Relationships between plasma lipids, proteins, surface tension and post-dive bubbles.

Decompression sickness (DCS) in divers is caused by bubbles of inert gas. When DCS occurs, most bubbles can be found in the venous circulation: venous gas emboli (VGE). Bubbles are thought to be stabilized by low molecular weight surfactant reducing the plasma-air surface tension (γ). Proteins may play a role as well. We studied the interrelations between these substances, γ and VGE, measured before and after a dry dive simulation. VGE of 63 dive simulations (21-msw/40-minute profile) of 52 divers was examined 40, 80, 120 and 160 minutes after surfacing (precordial Doppler method) and albumin, total protein, triglycerides, total cholesterol and free fatty acids were determined pre- and post-exposure. To manipulate blood plasma composition, half of the subjects obtained a fat-rich breakfast, while the other half got a fat-poor breakfast pre-dive. Eleven subjects obtained both. VGE scores measured with the precordial Doppler method were transformed to the logarithm of Kisman Integrated Severity Scores. With statistical analysis, including (partial) correlations, it could not be established whether γ as well as VGE scores are related to albumin, total protein or total cholesterol. With triglycerides and fatty acids correlations were also lacking, despite the fact that these compounds varied substantially. The same holds true for the paired differences between the two exposures of the 11 subjects. Moreover, no correlation between surface tension and VGE could be shown. From these findings and some theoretical considerations it seems likely that proteins lower surface tension rather than lipids. Since the findings are not in concordance with the classical surfactant hypothesis, reconsideration seems necessary.

Effect of hyperbaric oxygen on the growth and susceptibility of facultatively anaerobic bacteria and bacteria with oxidative metabolism to selected antibiotics.

Wild strains of Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis were tested in an experimental hyperbaric chamber to determine the possible effect of hyperbaric oxygen on the susceptibility of these strains to the antibiotics ampicillin, ampicillin + sulbactam, cefazolin, cefuroxime, cefoxitin, gentamicin, sulfamethoxazole + trimethoprim, colistin, oxolinic acid, ofloxacin, tetracycline, and aztreonam during their cultivation at 23 °C and 36.5 °C. Ninety-six-well inoculated microplates with tested antibiotics in Mueller-Hinton broth were cultured under standard incubator conditions (normobaric normoxia) for 24 h or in an experimental hyperbaric chamber (HAUX, Germany) for 24 h at 2.8 ATA of 100% oxygen (hyperbaric hyperoxia). The hyperbaric chamber was pressurised with pure oxygen (100%). Both cultures (normoxic and hyperoxic) were carried out at 23 °C and 36.5 °C to study the possible effect of the cultivation temperature. No significant differences were observed between 23 and 36.5 °C cultivation with or without the 2-h lag phase in Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis. Cultivation in a hyperbaric chamber at 23 °C and 36.5 °C with or without a 2-h lag phase did not produce significant changes in the minimum inhibitory concentration (MIC) of Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis. For the tested strains of Pseudomonas aeruginosa, the possible effect of hyperbaric oxygen on their antibiotic sensitivity could not be detected because the growth of these bacteria was completely inhibited by 100% hyperbaric oxygen at 2.8 ATA under all hyperbaric conditions tested at 23 °C and 36.5 °C. Subsequent tests with wild strains of pseudomonads, burkholderias, and stenotrophomonads not only confirmed the fact that these bacteria stop growing under hyperbaric conditions at a pressure of 2.8 ATA of 100% oxygen but also indicated that inhibition of growth of these bacteria under hyperbaric conditions is reversible.

COVID-19 infection prevention and control management during hyperbaric oxygen therapy: a best practice implementation project.

OBJECTIVE: This implementation project compared standard operating procedures, accepted preventive measures, and disinfection procedures between the initial stage of the COVID-19 pandemic (first wave: March 15 to May 31, 2020) and the later stages of the pandemic (second and third waves: September 1, 2020 to January 31, 2021). INTRODUCTION: This project sought to improve compliance with international evidence-based guidelines and clinical standards for the prevention and control of COVID-19 infection during hyperbaric oxygen therapy taking into account the conditions of the local hospital. METHODS: Guided by the JBI evidence implementation framework, seven evidence-based audit criteria were developed for the prevention and control of COVID-19 infection during hyperbaric oxygen therapy. A questionnaire was used to measure compliance in baseline and follow-up audits. RESULTS: Differences between the baseline and follow-up audits were noted for criteria 6 and 7. Criterion 6 increased from 0% to 100% as the hyperbaric facility was equipped with certified ultraviolet-C radiation for air disinfection during the later period, but this equipment was not available in the initial period of the pandemic. Criterion 7 dropped from 100% in the baseline audit to 0% in the follow-up audit because of a significant increase in the operational burden of the treatment capacity of the facility, which made it impossible to comply with the recommended distancing between patients. CONCLUSIONS: Differences were found in preventive measures, disinfection procedures, work organization, and approach to care strategy. The project objectives were met and the implementation strategies proved effective. Larger sample sizes would need be needed to confirm the reproducibility of the results.

