Diving and hyperbaric medicine最新文献

Introduction: This study analysed the treatment outcomes of patients that received hyperbaric oxygen treatment (HBOT) for retinal artery occlusion (RAO) at the Royal Brisbane and Women's Hospital in Brisbane, Australia between 2015 and 2021.

Methods: Retrospective study from patient records including 22 eyes from 22 patients that received HBOT for either central RAO (17 patients) or branch RAO (five patients). Patients received the Royal Brisbane and Women's Hospital RAO protocol for their HBOT. Analysis included best corrected visual acuity pre- and post-treatment, subjective improvements, side effects and patient risk factors were also recorded.

Results: Improvement in best corrected visual acuity was LogMAR -0.2 for central RAO on average with 8/17 (47%) experiencing objective improvement, 5/17 (29%) experienced no change and 4/22 (24%) experienced a reduction in best corrected visual acuity. Subjective improvement (colour perception or visual fields) was reported in an additional 4/17 patients, resulting in 12/17 (71%) reporting improvement either in visual acuity or subjectively. There was no improvement in the best corrected visual acuity of any of the five patients suffering from branch RAO. Cardiovascular risk factors present in the cohort included hypertension, hypercholesterolaemia, previous cardiovascular events, cardiac disease and smoking. Limited side effects were experienced by this patient cohort with no recorded irreversible side effects.

Conclusions: Hyperbaric oxygen treatment appears a safe, beneficial treatment for central RAO. No benefit was demonstrated in branch RAO although numbers were small. Increased awareness of HBOT for RAO resulting in streamlined referrals and transfers and greater uptake of this intervention may further improve patient outcomes.

Introduction: Hypoxia can cause central nervous system dysfunction and injury. Hypoxia is a particular risk during rebreather diving. Given its subtle symptom profile and its catastrophic consequences there is a need for reliable hypoxia monitoring. Electroencephalography (EEG) is being investigated as a real time monitor for multiple diving problems related to inspired gas, including hypoxia.

Methods: A systematic literature search identified articles investigating the relationship between EEG changes and acute cerebral hypoxia in healthy adults. Quality of clinical evidence was assessed using the Newcastle-Ottawa scale.

Results: Eighty-one studies were included for analysis. Only one study investigated divers. Twelve studies described quantitative EEG spectral power differences. Moderate hypoxia tended to result in increased alpha activity. With severe hypoxia, alpha activity decreased whilst delta and theta activities increased. However, since studies that utilised cognitive testing during the hypoxic exposure more frequently reported opposite results it appears cognitive processing might mask hypoxic EEG changes. Other analysis techniques (evoked potentials and electrical equivalents of dipole signals), demonstrated sustained regulation of autonomic responses despite worsening hypoxia. Other studies utilised quantitative EEG analysis techniques, (Bispectral index [BISTM], approximate entropy and Lempel-Ziv complexity). No change was reported in BISTM value, whilst an increase in approximate entropy and Lempel-Ziv complexity occurred with worsening hypoxia.

Conclusions: Electroencephalographic frequency patterns change in response to acute cerebral hypoxia. There is paucity of literature on the relationship between quantitative EEG analysis techniques and cerebral hypoxia. Because of the conflicting results in EEG power frequency analysis, future research needs to quantitatively define a hypoxia-EEG response curve, and how it is altered by concurrent cognitive task loading.

Background: There is an increasing interest in 'transfer under pressure' (TUP) decompression in commercial diving, bridging traditional surface-oriented diving and saturation diving. In TUP diving the diver is surfaced in a closed bell and transferred isobarically to a pressure chamber for final decompression to surface pressure.

Methods: Tables for air diving and air and oxygen decompression have been compared for total decompression time (TDT), oxygen breathing time as well as high and low gradient factors (GF high and low). These have been considered surrogate outcome measures of estimated decompression sickness probability (P_DCS).

Results: Six decompression tables from DadCoDat (DCD, The Netherlands), Defence and Civil Institute of Environmental Medicine (DCIEM, Canada), Comex MT92 tables (France) and the United States Navy (USN) have been compared. In general, USN and DCD procedures advised longer TDT and oxygen breathing time and had a lower GF high compared to MT92 and DCIEM tables. GF low was significantly higher in USN procedures compared to DCD and one of the MT92 tables due to a shallower first stop in many USN profiles compared to the two others. Allowance and restrictions for repetitive diving varied extensively between the six procedures. While USN procedures have been risk-assessed by probabilistic models, no detailed documentation is available for any of the tables regarding validation in experimental and operational diving.

