Sudden cardiac death during scuba diving: a case report of a patient with unknown hypertrophic cardiomyopathy

Background

Scuba diving is a recreational activity usually considered at low impact on cardiovascular system. However, when diving, increased ambient pressure exerts several effects on the cardiovascular and pulmonary systems, mainly due to redistribution of peripheral blood into the central circulation. This phenomenon, also known as blood shift, may produce a significant overload on a non-healthy heart.

Case summary

We present the case of a female patient who experienced sudden cardiac death during scuba diving: post-mortem cardiac magnetic resonance and autopsy revealed that the patient was affected by previously unknown hypertrophic cardiomyopathy.

Discussion

Diving exposes the body to significant physiological changes that may overstress a diseased heart. This case suggests the need for some cardiovascular exams, such as an echocardiogram or, at least, an electrocardiogram, for screening cardiovascular abnormalities in subjects who wish to practice scuba diving.

Recreational specialization and the marine-based conservation behaviour intention of recreational divers in Hong Kong

This study examined divers' recreational specialization, pro-environmental attitudes, and marine-based conservation behaviour intentions. A questionnaire-based data collection approach was used to survey 398 divers who visited popular diving sites in Hong Kong by employing structural equation modelling to determine the potential relationships among the proposed variables. The results showed a statistically positive relationship between divers' recreational specialization and their pro-environmental attitudes, along with a statistically valid relationship between divers' recreational specialization and their marine-based conservation behaviour intentions. However, divers' pro-environmental attitudes were not statistically significant with their marine-based conservation behaviour intentions; thus, the discrepancy regarding different research findings between the current and previous studies was further discussed. In particular, our findings confirmed that recreational specialization could be a reliable predictor of divers' pro-environmental attitudes and marine-based conservation behaviour intentions to fill the research gaps regarding scuba diving-based nature tourism in Hong Kong. Consequently, management implications and recommendations were presented in accordance with the development of marine environmental conservation and sustainable scuba diving tourism in Hong Kong.

Fatal diving accidents in Genoa (North-West Italy) from 1968 to 2021: Forensic approach and literature review

Scuba diving is one of the most common and practised water sport activities in Genoa, especially in the more recent years. Although scuba diving is generally considered a safe activity, this does not exclude the possibility of serious or fatal accidents from happening. This retrospective study investigates the case history of deaths resulting from diving accidents recorded by the Municipal Morgue of Genoa over a period of 53 years, specifically from 1968 to 2021. Of the total 52 deaths covered by the study, 48 were male with an age range of 16-71 years. In 25 of these subjects, pre-existing pathological conditions of a cardiovascular nature, not recognised at the time of death, were reported. Out of the total deaths studied, 9 subjects died following a diving accident related to free diving, while 43 subjects died from scuba or rebreather diving. Among the latter subjects, the cause of death was attributed to drowning in 17 cases, arterial gas embolism (AGE) from pulmonary over-distension in 11 cases, cardio-circulatory arrest (CA) favoured by pre-existing and non-existing heart disease known prior to the death in 10 cases, decompression sickness (DCS) in 2 cases, a combination of DCS and AGE in 2 cases and oxygen intoxication in 1 case. Twelve of the fatal accidents occurred in the marine area near the village of Arenzano, where the shipwreck of the oil tanker, the "Haven", sank in 1991 and is today the largest shipwreck explored by divers in the Mediterranean Sea. In all cases of diving deaths, a multi-disciplinary approach is important: in particular, the role of the forensic pathologist is essential in order to accurately reconstruct the dynamics of the accident, thus identifying the predisposing or triggering factors that led to death, and defining the cause of it.

Recommendations on scuba diving in Birt-Hogg-Dubé syndrome

INTRODUCTION

Although very uncommon, severe injury and death can occur during scuba diving. One of the main causes of scuba diving fatalities is pulmonary barotrauma due to significant changes in ambient pressure. Pathology of the lung parenchyma, such as cystic lesions, might increase the risk of pulmonary barotrauma.

AREAS COVERED

Birt-Hogg-Dubé syndrome (BHD), caused by pathogenic variants in the FLCN gene, is characterized by skin fibrofolliculomas, an increased risk of renal cell carcinoma, multiple lung cysts and spontaneous pneumothorax. Given the pulmonary involvement, in some countries patients with BHD are generally recommended to avoid scuba diving, although evidence-based guidelines are lacking. We aim to provide recommendations on scuba diving for patients with BHD, based on a survey of literature on pulmonary cysts and pulmonary barotrauma in scuba diving.

EXPERT OPINION

In our opinion, although the absolute risks are likely to be low, caution is warranted. Given the relative paucity of literature and the potential fatal outcome, patients with BHD with a strong desire for scuba diving should be informed of the potential risks in a personal assessment. If available a diving physician should be consulted, and a low radiation dose chest computed tomography (CT)-scan to assess pulmonary lesions could be considered.

A review of 149 Divers Alert Network emergency call records involving diving minors

INTRODUCTION

Minors have been scuba diving for decades, and while the initial concerns about potential long-term complications related to bone development appear to be unfounded, the incidence of scuba diving injuries among them has been poorly studied.

METHODS

We reviewed 10,159 cases recorded in the DAN Medical Services call centre database from 2014 through 2016 and identified 149 cases of injured divers younger than 18 years. Records were analysed for case categorisation on the most common dive injuries. Information about demographics, level of training, risk factors, and relevant behavioural aspects were collected when available.

RESULTS

While the most common reason for the call was to rule out decompression sickness, the majority of cases pertained to ear and sinus issues. However, 15% of the dive-related injuries involving minors had a final diagnosis of pulmonary barotrauma (PBt). While no reliable data is available on the incidence of PBt in adult divers, the authors' impression based on personal experience suggests that the number of cases of PBt in minors trends higher than in the general diving population. The narratives on some relevant records describe unmanageable levels of anxiety leading to panic.

CONCLUSIONS

Based on the results and narratives on these cases, it is reasonable to infer that psychological immaturity, suboptimal management of adverse situations, and inadequate supervision might have led to severe injuries among these minor divers.

Are the seafloors of marine protected areas sinks for marine litter? Composition and spatial distribution in Cabrera National Park

The seafloors of oceans and seas are becoming major sinks for marine litter (ML) at a global scale and especially within the Mediterranean Sea. Within global oceans and seas, Marine Protected Areas (MPAs) have been established to protect and conserve marine habitats and increase marine biodiversity. In this study, extensive coastal shallow scuba diving surveys were conducted in 2019 and 2020 to identify the distribution of ML in the MPA of Cabrera Marine-Terrestrial National Park (Cabrera MPA) in the Balearic Islands. Approximately 900 items weighing 70.1 kg were collected throughout the MPA during the underwater surveys. Glass bottles, including pieces (25-30%) and glass or ceramic fragments >2.5 cm (8-19%) were the most common identified items followed by plastic food containers and plastic bags (~8%). Overall, 75% of the abundance of collected ML was observed during the first year. In terms of the protection status of the different locations, similar abundances of ML were found in public access areas and no-take areas. Additionally, no significant differences were identified according to location indicating that ML on the seafloor was homogeneous within the studied shallow coastal areas. Overall, the results indicate that Cabrera MPA is a hotspot for ML and mitigation actions and measures, such as annual cleaning efforts, can help to prevent and minimize ML accumulation on the seafloor.

