Chain of events analysis in diving accidents treated by the Royal Netherlands Navy 1966-2023.

Introduction: Diving injuries are influenced by a multitude of factors. Literature analysing the full chain of events in diving accidents influencing the occurrence of diving injuries is limited. A previously published 'chain of events analysis' (CEA) framework consists of five steps that may sequentially lead to a diving fatality. This study applied four of these steps to predominately non-lethal diving injuries and aims to determine the causes of diving injuries sustained by divers treated by the Diving Medical Centre of the Royal Netherlands Navy. Methods: This retrospective cohort study was performed on diving injuries treated by the Diving Medical Centre between 1966 and 2023. Baseline characteristics and information pertinent to all four steps of the reduced CEA model were extracted and recorded in a database. Results: A total of 288 cases met the inclusion criteria. In 111 cases, all four steps of the CEA model could be applied. Predisposing factors were identified in 261 (90%) cases, triggers in 142 (49%), disabling agents in 195 (68%), and 228 (79%) contained a (possible-) disabling condition. The sustained diving injury led to a fatality in seven cases (2%). The most frequent predisposing factor was health conditions (58%). Exertion (19%), primary diver errors (18%), and faulty equipment (17%) were the most frequently identified triggers. The ascent was the most frequent disabling agent (52%). Conclusions: The CEA framework was found to be a valuable tool in this analysis. Health factors present before diving were identified as the most frequent predisposing factors. Arterial gas emboli were the most lethal injury mechanism.

Pulmonary oxygen toxicity breath markers after heliox diving to 81 metres.

Pulmonary oxygen toxicity (POT), an adverse reaction to an elevated partial pressure of oxygen in the lungs, can develop as a result of prolonged hyperbaric hyperoxic conditions. Initially starting with tracheal discomfort, it results in pulmonary symptoms and ultimately lung fibrosis. Previous studies identified several volatile organic compounds (VOCs) in exhaled breath indicative of POT after various wet and dry hyperbaric hypoxic exposures, predominantly in laboratory settings. This study examined VOCs after exposures to 81 metres of seawater by three navy divers during operational heliox diving. Univariate testing did not yield significant results. However, targeted multivariate analysis of POT-associated VOCs identified significant (P = 0.004) changes of dodecane, tetradecane, octane, methylcyclohexane, and butyl acetate during the 4 h post-dive sampling period. No airway symptoms or discomfort were reported. This study demonstrates that breath sampling can be performed in the field, and VOCs indicative of oxygen toxicity are exhaled without clinical symptoms of POT, strengthening the belief that POT develops on a subclinical-to-symptomatic spectrum. However, this study was performed during an actual diving operation and therefore various confounders were introduced, which were excluded in previous laboratory studies. Future studies could focus on optimising sampling protocols for field use to ensure uniformity and reproducibility, and on establishing dose-response relationships.

Self-reported vitality and health status are higher in Dutch submariners than in the general population.

Introduction: Living aboard submarines has a potential negative effect on health. Although studies have evaluated specific health hazards and short-term outcomes, long-term health effects have not been investigated in this population. Methods: Veteran submariners were contacted through the veterans' society and administered a World Health Organisation validated questionnaire (SF-36) assessing their physical, emotional, and social functioning. Scores were compared with those of the general (reference) population and scores in veteran submariners were differentiated by rank, time at sea and time in service. Statistical analyses were performed using the Wilcoxon signed rank and Kruskal-Wallis tests. Results: Of the 1,025 submariners approached in December 2019, 742 (72.4%) completed and returned the questionnaire before July 2020. All 742 were men, of median age 68 (interquartile range [IQR] 59-76) years (range 34-99 years). Of these subjects, 10.3% were current smokers, 64.4% were former smokers and 23.7% had never smoked. Submariners scored significantly better (P < 0.001) than the general population on all eight domains of the SF-36. Except for 'pain' and 'change in health status over the last year', scores for all domains decreased with age. Scores were not significantly affected by smoking status, rank, service, and time at sea. Conclusions: Dutch veteran submariners have better self-reported vitality and health status than the general Dutch population. Rank, service, and time at sea did not significantly affect scores of Dutch submariners.

