfunction

Impaired flow mediated dilation (FMD), an index of vascular stress, is known after SCUBA diving. This is related to a dysfunction of nitric oxide (NO) availability and a disturbance of the redox status, possibly induced by hyperoxic/hyperbaric gas breathing. SCUBA diving is usually performed with a mask only covering “half face” (HF) and therefore forcing oral breathing. Nasal NO production is involved in vascular homeostasis and, as consequence, can significantly reduce NO possibly promoting vascular dysfunction. More recently, the utilization of “full-face” (FF) mask, allowing nasal breathing, became more frequent, but no reports are available describing their effects on vascular functions in comparison with HF masks. In this study we assessed and compared the effects of a standard shallow dive (20 min at 10 m) wearing either FF or a HF mask on different markers of vascular function (FMD), oxidative stress (ROS, 8-iso-PGF2α) and NO availability and metabolism (NO₂, NOx and 3-NT and iNOS expression). Data from a dive breathing a hypoxic (16% O₂ at depth) gas mixture with HF mask are shown allowing hyperoxic/hypoxic exposure. Our data suggest that nasal breathing might significantly reduce the occurrence of vascular dysfunction possibly due to better maintenance of NO production and bioavailability, resulting in a better ability to counter reactive oxygen and nitrogen species. Besides the obvious outcomes in terms of SCUBA diving safety, our data permit a better understanding of the effects of oxygen concentrations, either in normal conditions or as a strategy to induce selected responses in health and disease.

Intra-Individual Test-Retest Variation Regarding Venous Gas Bubble Formation During High Altitude Exposures

INTRODUCTION: Hypobaric decompression sickness remains a problem during high-altitude aviation. The prevalence of venous gas emboli (VGE) serves as a marker of decompression stress and has been used as a method in evaluating the safety/risk associated with aviation profiles and/or gas mixtures. However, information is lacking concerning the variability of VGE formation when exposed to the same hypobaric profile on different occasions. In this paper, intra-individual test-retest variation regarding bubble formation during repeated hypobaric exposures is presented. The data can be used to determine the sample size needed for statistical power.METHOD: A total of 19 male, nonsmoking subjects volunteered for altitude exposures to 24,000 ft (7315 m). VGE was measured using ultrasound scanning and scored according to the Eftedal-Brubakk (EB) scale. Intraindividual test-retest variation in bubble formation (maximum VGE) was evaluated in subjects exposed more than once to hypobaric pressure. The statistical reliability was examined between paired exposures using the Intraclass Correlation test. G*Power version 3.1.9.6 was used for power calculations.RESULTS: During repeated 20-30 and 70-min exposures to 24,000 ft, 42% (N = 19, CI 23-67%) and 29% (N = 7, CI 5-70%) of the subjects varied between maximum EB scores < 3 and ≥ 3. The sample size needed to properly reject statistical significance of 1 EB step nominal difference between two paired exposures varied between 29-51 subjects.CONCLUSION: The large intraindividual test-retest variations in bubble grades during repeated hypobaric exposures highlight the need for relatively large numbers of subjects to reach statistical power when there are no or small differences in decompression stress between the exposures.Ånell R, Grönkvist M, Eiken O, Elia A, Gennser M. Intra-individual test-retest variation regarding venous gas bubble formation during high altitude exposures. Aerosp Med Hum Perform. 2022; 93(1):46-49.

The Relationship between Ozone and Human Blood in the Course of a Well-Controlled, Mild, and Transitory Oxidative Eustress

In the last twenty years there has been a proliferation of articles on the therapeutic use of ozone. As it is well-known, the term ozone therapy is very broad. It ranges from either systemic or loco-regional administration of unstable gaseous oxygen/ozone mixtures to the topical application of stable ozonated derivatives. Anyway, in relation to the absence of specific receptors and the extreme reactivity with the biological liquids with which it comes into contact, gaseous ozone cannot be classified as either a drug or a pro-drug. When the gaseous ozone impacts a biological matrix, both reactive oxygen species (ROS) and lipid oxidation products (LOPs) are formed. They represent the effector molecules responsible for modulating the therapeutic activity in the body. Apart from the merits of the action mechanisms resulting from the use of ozone, this article seeks to validate the practice of ozone therapy as an adjuvant treatment in full compliance with the physiology of the whole organism.

