Breathing Gas Research Articles

Validation of a sensor system for the measurement of breath ammonia using selected-ion flow-tube mass spectrometry

The measurement of trace breath gases is of growing interest for its potential to provide non-invasive physiological information in health and disease. While instrumental techniques such as selected-ion flow-tube mass spectrometry (SIFT-MS) can achieve this, these are less suitable for clinical application. Sensitive sensor-based systems for breath ammonia could be more widely deployed, but have proven challenging to develop. This work demonstrates the sequential analytical validation of an electrochemical impedance-based sensor system for the measurement of ammonia in breath using SIFT-MS. Qualitative and relative responses between the two methods were comparable, although there were consistent differences in absolute concentration. When tested in artificial breath ammonia, sensors had a relative impedance sensitivity of 3.43 × 10-5ppbv-1for each breath in the range of 249-1653 ppbv (r2= 0.87,p< 0.05). When correlated with SIFT-MS using human breath (n= 14), ammonia was detected in the range of 100-700 ppbv (r= 0.78,p< 0.001), demonstrating acceptable sensitivity, reproducibility and dynamic range for clinical application.

Evaluations of a Cutaneous Wound Healing Model Using Oxygen Enhanced - Dynamic Contrast Enhanced Photoacoustic Imaging (OE-DCE PAI).

Preclinical models of cutaneous wound healing can be useful for improving clinical wound care. Oxygen Enhanced Photoacoustic imaging (OE PAI) can measure oxygenation, and Dynamic Contrast Enhanced (DCE) PAI can measure vascular perfusion. We investigated how a combined OE-DCE PAI protocol can measure vascular oxygenation and perfusion to a cutaneous healing model. We developed a cutaneous "punch" wound model and photographed the wounds to track healing for 9 days. We performed OE-DCE PAI on Day 0, 3, 6, and 9. OE PAI was performed with 21% O2 and 100% O2 breathing gases to measure oxyhemoglobin (HbO2), deoxyhemoglobin (Hb), total hemoglobin (HbT), and oxygen saturation (%sO2), along with changes in these parameters caused by a change in breathing gas (ΔHb, ΔHbO2, ΔHbT, ΔsO2). To perform DCE PAI, indocyanine green (ICG) was administered intravenously while monitoring the PAI signal for 10min as the agent washed through the wound area, which was used to evaluate the wash-out rate. The average wound size was significantly smaller only by Day 6. For comparison, OE PAI measured a significant increase in HbO2, Hb, HbT, and %sO2 immediately after creating the wound, which significantly decreased by Day 3 and continued to decrease towards values for normal tissue by Day 9. The vascular wash-out rate significantly increased by Day 3, and continued to increase during the healing process. Notably, the wash-out rate can be assessed at a single PAI absorbance wavelength and by simply comparing signal amplitudes without advanced analysis, which may facilitate clinical translation. OE-DCE PAI can monitor significant changes in vascular perfusion and oxygenation prior to significant changes in cutaneous wound size. These results establish OE-DCE PAI as a tool for future pre-clinical wound healing studies and eventual clinical translation.

Design and Corrosion Resistance Performance of Nano-Multilayer Coatings for the Protection of Breathing Gas Cylinders Used in Diving

Seamless gas cylinders for diving exhibit excellent low-temperature impact performance, lightweight characteristics, and good corrosion resistance, making them widely applicable in underwater activities. However, during use, the peeling of paint or corrosion on the surface of these cylinders poses a significant threat to their safety. In this study, environmentally friendly arc ion plating technology was used to deposit TiBN, CrAlN, and nano-multilayer coatings of CrAlN/TiBN. The surface morphology, tribological properties, and corrosion resistance of these coatings were investigated. The results indicated that both CrAlN and CrAlN/TiBN coatings possess fewer droplets, pinholes, and pits, and the cross-section of the CrAlN/TiBN coating exhibits a denser structure. The preferred orientation for TiBN was identified as TiB2 (101), while that for CrAlN was Cr(Al)N (200), with the preferred orientation for CrAlN/TiBN being TiB2 (101). The friction measurements revealed that the lowest coefficient was observed in the CrAlN/TiBN coating (0.489), followed by CrAlN (0.491) and then TiBN (0.642). Electrochemical tests conducted in artificial seawater demonstrated that the self-corrosion potential was highest for the CrAlN/TiBN coating, followed by CrAlN and lastly TiBN. The developed TiBN-based nano-multilayer coatings hold substantial application value in protecting seamless gas cylinders used in diving.