Post COVID-19 fitness to dive assessment findings in occupational and recreational divers

INTRODUCTION

It is now known that COVID-19 has long term effects that may not correlate with clinical severity of disease. The known pulmonary and cardiovascular changes as well as thrombotic tendency could predispose to diving accidents. We aimed to investigate COVID-19 related changes that may cause disqualification from diving among divers who recovered from the disease.

METHODS

Occupational and recreational divers who applied for fitness to dive (FTD) assessment after COVID-19 infection were included. Routine FTD assessments were performed. Details of COVID-19 history were evaluated. Lung computed tomography (CT) scans were advised if not previously performed or if there were COVID-19 related changes in previous scans. Divers with pathological findings were restrained from diving and followed prospectively.

RESULTS

Forty-three divers were analysed. Thirteen divers were restrained from diving, all due to persistent COVID-19 related changes in lung CT. The prevalence of CT with at least one lung lesion was 68.2% at the time of diagnosis, 73.3% in the first three months after diagnosis and 19.2% later. The most common CT findings were glass ground opacities and fibrotic changes. Demographic characteristics and COVID-19 history of divers deemed 'unfit' were similar to those deemed 'fit'.

CONCLUSIONS

Divers who recover from COVID-19 should undergo FTD assessments before resuming diving. A chest CT performed at least three months after diagnosis may be suggested.

A Doppler ultrasound self-monitoring approach for detection of relevant individual decompression stress in scuba diving

Observing modern decompression protocols alone cannot fully prevent diving injuries especially in repetitive diving. Professional audio Doppler bubble measurements are not available to sports scuba divers. If those non-professionals were able to learn audio Doppler self-assessment for bubble grading, such skill could provide significant information on individual decisions with respect to diving safety. We taught audio Doppler self-assessment of subclavian and precordial probe position to 41 divers in a 45-min standardized, didactically optimized training. Assessment before and after air dives within sports diving limits was made through 684 audio Doppler measurements in dive-site conditions by both trained divers and a medical professional, plus additional 2D-echocardiography reference. In all dives (average maximum depth 22 m; dive time 44 min), 33% of all echocardiography measurements revealed bubbles. The specificity of audio bubble detection in combination of both detection sites was 95%, and sensitivity over all grades was 40%, increasing with higher bubble grades. Dive-site audio-Doppler-grading underestimated echo-derived bubble grades. Bubble detection sensitivity of audio Doppler self-assessments, compared to an experienced examiner, was 62% at subclavian and 73% at precordial position. 6 months after the training and 4.5 months after the last measurement, the achieved Doppler skill level remained stable. Audio Doppler self-assessment can be learned by non-professionals in a single teaching intervention. Despite accurate bubble grading is impossible in dive-site conditions, relevant high bubble grades can be detected by non-professionals. This qualitative information can be important in self-evaluating decompression stress and assessing measures for increased diving safety.

Does persistent (patent) foramen ovale closure reduce the risk of recurrent decompression sickness in scuba divers?

INTRODUCTION

Interatrial communication is associated with an increased risk of decompression sickness (DCS) in scuba diving. It has been proposed that there would be a decreased risk of DCS after closure of the interatrial communication, i.e., persistent (patent) foramen ovale (PFO). However, the clinical evidence supporting this is limited.

METHODS

Medical records were reviewed to identify Swedish scuba divers with a history of DCS and catheter closure of an interatrial communication. Thereafter, phone interviews were conducted with questions regarding diving and DCS. All Swedish divers who had had catheter-based PFO-closure because of DCS were followed up, assessing post-closure diving habits and recurrent DCS.

RESULTS

Nine divers, all with a PFO, were included. Eight were diving post-closure. These divers had performed 6,835 dives (median 410, range 140-2,200) before closure, and 4,708 dives (median 413, range 11-2,000) after closure. Seven cases with mild and 10 with serious DCS symptoms were reported before the PFO closure. One diver with a small residual shunt suffered serious DCS post-closure; however, that dive was performed with a provocative diving profile.

CONCLUSION

Divers with PFO and DCS continue to dive after PFO closure and this seems to be fairly safe. Our study suggests a conservative diving profile when there is a residual shunt after PFO closure, to prevent recurrent DCS events.

Ocular alterations in divers: 2 case reports and literature review

Scuba diving can be practiced recreationally or professionally. In both modalities the diver can be exposed to risks such as decompression syndrome and thus, the use of a hyperbaric chamber, hyper-oxygenation of the gas cylinder, barotrauma, and immersion in closed circuits. These situations have some phenomena in common, such as the great pressure differences, which can cause a wide range of alterations, including ophthalmological ones. The development of index myopia and nuclear cataract are ocular findings frequently associated with increased oxygen pressure. In this context, an imbalance is established between oxidative species and antioxidant defences, such as glutathione, which has a key role in maintaining the transparency of the lens. The cases are presented of 2 young coral fisher patients, who had recently developed a progressive myopisation associated with nuclear cataracts.

Considerations for scuba and breath-hold divers during the COVID-19 pandemic: A call for awareness

In late 2019, a highly pathogenic novel coronavirus (CoV), severe acute respiratory syndrome (SARS)-CoV-2 emerged from Wuhan, China and led to a global pandemic. SARS-CoV-2 has a predilection for the pulmonary system and can result in serious pneumonia necessitating hospitalisation. Computed tomography (CT) chest scans of patients with severe symptoms, show signs of multifocal bilateral ground or ground-glass opacities (GGO) associated with consolidation areas with patchy distribution. However, it is less well known that both asymptomatic and mild symptomatic patients may exhibit similar lung changes. Presumably, the various pathological changes in the lungs may increase the risk of adverse events during diving (e.g., lung barotrauma, pulmonary oedema, etc.), thus these lung manifestations need to be considered prior to allowing resumption of diving. Presently, it is not known how the structural changes in the lungs develop and to what extent they resolve, in particular in asymptomatic carriers and patients with mild disease. However, current evidence indicates that a month of recovery may be too short an interval to guarantee complete pulmonary restitution even after COVID-19 infections not demanding hospital care.

Impaired consciousness when scuba diving associated with vasovagal syncope

INTRODUCTION

Drowning is likely to result from impairment of consciousness when scuba diving. Causes include toxic effects of breathing gas, including nitrogen narcosis and oxygen toxicity, and arterial gas embolism.