Physiological effects of mixed-gas deep sea dives using a closed-circuit rebreather: a field pilot study

PURPOSE

Deep diving using mixed gas with closed-circuit rebreathers (CCRs) is increasingly common. However, data regarding the effects of these dives are still scarce. This preliminary field study aimed at evaluating the acute effects of deep (90-120 msw) mixed-gas CCR bounce dives on lung function in relation with other physiological parameters.

METHODS

Seven divers performed a total of sixteen open-sea CCR dives breathing gas mixture of helium, nitrogen and oxygen (trimix) within four days at 2 depths (90 and 120 msw). Spirometric parameters, SpO₂, body mass, hematocrit, short term heart rate variability (HRV) and critical flicker fusion frequency (CFFF) were measured at rest 60 min before the dive and 120 min after surfacing.

RESULTS

The median [1st-3rd quartile] of the forced vital capacity was lower (84% [76-93] vs 91% [74-107] of predicted values; p = 0.029), whereas FEV1/FVC was higher (98% [95-99] vs 95% [89-99]; p = 0.019) after than before the dives. The other spirometry values and SpO₂ were unchanged. Body mass decreased from 73.5 kg (72.0-89.6) before the dives to 70.0 kg (69.2-85.8) after surfacing (p = 0.001), with no change of hematocrit or CFFT. HRV was increased as indicated by the higher SDNN, RMSSD and pNN50 after than before dives.

CONCLUSION

The present observation represents the first original data regarding the effects of deep repeated CCR dives. The body mass loss and decrease of FVC after bounce dives at depth of about 100 msw may possibly impose an important physiological stress for the divers.

Flow field around bubbles on formation of air embolism in small vessels

An air embolism is induced by intravascular bubbles that block the blood flow in vessels, which causes a high risk of pulmonary hypertension and myocardial and cerebral infarction. However, it is still unclear how a moving bubble is stopped in the blood flow to form an air embolism in small vessels. In this work, microfluidic experiments, in vivo and in vitro, are performed in small vessels, where bubbles are seen to deform and stop gradually in the flow. A clot is always found to originate at the tail of a moving bubble, which is attributed to the special flow field around the bubble. As the clot grows, it breaks the lubrication film between the bubble and the channel wall; thus, the friction force is increased to stop the bubble. This study illustrates the stopping process of elongated bubbles in small vessels and brings insight into the formation of air embolism.

The protective effects of 1,3-butanediol acetoacetate diester on decompression sickness in rats

Inert gas bubbles are widely accepted as the causative factor of decompression sickness (DCS), resulting in gas embolism and systemic inflammatory responses. The anticonvulsive ketone ester 1,3-butanediol acetoacetate diester (BD-AcAc₂) was reported to have the characteristics of increasing blood oxygen partial pressure (ppO₂) and anti-inflammation and was thought to have the potential to reduce bubble formation and alleviate the pathological process of DCS. This study aims to investigate the potential protection of BD-AcAc₂ against DCS in a rat model. A single dose of BD-AcAc₂ was administered orally to adult male rats (5 g/kg body wt), followed by pharmacokinetic analysis or simulated air dives. After decompression, signs of DCS were monitored, and blood was sampled for biochemical measurements. Blood ketosis peaked at 2 h and lasted for more than 4 h. The incidence of DCS was decreased and postponed significantly in rats treated with BD-AcAc₂ compared with those treated with saline (P < 0.05). Although BD-AcAc₂ failed to reduce bubble load (P > 0.05), it showed an obvious decreasing trend. BD-AcAc₂ significantly increased blood ppO₂ and ameliorated oxidative and inflammatory responses, represented by increased plasma malondialdehyde (MDA), IL-1, IL-6, and TNF-α and decreased glutathione thiol (P < 0.05) levels, whereas blood pH remained unchanged (P > 0.05). These results suggest that BD-AcAc₂ exerted beneficial effects on DCS rats mainly related to increasing ppO₂ and anti-inflammatory and antioxidant properties. Together with its capacity for delaying central nervous system (CNS) oxygen toxicity seizures, BD-AcAc₂ might be an ideal drug candidate for DCS prevention and treatment.NEW & NOTEWORTHY This is the first study exploring the effects of BD-AcAc₂ on DCS prevention, and it was proven to be an efficient and simple method. The role of BD-AcAc₂ in increasing ppO₂, anti-inflammatory and antioxidant properties was thought to be the critical mechanism in DCS prevention.

