Decompression Illness in Repetitive Breath-Hold Diving: Why Ischemic Lesions Involve the Brain?

Nitrogen (N2) accumulation in the blood and tissues can occur due to breath-hold (BH) diving. Post-dive venous gas emboli have been documented in commercial BH divers (Ama) after repetitive dives with short surface intervals. Hence, BH diving can theoretically cause decompression illness (DCI). "Taravana," the diving syndrome described in Polynesian pearl divers by Cross in the 1960s, is likely DCI. It manifests mainly with cerebral involvements, especially stroke-like brain attacks with the spinal cord spared. Neuroradiological studies on Ama divers showed symptomatic and asymptomatic ischemic lesions in the cerebral cortex, subcortex, basal ganglia, brainstem, and cerebellum. These lesions localized in the external watershed areas and deep perforating arteries are compatible with cerebral arterial gas embolism. The underlying mechanisms remain to be elucidated. We consider that the most plausible mechanisms are arterialized venous gas bubbles passing through the lungs, bubbles mixed with thrombi occlude cerebral arteries and then expand from N2 influx from the occluded arteries and the brain. The first aid normobaric oxygen appears beneficial. DCI prevention strategy includes avoiding long-lasting repetitive dives for more than several hours, prolonging the surface intervals. This article provides an overview of clinical manifestations of DCI following repetitive BH dives and discusses possible mechanisms based on clinical and neuroimaging studies.

Incidence of cardiac arrhythmias and left ventricular hypertrophy in recreational scuba divers.

INTRODUCTION: The aims of this study were to investigate the potential impact of age, sex and body mass index (BMI) upon the incidence of arrhythmias pre- and post- diving, and to identify the prevalence of left ventricular hypertrophy (LVH) in older recreational divers. METHODS: Divers aged ≥ 40 years participating in group dive trips had ECG rhythm and echocardiograph recordings before and after diving. Arrhythmias were confirmed by an experienced human reader. LVH was identified by two-dimensional echocardiography. Weighted (0.5 fractional) values were used to account for participation by seven divers in 14 trips. RESULTS: Seventy-seven divers undertook 84 dive trips and recorded 677 dives. Among divers with no pre-trip arrhythmias (n = 55), we observed that 6.5 (12%) recorded post-trip arrhythmias and the median increase was 1.0 arrhythmia. In divers with pre-trip arrhythmias, 14.5 had a median of 1.0 fewer post-trip arrhythmias, 2.0 had no change and 5.5 had a median of 16.0 greater. Age, but neither sex nor BMI, was associated with change in the number of arrhythmias before and after dive trips (P = 0.02). The relative risk for experiencing a change in the frequency of arrhythmias after a diver trip, was 2.1 for each additional 10 years of age (95% CI 1.1, 4.0). Of the 60 divers with imaging of their heart, five had left ventricular hypertrophy. CONCLUSIONS: We observed a higher than expected prevalence of arrhythmias. Divers with pre-trip arrhythmias tended to be older than divers without pre-trip arrhythmias (P = 0.02). The prevalence of LVH in our cohort was one quarter of that found post-mortem in scuba fatalities.

Diving-related disorders in commercial breath-hold divers (Ama) of Japan.

Decompression illness (DCI) is well known in compressed-air diving but has been considered anecdotal in breath-hold divers. Nonetheless, reported cases and field studies of the Japanese Ama, commercial or professional breath-hold divers, support DCI as a clinical entity. Clinical characteristics of DCI in Ama divers mainly suggest neurological involvement, especially stroke-like cerebral events with sparing of the spinal cord. Female Ama divers achieving deep depths have rarely experienced a panic-like neurosis from anxiety disorders. Neuroradiological studies of Ama divers have shown symptomatic and/or asymptomatic ischaemic lesions situated in the basal ganglia, brainstem, and deep and superficial cerebral white matter, suggesting arterial insufficiency. The underlying mechanism(s) of brain damage in breath-hold diving remain to be elucidated; one of the plausible mechanisms is arterialization of venous nitrogen bubbles passing through right to left shunts in the heart or lungs. Although the treatment for DCI in Ama divers has not been specifically established, oxygen breathing should be given as soon as possible for injured divers. The strategy for prevention of diving-related disorders includes reducing extreme diving schedules, prolonging surface intervals and avoiding long periods of repetitive diving. This review discusses the clinical manifestations of diving-related disorders in Ama divers and the controversial mechanisms.