The Young Elite Swimmer and the Lung: An Editorial / El joven nadador de élite y el pulmón; un editorial

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Assessment of pulmonary oxygen toxicity in special operations forces divers under operational circumstances using exhaled breath analysis.

INTRODUCTION: The Netherlands Maritime Special Operations Forces use closed circuit oxygen rebreathers (O2-CCR), which can cause pulmonary oxygen toxicity (POT). Recent studies demonstrated that volatile organic compounds (VOCs) can be used to detect POT in laboratory conditions. It is unclear if similar VOCs can be identified outside the laboratory. This study hypothesised that similar VOCs can be identified after O2-CCR diving in operational settings. METHODS: Scenario one: 4 h O2-CCR dive to 3 metres' seawater (msw) with rested divers. Scenario two: 3 h O2-CCR dive to 3 msw following a 5 day physically straining operational scenario. Exhaled breath samples were collected 30 min before and 30 min and 2 h after diving under field conditions and analysed using gas chromatography-mass spectrometry (GC-MS) to reconstruct VOCs, whose levels were tested longitudinally using a Kruskal-Wallis test. RESULTS: Eleven divers were included: four in scenario one and seven in scenario two. The 2 h post-dive sample could not be obtained in scenario two; therefore, 26 samples were collected. GC-MS analysis identified three relevant VOCs: cyclohexane, 2,4-dimethylhexane and 3-methylnonane. The intensities of 2,4-dimethylhexane and 3-methylnonane were significantly (P = 0.048 and P = 0.016, respectively) increased post-dive relative to baseline (range: 212-461%) in both scenarios. Cyclohexane was increased not significantly (P = 0.178) post-dive (range: 87-433%). CONCLUSIONS: VOCs similar to those associated with POT in laboratory conditions were identified after operational O2-CCR dives using GC-MS. Post-dive intensities were higher than in previous studies, and it remains to be determined if this is attributable to different dive profiles, diving equipment or other environmental factors.

Systematic review on the effects of medication under hyperbaric conditions: consequences for the diver.

BACKGROUND: Physiological changes are induced by immersion, swimming and using diving equipment. Divers must be fit to dive. Using medication may impact the capacity to adapt to hyperbaric conditions. The aim of this systematic review is to assess the interaction of diving/hyperbaric conditions and medication and to provide basic heuristics to support decision making regarding fitness to dive in medicated divers. METHODS: This was a systematic review of human and animal studies of medications in the hyperbaric environment. Studies were subdivided into those describing a medication/hyperbaric environment interaction and those concerned with prevention of diving disorders. Studies without a relation to diving with compressed air, and those concerning oxygen toxicity, hyperbaric oxygen therapy or the treatment of decompression sickness were excluded. RESULTS: Forty-four studies matched the inclusion criteria. Animal studies revealed that diazepam and valproate gave limited protection against the onset of the high-pressure neurological syndrome. Lithium had a protective effect against nitrogen-narcosis and losartan reduced cardiac changes in repetitive diving. Human studies showed no beneficial or dangerous pressure-related interactions. In prevention of diving disorders, pseudoephedrine reduced otic barotrauma, vitamins C and E reduced endothelial dysfunction after bounce diving and hepatic oxidative stress in saturation diving. DISCUSSION AND CONCLUSIONS: Animal studies revealed that psycho-pharmaceuticals can limit the onset of neurologic symptoms and cardiovascular protective drugs might add a potential protective effect against decompression sickness. No evidence of significant risks due to changes in pharmacologic mechanisms were revealed and most medication is not a contraindication to diving. For improving decision making in prescribing medicine for recreational and occupational divers and to enhance safety by increasing our understanding of pharmacology in hyperbaric conditions, future research should focus on controlled human studies.

Decompression sickness, fatness and active hydrophobic spots.

