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.

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.

How fit are military hyperbaric personnel after an asymptomatic or mild symptomatic COVID-19 infection? A retrospective study.

INTRODUCTION: In the diving community there is a special need to know if asymptomatic or mild COVID-19 disease impacts the cardiopulmonary functioning of individuals with occupational exposure to extreme environments. To date, no controlled studies have been conducted comparing COVID-19-infected hyperbaric employees and non-COVID-19-infected peers in a military setting. METHODS: Between June 2020 and June 2021, healthy, hyperbaric, military personnel aged between 18 and 54 years old, who had recovered from asymptomatic or subclinical COVID-19 disease at least one month earlier, were analysed. Non-COVID-infected peers with medical assessments during the same period were used as the control group. Somatometry, spirometry, VO2 max, and DLCO were measured for each group. RESULTS: No clinically relevant differences in somatometry, lung function tests, and exercise testing were found between the COVID-19 group and the controls. However, the percentage of individuals with a decrease in estimated VO2-max of 10% or more was significantly greater in the COVID group than in the control group (24 vs. 7.8%, P = 0.004). CONCLUSIONS: After asymptomatic or mild symptomatic COVID-19 infections, military hyperbaric employees are as fit as those who had not encountered COVID-19. As this research was based on a military population, it cannot be extrapolated to a nonmilitary population. Further studies in nonmilitary populations are necessary to determine the medical relevance of the present findings.

The lower limit for FEV1/FVC in dive medical assessments: a retrospective study.

INTRODUCTION: Interpreting pulmonary function test (PFT) results requires a valid reference set and a cut-off differentiating pathological from physiological pulmonary function; the lower limit of normal (LLN). However, in diving medicine it is unclear whether an LLN of 2.5% (LLN-2.5) or 5% (LLN-5) in healthy subjects constitutes an appropriate cut-off. METHODS: All PFTs performed at the Royal Netherlands Navy Diving Medical Centre between 1 January 2015 and 1 January 2021 resulting in a forced vital capacity (FVC), forced expiratory volume in one second (FEV1) and/or FEV1/FVC with a Z-score between -1.64 (LLN-5) and -1.96 (LLN-2.5) were included. Records were screened for additional tests, referral to a pulmonary specialist, results of radiological imaging, and fitness to dive. RESULTS: Analysis of 2,108 assessments in 814 subjects showed that 83 subjects, 74 men and nine women, mean age 32.4 (SD 8.2) years and height 182 (7.0) cm, had an FVC, FEV1 and/or FEV1/FVC with Z-scores between -1.64 and -1.96. Of these 83 subjects, 35 (42%) underwent additional tests, 77 (93%) were referred to a pulmonary specialist and 31 (37%) underwent high-resolution CT-imaging. Ten subjects (12%) were declared 'unfit to dive' for various reasons. Information from their medical history could have identified these individuals. CONCLUSIONS: Use of LLN-2.5 rather than LLN-5 for FEV1/FVC in asymptomatic individuals reduces additional investigations and referrals to a pulmonary specialist without missing important diagnoses, provided a thorough medical history is taken. Adoption of LLN-2.5 could save resources spent on diving medical assessments and protect subjects from harmful side effects associated with additional investigations, while maintaining an equal level of safety.

Routine Chest X-Rays Are Inaccurate in Detecting Relevant Intrapulmonary Anomalies During Medical Assessments of Fitness to Dive.

Introduction: Intrapulmonary pathology, such as bullae or blebs, can cause pulmonary barotrauma when diving. Many diving courses require chest X-rays (CXR) or high-resolution computed tomography (HRCT) to exclude asymptomatic healthy individuals with these lesions. The ability of routine CXRs and HRCT to assess fitness to dive has never been evaluated. Methods: Military divers who underwent yearly medical assessments at the Royal Netherlands Navy Diving Medical Center, including CXR at initial assessment, and who received a HRCT between January and June 2018, were included. The correlations of CXR and HRCT results with fitness to dive assessments were analyzed using Fisher's exact tests. Results: This study included 101 military divers. CXR identified bullae or blebs in seven divers, but HRCT found that these anomalies were not present in three subjects and were something else in four. CXR showed no anomalies in 94 subjects, but HRCT identified coincidental findings in 23 and bullae or blebs in seven. The differences between CXR and HRCT results were statistically significant (p = 0.023). Of the 34 subjects with anomalies on HRCT, 18 (53%) were disqualified for diving. Discussion: Routine CXR in asymptomatic military divers does not contribute to the identification of relevant pathology in fitness to dive assessments and has a high false negative rate (32%). HRCT is more diagnostic than CXR but yields unclear results, leading to disqualification for diving. Fitness to dive tests should exclude routine CXR; rather, HRCT should be performed only in subjects with clinical indications.

