Evaluation of North Sea saturation procedures through divers monitoring.

BACKGROUND: Saturation diving is a standard method of intervention for commercial diving during offshore operations. Current saturation procedures achieve a high level of safety with regards to decompression sickness but still put the divers under multiple stressors: 1) Environmental stress (long confinement, heat/cold, dense gases, high oxygen levels), 2) Work stress (muscular fatigue, psychological pressure, breathing equipment, etc.), 3) venous gas emboli associated with decompression, 4) Inflammation related to oxidative stress and microparticles. We present the results of a saturation divers monitoring campaign performed in the North Sea Danish sector, on the Tyra field, during 2022. The study was supported by TotalEnergies, the field operator, and performed by Boskalis Subsea Services, the diving contractor, onboard the diving support vessel Boka Atlantis. The objective was twofold: document the level of diving stress during saturation operations in the Danish sector, and compare the performances of two saturation procedures, the Boskalis and the NORSOK procedures. MATERIALS AND METHODS: Fourteen divers volunteered for the study. The monitoring package include weight and temperature measurements, psychomotor tests (objective evaluation) and questionnaires (subjective evaluation), Doppler bubble detection and bioimpedance. The results were presented in a radar diagram that provides a general view of the situation. RESULTS: The data were analysed along 3 dimensions: work and environmental, desaturation bubbles, oxidative stress and inflammation. The results showed little or no variations from the reference values. No bubbles were detected after excursion dives and the final decompression, except for two divers with a grade 1 after arriving at surface. No statistical difference could be found between the Boskalis and the NORSOK saturation procedures. CONCLUSIONS: At a depth of 40-50 msw corresponding to the Danish sector, the two saturation procedures monitored induce no or little stress to the divers. The divers know how to manage their diet, equilibrate their hydration and pace their effort. Data available on divers' post saturation period show a recovery over the 24-48 hours following the end of the decompression. Further research should focus on diving deeper than 100 msw where a greater stress can be anticipated.

Advanced high pressure hyperbaric techniques in tunnelling.

Work in compressed air and diving are both occupational activities that have been around since the mid-19th century, and those undertaking their work under elevated pressure. Meeting the demand to go to "higher pressure for longer" in tunneling has lagged in diving, but both activities have found it necessary to adopt mixed gas breathing and saturation exposure techniques. This paper explains how work in hyperbaric conditions at high pressure is undertaken in tunneling and is illustrated by the hyperbaric activity likely to be involved in constructing a large-diameter road tunnel below a body of water such as an estuary. It also explores the practical differences between work in compressed air and diving.

Cardiovascular effects of breath-hold diving at altitude.

Hypoxia, centralization of blood in pulmonary vessels, and increased cardiac output during physical exertion are the pathogenetic pathways of acute pulmonary edema observed during exposure to extraordinary environments. This study aimed to evaluate the effects of breath-hold diving at altitude, which exposes simultaneously to several of the stimuli mentioned above. To this aim, 11 healthy male experienced divers (age 18-52y) were evaluated (by Doppler echocardiography, lung echography to evaluate ultrasound lung B-lines (BL), hemoglobin saturation, arterial blood pressure, fractional NO (Nitrous Oxide) exhalation in basal condition (altitude 300m asl), at altitude (2507m asl) and after breath-hold diving at altitude. A significant increase in E/e' ratio (a Doppler-echocardiographic index of left atrial pressure) was observed at altitude, with no further change after the diving session. The number of BL significantly increased after diving at altitude as compared to basal conditions. Finally, fractional exhaled nitrous oxide was significantly reduced by altitude; no further change was observed after diving. Our results suggest that exposure to hypoxia may increase left ventricular filling pressure and, in turn, pulmonary capillary pressure. Breath-hold diving at altitude may contribute to interstitial edema (as evaluated by BL score), possibly because of physical efforts made during a diving session. The reduction of exhaled nitrous oxide at altitude confirms previous reports of nitrous oxide reduction after repeated exposure to hypoxic stimuli. This finding should be further investigated since reduced nitrous oxide production in hypoxic conditions has been reported in subjects prone to high-altitude pulmonary edema.