Hyperoxic Effects on Decompression Strain During Alternating High and Moderate Altitude Exposures

INTRODUCTION: In fighter aircraft, long-duration high-altitude sorties are typically interrupted by refueling excursions to lower altitude. In normoxia, excursions to moderate cabin altitude may increase the occurrence of venous gas emboli (VGE) at high cabin altitude. The aim was to investigate the effect of hyperoxia on VGE and decompression sickness (DCS) during alternating high and moderate altitude exposure.METHODS: In an altitude chamber, 13 healthy men were exposed to three different conditions: A) 90 min at 24,000 ft (7315 m) breathing normoxic gas (54% O₂; H-NOR); B) 90 min at 24,000 ft breathing hyperoxic gas (90% O₂; H-HYP); and C) three 30-min exposures to 24,000 ft interspersed by two 30-min exposures to 18,000 ft (5486 m) breathing 90% O₂ (ALT-HYP). VGE occurrence was evaluated from cardiac ultrasound imaging. DCS symptoms were rated using a scale.RESULTS: DCS occurred in all conditions and altogether in 6 of the 39 exposures. The prevalence of VGE was similar in H-NOR and H-HYP throughout the exposures. During the initial 30 min at 24,000 ft, the prevalence of VGE was similar in ALT-HYP as in the other two conditions, whereas, after the first excursion to 18,000 ft, the VGE score was lower in ALT-HYP than in H-NOR and H-HYP.DISCUSSION: Hyperoxic excursions from 24,000 to 18,000 ft reduces VGE occurrence, presumably by facilitating diffusive gas exchange across the bubble surfaces, increasing the share of bubble content contributed by oxygen. Still, the excursions did not abolish the DCS risk.Ånell R, Grönkvist M, Gennser M, Eiken O. Hyperoxic effects on decompression strain during alternating high and moderate altitude exposures. Aerosp Med Hum Perform. 2021; 92(4):223230.

Discrimination of ablation, shielding, and interface layer effects on the steady-state formation of persistent bubbles under liquid flow conditions during laser synthesis of colloids

Over the past decade, laser ablation in liquids (LAL) was established as an innovative nanoparticle synthesis method obeying the principles of green chemistry. While one of the main advantages of this method is the absence of stabilizers leading to nanoparticles with “clean” ligand-free surfaces, its main disadvantage is the comparably low nanoparticle production efficiency dampening the sustainability of the method and preventing the use of laser-synthesized nanoparticles in applications that require high amounts of material. In this study, the effects of productivity-dampening entities that become particularly relevant for LAL with high repetition rate lasers, i.e., persistent bubbles or colloidal nanoparticles (NPs), on the synthesis of colloidal gold nanoparticles in different solvents are studied. Especially under batch ablation conditions in highly viscous liquids with prolonged ablation times both shielding entities are closely interconnected and need to be disentangled. By performing liquid flow-assisted nanosecond laser ablation of gold in liquids with different viscosity and nanoparticle or bubble diffusivity, it is shown that a steady-state is reached after a few seconds with fixed individual contributions of bubble- and colloid-induced shielding effects. By analyzing dimensionless numbers (i.e., Axial Peclet, Reynolds, and Schmidt) it is demonstrated how these shielding effects strongly depend on the liquid’s transport properties and the flow-induced formation of an interface layer along the target surface. In highly viscous liquids, the transport of NPs and persistent bubbles within this interface layer is strongly diffusion-controlled. This diffusion-limitation not only affects the agglomeration of the NPs but also leads to high local densities of NPs and bubbles near the target surface, shielding up to 80% of the laser power. Hence, the ablation rate does not only depend on the total amount of shielding matter in the flow channel, but also on the location of the persistent bubbles and NPs. By comparing LAL in different liquids, it is demonstrated that 30 times more gas is produced per ablated amount of substance in acetone and ethylene glycol compared to ablation in water. This finding confirms that chemical effects contribute to the liquid’s decomposition and the ablation yield as well. Furthermore, it is shown that the highest ablation efficiencies and monodisperse qualities are achieved in liquids with the lowest viscosities and gas formation rates at the highest volumetric flow rates.

