Oxygen content in semi-closed rebreathing apparatuses for underwater use : Measurements and modeling

The present series of unmanned hyperbaric tests were conducted in order to investigate the oxygen fraction variability in semi-closed underwater rebreathing apparatuses. The tested rebreathers were RB80 (Halcyon dive systems, High springs, FL, USA), IS-Mix (Interspiro AB, Stockholm, Sweden), CRABE (Aqua Lung, Carros Cedex, France), and Viper+ (Cobham plc, Davenport, IA, USA). The tests were conducted using a catalytically based propene combusting metabolic simulator. The metabolic simulator connected to a breathing simulator, both placed inside a hyperbaric pressure chamber, was first tested to demonstrate its usefulness to simulate human respiration in a hyperbaric situation. Following this the metabolic simulator was shown to be a useful tool in accident investigations as well as to assess the impact of different engineering designs and physiological variables on the oxygen content in the gas delivered to the diver by the rebreathing apparatuses. A multi-compartment model of the oxygen fractions was developed and compared to the previously published single-compartment models. The root mean squared error (RMSE) of the multi-compartment model was smaller than the RMSE for the single-compartment model, showing its usefulness to estimate the impact of different designs and physiological variables on the inspired oxygen fraction.QC 20150903</p

Oxygen content in semi-closed rebreathing apparatuses for underwater use : Measurements and modeling

The present series of unmanned hyperbaric tests were conducted in order to investigate the oxygen fraction variability in semi-closed underwater rebreathing apparatuses. The tested rebreathers were RB80 (Halcyon dive systems, High springs, FL, USA), IS-Mix (Interspiro AB, Stockholm, Sweden), CRABE (Aqua Lung, Carros Cedex, France), and Viper+ (Cobham plc, Davenport, IA, USA). The tests were conducted using a catalytically based propene combusting metabolic simulator. The metabolic simulator connected to a breathing simulator, both placed inside a hyperbaric pressure chamber, was first tested to demonstrate its usefulness to simulate human respiration in a hyperbaric situation. Following this the metabolic simulator was shown to be a useful tool in accident investigations as well as to assess the impact of different engineering designs and physiological variables on the oxygen content in the gas delivered to the diver by the rebreathing apparatuses. A multi-compartment model of the oxygen fractions was developed and compared to the previously published single-compartment models. The root mean squared error (RMSE) of the multi-compartment model was smaller than the RMSE for the single-compartment model, showing its usefulness to estimate the impact of different designs and physiological variables on the inspired oxygen fraction.QC 20150903</p

Safety algorithm for predicting PO2 in electronic closed circuit rebreathers

Poster at UHMS Annual Scientific Meeting 2016</p

Strategic development of environmental impact assessment decision support tool for offshore energy enables decreased costs, increased utilization, and quality

In the transition to a sustainable energy system, there is an urgent need for expansion of offshore renewable energy installations. To ensure sustainable development also with respect to the marine environment, a variety of decision support tools (DSTs) are currently under development, aiming at potentially increased quality and efficiency for environmental risk assessment (EIA) of planned offshore energy installations. However, the savings potential of a DSTs is to a large extent governed by the timing of the DST development, which in turn is directly dependent on the investment rate over time. A set of development scenarios were evaluated, simulating different degrees of strategic implementation and successful utilization of the DST for offshore energy. Using the situation in Sweden as a case study, we demonstrate that a planned investment can lead to considerably lower total costs for the EIA at a national level, at the same time allowing for improved quality of the EIA in line with the ambitions in both marine spatial planning and existing goals within marine environmental management. © 2023 The Author(s

Agreement between ultrasonic bubble grades using a handheld self-positioning Doppler product and 2D cardiac ultrasound

(Plogmark O, Hjelte C, Ekström M, Frånberg O. Agreement between ultrasonic bubble grades using a handheld self-positioning Doppler product and 2D cardiac ultrasound. Diving and Hyperbaric Medicine. 2022 December 20;52(4):281−285. doi: 10.28920/dhm52.4.281-285. PMID: 36525686.) Introduction: Intravascular bubble load after decompression can be detected and scored using ultrasound techniques that measure venous gas emboli (VGE). The aim of this study was to analyse the agreement between ultrasonic bubble grades from a handheld self-positioning product, the O’Dive™, and cardiac 2D ultrasound after decompression. Methods: VGE were graded with both bilateral subclavian vein Doppler ultrasound (modified Spencer scale) and 2D cardiac images (Eftedal Brubakk scale). Agreement was analysed using weighted kappa (Kw ). Analysis with Kw was made for all paired grades, including measurements with and without zero grades, and for each method’s highest grades after each dive. Results: A total of 152 dives yielded 1,113 paired measurements. The Kw agreement between ultrasound VGE grades produced by cardiac 2D images and those from the O’Dive was ‘fair’; when zero grades were excluded the agreement was ‘poor’. The O’Dive was found to have a lower sensitivity to detect VGE compared to 2D cardiac image scoring. Conclusions: Compared to 2D cardiac image ultrasound, the O’Dive yielded generally lower VGE grades, which resulted in a low level of agreement (fair to poor) with Kw

Proposed Thalmann algorithm air diving decompression table for the Swedish Armed Forces