Effect of feathers on drag in plunge-diving birds.

This study explores the impact of feathers on the hydrodynamic drag experienced by diving birds, which is critical to their foraging efficiency and survival. Employing a novel experimental approach, we analyzed the kinematics of both feathered and nonfeathered projectiles during their transition from air to water using high-speed imaging and an onboard accelerometer. The drag coefficients were determined through two methods: a direct calculation from the acceleration data and a theoretical approach fitted to the observed velocity profiles. Our results indicate that feathers significantly increase the drag force during water entry, with feathered projectiles exhibiting approximately double the drag coefficient of their smooth counterparts. These findings provide new insights into the role of avian feather morphology in diving mechanics and have potential implications for the design of bioinspired aquatic vehicles in engineering. The study also discusses the biological implications of increased drag due to feathers and suggests that factors such as body shape might play a more critical role in the diving capabilities of birds than previously understood.

Specialized diving traits in the generalist morphology of Fulica (Aves, Rallidae).

Foot-propelled diving comprises the primary locomotion-based feeding strategy for many birds, including families such as Phalacrocoracidae, Anhingidae, Podicipedidae, Gaviidae, and the diving ducks within Anatidae. While the morphology of specialized divers is well known, the corresponding morphology is less known for birds not as specialized but capable of diving, such as the coots (Rallidae, Fulica spp.). To compare the osteology of Fulica with other (non-diving) Rallidae, and with foot-propelled diving birds that are distantly related, we considered osteological characters, as well as the proportion of the hind limb bones and the femoral splay angle to construct a phylomorphospace, and to perform a comparative disparity analysis considering ecomorphologically relevant characters related to swimming and diving. Coots resulted to be significantly disparate from other Rallidae showing many traits of specialized foot-propelled divers, but only noticeable when compared with other rallids, as the degree of development of these traits is markedly less than in loons, grebes, or cormorants. This may correspond to a stabilizing selection of characteristics associated with a generalist morphology in Fulica. Studying adaptation in generalist taxa broadens our understanding of ecomorphologically significant features, thereby enabling us to generalize their evolutionary patterns.

Effects of CO2 on the occurrence of decompression sickness: review of the literature.

Introduction: Inhalation of high concentrations of carbon dioxide (CO2) at atmospheric pressure can be toxic with dose-dependent effects on the cardiorespiratory system or the central nervous system. Exposure to both hyperbaric and hypobaric environments can result in decompression sickness (DCS). The effects of CO2 on DCS are not well documented with conflicting results. The objective was to review the literature to clarify the effects of CO2 inhalation on DCS in the context of hypobaric or hyperbaric exposure. Methods: The systematic review included experimental animal and human studies in hyper- and hypobaric conditions evaluating the effects of CO2 on bubble formation, denitrogenation or the occurrence of DCS. The search was based on MEDLINE and PubMed articles with no language or date restrictions and also included articles from the underwater and aviation medicine literature. Results: Out of 43 articles, only 11 articles were retained and classified according to the criteria of hypo- or hyperbaric exposure, taking into account the duration of CO2 inhalation in relation to exposure and distinguishing experimental work from studies conducted in humans. Conclusions: Before or during a stay in hypobaric conditions, exposure to high concentrations of CO2 favors bubble formation and the occurrence of DCS. In hyperbaric conditions, high CO2 concentrations increase the occurrence of DCS when exposure occurs during the bottom phase at maximum pressure, whereas beneficial effects are observed when exposure occurs during decompression. These opposite effects depending on the timing of exposure could be related to 1) the physical properties of CO2, a highly diffusible gas that can influence bubble formation, 2) vasomotor effects (vasodilation), and 3) anti-inflammatory effects (kinase-nuclear factor and heme oxygenase-1 pathways). The use of O2-CO2 breathing mixtures on the surface after diving may be an avenue worth exploring to prevent DCS.