The role of intestinal microbiota in the pathogenesis of colorectal carcinoma.

The symbiotic relationship between intestinal microbiota and the host is a major mechanism of prevention against the development of chronic and metabolic diseases. The intestinal microbiota provides several physiological functions of the organism from the creation of a natural functional barrier with a subsequent immunostimulatory activity up to affecting the energy metabolism of the host. Disruption of physiological intestinal microbiota is reported as one of the major etiological factors of initiation and progression of colorectal carcinoma (CRC). Chronic low-grade inflammation is associated with the development of CRC, through the production of inflammatory cytokines and reactive oxygen species. CRC occurs in association with high-protein and high-fat diets in combination with low-fiber intake. The problem of intestinal dysbiosis and oncological diseases is a multidisciplinary problem and it is necessary to focus on several fields of medicine such as public health, clinical pharmacology, and internal medicine. The aim of this review is describing the role of gut dysbiosis in pathogenesis of colorectal carcinoma.

Experimental use of flow cytometry to detect bacteria viability after hyperbaric oxygen exposure: Work in progress report.

INTRODUCTION: Hyperbaric oxygen treatment (HBOT), based on inhaling pure oxygen under elevated ambient pressure, is used as adjuvant intervention to promote healing in infected wounds. Despite extensive clinical evidence of beneficial effects of HBOT in soft tissue infections the mechanism of action remains to be elucidated. The aim of this study was to evaluate the use of flow cytometry as a novel method to assess the viability of pathogenic bacteria after hyperbaric oxygen (HBO) exposure. METHODS: Bacterial strains associated with soft tissues infections: Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus were exposed to oxygen at 2.8 atmospheres absolute (atm abs) (283.6 kPa) pressure for 45, 90, or 120 min, then stained with propidium iodide and thiazole orange and analysed by flow cytometry. RESULTS: Escherichia coli and Staphylococcus aureus showed no change in viability, nor morphology, the viability of Pseudomonas aeruginosa reduced in a dose-dependent manner and Klebsiella pneumoniae also showed dye uptake after HBO. CONCLUSIONS: These initial results, indicate diverse sensitivity of bacteria to HBO, and suggest that flow cytometry can be used to monitor viability and morphological changes triggered by HBO exposure in bacteria.

Effect of hyperbaric air on endotoxin from Bacteroides fragilis strains.

The aim of the project was to determine any effect of hyperbaric air on Bacteroides fragilis strains cultivated under hyperbaric conditions. Previously, it was hypothesized that there was a correlation between the presence of Bacteroides bacteria in patients preferring a meaty diet and cancer of the small intestine, and particularly of the large intestine and rectum. With respect to the fact that Bacteroides fragilis (BAFR) group are important producers of endotoxins, measurement and statistical evaluation of endotoxin production by individual strains of isolated Bacteroides species were used to compare bacteria isolated from various clinical samples from patients with colon and rectum cancer in comparison with strains isolated from other non-cancer diagnoses. Endotoxin production was proven by quantitative detection using the limulus amebocyte lysate (LAL) test in EU/mL. Production of endotoxins in these bacteria cultured under hyperbaric air conditions was higher than those strains cultured under normobaric anaerobic conditions. But these differences in endotoxin production were not statistically significant (t test with log-transformed data, p value = 0.0910). Based on a two-tier t test for lognormal data, it is possible to cautiously conclude that a statistically significant difference was found between endotoxin production by Bacteroides fragilis strains isolated from non-carcinoma diagnoses (strains (1-6) and strains isolated from colorectal carcinoma diagnoses (strains 7-8; Wilcoxon non-parametric test p = 0.0132; t test = 0.1110; t test with log-transformed data, p value = 0.0294).

Functional comparison between critical flicker fusion frequency and simple cognitive tests in subjects breathing air or oxygen in normobaria.

INTRODUCTION: Measurement of inert gas narcosis and its degree is difficult during operational circumstances, hence the need for a reliable, reproducible and adaptable tool. Although being an indirect measure of brain function, if reliable, critical flicker fusion frequency (CFFF) could address this need and be used for longitudinal studies on cortical arousal in humans. METHODS: To test the reliability of this method, the comparison between CFFF and three tests (Math-Processing Task, Trail-Making Task, and Perceptual Vigilance Task) from the Psychology Experiment Building Language battery (PEBL) were used to evaluate the effect of 10 minutes of 100% normobaric oxygen breathing on mental performance in 20 healthy male volunteers. RESULTS: Breathing normobaric oxygen significantly improved all but one of the measured parameters, with an increase of CFFF (117.3 ± 10.04% of baseline, P < 0.0001) and a significant reduction of time to complete in both the math-processing (2,103 ± 432.1 ms to 1,879 ± 417.5 ms, P = 0.0091) and trail-making tasks (1,992 ± 715.3 to 1,524 ± 527.8 ms, P = 0.0241). The magnitude of CFFF change and time to completion of both tests were inversely correlated (Pearson r = -0.9695 and -0.8731 respectively, P < 0.0001). The perceptual vigilance task did not show a difference between air and O2 (P > 0.4). CONCLUSIONS: The CFFF test provides an assessment of cognitive function that is similar to some tests from PEBL, but requires a less complicated set up and could be used under various environmental conditions including diving. Further research is needed to assess the combined effects of increased pressure and variations in inspired gas mixtures during diving.