Optimization of upper respiratory tract cancer diagnosis method based on exhaled breath gas analysis

Introduction. Head and neck tumors comprise about 7 % of all malignant neoplasms. In the head and neck area, tumors are usually located on the tongue (25–40 %) and floor of mouth (15–20 %). In the majority of cases, diagnosis, especially at early disease stages, is based on clinical and histopathological evaluation of tumor process. However, recently development and implementation of non-invasive techniques of early diagnosis of upper respiratory tract tumors through detection of pathognomonic volatile tumor markers in the exhaled air has become topical.Aim. To evaluate diagnostic accuracy of sensory gas analysis device and artificial neural network for examination of exhaled gas samples from patients with oropharyngeal, laryngeal, laryngopharyngeal cancer and to establish the optimal conditions for sampling.Materials and methods. The study included 28 patients with oropharyngeal, laryngeal, laryngopharyngeal cancers and 25 healthy volunteers. The proposed technique is based on analysis of samples of exhaled gas from the studied individuals using a diagnostic device developed by the authors. The device detects volatile compounds in the exhaled air using a set of semiconductor sensors with subsequent analysis by a neural network. The exhaled air was sampled using two methods: in the morning in the fasted state before daily hygienic procedures and physical activity (prepared samples) and in the context of everyday life, nutrition and hygiene without restrictions before sampling (non-prepared samples).Results. Based on the signals from the sensors, the neural network classified and detected patients with malignant tumors. Accuracy of the prepared samples from healthy volunteers and patients with oropharyngeal, laryngeal, laryngopharyngeal cancers was 79.17 %, of non-prepared – 84.09 %.Conclusion. High diagnostic accuracy of the developed technique of non-invasive diagnosis of malignant tumors of the oropharyngeal, laryngeal, laryngopharyngeal areas using exhaled air samples which does not require special preparation of the studied samples was demonstrated.

MoSe2-Layered Nanosheet Decorated SnO2 Hollow Nanofiber-Based Highly Sensitive and Selective Room Temperature H2S Gas Sensor.

In this work, we successfully demonstrated a MoSe2@SnO2 nanocomposite-based room temperature H2S gas sensor. A sensing mechanism was proposed based on experimental results and density functional theory calculations. The FESEM micrographs of the heterostructure formed by hydrothermally grown MoSe2-layered nanosheets and SnO2-hollow nanofiber result in a high surface area for H2S gas adsorption. On exposure to calcination, the electro-spun PVP/SnO2 nanofiber undergoes the Kirkendall phenomenon, resulting in 94.6 nm thick hollow nanofibers. The combination of TMD@SMO shows an abundance of charge transfer, resulting in an excellent response toward H2S gas. The MoSe2@SnO2 detects a low concentration of 500 ppb with a relative response of ∼19.9% at room temperature (RT). The simulation, using density functional theory (DFT), discloses that the adsorption energies ranged from -0.3645 to -0.5193 eV, indicating reduced bond lengths and significant H2S interactions. The sensor proves an excellent sensitivity toward H2S gas, ranging from 100 ppm to 500 ppb, with a LoD of ∼15 ppb at RT. As the sensor worked at RT with accuracy and reliability, consistent performance was observed upon exposure to various humidity levels, making it suitable for exhaled breath gas sensors. The sensor, as developed, also exhibited a good selectivity toward H2S gas in contrast to other gases as well as stability and longevity over time.

Machine learning-based phenogroups and prediction model in patients with functional gastrointestinal disorders to reveal distinct disease subsets associated with gas production.