METHODS

Review of the medical records of scuba divers who had impaired consciousness underwater that could not be attributed to toxic effects of breathing gas or arterial gas embolism.

RESULTS

Four scuba divers had episodes of impaired consciousness when at shallow depths (8-18 m) underwater. The descriptions of the episodes were very similar. Three had histories of recurrent episodes of vasovagal syncope on land.

CONLCUSIONS

Absence of other causes for their impaired consciousness underwater leads to the conclusion that the probable cause was vasovagal syncope.

Comparison of tissue oxygenation achieved breathing oxygen using different delivery devices and flow rates

INTRODUCTION

Divers with suspected decompression illness require high concentration oxygen (O₂). There are many different O₂ delivery devices, with few data comparing their performance. This study evaluated O₂ delivery, using tissue O₂ partial pressure (P_tcO₂), in healthy divers breathing O₂ via three different delivery devices.

METHODS

Twelve divers had P_tcO₂ measured at six limb sites. Participants breathed O₂ from: a demand valve using an intraoral mask with a nose clip (NC); a medical O₂ rebreathing system (MORS) with an oronasal mask and with an intraoral mask; and a non-rebreather mask (NRB) at 15 or 10 L·min⁻¹ O₂ flow. In-line inspired O₂ F_IO₂) and nasopharyngeal F_IO₂ were measured. Participants provided subjective ratings of device comfort, ease of breathing, and overall ease of use.

RESULTS

P_tcO₂ values and nasopharyngeal FIO₂ were similar with the demand valve with intraoral mask, MORS with both masks and the NRB at 15 L·min⁻¹. P_tcO₂ and nasopharyngeal F_IO₂ values were significantly lower with the NRB at 10 L·min⁻¹. The NRB was rated as the most comfortable to wear, easiest to breathe with, and overall the easiest to use.

CONCLUSION

Of the commonly available devices promoted for O₂ delivery to injured divers, similar PtcO₂ and nasopharyngeal F_IO₂ values were obtained with the three devices tested: MORS with an oronasal or intraoral mask, demand valve with an intraoral mask and NRB at a flow rate of 15 L·min⁻¹. P_tcO₂ and nasopharyngeal F_IO₂ values were significantly lower when the flow rate using the NRB was decreased to 10 L·min⁻¹.

Thermal balance of spinal cord injured divers during cold water diving: A case control study

INTRODUCTION

This study compared the thermal balance of spinal cord injured (SCI) divers and able-bodied (AB) divers during recreational cold-water dives.

METHODS

Ten divers (5 AB, 5 SCI) in matched pairs dived in a shallow lake (temperature 6°C) for 30 to 36 min wearing 5 mm 'Long John' neoprene wetsuits. A gastrointestinal temperature radio pill recorded gastro-intestinal temperature (T_gi) prior to, immediately after and at 5, 10, 15, 30, 60, 120 min post-dive. Subjective ratings of temperature perception were recorded concomitantly using a visual analogue scale (VAS).

RESULTS

No difference between SCI and AB divers in Tgi before the dive was observed (P = 0.85). After the dive, SCI divers cooled significantly more than AB at all measured time intervals (P < 0.001). Post dive, the mean maximum fall in Tgi during the recovery phase in SCI divers was 0.85°C (SD 0.20) and in the AB group was 0.48°C (0.48). In addition, there was greater individual variation in SCI divers compared to AB divers. There were no statistically significant differences in temperature perception between the groups either before or at any time after the dives.

CONCLUSIONS

In contrast to AB divers, divers with SCI were unable to maintain Tgi during short shallow dives in 6°C water and their temperatures fell further post-dive. The reduction in Tgi was not reflected in the subjective ratings of temperature perception by the SCI divers. The study was too small to assess how the level of spinal injury influenced thermal balance.

Endothelial function may be enhanced in the cutaneous microcirculation after a single air dive

INTRODUCTION

The effects of scuba diving on the vessel wall have been studied mainly at the level of large conduit arteries. Data regarding the microcirculation are scarce and indicate that these two vascular beds are affected differently by diving.

METHODS

We assessed the changes in cutaneous microcirculation before an air scuba dive, then 30 min and 24 h after surfacing. Endothelium-dependent and independent vasomotion were successively elicited by iontophoretic administration of acetylcholine and sodium nitroprusside respectively, and cutaneous blood flux was monitored by laser Doppler flowmetry.

RESULTS

The response to sodium nitroprusside was significantly lower 30 min after surfacing than before diving (50 (SEM 6)% of the pre-dive values, P = 0.0003) and returned to normal values 24 h post-dive (102 (29)% of the pre-dive values, P = 0.113). When compared to pre-dive values, acetylcholine elicited a hyperaemia which was not statistically different 30 min after surfacing (123 (17)% of the pre-dive values, P = 0.230), but significantly increased 24 h post-dive (148 (10)% of the pre-dive values, P = 0.005).

CONCLUSION

Microvascular smooth muscle function is transiently impaired after diving. On the contrary, microvascular endothelial function is enhanced for up to 24 h after diving. This further suggests that the microcirculation reacts differently than large conduit arteries to scuba diving. The impact of modifications occurring in the microvascular bed on the physiological effects of diving merits further study.

Anxiety impact on scuba performance and underwater cognitive processing ability

INTRODUCTION

Anxiety is a substantial consideration in scuba diving and may influence a diver's performance and cognitive activities. This study aimed to simultaneously observe the effect of anxiety trait on actual diving performance and underwater cognitive processing ability.

METHODS

Twenty-seven scuba divers completed the STAI-T component of the State-Trait Anxiety Inventory, and were subdivided into two groups on the basis of trait anxiety scores ≥ 39 and < 39. Scuba diving performance was measured in a pool. The completion time of four standardised scuba skills was recorded by a diving instructor. The correct completion rate and response time for a cognitive function assessment (number-Stroop test) were measured both on land ('dry') and underwater at 5 metres' fresh water.

RESULTS

Anxiety trait was associated with prolonged mask clearing: mean completion time 7.1 (SD 3.2) s vs. 10.8 (5.4) s in low and high anxiety trait divers respectively (P = 0.04). Low (vs high) anxiety trait divers had reduced response times for the number-Stroop test: 49.8 (3.0) s vs. 53.3 (5.4) s (P = 0.04) dry, and 64.4 (5.0) s vs. 72.5 (5.5) s (P < 0.01) underwater. Performance of other skills was not significantly affected by trait anxiety nor correlated with the number-Stroop test results.

CONCLUSIONS

Personal anxiety trait prolongs mask clearing and underwater cognitive processing ability but the latter did not affect execution of other underwater scuba diving skills.

