The effect of a single closed-circuit rebreather decompression dive in extremely cold water to cardiac function

PURPOSE

Dive-induced cardiac and hemodynamic changes are caused by various mechanisms, and they are aggravated by cold water. Therefore, aging divers with pre-existing cardiovascular conditions may be at risk of acute myocardial infarction, heart failure, or arrhythmias while diving. The aim of this study was to assess the effect of a single decompression CCR dive in arctic cold water on cardiac function in Finnish technical divers.

METHODS

Thirty-nine divers performed one identical 45 mfw CCR dive in 2-4 °C water. Hydration and cardiac functions were assessed before and after the dive. Detection of venous gas embolization was performed within 120 min after the dive.

RESULTS

The divers were affected by both cold-water-induced hemodynamic changes and immersion-related fluid loss. Both systolic and diastolic functions were impaired after the dive although the changes in cardiac functions were subtle. Venous inert gas bubbles were detected in all divers except for one. Venous gas embolism did not affect systolic or diastolic function.

CONCLUSION

A single trimix CCR dive in arctic cold water seemed to debilitate both systolic and diastolic function. Although the changes were subtle, they appeared parallel over several parameters. This indicates a real post-dive deterioration in cardiac function instead of only volume-dependent changes. These changes are without a clinical significance in healthy divers. However, in a population with pre-existing or underlying heart problems, such changes may provoke symptomatic problems during or after the dive.

An evaluation of the NUI Compact Chest Compression Device (NCCD), a mechanical CPR device suitable for use in the saturation diving environment

Introduction

Provision of manual chest compressions in a diving bell using a conventional technique is often impossible, and alternative techniques are poorly evidenced in terms of efficacy and sustainability. The first mechanical cardiopulmonary resuscitation (CPR) device suitable for use in this environment, the NUI Compact Chest Compression Device (NCCD), has recently been designed and manufactured. This study assessed both the efficacy of the device in delivering chest compressions to both prone and seated manikins, and the ability of novice users to apply and operate it.

Methods

Compression efficacy was assessed using a Resusi Anne QCPR intelligent manikin, and the primary outcome was the proportion of compressions delivered to target depth (50-60 mm). The gold standard was that achieved by expert CPR providers delivering manual CPR; the LUCAS 3 mCPR device was a further comparator.

Results

The NCCD delivered 100% of compressions to target depth compared to 98% for the gold standard (interquartile range 1.5%) and 98% for the LUCAS 3 when applied to both supine and seated manikins. The NCCD sometimes became dislodged and had to be reapplied when used with a seated manikin.

Conclusions

The NCCD can deliver chest compressions at target rate and depth to both supine and seated manikins with efficacy equivalent to manual CPR and the LUCAS 3. It can become dislodged when applied to a seated manikin; its design has now been altered to prevent this. New users can be trained in use of the NCCD quickly, but practise is required to ensure effective use.

A retrospective review of divers treated for inner ear decompression sickness at Fiona Stanley Hospital hyperbaric medicine unit 2014-2020

Introduction

Inner ear decompression sickness (IEDCS) is increasingly recognised in recreational diving, with the inner ear particularly vulnerable to decompression sickness in divers with a right-to-left shunt, such as is possible through a persistent (patent) foramen ovale (PFO). A review of patients treated for IEDCS at Fiona Stanley Hospital Hyperbaric Medicine Unit (FSH HMU) in Western Australia was performed to examine the epidemiology, risk factors for developing this condition, the treatment administered and the outcomes of this patient population.

Methods

A retrospective review of all divers treated for IEDCS from the opening of the FSH HMU on 17 November 2014 to 31 December 2020 was performed. Patients were included if presenting with vestibular or cochlear dysfunction within 24 hours of surfacing from a dive, and excluded if demonstrating features of inner ear barotrauma.

Results

There were a total of 23 IEDCS patients and 24 cases of IEDCS included for analysis, with 88% experiencing vestibular manifestations and 38% cochlear. Median dive time was 40 minutes and median maximum depth was 24.5 metres. The median time from surfacing to hyperbaric oxygen treatment (HBOT) was 22 hours. Vestibulocochlear symptoms fully resolved in 67% and complete symptom recovery was achieved in 58%. A PFO was found in 6 of 10 patients who subsequently underwent investigation with bubble contrast echocardiography upon follow-up.