Conclusions: Absence of experimental testing of the candidate tables precludes firm conclusions regarding differences in P_DCS. All candidate tables are recognised internationally as well as within their national jurisdictions, and final decisions on procedure preference may depend on factors other than estimated P_DCS. USN and DCD procedures would be expected to have lower P_DCS than MT92 and DCIEM procedures, but the magnitude of these differences is not known.

Introduction: The performance of the Shangrila590 hyperbaric ventilator (Beijing Aeonmed Company, Beijing, China) was evaluated during volume-controlled ventilation.

Methods: Experiments were conducted in a multiplace hyperbaric chamber at 101, 152, 203, and 284 kPa (1.0, 1.5, 2.0 and 2.8 atmospheres absolute [atm abs]). With the ventilator in volume control ventilation (VCV) mode and connected to a test lung, comparison was made of the set tidal volume (VTset) versus delivered tidal volume (VT) and minute volume (MV) at VTset between 400 and 1,000 mL. Peak inspiratory pressure was also recorded. All measurements were made across 20 respiratory cycles.

Results: Across all ambient pressures and ventilator settings the difference between VTset and actual VT and between predicted MV and actual MV were small and clinicially insignificant despite reaching statistical significance. Predictably, Ppeak increased at higher ambient pressures. With VTset 1,000 mL at 2.8 atm abs the ventilator produced significantly greater VT, MV and Ppeak.

Conclusions: This new ventilator designed for use in hyperbaric environments performs well. It provides relatively stable VT and MV during VCV with VTset from 400 mL to 800 mL at ambient pressures from 1.0 to 2.8 atm abs, as well as VTset 1,000 mL at ambient pressures from 1.0 to 2.0 atm abs.

Introduction: Hyperbaric oxygen treatment (HBOT) has fourteen approved indications in the management of acute and chronic diseases in various medical specialties. However, lack of physician knowledge and exposure to hyperbaric medicine may hinder the ability of patients to access this treatment option for approved indications. We aimed to determine the prevalence and nature of HBOT-related learning objectives in Canadian undergraduate medical education programs.

Methods: Pre-clerkship and clerkship learning objectives from responding Canadian medical schools' curricula were reviewed. These were acquired through the school websites or by emailing the faculties. Descriptive statistics were used to summarise the number of hyperbaric medicine objectives taught in Canadian medical schools, and within each institution.

Results: Learning objectives from seven of the 17 Canadian medical schools were received and reviewed. From the curriculum of the responding schools, only one objective was found to be related to hyperbaric medicine. Hyperbaric medicine was absent from the other six schools' objectives.

Conclusions: Based on the responding Canadian medical schools, hyperbaric medicine objectives were mostly absent from undergraduate medical curricula. These findings illustrate a possible gap in HBOT education and the need for discussion regarding the design and implementation of HBOT educational initiatives in medical training.

Carbon monoxide (CO) poisoning can cause neurological complications such as movement disorders and cognitive impairment through hypoxic brain damage. Although peripheral neuropathy of the lower extremities is a known complication of CO poisoning, hemiplegia is very rare. In our case, a patient who developed left hemiplegia due to acute CO poisoning received early hyperbaric oxygen treatment (HBOT). The patient had left hemiplegia and anisocoria at the beginning of HBOT. Her Glasgow coma score was 8. A total of five sessions of HBOT at 243.2 kPa for 120 minutes were provided. At the end of the 5th session, the patient's hemiplegia and anisocoria were completely resolved. Her Glasgow coma score was 15. After nine months of follow-up, she continues to live independently with no sequelae, including delayed neurological sequelae. Clinicians should be aware that CO poisoning can (rarely) present with hemiplegia.

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.

Introduction: Hyperbaric chamber ventilation (HCV) refers to the intentional introduction of fresh gas, whether air, oxygen, or heliox, into a pressurised hyperbaric chamber in order to remove stale or otherwise compromised gas. The minimum required continuous HCV rate is usually determined by mathematical models derived from the contaminant mass balance within a well-stirred compartment. Non-uniform contaminant distribution patterns inside a hyperbaric chamber could emerge and invalidate the predictions of well-stirred models.

Methods: Contaminant distribution was investigated inside a clinical hyperbaric chamber with the aim of comparing well-stirred model predictions with the actual contaminant concentration measurements.

Results: Local ventilation effectiveness inside a clinical hyperbaric chamber may be compromised, leading to higher contaminant concentration values compared to the predictions of a mathematical model with a well-stirred assumption.

Conclusions: A well-stirred assumption in mathematical models is a useful simplification that allows reasonably accurate estimates of HCV requirements. However, local ventilation effectiveness values in a particular hyperbaric chamber might vary, with the potential for hazardous contaminant accumulation in under-ventilated zones.