EUBS 2017 has left us with more questions than answers, on the topic of post-dive bubbles.
Ballestra presented the preliminary results of an exploratory study of the effects of sonic vibrations on post-dive venous gas emboli detected by transthoracic echocardiography1. (more…)
Historically, alcohol was used to treat bends in Greek sponge divers. In the late 1980s attempts to verify the possible beneficial effects of ethanol on prevention of DCS led to prevailing opinions that there was no proven benefit and that divers should not drink and dive. On the other hand, the assumption that wine drinking has beneficial effects on general health is still propagated. (more…)
In the July 2015 issue of Undercurrent, an article titled “A better heart-check tool than a stress test?” discusses the possible benefits of a coronary calcium scan for older divers to reduce the risk of experiencing a heart attack while diving.1 This article is a follow-up to a May 2015 Undercurrent report about an overweight 65-year-old diver who died shortly into his dive while on a dive trip.2 That article, which considered preventive options such as a stress test, also presented views from Dr. Alfred Bove and DAN’s Dr. Petar Denoble and Dr. James Chimiak, who agreed with the American College of Physicians (ACP) guidelines that recommend a graded and individualized approach to preventive testing and diagnostics.
Another physician suggests in the July 2015 article, however, that older divers should have a coronary calcium scan, which he claims may provide information that will help them avoid a heart attack on their dive trips. Many walk-in clinics offer the test at a low price. “A coronary calcium scan can tell you years before a positive stress test that you are headed in that direction [of significant coronary disease] so that you can do some kind of intervention,” he said. While the statement has merit, it may be misleading in this context.
In a recent paper published in the Journal of the American College of Cardiology, Jakub Honek and coauthors presented their findings concerning diving with PFO (patent foramen ovale) closures.
To examine PFO closure and susceptibility to DCS, the researchers focused their study on two groups: 19 divers who had large persistent PFOs and 15 divers who had their PFO surgically closed.
It is the last day of the official SPUMS 2014 Scientific Conference, and recommendations regarding patent foramen ovale (PFO) and diving have been discussed. The following is proposed for consideration as the SPUMS position (final paper not yet edited):
Does the selective vulnerability of the inner ear to DCS help explain the disconnect between a prevalent risk factor and a rare disease?
In his presentation at SPUMS 2014, Dr. Simon Mitchell has summarized the work he and Dr. David Doolette have done regarding the pathophysiology of inner ear decompression sickness (IEDCS) as well as some recent publications from other authors.
Mitchell addressed the reservations some experts have when it comes to the causal relationship of patent foramen ovale (PFO) and decompression sickness (DCS). Some experts say there is a disconnect; PFO must be present in many divers (one quarter), but DCS occurs only in few. Wilmshurst responds to this disconnect asserting that only divers with a large PFO are at risk and this is generally in line with the DCS statistics.
Presentations at SPUMS continue…
Peter Wilmshurst’s series of cases shows that 79% of all skin DCS have PFO, 10% lung disease and only remaining cases occur in divers with closed PFO due to severe dive exposure. Similar statistics were provided for inner ear DCS and neurological DCS. Other authors dispute association of PFO with spinal form of DCS and say only cerebral DCS appears to be associated. Nevertheless, a large number of DCS cases could be avoided if the diver was aware of PFO and exercised caution.
How safe is the option of transcatheter closure?
Mark Turner, another cardiologist from the United Kingdom, provided a detailed presentation of the procedure, pitfalls and outcomes. The overall outcome: Successful with very low rate of adverse events.
At the 43rd Annual Scientific Meeting of South Pacific Underwater Medical Society going on May 18 – 25, 2014, a key theme is PFO and diving. The keynote speaker is Dr. Peter Wilmshurst, the cardiologist and diving physician who first described the association between PFO and decompression sickness in 1986. Here, he presented his findings in several hundred cases of DCS. His insight into this problem is most valuable and we are looking forward to the publication of a synthesis of his findings.
Endothelium is a single cell layer lining the inner surface of blood vessels. It plays an important role in the regulation of circulation and reaction to various kinds of stress. Endothelial dysfunction is associated with the progression of atherosclerosis of blood vessels and heart disease.
Recently it has been shown that underwater diving may transiently decrease the post-ischemic flow mediated dilation (FMD), which is an indicator of endothelial function. This has caused some divers concern and raised questions in the media about the safety of various aspects of diving.
The FMD is a test that uses the ultrasound Doppler method to measure the diameter of brachial artery (the main artery in the upper arm) before and after a five-minute forearm ischemia caused by external compression with a blood pressure measurement cuff. The average diameter of the brachial artery in adults is about four to five millimeters. After the five minutes of circulation occlusion, the flow through the artery increases and the artery diameter increases for about seven to 10 percent of its initial value. This is called the flow mediated dilatation – FMD.