Conclusions

IEDCS occurred predominantly after non-technical repetitive air dives and ongoing symptoms and signs were often observed after HBOT. Appropriate follow-up is required given the high prevalence of PFO in these patients.

Delivering manual cardiopulmonary resuscitation (CPR) in a diving bell: an analysis of head-to-chest and knee-to-chest compression techniques

Introduction

Chest compression often cannot be administered using conventional techniques in a diving bell. Multiple alternative techniques are taught, including head-to-chest and both prone and seated knee-to-chest compressions, but there are no supporting efficacy data. This study evaluated the efficacy, safety and sustainability of these techniques.

Methods

Chest compressions were delivered by a team of expert cardiopulmonary resuscitation (CPR) providers. The primary outcome was proportion of chest compressions delivered to target depth compared to conventional CPR. Techniques found to be safe and potentially effective by the study team were further trialled by 20 emergency department staff members.

Results

Expert providers delivered a median of 98% (interquartile range [IQR] 1.5%) of chest compressions to the target depth using conventional CPR. Only 32% (IQR 60.8%) of head-to-chest compressions were delivered to depth; evaluation of the technique was abandoned due to adverse effects. No study team member could register sustained compression outputs using prone knee-to-chest compressions. Seated knee-to-chest were delivered to depth 12% (IQR 49%) of the time; some compression providers delivered > 90% of compressions to depth.

Conclusions

Head-to-chest compressions have limited efficacy and cause harm to providers; they should not be taught or used. Prone knee-to-chest compressions are ineffective. Seated knee-to-chest compressions have poor overall efficacy but some providers deliver them well. Further research is required to establish whether this technique is feasible, effective and sustainable in a diving bell setting, and whether it can be taught and improved with practise.

Feasibility of chest ultrasound up to 42 m underwater

After recent advancements, ultrasound has extended its applications from bedside clinical practice to wilderness medicine. Performing ultrasound scans in extreme environments can allow direct visualization of unique pathophysiological adaptations but can be technically challenging. This paper summarizes how a portable ultrasound apparatus was marinized to let scientific divers and sonographers perform ultrasound scans of the lungs underwater up to - 42 m. A metallic case protected the ultrasound apparatus inside; a frontal transparent panel with a glove allowed visualization and operation of the ultrasound by the diving sonographer. The inner pressure was equalized with environmental pressure through a compressed air tank connected with circuits similar to those used in SCUBA diving. Finally, the ultrasound probe exited the metallic case through a sealed aperture. No technical issues were reported after the first testing step and the real experiments.

Takotsubo cardiomyopathy findings on cardiac magnetic resonance imaging following immersion pulmonary oedema

Immersion pulmonary oedema (IPO) can affect sea swimmers, snorkelers, and scuba divers. It can be fatal and cases are often mistaken for drowning. There has been an association between IPO and the development of takotsubo cardiomyopathy. We present a case study of a diver rescued from the water with IPO, who was subsequently found to have takotsubo cardiomyopathy on cardiac magnetic resonance imaging (CMR). This case demonstrates CMR findings as well as follow- up investigation results. The diver's and instructor's perspective during the initial dive incident are also described.

Influence of atmospheric pressure changes on dentin bond strength of conventional, bulk-fill and single-shade resin composites

INTRODUCTION

The purpose of this study was to investigate the dentin bond strength of composite resins in response to environmental pressure changes.

METHODS

Ninety extracted human molar teeth were used. A mould (3 mm x 4 mm) was adapted on dentin, resin composites (conventional [n = 30] and single-shade composites [Ohmnicroma] [n = 30]) were filled in two increments of 2 mm. The bulk-fill composites (n = 30) were filled with one 4 mm increment. The specimens were stored for 30 days in artificial saliva. The specimens were exposed to hyperbaric pressure (283.6 kPa; 2.8 atmospheres absolute [atm abs]) or hypobaric pressure (34.4 kPa; 0.34 atm abs) once daily for 30 days and the control group was stored at atmospheric pressure for 30 days. The bond strength was tested with a universal testing machine and the failures were examined with a stereomicroscope and scanning electron microscope. Statistical analyses were performed using analysis of variance with post hoc tests, and the Weibull analysis.