Hyperacute brain magnetic resonance imaging of decompression illness in a commercial breath-hold diver.

Decompression illness in breath-hold diving is a rare dysbaric disease mainly characterized by stroke-like neurological disorders. The early use of DWI-MRI combined with ADC map in suspected cases can help in the early diagnosis and treatment.

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.

Risk factors for cardiovascular disease among active adult US scuba divers.

Cardiovascular factors among uninjured active adult recreational scuba divers in the USA are described. Scuba diving as an activity was included in 2011, 2013, and 2015 Behavioral Risk Factor Surveillance System data. One-third of active US scuba divers were aged ≥50 years and/or reported prior high cholesterol, around half were overweight, more than half reported having smoked cigarettes, and 32% reported hypertension or borderline hypertension. High cholesterol, hypertension, high body mass index, and smoking status should all be addressed during routine diving fitness physician assessments, to reduce the risk of mortality while diving.

The healthy diver: A cross-sectional survey to evaluate the health status of recreational scuba diver members of Divers Alert Network (DAN).

BACKGROUND: Scuba diver fitness is paramount to confront environmental stressors of diving. However, the diving population is aging and the increasing prevalence of diseases may be a concern for diver fitness. PURPOSE: The purpose of this study is to assess the demographics, lifestyle factors, disease prevalence, and healthcare access and utilization of Divers Alert Network (DAN) members and compare them with those from the general population. METHODS: DAN membership health survey (DMHS) was administered online in 2011 to DAN members in the United States (US). Health status of DMHS respondents was compared with the general US population data from the Center for Disease Control and Prevention's Behavioral Risk Factor Surveillance System using two-sided student's t-tests and Mantel-Haenszel chi-square tests. Univariate and multivariate logistic regression analyses were conducted to identify factors associated with healthcare utilization among the DMHS participants. RESULTS: Compared to the general US population, the DMHS population had lower prevalence of asthma, heart attack, angina, stroke, diabetes, hypertension, hypercholesterolemia, and disabilities (p<0.01); more heavy alcohol drinkers, and fewer smokers (p<0.01); and greater access and utilization (routine checkup) of healthcare (p<0.01). Healthcare utilization in males was lower than among females. Increasing age and increase in the number of chronic illnesses were associated with increased healthcare utilization. CONCLUSIONS: DAN members are healthier than the general US population. DAN members also have better access to healthcare and utilize healthcare for preventive purposes more often than the general population. DAN members appear to have a better fitness level than their non-diving peers.

Simulated High Altitude Helium-Oxygen Diving.

BACKGROUND: Experience with commercial heliox diving at high altitude is limited. The purpose of this study was to evaluate the effects of acute high-altitude exposure on fitness to dive and the safety of decompression after heliox diving while using U.S. Navy heliox decompression tables with Cross correction. METHOD: Four professional male divers were consecutively decompressed in a hypo- and hyperbaric chamber to altitudes of 3000 m (9842.5 ft), 4000 m (13,123.4 ft), and 5200 m (17,060.4 ft) during the 8-d study. The dive profiles tested were to 30 m (98.4 ft) for 60 min at all three altitudes and, in addition, a dive to 50 m (164 ft) for 60 min at 5200 m altitude. The decompression followed the U.S. Navy heliox decompression table. The safety of decompression was evaluated by precordial Doppler venous gas emboli (VGE) monitoring during the decompression stages and postdive monitoring of the divers for symptoms of decompression sickness (DCS). Effects of altitude exposure were measured as subjective rating and EEG signs of sleepiness and fatigue, clinical symptoms of high altitude disease, and fitness to dive. RESULTS: A total of 24 person-dives were conducted. There were no VGE detected during the decompression and no postdive symptoms of decompression illness. Both the EEG findings and subjective evaluation indicated increased sleepiness and fatigue at 3000 m, 4000 m, and 5200 m, all compared with the sea level baseline. During the diving phase, both the EEG findings and subjective evaluation scores returned to the baseline and the divers successfully completed diving. DISCUSSION: Diving at high altitude with a short acclimatization period appears safe despite divers exhibiting clinical symptoms and EEG signs of impairment by hypoxia at high altitude. Despite a small number of dives, the results of this study indicate that our application of U.S. Navy standard heliox decompression tables with Cross correction is effective and could be used for underwater constructions up to 5200 m altitude, with due caution.Shi L, Zhang Y, Tetsuo K, Shi Z, Fang Y, Denoble PJ, Li Y. Simulated high altitude helium-oxygen diving. Aerosp Med Hum Perform. 2017; 88(12):1088-1093.