Symptom-based subtyping for functional gastrointestinal disorders (FGIDs) has limited value in identifying underlying mechanisms and guiding therapeutic strategies. Small intestinal dysbiosis is implicated in the development of FGIDs. We tested if machine learning (ML) algorithms utilizing both gastrointestinal (GI) symptom characteristics and lactulose breath tests could provide distinct clusters. This was a prospective cohort study. We performed lactulose hydrogen methane breath tests and hydrogen sulfide breath tests in 508 patients with GI symptoms. An unsupervised ML algorithm was used to categorize subjects by integrating GI symptoms and breath gas characteristics. Generalized Estimating Equation (GEE) models were used to examine the longitudinal associations between cluster patterns and breath gas time profiles. An ML-based prediction model for identifying excessive gas production in FGIDs patients was developed and internal validation was performed. FGIDs were confirmed in 300 patients. K-means clustering identified 4 distinct clusters. Cluster 2, 3, and 4 showed enrichments for abdominal distention and diarrhea with a high proportion of excessive gas production, whereas Cluster 1 was characterized by moderate lower abdominal discomforts with the most psychological complaints and the lowest proportion of excessive gas production. GEE models showed that breath gas concentrations varied among different clusters over time. We further sought to develop an ML-based prediction model to determine excessive gas production. The model exhibited good predictive capabilities. ML-based phenogroups and prediction model approaches could provide distinct FGIDs subsets and efficiently determine FGIDs subsets with greater gas production, thereby facilitating clinical decision-making and guiding treatment.

Normobaric Hypoxia Symptom Recognition in Three Training Sessions

INTRODUCTION: Hypoxia training is mandatory for military pilots, but variability in hypoxia symptoms challenges the training. In a previous study we showed that 64% of pilots recognized hypoxia faster in their second normobaric hypoxia session conducted 2.4 yr after the first. Our aim here was to evaluate whether a third session conducted 5.0 yr after the first would provide further benefit. METHODS: This study was conducted under normobaric conditions in a tactical F/A-18C Hornet simulator in three sessions in which the pilots performed visual identification missions and breathed 21% oxygen in nitrogen. The breathing gas was changed to a hypoxic mixture containing either 8%, 7%, or 6% oxygen in nitrogen without the pilot’s knowledge. Data were collected from 102 military pilots. The primary outcome was the time taken for initial identification of hypoxia symptoms. RESULTS: Hypoxia symptoms were recognized on average in the first session in 8% oxygen in 100 s, 7% oxygen in 90 s, and 6% oxygen in 78 s; in the second in 87 s, 80 s, and 71 s, respectively; and in the third in 79 s, 67 s, and 64 s, respectively. In 2 sessions 20 pilots and in each 3 training sessions 3 pilots had slow recognition times. DISCUSSION: Hypoxia symptom recognition improved the further the repeated normobaric hypoxia training went. More emphasis should be put on the 23% group of slow hypoxia symptom recognizers and more customized hypoxia training for them should be offered. Leinonen AM, Varis NO, Kokki HJ, Leino TK. Normobaric hypoxia symptom recognition in three training sessions. Aerosp Med Hum Perform. 2024; 95(10):758–764.

S730 The Use of Non-Fasting Breath Gas Levels to Predict Response to a FODMAP Restricted Diet

S730 The Use of Non-Fasting Breath Gas Levels to Predict Response to a FODMAP Restricted Diet

S830 Comparison of Weekday and Weekend Dietary, Symptom, and Breath Gas Profiles in Adults With GI Symptoms

S830 Comparison of Weekday and Weekend Dietary, Symptom, and Breath Gas Profiles in Adults With GI Symptoms

A review of nutritional recommendations for scuba divers.

