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Association of microparticles and neutrophil activation with decompression sickness
Abstract
Decompression sickness (DCS) is a systemic disorder assumed due to gas bubbles, but additional factors are likely to play a role. Circulating microparticles, vesicular structures with diameters of 0.1 to 1.0 µm, have been implicated but data in human divers has been lacking. We hypothesized that the number of blood-borne annexin V-positive microparticles (MPs) and neutrophil activation assessed as surface myeloperoxidase (MPO) staining would differ between SCUBA divers suffering from DCS versus 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 hours 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 versus 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 non-steroidal anti-inflammatory agents or emergency oxygen treatment, and 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 MPs production and neutrophil activation exhibit strong associations with DCS.
Copyright © 2015, Journal of Applied Physiology.
... Therefore, additional pathological mechanisms contributing to the occurrence of DCS might be involved [2,3]. For example, functional changes in vascular wall, repeatedly observed by impaired flow-mediated dilation (FMD), endothelial microparticles or oxidative stress following the dive have been linked to the presence of VGE [4][5][6][7] but also to decompression 'stress' without significant VGE presence [8]. Nonetheless, the exact involvement of each of those mechanisms contributing to DCS remains unclear. ...
... Conversely, decreased VGE production might change FMD by provoking less mechanical or biochemical endothelial reactions. Finally, it is entirely possible that there is no direct relationship between VGE and FMD, but that both are simply caused by the same mechanism through, for instance, a relationship between VGE levels and the presence of endothelial microparticles (MP) [8,43]. Either by shear forces or by mechanical/biochemical damage to the endothelial cell wall, VGE might cause the release of endothelial MP, which ...
... Conversely, decreased VGE production might change FMD by provoking less mechanical or biochemical endothelial reactions. Finally, it is entirely possible that there is no direct relationship be-tween VGE and FMD, but that both are simply caused by the same mechanism through, for instance, a relationship between VGE levels and the presence of endothelial microparticles (MP) [8,43]. Either by shear forces or by mechanical/biochemical damage to the endothelial cell wall, VGE might cause the release of endothelial MP, which will, unlike VGE, readily pass the pulmonary capillary filter. ...
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.
... Several reports over the past two decades have shown that exposure to hyperbaric environments and subsequent decompression have many physiological implications, including reduction in endothelial function, activation of the immune system (Brubakk et al., 2005;Thom et al., 2012Thom et al., , 2015 and the well documented bubbles formation. The causal relationship between venous gas emboli formation and other decompression-related physiological alterations, is yet to be understood (Møllerløkken and Brubakk, 2009) and due to large inter-personal variability (Papadopoulou et al., 2018), venous gas emboli are a poor surrogate for decompression sickness (Doolette, 2016) on an individual basis. ...
... In fact, it has been demonstrated that individuals suffering from decompression sickness present higher levels of circulating MPs, as well as higher levels of MPO expression, for long periods after the appearance of the symptoms, although altered levels of such markers are also observed in symptom free individuals that were submitted to hyperbaric exposure. It seems, however, that in asymptomatic individuals the time for the resolution of the alterations is shorter and the change magnitude is lower (Thom et al., 2015). ...
... The results obtained in the present study demonstrated that MPs subtypes have little and not statistically significant correlation among each other, which contradicts another study previously published (Thom et al., 2015). The reason for contradiction would require further investigation. ...
The purpose of this study was to analyze the correlation between decompression-related physiological stress markers, given by inflammatory processes and immune system activation and changes in Heart Rate Variability, evaluating whether Heart Rate Variability can be used to estimate the physiological stress caused by the exposure to hyperbaric environments and subsequent decompression. A total of 28 volunteers participated in the experimental protocol. Electrocardiograms were performed; blood samples were obtained for the quantification of red cells, hemoglobin, hematocrit, neutrophils, lymphocytes, platelets, aspartate transaminase (AST), alanine aminotransferase (ALT), and for immunophenotyping and microparticles (MP) research through Flow Cytometry, before and after each experimental protocol from each volunteer. Also, myeloperoxidase (MPO) expression and microparticles (MPs) deriving from platelets, neutrophils and endothelial cells were quantified. Negative associations between the standard deviation of normal-to-normal intervals (SDNN) in the time domain, the High Frequency in the frequency domain and the total number of circulating microparticles was observed (p-value = 0.03 and p-value = 0.02, respectively). The pre and post exposure ratio of variation in the number of circulating microparticles was negatively correlated with SDNN (p-value = 0.01). Additionally, a model based on the utilization of Radial Basis Function Neural Networks (RBF-NN) was created and was able to predict the SDNN ratio of variation based on the variation of specific inflammatory markers (RMSE = 0.06).
... This investigation was prompted because translation of findings from the murine decompression model to humans requires additional study. MPs elevations have been shown in divers, with some sub-types, such as those from neutrophils and platelets, being significantly higher in individuals suffering from DCS than in asymptomatic divers 22 . However, no investigation has been done examining an association between MPs and IL-1β in human divers. ...
... Additionally, the time course for increases in MPs production needs further study because in mice it appears to be initiated during the high pressure exposure, rather than a phenomenon that develops after decompression 11 . Recent studies suggest that MPs may provide an explanatory link between bubbles and DCS 4,8,22 . With these issues in mind, we obtained blood from research subjects before, during, and after simulated dives in a hyperbaric chamber. ...
... The variability within our pre-dive data is comparable to that observed in human populations studied for reasons other than diving, and similar to results observed in divers without DCS 22,[28][29][30] . However, it is greater than we have observed in several prior investigations 6,7,10,31,32 . ...
Production of blood-borne microparticles (MPs), 0.1–1 µm diameter vesicles, and interleukin (IL)-1β in response to high pressure is reported in lab animals and associated with pathological changes. It is unknown whether the responses occur in humans, and whether they are due to exposure to high pressure or to the process of decompression. Blood from research subjects exposed in hyperbaric chambers to air pressure equal to 18 meters of sea water (msw) for 60 minutes or 30 msw for 35 minutes were obtained prior to and during compression and 2 hours post-decompression. MPs and intra-particle IL-1β elevations occurred while at pressure in both groups. At 18 msw (n = 15) MPs increased by 1.8-fold, and IL-1β by 7.0-fold (p < 0.05, repeated measures ANOVA on ranks). At 30 msw (n = 16) MPs increased by 2.5-fold, and IL-1β by 4.6-fold (p < 0.05), and elevations persisted after decompression with MPs elevated by 2.0-fold, and IL-1β by 6.0-fold (p < 0.05). Whereas neutrophils incubated in ambient air pressure for up to 3 hours ex vivo did not generate MPs, those exposed to air pressure at 180 kPa for 1 hour generated 1.4 ± 0.1 MPs/cell (n = 8, p < 0.05 versus ambient air), and 1.7 ± 0.1 MPs/cell (p < 0.05 versus ambient air) when exposed to 300 kPa for 35 minutes. At both pressures IL-1β concentration tripled (p < 0.05 versus ambient air) during pressure exposure and increased 6-fold (p < 0.05 versus ambient air) over 2 hours post-decompression. Platelets also generated MPs but at a rate about 1/100 that seen with neutrophils. We conclude that production of MPs containing elevated concentrations of IL-1β occur in humans during exposure to high gas pressures, more so than as a response to decompression. While these events may pose adverse health threats, their contribution to decompression sickness development requires further study.
... However, the inconsistent presence of bubbles in human studies has prompted investigations that are focused instead on inflammatory pathways [1][2][3]. A body of work implicates a subset of extracellular vesicles (EVs), 0.1 to 1 µm microparticles (MPs), that are elevated in humans and rodent models exposed to high gas pressure and rise further after decompression [4][5][6][7][8][9][10][11][12][13][14][15]. MPs initiate a systemic inflammatory response related to neutrophil activation [13,[16][17][18]. ...
... This study demonstrates that MPs elevations and neutrophil activation in CCR divers mirror changes previously reported in air-breathing divers, where oxygen partial pressures were variable and often higher [4,5,[7][8][9]11,12,14]. Changes in MPs subgroups expressing different cell-specific proteins and concurrent changes in IL-1β, NOS2, and pGSN provide additional insight. ...
Blood-borne extracellular vesicles and inflammatory mediators were evaluated in divers using a closed circuit rebreathing apparatus and custom-mixed gases to diminish some diving risks. “Deep” divers (n = 8) dove once to mean (±SD) 102.5 ± 1.2 m of sea water (msw) for 167.3 ± 11.5 min. “Shallow” divers (n = 6) dove 3 times on day 1, and then repetitively over 7 days to 16.4 ± 3.7 msw, for 49.9 ± 11.9 min. There were statistically significant elevations of microparticles (MPs) in deep divers (day 1) and shallow divers at day 7 that expressed proteins specific to microglia, neutrophils, platelets, and endothelial cells, as well as thrombospondin (TSP)-1 and filamentous (F-) actin. Intra-MP IL-1β increased by 7.5-fold (p < 0.001) after day 1 and 41-fold (p = 0.003) at day 7. Intra-MP nitric oxide synthase-2 (NOS2) increased 17-fold (p < 0.001) after day 1 and 19-fold (p = 0.002) at day 7. Plasma gelsolin (pGSN) levels decreased by 73% (p < 0.001) in deep divers (day 1) and 37% in shallow divers by day 7. Plasma samples containing exosomes and other lipophilic particles increased from 186% to 490% among the divers but contained no IL-1β or NOS2. We conclude that diving triggers inflammatory events, even when controlling for hyperoxia, and many are not proportional to the depth of diving.
... On the comments for the viewpoint, Foster et al. (2016) discussed some pathogenetic factors including increase in cardiac output or cerebral blood flow, hypercapnia, and hypoxia. In compressed-air diving, other factors like vascular dysfunction, microparticles, and neutrophil activation have been identified as potential contributors (Thom et al., 2015). Recently, Barak et al. (2020) have also described in BH diving that microparticles play an essential role in endothelial dysfunction of the brain. ...
... Small amounts of intravascular bubble cause endothelial dysfunction (Nossum et al., 2002;Theunissen et al., 2013;Barak et al., 2020), may form thrombi and affect arterial occlusion of the brain. Or microparticles may induce bubble nucleation and contribute to vascular injuries (Thom et al., 2015;Barak et al., 2020). The progressive evolution of neurological disorders in most Ama divers seems compatible with gradual bubble growth. ...
Nitrogen (N 2 ) accumulation in the blood and tissues can occur due to breath-hold (BH) diving. Post-dive venous gas emboli have been documented in commercial BH divers (Ama) after repetitive dives with short surface intervals. Hence, BH diving can theoretically cause decompression illness (DCI). “Taravana,” the diving syndrome described in Polynesian pearl divers by Cross in the 1960s, is likely DCI. It manifests mainly with cerebral involvements, especially stroke-like brain attacks with the spinal cord spared. Neuroradiological studies on Ama divers showed symptomatic and asymptomatic ischemic lesions in the cerebral cortex, subcortex, basal ganglia, brainstem, and cerebellum. These lesions localized in the external watershed areas and deep perforating arteries are compatible with cerebral arterial gas embolism. The underlying mechanisms remain to be elucidated. We consider that the most plausible mechanisms are arterialized venous gas bubbles passing through the lungs, bubbles mixed with thrombi occlude cerebral arteries and then expand from N 2 influx from the occluded arteries and the brain. The first aid normobaric oxygen appears beneficial. DCI prevention strategy includes avoiding long-lasting repetitive dives for more than several hours, prolonging the surface intervals. This article provides an overview of clinical manifestations of DCI following repetitive BH dives and discusses possible mechanisms based on clinical and neuroimaging studies.
... Cytokine release, complement activation and microparticle production are part of this inflammatory milieu and may contribute to tissue injury. 4,5 The variability in the activation of inflammatory processes could contribute to the differences between individuals in susceptibility to DCS as well as the highly variable clinical presentations which can range from a mild syndrome to a life threatening condition. 5 ...
... 4,5 The variability in the activation of inflammatory processes could contribute to the differences between individuals in susceptibility to DCS as well as the highly variable clinical presentations which can range from a mild syndrome to a life threatening condition. 5 ...
Introduction:
The cutaneous form of decompression sickness (DCS) known as cutis marmorata is a frequent clinical presentation. Beyond a general acceptance that bubbles formed from dissolved inert gas are the primary vector of injury, there has been debate about pathophysiology. Hypotheses include: 1) local formation of bubbles in the skin or its blood vessels; 2) arterialisation of venous bubbles across a right to left shunt (RLS) with local amplification in bubble size after reaching supersaturated skin via the arterial circulation; and 3) passage of arterialised venous bubbles to the cerebral circulation with stimulation of a sympathetically mediated vasomotor response.
Methods:
Four divers exhibiting cutis marmorata had the underlying tissue examined with ultrasound 4-5.5 hours after appearance of the rash. All subsequently underwent transthoracic echocardiography with bubble contrast to check for a RLS.
Results:
In all cases numerous small bubbles were seen moving within the skin microvasculature. No bubbles were seen in adjacent areas of normal skin. All four divers had a large RLS.
Conclusion:
This is the first report of bubbles in skin affected by cutis marmorata after diving. The finding is most compatible with pathophysiological hypotheses one and two above. The use of ultrasound will facilitate further study of this form of DCS.
... Bubbles affect the body in multiple ways, one of which by reduced perfusion that can lead to organ ischaemia in small vessels, as well as causing mechanical compression and stretching of the blood vessels and nerves. Through adhesion-molecule-mediated endothelial activation, bubbles cause platelet and neutrophil activation which further can cause clotting and ischaemia [4]. These cells release micro-particles upon activation and cell apoptosis [4]. ...