RESULTS

Regardless of environmental pressure changes, the bulk-fill composites showed the highest bond strength. There was no significant difference in bond strength between the hypobaric and atmospheric pressure (control) groups after 30 days in all resins. The hyperbaric group showed lower bond strength for bulk-fill composites than the control group.

CONCLUSIONS

Dentists experienced in diving and aviation medicine should definitely take part in the initial and periodic medical examinations of divers and aircrew to give appropriate treatment. Bulk-fill composite resins can be preferred in divers and aircrew due to high bond strength values.

Pulmonary barotrauma with cerebral arterial gas embolism from a depth of 0.75-1.2 metres of fresh water or less: A case report

During underwater vehicle escape training with compressed air, a fit 26-year-old soldier suffered pulmonary barotrauma with cerebral arterial gas embolism after surfacing from a depth of 0.75-1.2 metres of freshwater or less. She presented with an altered level of consciousness. Rapid neurological examination noted slurred speech, a sensory deficit and right hemiparesis. Eleven hours after the accident, hyperbaric oxygen treatment was initiated using US Navy Treatment Table 6. The soldier almost completely recovered after repeated hyperbaric oxygen treatment. Given the very shallow depth this is an unusual case with only two similar case reports published previously.

Oxygen toxicity seizures during United States Navy Treatment Table 6: An acceptable risk in monoplace chambers?

INTRODUCTION

Hyperbaric oxygen treatment (HBOT) may be complicated by oxygen toxicity seizures, which typically occur with hyperbaric partial pressures of oxygen exceeding 203 kPa (2 atmospheres absolute). All other hyperbaric units in Australia exclusively use a multiplace chamber when treating with United States Navy Treatment Table 6 (USN TT6) due to this perceived risk. The purpose of this study was to determine the safety of a monoplace chamber when treating decompression illness (DCI) with USN TT6.

METHODS

A retrospective review of the medical records of all patients treated at Fiona Stanley Hospital Hyperbaric Medicine Unit with USN TT6 between November 2014 and June 2020 was undertaken. These data were combined with previous results from studies performed at our hyperbaric unit at Fremantle Hospital from 1989 to 2014, creating a data set covering a 30-year period.

RESULTS

One thousand treatments with USN TT6 were performed between 1989 and 2020; 331 in a monoplace chamber and 669 in a multiplace chamber. Four seizures occurred: a rate of 0.59% (1/167) in a multiplace chamber; and none in a monoplace chamber, indicating no statistically significant difference between seizures in a monoplace versus multiplace chamber (P = 0.31).

CONCLUSIONS

The rate of oxygen toxicity seizures in a monoplace chamber is not significantly higher than for treatment in the multiplace chamber. We conclude that using the monoplace chamber for USN TT6 in selected patients poses an acceptably low seizure risk.

Symptoms of central nervous system oxygen toxicity during 100% oxygen breathing at normobaric pressure with increasing inspired levels of carbon dioxide: a case report

The greatest danger faced by divers who use oxygen-enriched gas mixtures is central nervous system oxygen toxicity (CNS-OT). CNS-OT is characterised by convulsions resembling grand-mal epileptic seizures, which may terminate in drowning and death. Elevated arterial levels of carbon dioxide (CO₂) (hypercapnia) represent a major risk factor for CNS-OT when breathing hyperoxic gas mixtures. To reduce the risk of a diver being involved in a CNS-OT incident due to hypercapnia, candidates for combat diving are examined at our institute using a routine physiological training procedure, in which they are tested for CO₂ detection and retention. We present the case of a candidate for combat diving, who unexpectedly exhibited signs typical of CNS-OT while breathing pure oxygen under normobaric conditions with > 3 kPa inspired CO₂. Severe headache and nausea, as well as facial muscle twitching, appeared during one of these routine tests. Subsequent medical examination including neurological tests, magnetic resonance imaging and an electroencephalogram were unremarkable. To the best of our knowledge, an event such as this has never previously been published in the medical literature. We present a discussion of the case, and a review of the relevant literature regarding CO₂ as a risk factor for the development of CNS-OT.