Since decompression sickness (DCS) in humans was first described, mankind has embarked on an odyssey to prevent it. The demonstration that decompression releases bubbles, which mainly contain inert gas (nitrogen, helium), into the circulation and that the slower the decompression rate the lesser the incidence of DCS, resulted in 1908 in the publication of the first, reasonably safe diving tables. Besides the development of proper diving tables, the selection of divers is also of importance. A relationship between body composition and DCS was observed in dogs as long ago as the nineteenth century, an observation supported early in the twentieth century: "Really fat men should never be allowed to work in compressed air, and plump men should be excluded from high pressure caissons…or in diving to more than about 10 fathoms, and at this depth the time of their exposure should be curtailed. If deep diving is to be undertaken…. skinny men should be selected." Alas, nothing is that simple! From my own experience it was not always the fat diver who ended up in the treatment chamber with DCS. Therefore, other factors must be at play; gender, age, physical fitness, and the existence of a persistent foramen ovale (PFO) have all been studied as possible factors for the development of vascular gas bubbles and, therefore, for DCS. However, none of these factors, alone or in combination, explain why there are intra-individual or intra-cohort differences in bubble grades (BG). In other words, why does a dive I did today led to a high BG but the same dive next week lead to a low one? Or, why is there such a difference in BG amongst divers of more or less the same age, gender, body composition and physical fitness? In a letter in this issue, a novel hypothesis is postulated that may fill in these gaps; active hydrophobic spots (AHS). These AHS can be found at the luminal side of capillary, venous and arterial walls and have an oligolamellar lining. In an in vitro experiment, nanobubbles developed on AHS after a 'dive' to 1,000 kPa (90 msw). It appears that AHS consist of dipalmitoylphosphatidylcholine (DPPC), which is the main component of surfactant. It is proposed that DPPC may leak from the alveoli into the alveolar capillary and be transported to veins and arteries where it precipitates and forms AHS. Based on these ideas, it is hypothesized that AHS generate nanobubbles that can grow into microbubbles. When these microbubbles detach from the AHS they might also take along pieces of the AHS membrane making the AHS smaller or even disappear. This phenomenon could explain some of the earlier findings regarding the formation of microbubbles in divers. The fact that the presence of microbubbles differs between younger and older divers, after repetitive dives, and between experienced divers and novice divers can be explained by this model, and AHS may be the missing link we are looking for in our quest to understand and treat DCS. However, some reservations must be made. Firstly, these observations are derived from in vitro and animal experiments and whether or not they reflect a similar process in man remains unclear. Secondly, it appears that female divers have lower bubble grades after similar dives compared to male divers, suggesting lower decompression stress. If AHS is the main generator for microbubbles, there should be a difference in the presence of AHS between men and women. We do not know from these animal experiments whether there is a gender difference, neither does a literature search in PubMed provide us with an answer. Thirdly, as said before, DPPC is the main component of surfactant. All alveolar surfactant phospholipids, such as DPPC, are secreted to the alveolar space via exocystosis of the lamellar bodies (LB) from alveolar type II (ATII) cells. To form a functional air-blood barrier, alveolar type I and ATII cells are connected to each other by tight junctions. These tight junctions constitute the seal of the intercellular cleft and in that way form a true barrier between the alveolus and the capillary. Only small molecules like oxygen, carbon dioxide, etc. can penetrate through this barrier by themselves due to passive diffusion. All other (macro)molecules, including DPPC, need intermediate processes such as ion transport proteins, channels, metabolic pumps, etc. to gain access to the pulmonary capillary lumen. To my knowledge, no such mechanisms for DPPC or LB are known. A theoretical explanation might be the fact that the production of DPPC and the exocystosis of DPPC-containing LBs into the alveolar space can be stimulated by stretch. Stretch of the alveoli can switch on Ca2+ entry by either mechanosensitive channels, store-operated channels or second messenger-operated channels, which induces LB exocystosis. Furthermore, an ATP-release mechanism might also be responsible for the pulmonary alveolar mechanotransduction of LB. During diving, transpulmonary pressure changes occur which might induce additional alveolar stretch and thus, theoretically, an extra release of LB. However, whether or not such exocystosis of LB is vascularly orientated remains unclear. Besides which, the leakage of DPPC from the alveolus to the pulmonary capillary might also be as simple as a malfunction of the tight junction due to epithelial membrane damage as a result of diving. Finally, it is also possible that DPPC is produced in other non-ATII cells in our body of which we are currently unaware. To conclude, this is an interesting hypothesis regarding the origin of microbubbles. Whether or not DPPC and LB are the main reason for individual sensitivity to DCS remains unclear. Further research will hopefully identify if DPPC and LB are indeed the missing link or just another branch on the big tree of the genesis of decompression sickness.

