Relative hypoxemia at depth during breath-hold diving investigated through arterial blood gas analysis and lung ultrasound.

Pulmonary gas exchange in breath-hold diving (BHD) consists of a progressive increase in arterial partial pressures of oxygen ([Formula: see text]) and carbon dioxide ([Formula: see text]) during descent. However, recent findings have demonstrated that [Formula: see text] does not consistently rise in all subjects. This study aimed at verifying and explaining [Formula: see text] derangements during BHD analyzing arterial blood gases and searching for pulmonary alterations with lung ultrasound. After ethical approval, 14 fit breath-hold divers were included. Experiments were performed in warm water (temperature: 31°C). We analyzed arterial blood gases immediately before, at depth, and immediately after a breath-hold dive to -15 m of fresh water (mfw) and -42 mfw. Signs of lung interstitial edema and atelectasis were searched simultaneously with a marinized lung ultrasound. In five subjects (-15 mfw) and four subjects (-42 mfw), the [Formula: see text] at depth seems to decrease instead of increasing. [Formula: see text] and lactate showed slight variations. At depth, no lung ultrasound alterations were seen except in one subject (hypoxemia and B-lines at -15 mfw; B-lines at the surface). Lung interstitial edema was detected in 3 and 12 subjects after resurfacing from -15 to -42 mfw, respectively. Two subjects developed hypoxemia at depth and a small lung atelectasis (a focal pleural irregularity of triangular shape, surrounded by thickened B-lines) after resurfacing from -42 mfw. Current experiments confirmed that some BH divers can experience hypoxemia at depth. The hypothesized explanation for such a discrepancy is lung atelectasis, which could not be detected in all subjects probably due to limited time available at depth.NEW & NOTEWORTHY During breath-hold diving, arterial partial pressure of oxygen ([Formula: see text]) and arterial partial pressure of carbon dioxide ([Formula: see text]) are believed to increase progressively during descent, as explained by theory, previous end-tidal alveolar gas measurements, and arterial blood gas analysis in hyperbaric chambers. Recent experiments in real underwater environment found a paradoxical [Formula: see text] drop at depth in some divers. This work confirms that some breath-hold divers can experience hypoxemia at depth. The hypothesized explanation for such a discrepancy is lung atelectasis, as suggested by lung ultrasound findings.

Development of a graphical user interface for automatic separation of human voice from Doppler ultrasound audio in diving experiments.

Doppler ultrasound (DU) is used in decompression research to detect venous gas emboli in the precordium or subclavian vein, as a marker of decompression stress. This is of relevance to scuba divers, compressed air workers and astronauts to prevent decompression sickness (DCS) that can be caused by these bubbles upon or after a sudden reduction in ambient pressure. Doppler ultrasound data is graded by expert raters on the Kisman-Masurel or Spencer scales that are associated to DCS risk. Meta-analyses, as well as efforts to computer-automate DU grading, both necessitate access to large databases of well-curated and graded data. Leveraging previously collected data is especially important due to the difficulty of repeating large-scale extreme military pressure exposures that were conducted in the 70-90s in austere environments. Historically, DU data (Non-speech) were often captured on cassettes in one-channel audio with superimposed human speech describing the experiment (Speech). Digitizing and separating these audio files is currently a lengthy, manual task. In this paper, we develop a graphical user interface (GUI) to perform automatic speech recognition and aid in Non-speech and Speech separation. This constitutes the first study incorporating speech processing technology in the field of diving research. If successful, it has the potential to significantly accelerate the reuse of previously-acquired datasets. The recognition task incorporates the Google speech recognizer to detect the presence of human voice activity together with corresponding timestamps. The detected human speech is then separated from the audio Doppler ultrasound within the developed GUI. Several experiments were conducted on recently digitized audio Doppler recordings to corroborate the effectiveness of the developed GUI in recognition and separations tasks, and these are compared to manual labels for Speech timestamps. The following metrics are used to evaluate performance: the average absolute differences between the reference and detected Speech starting points, as well as the percentage of detected Speech over the total duration of the reference Speech. Results have shown the efficacy of the developed GUI in Speech/Non-speech component separation.

Effect of Anesthetic Carrier Gas on In Vivo Circulation Times of Intravenously Administered Phospholipid Oxygen Microbubbles in Rats.

