Selective vulnerability of the inner ear to decompression sickness in divers with right-to-left shunt: the role of tissue gas supersaturation

Extended lifetimes of bubbles at hyperbaric pressure may contribute to inner ear decompression sickness during saturation diving

Inner ear decompression sickness (IEDCS) may occur after upward or downward excursions in saturation diving. Previous studies in non-saturation diving strongly suggest IEDCS is caused by arterialization of small venous bubbles across intracardiac or intrapulmonary right-to-left shunts, and bubble growth through inward diffusion of supersaturated gas when they arrive in the inner ear. The present study used published saturation diving data, and models of inner ear inert gas kinetics and bubble dynamics in arterial conditions to assess whether IEDCS after saturation excursions could also be explained by arterialization of venous bubbles, and whether such bubbles might survive longer and be more likely to reach the inner ear under deep saturation diving conditions. Previous data show that saturation excursions produce venous bubbles. Modelling shows gas supersaturation in the inner ear persists longer than in the brain after such excursions, explaining why the inner ear would be more vulnerable to injury by arriving bubbles. Estimated survival of arterialized bubbles is significantly prolonged at high ambient pressure such that bubbles large enough to be filtered by pulmonary capillaries but able to cross right-to-left shunts are more likely to survive transit to the inner ear than at the surface. IEDCS after saturation excursions is plausibly caused by arterialization of venous bubbles whose prolonged arterial survival at deep depths suggests larger bubbles in greater numbers reach the inner ear.

Does hyperbaric oxygen cause narcosis or hyperexcitability? A quantitative EEG analysis

Divers breathe higher partial pressures of oxygen at depth than at the surface. The literature and diving community are divided on whether or not oxygen is narcotic. Conversely, hyperbaric oxygen may induce dose‐dependent cerebral hyperexcitability. This study evaluated whether hyperbaric oxygen causes similar narcotic effects to nitrogen, and investigated oxygen's hyperexcitability effect. Twelve human participants breathed “normobaric” air and 100% oxygen, and “hyperbaric” 100% oxygen at 142 and 284 kPa, while psychometric performance, electroencephalography (EEG), and task load perception were measured. EEG was analyzed with functional connectivity and temporal complexity algorithms. The spatial functional connectivity, estimated using mutual information, was summarized with the global efficiency network measure. Temporal complexity was calculated with a “default‐mode‐network (DMN) complexity” algorithm. Hyperbaric oxygen‐breathing caused no change in EEG global efficiency or in the psychometric test. However, oxygen caused a significant reduction of DMN complexity and a reduction in task load perception. Hyperbaric oxygen did not cause the same changes in EEG global efficiency seen with hyperbaric air, which likely related to a narcotic effect of nitrogen. Hyperbaric oxygen seemed to disturb the time evolution of EEG patterns that could be taken as evidence of early oxygen‐induced cortical hyperexcitability. These findings suggest that hyperbaric oxygen is not narcotic and will help inform divers' decisions on suitable gas mixtures.

Investigating critical flicker fusion frequency for monitoring gas narcosis in divers

INTRODUCTION

Critical flicker fusion frequency (CFFF) has been used in various studies to measure the cognitive effects of gas mixtures at depth, sometimes with conflicting or apparently paradoxical results. This study aimed to evaluate a novel automatic CFFF method and investigate whether CFFF can be used to monitor gas-induced narcosis in divers.

METHODS

Three hyperbaric chamber experiments were performed: 1) Automated and manual CFFF measurements during air breathing at 608 kPa (n = 16 subjects); 2) Manual CFFF measurements during air and heliox breathing at sea level (101.3 kPa) and 608 kPa (n = 12); 3) Manual CFFF measurements during oxygen breathing at sea level, 142 and 284 kPa (n = 10). All results were compared to breathing air at sea level.

RESULTS

Only breathing oxygen at sea level, and at 284 kPa, caused a significant decrease in CFFF (2.5% and 2.6% respectively compared to breathing air at sea level. None of the other conditions showed a difference with sea level air breathing.