Drinker driver flyer diver.

Blood alcohol concentrations above defined levels are detrimental to cognitive performance. Empirical and published evidence suggest that nitrogen narcosis is analogous to alcohol intoxication with both impairing prefrontal cortex function. Nitrogen narcosis is also known to have been a factor in fatal accidents. To examine the effects of nitrogen narcosis, a recent publication used the Iowa Gambling Task tool, to simulate dynamic real-life risky decision-making behaviour. If the reported outcomes are corroborated in larger rigorously designed studies it is likely to provide further evidence that divers may well experience the negative effects of a 'narcotic agent', even at relatively shallow depths. These deleterious effects may occur regardless of diving experience, aptitude or professional status. In 1872, English law made it an offence to be 'drunk' whilst in charge of horses, carriages, cattle and steam engines. Understanding the danger was easy, establishing who is 'drunk' in the eyes of the court required a legal definition. Driving above a 'legal limit' for alcohol was made illegal in the United Kingdom in 1967. The limit was set at 80 milligrams of alcohol per 100 millilitres of blood. It took just short of one hundred years to get from first introducing a restriction to specific activities, whilst under the influence of alcohol, to having a clear and well-defined enforceable law. The question surely is whether our modern society will tolerate another century before legally defining safe parameters for nitrogen narcosis?

Clinical utility of dipstick urinalysis in assessing fitness to dive in military divers, submariners, and hyperbaric personnel.

Introduction: Routine dipstick urinalysis is part of many dive medical assessment protocols. However, this has a significant chance of producing false-positive or false-negative results in asymptomatic and healthy individuals. Studies evaluating the value of urinalysis in dive medical assessments are limited. Methods: All results from urinalysis as part of dive medical assessments of divers, submarines, and hyperbaric personnel of the Royal Netherlands Navy from 2013 to 2023 were included in this study. Additionally, any information regarding additional testing, referral, or test results concerning the aforementioned was collected. Results: There were 5,899 assessments, resulting in 46 (0.8%) positive dipstick urinalysis results, predominantly microscopic haematuria. Females were significantly overrepresented, and revisions resulted in significantly more positive test results than initial assessments. Lastly, almost half of the cases were deemed fit to dive, while the other half were regarded as temporarily unfit. These cases required additional testing, and a urologist was consulted three times. Conclusions: To our knowledge, this is the most extensive study evaluating urinalysis in dive medical assessments. In our military population, the incidence of positive test results is very low, and there have not been clinically relevant results over a period of 10 years. Therefore, routinely assessing urine in asymptomatic healthy military candidates is not cost-effective or efficacious. The authors advise taking a thorough history for fitness to dive assessments and only analysing urine when a clinical indication is present.

Killer whale respiration rates.

Measuring breathing rates is a means by which oxygen intake and metabolic rates can be estimated to determine food requirements and energy expenditure of killer whales (Orcinus orca) and other cetaceans. This relatively simple measure also allows the energetic consequences of environmental stressors to cetaceans to be understood but requires knowing respiration rates while they are engaged in different behaviours such as resting, travelling and foraging. We calculated respiration rates for different behavioural states of southern and northern resident killer whales using video from UAV drones and concurrent biologging data from animal-borne tags. Behavioural states of dive tracks were predicted using hierarchical hidden Markov models (HHMM) parameterized with time-depth data and with labeled tracks of drone-identified behavioural states (from drone footage that overlapped with the time-depth data). Dive tracks were sequences of dives and surface intervals lasting ≥ 10 minutes cumulative duration. We calculated respiration rates and estimated oxygen consumption rates for the predicted behavioural states of the tracks. We found that juvenile killer whales breathed at a higher rate when travelling (1.6 breaths min-1) compared to resting (1.2) and foraging (1.5)-and that adult males breathed at a higher rate when travelling (1.8) compared to both foraging (1.7) and resting (1.3). The juveniles in our study were estimated to consume 2.5-18.3 L O2 min-1 compared with 14.3-59.8 L O2 min-1 for adult males across all behaviours based on estimates of mass-specific tidal volume and oxygen extraction. Our findings confirm that killer whales take single breaths between dives and indicate that energy expenditure derived from respirations requires using sex, age, and behavioural-specific respiration rates. These findings can be applied to bioenergetics models on a behavioural-specific basis, and contribute towards obtaining better predictions of dive behaviours, energy expenditure and the food requirements of apex predators.