The extent of FMD may be decreased by various factors like exercise, obesity, hormonal status, diurnal changes, fatty meals, acute/chronic moderate to severe alcohol consumption, etc. On the other hand, dietary factors such as light alcohol consumption, chocolate, and various medications like nitroglycerine and statins may transiently increase FMD.
It has been also shown that FMD is transiently reduced after a single compressed air dive, breathing 60% oxygen at surface, a breath-hold dive and a nitrox dive. Both the increased partial pressure of oxygen and circulating gas bubbles have been suspected as possible causes. Oxygen does affect the metabolism and availability of nitric oxide (NO), which plays an important role in the relaxation of arteries, but the effects of it on the FMD are controversial.
What does it mean for divers?
In general, reported transient changes in FMD are not specific for diving. They appear to be a common endothelial response to a variety of stressors as a part of normal defense mechanisms including self-repair. If the stressors become excessive and exposure chronic, the endothelium may be harmed beyond repair. In extreme cases, dysfunctional endothelium in coronary artery disease may paradoxically cause narrowing of arteries in response to exercise and provoke angina or myocardial infarction. Nothing indicates that diving could reach significance of such an excessive and chronic stressor that it could acutely or in the long-term affect the health of divers through reduced FMD.
So far, only transient decreases of the brachial artery FMD after diving have been reported in asymptomatic divers. FMD is equally affected by repeated breath-hold diving and a single scuba dive on air. Nitrox diving reportedly causes a larger decrease of FMD than air diving. This would be consistent with the dose-dependent effects of hyperoxia; however, hyperbaric oxygen treatment which exposes patients to a much higher partial pressure of oxygen than diving does not appear to affect the FMD. The possible dose-dependent effect of circulating gas bubbles has not been studied, but the greater decrease of FMD observed in nitrox, which is supposed to generate less bubbles, versus air diving is counterintuitive. Most importantly, there is no obvious acute or long-term harm (diseases, increased mortality) associated with reduced FMD after diving.
Having a bite of chocolate or large dose of vitamin C one hour before a dive may prevent the FMD decrease. However, the transient decrease of FMD described so far is not an injury and prevention is not necessary, regardless of how tempting the chocolate is.
Post written by: Petar Denoble, MD, D.Sc.
In a recent report on diving fatalities in Australia during 2009, Lippmann and colleagues identified 12 cases among breath-hold (BH) and 9 cases among scuba divers (SD). Cardiovascular disease was the apparent disabling condition in 3 BH and 3 SD fatalities, and possibly in 4 more BH and 3 SD fatality cases.
In comparison to the period 1977 – 2005 when 18% of deaths were caused by apparent cardiovascular diseases, the proportion in 2009 is much higher and more in-line with what DAN America reported for the period 1992-2003. Authors assume that this is probably due to the increased participation of older divers, which makes the current population of divers in Australia closer in age to the population of recreational divers in the United States. In this series, the age range of the victims who likely died of cardiac cause was 50 to 63 years. Seven out of 12 BH fatalities and four out of nine SC were older than 50 years.
Other causes of disabling conditions in BH were apneic hypoxia (3) and aspiration (2), while in SC fatalities there were two cases of seizures and two of probable cerebral arterial gas embolism (CAGE). Being over-weighted and failure to establish positive buoyancy needed to surface contributed to three deaths.
Besides the cardiac disease that may not be diagnosed previously, many victims may not have been physically fit for diving. Many were overweight and in one case the victim was extremely obese. A medical statement is not mandatory for snorkeling; however, this snorkel operator required a medical statement, but the extremely obese victim failed to declare various medical conditions (asthma, hypertension, arrhythmia and depression) and the medications she was taking. She died quietly, at the surface, a few meters from the boat. The autopsy did not document any apparent cause. While the authors justifiably suggest that in the case of an unfit customer who insists on snorkeling she could be assigned a personal guide, in this particular case even that may not have prevented the fatal outcome.
In some cases victims knew that they had conditions which may turn fatal in diving (seizures, poor physical fitness) but failed to report them. However, most victims who died of cardiac causes in this series were apparently healthy. Age itself is not a disease, but it is associated with increasing incidence of coronary artery disease, which may remain asymptomatic for a long time. The discussion of who should undergo additional medical testing and how often is ongoing with no satisfactory answer in sight.
This paper provides detailed accounts of each accident with an extensive expert comment and thus it makes a worthy read for all divers.
Source:
Lippmann J, Lawrence C, Fock Andrew, Wodal T, Jamieson S. Provisional report on diving-related fatalities in Australian waters 2009. Diving and Hyperbaric Medicine. 2013. December; 43(4):194-217.
Post written by: Petar Denoble, MD, D.Sc.
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