Modern assessment of pulmonary function in divers cannot rely on old reference values.

INTRODUCTION: Pulmonary function testing (PFT) is an important part of dive medical examinations. Depending on the standard used to assess fitness to dive, different reference sets and fixed cut-off points are used. Reference values are part of an ongoing debate regarding the validity and accuracy related to different age groups, sex and ethnic backgrounds. The Global Lung Initiative (GLI) has provided an all-age reference set which corrects for sex and ethnicity (GLI-2012); this has had substantial impact on pulmonary medicine. METHOD: We present an algorithm that can be used to standardise analysis of PFT in divers using the GLI-2012 reference set. Differences in the analysis of PFT between the ECSC/ERS-1993 and the GLI-2012 reference values are illustrated by means of three case reports. CONCLUSION: Using a valid database of reference values increases accuracy and might prevent additional medical investigations and/or incorrect assessment of fitness to dive. Although our algorithm needs further evaluation to ensure its validity, the preliminary results are promising. Whatever algorithm is used, we urge dive medical physicians to consider using valid reference sets when analysing PFT for assessment of fitness to dive.

Otitis externa in military divers: more frequent and less harmful than reported.

INTRODUCTION: Although otitis externa (OE) is a common disease, data related to (military) divers are limited. This study aimed to determine the incidence of OE in military divers during their initial training. We also wished to consider seasonal influences on incidence and whether early detection increases completion of the diving course. METHODS: From January 2011 to October 2016 the Royal Netherlands Navy Diving School trained 189 divers. Up to December 2015 we used the training records for the analyses. From January 2016 onward all divers were prospectively screened. Pearson's chi-squared 2 and Fisher's exact tests were used to analyse the data. RESULTS: In the 162 included divers, 30 cases of OE were identified. The incidence in 2016 was significantly higher than in 2011-2015 (17/35 (49%) versus 13/127 (10%), P < 0.001). Almost all cases developed after three weeks of diving. No influence of season was found (P = 0.354). Early diagnosis and treatment of OE does not seem to affect completion of diving courses (P = 0.28). Only in three cases did a diver have to discontinue the course due to OE. DISCUSSION: This study suggests that OE is more frequent among military divers than earlier reported, most likely caused by prolonged water exposure. Diving activities can often be continued with standard topical treatment.

Argon used as dry suit insulation gas for cold-water diving.

BACKGROUND: Cold-water diving requires good thermal insulation because hypothermia is a serious risk. Water conducts heat more efficiently compared to air. To stay warm during a dive, the choice of thermal protection should be based on physical activity, the temperature of the water, and the duration of exposure. A dry suit, a diving suit filled with gas, is the most common diving suit in cold water. Air is the traditional dry suit inflation gas, whereas the thermal conductivity of argon is approximately 32% lower compared to that of air. This study evaluates the benefits of argon, compared to air, as a thermal insulation gas for a dry suit during a 1-h cold-water dive by divers of the Royal Netherlands Navy. METHODS: Seven male Special Forces divers made (in total) 19 dives in a diving basin with water at 13 degrees C at a depth of 3 m for 1 h in upright position. A rubber dry suit and woollen undergarment were used with either argon (n = 13) or air (n = 6) (blinded to the divers) as suit inflation gas. Core temperature was measured with a radio pill during the dive. Before, halfway, and after the dive, subjective thermal comfort was recorded using a thermal comfort score. RESULTS: No diver had to abort the test due to cold. No differences in core temperature and thermal comfort score were found between the two groups. Core temperature remained unchanged during the dives. Thermal comfort score showed a significant decrease in both groups after a 60-min dive compared to baseline. CONCLUSIONS: In these tests the combination of the dry suit and undergarment was sufficient to maintain core temperature and thermal comfort for a dive of 1h in water at 13 degrees C. The use of argon as a suit inflation gas had no added value for thermal insulation compared to air for these dives.