Scuba diving is an increasingly popular activity that involves the use of specialized equipment and compressed air to breathe underwater. Scuba divers are subject to the physiological consequences of being immersed in a high-pressure environment, including, but not limited to, increased work of breathing and kinetic energy expenditure, decreased fluid absorption, and alteration of metabolism. Individual response to these environmental stressors may result in a differential risk of decompression sickness, a condition thought to result from excess nitrogen bubbles forming in a diver's tissues. While the mechanisms of decompression sickness are still largely unknown, it has been postulated that this response may further be influenced by the diver's health status. Nutritional intake has direct relevancy to inflammation status and oxidative stress resistance, both of which have been associated with increased decompression stress. While nutritional recommendations have been determined for saturation divers, these recommendations are likely overly robust for recreational divers, considering that the differences in time spent under pressure and the maximum depth could result nonequivalent energetic demands. Specific recommendations for recreational divers remain largely undefined. This narrative review will summarize existing nutritional recommendations and their justification for recreational divers, as well as identify gaps in research regarding connections between nutritional intake and the health and safety of divers. Following recommendations made by the Institute of Medicine and the Naval Medical Research Institute of Bethesda, recreational divers are advised to consume ~170-210 kJ·kg-1 (40-50 kcal·kg-1) body mass, depending on their workload underwater, in a day consisting of 3 hours' worth of diving above 46 msw. Recommendations for macronutrient distribution for divers are to derive 50% of joules from carbohydrates and less than 30% of joules from fat. Protein consumption is recommended to reach a minimum of 1 g of protein·kg-1 of body mass a day to mitigate loss of appetite while meeting energetic requirements. All divers should take special care to hydrate themselves with an absolute minimum of 500 ml of fluid per hour for any dive longer than 3 hours, with more recent studies finding 0.69 liters of water two hours prior to diving is most effective to minimize bubble loads. While there is evidence that specialized diets may have specific applications in commercial or military diving, they are not advisable for the general recreational diving population considering the often extreme nature of these diets, and the lack of research on their effectiveness on a recreational diving population. Established recommendations do not account for changes in temperature, scuba equipment, depth, dive time, work of breathing, breathing gas mix, or individual variation in metabolism. Individual recommendations may be more accurate when accounting for basal metabolic rate and physical activity outside of diving. However, more research is needed to validate these estimates against variation in dive profile and diver demographics.

Accelerating the Diagnosis of Pandemic Infection Based on Rapid Sampling Algorithm for Fast-Response Breath Gas Analyzers.

This paper presents a novel technique for extracting the alveolar part of human breath. Gas exchange occurs between blood and inhaled air in the alveoli, which is helpful in medical diagnostics based on breath analysis. Consequently, the alveolar portion of the exhaled air contains specific concentrations of endogenous EVOC (exogenous volatile organic compound), which, among other factors, depend on the person's health condition. As this part of the breath enables the screening for diseases, accurate sample collection for testing is crucial. Inaccurate sampling can significantly alter the composition of the specimen, alter the concentration of EVOC (biomarkers) and adversely affect the diagnosis. Furthermore, the volume of alveolar air is minimal (usually <350 mL), especially in the case of people affected by respiratory system problems. For these reasons, precise sampling is a key factor in the effectiveness of medical diagnostic systems. A new technique ensuring high accuracy and repeatability is presented in the article. It is based on analyzing the changes in carbon dioxide concentration in human breath using a fast and compensated non-dispersive infrared (NDIR) sensor and the simple moving adjacent average (SMAA) algorithm. Research has shown that this method accurately identifies exhalation phases with an uncertainty as low as 20 ms. This provides around 350 ms of breath duration for carrying out additional stages of the diagnostic process using various types of analyzers.

A Prototype of Graphene E-Nose for Exhaled Breath Detection and Label-Free Diagnosis of Helicobacter Pylori Infection.