Cerebrospinal Fluid Cavitation as a Mechanism of Blast-Induced Traumatic Brain Injury: A Review of Current Debates, Methods, and Findings

Cavitation has gained popularity in recent years as a potential mechanism of blast-induced traumatic brain injury (bTBI). This review presents the most prominent debates on cavitation; how bubbles can form or exist within the cerebrospinal fluid (CSF) and brain vasculature, potential mechanisms of cellular, and tissue level damage following the collapse of bubbles in response to local pressure fluctuations, and a survey of experimental and computational models used to address cavitation research questions. Due to the broad and varied nature of cavitation research, this review attempts to provide a necessary synthesis of cavitation findings relevant to bTBI, and identifies key areas where additional work is required. Fundamental questions about the viability and likelihood of CSF cavitation during blast remain, despite a variety of research regarding potential injury pathways. Much of the existing literature on bTBI evaluates cavitation based off its prima facie plausibility, while more rigorous evaluation of its likelihood becomes increasingly necessary. This review assesses the validity of some of the common assumptions in cavitation research, as well as highlighting outstanding questions that are essential in future work.

First impressions: Use of the Azoth Systems O'Dive subclavian bubble monitor on a liveaboard dive vessel

INTRODUCTION

The Azoth Systems O'Dive bubble monitor is marketed at recreational and professional divers as a tool to improve personal diving decompression safety. We report the use of this tool during a 12-day dive trip aboard a liveaboard vessel.

METHODS

Six divers were consistently monitored according to the user manual of the O'Dive system. Data were synchronised with the Azoth server whenever possible (depending on cell phone data signal). Information regarding ease of use, diver acceptance and influence on dive behaviour were recorded.

RESULTS

In total, 157 dives were completely monitored over 11 diving days. Formal evaluations were only available after six days because of internet connection problems. Sixty-one dives resulted in the detection of bubbles, mostly in one diver, none of which produced any symptoms of decompression illness.

CONCLUSIONS

The O'Dive system may contribute to increasing dive safety by making divers immediately aware of the potential consequences of certain types of diving behaviour. It was noted that bubble monitoring either reinforced divers in their safe diving habits or incited them to modify their dive planning. Whether this is a lasting effect is not known.

Xuebijing attenuates decompression-induced lung injuries

INTRODUCTION

The lung is among the primary organs involved in decompression sickness (DCS). Xuebijing (XBJ), a traditional Chinese medicine, has been widely used in the treatment of various acute lung diseases. This study aimed to explore potential benefit of XBJ on lung injuries induced by DCS in a rabbit model.

METHODS

Twenty-four male New Zealand white rabbits underwent a simulated air dive to 50 meters' sea water for 60 min with 2.5 min decompression, and received an intravenous injection of XBJ (5 ml·kg^-1) or an equal volume of saline immediately following decompression. DCS signs were monitored for 24 h, and blood was sampled before simulated diving and at 6 h and 12 h following decompression for determination of inflammatory indices. Lung tissues were sampled after euthanasia for histology analysis and lung water content, as well as tumour necrosis factor-α level. Another six rabbits were used as control.

RESULTS

XBJ significantly ameliorated lung injuries (lung wet/dry ratio and total protein content in bronchoalveolar lavage fluid), and notably inhibited systemic (serum level of interleukin-1β) and local (tumour necrosis factor-α in bronchoalveolar lavage fluid) inflammation responses.

CONCLUSIONS

The results strongly suggest the benefits of XBJ on ameliorating DCS lung injuries, which is possibly via inhibiting systemic and local inflammation. XBJ may be a potential candidate for the treatment of decompression-induced lung injuries.

A Bayesian nested patch occupancy model to estimate steelhead movement and abundance

Anthropogenic impacts on riverine systems have, in part, led to management concerns regarding the population status of species using these systems. In an effort to assess the efficacy of restoration actions, and in order to improve monitoring of species of concern, managers have turned to PIT (passive integrated transponder) tag studies with in-stream detectors to monitor movements of tagged individuals throughout river networks. However, quantifying movements in a river network using PIT tag data with incomplete coverage and imperfect detections presents a challenge. We propose a flexible Bayesian analytic framework that models the imperfectly detected movements of tagged individuals in a nested PIT tag array river network. This model structure provides probabilistic estimates of up-stream migration routes for each tagged individual based on a set of underlying nested state variables. These movement estimates can be converted into abundance estimates when an estimate of abundance is available for a location within the river network. We apply the model framework to data from steelhead (Oncorhynchus mykiss) in the Upper Columbia River basin and evaluate model performance (precision/variance of simulated population sizes) as a function of population tagging rates and PIT tag array detection probability densities within the river system using a simulation framework. This simulation framework provides both model validation (precision) and the ability to evaluate expected performance improvements (variance) due to changes in tagging rates or PIT receiver array configuration. We also investigate the impact of different network configurations on model estimates. Results from such investigations can help inform decisions regarding future monitoring and management.