Effects of recreational scuba diving on erythropoiesis-"normobaric oxygen paradox" or "plasma volume regulation" as a trigger for erythropoietin?

PURPOSE

Previous studies have shown an increase in erythrocyte lipid peroxidation and a decrease in red blood cell (RBC) count, hemoglobin, and hematocrit after only one recreational scuba diving session. The aim of this study was to examine the effect of repetitive scuba diving on RBC parameters and erythropoiesis.

METHODS

Divers (N = 14) conducted one dive per week over 5 weeks at a depth of 20-30 m for 30 min. For measuring RBC parameters, erythropoietin, iron, and ferritin, blood samples were collected before and after the first, third, and fifth dive.

RESULTS

Between pre- and post-dive results, a statistically significant increase in RBC count, hemoglobin, hematocrit, mean corpuscular volume (MCV), RBC distribution width (RDW), iron, and ferritin was observed. Analysis of the results between the first, third, and fifth dive showed that the erythropoietin increase at the third (pre-dive p = 0.009; post-dive p = 0.004) and fifth dive (pre-dive p < 0.001; post-dive p = 0.003) was not accompanied by changes in RBC count, hemoglobin, iron, and ferritin. In parallel, a continuous increase in hematocrit, MCV, and RDW was observed, whereas mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC) decreased.

CONCLUSIONS

Changes in RBC indices and EPO elevation indicate that the occasional switch from hyperoxia to normoxia or mechanisms for plasma volume regulation may be a step in the maintenance of erythropoiesis.

Ecological impacts and management strategies for recreational diving: A review

Recreational diving is an expanding branch of ecotourism that when poorly managed, may cause considerable impacts to benthic organisms. Such impacts become a matter of concern in popular diving destinations. A systematic literature review was used to verify the characteristics of divers who cause damage to reefs, the effects on benthic organisms, and the range of management interventions available. We describe the knowledge gaps, addressed challenges and propose solutions hoping to reach successful management of diving tourism industry. We identified three main challenges on recreational diving management frameworks and discussed actions to overcome such challenges. The challenges are related to (1) the lack of baseline data and long-term monitoring; (2) integration of scientific research and management; and (3) adaptive management strategies and stakeholder involvement.

A new form of admissible pressure for Haldanian decompression models

In this article, we propose and study a new form of admissible pressure in the Haldanian framework. We then use it to study the surjectivity of the Gradient Factors on the space of the reachable decompression profiles, and investigate a particular case. This case leads to the proposition of a decompression strategy, whose crucial parameter is the ascent rate. An appropriate ascent rate is suggested as recommended by COMEX, through a physiologically relevantmethod. This new strategy enables the unification of the COMEX approach (not based on a tissuesaturation theory), with the Haldanian method.

Descriptive study of diving injuries in the Canary Islands from 2008 to 2017

INTRODUCTION

This research reports the epidemiology of diving injuries managed in the Hyperbaric Medicine Unit of the Canary Islands University Hospital.

METHODS

Data were extracted from the clinical records of all divers injured and admitted to the unit for treatment of dysbaric diving injuries between 2008 and 2017, inclusive.

RESULTS

One-hundred and thirty diving injuries were recorded. Most (71%) occurred in men and 43% were foreigners. Eighteen per cent either had no diving certification or that information was not recorded in the clinical chart. Only a third of the 40% of divers who had some form of on-site first aid treatment received oxygen and oral rehydration. Type 1 decompression sickness (DCS) was diagnosed in 56 divers (43%) and Type 2 in 67 (52%), whilst seven were treated for omitted decompression. At discharge, 122 (94%) were asymptomatic, whilst 5% experienced some residual sensory or other changes. One diver who presented late remained quadriparetic and one, admitted in a state of coma, died. Only 76% of the injured divers had specific diving accident insurance and, of those, 58% were foreign divers.

CONCLUSIONS

Over half of the injured divers did not receive any on-site first aid. The majority (94%) of treated injured divers were discharged without sequelae. Based on these data, several public health recommendations for the Canary Islands are made.

Decompression illness and other injuries in a recreational dive charter operation

INTRODUCTION

Health and safety within the recreational diving industry are poorly described. We aimed to obtain the true prevalence of decompression illness (DCI) and other diving and non-diving injuries, including occupational injuries, in a large recreational diving charter operation.

METHODS

A New Zealand recreational diving operator keeps detailed records of diving activity and event/incident reports. We extracted passenger and crew numbers, dive numbers and incident statistics from all boat trips and associated work-related injuries between 01 January 2008 and 31 December 2014. The records of divers referred to the regional hyperbaric unit for suspected DCI were reviewed retrospectively. Using these data the prevalence of DCI and non-diving injuries were calculated.

RESULTS

There were 65,536 person-trips to sea and 57,072 divers undertook 97,144 dives. Fifty-five injury events were documented over seven years, 31 in customers and 24 in staff. Four divers (including one staff member) diagnosed with DCI underwent recompression therapy, giving a prevalence of 0.41 cases requiring recompression per 10,000 dives, or one case per 24,386 dives, whilst five other divers were assessed as not having DCI. There was one cardiac-related fatality. Thirty-five non-diving injuries (mainly lacerations and minor musculoskeletal injuries) were documented in 30 people resulting in 10 consulting a general practitioner and seven presenting to the local regional hospital emergency department.

CONCLUSIONS

DCI requiring recompression was relatively rare in this supervised recreational diving operation. Minor non-diving injuries were the most common adverse event. Compared to other adventure sports, the prevalence of injury in recreational scuba diving is low.

Comparison of tissue oxygenation achieved breathing oxygen from a demand valve with four different mask configurations

INTRODUCTION

High concentration normobaric oxygen (O₂) is a priority in treating divers with suspected decompression illness. The effect of different O₂ mask configurations on tissue oxygenation when breathing with a demand valve was evaluated.

METHODS

Sixteen divers had tissue oxygen partial pressure (PtcO₂) measured at six limb sites. Participants breathed O₂ from a demand valve using: an intraoral mask (IOM®) with and without a nose clip (NC), a pocket face mask and an oronasal mask. In-line inspired O₂ (FIO₂) and nasopharyngeal FIO₂ were measured. Participants provided subjective ratings of mask comfort, ease of breathing and holding in position.

RESULTS

PtcO₂ values and nasopharyngeal FIO₂ (median and range) were greatest using the IOM with NC and similar with the IOM without NC. O₂ measurements were lowest with the oronasal mask which also was rated as the most difficult to breathe from and to hold in position. The pocket face mask was reported as the most comfortable to wear. The NC was widely described as uncomfortable. The IOM and pocket face mask were rated best for ease of breathing. The IOM was rated as the easiest to hold in position.

CONCLUSION

Of the commonly available O₂ masks for use with a demand valve, the IOM with NC achieved the highest PtcO₂ values. PtcO₂ and nasopharyngeal FIO₂ values were similar between the IOM with and without NC. Given the reported discomfort of the NC, the IOM without NC may be the best option.