Selected and shared hematological responses to apnea in elite human free divers and northern elephant seals (Mirounga angustirostris).

Despite elite human free divers achieving incredible feats in competitive free diving, there has yet to be a study that compares consummate divers, (i.e. northern elephant seals) to highly conditioned free divers (i.e., elite competitive free-diving humans). Herein, we compare these two diving models and suggest that hematological traits detected in seals reflect species-specific specializations, while hematological traits shared between the two species are fundamental mammalian characteristics. Arterial blood samples were analyzed in elite human free divers (n = 14) during a single, maximal volitional apnea and in juvenile northern elephant seals (n = 3) during rest-associated apnea. Humans and elephant seals had comparable apnea durations (∼6.5 min) and end-apneic arterial Po2 [humans: 40.4 ± 3.0 mmHg (means ± SE); seals: 27.1 ± 5.9 mmHg; P = 0.2]. Despite similar increases in arterial Pco2 (humans: 33 ± 5%; seals: 16.3 ± 5%; P = 0.2), only humans experienced reductions in pH from baseline (humans: 7.45 ± 0.01; seals: 7.39 ± 0.02) to end apnea (humans: 7.37 ± 0.01; seals: 7.38 ± 0.02; P < 0.0001). Hemoglobin P50 was greater in humans compared to elephant seals (29.9 ± 1.5 and 28.7 ± 0.6 mmHg, respectively; P = 0.046). Elephant seals overall had higher carboxyhemoglobin (COHb) levels (5.9 ± 2.6%) compared to humans (0.8 ± 1.2%; P < 0.0001); however, following apnea, COHb was reduced in seals (baseline: 6.1 ± 0.3%; end apnea: 5.6 ± 0.3%) and was slightly elevated in humans (baseline: 0.7 ± 0.1%; end apnea: 0.9 ± 0.1%; P < 0.0002, both comparisons). Our data indicate that during static apnea, seals have reduced hemoglobin P50, greater pH buffering, and increased COHb levels. The differences in hemoglobin P50 are likely due to the differences in the physiological environment between the two species during apnea, whereas enhanced pH buffering and higher COHb may represent traits selected for in elephant seals.NEW & NOTEWORTHY This study uses similar methods and protocols in elite human free divers and northern elephant seals. Using highly conditioned divers (elite free-diving humans) and highly adapted divers (northern elephant seals), we explored which hematological traits are fundamentally mammalian and which may have been selected for. We found differences in P50, which may be due to different physiological environments between species, while elevated pH buffering and carbon monoxide levels might have been selected for in seals.

Assessment of plasma malondialdehyde levels among free-diver fishermen in southeast Maluku district: exploring influencing factors on oxidative stress.

BACKGROUND: Indonesia, with its expansive territorial waters, hosts numerous fishing communities residing on various islands. Many of these communities rely on diving activities, predominantly free diving without standardized safety equipment. This practice poses risks, including the potential for hypoxia-induced oxidative stress, which plays a role in disease pathogenesis. This study aimed to investigate the levels of malondialdehyde (MDA) in freediving fishermen and explore potential influencing factors. MATERIALS AND METHODS: The research involved 30 freediving fishermen, aged 20-60, who engaged in diving at least twice weekly over the last 3 months. Blood plasma MDA levels were assessed using the Will method. RESULTS: Results revealed a median age of 40.5 years (range: 20-59), a body mass index of 23.1 ± 2.8, and a mean blood pressure of 132/85 mmHg. A significant portion of the subjects exhibited smoking habits (90%) and alcohol consumption (76.7%). The median MDA level among subjects was measured at 0.42 nmol/mL (range: 0.34-0.70). However, no discernible relationship was found between smoking habits, alcohol consumption, and MDA level categories, as determined by the Fisher exact test (p > 0.05). CONCLUSIONS: While these findings shed light on the MDA levels in freediving fishermen, further research is warranted to explore additional factors that may influence these levels. This comprehensive understanding is crucial for addressing the health risks associated with free diving practices in this unique population.