Ulinastatin: A Potential Alternative to Glucocorticoid in the Treatment of Severe Decompression Sickness

Inflammatory reaction is the crux in various clinical critical diseases including decompression sickness (DCS). Ulinastatin (UTI), a potent anti-inflammatory agent, has been used clinically, including as a substitution for steroids. This study aimed to explore the potential effects of UTI upon DCS in a rabbit model. Eighty-eight rabbits were subjected to simulated diving to 6 atmospheres absolute (ATA) for 60 min with 2.5-minute decompression. Three doses of UTI (15/7.5/3.75 × 10⁵ U/kg) or saline were intravenously administered immediately following decompression. Circulating bubbles were monitored for 3 h following decompression and DCS signs were evaluated for 24 h. Blood was sampled 8 times during 72 h after decompression for inflammatory, endothelial, oxidative and routine blood indices. Lung tissues were also sampled for evaluating endothelial function. Another six rabbits were used as Normal controls. In the high dose UTI group the mortality, general morbidity and incidence of severe DCS was decreased from 31.25 to 9.38% (P = 0.030), 84.38 to 62.50% (P = 0.048) and 46.88 to 21.88% (P = 0.035), respectively. The high dose of UTI significantly postponed the occurrence of DCS (P = 0.030) and prolonged survival time (P = 0.009) compared with the Saline group, and significantly ameliorated inflammation responses, endothelial injuries and oxidative damage. The results strongly suggest the benefit of UTI on DCS, especially for severe cases. Large doses are needed to achieve significant effects. UTI may be a potential ideal pharmacological candidate for the treatment of severe DCS.

Bubbles Moving in Blood Flow in a Microchannel Network: The Effect on the Local Hematocrit

Air inside of blood vessels is a phenomenon known as gas embolism. During the past years, studies have been performed to assess the influence of air bubbles in microcirculation. In this study, we investigated the flow of bubbles in a microchannel network with several bifurcations, mimicking part of a capillary system. Thus, two working fluids were used, composed by sheep red blood cells (RBCs) suspended in a Dextran 40 solution with different hematocrits (5% and 10%). The experiments were carried out in a polydimethylsiloxane (PDMS) microchannel network fabricated by a soft lithography. A high-speed video microscopy system was used to obtain the results for a blood flow rate of 10 µL/min. This system enables the visualization of bubble formation and flow along the network. The results showed that the passage of air bubbles strongly influences the cell's local concentration, since a higher concentration of cells was observed upstream of the bubble, whereas a lower local hematocrit was visualized at the region downstream of the bubble. In bifurcations, bubbles may split asymmetrically, leading to an uneven distribution of RBCs between the outflow branches.

Biphasic effects of autophagy on decompression bubble-induced endothelial injury

Endothelial dysfunction induced by bubbles plays an important role in decompression sickness (DCS), but the mechanism of which has not been clear. The present study was to investigate the role of autophagy in bubble‐induced endothelial injury. Human umbilical vein endothelial cells (HUVECs) were treated with bubbles, autophagy markers and endothelial injury indices were determined, and relationship strengths were quantified. Effects of autophagy inhibitor 3‐methyladenine (3‐MA) were observed. Bubble contact for 1, 5, 10, 20 or 30 minutes induced significant autophagy with increases in LC3‐II/I ratio and Beclin‐1, and a decrease in P62, which correlated with bubble contact duration. Apoptosis rate, cytochrome C and cleaved caspase‐3 increased, and cell viability decreased following bubble contact for 10, 20 or 30 minutes, but not for 1 or 5 minutes. Injuries in HUVECs were correlated with LC3‐II/I ratio and partially reversed by 3‐MA in 10, 20 or 30 minutes contact, but worsened in 1 or 5 minutes. Bubble pre‐conditioning for 1 minutes resulted in increased cell viability and decreased apoptosis rate compared with no pre‐conditioning, and 30‐minutes pre‐conditioning induced opposing changes, all of which were inhibited by 3‐MA. In conclusion, autophagy was involved and played a biphasic role in bubble‐induced endothelial injury.