... Through adhesion-molecule-mediated endothelial activation, bubbles cause platelet and neutrophil activation which further can cause clotting and ischaemia [4]. These cells release micro-particles upon activation and cell apoptosis [4]. Once bubbles form, they create a foreign body interface to which platelets adhere. ...
Background
The case reinforces the importance of stepping back and looking at every possibility along with multiple co-existing pathologies. It takes into account the thought process of multiple systems and a multidisciplinary team approach. Learning points to take are that decompression illness can present atypically, but one must exclude other causes.
Case presentation
We present the case of a 42-year-old male from the West Midlands, UK, who attended the emergency department post-scuba diving with confusion, light-headedness, left arm weakness, and bilateral paraesthesia of the hands. Post-diving, he displayed typical symptoms of decompression illness. He attended the hyperbaric decompression chamber before attending the emergency department but to no resolve. A computed tomography of the head showed no signs of intracranial pathology. He had another session in the hyperbaric oxygen chamber but to no success. Upon admission, his blood showed polycythaemia. His saturation had dropped to 91% on room air, and a computed tomography pulmonary angiogram revealed no obvious cause. A magnetic resonance imaging of his head revealed some deep periventricular ischaemic changes, old and new, however no signs of gas embolism or poor flow. A bubble echo confirmed a patent foramen ovale. A leptospirosis and a vasculitis screen were both negative. Symptoms had slowly improved but he was left with a left arm motor weakness, and the team was left puzzled as to what could have caused his signs and symptoms. Through a diagnosis of exclusion, decompression sickness was the conclusive diagnosis. The patient made a full recovery.
Conclusions
Decompression illness results as a sudden decrease in pressures during underwater ascent; it is caused by nitrogen bubbles forming in tissue. Additionally, a patent foramen ovale allows arterial gas emboli to cause further harm. Type 2 decompression sickness is the more severe form and includes neurological, respiratory, and cardiovascular symptoms.
... New recently developed hypotheses indicating that inert gas embolism can trigger cell-mediated mechanisms assimilating DCS to an inflammatory disease (Thom et al., 2015) make the presence of even "silent bubbles" worth considering and investigating to identify further risk factors that may correlate with an increase in the incidence of bubble formation and DCS. ...
... But the main focus of this analysis was to investigate how certain risk factors may influence bubble formation (in particular high bubble grades) and DCS and the capacity to predict DCS trough the current decompression models, considering that in recent years diving medicine experts began to suspect that bubble formation and DCS occurrence could be linked not "only" to the dive profile but also to certain pre-dive conditions (Theunissen et al., 2013(Theunissen et al., , 2015 and possibly to specific individual predisposition as already confirmed in a other diving related illnesses (Cialoni et al., 2015). The relation between bubble formation and DCS also seems to be more complex than previously believed and DCS in the presence of high bubble grades to be possibly influenced by other peripheral variables (Thom et al., 2015). ...
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.
... On the one hand, it has been shown that circulating bubbles can lead to endothelial dysfunction (Nossum et al. 2002) through either direct contact between microbubbles and endothelial cells Sobolewski et al. 2011) or activation of the coagulation cascade (Pontier et al. 2008aLambrechts et al. 2015). Activation of haemostatic pathways participates in the post-dive increase of circulating microparticles which in turn leads to leukocytes activation (Ersson et al. 2002;Yang et al. 2015a) and adhesion to the endothelium (Thom et al. 2015). On the other hand, impaired FMD (Brubakk et al. 2005;Theunissen et al. 2013a) and increased oxidative stress (Obad et al. 2007a;Theunissen et al. 2013b) were also reported postdive even in the absence of VGE. ...
... Besides a direct mechanical action Sobolewski et al. 2011), putative mechanisms by which VGE could impair vascular function include ROS (Obad et al. 2007a(Obad et al. , 2010Theunissen et al. 2015). In this regard, previous studies showed that (1) both oxidative stress (Mazur et al. 2016) and platelet activation (Baj et al. 2000;Pontier et al. 2008b) correlate with decompression stress, (2) pretreatment with anticoagulant decreases oxidative stress after the dive, even in the absence of DCS (Lambrechts et al. 2015) and (3): MPs released during the dive predominantly originate from platelets (Pontier et al. 2012;Thom et al. 2015) and exert a deleterious effect on vessel walls (Thom et al. 2011). With these data in mind, we thus sought whether the preventive action of pre-dive vibrations on vascular dysfunction could be related to an action on haemostasis pathways. ...
Purpose:
Previous studies have shown vascular dysfunction of main conductance arteries and microvessels after diving. We aim to evaluate the impact of bubble formation on vascular function and haemostasis. To achieve this, we used a vibration preconditioning to influence bubble levels without changing any other parameters linked to the dive.
Methods:
Twentty-six divers were randomly assigned to one of three groups: (1) the "vibrations-dive" group (VD; n = 9) was exposed to a whole-body vibration session 30 min prior the dive; (2) the "diving" group (D; n = 9) served as a control for the effect of the diving protocol; (3) The "vibration" protocol (V; n = 8) allowed us to assess the effect of vibrations without diving. Macro- and microvascular function was assessed for each subject before and after the dive, subsequently. Bubble grades were monitored with Doppler according to the Spencer grading system. Blood was taken before and after the protocol to assess any change of platelets or endothelial function.
Results:
Bubble formation was lower in the VD than the diving group. The other measured parameters remained unchanged after the "vibration" protocol alone. Diving alone induced macrovascular dysfunction, and increased PMP and thrombin generation. Those parameters were no longer changed in the VD group. Conversely, a microvascular dysfunction persists despite a significant decrease of circulating bubbles.
Conclusions:
Finally, the results of this study suggest that macro- but not microvascular impairment results at least partly from bubbles, possibly related to platelet activation and generation of pro-coagulant microparticles.
... For instance, in cancer, they act as drivers of niche establishment [11][12][13][14]. Increased MP production also occurs in SCUBA divers during decompression [15,16]. In contrast to these examples of MPs in illness, physical exercise can modulate MP production as a signalling component in beneficial vascular adaptations that enhance blood flow to muscles [17]. ...
The deformation of cellular membranes regulates trafficking processes, such as exocytosis and endocytosis. Classically, the Helfrich continuum model is used to characterize the forces and mechanical parameters that cells tune to accomplish membrane shape changes. While this classical model effectively captures curvature generation, one of the core challenges in using it to approximate a biological process is selecting a set of mechanical parameters (including bending modulus and membrane tension) from a large set of reasonable values. We used the Helfrich model to generate a large synthetic dataset from a random sampling of realistic mechanical parameters and used this dataset to train machine-learning models. These models produced promising results, accurately classifying model behaviour and predicting membrane shape from mechanical parameters. We also note emerging methods in machine learning that can leverage the physical insight of the Helfrich model to improve performance and draw greater insight into how cells control membrane shape change.
... The literature has identified several contributing factors to pressure exposures and DCS, such as vascular dysfunction, oxidative stress, and blood-borne microparticles (MPs) [26,27], which have been considered potential targets for pre-conditioning interventions. MPs are of particular interest since a growing body of data suggest that they are a potential bubble nucleation site and play a role in DCS pathophysiology [27][28][29][30][31]. MPs are 0.1-1 µm vesicles generated by an outward budding of the plasma membrane in a process that results in the surface expression of phosphatidylserine. ...
Oxygen is a powerful trigger for cellular reactions, but there are few comparative investigations assessing the effects over a large range of partial pressures. We investigated a metabolic response to single exposures to either normobaric (10%, 15%, 30%, 100%) or hyperbaric (1.4 ATA, 2.5 ATA) oxygen. Forty-eight healthy subjects (32 males/16 females; age: 43.7 ± 13.4 years, height: 172.7 ± 10.07 cm; weight 68.4 ± 15.7 kg) were randomly assigned, and blood samples were taken before and 2 h after each exposure. Microparticles (MPs) expressing proteins specific to different cells were analyzed, including platelets (CD41), neutrophils (CD66b), endothelial cells (CD146), and microglia (TMEM). Phalloidin binding and thrombospondin-1 (TSP), which are related to neutrophil and platelet activation, respectively, were also analyzed. The responses were found to be different and sometimes opposite. Significant elevations were identified for MPs expressing CD41, CD66b, TMEM, and phalloidin binding in all conditions but for 1.4 ATA, which elicited significant decreases. Few changes were found for CD146 and TSP. Regarding OPB, further investigation is needed to fully understand the future applications of such findings.
... Cell-derived or EVs, including microparticles and exosomes, are highly exhibit in body fluids such as blood circulation [26,27]. EVs are particles with a phospholipid bilayer that are naturally released by cells and have no functional nucleus. ...
Background:
Increased inflammation activates blood coagulation system, higher platelet activation plays a key role in the pathophysiology of ischemic stroke (IS). During platelet activation and aggregation process, platelets may cause increased release of several proinflammatory, and prothrombotic mediators, including microRNAs (miRNAs) and extracellular vesicles (EVs). In the current study we aimed to assess circulating miRNAs profile related to platelet function and inflammation and circulating EVs from platelets, leukocytes, and endothelial cells to analyse their diagnostic and predictive utility in patients with acute IS.
Methods:
The study population consisted of 28 patients with the diagnosis of the acute IS. The control group consisted of 35 age- and gender-matched patients on acetylsalicylic acid (ASA) therapy without history of stroke and/or TIA with established stable coronary artery disease (CAD) and concomitant cardiovascular risk factors. Venous blood samples were collected from the control group and patients with IS on ASA therapy (a) 24 h after onset of acute IS, (b) 7-days following index hospitalization. Flow cytometry was used to determine the concentration of circulating EVs subtypes (from platelets, leukocytes, and endothelial cells) in platelet-depleted plasma and qRT-PCR was used to determine several circulating plasma miRNAs (miR-19a-3p, miR-186-5p and let-7f).
Results:
Patients with high platelet reactivity (HPR, based on arachidonic acid-induced platelet aggregometry) had significantly elevated platelet-EVs (CD62+) and leukocyte-EVs (CD45+) concentration compared to patients with normal platelet reactivity at the day of 1 acute-stroke (p = 0.012, p = 0.002, respectively). Diagnostic values of baseline miRNAs and EVs were evaluated with receiver operating characteristic (ROC) curve analysis. The area under the ROC curve for miR-19a-3p was 0.755 (95% CI, 0.63-0.88) p = 0.004, for let-7f, it was 0.874 (95% CI, 0.76-0.99) p = 0.0001; platelet-EVs was 0.776 (95% CI, 0.65-0.90) p = 0.001, whereas for leukocyte-EVs, it was 0.715 (95% CI, 0.57-0.87) p = 0.008. ROC curve showed that pooling the miR-19a-3p expressions, platelet-EVs, and leukocyte-EVs concentration yielded a higher AUC than the value of each individual biomarker as AUC was 0.893 (95% CI, 0.79-0.99). Patients with moderate stroke had significantly elevated miR-19a-3p expression levels compared to patients with minor stroke at the first day of IS. (AUC: 0.867, (95% CI, 0.74-0.10) p = 0.001).
Conclusion:
Combining different biomarkers of processes underlying IS pathophysiology might be beneficial for early diagnosis of ischemic events. Thus, we believe that in the future circulating biomarkers might be used in the prehospital phase of IS. In particular, circulating plasma EVs and non-coding RNAs including miRNAs are interesting candidates as bearers of circulating biomarkers due to their high stability in the blood and making them highly relevant biomarkers for IS diagnostics.
... However, even in SCUBA divers, DCS is not solely dependent on gas bubble load, but also additional factors including endothelial dysfunction 27 and microparticle formation. 28 DCS in breathhold divers has been linked to these factors. 22 There are also numerous reports of white matter lesions consistent with neurological DCS in Ama divers (traditional Japanese and Korean pearl and seafood divers) as well as DCS in freedivers and spearfishers. ...
Objectives
During apnea diving, a patent foramen ovale (PFO) may function as a pressure relief valve under conditions of high pulmonary pressure, preserving left-ventricular output. However, PFO prevalence in apneic divers has not been previously reported. We aimed to determine the prevalence of PFO in apneic divers compared to non-diver controls.
Design
Cross Sectional
Method
Apnea divers were recruited from a training camp in Cavtat, Croatia and the diving community of Split, Croatia. Controls were recruited from the population of Split, Croatia and Eugene, Oregon, USA. Participants were instrumented with an intravenous catheter and underwent PFO screening utilizing transthoracic saline contrast echocardiography with and without the release of a Valsalva maneuver. Appearance of microbubbles in the left heart within 3 cardiac cycles indicated the presence of PFO. Lung function was measured with spirometry. Comparison of PFO prevalence was conducted using a chi-square analysis, p <0.05.
Results
Apnea divers had a significantly higher prevalence of PFO (19 of 36, 53%) compared to Controls (9 of 36, 25%)(X² (1, N = 72) = 5.844, p = .0156).
Conclusion
Why PFO prevalence is greater in apnea divers remains unknown, though hyperbaria during an apnea dive results in a translocation of blood volume centrally with a concomitant reduction in lung volume and alveolar hypoxia during ascent results in hypoxic pulmonary vasoconstriction. In combination, these conditions increase pulmonary arterial pressure, subsequently increasing right-atrial pressure allowing for right-to-left blood flow through a PFO which may be beneficial for preserving cardiac output and reducing capillary hydrostatic forces.