OBJECTIVE: For the treatment of tumor hypoxia, microbubbles comprising oxygen as a majority component of the gas core with a stabilizing shell may be used to deliver and release oxygen locally at the tumor site through ultrasound destruction. Previous work has revealed differences in circulation half-life in vivo for perfluorocarbon-filled microbubbles, typically used as ultrasound imaging contrast agents, as a function of anesthetic carrier gas. These differences in circulation time in vivo were likely due to gas diffusion as a function of anesthetic carrier gas, among other variables. This work has motivated studies to evaluate the effect of anesthetic carrier gas on oxygen microbubble circulation dynamics. METHODS: Circulation time for oxygen microbubbles was derived from ultrasound image intensity obtained during longitudinal kidney imaging. Studies were constructed for rats anesthetized on inhaled isoflurane with either pure oxygen or medical air as the anesthetic carrier gas. RESULTS: Results indicated that oxygen microbubbles were highly visible via contrast-specific imaging. Marked signal enhancement and duration differences were observed between animals breathing air and oxygen. Perhaps counterintuitively, oxygen microbubbles disappeared from circulation significantly faster when the animals were breathing pure oxygen compared with medical air. This may be explained by nitrogen counterdiffusion from blood into the bubble, effectively changing the gas composition of the core, as has been observed in perfluorocarbon core microbubbles. CONCLUSION: Our findings suggest that the apparent longevity and persistence of oxygen microbubbles in circulation may not be reflective of oxygen delivery when the animal is anesthetized breathing air.

An open-source framework for synthetic post-dive Doppler ultrasound audio generation.

Doppler ultrasound (DU) measurements are used to detect and evaluate venous gas emboli (VGE) formed after decompression. Automated methodologies for assessing VGE presence using signal processing have been developed on varying real-world datasets of limited size and without ground truth values preventing objective evaluation. We develop and report a method to generate synthetic post-dive data using DU signals collected in both precordium and subclavian vein with varying degrees of bubbling matching field-standard grading metrics. This method is adaptable, modifiable, and reproducible, allowing for researchers to tune the produced dataset for their desired purpose. We provide the baseline Doppler recordings and code required to generate synthetic data for researchers to reproduce our work and improve upon it. We also provide a set of pre-made synthetic post-dive DU data spanning six scenarios representing the Spencer and Kisman-Masurel (KM) grading scales as well as precordial and subclavian DU recordings. By providing a method for synthetic post-dive DU data generation, we aim to improve and accelerate the development of signal processing techniques for VGE analysis in Doppler ultrasound.

Volume 50: The UHM Journal celebrates a milestone with the publication of this issue.

As the UHMS observes the distinguished anniversary of the publication of 50 volumes of the Undersea and Hyperbaric Medicine Journal, two of our past editors take a look at the evolution of our flagship publications.

Long term quality of life outcomes following surgical resection alone for benign paediatric intracranial tumours.

PURPOSE: Survivors of paediatric intracranial tumours are at increased risk of psychosocial, neuro-developmental, and functional impairment. This study aimed to evaluate long-term health-related quality-of-life (HRQOL) outcomes in patients with benign paediatric brain tumours treated curatively with surgical resection alone. METHODOLOGY: This was a cross-sectional study of patients with benign paediatric intracranial tumours managed with surgery alone between 2000 and 2015. Eligible patients with a minimum of 5-years follow-up after surgery were identified. Validated health-related quality of life (HRQOL) questionnaires were administered: SF-36, QLQ-BN20, QLQ-C30 and PedsQL™. RESULTS: Twenty-three patients participated (median age at surgery 13 years; range 1-18; 12 male). The most common diagnosis was pilocytic astrocytoma (n = 15). Median time from surgery to participation was 11 years(range 6-19). Fourteen patients achieved A-level qualifications and two obtained an undergraduate degree. Twelve patients were employed, eight were studying and three were unemployed or volunteering. HRQOL outcomes demonstrated significant limitation from social functioning (p = 0.03) and cognitive functioning (p = 0.023) compared to the general population. Patients also experienced higher rates of loss of appetite (p = 0.009) and nausea and vomiting (p = 0.031). Ten patients were under transitional teenager and young-adult (TYA) clinic follow-up. TYA patients achieved higher levels of education (p = 0.014), were more likely to hold a driver's license (p = 0.041) compared to patients not followed-up through these services. CONCLUSIONS: Childhood brain-tumour survivors have a greater risk of developing psychological, neuro-cognitive and physical impairment. Early comprehensive assessment, specialist healthcare and TYA services are vital to support these patients.

Deep Learning-Based Venous Gas Emboli Grade Classification in Doppler Ultrasound Audio Recordings.