CONCLUSIONS

CFFF did not significantly change in our experiments when breathing air at 608 kPa compared to air breathing at sea level pressure using both devices. Based on our results CFFF does not seem to be a sensitive tool for measuring gas narcosis in divers in our laboratory setting.

Bubbles in the skin microcirculation underlying cutis marmorata in decompression sickness: Preliminary observations

INTRODUCTION

The cutaneous form of decompression sickness (DCS) known as cutis marmorata is a frequent clinical presentation. Beyond a general acceptance that bubbles formed from dissolved inert gas are the primary vector of injury, there has been debate about pathophysiology. Hypotheses include: 1) local formation of bubbles in the skin or its blood vessels; 2) arterialisation of venous bubbles across a right to left shunt (RLS) with local amplification in bubble size after reaching supersaturated skin via the arterial circulation; and 3) passage of arterialised venous bubbles to the cerebral circulation with stimulation of a sympathetically mediated vasomotor response.

METHODS

Four divers exhibiting cutis marmorata had the underlying tissue examined with ultrasound 4-5.5 hours after appearance of the rash. All subsequently underwent transthoracic echocardiography with bubble contrast to check for a RLS.

RESULTS

In all cases numerous small bubbles were seen moving within the skin microvasculature. No bubbles were seen in adjacent areas of normal skin. All four divers had a large RLS.

CONCLUSION

This is the first report of bubbles in skin affected by cutis marmorata after diving. The finding is most compatible with pathophysiological hypotheses one and two above. The use of ultrasound will facilitate further study of this form of DCS.

DCS or DCI? The difference and why it matters

There are few issues that generate as much confusion in diving medicine as the nomenclature of bubble-induced dysbaric disease. Prior to the late 1980s, the diagnosis 'decompression sickness' (DCS) was invoked for symptoms presumed to arise as a consequence of bubble formation from dissolved inert gas during or after decompression. These bubbles were known to form within tissues, and also to appear in the venous blood (presumably after forming in tissue capillaries). A second diagnosis, 'arterial gas embolism' (AGE) was invoked for symptoms presumed to arise when bubbles were introduced directly to the arterial circulation as a consequence of pulmonary barotrauma.

This approach was predicated on an assumption that the underlying pathophysiology could usually be inferred from the nature and tempo of resulting symptoms. DCS was considered to exhibit a slower more progressive onset, symptoms were protean (including pain, rash, paraesthesias, subcutaneous swelling, and neurological symptoms), and the neurological manifestations were mainly attributable to spinal cord or inner ear involvement. In contrast, AGE was considered to exhibit a more precipitous onset (often immediately on surfacing), and the principal manifestation was stroke-like focal neurological impairment suggestive of cerebral involvement.

In 1989 an association between a large persistent ('patent') foramen ovale (PFO) and serious neurological DCS was independently reported by two groups, and subsequently corroborated for neurological, inner ear, and cutaneous DCS by multiple studies. The assumed pathophysiological role of a PFO in this setting was to allow bubbles formed from inert gas in the venous blood to avoid removal in the pulmonary circulation and to enter the arterial circulation. These bubbles could then pass to the microcirculation of vulnerable target tissues where inward diffusion of supersaturated inert gas from the surrounding tissue could cause them to grow.

This emergence of 'arterialisation' of venous bubbles as an important vector of harm in some forms of DCS resulted in a challenge to the use of traditional 'DCS/AGE' terminology. It was suggested that very early onset of cerebral symptoms after diving could be explained not only by arterial bubbles introduced by pulmonary barotrauma, but also by venous bubbles crossing a PFO into the arterial circulation. Moreover, once venous bubbles had entered the arterial circulation they were then technically 'arterial gas emboli'; thus creating confusion with arterial gas emboli from pulmonary barotrauma. To many commentators, it made little sense to use diagnostic labels (DCS and AGE) that implied a particular pathophysiology when the two disorders might be difficult to tell apart, and had mechanistic processes in common.