Vibration and bubbles: a systematic review of the effects of helicopter retrieval on injured divers

INTRODUCTION

Vibration from a helicopter during aeromedical retrieval of divers may increase venous gas emboli (VGE) production, evolution or distribution, potentially worsening the patient's condition.

AIM

To review the literature surrounding the helicopter transport of injured divers and establish if vibration contributes to increased VGE.

METHOD

A systematic literature search of key databases was conducted to identify articles investigating vibration and bubbles during helicopter retrieval of divers. Level of evidence was graded using the Oxford Centre for Evidence-Based Medicine guidelines. A modified quality assessment tool for studies with diverse designs (QATSDD) was used to assess the overall quality of evidence.

RESULTS

Seven studies were included in the review. An in vitro research paper provided some evidence of bubble formation with gas supersaturation and vibration. Only one prospective intervention study was identified which examined the effect of vibration on VGE formation. Bubble duration was used to quantify VGE load with no difference found between the vibration and non-vibration time periods. This study was published in 1980 and technological advances since that time suggest cautious interpretation of the results. The remaining studies were retrospective chart reviews of helicopter retrieval of divers. Mode of transport, altitude exposure, oxygen and intravenous fluids use were examined.

CONCLUSION

There is some physical evidence that vibration leads to bubble formation although there is a paucity of research on the specific effects of helicopter vibration and VGE in divers. Technological advances have led to improved assessment of VGE in divers and will aid in further research.

A diver with immersion pulmonary oedema and prolonged respiratory symptoms

Immersion pulmonary oedema (IPE) is particularly associated with an excessive reaction to exercise and/or cold stress. IPE usually resolves without recompression therapy within a day or two. Herein we report a diver diagnosed with IPE, in whom symptoms persisted for five days. A 58-year-old man presented with sudden onset of dyspnoea, cough and haemoptysis after surfacing. He was an experienced diving instructor with a history of moderate mitral valve regurgitation. While IPE was diagnosed and oxygen administered, respiratory symptoms deteriorated, and serum C-reactive protein elevated. No evidence of infection was seen. Three hyperbaric oxygen treatments were given on the basis of suspected decompression sickness, and symptoms subsequently resolved. The recently diagnosed mitral valve regurgitation and inflammatory response were considered to have contributed to the prolongation of symptoms.

Time to stop mucking around? Impacts of underwater photography on cryptobenthic fauna found in soft sediment habitats

Scuba diving tourism is a sustainable source of income for many coastal communities, but can have negative environmental impacts if not managed effectively. Diving on soft sediment habitats, typically referred to as 'muck diving', is a growing multi-million dollar industry with a strong focus on photographing cryptobenthic fauna. We assessed how the environmental impacts of scuba divers are affected by the activity they are engaged in while diving and the habitat they dive in. To do this, we observed 66 divers on coral reefs and soft sediment habitats in Indonesia and the Philippines. We found diver activity, specifically interacting with and photographing fauna, causes greater environmental disturbances than effects caused by certification level, gender, dive experience or age. Divers touched the substrate more often while diving on soft sediment habitats than on coral reefs, but this did not result in greater environmental damage on soft sediment sites. Divers had a higher impact on the substrate and touch animals more frequently when observing or photographing cryptobenthic fauna. When using dSLR-cameras, divers spent up to five times longer interacting with fauna. With the unknown, long-term impacts on cryptobenthic fauna or soft sediment habitats, and the increasing popularity of underwater photography, we argue for the introduction of a muck diving code of conduct.

Probabilistic pharmacokinetic models of decompression sickness in humans: Part 2, coupled perfusion-diffusion models

Decompression sickness (DCS) can be experienced following a reduction in ambient pressure; such as that associated with diving or ascent to high altitudes. DCS is believed to result when supersaturated inert gas dissolved in biological tissues exits solution and forms bubbles. Models to predict the probability of DCS are typically based on nitrogen and/or helium gas uptake and washout in several theoretical tissues, each represented by a single perfusion-limited compartment. It has been previously shown that coupled perfusion-diffusion compartments are better descriptors than solely perfusion-based models of nitrogen and helium uptake and elimination kinetics observed in the brain and skeletal muscle of sheep. In this work, we examine the application of these coupled pharmacokinetic structures with at least one diffusion compartment to the prediction of the incidence of decompression sickness in humans. We compare these models to LEM-NMRI98, a well-described U.S. Navy gas content model, consisting of three uncoupled perfusion-limited compartments incorporating oxygen and linear-exponential kinetics. Pharmacokinetic gas content models with a diffusion component describe the probability of DCS in human bounce dives made with air, single non-air bounce dives, and oxygen decompression dives better than LEM-NMRI98. However, for the full data set, LEM-NMRI98 remains the best descriptor of the data.

Turkish recreational divers: a comparative study of their demographics, diving habits, health and attitudes towards safety

INTRODUCTION

In Turkey, scuba diving has become more popular and accessible in the past decade and there has been a commensurate rise in the number of certified divers. This new generation of recreational divers has not been described in detail previously. The aim of this study was to profile this group, while investigating any gender differences and making comparisons with the global diving community.

METHODS

Turkish dive club members and diving forum⁄blog readers were invited to complete an online questionnaire investigating their demography, medical issues and diving history and habits.

RESULTS

The questionnaire was completed by 303 female and 363 male divers. Significant differences were found between the sexes in terms of demographics, diving experience and attitudes toward safety. Previous or ongoing medical conditions were reported by 100 female divers and 141 males. Only 29% of females and 22% of males had been examined by a physician trained to conduct assessments of fitness to dive. Female divers did not report problems while diving during menstruation or while taking oral contraceptives. There was no significant difference in the occurrence of decompression sickness (DCS) and DCS-like symptoms between the sexes.

CONCLUSION

This is the largest study to date conducted on recreational divers in Turkey and so carries some value. It profiles their physical and behavioral attributes as well as differences in diving practices between the sexes in Turkey. Our findings should have implications for medical screening and dive training standards.

Chain of events analysis for a scuba diving fatality

INTRODUCTION

A scuba diving fatality usually involves a series of related events culminating in death. Several studies have utilised a chain of events-type analysis (CEA) to isolate and better understand the accident sequence in order to facilitate the creation of relevant countermeasures. The aim of this research was to further develop and better define a process for performing a CEA to reduce potential subjectivity and increase consistency between analysts.

METHODOLOGY

To develop more comprehensive and better-defined criteria, existing criteria were modified and a template was created and tested using a CEA. Modifications comprised addition of a category for pre-disposing factors, expansion of criteria for the triggers and disabling agents present during the incident, and more specific inclusion criteria to better encompass a dataset of 56 fatalities. Four investigators (raters) used both the previous criteria and this template, in randomly assigned order, to examine a sample of 13 scuba diver deaths. Individual results were scored against the group consensus for the CEA. Raters' agreement consistency was compared using the Index of Concordance and intra-class correlation coefficients (ICC).

