Dysbarism: An Overview of an Unusual Medical Emergency

Dysbarism is a general term which includes the signs and symptoms that can manifest when the body is subject to an increase or a decrease in the atmospheric pressure which occurs either at a rate or duration exceeding the capacity of the body to adapt safely. In the following review, we take dysbarisms into account for our analysis. Starting from the underlying physical laws, we will deal with the pathologies that can develop in the most frequently affected areas of the body, as the atmospheric pressure varies when acclimatization fails. Manifestations of dysbarism range from itching and minor pain to neurological symptoms, cardiac collapse, and death. Overall, four clinical pictures can occur: decompression illness, barotrauma, inert gas narcosis, and oxygen toxicity. We will then review the clinical manifestations and illustrate some hints of therapy. We will first introduce the two forms of decompression sickness. In the next part, we will review the barotrauma, compression, and decompression. The last three parts will be dedicated to gas embolism, inert gas narcosis, and oxygen toxicity. Such an approach is critical for the effective treatment of patients in a hostile environment, or treatment in the emergency room after exposure to extreme physical or environmental factors.

Possibilities of ultrasound methods in the diagnosis of decompression sickness

Aim of the work: to conduct a comparative analysis of methods of ultrasound examination of the right heart with audio and visual indication of intravascular decompression gas formation in divers after diving.Materials and methods. An examination of the right heart in divers after 152 man-descents was carried out. Intravascular decompression gas production was assessed by ultrasound using sound location based on the Doppler effect and transthoracic two-dimensional echocardiography.Results and discussion. Both methods make it possible to determine intravascular decompression gas formation after a diving descent, correlate with the clinical picture of acute decompression sickness and should be used in the medical support of diving descents. At the same time, the method of ultrasound examination based on transthoracic two-dimensional echocardiography turned out to be more sensitive in determining gas bubbles in the right heart as compared to auditory location with the Doppler effect.

Flying after diving: a questionnaire-based evaluation of pre-flight diving behaviour in a recreational diving cohort

Introduction: Divers are recommended to observe a pre-flight surface interval (PFSI) ≥ 24 hours before boarding a plane following a diving vacation. Decompression sickness (DCS) symptoms may occur during or post-flight. This study aimed to examine the adherence of PFSI ≥ 24 in vacationing divers, and if any perceived signs and symptoms of DCS during or after flight were experienced. Methods: An anonymous online survey was publicised through diving exhibitions and social media. Data included diver/diving demographics, PFSI before flight, flight details, and perceived signs and symptoms of DCS during or after flight. Results: Data from 316 divers were examined (31% female) with the age range 1-75 years (median 49). Divers recorded 4,356 dives in the week preceding the flight, range 1-36 (median 14). Overall, 251/316 (79%) respondents reported a PFSI of ≥ 24 hours. PFSIs of < 12 hours were reported by 6 respondents. Diagnosed and treated DCS developing during, and post flight was reported by 4 divers with PFSIs ≥ 24 hours and by 2 divers with PFSIs < 24 hours. Fifteen divers boarded a plane with perceived symptoms of DCS. Conclusions: These data suggest that most divers in this study observed the recommendations of a ≥ 24 hour PFSI with safe outcomes.

Inner ear barotrauma and inner ear decompression sickness: a systematic review on differential diagnostics

Introduction: Inner ear barotrauma (IEBt) and inner ear decompression sickness (IEDCS) are the two dysbaric inner ear injuries associated with diving. Both conditions manifest as cochleovestibular symptoms, causing difficulties in differential diagnosis and possibly delaying (or leading to inappropriate) treatment. Methods: This was a systematic review of IEBt and IEDCS cases aiming to define diving and clinical variables that help differentiate these conditions. The search strategy consisted of a preliminary search, followed by a systematic search covering three databases (PubMed, Medline, Scopus). Studies were included when published in English and adequately reporting one or more IEBt or IEDCS patients in diving. Concerns regarding missing and duplicate data were minimised by contacting original authors when necessary. Results: In total, 25 studies with IEBt patients (n = 183) and 18 studies with IEDCS patients (n = 397) were included. Variables most useful in differentiating between IEBt and IEDCS were dive type (free diving versus scuba diving), dive gas (compressed air versus mixed gas), dive profile (mean depth 13 versus 43 metres of seawater), symptom onset (when descending versus when ascending or surfacing), distribution of cochleovestibular symptoms (vestibular versus cochlear) and absence or presence of other DCS symptoms. Symptoms of difficult middle ear equalisation or findings consistent with middle ear barotrauma could not be reliably assessed in this context, being insufficiently reported in the IEDCS literature. Conclusions: There are multiple useful variables to help distinguish IEBt from IEDCS. Symptoms of difficult middle ear equalisation or findings consistent with middle ear barotrauma require further study as means of distinguishing IEBt and IEDCS.