An alternative approach derived at a UHMS workshop in 1991 was to shift from nomenclature that implied a particular pathophysiology, to a descriptive system that lumped both DCS and AGE together under the label "decompression illness" (DCI). Using this system, terms to describe the organ system(s) involved and the progression of symptoms were applied. For example, a diver with worsening upper arm pain after a dive could be suffering 'progressive musculoskeletal DCI'; and a diver who lost consciousness immediately on surfacing but regained consciousness minutes later would be considered to be suffering 'remitting cerebral DCI'. Classifying cases in this manner made considerable sense at a clinical level, particularly given that there was an emerging consensus that manifestations of DCS and AGE that potentially overlapped did not require different approaches to recompression treatment.

This descriptive classification of bubble-induced dysbaric disease gained substantial traction in the community, though not always with a full appreciation by users of the intended nuances of its application. Indeed, it became increasingly common over time to see the terms DCS and DCI used interchangeably; for example, authors using the term DCI to specifically infer the consequences of bubble formation from dissolved gas. This highlights one of the shortcomings of the DCI terminology: it becomes confusing when discussing dysbaric disease at a theoretical or experimental level when the nature of the insult is known or there is a specific intent to discuss bubble formation either from dissolved gas or from pulmonary barotrauma.

The potential for confusion between mechanisms and manifestations of DCS and AGE as one of the principle drivers for adopting the DCI terminology deserves further discussion. It is tempting to suggest that if venous bubbles cross a PFO into the arterial blood then any resulting symptoms should be considered a manifestation of 'AGE'. However, there seems little sense in re-naming the primary pathophysiological event (DCS caused by bubble formation from inert gas) just because the bubbles have distributed elsewhere; especially using a name that commonly infers a completely different primary event (bubble formation from pulmonary barotrauma). Moreover, there are grounds for suggesting that these two processes may not be as difficult to distinguish as previously believed. Venous inert gas bubbles are small, and of a similar size distribution to those used as bubble contrast during PFO testing. Decades of experience in testing thousands of divers (and other patients) for PFO using bubble-contrast echocardiograpy have shown that even when strongly positive (that is, large showers of bubbles enter the arterial circulation), symptoms of any sort are very rare. There are sporadic reports of evanescent visual or cerebral symptoms, but (to this author's knowledge) reports of the focal or multifocal cerebral infarctions that can be caused by large arterial bubbles introduced iatrogenically or by pulmonary barotrauma are lacking. One could argue that in the context of PFO testing the brain is not supersaturated with inert gas (which might cause small arterial bubbles to grow), but being such a 'fast tissue' nor is it likely to be after diving. Thus, while sustained showers of small inert gas bubbles crossing a PFO after diving appeal as a plausible cause of transient visual symptoms or dysexecutive syndromes after diving, they are less likely to be the cause of dramatic stroke-like events occurring early after surfacing.

In the final edition of Bennett and Elliott it was suggested that one editorial approach to the terminology conundrum would be to utilise the traditional terminology (DCS and AGE) when referring specifically to the pathophysiology and manifestations of bubble formation from dissolved inert gas or pulmonary barotrauma respectively, and to utilise the descriptive (DCI) terminology in clinical discussions when a collective term is useful, or when discussing individual patients where there is either ambiguity about pathophysiology or no need to attempt a distinction. Diving and Hyperbaric Medicine recommends a similar approach. The journal is reluctant to attempt to generate or apply hard 'rules' in relation to terminology of bubble-induced dysbaric disease, but we strongly discourage use of the term 'arterial gas emboli(ism)' to characterise venous inert gas bubbles that cross a right-to-left shunt such as a PFO. The pathophysiological consequences of bubble formation from dissolved inert gas should be regarded as decompression sickness (DCS). There is an expectation that authors are cognisant of the above issues and attempt to adopt terminology that reflects these considerations and best suits the circumstances of their manuscript.

Risk mitigation in divers with persistent (patent) foramen ovale

In this issue, Anderson and colleagues report follow-up of divers who were found to have a persistent (patent) foramen ovale (PFO) or, in eleven cases, an atrial septal defect (ASD). In most divers diagnosis followed an episode of decompression illness (DCI). The efficacy of closure of the PFO/ASD in preventing future DCI was compared with conservative diving. They reported that in the closure group the occurrence of confirmed DCI decreased significantly compared with pre-closure, but in the conservative group this reduction was not significant.