... MBP has since been implicated in development of delayed neurological sequelae in humans based on its appearance in the cerebrospinal fluid of symptomatic patients (Beppu et al., 2012;Ide and Kamijo, 2009;Kamijo et al., 2007;Kuroda et al., 2016). Plans are underway to investigate blood-borne MPs in CO-poisoned patients using some of the same methods we have used in other clinical studies (Thom et al., 2015). Importantly, results from the current study suggest a number of possible therapeutic opportunities because of the on-going nature of CO-induced neuroinflammation lasting weeks and the cyclic mechanism between blood-borne and CNS leukocytes. ...
We hypothesized that carbon monoxide (CO) establishes an inflammatory cycle mediated by microparticles (MPs). Mice exposed to a CO protocol (1000 ppm for 40 min and then 3000 ppm for 20 min) that causes neuroinflammation exhibit NF-κB activation in astrocytes leading to generation of MPs expressing thrombospondin-1(TSP-1) that collect in deep cervical lymph nodes draining the brain glymphatic system. TSP-1 bearing MPs gain access to the blood stream where they activate neutrophils to generate a new family of MPs, and also stimulate endothelial cells as documented by leakage of intravenous 2000 kDa dextran. At the brain microvasculature, neutrophil and MPs sequestration, and myeloperoxidase activity result in elevations of the p65 subunit of NF-κB, serine 536 phosphorylated p65, CD36, and loss of astrocyte aquaporin-4 that persist for at least 7 days. Knock-out mice lacking the CD36 membrane receptor are resistant to all CO inflammatory changes. Events triggered by CO are recapitulated in naïve wild type mice injected with cervical node MPs from CO-exposed mice, but not control mice. All MPs-mediated events are inhibited with a NF-κB inhibitor, a myeloperoxidase inhibitor, or anti-TSP-1 antibodies. We conclude that astrocyte-derived MPs expressing TSP-1 establish a feed-forward neuroinflammatory cycle involving endothelial CD36-to-astrocyte NF-κB crosstalk. As there is currently no treatment for CO-induced neurological sequelae, these findings pose several possible sites for therapeutic interventions.
... 29 It was suggested that intravascular microparticles following breath-hold dives initiate a systemic inflammatory process including neutrophil activation. 30 It is possible that some forms of neurological DCI are a "reversible cerebral vasoconstriction syndrome" resulting from a transient segmental constriction of cerebral arteries. 31 However, some Ama divers with neurological DCI showed large multifocal ischaemic cerebral lesions on MRI studies. ...
Decompression illness (DCI) is well known in compressed-air diving but has been considered anecdotal in breath-hold divers. Nonetheless, reported cases and field studies of the Japanese Ama, commercial or professional breath-hold divers, support DCI as a clinical entity. Clinical characteristics of DCI in Ama divers mainly suggest neurological involvement, especially stroke-like cerebral events with sparing of the spinal cord. Female Ama divers achieving deep depths have rarely experienced a panic-like neurosis from anxiety disorders. Neuroradiological studies of Ama divers have shown symptomatic and/or asymptomatic ischaemic lesions situated in the basal ganglia, brainstem, and deep and superficial cerebral white matter, suggesting arterial insufficiency. The underlying mechanism(s) of brain damage in breath-hold diving remain to be elucidated; one of the plausible mechanisms is arterialization of venous nitrogen bubbles passing through right to left shunts in the heart or lungs. Although the treatment for DCI in Ama divers has not been specifically established, oxygen breathing should be given as soon as possible for injured divers. The strategy for prevention of diving-related disorders includes reducing extreme diving schedules, prolonging surface intervals and avoiding long periods of repetitive diving. This review discusses the clinical manifestations of diving-related disorders in Ama divers and the controversial mechanisms.
... Critically, this pattern is reversed at 40-44 h after surfacing from diving, following exposure to HBO. The role of neutrophil activation and vascular damage following microparticle release has been welldocumented, with studies showing that exposure to inert gases at high pressure generates oxidative stress (Thom et al., 2011(Thom et al., , 2014(Thom et al., , 2015. Furthermore, uneventful diving triggers a similar shift in transcriptional pattern, with upregulation of genes expressed by myeloid cells and down regulation of CD8+ lymphocyteexpressed genes (Eftedal et al., 2013). ...
Decompression sickness (DCS) develops due to inert gas bubble formation in the circulation, leading to a wide range of potentially serious clinical manifestations. Its pathophysiology remains incompletely understood. In this study, we aim to explore changes in the human leukocyte transcriptome in divers with DCS compared to closely matched unaffected controls after uneventful diving. Cases (n = 7) were divers developing the typical cutis marmorata rash after diving with a confirmed clinical diagnosis of DCS. Controls (n = 6) were healthy divers who surfaced from a ≥25 msw dive without decompression violation or evidence of DCS. Blood was sampled at two separate time points – within 8 hours of dive completion and 40-44 hours later. Transcriptome analysis by RNA-Sequencing followed by bioinformatic analysis was carried out to identify differentially expressed genes and relate their function to biological pathways. In DCS cases, we identified enrichment of transcripts involved in acute inflammation, activation of innate immunity and free radical scavenging pathways, with specific upregulation of transcripts related to neutrophil function and degranulation. DCS-induced transcriptomic events were reversed at the second time point following exposure to hyperbaric oxygen. The observed changes are consistent with findings from animal models of DCS and highlight a continuum between the responses elicited by uneventful diving and diving complicated by DCS. This study sheds light on the inflammatory pathophysiology of DCS and the associated immune response. Such data may potentially be valuable in the search for novel treatments targeting this disease.
... The solid and broken red lines are the tensions for a τ tiss1/2 of 5 s (τ 5 ) and 50 s (τ 50 ), respectively. or blockage, or initiate an immune response (Ward et al., 1987(Ward et al., , 1990Kayar et al., 1997;Thom et al., 2011Thom et al., , 2012Thom et al., , 2013Thom et al., , 2015. It is known that terrestrial mammals and humans can cope with some supersaturation and asymptomatic gas bubble formation, but any decompression has a finite probability of DCS (Berghage et al., 1974;Weathersby et al., 1984;Lillo et al., 2002;Fahlman, 2017). ...
Decompression theory has been mainly based on studies on terrestrial mammals, and may not translate well to marine mammals. However, evidence that marine mammals experience gas bubbles during diving is growing, causing concern that these bubbles may cause gas emboli pathology (GEP) under unusual circumstances. Marine mammal management, and usual avoidance, of gas emboli and GEP, or the bends, became a topic of intense scientific interest after sonar-exposed, mass-stranded deep-diving whales were observed with gas bubbles. Theoretical models, based on our current understanding of diving physiology in cetaceans, predict that the tissue and blood N 2 levels in the bottlenose dolphin ( Tursiops truncatus ) are at levels that would result in severe DCS symptoms in similar sized terrestrial mammals. However, the dolphins appear to have physiological or behavioral mechanisms to avoid excessive blood N 2 levels, or may be more resistant to circulating bubbles through immunological/biochemical adaptations. Studies on behavior, anatomy and physiology of marine mammals have enhanced our understanding of the mechanisms that are thought to prevent excessive uptake of N 2 . This has led to the selective gas exchange hypothesis, which provides a mechanism how stress-induced behavioral change may cause failure of the normal physiology, which results in excessive uptake of N 2 , and in extreme cases may cause formation of symptomatic gas emboli. Studies on cardiorespiratory function have been integral to the development of this hypothesis, with work initially being conducted on excised tissues and cadavers, followed by studies on anesthetized animals or trained animals under human care. These studies enabled research on free-ranging common bottlenose dolphins in Sarasota Bay, FL, and off Bermuda, and have included work on the metabolic and cardiorespiratory physiology of both shallow- and deep-diving dolphins and have been integral to better understand how cetaceans can dive to extreme depths, for long durations.
... Apart from these modulation activities, Xie et al 46 demonstrated that PMPs obtained from PFP primed the PMN respiratory burst activated by fMLP. Also, the role of MPs in neutrophil activation has been mentioned in connection with decompression sickness, 48 a systemic disorder due to gas bubbles in the blood. ...
In the past few years, interest has increased in cell-derived microparticles (MPs), which are defined by their size of from 0.1 to 1 μm, and can be derived from various cell types, including endothelial cells, leukocytes, red blood cells (RBCs), and platelets. These MPs carry negatively charged phosphatidylserine (PS) on their surfaces and proteins packaged from numerous cellular components. MPs that have been shed by the body can play important roles in the pathophysiology of diseases and can affect various biological systems. Among these systems, the immune components have been shown to be modulated by MPs. Therefore, understanding the roles of MPs in the immune system is crucial to developing alternative therapeutic treatments for diseases. This review describes the effects of MPs on various immune cells and provides plausible potential applications of the immune-modulating properties of MPs in clinical medicine.
... Indirect activation of the complement system can also occur through endothelial damage, platelet aggregation (del Conde et al. 2005;Peerschke et al. 2008) or through activation of the coagulation cascade (Barack and Katz 2005). Increased microparticles (MPs) carrying immune activation proteins have been linked with DCS in humans as compared with asymptomatic divers (Thom et al. 2015), and increased MPs have been measured following dives in Steller sea lions as an indicator of decompression stress (Fahlman et al. 2016). Future studies focusing on the interrelationship of these occurences should be developed to better understand the blood processes in marine mammals during diving. ...
Immune responses to nitrogen gas bubbles, particularly activation of inflammation via the complement cascade, have been linked to the development of symptoms and damage associated with decompression sickness (DCS) in humans. Marine mammals were long thought not to be susceptible to such dive-related injury, yet evidence of DCS-like injury and new models of tissue nitrogen super-saturation suggest that bubbles may routinely form. As such, it is possible that marine mammals have protective adaptations that allow them to deal with a certain level of bubble formation during normal dives, without acute adverse effects. This work evaluated the complement response, indicative of inflammation, to in vitro nitrogen bubble exposures in several marine mammal species to assess whether a less-responsive immune system serves a protective role against DCS-like injury in these animals. Serum samples from beluga (Delphinapterus leucas), and harbor seals (Phoca vitulina) (relatively shallow divers) and deep diving narwhal (Monodon monoceros), and Weddell seals (Leptonychotes weddellii) were exposed to nitrogen bubbles in vitro. Complement activity was evaluated by measuring changes in the terminal protein C5a in serum, and results suggest marine mammal complement is less sensitive to gas bubbles than human complement, but the response varies between species. Species-specific differences may be related to dive ability, and suggest moderate or shallow divers may be more susceptible to DCS-like injury. This information is an important consideration in assessing the impact of changing dive behaviors in response to anthropogenic stressors, startle responses, or changing environmental conditions that affect prey depth distributions.
... 17 the changes in FMD amplitude after the dive cannot be directly correlated with the risk for decompression sickness to occur, but rather can act as a marker for the "oxidative stress", 18 which can be induced by bubbles and/or circulating microparticles 19 and by the increased oxygen pressure in the lungs and blood during diving. 20 Pre-dive administration of antioxidant drugs only partially reverses the postdive FMD changes, indicating that the oxidative stress is not the only culprit here. 21,22 Which mechanisms exactly underpin these phenomena are not known. ...
Our understanding of decompression physiopathology has slowly improved during this last decade and some uncertainties have disappeared. A better understanding of anatomy and functional aspects of patent foramen ovale (PFO) have slowly resulted in a more liberal approach toward the medical fitness to dive for those bearing a PFO. Circulating vascular gas emboli (VGE) are considered the key actors in development of decompression sickness and can be considered as markers of decompression stress indicating induction of pathophysiological processes not necessarily leading to occurrence of disease symptoms. During the last decade, it has appeared possible to influence post-dive VGE by a so-called "preconditioning" as a pre-dive denitrogenation, exercise or some pharmacological agents. In the text we have deeply examined all the scientific evidence about this complicated but challenging theme. Finally, the role of the "normobaric oxygen paradox" has been clarified and it is not surprising that it could be involved in neuroprotection and cardioprotection. However, the best level of inspired oxygen and the exact time frame to achieve optimal effect is still not known. The aim of this paper was to reflect upon the most actual uncertainties and distil out of them a coherent, balanced advice towards the researchers involved in gas-bubbles-related pathologies.
... • The bubbles in the venous system trigger biological reactions with the vascular endothelium that create microparticles. These microparticles can pass in the arterial system and provoke a tissue inflammation similar to the one caused by bubbles (Thom et al., 2013(Thom et al., , 2015Yang et al., 2015). ...
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.
... We should also point out that NO X changes could be partly due to the known pro-inflammatory effect of diving and the observed increase of circulating MPs post diving; these aspects deserve further investigation and are part of our continuing field research action. (Thom et al., 1985). ...
Introduction: Nitric oxide (NO) plays an important role in the physiology and pathophysiology of diving, and the related endothelial dysfunction and oxidative stress roles have been extensively investigated. However, most available data have been obtained before and after the dive, whilst, as far as we know, no data is available about what happens during the water immersion phase of dive. The scope of this study is to investigate the Nitrate and Nitrite (NOX) concentration and the total plasma antioxidant capacity (TAC) before, during and after a single SCUBA dive in healthy scuba diving volunteers, as well as to look for evidence of a possible relationship with venous gas bubble formation.
Materials and Methods: Plasma, obtained from blood of 15 expert SCUBA divers, 13 male and 2 female, was investigated for differences in NOX and TAC values in different dive times. Differences in NOX and TAC values in subjects previously known as “bubble resistant” (non-bubblers – NB) and “bubble prone” (Bubblers – B) were investigated.
Results: We found a statistically significant increase of NOX plasma concentration in the “bottom blood draw” and in the “safety stop blood draw” as compared to the basal pre diving condition. We did not find any difference in NOX plasma concentration between the basal value and the post diving samples. We did not find any significant statistical difference in TAC in the bottom blood sample, while the safety-stop and the post-dive samples showed higher TAC values compared with the basal value. We did not find any difference in NOX and TAC mean values between non-bubblers and Bubblers.