Diverse Structural Conversion and Aggregation Pathways of Alzheimer's Amyloid-β (1-40)

Complex amyloid aggregation of amyloid-β (1-40) (Aβ_1-40) in terms of monomer structures has not been fully understood. Herein, we report the microscopic mechanism and pathways of Aβ_1-40 aggregation with macroscopic viewpoints through tuning its initial structure and solubility. Partial helical structures of Aβ_1-40 induced by low solvent polarity accelerated cytotoxic Aβ_1-40 amyloid fibrillation, while predominantly helical folds did not aggregate. Changes in the solvent polarity caused a rapid formation of β-structure-rich protofibrils or oligomers via aggregation-prone helical structures. Modulation of the pH and salt concentration transformed oligomers to protofibrils, which proceeded to amyloid formation. We reveal diverse molecular mechanisms underlying Aβ_1-40 aggregation with conceptual energy diagrams and propose that aggregation-prone partial helical structures are key to inducing amyloidogenesis. We demonstrate that context-dependent protein aggregation is comprehensively understood using the macroscopic phase diagram, which provides general insights into differentiation of amyloid formation and phase separation from unfolded and folded structures.

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

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.

AltitudeOmics: effect of reduced barometric pressure on detection of intrapulmonary shunt, pulmonary gas exchange efficiency, and total pulmonary resistance

Blood flow through intrapulmonary arteriovenous anastomoses (QIPAVA) occurs in healthy humans at rest and during exercise when breathing hypoxic gas mixtures at sea level and may be a source of right-to-left shunt. However, at high altitudes, QIPAVA is reduced compared with sea level, as detected using transthoracic saline contrast echocardiography (TTSCE). It remains unknown whether the reduction in QIPAVA (i.e., lower bubble scores) at high altitude is due to a reduction in bubble stability resulting from the lower barometric pressure (PB) or represents an actual reduction in QIPAVA. To this end, QIPAVA, pulmonary artery systolic pressure (PASP), cardiac output (QT), and the alveolar-to-arterial oxygen difference (AaDO2) were assessed at rest and during exercise (70-190 W) in the field (5,260 m) and in the laboratory (1,668 m) during four conditions: normobaric normoxia (NN; [Formula: see text] = 121 mmHg, PB = 625 mmHg; n = 8), normobaric hypoxia (NH; [Formula: see text] = 76 mmHg, PB = 625 mmHg; n = 7), hypobaric normoxia (HN; [Formula: see text] = 121 mmHg, PB = 410 mmHg; n = 8), and hypobaric hypoxia (HH; [Formula: see text] = 75 mmHg, PB = 410 mmHg; n = 7). We hypothesized QIPAVA would be reduced during exercise in isooxic hypobaria compared with normobaria and that the AaDO2 would be reduced in isooxic hypobaria compared with normobaria. Bubble scores were greater in normobaric conditions, but the AaDO2 was similar in both isooxic hypobaria and normobaria. Total pulmonary resistance (PASP/QT) was elevated in HN and HH. Using mathematical modeling, we found no effect of hypobaria on bubble dissolution time within the pulmonary transit times under consideration (<5 s). Consequently, our data suggest an effect of hypobaria alone on pulmonary blood flow. NEW & NOTEWORTHY Blood flow through intrapulmonary arteriovenous anastomoses, detected by transthoracic saline contrast echocardiography, was reduced during exercise in acute hypobaria compared with normobaria, independent of oxygen tension, whereas pulmonary gas exchange efficiency was unaffected. Modeling the effect(s) of reduced air density on contrast bubble lifetime did not result in a significantly reduced contrast stability. Interestingly, total pulmonary resistance was increased by hypobaria, independent of oxygen tension, suggesting that pulmonary blood flow may be changed by hypobaria.