It is believed there are three requirements for a diver to suffer shunt-mediated DCI: A significant right-to-left shunt (usually a large PFO but sometimes an ASD or pulmonary arteriovenous malformation). Venous bubbles nucleated during decompression circumvent the lung filter by passing through the shunt. Target tissues are supersaturated with dissolved inert gas, so that they are able to amplify embolic bubbles. All three are required because DCI does not occur after contrast echocardiography when bubbles cross a right-to-left shunt.

Therefore, there are two ways that a diver who has suffered shunt-mediated DCI may continue to dive - either their shunt is sealed or future dives should be so conservative that venous bubbles are not liberated and/or critical tissues are not able to amplify embolic bubbles.

PFO/ASD closure will give divers a risk of DCI comparable to the risk in others without a right-to-left shunt, if the procedure adequately seals the shunt. Closure of the shunt will not prevent a diver suffering DCI by other mechanisms, such as when there is arterial gas embolism (AGE) as a result of pulmonary barotrauma or when the dive profile is provocative (e.g., if there is rapid ascent or missed decompression stops). Conservative diving will be effective only if all the dives performed are truly conservative and prevent bubble nucleation and/or amplification.

The study by Anderson et al. has a number of serious limitations. The study was small with only 62 self-selected divers, who self-reported outcomes. Eleven divers had not had DCI when their PFO or ASD was detected. Initially 36 divers were classified as closure and 26 as conservative treatment, but six subjects crossed from the conservative group to the closure group. Three of the six dived in the conservative group before having closure and are classified in both groups depending on whether the dives performed were before or after closure. As a result, there were 42 in the closure group and 23 in the conservative group.

Randomisation to the treatment groups was not possible and its absence results in imbalance. Because the closure group is approximately twice as large as the conservative group, similar changes in incidence would have a greater probability of achieving statistical significance in the former. Large shunts were present in more than three-quarters of the closure group but fewer than half of the conservative group. The authors have three definitions of a 'large' PFO, so the definition of large was inconsistent. All ASDs were considered to be large.

When dealing with small numbers, one needs patient-level data, but that is lacking and may mask inconsistency in management. The divers were investigated and treated in at least 38 hospitals (some divers did not state where they were treated). We do not know what devices were used for PFO/ASD closure, and closure effectiveness varies, or what tests were performed to assess the effectiveness of closure.

The primary end-point was not different between the two groups because only two episodes of confirmed DCI occurred in each group. The authors also considered a softer and subjective end-point, possible DCI.

Crucially we are not told what the divers in the conservative group were told constitutes a conservative dive and whether it was consistent. Nor are we told whether they followed the advice given. That is important because it appears that incidence of possible DCI increased considerably in only the conservative group, which means either that the advice they were given on what constitutes a conservative dive was flawed, that the divers failed to follow good advice or that they frequently reported innocent symptoms as possible DCI, because knowledge that they had a PFO may have increased their reporting - introducing further bias.

There should be assessment of whether DCI after the intervention was shunt-mediated or had another cause. For that assessment, one needs to know details of the dives resulting in symptoms, clinical manifestations and latency of onset.

I have investigated 20 divers who had DCI after PFO closure. In five divers, a contrast echocardiogram showed a significant residual shunt. Typically, the diver had their closure procedure by a cardiologist lacking knowledge of diving medicine and no post-closure contrast echocardiogram was performed. In one case, the diver's PFO was closed but they had a residual pulmonary shunt that was not detected. In those cases where there is a significant residual shunt, the dive profiles, clinical manifestations and latencies of onset were typical of shunt-mediated DCI.

Three divers, who had PFO closure with no residual shunt, subsequently had neurological symptoms with manifestations consistent with AGE secondary to pulmonary barotrauma. High resolution CT scans of their chests showed pulmonary bullae and emphysema.

The remaining divers seen had no residual shunt but had performed highly provocative dives, usually much deeper than 50 metres' sea water (msw). The most recent case that I saw had dived to 102 metres' fresh water (mfw) in a lake at high altitude breathing trimix.