Diving with hypertension and antihypertensive drugs

Hypertension is a common condition, which is highly prevalent amongst scuba divers. As a consequence, a substantial proportion of divers are hypertensive and/or on antihypertensive drugs when diving. In this article, we review available literature on the possible risks of diving in the presence of hypertension and antihypertensive drugs. Guidelines are presented for the diving physician for the selection of divers with hypertension suitable for diving, along with advice on antihypertensive treatment best compatible with scuba diving.

Monoplace chamber treatment of decompression illness: Review and commentary

This paper summarises the history and capabilities of monoplace chambers in treatment of decompression illness (DCI); both in support of diving operations and in the hospital setting. In the field, monoplace hyperbaric chambers provide victims of DCI immediate access to recompression in settings where traditional multiplace chambers are not available. Alternatively, they may facilitate pressurised transport to a multiplace chamber for continued management. Recently, collapsible lightweight versions have improved suitability for field deployment aboard small vessels in remote settings, and for use by less technically capable military, occupational and civilian operators. The resulting elimination of treatment delays may prove lifesaving and central nervous system sparing, and avoid subsequent diving fitness disqualification. Monoplace chambers thus facilitate diving operations that would otherwise be difficult to condone on health and safety grounds. The 1960s saw the introduction of multiplace hyperbaric chambers into the hospital setting, as a number of non-diving conditions appeared to benefit from hyperbaric oxygen. This coincided with interest in hyperbaric oxygen as a solid tumour radiation sensitiser. Development of a novel acrylic-hulled single occupancy chamber enabled patients to undergo radiotherapy while pressurised within its oxygen atmosphere. Increasing numbers of health care facilities adopted this chamber type as a more economical, less complex alternative to the multiplace chamber. Incorporation of relevant biomedical technologies have allowed monoplace chambers to support increasingly complex patients in a safe, effective manner. Despite these advances, criticism of medical centre-based monoplace chamber treatment of DCI exists. This paper evaluates this controversy and presents relevant counter-arguments.

Diving after SARS-CoV-2 (COVID-19) infection: Fitness to dive assessment and medical guidance

Scuba diving is a critical activity for commercial industry, military activities, research, and public safety, as well as a passion for many recreational divers. Physicians are expected to provide return-to-diving recommendations after SARS-CoV-2 (COVID-19) infection based upon the best available evidence, often drawn from experience with other, similar diseases. Scuba diving presents unique physiologic challenges to the body secondary to immersion, increased pressure and increased work of breathing. The long-term sequelae of COVID-19 are still unknown, but if they are proven to be similar to other coronaviruses (such as Middle East respiratory syndrome or SARS-CoV-1) they may result in long-term pulmonary and cardiac sequelae that impact divers' ability to safely return to scuba diving. This review considers available literature and the pathophysiology of COVID-19 as it relates to diving fitness, including current recommendations for similar illnesses, and proposes guidelines for evaluation of divers after COVID-19. The guidelines are based upon best available evidence about COVID-19, as well as past experience with determination of diving fitness. It is likely that all divers who have contracted COVID-19 will require a medical evaluation prior to return to diving with emphasis upon pulmonary and cardiac function as well as exercise capacity.

Diving and attention deficit hyperactivity disorder

Attention deficit hyperactivity disorder (ADHD) is a psychiatric condition that affects attention, concentration, impulse control and awareness. Not only these symptoms, but also the medications used to treat ADHD (psychostimulants) pose a risk to both the diver and his or her buddy. This article presents guidelines for recreational diving in combination with ADHD and psychostimulants. These guidelines are based solely on 'expert' opinion and were adopted at a meeting of the Dutch Association for Diving Medicine in 2017.

Diving and antidepressants

Psychoactive drugs pose a risk to both the diver and his or her buddy. Little is known about the safety of diving with antidepressants. Amongst the potential interactions with the diving environment are: somnolence; convulsions; a bleeding tendency (potentially worsening decompression illness, DCI), alterations to glucose metabolism and psychiatric side effects. Fluoxetine may potentially reduce the inflammatory process associated with DCI. This article presents guidelines for recreational diving in combination with antidepressants. These guidelines were endorsed at a meeting of the Dutch Association for Diving Medicine in 2015 and are solely based on 'expert' opinion.