Discussion: Our protocol, by including underwater blood drawing, allowed to monitor plasma NOX changes occurred during diving activity, and not only by comparing pre and post diving values. It is particularly interesting to note that the increased NOX values found at the bottom and at the safety stop were not observed at post dive sampling (T0, T30, T60), showing a very rapid return to the pre-dive values. In this preliminary study we did not find any relationship between bubble formation and changes in NOX parameters and TAC response.
... Finally, and considering the effects described here of the mtDNA and other inflammatory markers, whilst relying on the work of Sibilia (2007), it would seem that DCS may be qualified as an auto-inflammatory disorder -it continues despite the disappearance of the sterile bubbles, the air in the bubbles not strictly speaking being a pathogenic and neutrophilic element (Thom et al., 2015). In which case it would seem interesting to research the genetic or epigenetic predispositions favoring DCS. ...
Circulating mitochondrial DNA (mtDNA) is receiving increasing attention as a danger-associated molecular pattern in conditions such as autoimmunity or trauma. In the context of decompression sickness (DCS), the course of which is sometimes erratic, we hypothesize that mtDNA plays a not insignificant role particularly in neurological type accidents. This study is based on the comparison of circulating mtDNA levels in humans presenting with various types of diving accidents, and punctured upon their admission at the hyperbaric facility. One hundred and fourteen volunteers took part in the study. According to the clinical criteria there were 12 Cerebro DCS, 57 Medullary DCS, 15 Vestibular DCS, 8 Ctrl+ (accident-free divers), and 22 Ctrl- (non-divers). This work demonstrates that accident-free divers have less mtDNA than non-divers, which leads to the assumption that hyperbaric exposure degrades the mtDNA. mtDNA levels are on average greater in divers with DCS compared with accident-free divers. On another hand, the amount of double strand DNA (dsDNA) is neither significantly different between controls, nor between the different DCS types. Initially the increase in circulating oligonucleotides was attributed to the destruction of cells by bubble abrasion following necrotic phenomena. If there really is a significant difference between the Medullary DCS and the Ctrl-, this difference is not significant between these same DCS and the Ctrl+. This refutes the idea of massive degassing and suggests the need for new research in order to verify that oxidative stress could be a key element without necessarily being sufficient for the occurrence of a neurological type of accident.
... A variety of mechanisms to account for a stable distribution of micronuclei sizes have been proposed: crevice models, 34 caveolae structures, and even the presence of microparticles in the blood. 33 Perhaps those few with DCS from APT have a propensity for large stabilized micronuclei that quickly transform into bubbles during the short interval of nitrogen (N 2 ) supersaturation. Denitrogenation time before ascent must counter the hypoxia training time at altitude so as to minimize the risk of DCS. ...
INTRODUCTION: A review of decompression sickness (DCS) cases associated with the NASA altitude physiological training (APT) program at the Johnson Space Center (JSC) motivated us to place our findings into the larger context of DCS prevalence from other APT centers.METHODS: We reviewed JSC records from 1999 to 2016 and 14 publications from 1968 to 2004 about DCS prevalence in other APT programs. We performed a meta-analysis of 15 APT profiles (488 cases / 385,116 exposures). We used meta-regression to evaluate the relation between estimated exposures and probability of DCS in a test group, accounting for the heterogeneity between studies.RESULTS: Our in-house review identified 6 Type I DCS (1 from an inside observer) and 1 Type II DCS. There were 6 cases in 9560 student hypobaric exposures from 3 NASA training flights; a student pooled prevalence rate of 0.44 cases / 1000 exposures compared to 1.44 cases / 1000 from 12 published APT profiles. The overall pooled DCS prevalence rate was 1.16 cases / 1000 exposures. There was substantial heterogeneity in DCS prevalence across studies. Denitrogenation time, exposure pressure, and exposure time were associated with probability of DCS in the meta-regression model.CONCLUSIONS: While the overall DCS prevalence rate is relatively low, there is marked heterogeneity among profiles. The pooled DCS prevalence rate estimate for the NASA profiles was lower than the overall rate. Variability in APT profile DCS prevalence could be further explained given student level and additional test-level covariates.Conkin J, Sanders RW, Koslovsky MD, Wear ML, Kozminski AG, Abercromby AFJ. A systematic review and meta-analysis of decompression sickness in altitude physiological training. Aerosp Med Hum Perform. 2018; 89(11):941-951.
... Beyond the well-known thrombotic role of platelets, it would also be interesting to consider the involvement of the platelets in the immune response (Harifi and Sibilia, 2016). In fact, according to the work of Sibilia (2007), it would seem that DCS can be qualified as a disorder that is auto-inflammatory (it continues despite the disappearance of the bubbles), sterile (the air in the bubbles is not strictly speaking a pathogenic element) and it is neutrophilic in type (Chen and Nunez, 2010;Thom et al., 2015). ...
In its severest forms, decompression sickness (DCS) may extend systemically and/or induce severe neurological deficits, including paralysis or even death. It seems that the sterile and ischemic inflammatory phenomena are consecutive to the reaction of the bubbles with the organism and that the blood platelet activation plays a determinant role in the development of DCS. According to the hypotheses commonly put forward, the bubbles could either activate the platelets by direct contact or be the cause of abrasion of the vascular epithelium, which would expose the basal plate glycogen and then prompt the platelets to activate. The purpose of this study is to confirm anti-platelet drugs specific to GPIIb/IIIa integrin could prevent DCS, using a rat model. There is a significant difference concerning the incidence of the drug on the clinical status of the rats (p = 0.016), with a better clinical outcome for rats treated with tirofiban (TIR) compared with the control rats (p = 0.027), even if the three anti-GPIIb/IIIa agents used have limited respiratory distress. TIR limited the decrease in platelet counts following the hyperbaric exposure. TIR help to prevent from DCS. TIR is specific to GPIIb/IIIa whereas eptifibatide and abciximab could inhibit αVβ3 and αMβ2 involved in communication with the immune system. While inhibiting GPIIb/IIIa could highlight a platelet-dependent inflammatory pathway that improves DCS outcomes, we wonder whether inhibiting the αVβ3 and αMβ2 communications is not a wrong approach for limiting mortality in DCS. © 2018 Lambrechts, de Maistre, Abraini, Blatteau, Risso and Vallée.
... In the case of factor Va and VIIIa, a 10-fold, while in the case of factor IXa, a 2-fold concentration of factor binding sites was observed in the above mentioned studies [69][70][71]. Another factor, von Willebrand Factor (vWF), an interaction partner of both glycoproteins GPIb and GPIIbIIIa, was found to be attached to platelet-and also to endothelial cell-derived EVs [72,73]. Together, the accumulation of PS and of other coagulation factor binding sites enables the surface of platelet MPs to enhance coagulation approximately 50-100-fold as compared to platelets [74]. ...
Extracellular vesicles such as exosomes, microvesicles, apoptotic bodies, and large oncosomes have been shown to participate in a wide variety of biological processes and are currently under intense investigation in many different fields of biomedicine. One of the key features of extracellular vesicles is that they have relatively large surface compared to their volume. Some extracellular vesicle surface molecules are shared with those of the plasma membrane of the releasing cell, while other molecules are characteristic for extracellular vesicular surfaces. Besides proteins, lipids, glycans, and nucleic acids are also players of extracellular vesicle surface interactions. Being secreted and present in high number in biological samples, collectively extracellular vesicles represent a uniquely large interactive surface area which can establish contacts both with cells and with molecules in the extracellular microenvironment. Here, we provide a brief overview of known components of the extracellular vesicle surface interactome and highlight some already established roles of the extracellular vesicle surface interactions in different biological processes in health and disease.
... All of these have been proven to trigger diving-related physiological changes. Indeed, altered vascular permeability , platelet aggregation (Pontier et al., 2012), release of microparticles and inflammation (Thom et al., 2015), as well as oxidative stress have been evidenced post-dive. Recently, we found that plasmatic concentration of AngII was decreased after the dive in asymptomatic rats but not animals which suffered DCS . ...
Introduction: Commercial divers, high altitude pilots, and astronauts are exposed to some inherent risk of decompression sickness (DCS), though the mechanisms that trigger are still unclear. It has been previously showed that diving may induce increased levels of serum angiotensin converting enzyme. The renin angiotensin aldosterone system (RAAS) is one of the most important regulators of blood pressure and fluid volume. The purpose of the present study was to control the influence of angiotensin II on the appearance of DCS.
Methods: Sprague Dawley rats have been pre-treated with inhibitor of angiotensin II receptor type 1 (losartan; 10 mg/kg), angiotensin-converting enzyme (ACE) inhibitor (enalapril; 10 mg/kg), and calcium-entry blocker (nifedipine; 20 mg/kg). The experimental groups were treated for 4 weeks before exposure to hyperbaric pressure while controls were not treated. Seventy-five rats were subjected to a simulated dive at 1000 kPa absolute pressure for 45 min before starting decompression. Clinical assessment took place over a period of 60 min after surfacing. Blood samples were collected for measurements of TBARS, interleukin 6 (IL-6), angiotensin II (ANG II) and ACE.
Results: The diving protocol induced 60% DCS in non-treated animals. This ratio was significantly decreased after treatment with enalapril, but not other vasoactive drugs. Enalapril did not change ANG II or ACE concentration, while losartant decreased post dive level of ACE but not ANG II. None of the treatment modified the effect of diving on TBARS and IL-6 values.
Conclusion: Results suggests that the rennin angiotensin system is involved in a process of triggering DCS but this has to be further investigated. However, a vasorelaxation mediated process, which potentially could increase the load of inert gas during hyperbaric exposure, and antioxidant properties were excluded by our results.
... Moreover, oxygen prebreathing has shown protective effect on bubble production and platelets activation; deeply, it has been shown correlation among oxygen partial pressure breathing and modulation of reactive oxygen species and related antioxidant enzyme (Landolfi et al., 2006;Bosco et al., 2010;Morabito et al., 2011). Thom et al. (2015) offered a novel opportunity to explore associations of circulating microparticles and neutrophil activation that may contribute to development of DCS. Further work will be needed to explain and clarify DCS pathophysiology. ...
Man’s experience and exploration of the underwater environment has been recorded from ancient times and today encompasses large sections of the population for sport enjoyment, recreational and commercial purpose, as well as military strategic goals. Knowledge, respect and maintenance of the underwater world is an essential development for our future and the knowledge acquired over the last few dozen years will change rapidly in the near future with plans to establish secure habitats with specific long-term goals of exploration, maintenance and survival. This summary will illustrate briefly the physiological changes induced by immersion, swimming, breath-hold diving and exploring while using special equipment in the water. Cardiac, circulatory and pulmonary vascular adaptation and the pathophysiology of novel syndromes have been demonstrated, which will allow selection of individual characteristics in order to succeed in various environments. Training and treatment for these new microenvironments will be suggested with description of successful pioneers in this field. This is a summary of the physiology and the present status of pathology and therapy for the field.
... These MPs cause platelet aggregation and inflammation, and neutrophil activation. An association has been shown between MPs and decompression sickness (Thom et al., 2015). Madden and Laden (2009) even suggested that endothelial malfunction and MPs, not gas bubbles, may be the underlying cause of DCI. ...
Decompression illness (DCI) occurs following a reduction in ambient pressure. Decompression bubbles can expand and develop only from pre-existing gas micronuclei. The different hypotheses hitherto proposed regarding the nucleation and stabilization of gas micronuclei have never been validated. It is known that nanobubbles form spontaneously when a smooth hydrophobic surface is submerged in water containing dissolved gas. These nanobubbles may be the long sought-after gas micronuclei underlying decompression bubbles and DCI. We exposed hydrophobic and hydrophilic silicon wafers under water to hyperbaric pressure. After decompression, bubbles appeared on the hydrophobic but not the hydrophilic wafers. In a further series of experiments, we placed large ovine blood vessels in a cooled high pressure chamber at 1,000 kPa for about 20 h. Bubbles evolved at definite spots in all the types of blood vessels. These bubble-producing spots stained positive for lipids, and were henceforth termed “active hydrophobic spots” (AHS). The lung surfactant dipalmitoylphosphatidylcholine (DPPC), was found both in the plasma of the sheep and at the AHS. Bubbles detached from the blood vessel in pulsatile flow after reaching a mean diameter of ~1.0 mm. Bubble expansion was bi-phasic—a slow initiation phase which peaked 45 min after decompression, followed by fast diffusion-controlled growth. Many features of decompression from diving correlate with this finding of AHS on the blood vessels. (1) Variability between bubblers and non-bubblers. (2) An age-related effect and adaptation. (3) The increased risk of DCI on a second dive. (4) Symptoms of neurologic decompression sickness. (5) Preconditioning before a dive. (6) A bi-phasic mechanism of bubble expansion. (7) Increased bubble formation with depth. (8) Endothelial injury. (9) The presence of endothelial microparticles. Finally, constant contact between nanobubbles and plasma may result in distortion of proteins and their transformation into autoantigens.
... The possibility that external factors such as naval sonar could interfere with the cause of DCS in whales [21,24] confirms the many and variegated factors that may be involved in the pathogenetic mechanism of dysbaric bubble-generated injuries as well as Taravana. Thom's hypothesis, postulating that scubarelated DCS could also be involved in Taravana also needs consideration and opens new avenues for investigation [25]. ...
Abstract
INTRODUCTION:
Neurological symptoms after breathhold (BH) diving are often referred to as "Taravana" and considered a form of decompression sickness. However, the presence of "high" gas embolism after BH diving has never been clearly shown. This study showed high bubble formation after BH diving.