Effect of skull morphology on fox snow diving.

Certain fox species plunge-dive into snow to catch prey (e.g., rodents), a hunting mechanism called mousing. Red and arctic foxes can dive into snow at speeds ranging between 2 and 4 m/s. Such mousing behavior is facilitated by a slim, narrow facial structure. Here, we investigate how foxes dive into snow efficiently by studying the role of skull morphology on impact forces it experiences. In this study, we reproduce the mousing behavior in the lab using three-dimensional (3D) printed fox skulls dropped into fresh snow to quantify the dynamic force of impact. Impact force into snow is modeled using hydrodynamic added mass during the initial impact phase. This approach is based on two key facts: the added mass effect in granular media at high Reynolds numbers and the characteristics of snow as a granular medium. Our results show that the curvature of the snout plays a critical role in determining the impact force, with an inverse relationship. A sharper skull leads to a lower average impact force, which allows foxes to dive head-first into the snow with minimal tissue damage.

Biomechanical analysis of little penguins' underwater locomotion from the free-ranging dive data.

Penguins are proficient swimmers, and their survival depends on their ability to catch prey. The diving behaviour of these fascinating birds should then minimize the associated energy cost. For the first time, the energy cost of penguin dives is computed from the free-ranging dive data, on the basis of an existing biomechanical model. Time-resolved acceleration and depth data collected for 300 dives of little penguins (Eudyptula minor) are specifically employed to compute the bird dive angles and swimming speeds, which are needed for the energy estimate. We find that the numerically obtained energy cost by using the free-ranging dive data is not far from the minimum cost predicted by the model. The outcome, therefore, supports the physical soundness of the chosen model; however, it also suggests that, for closer agreement, one should consider previously neglected effects, such as those due to water currents and those associated with motion unsteadiness. Additionally, from the free-ranging dive data, we calculate hydrodynamic forces and non-dimensional indicators of propulsion performance - Strouhal and Reynolds numbers. The obtained values further confirm that little penguins employ efficient propulsion mechanisms, in agreement with previous investigations.

Cardiovascular considerations on recreational scuba diving. SEC-Clinical Cardiology Association/SEC-Working Group on Sports Cardiology consensus document.

The practice of recreational scuba diving has increased worldwide, with millions of people taking part each year. The aquatic environment is a hostile setting that requires human physiology to adapt by undergoing a series of changes that stress the body. Therefore, physical fitness and control of cardiovascular risk factors are essential for practicing this sport. Medical assessment is not mandatory before participating in this sport and is only required when recommended by a health questionnaire designed for this purpose. However, due to the significance of cardiovascular disease, cardiology consultations are becoming more frequent. The aim of the present consensus document is to describe the cardiovascular physiological changes that occur during diving, focusing on related cardiovascular diseases, their management, and follow-up recommendations. The assessment and follow-up of individuals who practice diving with previous cardiovascular disease are also discussed. This document, endorsed by the Clinical Cardiology Association of the Spanish Society of Cardiology (SEC) and the SEC Working Group on Sports Cardiology of the Association of Preventive Cardiology, aims to assist both cardiologists in evaluating patients, as well as other specialists responsible for assessing individuals' fitness for diving practice.

Oxy-Inflammation in Humans during Underwater Activities.