Cerebrospinal vascular diseases misdiagnosed as decompression illness: the importance of considering other neurological diagnoses.

The diagnosis of decompression illness (DCI), which is based on a history of decompression and clinical findings, can sometimes be confounded with other vascular events of the central nervous system. The authors report three cases of divers who were urgently transported to a hyperbaric facility for hyperbaric oxygen treatment of DCI which at admission turned out to be something else. The first case, a 45-year-old experienced diver with unconsciousness, was clinically diagnosed as having experienced subarachnoid hemorrhage, which was confirmed by CT scan. The second case, a 49-year-old fisherman with a hemiparesis which occurred during diving, was diagnosed as cerebral stroke, resulting in putaminal hemorrhage. The third case, a 54-year-old fisherman with sensory numbness, ataxic gait and urinary retention following sudden post-dive onset of upper back pain, was diagnosed as spinal epidural hematoma; he also showed blood collection in the spinal canal. Neurological insults following scuba diving can present clinically with confusing features of cerebral and/or spinal DCI. We emphasize the importance of considering cerebral and/or spinal vascular diseases as unusual causes of neurological deficits after or during diving.

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.

The probability and severity of decompression sickness.

Decompression sickness (DCS), which is caused by inert gas bubbles in tissues, is an injury of concern for scuba divers, compressed air workers, astronauts, and aviators. Case reports for 3322 air and N2-O2 dives, resulting in 190 DCS events, were retrospectively analyzed and the outcomes were scored as (1) serious neurological, (2) cardiopulmonary, (3) mild neurological, (4) pain, (5) lymphatic or skin, and (6) constitutional or nonspecific manifestations. Following standard U.S. Navy medical definitions, the data were grouped into mild-Type I (manifestations 4-6)-and serious-Type II (manifestations 1-3). Additionally, we considered an alternative grouping of mild-Type A (manifestations 3-6)-and serious-Type B (manifestations 1 and 2). The current U.S. Navy guidance allows for a 2% probability of mild DCS and a 0.1% probability of serious DCS. We developed a hierarchical trinomial (3-state) probabilistic DCS model that simultaneously predicts the probability of mild and serious DCS given a dive exposure. Both the Type I/II and Type A/B discriminations of mild and serious DCS resulted in a highly significant (p << 0.01) improvement in trinomial model fit over the binomial (2-state) model. With the Type I/II definition, we found that the predicted probability of 'mild' DCS resulted in a longer allowable bottom time for the same 2% limit. However, for the 0.1% serious DCS limit, we found a vastly decreased allowable bottom dive time for all dive depths. If the Type A/B scoring was assigned to outcome severity, the no decompression limits (NDL) for air dives were still controlled by the acceptable serious DCS risk limit rather than the acceptable mild DCS risk limit. However, in this case, longer NDL limits were allowed than with the Type I/II scoring. The trinomial model mild and serious probabilities agree reasonably well with the current air NDL only with the Type A/B scoring and when 0.2% risk of serious DCS is allowed.

Ten years of recreational diving fatalities in the United States and Canada: harvesters vs non-harvesters.

Adult male recreational diver fatalities (n = 698) in North America from 2004 to 2013 were examined. Compared with non-harvesters, boat (86 vs 59%), solo (26 vs 13%) and night diving (10 vs 3%) were more common among harvesters. Of the divers who were low-on or out-of air, 20% were harvesters and 11% non-harvesters (OR = 2.0, P = 0.03).

Factors influencing adherence to pre-dive checklists among recreational scuba divers.