MATERIALS AND METHODS:
We performed transthoracic echocardiography on a 53-year-old male spearfishing diver (180 cm; 80 kg; BMI 24.7) 15 minutes before diving and at 15-minute intervals for 90 minutes after diving in a 42-meter-deep pool. Number of dives, bottom time and surface intervals were freely determined by the diver. Dive profiles were digitally recorded for depth, time and surface interval, using a freediving computer. Relative surface interval (surface interval/diving time) and gradient factor were calculated.
REULTS:
High bubble grades were found in all the recorded echocardiograms. From the first to third recording (45 minutes), Grade 4 Eftedal-Brubakk (EB) bubbles were observed. The 60-, 75- and 90-minute recordings showed a reduction to Grades 3, 2 and 1 EB. Mean calculated GF for every BH dive was 0.22; maximum GF after the last dive was 0.33.
CONCLUSIONS:
High bubble grades can occur in BH diving, as confirmed by echocardiographic investigation. Ordinary methods to predict inert gas supersaturation may not able to predict Taravana cases.
... Monitoring physiological parameters will reflect an individual's response to diving, rather than relying on a general model, and thereby may increase diving safety [69]. To date, wearable means to measure and evaluate the onset of DCI have not emerged, although there has been some related laboratory and animal work published in recent years [67], [69], [70] - [72]. These methodologies could be converted to wearable approaches to satisfy the need for real-time monitoring [65]. ...
The physiologic response of the human body to different environments is a complex phenomenon to ensure survival. Immersion and compressed gas diving, together trigger a set of responses. Monitoring those responses in real-time may increase our understanding of these and help to develop safety procedures and equipment. This review outlines diving physiology and diseases and identifies physiological parameters worthy of monitoring. Subsequently, we have investigated technological approaches matched to those in order to evaluated their capability for underwater application. We focused on wearable biomedical monitoring technologies, or those which could be transformed to wearables. We have also reviewed current safety devices, including dive computers and their underlying decompression models and algorithms. The review outlines the necessity for biomedical monitoring in scuba diving and should encourage research and development of new methods to increase diving safety.
... It also allowed us to check for any slower changes which may occur further from the dive. As previously cited, Dujic et al. showed that divers developed asymptomatic physiological modifications following this dive profile [2,18]. Interestingly, this current study identified no changes in the diver's plasma proteome. ...
... Several drugs were confirmed to be preventive to DCS partially through their endothelial-protective properties (Møllerløkken et al., 2006;Ni et al., 2011;Zhang et al., 2014Zhang et al., , 2016aBlatteau et al., 2015). It is now widely accepted that endothelial injury plays a significant role in the progress of DCS (Levett and Millar, 2008;Brubakk and Mollerlokken, 2009;Klinger et al., 2011;Vann et al., 2011;Thom et al., 2015). ...
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.
... 21 Although the magnitude of FMD changes postdive cannot be placed in correlation with the risk of developing DCS, it is clearly an indicator of so-called " decompression stress " and has been linked to the presence of VGE, of endothelial microparticles, 1 and oxidative stress induced by high partial pressures of oxygen during the dive. 35 Administration of antioxidants before the dive only partially prevents postdive alteration of FMD, 27 , 28 indicating that oxidative stress is not the only factor contributing to the postdive vascular dysfunction. ...
Background:
Using ultrasound imaging, vascular gas emboli (VGE) are observed after asymptomatic scuba dives and are considered a key element in the potential development of decompression sickness (DCS). Diving is also accompanied with vascular dysfunction, as measured by flow-mediated dilation (FMD). Previous studies showed significant intersubject variability to VGE for the same diving exposure and demonstrated that VGE can be reduced with even a single pre-dive intervention. Several preconditioning methods have been reported recently, seemingly acting either on VGE quantity or on endothelial inflammatory markers.
Methods:
Nine male divers who consistently showed VGE postdive performed a standardized deep pool dive (33 m/108 ft, 20 min in 33°C water temperature) to investigate the effect of three different preconditioning interventions: heat exposure (a 30-min session of dry infrared sauna), whole-body vibration (a 30-min session on a vibration mattress), and dark chocolate ingestion (30 g of chocolate containing 86% cocoa). Dives were made one day per week and interventions were administered in a randomized order.
Results:
These interventions were shown to selectively reduce VGE, FMD, or both compared to control dives. Vibration had an effect on VGE (39.54%, SEM 16.3%) but not on FMD postdive. Sauna had effects on both parameters (VGE: 26.64%, SEM 10.4%; FMD: 102.7%, SEM 2.1%), whereas chocolate only improved FMD (102.5%, SEM 1.7%).
Discussion:
This experiment, which had the same subjects perform all control and preconditioning dives in wet but completely standardized diving conditions, demonstrates that endothelial dysfunction appears to not be solely related to VGE.Germonpré P, Balestra C. Preconditioning to reduce decompression stress in scuba divers. Aerosp Med Hum Perform. 2017; 88(2):114-120.
... Interestingly changes in gene expres-sion due to oxidative stress during scuba diving are linked to neutrophil activation, subsequent vascular injuries and microparticle formation [21]. The production of microparticle and neutrophil activation exhibits a strong association with decompression sickness [22]. Frequent and highly intense dive training may have already led to longer-lasting adaptation processes on the level of gene transcription. ...
Background:
Oxidative stress caused by elevated partial pressure of oxygen during diving is a major contributor of inflammation and apoptosis. The underlying molecular mechanisms are poorly understood. The aim of the study was to describe apoptotic gene regulation induced by a single air dive.
Methods:
19 healthy volunteers were exposed to a 30-minute dive at 2.8 atmospheres (ATA) absolute in a pressure chamber in ambient air. Blood samples were obtained before, directly after and 24 hours after exposure. Gene expressions of Bcl-2, Bcl-xL and Bax were analyzed in mononuclear cell extracts by real-time polymerase chain reaction (PCR). Circulating nucleosomes were measured in serum before exposure and 24 hours afterward.
Results:
The pro-apoptotic Bax expression was not significantly increased (p=0.74) directly after the dive but was induced (2.22 ± 0.85-fold) after 24 hours (p ≤ 0.01). Bcl-2 expression was not changed significantly directly after (p = 0.11) but was 1.88 ± 1.08-fold higher after 24 hours (p ≤ 0.01). Bcl-xL expression was not elevated significantly (p = 0.54) but was 2.04 ± 1.02-fold higher after 24 hours (p ≤ 0.01). The level of nucleosomes did not change after 24 hours compared to baseline.
Conclusion:
A single air dive at 2.8 ATA for 30 minutes causes an upregulation of pro- and anti-apoptotic genes but did not elevate circulating nucleosomes. In a single air dive the upregulation of anti-apoptotic Bcl-2 family members may counteract the pro-apoptotic potential of Bax.
This project investigated glial-based lymphatic (glymphatic) function and its role in a murine model of decompression sickness (DCS). DCS pathophysiology is traditionally view as being related to gas bubble formation from insoluble gas on decompression. However, a body of work implicates a role for a sub-set of inflammatory extracellular vesicles, 0.1 to 1 µm microparticles (MPs) that are elevated in humans and rodent models in response to high gas pressure and rise further after decompression. Herein we describe immunohistochemical and Western blot evidence showing that following high air pressure exposure there are elevations of astrocyte NF-κB and microglial ionized calcium-binding adaptor protein-1 (IBA-1) along with fluorescence contrast and MRI findings of an increase in glymphatic flow. Concomitant elevations of CNS-derived MPs co-expressing thrombospondin-1 (TSP) drain to deep cervical nodes and then to blood where they cause neutrophil activation. A new set of blood-borne MPs are generated that express filamentous actin at the surface which exacerbate neutrophil activation. Blood-brain barrier integrity is disrupted due to activated neutrophil sequestration that causes further astrocyte and microglial perturbation. When post-decompression node or blood MPs are injected into naïve mice the same spectrum of abnormalities occur and they are blocked with co-administration of antibody to TSP. We conclude that high pressure/decompression causes neuroinflammation with an increased glymphatic flow. The resulting systemic liberation of TSP-expressing MPs sustains the neuroinflammatory cycle lasting for days.
INTRODUCTION: The U.S. Navy experienced a series of physiological events in aircrew involving primarily the F/A-18 airframe related to rapid decompression of cabin pressures, of which aviation decompression sickness (DCS) was felt to contribute. The underlying pathophysiology of aviation DCS is the same as that of diving-related. However, based on the innate multifactorial circumstances surrounding hypobaric DCS, in clinical practice it continues to be unpredictable and less familiar as it falls at the intersect of aerospace and hyperbaric medicine. This retrospective study aimed to review the case series diagnosed as aviation DCS in a collaborative effort between aerospace specialists and hyperbaricists to increase appropriate identification and treatment of hypobaric DCS. METHODS: We identified 18 cases involving high-performance aircraft emergently treated as aviation DCS at a civilian hyperbaric chamber. Four reviewers with dual training in aviation and hyperbaric medicine retrospectively reviewed cases and categorized presentations as “DCS” or “Alternative Diagnosis”. RESULTS: Reviewers identified over half of presenting cases could be attributed to an alternative diagnosis. In events that occurred at flight altitudes below 17,000 ft (5182 m) or with rapid decompression pressure changes under 0.3 atm, DCS was less likely to be the etiology of the presenting symptoms. CONCLUSIONS: Aviation physiological events continue to be difficult to diagnose. This study aimed to better understand this phenomenon and provide additional insight and key characteristics for both flight physicians and hyperbaric physicians. As human exploration continues to challenge the limits of sustainable physiology, the incidence of aerospace DCS may increase and underscores our need to recognize and appropriately treat it. Kutz CJ, Kirby IJ, Grover IR, Tanaka HL. Aviation decompression sickness in aerospace and hyperbaric medicine . Aerosp Med Hum Perform. 2023; 94(1):11–17.
Decompression sickness, in which bubbles formed from dis-olved gas (usually nitrogen) cause tissue and vascular injury after a reducion in environmental pressure, may occur in diving, aviation, and spaceflight. Arterial gas embolism, in which bubbles introduced into the arterial circulation cause multifocal ischemia, may occur after diving-related, iatrogenic, or accidental pulmonary barotrauma or by direct iatrogenic introduction of gas into the vasculature. Because it may be difficult to clinically differentiate decompression sickness from arterial gas embolism in divers and the treatment protocols for the two disorders are the same, the term “decompression illness” is sometimes used to indicate the presence of decompression sickness, arterial gas embolism, or both, but the separate terms are used here. Divers with nonspecific symptoms may present to clinicians who have received no specific training during medical school or residency in dealing with these disorders, which can pose challenges in the differential diagnosis and choice of appropriate treatment.
Objectives
This study aimed to compare the efficacy and safety of ablation with high and low power settings using either a flexible tip or straight SF tip irrigated catheter in the left ventricle (LV) using a peripheral microemboli monitoring system.
Background
The microemboli risk of flexible and straight SF tip irrigated catheters in creating ablative lesions in the LV at variable power settings has not been adequately assessed.
Methods
Six pigs underwent catheter ablation in the LV using a flexible tip or straight SF tip catheter with 2 energy settings (30 or 50 W, 30 seconds, irrigation saline 17 mL/min).
Results
A total of 79 radiofrequency (RF) applications were assessed. High power settings via a flexible tip formed a significantly higher arterial microbubble volume in the extracorporeal circulation (P = 0.005). Notably, RF applications with a steam pop induced an exponential increase of microbubble volume with both catheters. A higher power setting induced a significantly higher number of microembolic signals on carotid artery Doppler ultrasound with a flexible tip irrigated catheter (P < 0.001). Similarly, the straight SF tip irrigated catheter tended to increase the number of microembolic signals with 50 W (P = 0.091).
Conclusions
RF ablation at high power settings in the LV carries a risk of microembolic events compared with lower power settings. When high power settings are used for creating ablative lesions for deep intramural foci in the LV, the risk of microembolic events induced by RF ablation should be carefully monitored.
Plasma gelsolin (pGSN) levels fall in association with diverse inflammatory conditions. We hypothesized pGSN would decrease due to the stresses imposed by high pressure and subsequent decompression, and repletion would ameliorate injuries in a murine decompression sickness (DCS) model. Research subjects were found to exhibit a modest decrease in pGSN level while at high pressure and a profound decrease after decompression. Changes occurred concurrent with elevations of circulating microparticles (MPs) carrying interleukin (IL)-1β. Mice exhibited a comparable decrease in pGSN after decompression along with elevations of MPs carrying IL-1β. Infusion of recombinant human (rhu)-pGSN into mice before or after pressure exposure abrogated these changes and prevented capillary leak in brain and skeletal muscle. Human and murine MPs generated under high pressure exhibited surface filamentous (F-) actin to which pGSN binds, leading to particle lysis. Additionally, human neutrophils exposed to high air pressure exhibit an increase in surface F-actin that is diminished by rhu-pGSN resulting in inhibition of MPs production. Administration of rhu-pGSN may have benefit as prophylaxis or treatment for DCS.