Underwater activities are characterized by an imbalance between reactive oxygen/nitrogen species (RONS) and antioxidant mechanisms, which can be associated with an inflammatory response, depending on O2 availability. This review explores the oxidative stress mechanisms and related inflammation status (Oxy-Inflammation) in underwater activities such as breath-hold (BH) diving, Self-Contained Underwater Breathing Apparatus (SCUBA) and Closed-Circuit Rebreather (CCR) diving, and saturation diving. Divers are exposed to hypoxic and hyperoxic conditions, amplified by environmental conditions, hyperbaric pressure, cold water, different types of breathing gases, and air/non-air mixtures. The "diving response", including physiological adaptation, cardiovascular stress, increased arterial blood pressure, peripheral vasoconstriction, altered blood gas values, and risk of bubble formation during decompression, are reported.

The interaction of breath holding and muscle mechanoreflex on cardiovascular responses in breath-hold divers and non-breath-hold divers.

Cardiovascular responses to diving are characterized by two opposing responses: tachycardia resulting from exercise and bradycardia resulting from the apnea. The convergence of bradycardia and tachycardia may determine the cardiovascular responses to diving. The purpose of this study was to investigate the interaction of breath holding and muscle mechanoreflex on cardiovascular responses in breath-hold divers (BHDs) and non-BHDs. We compared the cardiovascular responses to combined apnea and the mechanoreflex in BHDs and non-BHDs. All participants undertook three trials-apnea, passive leg cycling (PLC), and combined trials-for 30 s after rest. Cardiovascular variables were measured continuously. Nine BHD (male:female, 4:5; [means ± SD] age, 35 ± 6 years; height, 168.6 ± 4.6 cm; body mass, 58.4 ± 5.9 kg) and eight non-BHD (male:female, 4:4; [means ± SD] age, 35 ± 7 years; height, 163.9 ± 9.1 cm; body mass, 55.6 ± 7.2 kg) participants were included. Compared to the resting baseline, heart rate (HR) and cardiac output (CO) significantly decreased during the combined trial in the BHD group, while they significantly increased during the combined trials in the non-BHD group (P < 0.05). Changes in the HR and CO were significantly lower in the BHD group than in the non-BHD group in the combined trial (P < 0.05). These results suggest that bradycardia with apnea in BHDs is prioritized over tachycardia with the mechanoreflex, whereas that in non-BHDs is not. This finding implies that diving training changes the interaction between apnea and the mechanoreflex in cardiovascular control.

Decompression illness: a comprehensive overview.

Decompression illness is a collective term for two maladies (decompression sickness [DCS] and arterial gas embolism [AGE]) that may arise during or after surfacing from compressed gas diving. Bubbles are the presumed primary vector of injury in both disorders, but the respective sources of bubbles are distinct. In DCS bubbles form primarily from inert gas that becomes dissolved in tissues over the course of a compressed gas dive. During and after ascent ('decompression'), if the pressure of this dissolved gas exceeds ambient pressure small bubbles may form in the extravascular space or in tissue blood vessels, thereafter passing into the venous circulation. In AGE, if compressed gas is trapped in the lungs during ascent, pulmonary barotrauma may introduce bubbles directly into the pulmonary veins and thence to the systemic arterial circulation. In both settings, bubbles may provoke ischaemic, inflammatory, and mechanical injury to tissues and their associated microcirculation. While AGE typically presents with stroke-like manifestations referrable to cerebral involvement, DCS can affect many organs including the brain, spinal cord, inner ear, musculoskeletal tissue, cardiopulmonary system and skin, and potential symptoms are protean in both nature and severity. This comprehensive overview addresses the pathophysiology, manifestations, prevention and treatment of both disorders.

Breathing patterns and associated cardiovascular changes in intermittently breathing animals: (Partially) correcting a semantic quagmire.