In contrast, several hundred divers in whom I diagnosed a PFO and who elected to dive conservatively had not reported further DCI. I advised them that I have never seen shunt-mediated DCI after dives breathing air to depths of 15 msw or less provided no rules were broken. So I set that as the depth limit or allow them to dive to greater depths breathing nitrox so that there are equivalent partial pressures of nitrogen (e.g., 19 msw with nitrox 32 or 23 msw with nitrox 40) provided they use an air decompression table/algorithm. Alternatively, one can dive using the DCIEM recreational air diving table.

Recurrence of DCI after PFO closure may be the result of a residual shunt or may have other causes. It is difficult to draw conclusions about the safety of 'conservative' diving unless one knows what the divers were advised constitutes conservative dives and whether they adhered to the advice.

The effectiveness of risk mitigation interventions in divers with persistent (patent) foramen ovale

INTRODUCTION

Persistent (patent) foramen ovale (PFO) is a recognized risk for decompression sickness (DCS) in divers, which may be mitigated by conservative diving or by PFO closure. Our study aimed to compare the effectiveness of these two risk mitigation interventions.

METHODS

This was a prospective study on divers who tested positive for PFO or an atrial septal defect (ASD) and either decided to continue diving without closure ('conservative group'), or to close their PFO/ASD and continue diving ('closure group'). Divers' characteristics, medical history, history of diving and history of DCS were reported at enrollment and annually after that. The outcome measures were the incidence rate of DCS, frequency and intensity of diving activities, and adverse events of closure.

RESULTS

Divers in both groups dived less and had a lower incidence rate of confirmed DCS than before the intervention. In the closure group (n = 42) the incidence rate of confirmed DCS decreased significantly. Divers with a large PFO experienced the greatest reduction in total DCS. In the conservative group (n = 23), the post-intervention decrease in confirmed DCS incidence rate was not significant. Of note, not all divers returned to diving after closure. Seven subjects reported mild adverse events associated with closure; one subject reported a serious adverse event.

CONCLUSIONS

PFO closure should be considered on an individual basis. In particular, individuals who are healthy, have a significant DCS burden, a large PFO or seek to pursue advanced diving may benefit from closure.

SCUBA Medicine for otolaryngologists: Part I. Diving into SCUBA physiology and injury prevention

OBJECTIVES

Introduce pertinent self-contained underwater breathing apparatus (SCUBA) physiology and corresponding terminology. Appreciate the scope of diving and related otolaryngological injury. Illustrate pathophysiologic mechanisms for diving injuries. Summarize strategies for ear, paranasal sinus, and lung barotrauma prevention, including medical optimization and autoinsufflation techniques.

METHODS

We conducted a review of the available medical and diving literature in English, German, Spanish, Italian Turkish, and French to determine the degree of evidence or lack thereof behind recommendations for treating SCUBA divers. The databases of PubMed, Ovid Medline, and the Cochrane library, as well available textbooks, were queried for relevant data.

RESULTS

Divers are subjected to large pressure gradients within the first few meters of descent. This can lead to gas embolism formation as well as barotrauma secondary to gas expansion/compression in potential closed spaces such as the middle ear, paranasal sinuses, and lungs. Physicians can minimize the risk of injury by counseling patients regarding proper equalization and descent/ascent techniques, and optimizing sinonasal and eustachian tube function. The use of decongestants is controversial.

CONCLUSIONS

Diving is an increasingly popular sport with predominantly otolaryngologic manifestations of injury and disease. Treating SCUBA divers requires a firm understanding of how physiology is altered underwater. This review presents the relevant background information using illustrations to understand the environmental forces acting on divers and how to prevent injury. Laryngoscope, 130:52-58, 2020.

SCUBA Medicine for Otolaryngologists: Part II. Diagnostic, Treatment, and Dive Fitness Recommendations

OBJECTIVES

Challenge current practices and misconceptions in treating recreational SCUBA (Self-contained underwater breathing apparatus) divers. Differentiate patients who are fit to dive and those with relative and absolute contraindications. Redefine the standard of care for fitness to dive parameters based on the most up-to-date evidence.