Decompression sickness (DCS) is a complex and poorly understood systemic disease with wide inter-individual resistance variability. We selectively bred rats with a 3-fold greater resistance to DCS than standard ones. To investigate possible physiological mechanisms underlying the resistance to DCS, including sex-related differences in these mechanisms, 15 males and 15 females resistant to DCS were compared with aged-matched standard Wistar males (n=15) and females (n=15). None of these individuals had been previously exposed to hyperbaric treatment. Comparison of the allelic frequencies of SNPs showed a difference of one SNP located on the X chromosome. Compared with non-resistant rats, the neutrophil-to-lymphocyte ratio and the plasmatic activity of coagulation Factor X were significantly higher in DCS-resistant individuals regardless of their sex. The maximal relaxation elicited by sodium nitroprusside was lower in DCS-resistant individuals regardless of their sex. Males but not females resistant to DCS exhibited higher neutrophil and lymphocyte counts, higher prothrombin time whereas lower mitochondrial basal O 2 consumption and citrate synthase activity. Principal Components Analysis showed that two principal components discriminate the DCS-resistant males but not females from the non-resistant ones. These components were loaded with aPTT, MLR, PT, FX, Fib, for PC1, and ARBC and ANC for PC2. In conclusion, the mechanisms which drive the resistance to DCS appear different between males and females; lower coagulation tendency and enhanced inflammatory response to decompression stress might be key for resistance in males. The involvement of these physiological adaptations in resistance to DCS must now be confirmed.
Introduction: Internationally it is estimated that six million people participate in self-contained underwater breathing apparatus (SCUBA) diving each year. Registries suggest a significant proportion of divers have a current or historical diagnosis of asthma. Previously individuals with asthma were prohibited from diving, however, several contemporary guidelines suggest a select population of patients with asthma may be able to dive with an acceptable degree of risk.
Areas covered: Divers with asthma may be at an increased risk of a variety of diving-related medical injuries including; pulmonary barotrauma (PBT), pneumothorax, pneumomediastinum, arterial gas embolism (AGE), reduction in pulmonary function, bronchospasm and decompression sickness (DCS). This article will discuss the latest evidence on the incidence of adverse events in diving with a focus on those caused by asthma.
Expert opinion: Physicians can be faced with the difficult task of counseling patients with asthma who wish to dive. This review article will aim to explore the current guidelines which can assist a physician in providing a comprehensive dive safety assessment.
The pathogenesis of predominantly neurological decompression sickness (DCS) is multifactorial. In SCUBA diving, besides gas bubbles, DCS has been linked to microparticle release, impaired endothelial function, and platelet activation. This study focused on vascular damage and its potential role in the genesis of DCS in breath-hold diving. Eleven breath-hold divers participated in a field study comprising eight deep breath-hold dives with short surface periods and repetitive breath-hold dives lasting for 6 h. Endothelium-dependent vasodilation of the brachial artery, via flow-mediated dilation (FMD), and the number of microparticles (MPs) were assessed before and after each protocol. All measures were analyzed by two-way within-subject ANOVA (2 × 2 ANOVA; factors: time and protocol). Absolute FMD was reduced following both diving protocols (p < 0.001), with no interaction (p = 0.288) or main effect of protocol (p = 0.151). There was a significant difference in the total number of circulating MPs between protocols (p = 0.007), where both increased post-dive (p = 0.012). The number of CD31+/CD41- and CD66b+ MP subtypes, although different between protocols (p < 0.001), also increased by 41.0% ± 56.6% (p = 0.050) and 60.0% ± 53.2% (p = 0.045) following deep and repetitive breath-hold dives, respectively. Both deep and repetitive breath-hold diving lead to endothelial dysfunction that may play an important role in the genesis of neurological DCS.
Hyperbaric oxygen (HBO2) became a mainstay for treating decompression sickness (DCS) because bubbles are associated with the disorder. Inflammatory processes including production of circulating microparticles (MPs) have now been shown to occur with DCS, leading to questions regarding pathophysiology and the role for HBO2. We investigated effects of HBO2 on mice exposed to 790 kPa air pressure for 2 h, which triggers elevations of MPs ladened with interleukin (IL)-1β that cause diffuse vascular injuries. Exposure to 283 kPa O2 (HBO2) inhibited MP elevations at 2 h postdecompression by 50% when applied either prophylactically or as treatment after decompression, and the MP number remained suppressed for 13 h in the prophylactic group. Particle content of IL-1β at 2 h postdecompression was 139.3 ± 16.2 [means ± SE; n = 11, P < 0.05) pg/million MPs vs. 8.2 ± 1.0 ( n = 15) in control mice, whereas it was 31.5 ± 6.1 ( n = 6, not significant vs. control (NS)] in mice exposed to HBO2 prophylactically, and 16.6 ± 6.3 ( n = 7, NS) when HBO2 was administered postdecompression. IL-1β content in MPs was similar in HBO2-exposed mice at 13 h postdecompression. HBO2 also inhibited decompression-associated neutrophil activation and diffuse vascular leak. Immunoprecipitation studies demonstrated that HBO2 inhibits high-pressure-mediated neutrophil nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3 inflammasome oligomerization. Furthermore, MPs isolated from decompressed mice cause vascular injuries when injected into naïve mice, but if decompressed mice were exposed to HBO2 before MP harvest, vascular injuries were inhibited. We conclude that HBO2 impedes high-pressure/decompression-mediated inflammatory events by inhibiting inflammasome formation and IL-1β production. NEW & NOTEWORTHY High pressure/decompression causes vascular damage because it stimulates production of microparticles that contain high concentrations of interleukin-1β, and hyperbaric oxygen can prevent injuries.
We examined if the diving-induced vascular changes in the peripheral and cerebral circulation could be prevented by oral antioxidant supplementation. Fourteen divers performed a single SCUBA dive to 18 msw for 47 mins. Twelve of the divers participated in a follow-up study involving breathing 60% oxygen at ambient pressure for 47 mins. Prior to both studies, participants ingested vitamin C (2g/day) or a placebo capsule for six days. After two-week washout, the study was repeated with the different condition. Endothelium-dependent vasodilator function of the brachial artery was assessed pre- and post-intervention using the flow mediated dilation (FMD) technique. Transcranial Doppler ultrasound was used to measure intra-cranial blood velocities pre- and for 90 minutes post-intervention. FMD was reduced by ∼32.8% and ∼21.2% post-dive in the placebo and vitamin C trial and post-hyperoxic condition in the placebo trial by ∼28.2% (P<0.05). This reduction in FMD was attenuated by ∼10% following vitamin C supplementation in the hyperoxic study (P>0.05). Elevations in intra-cranial blood velocities 30 minutes after surfacing from diving were reduced in the vitamin C study compared to the placebo trial (P<0.05). O2 breathing had no post-intervention effects on intra-cranial velocities (P>0.05). Prophylactic ingestion of vitamin C effectively abrogated peripheral vascular dysfunction following exposure to 60% O2 but did not abolish the post-dive decrease in FMD. Transient elevations of intra-cranial velocities post-dive were reduced by vitamin C. These findings highlight the differential influence of vitamin C on peripheral and cerebral circulations following SCUBA diving, which are only partly mediated via hyperoxia.
Molecular oxygen (O2) is a vital element in human survival and plays a major role in a diverse range of biological and physiological processes. Although normobaric hyperoxia can increase arterial oxygen content (CaO2), it also causes vasoconstriction and hence reduces O2delivery in various vascular beds including the heart, skeletal muscle, and brain. Thus, a seemingly paradoxical situation exists in which the administration of oxygen may place tissues at increased risk of hypoxic stress. Nevertheless, with various degrees of effectiveness, and not without consequences, supplemental oxygen is used clinically in an attempt to correct tissue hypoxia (e.g. brain ischemia, traumatic brain injury, carbon monoxide poisoning, etc.), chronic hypoxemia (e.g. severe COPD, etc.), and to help with wound healing, necrosis, or reperfusion injuries (e.g. compromised grafts). Hyperoxia has also been used liberally by athletes in a belief that it offers performance enhancing benefits; such benefits also extend to hypoxemic patients both at rest and during rehabilitation. This review aims to provide a comprehensive overview of the effects of hyperoxia in humans from the 'bench-to-bedside'. The first section will focus on the basic physiological principles of partial pressure of arterial O2, CaO2, barometric pressure and how these changes lead to variation in regional O2delivery. The next section provides an overview of the evidence for and against the use of hyperoxia as an aid to enhance physical performance. The final section addresses pathophysiological concepts, clinical studies, and implications for therapy. The potential of O2toxicity and future research directions are also considered.
Introduction:
Decompression sickness (DCS) is a complex and poorly understood systemic disease caused by inadequate desaturation following a decrease of ambient pressure. Strong variability between individuals is observed for DCS occurrence. This raises questions concerning factors that may be involved in the inter-individual variability of DCS occurrence. This study aimed to experimentally assess the existence of heritable factors involved in DCS occurrence by selectively breeding individuals resistant to DCS from a population stock of wistar rats.
Methods:
52 males and 52 females Wistar rats were submitted to a simulated air dive known to reliably induce about 63% DCS: compression was performed at 100 kPa.min up to 1000 kPa absolute pressure before a 45 min long stay. Decompression was performed at 100 kPa.min with three decompression stops: 5 min at 200 kPa, 5 min at 160 kPa and 10 min at 130 kPa. Animals were observed for one hour to detect DCS symptoms. Individuals without DCS were selected and bred to create a new generation, subsequently subjected to the same hyperbaric protocol. This procedure was repeated up to the third generation of rats.
Results:
As reported previously, this diving profile induced 67% of DCS, and 33% asymptomatic animals in the founding population. DCS/asymptomatic ratio was not initially different between sexes, although males were heavier than females. In three generations, the outcome of the dive significantly changed from 33% to 67% asymptomatic rats, for both sexes. Interestingly, survival in females increased sooner than in males.
Conclusion:
This study offers evidence suggesting the inheritance of DCS resistance. Future research will focus on genetic and physiological comparisons between the initial strain and the new resistant population.
Bubble formation during scuba diving might induce decompression sickness.
This prospective randomised and double-blind study included 108 advanced recreational divers (38 females). Fifty-four pairs of divers, 1 breathing air and the other breathing nitrox28 undertook a standardised dive (24 ± 1 msw; 62 ± 5min) in the Red Sea. Venous gas bubbles were counted (Doppler) 30–<45 min (early) and 45–60 min (late) post-dive at jugular, subclavian and femoral sites.
Only 7% (air) vs. 11% (air28®) (n.s.) were bubble-free after a dive. Independent of sampling time and breathing gas, there were more bubbles in the jugular than in the femoral vein. More bubbles were counted in the air-group than in the air28-group (pooled vein: early: 1845 vs. 948; P = 0.047, late: 1817 vs. 953; P = 0.088). The number of bubbles was sex-dependent. Lastly, 29% of female air divers but only 14% of male divers were bubble-free (P = 0.058).
Air28® helps to reduce venous gas emboli in recreational divers. The bubble number depended on the breathing gas, sampling site and sex. Thus, both exact reporting the dive and in particular standardising sampling characteristics seem mandatory to compare results from different studies to further investigate the hitherto incoherent relation between inert gas bubbles and DCS.
Predicated on evidence that diving-related microparticle generation is an oxidative stress response, this study investigated the role oxygen plays in augmenting production of annexin V-positive microparticles associated with open-water SCUBA diving and whether elevations can be abrogated by ascorbic acid. Following a cross-over study design, 14 male subjects ingested placebo and 2-3 weeks later ascorbic acid (2 g) daily for 6 days prior to performing either a 47 minute dive to 18 meters of sea water while breathing air (~222 kPa N2/59 kPa O2), or breathing a mixture of 60% O2/balance N2 from a tight-fitting face mask at atmospheric pressure for 47 minutes (~ 40 kPa N2/59 kPa O2). Within 30 minutes after the 18 meter dive in the placebo group, neutrophil activation and platelet-neutrophil interactions occurred, and total number of microparticles as well as sub-groups bearing CD66b, CD41, CD31, CD142 proteins or nitrotyrosine increased approximately 2-fold. No significant elevations occurred among divers after ingesting ascorbic acid, nor were elevations identified in either group after breathing 60% O2. Ascorbic acid had no significant effect on post-dive intravascular bubble production quantified by trans-thoracic echocardiography. We conclude that high pressure nitrogen plays a key role in neutrophil and microparticle-associated changes with diving and that responses can be abrogated by dietary ascorbic acid supplementation.
Copyright © 2015, American Journal of Physiology - Regulatory, Integrative and Comparative Physiology.
This investigation was to elucidate the mechanism for microparticle (MPs) formation triggered by exposures to high pressure inert gases. Human neutrophils generate MPs at a threshold of ~ 186 kPa with exposures of 30 minutes or more. Murine cells are similar but MPs production occurs at a slower rate and continues for ~ 4 hours whether cells remain under pressure, or not. Neutrophils exposed to elevated gas but not hydrostatic pressure produce MPs according to the potency series: argon ~ nitrogen > helium. Following a similar pattern, gases activate type-2 nitric oxide synthase (NOS-2) and NADPH oxidase (NOX). MPs production does not occur with neutrophils exposed to a NOX inhibitor (Nox2ds), a NOS-2 inhibitor (1400W), or with cells from mice lacking NOS-2. Reactive species cause S-nitrosylation of cytosolic actin that enhances actin polymerization. Protein crosslinking and immunoprecipitation studies indicate that increased polymerization occurs because of associations involving vasodilator stimulated phosphoprotein, focal adhesion kinase, the H+/K+ ATPase β (flippase), the hematopoietic cell multidrug resistance protein ABC transporter (floppase) and protein disulfide isomerase in proximity to short actin filaments. Using chemical inhibitors or reducing cell concentrations of any of these proteins with small inhibitory RNA abrogates NOS-2 activation, reactive species generation, actin polymerization and MPs production. These effects were also inhibited in cells exposed to ultraviolet light which photo-reverses S-nitrosylated cysteine residues and by co-incubations with the antioxidant ebselen or cytochalasin D. The auto-catalytic cycle of protein activation is initiated by inert gas-mediated singlet O2 production.