Many animal species do not breathe in a continuous, rhythmic fashion, but rather display a variety of breathing patterns characterized by prolonged periods between breaths (inter-breath intervals), during which the heart continues to beat. Examples of intermittent breathing abound across the animal kingdom, from crustaceans to cetaceans. With respect to human physiology, intermittent breathing-also termed 'periodic' or 'episodic' breathing-is associated with a variety of pathologies. Cardiovascular phenomena associated with intermittent breathing in diving species have been termed 'diving bradycardia', 'submersion bradycardia', 'immersion bradycardia', 'ventilation tachycardia', 'respiratory sinus arrhythmia' and so forth. An examination across the literature of terminology applied to these physiological phenomena indicates, unfortunately, no attempt at standardization. This might be viewed as an esoteric semantic problem except for the fact that many of the terms variously used by different authors carry with them implicit or explicit suggestions of underlying physiological mechanisms and even human-associated pathologies. In this article, we review several phenomena associated with diving and intermittent breathing, indicate the semantic issues arising from the use of each term, and make recommendations for best practice when applying specific terms to particular cardiorespiratory patterns. Ultimately, we emphasize that the biology-not the semantics-is what is important, but also stress that confusion surrounding underlying mechanisms can be avoided by more careful attention to terms describing physiological changes during intermittent breathing and diving.

A novel method for tracking nitrogen kinetics in vivo under hyperbaric conditions using radioactive nitrogen-13 gas and positron emission tomography.

Decompression sickness (DCS) is caused by gaseous nitrogen dissolved in tissues forming bubbles during decompression. To date, no method exists to identify nitrogen within tissues, but with advances in positron-emission tomography (PET) technology, it may be possible to track gaseous radionuclides into tissues. We aimed to develop a method to track nitrogen movement in vivo and under hyperbaric pressure that could then be used to further our understanding of DCS using nitrogen-13 (13N2). A single anesthetized female Sprague-Dawley rat was exposed to 625 kPa, composed of air, isoflurane, and 13N2 for 10 min. The PET scanner recorded 13N2 during the hyperbaric exposure with energy windows of 250-750 keV. The PET showed an increase in 13N2 concentration in the lung, heart, and abdominal regions, which all reached a plateau after ∼4 min. This showed that it is possible to gain noninvasive in vivo measurements of nitrogen kinetics through the body while at hyperbaric pressures. Tissue samples showed radioactivity above background levels in the blood, brain, liver, femur, and thigh muscle when assessed using a γ counter. The method can be used to evaluate an array of challenges to our understanding of decompression physiology by quantifying nitrogen load through γ counts of 13N2, and signal intensity of the PET. Further development of the method will improve the specificity of the measured outcomes, and enable it to be used with larger mammals, including humans.NEW & NOTEWORTHY This article describes a method for the in vivo quantification and tracking of nitrogen through the mammalian body whilst exposed to hyperbaric pressure. The method has the potential to further our understanding of decompression sickness, and quantitatively evaluate the effectiveness of both the treatment and prevention of decompression sickness.

Stress biomarker changes following a series of repeated static and dynamic apneas in non-divers.

PURPOSE: This study examined the magnitude of physiological strain imposed by repeated maximal static and dynamic apneas through assessing a panel of stress-related biomarkers. METHODS: Eleven healthy men performed on three separate occasions (≥72-h apart): a series of five repeated maximal (i) static (STA) or (ii) dynamic apneas (DYN) or (iii) a static eupneic protocol (CTL). Venous blood samples were drawn at 30, 90, and 180-min after each protocol to determine ischaemia modified albumin (IMA), neuron-specific enolase (NSE), myoglobin, and high sensitivity cardiac troponin T (hscTnT) concentrations. RESULTS: IMA was elevated after the apnoeic interventions (STA,+86%;DYN,+332%,p ≤ 0.047) but not CTL (p = 0.385). Myoglobin was higher than baseline (23.6 ± 3.9 ng/mL) 30-min post DYN (+70%,38.8 ± 13.3 ng/mL,p = 0.030). A greater myoglobin release was recorded in DYN compared with STA and CTL (p ≤ 0.035). No changes were observed in NSE (p = 0.207) or hscTnT (p = 0.274). CONCLUSIONS: Five repeated maximal DYN led to a greater muscle injury compared with STA but neither elicited myocardial injury or neuronal-parenchymal damage.