METHODS

We conducted a review of the available medical and diving literature in English, German, Spanish, Italian, Turkish, and French to determine the degree of evidence or lack thereof behind recommendations for treating SCUBA divers. The databases of PubMed, Ovid Medline, and Cochrane library, as well as available textbooks, were queried for relevant data.

RESULTS

Current recommendations regarding fitness to dive are overly prohibitive given the available evidence. Insufficient evidence currently exists to justify the level of certainty with which some recommendations have been made previously. This is particularly true with regard to postsurgical patients, including those who have undergone stapedectomy or skull base repairs. Updated treatment guidelines, particularly those regarding the timely differentiation of barotrauma and decompression sickness, as well as clearance for return to diving following surgery or trauma, are presented herein.

CONCLUSION

Current guidelines for otorhinolaryngologists governing the diagnosis and treatment of SCUBA divers are lacking and in some instances founded on insufficient evidence. We present an up-to-date, comprehensive guide for otorhinolaryngologists to utilize going forward. Laryngoscope, 130:59-64, 2020.

Prevalence and Risk Factors for Hearing Loss in Chilean Shellfish Divers

BACKGROUND

Diving within artisanal fishing is a profession carried out by many men in coastal communities of southern Chile. These shellfish divers use surface supplied air for breathing. Among potential health threats are occupational accidents, decompression sickness and barotrauma. Repeated middle and inner ear barotrauma and decompression sickness of the ear may result in hearing loss.

OBJECTIVE

To determine the prevalence of hearing loss and related risk factors in artisanal shellfish divers.

METHODS

A cross-sectional study including 125 male shellfish divers was carried out in a coastal village in southern Chile. Participants were interviewed using a standard Spanish questionnaire adapted for this population. Hearing loss was assessed through audiometry. Any hearing loss, sensorineural hearing loss and other types of hearing loss (conduction, unilateral and mixed) were used as the outcomes. Bivariate and multiple logistic regression models were carried out to identify risk factors for hearing loss.

FINDINGS

Median duration on the job was 25 years (range 1-52), 64% of divers had a low level of schooling and 52% reported not knowing how to use decompression tables. Most (86%) of the divers dove deeper than 30 meters exceeding the 20 meters permitted by law. The majority (80%) reported having experienced several episodes of type II decompression sickness during their working life. The prevalence of any type of hearing loss was 54.4%: 29.0% presented sensorineural hearing loss and 25.6% presented other types of hearing impairment. After adjustment for age and other potential risk factors, diving more than 25 years was the main predictor for all kinds of hearing loss under study.

CONCLUSIONS

Hearing loss is frequent in artisanal shellfish divers and safety measures are limited. Although based on small numbers and lacking an unexposed comparison group, our results suggest the need for community-based interventions.

Reliability of right-to-left shunt screening in the prevention of scuba diving related-decompression sickness

OBJECTIVES

The aim of this study was to investigate the relationship between right-to-left shunt (RLS) and the clinical features of decompression sickness (DCS) in scuba divers and to determine the potential benefit for screening this anatomical predisposition in primary prevention.

METHODS

634 injured divers treated in a single referral hyperbaric facility for different types of DCS were retrospectively compared to 259 healthy divers. All subjects had a RLS screening by contrast Transcranial Doppler (TCD) ultrasound according to a standardized method. The number of bubbles detected defined the degree of RLS (small if 5-20 bubbles, large if >20 bubbles).

RESULTS

TCD detected 63% RLS in DCS group versus 32% in the control group (p<0.0001) The overall prevalence of RLS was higher in divers presenting a cerebral DCS (OR, 5.3 [95% CI, 3.2-8.9]; p<0.0001), a spinal cord DCS (OR, 2.1 [95% CI, 1.4-3.1]; p<0.0001), an inner ear DCS (OR, 11.8 [95% CI, 7.4-19]; p<0.0001) and a cutaneous DCS (OR, 17.3 [95% CI, 3.9-77]; p<0.0001) compared to the control group, but not in divers experiencing ambiguous symptoms or musculoskeletal DCS. There was in increased risk of DCS with the size of RLS. The determination of diagnostic accuracy of TCD testing through the estimation of likelihood ratios revealed that predetermination of RLS did not change significantly the prediction of developing or not a DCS event.