Helicobacter pylori (HP), a common microanaerobic bacteria that lives in the human mouth and stomach, is reported to infect ≈50% of the global population. The current diagnostic methods for HP are either invasive, time-consuming, or harmful. Therefore, a noninvasive and label-free HP diagnostic method needs to be developed urgently. Herein, reduced graphene oxide (rGO) is composited with different metal-based materials to construct a graphene-based electronic nose (e-nose), which exhibits excellent sensitivity and cross-reactive response to several gases in exhaled breath (EB). Principal component analysis (PCA) shows that four typical types of gases in EB can be well discriminated. Additionally, the potential of the e-nose in label-free detection of HP infection is demonstrated through the measurement and analysis of EB samples. Furthermore, a prototype of an e-nose device is designed and constructed for automatic EB detection and HP diagnosis. The accuracy of the prototype machine integrated with the graphene-based e-nose can reach 92% and 91% in the training and validation sets, respectively. These results demonstrate that the highly sensitive graphene-based e-nose has great potential for the label-free diagnosis of HP and may become a novel tool for non-invasive disease screening and diagnosis.

Hypoxic irreversible brain cells damage, associated risk factors and antihypoxants

It is reported that in the final stage of many diseases the immediate cause of biological death in humans and warm-blooded animals is hypoxic irreversible damage to brain cells. This explains the fact that to prevent biological death in all critical conditions without exception, inhalation with breathing gases containing oxygen has long been successfully used. This is also why oxygenation of the blood is considered one of the main conditions for preserving human life in all critical situations and forms the basis of emergency medical care in the intensive care unit. However, inhalation of oxygen gas and increasing blood oxygen saturation should be carried out as early as possible, and more precisely - before the onset of the stage of hypoxic irreversible damage in brain cells. The fact is that after the onset of irreversible damage brain cells die even in the presence of oxygen. In this connection, the mechanisms of adaptation of the organism to oxygen deficiency play a great role for longer preservation of brain cells viability and human life in conditions of hypoxemia. In order to increase resistance to hypoxemia, antihypoxants are traditionally used. But they can preserve the viability of brain cells not always, but only if they are introduced into the body before the onset of hypoxic irreversible damage to brain cells and in the case of unused reserves of adaptation to hypoxemia in the body. Risk factors of hypoxic irreversible damage of brain cells are indicated, among which excessively long duration of hypoxemia and hyperthermia are emphasized. It is shown that the most important circumstance for the development of hypoxic irreversible damage of brain cells is not so much the degree of hypoxemia as the degree of hypoxia of brain tissue and its duration, which exceeds the period of human resistance to hypoxia. It has been shown that human resistance to hypoxia can be assessed using the Stange test. It has been reported that fever and local cerebral hyperthermia decrease, and hibernation and local cerebral hypothermia increase, the resistance of brain cells to hypoxia. In this regard, recommendations not only to eliminate fever and local inflammatory processes in the head, but also recommendations to reduce brain temperature are highly appropriate to improve resistance to hypoxia. It is pointed out that among the methods of local therapeutic hypothermia, targeted temperature management is the most advanced. In addition, it is reported that in recent years a new group of promising antihypoxants - alkaline solutions of hydrogen peroxide - has been created. It is shown that hydrogen peroxide is able to decompose very quickly into water and oxygen gas under the action of catalase, which is found in all tissues. The peculiarities of using alkaline solutions of hydrogen peroxide as antihypoxants we all have to study in the future.

Validation of a Hand-Held Point-of-Care Device to Measure Breath Hydrogen and Its Utility in Detecting Response to Antibiotic Treatment.

Breath testing for small intestinal bacterial overgrowth (SIBO) is typically performed using clinic-based equipment or single-use test kits. This study aimed to evaluate the utility of a portable, point-of-care breath analysis device (AIRE®, FoodMarble) in patients suspected to have SIBO. A technical assessment including a comparison to existing mail-in kits was first performed. Then, postprandial breath hydrogen levels of patients before and after antibiotic treatment were gathered and compared to levels seen in a healthy cohort. For the comparison, 50 patients suspected of having SIBO were provided with an AIRE device and performed concurrent LHBTs at-home with a mail-in breath test kit. For the postprandial analysis, twenty-four patients with chronic GI symptoms measured their postprandial hydrogen for 7days prior to antibiotic treatment and for 7days after treatment. 10 healthy controls also measured their postprandial hydrogen for 7days. Substantial agreement was demonstrated between AIRE and the mail-in kits for the performance of lactulose hydrogen breath tests (κ = 0.8). Prior to treatment, patients had significantly greater daily postprandial hydrogen than healthy controls (p < 0.001). The mean postprandial hydrogen of patients reduced significantly after treatment (p < 0.001). Measuring postprandial hydrogen shows potential as a means of differentiating patients with chronic GI symptoms from healthy controls and may be useful in monitoring patients before, during, and after treatment. Future studies could help determine if pre-treatment breath gas levels are predictive of response to antibiotic treatment.