Longitudinal screening of hearing threshold in navy divers: is diving really a hazard?

INTRODUCTION: Hearing loss (HL) is common in the adult working population. It is widely assumed that diving is a risk factor for HL. However, studies with sufficient follow-up comparing HL in divers to non-divers are limited. This study aimed to assess the hearing threshold (HT) of Royal Netherlands Navy divers who had been diving for more than 15 years and to compare it to the ISO standard 7029:2017 reference table. METHODS: In this 25-year retrospective cohort study the Royal Netherlands Navy Diving Medical Centre audited the medical records of 1,117 Navy divers. Yearly dive medical assessments were performed according to professional standards, including audiometry. HTs were compared to the ISO 7029:2017 reference table, including Z-distribution, using paired t-tests. RESULTS: Thirty-five divers were included who had been diving for 15 years or longer. The HT increased significantly in nine of the 16 measured frequencies, while the Z-score decreased significantly in nine of the 16 tested frequencies (eight in both ears). In the 25-year follow-up the pattern was more obvious, with one significantly increased HT, and 10 significantly decreased Z-scores. DISCUSSION: The absolute HT increases after 15 years of military diving, but less than would be expected from normal age-related deterioration. Moreover, when comparing Z-scores, this sample of divers actually hear better than non-divers. We conclude that military diving is not an increased risk for HL compared to regular occupational hazards and suggest withdrawing the requirement for routine yearly audiometric evaluation as part of a dive medical examination.

The association between abdominal visceral fat and carotid stiffness is mediated by circulating inflammatory markers in uncomplicated type 2 diabetes.

Central obesity, insulin resistance, inflammation, as well as vascular changes are common in patients with type 2 diabetes. In this study we assessed the relationship among stiffness of the carotid artery, visceral fat, and circulating inflammatory markers in type 2 diabetic subjects. Carotid stiffness, quantified as the distensibility coefficient (DC), was measured by ultrasound in asymptomatic, normotensive patients with uncomplicated, well-controlled type 2 diabetes and in controls. Body fat distribution was quantified by magnetic resonance imaging. In patients, the carotid DC was inversely associated with visceral fat area (r = -0.660; P = 0.005) and plasma levels of C-reactive protein (CRP; r = -0.687; P = 0.002), but most strongly with plasma IL-6 (r = -0.766; P < 0.001). In multivariate analysis, the association between DC and visceral fat disappeared after adjustment for CRP and IL-6. Correction for age, body mass index, blood pressure, glycosylated hemoglobin, or fasting plasma glucose did not affect the association between carotid DC and inflammatory markers. Thus, carotid stiffness is associated with visceral obesity in patients with uncomplicated type 2 diabetes, but this association seems to be mediated by circulating IL-6 and CRP, of which IL-6, at least in part, originates from adipose tissue and stimulates hepatic CRP production.

Diastolic dysfunction is associated with altered myocardial metabolism in asymptomatic normotensive patients with well-controlled type 2 diabetes mellitus.

OBJECTIVES: This study evaluated myocardial function in relation to high-energy phosphate (HEP) metabolism in asymptomatic patients with uncomplicated type 2 diabetes mellitus using magnetic resonance (MR) techniques. BACKGROUND: Myocardial dysfunction may occur in patients with type 2 diabetes mellitus in the absence of coronary artery disease or left ventricular (LV) hypertrophy. The mechanisms underlying this diabetic cardiomyopathy are largely unknown, but may involve altered myocardial energy metabolism. METHODS: We assessed myocardial systolic and diastolic function and HEP metabolism in 12 asymptomatic normotensive male patients with recently diagnosed, well-controlled type 2 diabetes and 12 controls, using MR imaging and phosphorus-31-nuclear MR spectroscopy (31P-MRS) on a 1.5 T clinical scanner; 31P-MR spectra were quantified, and myocardial HEP metabolism was expressed as phosphocreatine to adenosine-triphosphate (PCr/ATP) ratio. RESULTS: No differences were found in LV mass and systolic function between patients and controls. However, early (E) acceleration peak, deceleration peak, peak filling rate, and transmitral early-to-late diastolic peak flow (E/A) ratio, all indexes of diastolic function, were significantly decreased in patients compared with controls (p < 0.02). In addition, myocardial PCr/ATP in patients was significantly lower than in controls (1.47 vs. 1.88, p < 0.01). Inverse associations were found between myocardial PCr/ATP and E acceleration peak, E deceleration peak, and E peak filling rate (all, p < 0.05). CONCLUSIONS: These results indicate that altered myocardial energy metabolism may contribute to LV diastolic functional changes in patients with recently diagnosed, well-controlled and uncomplicated type 2 diabetes.