Periorbital emphysema after a wet chamber dive

Although periorbital emphysema (PE) is commonly associated with orbital fractures, it may develop without any fracture or significant trauma in circumstances such as post-surgery, infection, forceful nose blowing, sneezing, and weight lifting. We report on a healthy military diver who developed PE following a wet chamber dive. A diagnosis of PE secondary to sinus barotrauma was reached. He was treated conservatively without medication and his symptoms recovered completely within 10 days. To the best of our knowledge, only five cases of diving-related PE have been reported in the literature. Analysis of these cases and ours revealed that facial trauma, repeated forceful Valsalva manoeuvres and recent upper respiratory tract infection are probable risk factors for diving-related PE.

Observational study of potential risk factors of immersion pulmonary edema in healthy divers: exercise intensity is the main contributor

BACKGROUND

The risk factors of pulmonary edema induced by diving in healthy subjects are not well known. The aim of the present study was to assess the parameters contributing to the increase in extravascular lung water after diving.

METHODS

This study was carried out in a professional diving institute. All divers participating in the teaching program from June 2012 to June 2014 were included in the study. Extravascular lung water was assessed using the detection of ultrasound lung comets (ULC) by chest ultrasonography. Clinical parameters and dive profiles were recorded using a questionnaire and a dive computer.

RESULTS

One-hundred six divers were investigated after 263 dives. They used an open-circuit umbilical supplying compressed gas diving apparatus in 202 cases and a self-contained underwater breathing apparatus in 61 cases. A generalized linear mixed model analysis was performed which demonstrated that the dive induced a significant increase in ULC score (incidence rate ratio: 3.16). It also identified that the predictive variable of increased extravascular lung water after the dive was the exercise intensity at depth (z = 3.99, p < 0.0001). The other parameters studied such as the water temperature, dive profile, hyperoxic exposure, or anthropometric data were not associated with the increase in extravascular lung water after the dive.

CONCLUSIONS

In this study, the exercise intensity was the main contributor to the increase in extravascular lung water in healthy divers. To improve the prevention of immersion pulmonary edema, the exercise intensity experienced during the dive should thus be adapted to the aerobic fitness level of the divers.

The effect of hyperbaric air on the electric activity of neuronal in vitro networks

Breathing hyperbaric air or gas mixtures, for example during diving or when working underwater is known to alter the electrophysiological behavior of neuronal cells, which may lead to restricted cognition. During the last few decades, only very few studies into hyperbaric effects have been published, especially for the most relevant pressure range of up to 10 bar. We designed a pressurized measuring chamber to record pressure effects on the electrical activity of neuronal networks formed by primary cells of the frontal cortex of NMRI mice. Electrical activity was recorded with multi-electrode arrays (MEAs) of glass neuro chips while subjected to a step-by-step pressure increase from atmospheric pressure (1 bar) to 2 and 4 bar, followed by a decompression to 1 bar, in order to record recovery effects. The effects of pressure on the total spike rates (TSRs), which were averaged from at least 45 chips, were detected in two cell culture media with different compositions. In a DMEM medium with 6% horse serum, the TSR was increased by 19% after a pressure increase to 2 bar and remained stable at 4 bar. In NMEM medium with 2% B27, the TSR was not altered by a pressure increase to 2 bar but increased by 9% at 4 bar. After decompression to 1 bar, the activities decreased to 76% and 101% of their respective control levels in the two media. MEA recordings from neuronal networks in miniaturized hyperbaric measuring chambers provide new access for exploring the neuronal effects of hyperbaric breathing gases.

Auditory complaints in scuba divers: an overview

Pre-1970s, diving was seen as a predominantly male working occupation. Since then it has become a popular hobby, with increasing access to SCUBA diving while on holiday. For a leisure activity, diving puts the auditory system at the risk of a wide variety of complaints. However, there is still insufficient consensus on the frequency of these conditions, which ultimately would require more attention from hearing-healthcare professionals. A literature search of epidemiology studies of eight auditory complaints was conducted, using both individual and large-scale diving studies, with some reference to large-scale non-diving populations . A higher incidence was found for middle ear barotrauma, eustachian tube dysfunction, and alternobaric vertigo with a high correlation among females. Comparing these findings with a non-diving population found no statistically significant difference for hearing loss or tinnitus. Increased awareness of health professionals is required, training, and implementation of the Frenzel technique would help resolve the ambiguities of the Valsalva technique underwater.