Oxidative stress in breath-hold divers after repetitive dives.

INTRODUCTION: Hyperoxia causes oxidative stress. Breath-hold diving is associated with transient hyperoxia followed by hypoxia and a build-up of carbon dioxide (CO2), chest-wall compression and significant haemodynamic changes. This study analyses variations in plasma oxidative stress markers after a series of repetitive breath-hold dives. METHODS: Thirteen breath-hold divers were asked to perform repetitive breath-hold dives to 20 metres' depth to a cumulative breath-hold time of approximately 20 minutes over an hour in the open sea. Plasma nitric oxide (NO), peroxinitrites (ONOO⁻) and thiols (R-SH) were measured before and after the dive sequence. RESULTS: Circulating NO significantly increased after successive breath-hold dives (169.1 ± 58.26% of pre-dive values; P = 0.0002). Peroxinitrites doubled after the dives (207.2 ± 78.31% of pre-dive values; P = 0.0012). Thiols were significantly reduced (69.88 ± 19.23% of pre-dive values; P = 0.0002). CONCLUSION: NO may be produced by physical effort during breath-hold diving. Physical exercise, the transient hyperoxia followed by hypoxia and CO2 accumulation would all contribute to the increased levels of superoxide anions (O2²â»). Since interaction of O2²â» with NO forms ONOO⁻, this reaction is favoured and the production of thiol groups is reduced. Oxidative stress is, thus, present in breath-hold diving.

Repetitive paired stimulation of nasotrigeminal and peripheral chemoreceptor afferents cause progressive potentiation of the diving bradycardia.

Hallmarks of the mammalian diving response are protective apnea and bradycardia. These cardiorespiratory adaptations can be mimicked by stimulation of the trigeminal ethmoidal nerve (EN5) and reflect oxygen-conserving mechanisms during breath-hold dives. Increasing drive from peripheral chemoreceptors during sustained dives was reported to enhance the diving bradycardia. The underlying neuronal mechanisms, however, are unknown. In the present study, expression and plasticity of EN5-bradycardias after paired stimulation of the EN5 and peripheral chemoreceptors was investigated in the in situ working heart-brain stem preparation. Paired stimulations enhanced significantly the bradycardic responses compared with EN5-evoked bradycardia using submaximal stimulation intensity. Alternating stimulations of the EN5 followed by paired stimulation of the EN5 and chemoreceptors (10 trials, 3-min interval) caused a progressive and significant potentiation of EN5-evoked diving bradycardia. In contrast, bradycardias during paired stimulation remained unchanged during repetitive stimulation. The progressive potentiation of EN5-bradycardias was significantly enhanced after microinjection of the 5-HT(3) receptor agonist (CPBG hydrochloride) into the nucleus tractus solitarii (NTS), while the 5-HT(3) receptor antagonist (zacopride hydrochloride) attenuated the progressive potentiation. These results suggest an integrative function of the NTS for the multimodal mediation of the diving response. The potentiation or training of a submaximal diving bradycardia requires peripheral chemoreceptor drive and involves neurotransmission via 5-HT(3) receptor within the NTS.

Expression of histamine receptors and effect of histamine in the rat carotid body chemoafferent pathway.

Chemosensory information from peripheral arterial oxygen sensors in the carotid body is relayed by petrosal ganglion neurons to the respiratory networks in the medulla oblongata. Biogenic amines, including histamine, released from glomus (type I) cells of the carotid body are considered to be primary transmitters in hypoxic chemosensitivity. Immunocytochemistry at light-and electron-microscopical levels, and RT-PCR, revealed the expression of histamine receptors 1 and 3 as well as histidine decarboxylase in the rat carotid body glomus cells and petrosal ganglion neurons. Histamine receptors 1 and 3, but not histidine decarboxylase, were also observed in the ventrolateral, intermediate and commissural subnuclei of the nucleus tractus solitarii in the medulla oblongata. In order to examine the possible role of histamine in the afferent branch of the respiratory system, we applied histamine receptor 1 and 3 agonists to the carotid body, which caused a mildly increased phrenic nerve activity in a working heart-brainstem preparation. Moreover, microinjection of antagonists of histamine receptors 1 and 3 into the nucleus tractus solitarii caused significant changes in the inspiratory timing and the chemoreceptor response. Our data show that histamine acting via histamine receptors 1 and 3 plays an important neuromodulatory role in the afferent control of chemosensitivity.