Development of polyimide nanofiber aerogels with a 3D multi-level pore structure: A new sensor for colorimetric detection of breath acetone

Polyimide nanofiber aerogels loaded with thymol blue and hydroxylamine sulfate (TB-HAS@PI NFAs) were synthesized and employed as a novel sensor for colorimetric detection of breath acetone (BrAce). The enhancement of 3D multi-level pore structure of TB-HAS@PI NFAs for sensing performance was elucidated through systematical characterization results. Because the designed sensing system relied on the specific reaction of HAS with acetone, TB-HAS@PI NFAs exhibited a more sensitive response ability to acetone, ensuring that the colorimetric sensing detection will not be interfered by other coexisting gas in exhaled breath. Moreover, the sensor demonstrated a rapid response, with color changes quantitatively measured within 30 s of exposure to acetone gas. Importantly, the feasibility and accuracy of established method were confirmed through comparison with GC–MS. This research provided a promising strategy for daily health management of healthy people and diabetics.

Methane gas in breath test is associated with non-alcoholic fatty liver disease

Although the associations between a patient’s body mass index (BMI) and metabolic diseases, as well as their breath test results, have been studied, the relationship between breath hydrogen/methane levels and metabolic diseases needs to be further clarified. We aimed to investigate how the composition of exhaled breath gases relates to metabolic disorders, such as diabetes mellitus, dyslipidemia, hypertension, and nonalcoholic fatty liver disease (NAFLD), and their key risk factors. An analysis was performed using the medical records, including the lactulose breath test (LBT) data of patients who visited the Ajou University Medical Center, Suwon, Republic of Korea, between January 2016 and December 2021. The patients were grouped according to four different criteria for LBT hydrogen and methane levels. Of 441 patients, 325 (72.1%) had positive results for methane only (hydrogen < 20 parts per million [ppm] and methane ⩾ 3 ppm). BMIs and NAFLD prevalence were higher in patients with only methane positivity than in patients with hydrogen and methane positivity (hydrogen ⩾ 20 ppm and methane ⩾ 3 ppm). According to a multivariate analysis, the odds ratio of only methane positivity was 2.002 (95% confidence interval [CI]: 1.244–3.221, P = 0.004) for NAFLD. Our results demonstrate that breath methane positivity is related to NAFLD and suggest that increased methane gas on the breath tests has the potential to be an easily measurable biomarker for NAFLD diagnosis.

Stability of selected exhaled breath volatiles stored in Tenax® TA adsorbent tubes at −80 °C

Preservation of the breath sample integrity during storage and transport is one of the biggest challenges in off-line exhaled breath gas analysis. In this context, adsorbent tubes are frequently used as storage containers for use with analytical methods employing gas chromatography with mass spectrometric detection. The key objective of this short communication is to provide data on the recovery of selected breath volatiles from Tenax® TA adsorbent tubes that were stored at −80 °C for up to 90 d. For this purpose, an Owlstone Medical’s ReCIVA® Breath Sampler was used for exhaled breath collection. The following fifteen compounds, selected to cover a range of chemical properties, were monitored for their stability: isoprene, n-heptane, n-nonane, toluene, p-cymene, allyl methyl sulfide, 1-(methylthio)-propane, 1-(methylthio)-1-propene, α-pinene, DL-limonene, β-pinene, γ-terpinene, 2-pentanone, acetoin and 2,3 butanedione. All compounds, but one (acetoin), were found to be stable during the first 4 weeks of storage (recovery within ± 2 × RSD). Furthermore, n-nonane was stable during the whole of the investigated period.