RESULTS

The template is presented. The index of concordance between the raters increased from 62% (194⁄312) using the previous criteria to 82% (257⁄312) with use of this template indicating a substantially higher inter-rater agreement when allocating criteria. The agreement in scoring with and without template use was also quantified by ICC which were generally graded as low, illustrating a substantial change in consistency of scoring before and after template use.

CONCLUSION

The template for a CEA for a scuba diving fatality improves consistency of interpretation between users and may improve comparability of diving fatality reports.

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.

Superior canal dehiscence syndrome associated with scuba diving

A 28-year-old female diver presented with dizziness and difficulty clearing her left ear whilst scuba diving. Her pure-tone audiometry and tympanometry were normal. Testing of Eustachian tube function revealed tubal stenosis. Video-oculography revealed a predominantly torsional nystagmus while the patient was in the lordotic position. Fistula signs were positive. High-resolution computed tomography (HRCT) of the temporal bone revealed a diagnosis of bilateral superior semicircular canal dehiscence (SCDS). Cervical vestibular-evoked myogenic potential (cVEMP) testing showed that the amplitude of the cVEMP measured from her left ear was larger than that from the right. In electronystagmography (ENG), nose-pinched Valsalva manoeuvres caused eye movements to be mainly directed counterclockwise with a vertical component. Tullio phenomenon was also positive for both ears. SCDS patients tend to be misdiagnosed and misunderstood; common misdiagnoses in these cases are alternobaric vertigo (AV), inner ear barotrauma, and inner-ear decompression sickness. It is difficult to diagnose vertigo attacks after scuba diving as SCDS; however, when the patient develops sound- and/or pressure-induced vertical-torsional nystagmus, HRCT should be conducted to confirm a diagnosis of SCDS.

Probabilistic pharmacokinetic models of decompression sickness in humans, part 1: Coupled perfusion-limited compartments

Decompression sickness (DCS) is a disease caused by gas bubbles forming in body tissues following a reduction in ambient pressure, such as occurs in scuba diving. Probabilistic models for quantifying the risk of DCS are typically composed of a collection of independent, perfusion-limited theoretical tissue compartments which describe gas content or bubble volume within these compartments. It has been previously shown that 'pharmacokinetic' gas content models, with compartments coupled in series, show promise as predictors of the incidence of DCS. The mechanism of coupling can be through perfusion or diffusion. This work examines the application of five novel pharmacokinetic structures with compartments coupled by perfusion to the prediction of the probability and time of onset of DCS in humans. We optimize these models against a training set of human dive trial data consisting of 4335 exposures with 223 DCS cases. Further, we examine the extrapolation quality of the models on an additional set of human dive trial data consisting of 3140 exposures with 147 DCS cases. We find that pharmacokinetic models describe the incidence of DCS for single air bounce dives better than a single-compartment, perfusion-limited model. We further find the U.S. Navy LEM-NMRI98 is a better predictor of DCS risk for the entire training set than any of our pharmacokinetic models. However, one of the pharmacokinetic models we consider, the CS2T3 model, is a better predictor of DCS risk for single air bounce dives and oxygen decompression dives. Additionally, we find that LEM-NMRI98 outperforms CS2T3 on the extrapolation data.

Mishaps and unsafe conditions in recreational scuba diving and pre-dive checklist use: a prospective cohort study

Background

Recreational scuba diving involves the use of complex instruments and specialized skills in an unforgiving environment. Errors in dive preparation in such an environment may lead to unsafe conditions, mishaps, injuries and fatalities. Diving mishaps can be major and minor based on their potential to cause injury and the severity of the resulting injury. The objective of this study is to assess the incidence of diving mishaps and unsafe conditions, and their associations with the participants’ routine use of their own checklists.

Methods

Between June and August 2012, 426 divers participated in the control group of a randomized trial to evaluate the effectiveness of an intervention pre-dive checklist. The current nested analysis prospectively follows the control participants, who did not receive the intervention checklist. Poisson regression models with generalized estimating equations were used to estimate rate ratios comparing written checklist use with memorized and no checklist use.

Results

The overall incidence of major mishaps and minor mishaps was 11.2 and 18.2 per 100 dives, respectively. Only 8% participants reported written checklist use, 71% reported using memorized checklists, and 21% did not use any checklist. The rate ratio for written checklist use as compared to using a memorized or no checklist was 0.47 (95%CI: 0.27, 0.83) for all mishaps (major and minor combined), and 0.31 (95% CI: 0.10, 0.93) for major mishaps. The rate of mishaps among memorized checklist users was similar to no checklist users.

Conclusion

This study reinforces the utility of written checklists to prevent mishaps and, potentially, injuries and fatalities.

A comparative evaluation of two decompression procedures for technical diving using inflammatory responses: compartmental versus ratio deco

INTRODUCTION

The aim of this study was to compare two decompression procedures commonly adopted by technical divers: the ZH-L16 algorithm modified by 30/85 gradient factors (compartmental decompression model, CDM) versus the 'ratio decompression strategy' (RDS). The comparison was based on an analysis of changes in diver circulating inflammatory profiles caused by decompression from a single dive.

METHODS

Fifty-one technical divers performed a single trimix dive to 50 metres' sea water (msw) for 25 minutes followed by enriched air (EAN50) and oxygen decompression. Twenty-three divers decompressed according to a CDM schedule and 28 divers decompressed according to a RDS schedule. Peripheral blood for detection of inflammatory markers was collected before and 90 min after diving. Venous gas emboli were measured 30 min after diving using 2D echocardiography. Matched groups of 23 recreational divers (dive to 30 msw; 25 min) and 25 swimmers were also enrolled as control groups to assess the effects of decompression from a standard air dive or of exercise alone on the inflammatory profile.

RESULTS

Echocardiography at the single 30 min observation post dive showed no significant differences between the two decompression procedures. Divers adopting the RDS showed a worsening of post-dive inflammatory profile compared to the CDM group, with significant increases in circulating chemokines CCL2 (P = 0.001) and CCL5 (P = 0.006) levels. There was no increase in chemokines following the CDM decompression. The air scuba group also showed a statistically significant increase in CCL2 (P < 0.001) and CCL5 (P = 0.003) levels post dive. No cases of decompression sickness occurred.

CONCLUSION

The ratio deco strategy did not confer any benefit in terms of bubbles but showed the disadvantage of increased decompression-associated secretion of inflammatory chemokines involved in the development of vascular damage.