Assessment of the condition of conditioned reflex activity in the process of liquid respiration

Introduction. Liquid respiration is the ability of mammalian lungs to receive oxygen dissolved in a liquid for respiration and release carbon dioxide into it. A promising field of application is the provision of marine operations. For the use of liquid respiration during deep-sea operations, the technology must ensure the normal functioning of all organs and systems of the body, prevent decompression sickness, and allow conscious activity. The study aims to assess the safety of conditioned reflex activity during independent liquid respiration in laboratory animals in normobaric conditions. Materials and methods. We performed the study on male Syrian hamsters aged four months, weighing 120-140 g. Researchers have developed a stand with an eight-level maze with a lock. We immersed the labyrinth in an aquarium. The scientists carried out the study in two stages. At the first stage, we have developed in animals a conditioned reflex of actively avoiding drowning in conditions of breathing air. The researchers placed the animal on the lower level, then immersed the maze in an aquarium filled with water at a speed that only the animal's head was above the water level. The threat of drowning prompted the animal to search for a passage to a higher level. The training was three times a day for ten days. At the second stage, scientists studied the influence of various conditions of liquid respiration on the state of the conditioned reflex activity of animals. We used two respiratory fluids - perfluorohexane (PFH) and perfluorodecalin (PFD) in three temperature regimes: 22.0, 27.0, and 32.0°C. The researchers filled the aquarium with two oxygenated respiratory fluids of the required temperature instead of water. We have entirely immersed the maze with the animal fixed at the lower level in the aquarium. After switching to liquid respiration, scientists removed the animal from fixation. From the moment of removal from fixation, the countdown of the passage of the maze began. First, we assessed the condition of conditioned reflex activity by the number of animals in the group that successfully passed the maze and the average time of its passage. Results. Animals on liquid respiration in perfluorohexane successfully passed the labyrinth in all temperature conditions. The average transit time at 22.0°C was 323±94 s; 27.0°C - 45±12 s; 32.0°C - 147±101 s. Animals on liquid respiration in perfluorodecalin successfully passed the labyrinth at a temperature of 27.0°C; the average passage time is 131±79 s; at a temperature of 32.0°C, 20% of animals successfully passed the labyrinth, the average time is 32.5 s; at a temperature of 22.0°C, none of the animals passed the maze. Conclusions. Conditioned reflex activity during independent liquid respiration in small laboratory animals in normobaric conditions persists and depends on the physico-chemical properties and temperature of the respiratory fluid.

Revisiting decompression sickness risk and mobility in the context of the SmartSuit, a hybrid planetary spacesuit

Gas pressurized spacesuits are cumbersome, cause injuries, and are metabolically expensive. Decreasing the gas pressure of the spacesuit is an effective method for improving mobility, but reduction in the total spacesuit pressure also results in a higher risk for decompression sickness (DCS). The risk of DCS is currently mitigated by breathing pure oxygen before the extravehicular activity (EVA) for up to 4 h to remove inert gases from body tissues, but this has a negative operational impact due to the time needed to perform the prebreathe. In this paper, we review and quantify these important trade-offs between spacesuit pressure, mobility, prebreathe time (or risk of DCS), and space habitat/station atmospheric conditions in the context of future planetary EVAs. In addition, we explore these trade-offs in the context of the SmartSuit architecture, a hybrid spacesuit with a soft-robotic layer that, not only increases mobility with assistive actuators in the lower body, but it also applies some level of mechanical counterpressure (MCP). The additional MCP in hybrid spacesuits can be used to supplement the gas pressure (i.e., increasing the total spacesuit pressure), therefore reducing the risk of DCS (or reduce prebreathe time). Alternatively, the MCP can be used to reduce the gas pressure (i.e., maintaining the same total spacesuit pressure), therefore increasing mobility. Finally, we propose a variable pressure concept of operations for the SmartSuit spacesuit. Our framework quantifies critical spacesuit and habitat trade-offs for future planetary exploration and contributes to the assessment of human health and performance during future planetary EVAs.

Increased Risk of Decompression Sickness When Diving With a Right-to-Left Shunt: Results of a Prospective Single-Blinded Observational Study (The “Carotid Doppler” Study)

Introduction: Divers with a patent Foramen Ovale (PFO) have an increased risk for decompression sickness (DCS) when diving with compressed breathing gas. The relative risk increase, however, is difficult to establish as the PFO status of divers is usually only determined after a DCS occurrence.Methods: This prospective, single-blinded, observational study was designed to collect DCS data from volunteer divers after screening for right-to-left shunt (RLS) using a Carotid Doppler test. Divers were blinded to the result of the test, but all received a standardized briefing on current scientific knowledge of diving physiology and “low-bubble” diving techniques; they were then allowed to dive without restrictions. After a mean interval of 8 years, a questionnaire was sent collecting data on their dives and cases of DCS (if any occurred).Results: Data was collected on 148 divers totaling 66,859 dives. There was no significant difference in diving data between divers with or without RLS. Divers with RLS had a 3.02 times higher incidence of (confirmed) DCS than divers without RLS (p = 0.04). When all cases of (confirmed or possible DCS) were considered, the Relative Risk was 1.42 (p = 0.46). DCS occurred mainly in divers who did not dive according to “low-bubble” diving techniques, in both groups.Conclusion: This prospective study confirms that DCS is more frequent in divers with RLS (such as a PFO), with a Relative Risk of 1.42 (all DCS) to 3.02 (confirmed DCS). It appears this risk is linked to diving behavior, more specifically diving to the limits of the adopted decompression procedures.