Advanced high pressure hyperbaric techniques in tunnelling

ABSTRACT Lamont D, Colvin A, Heili A, Ridley T, Slocombe R, Wendling J. Advanced high pressure hyperbaric techniques in tunnelling. Undersea Hyperb Med. 2024 Second Quarter; 51(2):159-171. Work in compressed air and diving are both occupational activities that have been around since the mid- 19th century, and those undertaking their work under elevated pressure. Meeting the demand to go to “higher pressure for longer” in tunneling has lagged in diving, but both activities have found it necessary to adopt mixed gas breathing and saturation exposure techniques. This paper explains how work in hyperbaric conditions at high pressure is undertaken in tunneling and is illustrated by the hyperbaric activity likely to be involved in constructing a large-diameter road tunnel below a body of water such as an estuary. It also explores the practical differences between work in compressed air and diving.

Relative Severity of Human Performance Decrements Recorded in Rapid vs. Gradual Decompression.

INTRODUCTION: Cabin decompression presents a threat in high-altitude-capable aircraft. A chamber study was performed to compare effects of rapid (RD) vs. gradual decompression and gauge impairment at altitude with and without hypoxia, as well as to assess recovery.METHODS: There were 12 participants who completed RD (1 s) and Gradual (3 min 12 s) ascents from 2743-7620 m (9000-25000 ft) altitude pressures while breathing air or 100% O₂. Physiological indices included oxygen saturation (SPo₂), heart rate (HR), respiration, end tidal O₂ and CO₂ partial pressures, and electroencephalography (EEG). Cognition was evaluated using SYNWIN, which combines memory, arithmetic, visual, and auditory tasks. The study incorporated ascent rate (RD, gradual), breathing gas (air, 100% O₂) and epoch (ground-level, pre-breathe, ascent-altitude, recovery) as factors.RESULTS: Physiological effects in hypoxic "air" ascents included decreased SPo₂ and end tidal O₂ and CO₂ partial pressures (hypocapnia), with elevated HR and minute ventilation (<mml:math id="im1" display="inline"><mml:mrow><mml:mover><mml:mtext>V</mml:mtext><mml:mo>˙</mml:mo></mml:mover></mml:mrow></mml:math>E); SPo₂ and HR effects were greater after RD (-7.3% lower and +10.0 bpm higher, respectively). HR and <mml:math id="im2" display="inline"><mml:mrow><mml:mover><mml:mtext>V</mml:mtext><mml:mo>˙</mml:mo></mml:mover></mml:mrow></mml:math>E decreased during recovery. SYNWIN performance declined during ascent in air, with key metrics, including composite score, falling further (-75% vs. -50%) after RD. Broad cognitive impairment was not recorded on 100% O₂, nor in recovery. EEG signals showed increased slow-wave activity during hypoxia.DISCUSSION: In hypoxic exposures, RD impaired performance more than gradual ascent. Hypobaria did not comprehensively impair performance without hypoxia. Lingering impairment was not observed during recovery, but HR and <mml:math id="im3" display="inline"><mml:mrow><mml:mover><mml:mtext>V</mml:mtext><mml:mo>˙</mml:mo></mml:mover></mml:mrow></mml:math>E metrics suggested compensatory slowing following altitude stress. Participants' cognitive strategy shifted as hypoxia progressed, with efficiency giving way to "satisficing," redistributing effort to easier tasks.Beer J, Mojica AJ, Blacker KJ, Dart TS, Morse BG, Sherman PM. Relative severity of human performance decrements recorded in rapid vs. gradual decompression. Aerosp Med Hum Perform. 2024; 95(7):353-366.

RESPIRATORY GASES USED IN PROFESSIONAL DIVING

An important role in the conception, design, manufacture and operation of underwater breathing apparatuses is played by the breathing gases used in these apparatuses. The type of breathing gas used is imposed by the type of diving device used and the diving technology adopted. For the correct choice of breathing gases in the various underwater breathing apparatuses and for the precise establishment of the diving technology, it is necessary to know in detail the physical characteristics of the gases used.