OBJECTIVE: Doppler ultrasound (DU) is used to detect venous gas emboli (VGE) post dive as a marker of decompression stress for diving physiology research as well as new decompression procedure validation to minimize decompression sickness risk. In this article, we propose the first deep learning model for VGE grading in DU audio recordings. METHODS: A database of real-world data was assembled and labeled for the purpose of developing the algorithm, totaling 274 recordings comprising both subclavian and precordial measurements. Synthetic data was also generated by acquiring baseline DU signals from human volunteers and superimposing laboratory-acquired DU signals of bubbles flowing in a tissue mimicking material. A novel squeeze-and-excitation deep learning model was designed to effectively classify recordings on the 5-class Spencer scoring system used by trained human raters. RESULTS: On the real-data test set, we show that synthetic data pretraining achieves average ordinal accuracy of 84.9% for precordial and 90.4% for subclavian DU which is a 24.6% and 26.2% increase over training with real-data and time-series augmentation only. The weighted kappa coefficients of agreement between the model and human ground truth were 0.74 and 0.69 for precordial and subclavian respectively, indicating substantial agreement similar to human inter-rater agreement for this type of data. CONCLUSION: The present work demonstrates the first application of deep-learning for DU VGE grading using a combination of synthetic and real-world data. SIGNIFICANCE: The proposed method can contribute to accelerating DU analysis for decompression research.

Presentation, management, and outcomes of cauda equina syndrome up to one year after surgery, using clinician and participant reporting: A multi-centre prospective cohort study.

Background: Cauda equina syndrome (CES) results from nerve root compression in the lumbosacral spine, usually due to a prolapsed intervertebral disc. Evidence for management of CES is limited by its infrequent occurrence and lack of standardised clinical definitions and outcome measures. Methods: This is a prospective multi-centre observational cohort study of adults with CES in the UK. We assessed presentation, investigation, management, and all Core Outcome Set domains up to one year post-operatively using clinician and participant reporting. Univariable and multivariable associations with the Oswestry Disability Index (ODI) and urinary outcomes were investigated. Findings: In 621 participants with CES, catheterisation for urinary retention was required pre-operatively in 31% (191/615). At discharge, only 13% (78/616) required a catheter. Median time to surgery from symptom onset was 3 days (IQR:1-8) with 32% (175/545) undergoing surgery within 48 h. Earlier surgery was associated with catheterisation (OR:2.2, 95%CI:1.5-3.3) but not with admission ODI or radiological compression. In multivariable analyses catheter requirement at discharge was associated with pre-operative catheterisation (OR:10.6, 95%CI:5.8-20.4) and one-year ODI was associated with presentation ODI (r = 0.3, 95%CI:0.2-0.4), but neither outcome was associated with time to surgery or radiological compression. Additional healthcare services were required by 65% (320/490) during one year follow up. Interpretation: Post-operative functional improvement occurred even in those presenting with urinary retention. There was no association between outcomes and time to surgery in this observational study. Significant healthcare needs remained post-operatively. Funding: DCN Endowment Fund funded study administration. Castor EDC provided database use. No other study funding was received.

Usability of mixed reality in awake craniotomy planning.

PURPOSE: This study aimed to describe our institutional use of a commercially available mixed reality viewer within a multi-disciplinary planning workflow for awake craniotomy surgery and to report an assessment of its usability. MATERIALS AND METHODS: Three Tesla MRI scans, including 32-direction diffusion tensor sequences, were reconstructed with BrainLab Elements auto-segmentation software. Magic Leap mixed reality viewer headsets were registered to a shared virtual viewing space to display image reconstructions. System Usability Scale was used to assess the usability of the mixed reality system. RESULTS: The awake craniotomy planning workflow utilises the mixed reality viewer to facilitate a stepwise discussion through four progressive anatomical layers; the skin, cerebral cortex, subcortical white matter tracts and tumour with surrounding vasculature. At each stage relevant members of the multi-disciplinary team review key operative considerations, including patient positioning, cortical and subcortical speech mapping protocols and surgical approaches to the tumour.The mixed reality system was used for multi-disciplinary awake craniotomy planning in 10 consecutive procedures over a 5-month period. Ten participants (2 Anaesthetists, 5 Neurosurgical trainees, 2 Speech therapists, 1 Neuropsychologist) completed System Usability Scale assessments, reporting a mean score of 71.5. Feedback highlighted the benefit of being able to rehearse important steps in the procedure, including patient positioning and anaesthetic access and visualising the testing protocol for cortical and subcortical speech mapping. CONCLUSIONS: This study supports the use of mixed reality for multidisciplinary planning for awake craniotomy surgery, with an acceptable degree of usability of the interface. We highlight the need to consider the requirements of non-technical, non-neurosurgical team members when involving mixed reality activities.