The study goal was to use membrane voltage changes during neurohypophysial action potential (AP) propagation as an index of nerve function to evaluate the role that circulating microparticles (MPs) play in causing central nervous system injury in response to decompression stress in a murine model. Mice studied 1 hour following decompression from 790 kPa air pressure for 2 hours exhibit a 45 % broadening of the neurohypophysial AP. Broadening did not occur if mice were injected with the MPs lytic agent polyethylene glycol telomere B immediately after decompression; were rendered thrombocytopenic or treated with an inhibitor of nitric oxide synthase-2 (iNOS) prior to decompression or in knock-out mice lacking myeloperoxidase or iNOS. If MPs were harvested from control (no decompression) mice and injected into naïve mice, no AP broadening occurred; but AP broadening was observed with injections of equal numbers of MPs from either wild type or iNOS KO mice subjected to decompression stress. Although not required for AP broadening, MPs from decompressed mice - but not control mice - exhibit NADPH oxidase activation. We conclude that inherent differences in MPs from decompressed mice, rather than elevated MPs numbers, mediate neurological injury and that a component of the perivascular response to MPs involves iNOS. Additional study is needed to determine the mechanism of AP broadening and also mechanisms for MPs generation associated with exposure to elevated gas pressure.
The study goal was to evaluate responses in humans following decompression from open-water SCUBA diving with the hypothesis that exertion underwater and use of a breathing mixture containing more oxygen and less nitrogen (enriched air nitrox, EAN) would alter annexin V-positive microparticles (MPs) production and size changes and neutrophil activation as well as their relationships to intravascular bubble formation. Twenty-four divers followed a uniform dive profile to 18 meters of sea water breathing air or 22.5 meters breathing 32% oxygen/68% nitrogen for 47 minutes either swimming with moderately heavy exertion underwater or remaining stationary at depth. Blood was obtained prior to and at 15 and 120 minutes post-dive. Intravascular bubbles were quantified by trans-thoracic echocardiography post-dive at 20 minute intervals for 2 hours. There were no significant differences in maximum bubble scores among the dives. MPs number increased 2.7-fold on average within 15 minutes after each dive; only the air-exertion dive resulted in a significant further increase to 5-fold over baseline at 2 hours post-dive. Neutrophil activation occurred after all dives. For the EAN-stationary at depth dive but not for other conditions the numbers of post-dive annexin V-positive particles above 1 µm in diameter were correlated with intravascular bubble scores (correlation coefficients ~ 0.9, p < 0.05). We conclude that post-decompression relationships among bubbles, MPs, platelet-neutrophil interactions and neutrophil activation appear to exist, but more study is required to improve confidence in the associations.
Inert gases diffuse into tissues in proportion to ambient pressure and when pressure is reduced, gas efflux forms bubbles due to the presence of gas cavitation nuclei that are predicted based on theory but have never been characterized. Decompression stress triggers elevations in number and diameter of circulating annexin V-coated microparticles (MPs) derived from vascular cells. Here we show that approximately 10% MPs from wild type (WT) but not inflammatory nitric oxide synthase (iNOS) knock-out (KO) mice increase in size when exposed to elevated air pressure ex vivo. This response is abrogated by a preceding exposure to hydrostatic pressure, demonstrating the presence of a pre-formed gas phase. These MPs have lower density than most particles, 10-fold enrichment in iNOS and generate commensurately more reactive nitrogen species (RNS). Surprisingly, RNS only slowly diffuse from within MPs unless particles are subjected to osmotic stress or membrane cholesterol is removed. WT mice treated with iNOS inhibitor and KO mice exhibit less decompression-induced neutrophil activation and vascular leak. Contrary to injecting naïve mice with MPs from wild type decompressed mice, injecting KO MPs triggers fewer pro-inflammatory events. We conclude that nitrogen dioxide is a nascent gas nucleation site synthesized in some MPs and is responsible for initiating post-decompression inflammatory injuries.
Decompression sickness is caused by gas bubbles released upon decompression. These bubbles have the potential to occlude blood vessels and damage the vascular endothelium. The aim of this study was to quantify damage to the vascular endothelium resulting from decompression by measuring endothelial microparticles (MP) and endothelial function.
Five healthy male volunteers undertook a simulated (hyperbaric chamber) air dive and 1 wk later a second dive breathing 100% oxygen at 283 kPa (18 msw) for 60 min bottom time, decompressed with 5-min stops at 161 kPa (6 msw) and 131 kPa (3 msw). Endothelial function was tested pre- and postdive by reactive hyperemia peripheral artery tonometry (RH-PAT) and CD105 (Endoglin) positive MP were quantified by flow cytometry. Plasma E- and P-selectin, interleukin-6, and serum cortisol were also quantified.
RH-PAT showed a significantly decreased endothelial function post-decompression after breathing air when compared to oxygen (-0.33 +/- 0.27 vs. +0.18 +/- 0.14). CD105 MP pre- and postdive showed no change on the oxygen dive (460 +/- 370 to 360 +/- 163), however, they increased after breathing air (440 +/- 70 to 1306 +/- 359). There was no change in expression of CD105 on MP. Furthermore no changes were observed in plasma E- or P-selectin, IL-6, or serum cortisol.
From the data, at least in the time frame involved, there appears to be no detectable physiological/stress response to decompression, rather decompression from breathing air probably caused mechanical damage to the endothelium, resulting in both MP release and a reduction in endothelial function.
Microparticles (MP) are shed into the circulation from endothelium following activation or apoptosis. Vascular cell adhesion molecule-1 (VCAM-1) is expressed on endothelial cells following activation and here we report quantification of VCAM-1 positive microparticles (VCAM + MP) following simulated SCUBA dives, breathing either air or oxygen. VCAM + MP were quantified pre-dive (09:00 and 13:00) and post-dive (+1, +3 and +15 h) on both air and oxygen dives and compared with control samples taken from the same subjects. VCAM + MP followed a similar trend in all experiments, however both dives caused a change in endothelial state, as measured by VCAM + MP. A significant increase in VCAM + MP was observed 1 h post-air dive relative to the control (p = 0.013), which was not observed after the oxygen dive (p = 0.095). Oxidative stress (TBARS) was correlated with VCAM + MP. Data presented highlights the potential of MP as a biological marker of both endothelial state and decompression illness.
Decompression sickness in diving is recognized as a multifactorial phenomenon, depending on several factors, such as decompression rate and individual susceptibility. The Doppler ultrasonic detection of circulating venous bubbles after diving is considered a useful index for the safety of decompression because of the relationship between bubbles and decompression sickness risk. The aim of this study was to assess the effects of ascent rate, age, maximal oxygen uptake (VO(2 max)), and percent body fat on the production of bubbles after diving. Fifty male recreational divers performed two dives at 35 m during 25 min and then ascended in one case at 9 m/min and in the other case at 17 m/min. They performed the same decompression stops in the two cases. Twenty-eight divers were Doppler monitored at 10-min intervals, until 60 min after surfacing, and the data were analyzed by Wilcoxon signed-rank test to compare the effect of ascent rate on the kinetics of bubbles. Twenty-two divers were monitored 60 min after surfacing. The effect on bubble production 60 min after surfacing of the four variables was studied in 47 divers. The data were analyzed by multinomial log-linear model. The analysis showed that the 17 m/min ascent produced more elevated grades of bubbles than the 9 m/min ascent (P < 0.05), except at the 40-min interval, and showed relationships between grades of bubbles and ascent rate and age and interaction terms between VO(2 max) and age, as well as VO(2 max) and percent body fat. Younger, slimmer, or aerobically fitter divers produced fewer bubbles compared with older, fatter, or poorly physically fit divers. These findings and the conclusions of previous studies performed on animals and humans led us to support that ascent rate, age, aerobic fitness, and adiposity are factors of susceptibility for bubble formation after diving.
Recruitment and activation of polymorphonuclear neutrophils (PMNs) reflects a primary immunological response to invading pathogens and has also emerged as a hallmark of vascular inflammation. One of the principal enzymes released upon PMN activation is myeloperoxidase (MPO), a heme protein that not only generates cytotoxic oxidants but also impacts deleteriously on nitric oxide-dependent signaling cascades within the vasculature. Because MPO also associates with the membrane of PMN, we evaluated whether MPO could also function as an autocrine modulator of PMN activation. The extent of PMN membrane-associated MPO was elevated in patients with acute inflammatory vascular disease compared with healthy individuals. Isolated PMNs bound free MPO by a CD11b/CD18 integrin-dependent mechanism. PMNs exposed to MPO were characterized by increased tyrosine phosphorylation and p38 mitogen-activated protein kinase activation. Also, nuclear translocation of NFκBin PMN was enhanced after incubation with MPO, as was surface expression of CD11b. Binding of PMN to MPO-coated fibronectin surfaces amplified PMN degranulation, as evidenced by increased release of MPO and elastase. MPO also augmented PMN-dependent superoxide ([Formula]) production, which was prevented by anti-CD11b antibodies, but not MPO inhibitors. Collectively, these results reveal that binding of MPO to CD11b/CD18 integrins stimulates PMN signaling pathways to induce PMN activation in a mechanism independent of MPO catalytic activity. These cytokine-like properties of MPO thus represent an additional dimension of the proinflammatory actions of MPO in vascular disease.
• atherosclerosis
• cytokine
• endothelium
• leukocyte
• nitric oxide
The problems encountered during scuba diving may be a contributing factor in an episode of decompression illness (DCI). Evidence exists that there may be a relationship between the position in the menstrual cycle and the occurrence of DCI. We examined, by prospective observation in female recreational scuba divers, any interaction between reported problems during diving (RPDD) and the position in the menstrual cycle. A total of 533 women, aged between 14 and 57 years, returned diaries for >6 months, with 61% returning diaries for 3 consecutive years. A total of 34,625 dives were reported within 11,461 menstrual cycles between 21 and 40 days in length, with 65% of women reporting at least one RPDD. Logistic regression showed a significant non-linear relationship between the position in the menstrual cycle and RPDD (p = 0.004). RPDD were not evenly distributed over the menstrual cycle; the rate per 1,000 dives varied from 39.2 at start of the cycle to 19.7 during week 3, and 31.9 in week 4. We concluded these field data suggest a possible correlation between the incidence of RPDD and the position in which they occurred in the menstrual cycle.
We hypothesized that pathological changes associated with elevations in annexin V-positive microparticles (MPs) following high pressure exposures can be abrogated by ascorbic acid in a murine model. Mice exposed for 2 hours to 790 kPa air and euthanized at 2 or 13 hours post-decompression exhibited over 3-fold elevations in circulating MPs as well as sub-groups bearing Ly6G, CD41, Ter119, CD31, and CD142 surface proteins. There was evidence of significant neutrophil activation, platelet-neutrophil interactions and vascular injury to brain, omentum, psoas and skeletal muscles assessed as leakage of high molecular weight dextran. Prophylactic ascorbic acid (500 mg/kg IP) administration prevented all post-decompression neutrophil changes and vascular injuries. Ascorbic acid administration immediately after decompression abrogated most changes, but evidence of vascular leakage in brain and skeletal muscle at 13 hours post-decompression persisted. No significant elevations in these parameters occurred after injection of ascorbic acid alone. The findings support the idea that MPs production occurring with exposures to elevated gas pressure is an oxidative stress response and that anti-oxidants may offer protection from pathological effects associated with decompression.
Copyright © 2015, Journal of Applied Physiology.
Background:
Venous gas emboli (VGE) have traditionally served as a marker for decompression stress after SCUBA diving and a reduction in bubble loads is a target for precondition procedures. However, VGE can be observed in large quantities with no negative clinical consequences. The effect of exercise before diving on VGE has been evaluated with mixed results. Microparticle (MP) counts and sub-type expression serve as indicators of vascular inflammation and DCS in mice. The goal of the present study is to evaluate the effect of anaerobic cycling (AC) on VGE and MP following SCUBA diving.
Methods:
Ten male divers performed two dives to 18 m for 41 min, one dive (AC) was preceded by a repeated-Wingate cycling protocol; a control dive (CON) was completed without exercise. VGE were analyzed at 15, 40, 80, and 120 min post-diving. Blood for MP analysis was collected before exercise (AC only), before diving, 15 and 120 min after surfacing.
Results:
VGE were significantly lower 15 min post-diving in the AC group, with no difference in the remaining measurements. MPs were elevated by exercise and diving, however, post-diving elevations were attenuated in the AC dive. Some markers of neutrophil elevation (CD18, CD41) were increased in the CON compared to the AC dive.
Conclusions:
The repeated-Wingate protocol resulted in an attenuation of MP counts and sub-types that have been related to vascular injury and DCS-like symptoms in mice. Further studies are needed to determine if MPs represent a risk factor or marker for DCS in humans.
The goals of this study were to investigate the difference in responses between a SCUBA dive preceded by aerobic exercise (EX) and a non-exercise control dive (CON), and further evaluate the potential relationship between venous gas emboli (VGE) and microparticles (MP). We hypothesized that exercise would alter the quantity and subtype of annexin V-positive MPs and VGE.
Nineteen divers performed 2 dives to 18 m sea water for 41 min separated by at least 3 days, one of which was preceded by 60 min of treadmill interval exercise. Blood was obtained before exercise, before diving, and 15 min, 2, 4, and 24 h after surfacing. Intravascular bubbles were quantified by transthoracic echocardiography at 15, 40, 80, and 120 min.
The median VGE remained unchanged between the 2 dives; however, there was a significant increase in VGE in the exercise dive at 40 and 80 min at rest. MPs were significantly elevated by approximately 2x at all time points following CON compared to EX. Markers of neutrophil and platelet activation were elevated by both dives and these elevations were attenuated in the EX dive.