Microbubble moving in blood flow in microchannels: effect on the cell-free layer and cell local concentration

Gas embolisms can hinder blood flow and lead to occlusion of the vessels and ischemia. Bubbles in microvessels circulate as tubular bubbles (Taylor bubbles) and can be trapped, blocking the normal flow of blood. To understand how Taylor bubbles flow in microcirculation, in particular, how bubbles disturb the blood flow at the scale of blood cells, experiments were performed in microchannels at a low Capillary number. Bubbles moving with a stream of in vitro blood were filmed with the help of a high-speed camera. Cell-free layers (CFLs) were observed downstream of the bubble, near the microchannel walls and along the centerline, and their thicknesses were quantified. Upstream to the bubble, the cell concentration is higher and CFLs are less clear. While just upstream of the bubble the maximum RBC concentration happens at positions closest to the wall, downstream the maximum is in an intermediate region between the centerline and the wall. Bubbles within microchannels promote complex spatio-temporal variations of the CFL thickness along the microchannel with significant relevance for local rheology and transport processes. The phenomenon is explained by the flow pattern characteristic of low Capillary number flows. Spatio-temporal variations of blood rheology may have an important role in bubble trapping and dislodging.

Controlled single bubble cavitation collapse results in jet-induced injury in brain tissue

Multiscale damage due to cavitation is considered as a potential mechanism of traumatic brain injury (TBI) associated with explosion. In this study, we employed a TBI relevant hippocampal ex vivo slice model to induce bubble cavitation. Placement of single reproducible seed bubbles allowed control of size, number, and tissue location to visualize and measure deformation parameters. Maximum strain value was measured at 45 µs after bubble collapse, presented with a distinct contour and coincided temporally and spatially with the liquid jet. Composite injury maps combined this maximum strain value with maximum measured bubble size and location along with histological injury patterns. This facilitated the correlation of bubble location and subsequent jet direction to the corresponding regions of high strain which overlapped with regions of observed injury. A dynamic threshold strain range for tearing of cerebral cortex was estimated to be between 0.5 and 0.6. For a seed bubble placed underneath the hippocampus, cavitation induced damage was observed in hippocampus (local), proximal cerebral cortex (marginal) and the midbrain/forebrain (remote) upon histological evaluation. Within this test model, zone of cavitation injury was greater than the maximum radius of the bubble. Separation of apposed structures, tissue tearing, and disruption of cellular layers defined early injury patterns that were not detected in the blast-exposed half of the brain slice. Ultrastructural pathology of the neurons exposed to cavitation was characterized by disintegration of plasma membrane along with loss of cellular content. The developed test system provided a controlled experimental platform to study cavitation induced high strain deformations on brain tissue slice. The goal of the future studies will be to lower underpressure magnitude and cavitation bubble size for more sensitive evaluation of injury.

Time Course of Endothelial Dysfunction Induced by Decompression Bubbles in Rats

Decompression stress can cause endothelial injury, leading to systematic inflammation and prothrombotic phenomena. Our previous work found that endothelial injury following decompression correlated positively with bubble formation. This study aimed to investigate the time course of endothelial injury and the relationship with bubble amounts. Rats were subjected to a simulated air dive to 7 ATA for 90 min with rapid decompression. Bubbles were detected ultrasonically at the root of pulmonary arteries following decompression. Surviving rats were randomly divided into six groups according to sampling time following decompression (2, 6, 12, 24, 48, and 72 h). Three parameters, serum levels of malondialdehyde (MDA), endothelin-1 (ET-1), and intercellular cell adhesion molecule-1 (ICAM-1) were identified from our previous study and measured. The level of MDA reached a peak level at 12 h post decompression, and then decreased gradually to control level before 72 h. For both ET-1 and ICAM-1, the greatest expression appeared at 24 h following surfacing, and the increases lasted for more than 72 h. These changes correlated positively with bubble counts at most detection time points. This study reveals the progress of endothelial dysfunction following decompression which provides guidance for timing the determination at least for the current model. The results further verify that bubbles are the causative agents of decompression induced endothelial damage and bubble amounts are an objective and suitable parameter to predict endothelial dysfunction. Most importantly, levels of endothelial biomarkers post dive may serve as sensitive parameters for assessing bubble load and decompression stress.

Endothelia-Targeting Protection by Escin in Decompression Sickness Rats

Endothelial dysfunction is involved in the pathogenesis of decompression sickness (DCS) and contributes substantively to subsequent inflammatory responses. Escin, the main active compound in horse chestnut seed extract, is well known for its endothelial protection and anti-inflammatory properties. This study aimed to investigate the potential protection of escin against DCS in rats. Escin was administered orally to adult male rats for 7 d (1.8 mg/kg/day) before a simulated air dive. After decompression, signs of DCS were monitored, and blood and pulmonary tissue were sampled for the detection of endothelia related indices. The incidence and mortality of DCS were postponed and decreased significantly in rats treated with escin compared with those treated with saline (P < 0.05). Escin significantly ameliorated endothelial dysfunction (increased serum E-selectin and ICAM-1 and lung Wet/Dry ratio, decreased serum NO), and oxidative and inflammatory responses (increased serum MDA, MPO, IL-6 and TNF-α) (P < 0.05 or P < 0.01). The results suggest escin has beneficial effects on DCS related to its endothelia-protective properties and might be a drug candidate for DCS prevention and treatment.