Effects of high-intensity interval training with hyperbaric oxygen.

Hyperbaric Oxygen (HBO2) has been proposed as a pre-conditioning method to enhance exercise performance. Most prior studies testing this effect have been limited by inadequate methodologies. Its potential efficacy and mechanism of action remain unknown. We hypothesized that HBO2 could enhance aerobic capacity by inducing mitochondrial biogenesis via redox signaling in skeletal muscle. HBO2 was administered in combination with high-intensity interval training (HIIT), a potent redox stimulus known to induce mitochondrial biogenesis. Aerobic capacity was tested during acute hypobaric hypoxia seeking to shift the limiting site of whole body V̇O2 from convection to diffusion, more closely isolating any effect of improved oxidative capacity. Healthy volunteers were screened with sea-level (SL) V̇O2peak testing. Seventeen subjects were enrolled (10 men, 7 women, ages 26.5±1.3 years, BMI 24.6±0.6 kg m-2, V̇O2peak SL = 43.4±2.1). Each completed 6 HIIT sessions over 2 weeks randomized to breathing normobaric air, "HIIT+Air" (PiO2 = 0.21 ATM) or HBO2 (PiO2 = 1.4 ATM) during training, "HIIT+HBO2" group. Training workloads were individualized based on V̇O2peak SL test. Vastus Lateralis (VL) muscle biopsies were performed before and after HIIT in both groups. Baseline and post-training V̇O2peak tests were conducted in a hypobaric chamber at PiO2 = 0.12 ATM. HIIT significantly increased V̇O2peak in both groups: HIIT+HBO2 31.4±1.5 to 35.2±1.2 ml kg-1·min-1 and HIIT+Air 29.0±3.1 to 33.2±2.5 ml kg-1·min-1 (p = 0.005) without an additional effect of HBO2 (p = 0.9 for interaction of HIIT x HBO2). Subjects randomized to HIIT+HBO2 displayed higher skeletal muscle mRNA levels of PPARGC1A, a regulator of mitochondrial biogenesis, and HK2 and SLC2A4, regulators of glucose utilization and storage. All other tested markers of mitochondrial biogenesis showed no additional effect of HBO2 to HIIT. When combined with HIIT, short-term modest HBO2 (1.4 ATA) has does not increase whole-body V̇O2peak during acute hypobaric hypoxia. (ClinicalTrials.gov Identifier: NCT02356900; https://clinicaltrials.gov/ct2/show/NCT02356900).

Facile Synthesis of Functionalised Hyperbranched Polymers for Application as Novel, Low Viscosity Lubricant Formulation Components.

A novel, previously unreported, method for synthesising hyperbranched (HB) materials is detailed. Their use as additives to produce lubricant formulations that exhibit enhanced levels of wear protection and improved low-temperature oil viscosity and flow is also reported. The lubricant formulations containing HB additives were found to exhibit both significantly lower viscosities and improved in-use film-forming properties than the current industry standard formulations. To achieve this, alkyl methacrylate oligomers (predominantly dimers and trimers) were synthesised using catalytic chain transfer polymerisation. These were then used as functional chain transfer agents (CTA) to control the polymerisation of divinyl benzene (DVB) monomers to generate highly soluble, high polydispersity HB polymers. The level of dimer/trimer purification applied was varied to define its influence on both these HB resultant structures and the resultant HB additives' performance as a lubricant additive. It was shown that, while the DVB acted as the backbone of the HB, the base oil solubility of the additive was imparted by the presence of the alkyl chains included in the structure via the use of the oligomeric CTAs.

Safety evaluation of carbon tetrafluoride as an inert hyperbaric breathing gas in Sprague-Dawley rats.

Carbon tetrafluoride (CF4) is an inert gas with higher molecular weight and lower water solubility than commonly used hyperbaric breathing gases. These inert gas properties decrease time required to decompress and avoid decompression sickness after deep dives. To assess CF4 toxicity, Sprague-Dawley rats were exposed to 8 atm absolute (ATA) air (10 males, 10 females) or 8 ATA 79% CF4/21% O2 (25 males, 25 females). Exposures were 30 min daily for 5 days. Rat behavior was normal throughout the testing period. There were no gross or microscopic pathology abnormalities following repeat dose exposure. Male body weight trends were similar between groups. Female body weight trends were 0.5 ± 0.8% day-1 for hyperbaric air exposure and - 0.2 ± 0.8% day-1 for hyperbaric CF4 exposure (P = 0.01) but remained within literature cited norms. Organ weights and hematologic indices remained within or near literature normal ranges. Clinical chemistry panels showed no signs of toxicity in renal or hepatic biomarkers. Polychromatic erythrocyte micronucleus frequency showed no chromosomal damage. Comet assay showed no DNA damage in lung tissue. Females exposed to CF4 had 2.5 times greater percent tail DNA in liver tissue than controls (P = 0.009). However this result remained within the normal range of local negative controls. A bacterial reverse mutation assay with exposure to 1 ATA 79% CF4/21% O2 for 72 h was nonmutagenic in four strains of Salmonella typhimurium and one strain of Escherichia coli. Overall, there was no evidence that CF4 caused organ toxicity or genetic toxicity.