We conclude that some of the differences observed between the EX and CON related to MPs, platelet, and neutrophil activation provide additional insight to the potential protective benefits of exercise, however, further study is needed to understand the mechanism and true potential of these benefits.
Bubble-induced platelet aggregation offers an index for evaluating decompression severity in humans and in a rat model of decompression sickness. Endothelial cells, blood platelets, or leukocytes shed microparticles (MP) upon activation and during cell apoptosis. The aim was to study blood platelet MP (PMP) release and bubble formation after a scuba-air dive in field conditions. Healthy, experienced divers were assigned to 1 experimental group (n = 10) with an open-sea air dive to 30 msw for 30 min and 1 control group (n = 5) during head-out water immersion for the same period. Bubble grades were monitored with a pulsed doppler according to Kissman Integrated Severity Score (KISS). Blood samples for platelet count (PC) and PMP (annexin V and CD41) were taken 1 h before and after exposure in both groups. The result showed a decrease in post-dive PC compared with pre-dive values in experimental group with no significant change in the control group. We observed a significant increase in PMP values after the dive while no change was revealed in the control group. There was a significant positive correlation between the PMP values after the dive and the KISS bubble score. The present study highlighted a relationship between the post-dive decrease in PC, platelet MP release, and bubble formation. Release of platelet MPs could reflect bubble-induced platelet aggregation and could play a key role in alteration of the coagulation. Further studies must investigate endothelial and leukocyte MP release in the same field conditions.
The goal of this study was to evaluate annexin V-positive microparticles (MPs) and neutrophil activation in humans following decompression from open-water SCUBA diving with the hypothesis that changes are related to intravascular bubble formation. Sixteen male volunteer divers followed a uniform profile of four daily SCUBA dives to 18 m of sea water for 47 min. Blood was obtained prior to and at 80 min following the first and fourth dives to evaluate the impact of repetitive diving, and intravascular bubbles were quantified by trans-thoracic echocardiography carried out at 20-min intervals for 2 h after each dive. MPs increased by 3.4-fold after each dive, neutrophil activation occurred as assessed by surface expression of myeloperoxidase and the CD18 component of β(2)-integrins, and there was an increased presence of the platelet-derived CD41 protein on the neutrophil surface indicating interactions with platelet membranes. Intravascular bubbles were detected in all divers. Surprisingly, significant inverse correlations were found among postdiving bubble scores and MPs, most consistently at 80 min or more after the dive on the fourth day. There were significant positive correlations between MPs and platelet-neutrophil interactions after the first dive and between platelet-neutrophil interactions and neutrophil activation documented as an elevation in β(2)-integrin expression after the fourth dive. We conclude that MPs- and neutrophil-related events in humans are consistent with findings in an animal decompression model. Whether there are causal relationships among bubbles, MPs, platelet-neutrophil interactions, and neutrophil activation remains obscure and requires additional study.
Studies in a murine model have shown that decompression stress triggers a progressive elevation in the number of circulating annexin V-coated microparticles derived from leukocytes, erythrocytes, platelets, and endothelial cells. We noted that some particles appeared to be larger than anticipated, and size continued to increase for ≥24 h postdecompression. These observations led to the hypothesis that inert gas bubbles caused the enlargement and particle size could be reduced by hydrostatic pressure. After demonstrating pressure-induced particle size reduction, we hypothesized that annexin V-positive particle changes associated with decompression contributed to their proinflammatory potential. Intravenous injection of naive mice with particles isolated from decompressed mice, but not control mice, caused intravascular neutrophil activation; perivascular neutrophil sequestration and tissue injuries were documented as elevations of vascular permeability and activated caspase-3. These changes were not observed if mice were injected with particles that had been subjected to hydrostatic recompression or particles that had been emulsified by incubation with polyethylene glycol telomere B surfactant. Hydrostatic pressure and surfactant incubation also altered the pattern of proteins expressed on the surface of particles. We conclude that proinflammatory events and vascular damage are due to enlargement of annexin V-coated particles and/or changes in surface marker protein pattern associated with provocative decompression. Injection of annexin V-coated particles from decompressed mice will recapitulate the pathophysiological vascular changes observed following decompression stress.
During SCUBA diving, breathing at increased pressure leads to a greater tissue gas uptake. During ascent, tissues may become supersaturated, and the gas is released in the form of bubbles that typically occur on the venous side of circulation. These venous gas emboli (VGE) are usually eliminated as they pass through the lungs, although their occasional presence in systemic circulation (arterialization) has been reported and it was assumed to be the main cause of the decompression sickness. The aims of the present study were to assess the appearance of VGE after air dives where no stops in coming to the surface are required and to assess their potential occurrence and frequency in the systemic circulation.
Twelve male divers performed six dives with 3 d of rest between them following standard no-decompression dive procedures: 18/60, 18/70, 24/30, 24/40, 33/15, and 33/20 (the first value indicates depth in meters of sea water and the second value indicates bottom time in minutes). VGE monitoring was performed ultrasonographically every 20 min for 120 min after surfacing.
Diving profiles used in this study produced unexpectedly high amounts of gas bubbles, with most dives resulting in grade 4 (55/69 dives) on the bubble scale of 0-5 (no to maximal bubbles). Arterializations of gas bubbles were found in 5 (41.7%) of 12 divers and after 11 (16%) of 69 dives. These VGE crossovers were only observed when a large amount of bubbles was concomitantly present in the right valve of the heart.
Our findings indicate high amounts of gas bubbles produced after no-decompression air dives based on standardized diving protocols. High bubble loads were frequently associated with the crossover of VGE to the systemic circulation. Despite these findings, no acute decompression-related pathology was detected.
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.
SCUBA diving is associated with generation of gas emboli due to gas release from the supersaturated tissues during decompression. Gas emboli arise mostly on the venous side of circulation, and they are usually eliminated as they pass through the lung vessels. Arterialization of venous gas emboli (VGE) is seldom reported, and it is potentially related to neurological damage and development of decompression sickness. The goal of the present study was to evaluate the generation of VGE in a group of divers using a mixture of compressed oxygen, helium, and nitrogen (trimix) and to probe for their potential appearance in arterial circulation. Seven experienced male divers performed three dives in consecutive days according to trimix diving and decompression protocols generated by V-planner, a software program based on the Varying Permeability Model. The occurrence of VGE was monitored ultrasonographically for up to 90 min after surfacing, and the images were graded on a scale from 0 to 5. The performed diving activities resulted in a substantial amount of VGE detected in the right cardiac chambers and their frequent passage to the arterial side, in 9 of 21 total dives (42%) and in 5 of 7 divers (71%). Concomitant measurement of mean pulmonary artery pressure revealed a nearly twofold augmentation, from 13.6 ± 2.8, 19.2 ± 9.2, and 14.7 ± 3.3 mmHg assessed before the first, second, and the third dive, respectively, to 26.1 ± 5.4, 27.5 ± 7.3, and 27.4 ± 5.9 mmHg detected after surfacing. No acute decompression-related disorders were identified. The observed high gas bubble loads and repeated microemboli in systemic circulation raise questions about the possibility of long-term adverse effects and warrant further investigation.
The best understood consequence of the collapse of lipid asymmetry is exposure of phosphatidylserine (PS) in the external leaflet of the plasma membrane bilayer, where it is known to serve at least two major functions: providing a platform for development of the blood coagulation cascade and presenting the signal that induces phagocytosis of apoptotic cells. Lipid asymmetry is collapsed by activation of phospholipid scramblase(s) that catalyze bidirectional transbilayer movement of the major classes of phospholipid. The protein corresponding to this activity is not yet known. Observations on cells from patients with Scott syndrome, a rare hereditary bleeding disorder resulting from impaired lipid scrambling, have shown that there are multiple activation pathways that converge on scramblase activity.
The term decompression illness (DCI) describes maladies resulting from inadequate decompression, but there is little consensus concerning clinically useful DCI subclasses. Our aim was to explore an objective DCI classification using multivariate statistics to assess naturally associated clusters of DCI manifestations. We also evaluated their mapping onto other DCI classifications and investigated the association with therapeutic outcome.
We defined the optimal number of clusters using "two-step" cluster analysis and Bayesian information criterion with confirmation by hierarchical clustering with squared Euclidian distances and Ward's method. The data were 1929 DCI cases reported by hyperbaric chambers to the Divers Alert Network (DAN America) from 1999-2003.
Four robust and highly significant clusters of DCI manifestations were demonstrated containing 300, 741, 333, and 555 patients. Each cluster had characteristic manifestations. Cluster 1 was effectively pain only. For Cluster 2, characteristic manifestations included numbness, paresthesia, and decreased skin sensitivity; for Cluster 3, malaise, paralysis, muscular weakness, and bladder-bowel dysfunction; and for Cluster 4, hearing loss, localized skin swelling, tinnitus, skin rash and mottling, confusion, dyspnea/chokes, muscular problems, vision problems, altered consciousness, headache, vertigo, nausea, fatigue, dizziness, and abnormal sensations.
Internal reliability was confirmed by arbitrarily dividing the dataset into two parts and repeating the analysis. The clusters mapped poorly onto traditional DCI categories (AGE, Type I DCS, Type II DCS), but more specifically onto the Perceived Severity Index (PSI). All three classification methods (DCI, Cluster, PSI) predicted complete relief of manifestations equally well. We conclude that cluster analysis is an objective method for classifying DCI manifestations independent of clinical judgment.
1. In the present study we have demonstrated that human peripheral blood granulocytes from elderly subjects exhibit reduced chemotaxis and degranulation in response to stimulation with fMet-Leu-Phe.
2. Cyclic AMP levels in non-stimulated cells were not significantly different (mean ± sem): 4.8 ± 0.6 and 3.9 ± 0.4 pmol/107 cells for young and elderly respectively. Stimulation with fMet-Leu-Phe (5 × 10−7 mol/l) for 30 s induced the production of cyclic AMP: 8.4 ± 0.5 and 6.7 ± 0.3 pmol/107 cells for young and elderly.
3. These findings, together with those previously published by us, suggest that cyclic AMP production and cellular functions which this molecule participates in are reduced in cells from elderly individuals.
This study identified the short- and long-term health effects among U.S. Navy divers (n = 328) who suffered decompression sickness (DCS) between January 1968 and December 1979 and compared their post-DCS hospitalization rates with a matched sample of divers (n = 1,086) who had no recorded diving accidents. Results identified 251 individuals (76.5%) whose records contained no diving-related medical events after the DCS incident; the other divers (23.5%) had records of a subsequent hospital admission and/or a physical disability separation. Only three physical disabilities were attributed to DCS or diving, and there were no DCS-related deaths. DCS divers had significantly higher rates than controls for total hospitalizations, symptoms and headache, and diseases of the arteries and veins. These two clusters, which included such conditions as pain in the joint, abnormal involuntary movement, pain in the limb, and arterial embolism, were identified as potential risks for divers who suffer a DCS mishap. Previous hospitalizations and age were not associated with DCS; however, divers in the DCS group were significantly heavier than all other divers.
In order to determine the effects of repetitive compression-decompression cycles on hematologic and hemostatic factors in humans, 14 subjects were exposed to 150 ft sea water gauge (fswg) for 30 min with standard U.S. Navy decompression on each of 12 consecutive days. Red blood cell number, volume, and size distribution; hemoglobin concentration; hematocrit; white blood cell number and differential counts; platelet number and volume; prothrombin and partial thromboplastin times; and fibrinogen and fibrin/fibrinogen degradation products were measured in venous blood samples collected before the first and after alternate dives. Subjects in the study had no symptoms other than pruritus and occasional fatigue following the exposures. More than 60% had venous gas emboli detectable by precordial doppler monitoring which generally persisted for 3-5 h after surfacing. Results show a small decrease in red cell mass, with an increase in size distribution and no change in mean corpuscular volume. No change in total white cell number was noted, but the basophilic granulocytes and atypical lymphocytes were elevated at the end of the series. A biphasic change was noted in monocyte number, and immature neutrophilic granulocytes were reduced. No change in platelet number or volume, or in the prothrombin/partial thromboplastine time, was apparent. Although fibrinogen concentration significantly decreased during the exposures, fibrin/fibrinogen degradation products remained undetectable. All changes remained in a clinically acceptable range.(ABSTRACT TRUNCATED AT 250 WORDS)
The relationship between the health status and physical characteristics of 185 U.S. Navy divers and their risk for experiencing decompression sickness was examined utilizing historical cohort design. Data on multiphasic medical examinations performed on these men between 1972-1978 were obtained. Cases of decompression sickness before and after examination were identified. Divers who did experience decompression sickness either before or after examination had significantly higher measures of skinfold thickness and weight when compared to those who remained free of decompression sickness. Those divers in the highest quartile of each of three significant skinfold thicknesses measured had risks for decompression sickness that were generally 9 to 10 times as great as those calculated for the combined lower 3 quartiles and 5 to 6 times as great as the average crude risk calculated for all Navy divers over the past 5 yr. These findings suggest that obesity may be a contributory factor to the occurrence of decompression sickness.
Intravascular bubbles formed by decompression have been measured in 7 living dogs to give 14 different determinations of size distribution. Larger bubbles were estimated by the terminal rise velocity technique using the Stokes equation, while smaller bubbles were determined simultaneously, using the Coulter counter. Bubble diameters of 19--700 micrometers were recorded, these reaching the venous sinus as showers of several hundred whose mean size tended to increase with post-decompression time. Average diameters were rather smaller than previously recorded from autopsy. The results are discussed as indicating that all venous bubbles were within a size range where they would be filtered out by the lungs unless this organ had been insulated.