CONCLUSION

The assessment of RLS remains indicated after an initial episode of spinal cord, cerebral, inner ear and cutaneous form of DCS but this approach is definitely not recommended in routine practice.

Patent Foramen Ovale (PFO), Personality Traits, and Iterative Decompression Sickness. Retrospective Analysis of 209 Cases

Introduction: There is a need to evaluate the influence of risk factors such as patency of foramen ovale (PFO) or "daredevil" psychological profile on contra-indication policy after a decompression sickness (DCS). Methods: By crossing information obtained from Belgian Hyperbaric Centers, DAN Emergency Hotline, the press, and Internet diving forums, it was possible to be accountable for the majority if not all DCS, which have occurred in Belgium from January 1993 to June 2013. From the available 594 records we excluded all cases with tentative diagnosis, medullary DCS or unreliability of reported dive profile, leaving 209 divers records with cerebral DCS for analysis. Demographics, dive parameters, and PFO grading were recorded. Twenty-three injured divers were tested using the Zuckerman's Sensation Seeking Scale V and compared to a matched group not involved in risky activities. Results: 41.2% of all injured came for iterative DCS. The average depth significantly increases with previous occurrences of DCS (1st DCS: 31.8 ± 7.9 mfw; 2nd DCS: 35.5 ± 9.8 mfw; 3rd DCS: 43.4 ± 6.1 mfw). There is also an increase of PFO prevalence among multiple injured divers (1st DCS: 66.4% 2nd & 3rd DCS: 100%) with a significant increase in PFO grade. Multiple-times injured significantly scored higher than control group on thrill and adventure seeking (TAS), experience seeking, boredom susceptibility and total score. Conclusion: There is an inability of injured diver to adopt conservative dive profile after a DCS. Further work is needed to ascertain whether selected personality characteristics or PFO should be taken into account in the clearance decision to resume diving.

Hyperbaric oxygen therapy for sudden sensorineural hearing loss in divers

OBJECTIVE

Sudden sensorineural hearing loss in divers may be caused by either inner-ear barotrauma or inner-ear decompression sickness. There is no consensus on the best treatment option. This study aimed to evaluate the therapeutic value of hyperbaric oxygen therapy for sudden sensorineural hearing loss in divers.

METHOD

A literature review and three cases of divers with sudden sensorineural hearing loss treated with hyperbaric oxygen therapy are presented.

RESULTS

Hyperbaric oxygen therapy resulted in hearing improvement in 80 per cent of patients: 39 per cent had hearing improvement and 41 per cent had full recovery.

CONCLUSION

Hyperbaric oxygen therapy improved hearing in divers with sudden sensorineural hearing loss.

Saturation diving; physiology and pathophysiology

In saturation diving, divers stay under pressure until most of their tissues are saturated with breathing gas. Divers spend a long time in isolation exposed to increased partial pressure of oxygen, potentially toxic gases, bacteria, and bubble formation during decompression combined with shift work and long periods of relative inactivity. Hyperoxia may lead to the production of reactive oxygen species (ROS) that interact with cell structures, causing damage to proteins, lipids, and nucleic acid. Vascular gas-bubble formation and hyperoxia may lead to dysfunction of the endothelium. The antioxidant status of the diver is an important mechanism in the protection against injury and is influenced both by diet and genetic factors. The factors mentioned above may lead to production of heat shock proteins (HSP) that also may have a negative effect on endothelial function. On the other hand, there is a great deal of evidence that HSPs may also have a "conditioning" effect, thus protecting against injury. As people age, their ability to produce antioxidants decreases. We do not currently know the capacity for antioxidant defense, but it is reasonable to assume that it has a limit. Many studies have linked ROS to disease states such as cancer, insulin resistance, diabetes mellitus, cardiovascular diseases, and atherosclerosis as well as to old age. However, ROS are also involved in a number of protective mechanisms, for instance immune defense, antibacterial action, vascular tone, and signal transduction. Low-grade oxidative stress can increase antioxidant production. While under pressure, divers change depth frequently. After such changes and at the end of the dive, divers must follow procedures to decompress safely. Decompression sickness (DCS) used to be one of the major causes of injury in saturation diving. Improved decompression procedures have significantly reduced the number of reported incidents; however, data indicate considerable underreporting of injuries. Furthermore, divers who are required to return to the surface quickly are under higher risk of serious injury as no adequate decompression procedures for such situations are available. Decompression also leads to the production of endothelial microparticles that may reduce endothelial function. As good endothelial function is a documented indicator of health that can be influenced by regular exercise, regular physical exercise is recommended for saturation divers. Nowadays, saturation diving is a reasonably safe and well controlled method for working under water. Until now, no long-term impact on health due to diving has been documented. However, we still have limited knowledge about the pathophysiologic mechanisms involved. In particular we know little about the effect of long exposure to hyperoxia and microparticles on the endothelium.