Immersion-Induced Mitral Regurgitation: A Novel Risk Factor for Swimming-Induced Pulmonary Edema.

Immersion pulmonary edema, more commonly referred to as swimming-induced pulmonary edema (SIPE), is a well-documented condition believed to be a result of immersion physiologic condition that is characterized by a peripheral-to-central redistribution of blood volume. It disproportionally affects young, healthy athletes with no clinically overt cardiovascular or pulmonary conditions. We present four cases of healthy athletes with previously documented SIPE, who participated in Institutional Review Board-approved clinical studies that examined the pathophysiologic condition and prevention of SIPE. During standard recumbent echocardiography, trivial mitral regurgitation was observed in all four individuals. Acute exacerbation of their mitral regurgitation was observed during immersion with both immersed resting and immersed exercise echocardiography, contributing to the development of SIPE. These observations demonstrate that the occurrence of subclinical or trivial mitral valve regurgitation during dry rest is a novel risk factor for SIPE. We propose the use of immersion echocardiography as a useful investigative tool for otherwise healthy individuals with SIPE and no previously explainable cause.

The Dewey Monitor: Pulse Oximetry can Warn of Hypoxia in an Immersed Rebreather Diver in Multiple Scenarios.

Divers who wish to prolong their time underwater while carrying less equipment often use devices called rebreathers, which recycle the gas expired after each breath instead of discarding it as bubbles. However, rebreathers' need to replace oxygen used by breathing creates a failure mechanism that can and frequently does lead to hypoxia, loss of consciousness, and death. The purpose of this study was to determine whether a pulse oximeter could provide a useful amount of warning time to a diver with a rebreather after failure of the oxygen addition mechanism. Twenty-eight volunteer human subjects breathed on a mixed-gas rebreather in which the oxygen addition system had been disabled. The subjects were immersed in water in four separate environmental scenarios, including cold and warm water, and monitored using pulse oximeters placed at multiple locations. Pulse oximeters placed on the forehead and clipped on the nasal ala provided a mean of 32 s (±10 s SD) of warning time to divers with falling oxygen levels, prior to risk of loss of consciousness. These devices, if configured for underwater use, could provide a practical and inexpensive alarm system to warn of impending loss of consciousness in a manner that is redundant to the rebreather.

Blood gas analyses in hyperbaric and underwater environments: a systematic review.

Pulmonary gas exchange during diving or in a dry hyperbaric environment is affected by increased breathing gas density and possibly water immersion. During free diving, there is also the effect of apnea. Few studies have published blood gas data in underwater or hyperbaric environments: this review summarizes the available literature and was used to test the hypothesis that arterial Po2 under hyperbaric conditions can be predicted from blood gas measurement at 1 atmosphere assuming a constant arterial/alveolar Po2 ratio (a:A). A systematic search was performed on traditional sources including arterial blood gases obtained on humans in hyperbaric or underwater environments. The a:A was calculated at 1 atmosphere absolute (ATA). For each condition, predicted arterial partial pressure of oxygen ([Formula: see text]) at pressure was calculated using the 1 ATA a:A, and the measured [Formula: see text] was plotted against the predicted value with Spearman correlation coefficients. Of 3,640 records reviewed, 30 studies were included: 25 were reports describing values obtained in hyperbaric chambers, and the remaining were collected while underwater. Increased inspired O2 at pressure resulted in increased [Formula: see text], although underlying lung disease in patients treated with hyperbaric oxygen attenuated the rise. [Formula: see text] generally increased only slightly. In breath-hold divers, hyperoxemia generally occurred at maximum depth, with hypoxemia after surfacing. The a:A adequately predicted the [Formula: see text] under various conditions: dry (r = 0.993, P < 0.0001), rest versus exercise (r = 0.999, P < 0.0001), and breathing mixtures (r = 0.995, P < 0.0001). In conclusion, pulmonary oxygenation under hyperbaric conditions can be reliably and accurately predicted from 1 ATA a:A measurements.