Pre-dive checklists can prevent mishaps, injuries, and deaths in recreational scuba diving. However, the prevalence of checklist use remains low. Understanding the environmental and individual factors influencing a diver's checklist use may help in promoting checklists. In the summer of 2012, 617 divers were enrolled in the intervention group of a cluster randomized trial. The divers received an intervention pre-dive checklist to use before they made dives. Logistic regression analyses were used to model adherence to pre-dive checklist with generalized estimating equations. About 70% divers (n=430) adhered to the intervention pre-dive checklist. Factors associated with greater adherence were the use of a diver's own written self-checklist - odds ratio (OR) = 2.48 (95% confidence interval: 0.95, 6.44), older age (⟩ 35 years) - OR = 1.67 (1.15, 2.42), and higher average annual dives (6-10 dives vs. 0-5 dives) - OR = 1.87 (1.09, 3.21). Factors associated with lower adherence were diving in North Carolina as compared to the Caribbean - OR = 0.42 (0.20, 0.85), non-white race - OR = 0.54 (0.27, 1.09), and female gender - OR = 0.77 (0.54, 1.12). Checklist adherence is also a function of risk perception, facilitators, and barriers. Future studies should try to understand diver risk perceptions, promote facilitators, and reduce barriers to foster the use of pre-dive checklists.

The effect of using a pre-dive checklist on the incidence of diving mishaps in recreational scuba diving: a cluster-randomized trial.

BACKGROUND: Scuba diving mishaps, caused by equipment problems or human errors, increase the occurrence of injuries and fatalities while diving. Pre-dive checklists may mitigate mishaps. This study evaluated the effect of using a pre-dive checklist on the incidence of diving mishaps in recreational divers. METHODS: A multi-location cluster-randomized trial with parallel groups and allocation concealment was conducted between 1 June and 17 August 2012. The participants had to be at least 18 years of age, permitted to dive by the dive operator and planning to dive on the day of participation. They were recruited at the pier and dive boats at four locations. The intervention group received a pre-dive checklist and post-dive log. The control group received a post-dive log only. The outcomes, self-reported major and minor mishaps, were prompted by a post-dive questionnaire. Mishap rates per 100 dives were compared using Poisson regression with generalized estimating equations. Intent-to-treat, per-protocol and marginal structural model analyses were conducted. RESULTS: A total of 1043 divers (intervention = 617; control = 426) made 2041 dives, on 70 location-days (intervention = 40; control = 30) at four locations. Compared with the control group, the incidence of major mishaps decreased in the intervention group by 36%, minor mishaps by 26% and all mishaps by 32%. On average, there was one fewer mishap in every 25 intervention dives. CONCLUSIONS: In this trial, pre-dive checklist use prevented mishaps which could lead to injuries and fatalities. Pre-dive checklists can increase diving safety and their use should be promoted. Trial Registration: ClinicalTrials.gov ID NCT01960738.

Simvastatin decreases incidence of decompression sickness in rats.

Decompression sickness (DCS) is a specific diving injury which sometimes may be life-threatening. Previous studies suggested that simvastatin (SIM) can protect against pathological inflammation and tissue damage. This study aimed to investigate whether SIM pretreatment could exert its beneficial effects on DCS. SIM was administered orally to adult male Sprague-Dawley rats for two weeks (2 mg/kg/day), then rats were subjected to a simulated dive at 700 kPa air pressure for 100 minutes before rapid decompression. After 30 minutes of symptom observation, lung tissue and blood samples were collected for further analysis. Compared to the vehicle-control, SIM pretreatment significantly decreased the incidence of DCS and ameliorated all parameters of pulmonary injuries, including lung dry/wet weight ratio, bronchoalveolar lavage fluid protein concentration, lung tissue malondialdehyde level and morphology. Moreover, SIM pretreatment abolished increases in systemic and pulmonary inflammation by reducing tumor necrosis factor-α levels in blood plasma and lung tissue. The results indicate that SIM may offer a novel pharmacological protection against injuries in DCS rats by inhibiting inflammatory responses. Further study is needed to understand the exact mechanisms.

Brain damage in commercial breath-hold divers.

BACKGROUND: Acute decompression illness (DCI) involving the brain (Cerebral DCI) is one of the most serious forms of diving-related injuries which may leave residual brain damage. Cerebral DCI occurs in compressed air and in breath-hold divers, likewise. We conducted this study to investigate whether long-term breath-hold divers who may be exposed to repeated symptomatic and asymptomatic brain injuries, show brain damage on magnetic resonance imaging (MRI). SUBJECTS AND METHODS: Our study subjects were 12 commercial breath-hold divers (Ama) with long histories of diving work in a district of Japan. We obtained information on their diving practices and the presence or absence of medical problems, especially DCI events. All participants were examined with MRI to determine the prevalence of brain lesions. RESULTS: Out of 12 Ama divers (mean age: 54.9±5.1 years), four had histories of cerebral DCI events, and 11 divers demonstrated ischemic lesions of the brain on MRI studies. The lesions were situated in the cortical and/or subcortical area (9 cases), white matters (4 cases), the basal ganglia (4 cases), and the thalamus (1 case). Subdural fluid collections were seen in 2 cases. CONCLUSION: These results suggest that commercial breath-hold divers are at a risk of clinical or subclinical brain injury which may affect the long-term neuropsychological health of divers.