Otitis externa in military divers: more frequent and less harmful than reported

INTRODUCTION

Although otitis externa (OE) is a common disease, data related to (military) divers are limited. This study aimed to determine the incidence of OE in military divers during their initial training. We also wished to consider seasonal influences on incidence and whether early detection increases completion of the diving course.

METHODS

From January 2011 to October 2016 the Royal Netherlands Navy Diving School trained 189 divers. Up to December 2015 we used the training records for the analyses. From January 2016 onward all divers were prospectively screened. Pearson's chi-squared 2 and Fisher's exact tests were used to analyse the data.

RESULTS

In the 162 included divers, 30 cases of OE were identified. The incidence in 2016 was significantly higher than in 2011-2015 (17/35 (49%) versus 13/127 (10%), P < 0.001). Almost all cases developed after three weeks of diving. No influence of season was found (P = 0.354). Early diagnosis and treatment of OE does not seem to affect completion of diving courses (P = 0.28). Only in three cases did a diver have to discontinue the course due to OE.

DISCUSSION

This study suggests that OE is more frequent among military divers than earlier reported, most likely caused by prolonged water exposure. Diving activities can often be continued with standard topical treatment.

A day in the life of a diabetic diver: the Undersea and Hyperbaric Medical Society/Divers Alert Network protocol for diving with diabetes in action

Some people with well-managed insulin-dependent diabetes can dive safely. Those cleared to participate should control tightly the variables that impact blood glucose levels, including activity, timing, food and insulin. Honest self-assessment is critical. A diabetic diver should cancel a dive if seasick, unusually anxious, or following significant high or low blood glucose levels in the preceding 24 hours. The diver should enter the water with a blood glucose level above 8.3 mmol·L⁻¹ and below 14 mmol·L⁻¹ with a stable or rising trend in blood glucose established with glucose tests at 90, 60, and 30 minutes prior to a dive. The diver should carry emergency glucose at all times and brief dive buddies about hypoglycaemia procedures. This is a personal account of the author's experience diving with type 1 diabetes and details how the UHMS/DAN recommendations are put into practice on dive days. Key elements of the self-assessment process, long- and rapid-acting insulin adjustments, meal timing, responses to blood glucose trends, handling hypoglycaemia and approaching multi-dive days are described. Some considerations for people using insulin pumps are also briefly discussed.

Recreational scuba diving in patients with congenital heart disease: Time for new guidelines

The number of recreational scuba divers is steadily increasing. In its latest recommendations, the French Federation of Undersea Studies and Sports listed congenital heart disease as a formal and final contraindication to scuba diving. On the other hand, with the progress made in their management, the prognosis and quality of life of patients with congenital heart diseases have improved considerably, enabling them to engage in physical and sports endeavours, which are known to confer general health and psychological benefits. As a consequence, the ability of these patients to dive has become a regular and recurrent issue. We review the various types of scuba diving, the physical performance required for its practice, its effects on cardiovascular function and the elements that need to be considered before recommending whether it can be practiced safely at various levels of difficulty. Because of the diversity and broad heterogeneity of congenital heart diseases, a detailed evaluation of each patient's performance based on clinical criteria common to all congenital heart diseases is recommended.

Assessing the Social Carrying Capacity of Diving Sites in Mabul Island, Malaysia

This study has explored social carrying capacity of an underwater environment based on divers' perceived crowding. Two dimensions were assessed, the number of divers seen and the proximity of diver. Data were obtained from a survey of 132 divers dived in Mabul Island, Malaysia during 2013-2014. Photographs depicting four levels of diver number and four levels of diver proximity in different combinations were shown to the respondents for assessing their acceptability. Between the two variables, the "number of divers" was the most influential factor for divers' perceived crowding. Divers would start to feel unacceptably crowded if 8-9 divers were visible to them at one time. Based on this, it is likely that the use level of diving sites in Mabul Island has already exceeded its social carrying capacity. Implications for future research and diving tourism management for Mabul Island are also discussed in the paper.

Diving and percutaneous closure of persistent (patent) foramen ovale

Paradoxical arterial gas embolism after diving, in patients with a persistent foramen ovale (PFO) is a potentially catastrophic complication that occurs when gas bubbles occlude blood flow at cardiac or cerebral level. Because the relationship between PFO and decompression illness is currently not clear, we should ensure that patients understand the uncertainties about the efficacy of transcatheter closure of a PFO and the possibility of complications if closure is decided upon. We report a female diver who developed temporary bradycardia, hypotension and evidence of myocardial ischaemia during a closure procedure.

A comparison of the tissue oxygenation achieved using different oxygen delivery devices and flow rates

INTRODUCTION

High-concentration normobaric oxygen (O₂) administration is the first-aid priority in treating divers with suspected decompression illness. The best O₂ delivery device and flow rate are yet to be determined.

AIM

To determine whether administering O₂ with a non-rebreather mask (NRB) at a flow rate of 10 or 15 L·min ⁻¹ or with a demand valve with oronasal mask significantly affects the tissue partial pressure of O₂ (PtcO₂) in healthy volunteer scuba divers.

METHODS

Fifteen certified scuba divers had PtcO₂ measured at six positions on the arm and leg. Measurements were taken with subjects lying supine whilst breathing O₂ from a NRB at 10 or 15·L·min⁻¹, a demand valve with an adult Tru-Fit oronasal mask and, as a reference standard, an oxygen 'head hood'. End-tidal carbon dioxide was also measured.

RESULTS

While none of the emergency delivery devices performed as well as the head hood, limb tissue oxygenation was greatest when O₂ was delivered via the NRB at 15 L·min⁻¹. There were no clinically significant differences in end-tidal carbon dioxide regardless of the delivery device or flow rate.

CONCLUSION

Based on transcutaneous oximetry values, of the commonly available emergency O₂ delivery devices, the NRB at 15 L·min ⁻¹ is the device and flow rate that deliver the most O₂ to body tissues and, therefore, should be considered as a first-line pre-hospital treatment in divers with suspected decompression illness.

[Scuba diving in children: Physiology, risks and recommendations]

INTRODUCTION

The increase in recreational scuba diving in recent years, including children, involves risks and the possibility of accidents. While legislation, conditions and risks of scuba diving are well documented in adults, scientific evidence in scuba diving by children and adolescents is sparse and isolated. Furthermore, existing guidelines and recommendations for adults cannot be transferred directly to children.

METHODS

These circumstances have led to the Group on Techniques of the Spanish Society of Pediatric Pulmonology (SENP) to perform a literature search to review and update the knowledge about scuba diving in children.

RESULTS

Physiological adaptations of the body are examined during the dive, as well as the anatomical and physiological characteristics of children that should be taken into account in scuba diving. The most common types of accidents and its causes, as well as the risks of scuba diving practice in children with previous diseases are discussed, along with details of the medical and psychological requirements for scuba diving to be considered in the assessment of child and adolescent.