Underwater and hyperbaric medicine as a branch of occupational and environmental medicine

Exposure to the underwater environment for occupational or recreational purposes is increasing. As estimated, there are around 7 million divers active worldwide and 300,000 more divers in Korea. The underwater and hyperbaric environment presents a number of risks to the diver. Injuries from these hazards include barotrauma, decompression sickness, toxic effects of hyperbaric gases, drowning, hypothermia, and dangerous marine animals. For these reasons, primary care physicians should understand diving related injuries and assessment of fitness to dive. However, most Korean physicians are unfamiliar with underwater and hyperbaric medicine (UHM) in spite of scientific and practical values.

From occupational and environmental medicine (OEM) specialist’s perspective, we believe that UHM should be a branch of OEM because OEM is an area of medicine that deals with injuries caused by physical and biological hazards, clinical toxicology, occupational diseases, and assessment of fitness to work. To extend our knowledge about UHM, this article will review and update on UHM including barotrauma, decompression illness, toxicity of diving gases and fitness for diving.

Reduced embolic load during clinical cardiopulmonary bypass using a 20 micron arterial filter

Objective:

To compare the efficiency of 20 and 40 µm arterial line filters during cardiopulmonary bypass for the removal of emboli from the extracorporeal circuit.

Methods:

Twenty-four adult patients undergoing surgery were perfused using a cardiopulmonary bypass circuit containing either a 20 µm or 40 µm arterial filter (n = 12 in both groups). The Emboli Detection and Classification system was used to count emboli upstream and downstream of the filter throughout cardiopulmonary bypass. The mean proportion of emboli removed by the filter was compared between the groups.

Results:

The 20 µm filter removed a significantly greater proportion of incoming emboli (0.621) than the 40 µm filter (0.334) (p=0.029). The superiority of the 20 µm filter persisted across all size groups of emboli larger than the pore size of the 40 µm filter.

Conclusion:

The 20 µm filter removed substantially more emboli than the 40 µm filter during cardiopulmonary bypass in this comparison.

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.

Decompression illness

Decompression illness is caused by intravascular or extravascular bubbles that are formed as a result of reduction in environmental pressure (decompression). The term covers both arterial gas embolism, in which alveolar gas or venous gas emboli (via cardiac shunts or via pulmonary vessels) are introduced into the arterial circulation, and decompression sickness, which is caused by in-situ bubble formation from dissolved inert gas. Both syndromes can occur in divers, compressed air workers, aviators, and astronauts, but arterial gas embolism also arises from iatrogenic causes unrelated to decompression. Risk of decompression illness is affected by immersion, exercise, and heat or cold. Manifestations range from itching and minor pain to neurological symptoms, cardiac collapse, and death. First-aid treatment is 100% oxygen and definitive treatment is recompression to increased pressure, breathing 100% oxygen. Adjunctive treatment, including fluid administration and prophylaxis against venous thromboembolism in paralysed patients, is also recommended. Treatment is, in most cases, effective although residual deficits can remain in serious cases, even after several recompressions.