Scuba diving injuries among Divers Alert Network members 2010-2011.

BACKGROUND: Scuba diving injuries vary greatly in severity and prognosis. While decompression sickness (DCS) and arterial gas embolism can be tracked easily, other forms of diving injury remain unaccounted for. PURPOSE: The purpose of this paper is to assess rates of overall self-reported scuba-diving-related injuries, self-reported DCS-like symptoms, and treated DCS and their association with diver certification level, diving experience and demographic factors. METHODS: We analyzed self-reported data from a Divers Alert Network membership health survey conducted during the summer of 2011. Poisson regression models with scaled deviance were used to model the relative rates of reported injuries. Models were adjusted for sex, age, body mass index (BMI) and average annual dives, based on the bias-variance tradeoff. RESULTS: The overall rate of diving-related injury was 3.02 per 100 dives, self-reported DCS symptoms was 1.55 per 1,000 dives and treated DCS was 5.72 per 100,000 dives. Diving-related injury and self-reported DCS symptom rates decreased for higher diver certification levels, increasing age, increasing number of average annual dives and for men; they increased for increasing BMI. CONCLUSIONS: Diving injury rates may be higher than previously thought, indicating a greater burden on the diving community. Self-reported DCS-like symptoms are a small fraction of all dive-related injuries and those receiving treatment for DCS are an even smaller fraction. The small number of divers seeking treatment may suggest the mild nature and a tendency towards natural resolution for most injuries.

Prevalence of cardiomegaly and left ventricular hypertrophy in scuba diving and traffic accident victims.

Although frequently asymptomatic, left ventricular hypertrophy (LVH) is an independent predictor of sudden cardiac death (SCD). We hypothesized that diving may increase the propensity for pre-existent LVH to cause a lethal arrhythmia (and SCD) and therefore the prevalence of LVH may be greater among scuba fatalities than among traffic fatalities. We compared autopsy data for 100 scuba fatalities with 178 traffic fatalities. Extracted data contained information on age, sex, height, body mass, heart mass (HM), left ventricular wall thickness (LVWT), interventricular wall thickness (IVWT), and degree of coronary artery stenosis. A case was classified as LVH if the LVWT was > 15 mm. Log risk models were used to compare HM and LVWT in two groups while controlling for body mass, body length, age and sex. The prevalence of LVH was compared using Pearson's test. The mean HM was 428.3 +/- 100 for divers and 387 +/- 87 for controls. The crude HM ratio for scuba fatalities vs. controls was 1.11 (1.05, 1.17), and when controlled for sex, age and body mass the ratio was 1.06 (1.01, 1.09). The mean LVWT was 15 +/- 3.5 for divers and 14 +/- 2.7 for controls (p = 0.0017). HM and LVWT measured at autopsy were greater in scuba than in traffic fatalities.

Per-capita claims rates for decompression sickness among insured Divers Alert Network members.

Decompression sickness (DCS) in recreational diving is a rare and usually self-limiting injury, but permanent disability can occur. Incidence rate estimates are difficult to establish because the number of divers at risk is usually unknown in population samples with well-documented DCS. We estimated the annual per-capita DCS incidence rates for 2000-2007 based on insurance claims submitted by members of the Divers Alert Network (DAN), Durham, N.C., with dive accident insurance. The overall per-capita DCS claims rate (DCR) was 20.5 per 10,000 member-years. Based on the age-adjusted DCR, males submitted 28% more claims than females. Male-to-female difference was greatest between 35 and 40 years of age and disappeared by the mid-50s. Highest rates were observed in the 30- to 39-year age category, after which DCR declined with increasing age. Highest yearly DCR was estimated in 2002. Insurance dropout rate was greater among those who had DCS in the first year of their insurance compared to those who did not have DCS in their first year.