CONCLUSIONS

A list of recommendations for scuba diving with compressed air in children is presented by a group of experts.

Orbital fracture in a professional diver: issues and management

BACKGROUND

We present a case report of a professional diver who sustained a fracture of the left orbital medial wall as well as floor exceeding 50% with orbital fat herniation blocking the maxillary sinus ostium. This may result in a closed cavity within the maxillary sinus that could potentially result in barotraumas during future diving. The aim of his surgery consists of repairing the orbital fracture and to aerating the sinus at the same sitting.

METHOD

A transconjunctival approach was used combined with endoscopic sinus surgery approach to the maxillary sinus. The orbital floor fracture was repaired with a titanium plate. A wide middle meatal antrostomy was performed. A size eight Foley's catheter was inserted into the maxillary sinus and the balloon inflated to elevate and support the displaced inferior orbital floor bone fragment. The balloon was left in situ for 4 weeks to support the mobile inferior orbital fragment till adequate bone healing and stability.

RESULTS

Patient recovered well. At 3 months post-operatively, the maxillary antrostomy remained patent, and a hyperbaric oxygen challenge test was performed with success. A repeat orbital CT scan 1 day after hyperbaric challenge showed no signs of air leakage, and the bony inferior orbital floor fracture has healed completely with the titanium plate in situ.

CONCLUSION

This is the first case report of repair of orbital floor fracture with simultaneous aeration of the maxillary sinus in a professional diver using a combined approach. The patient was able to resume his occupation as a professional diver following surgery.

The five-minute prebreathe in evaluating carbon dioxide absorption in a closed-circuit rebreather: a randomized single-blind study

INTRODUCTION

Closed-circuit underwater rebreather apparatus (CCR) recycles expired gas through a carbon dioxide (CO₂) 'scrubber'. Prior to diving, users perform a five-minute 'prebreathe' during which they self-check for symptoms of hypercapnia that might indicate a failure in the scrubber. There is doubt that this strategy is valid.

METHODS

Thirty divers were block-randomized to breathe for five minutes on a circuit in two of the following three conditions: normal scrubber, partly-failed scrubber, and absent scrubber. Subjects were blind to trial allocation and instructed to terminate the prebreathe on suspicion of hypercapnia.

RESULTS

Early termination was seen in 0/20, 2/20, and 15/20 of the normal, partly-failed, and absent absorber conditions, respectively. Subjects in the absent group experienced a steady, uncontrolled rise in inspired (PICO₂) and end-tidal CO₂ (PETCO₂). Seven subjects exhibited little or no increase in minute volume yet reported dyspnoea at termination, suggesting a biochemically-mediated stimulus to terminate. This was consistent with results in the partly-failed condition (which resulted in a plateaued mean PICO₂ near 20 mmHg), where a small increase in ventilation typically compensated for the inspired CO₂ increase. Consequently, mean PETCO₂ did not change and in the absence of a hypercapnic biochemical stimulus, subjects were very insensitive to this condition.

CONCLUSIONS

While prebreathes are useful to evaluate other primary functions, the five-minute prebreathe is insensitive for CO₂ scrubber faults in a rebreather. Partly-failed conditions are dangerous because most will not be detected at the surface, even though they may become very important at depth.

Assessing baseline levels of coral health in a newly established marine protected area in a global scuba diving hotspot

While coral reefs are increasingly threatened worldwide, they are also increasingly used for recreational activities. Given the environmental and socio-economic significance of coral reefs, understanding the links between human activities and coral health and evaluating the efficacy of marine protected areas (MPAs) as a management regime to prevent further deterioration are critically important. The aim of this study was to quantify indicators of coral health at sites inside and outside a newly rezoned MPA framework in the dive tourism hotspot of Koh Tao, Thailand. We found that patterns in the health and diversity of coral communities one year on did not reflect the protected status conferred by newly zoned MPAs, but instead reflected past history of recreational use around the island. Sites characterised as past high-use sites had lower mean percent cover of hard corals overall and of corals in the typically disease- and disturbance-susceptible family Acroporidae, but higher mean cover of species in the more weedy family Agariciidae. Past high use sites also had higher mean prevalence of infectious diseases and other indicators of compromised health. Sites within the newly established MPAs are currently subjected to higher levels of environmental and anthropogenic pressures, with sedimentation, algal overgrowth, feeding scars from Drupella snails, and breakage particularly prevalent compared to sites in non-MPA areas. Given the greater prevalence of these factors within protected sites, the capacity of the MPA framework to effectively prevent further deterioration of Koh Tao's reefs is unclear. Nevertheless, our study constitutes a strong baseline for future long-term evaluations of the potential of MPAs to maintain coral health and diversity on highly threatened reefs.

12-lead Holter monitoring in diving and water sports: a preliminary investigation

OBJECTIVE

To demonstrate the utility of 12-lead Holter monitoring underwater.

METHODS

A Holter monitor, recording a 12-lead electrocardiogram (ECG) underwater, was applied to 16 pre-trained volunteer scuba divers (13 males and three females). Dive computers were synchronized with the Holter recorder to correlate the ECG tracings with diving events. Our main objective was to demonstrate the utility of recording over a period of time a good quality 12-lead ECG underwater. The ECGs were analyzed for heart rate (HR), arrhythmias, conduction abnormalities and ischaemic events in relation to various stages of diving as follows: baseline, pre diving, diving, and post diving.

RESULTS

The ECG tracings were of good quality with minimal artefacts. Analysis of variance (ANOVA) demonstrated a significant difference in HR during the various diving stages (P < 0.0001). Other recorded ECG abnormalities included supraventricular ectopic beats (four cases), ventricular ectopic beats (eight cases) and ventricular couplets (two cases). Conduction abnormalities included rate-dependent right and left bundle branch block; however, these findings were previously known in these divers. No evidence of ischaemia was seen.

CONCLUSION

Continuous 12-lead Holter monitoring underwater can produce good quality tracings. Further studies are necessary to assess its usefulness in divers at risk for or with known coronary artery disease, and its comparison with other forms of cardiac stress tests.

Blood lead levels in scuba divers: a pilot study

INTRODUCTION

Lead is a toxic element which is known to accumulate in the body. Nevertheless, it is very widely used as a diving weight.

METHODS

Blood samples were taken from 20 recreational scuba divers to assess blood lead concentrations.

RESULTS

The last dive before blood sampling was an average of 4.8 weeks previously (range 1-18 weeks). All the samples were within the normal background range, the highest lead concentration being 44.8 µg∙L⁻¹ with an average concentration of 26.5 µg∙L⁻¹ (range 11.7-44.8 µg∙L⁻¹).

CONCLUSIONS

The results show no elevated blood lead concentrations in this group of divers compared to background levels. However, owing to the small number of divers studied and the variable, often long interval between the last dive and blood sampling, the results cannot be generalized.