The Swedish Armed Forces (SwAF) air dive tables are under revision. Currently, the air dive table from the U.S. Navy (USN) Diving Manual (DM) Rev. 6 is used with an msw-to-fsw conversion. Since 2017, the USN has been diving according to USN DM rev. 7, which incorporates updated air dive tables derived from the Thalmann Exponential Linear Decompression Algorithm (EL-DCM) with VVAL79 parameters. The SwAF decided to replicate and analyze the USN table development methodology before revising their current tables. The ambition was to potentially find a table that correlates with the desired risk of decompression sickness. New compartmental parameters for the EL-DCM algorithm, called SWEN21B, were developed by applying maximum likelihood methods on 2,953 scientifically controlled direct ascent air dives with known outcomes of decompression sickness (DCS). The targeted probability of DCS for direct ascent air dives was ≤1% overall and ≤1‰ for neurological DCS (CNS-DCS). One hundred fifty-four wet validation dives were performed with air between 18 to 57 msw. Both direct ascent and decompression stop dives were conducted, resulting in incidences of two joint pain DCS (18 msw/59 minutes), one leg numbness CNS-DCS (51 msw/10 minutes with deco-stop), and nine marginal DCS cases, such as rashes and itching. A total of three DCS incidences, including one CNS-DCS, yield a predicted risk level (95% confidence interval) of 0.4-5.6% for DCS and 0.0-3.6% for CNS-DCS. Two out of three divers with DCS had patent foramen ovale. The SWEN21 table is recommended for the SwAF for air diving as it, after results from validation dives, suggests being within the desired risk levels for DCS and CNS-DCS

The performance of 'temperature stick' carbon dioxide absorbent monitors in diving rebreathers

INTRODUCTION: Diving rebreathers use canisters containing soda lime to remove carbon dioxide (CO2) from expired gas. Soda lime has a finite ability to absorb CO₂. Temperature sticks monitor the exothermic reaction between CO₂ and soda lime to predict remaining absorptive capacity. The accuracy of these predictions was investigated in two rebreathers that utilise temperature sticks. METHODS: Inspiration and rEvo rebreathers filled with new soda lime were immersed in water at 19°C and operated on mechanical circuits whose ventilation and CO₂-addition parameters simulated dives involving either moderate exercise (6 MET) throughout (mod-ex), or 90 minutes of 6 MET exercise followed by 2 MET exercise (low-ex) until breakthrough (inspired PCO₂ [PiCO₂] = 1 kPa). Simulated dives were conducted at surface pressure (sea-level) (low-ex: Inspiration, n = 5; rEvo, n = 5; mod-ex: Inspiration, n = 7, rEvo, n = 5) and at 3-6 metres' sea water (msw) depth (mod-ex protocol only: Inspiration, n = 8; rEvo, n = 5). RESULTS: Operated at surface pressure, both rebreathers warned appropriately in four of five low-ex tests but failed to do so in the 12 mod-ex tests. At 3-6 msw depth, warnings preceded breakthrough in 11 of 13 mod-ex tests. The rEvo warned conservatively in all five tests (approximately 60 minutes prior). Inspiration warnings immediately preceded breakthrough in six of eight tests, but were marginally late in one test and 13 minutes late in another. CONCLUSION: When operated at even shallow depth, temperature sticks provided timely warning of significant CO₂ breakthrough in the scenarios examined. They are much less accurate during simulated exercise at surface pressure. Copyright: This article is the copyright of the authors who grant Diving and Hyperbaric Medicine a non-exclusive licence to publish the article in electronic and other forms

Randomised, controlled, open label, multicentre clinical trial to explore safety and efficacy of hyperbaric oxygen for preventing ICU admission, morbidity and mortality in adult patients with COVID-19

Introduction COVID-19 may cause severe pneumonitis and trigger a massive inflammatory response that requires ventilatory support. The intensive care unit (ICU)-mortality has been reported to be as high as 62%. Dexamethasone is the only of all anti-inflammatory drugs that have been tested to date that has shown a positive effect on mortality. We aim to explore if treatment with hyperbaric oxygen (HBO) is safe and effective for patients with severe COVID-19. Our hypothesis is that HBO can prevent ICU admission, morbidity and mortality by attenuating the inflammatory response. The primary objective is to evaluate if HBO reduces the number of ICU admissions compared with best practice treatment for COVID-19, main secondary objectives are to evaluate if HBO reduces the load on ICU resources, morbidity and mortality and to evaluate if HBO mitigates the inflammatory reaction in COVID-19. Methods and analysis A randomised, controlled, phase II, open label, multicentre trial. 200 subjects with severe COVID-19 and at least two risk factors for mortality will be included. Baseline clinical data and blood samples will be collected before randomisation and repeated daily for 7 days, at days 14 and 30. Subjects will be randomised with a computer-based system to HBO, maximum five times during the first 7 days plus best practice treatment or only best practice treatment. The primary endpoint, ICU admission, is defined by criteria for selection for ICU. We will evaluate if HBO mitigates the inflammatory reaction in COVID-19 using molecular analyses. All parameters are recorded in an electronic case report form. An independent Data Safety Monitoring Board will review the safety parameters. Ethics and dissemination The trial is approved by The National Institutional Review Board in Sweden (2020-01705) and the Swedish Medical Product Agency (5.1-2020-36673). Positive, negative and any inconclusive results will be published in peer-reviewed scientific journals with open access.open access</p