[Diagnosis and treatment of diving accidents. New German guidelines for diving accidents 2014-2017]

In 2015 the German Society for Diving and Hyperbaric Medicine (GTÜM) and the Swiss Underwater and Hyperbaric Medical Society (SUHMS) published the updated guidelines on diving accidents 2014-2017. These multidisciplinary guidelines were developed within a structured consensus process by members of the German Interdisciplinary Association for Intensive Care and Emergency Medicine (DIVI), the Sports Divers Association (VDST), the Naval Medical Institute (SchiffMedInst), the Social Accident Insurance Institution for the Building Trade (BG BAU), the Association of Hyperbaric Treatment Centers (VDD) and the Society of Occupational and Environmental Medicine (DGAUM). This consensus-based guidelines project (development grade S2k) with a representative group of developers was conducted by the Association of Scientific Medical Societies in Germany. It provides information and instructions according to up to date evidence to all divers and other lay persons for first aid recommendations to physician first responders and emergency physicians as well as paramedics and all physicians at therapeutic hyperbaric chambers for the diagnostics and treatment of diving accidents. To assist in implementing the guideline recommendations, this article summarizes the rationale, purpose and the following key action statements: on-site 100% oxygen first aid treatment, still patient positioning and fluid administration are recommended. Hyperbaric oxygen (HBO) recompression remains unchanged the established treatment in severe cases with no therapeutic alternatives. The basic treatment scheme recommended for diving accidents is hyperbaric oxygenation at 280 kPa. For quality management purposes there is a need in the future for a nationwide register of hyperbaric therapy.

Decompression induced bubble dynamics on ex vivo fat and muscle tissue surfaces with a new experimental set up

Vascular gas bubbles are routinely observed after scuba dives using ultrasound imaging, however the precise formation mechanism and site of these bubbles are still debated and growth from decompression in vivo has not been extensively studied, due in part to imaging difficulties. An experimental set-up was developed for optical recording of bubble growth and density on tissue surface area during hyperbaric decompression. Muscle and fat tissues (rabbits, ex vivo) were covered with nitrogen saturated distilled water and decompression experiments performed, from 3 to 0bar, at a rate of 1bar/min. Pictures were automatically acquired every 5s from the start of the decompression for 1h with a resolution of 1.75μm. A custom MatLab analysis code implementing a circular Hough transform was written and shown to be able to track bubble growth sequences including bubble center, radius, contact line and contact angles over time. Bubble density, nucleation threshold and detachment size, as well as coalescence behavior, were shown significantly different for muscle and fat tissues surfaces, whereas growth rates after a critical size were governed by diffusion as expected. Heterogeneous nucleation was observed from preferential sites on the tissue substrate, where the bubbles grow, detach and new bubbles form in turn. No new nucleation sites were observed after the first 10min post decompression start so bubble density did not vary after this point in the experiment. In addition, a competition for dissolved gas between adjacent multiple bubbles was demonstrated in increased delay times as well as slower growth rates for non-isolated bubbles.

A new measure of decompression sickness in the rat

In this study we assessed the reliability of a tilting-board grip score as a measure of decompression sickness in rats. In experiments using a hyperbaric compression/decompression protocol, rats were observed for signs of decompression sickness and their grip strength measured on a tilting particle board hinged to a metal frame. Angles at which rats lost grip were converted to gravitational vectors. Decreased mean grip scores following decompression were fitted to a logistic regression model with strain, age, and weight. Decrease in grip score was significantly associated with observed decompression sickness (P = 0.0036). The log odds ratio for decompression sickness = 1.40 (decrease in grip score). In rats with no decrease in mean grip score there was a 50% probability of decompression sickness (pDCS). This increased steadily with decreases in mean grip score. A decrease of 0.3 had a 60% pDCS, a decrease of 0.6 had a 70% pDCS, and a decrease of 2.1 had a 95% pDCS. The tilting board grip score is a reliable measure of the probability of decompression sickness.