Diving Hyperb Med
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This consensus statement is the result of a workshop at the SPUMS Annual Scientific Meeting 2014 with representatives of the UK Sports Diving Medical Committee (UKSDMC) present, and subsequent discussions including the entire UKSDMC. Right-to-left shunt across a persistent or patent foramen ovale (PFO) is a risk factor for some types of decompression illness. It was agreed that routine screening for PFO is not currently justifiable, but certain high risk sub-groups can be identified. ⋯ Reduction in gas load by limiting depth, repetitive dives and avoiding lifting and straining may all be appropriate. Divers may consider transcatheter device closure of the PFO in order to return to normal diving. If transcatheter PFO closure is undertaken, repeat bubble contrast echocardiography must be performed to confirm adequate reduction or abolition of the right-to-left shunt, and the diver should have stopped taking potent anti-platelet therapy (aspirin is acceptable).
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Right-to-left shunt across a persistent foramen ovale (PFO) has been associated with cutaneous, neurological and vestibular decompression illness (DCI). Percutaneous closure of a PFO has been used to reduce the risk of DCI. There are no randomised controlled trial data to support PFO closure for the prevention of decompression illness (DCI), so the need for audit data on the safety and efficacy of this technique has been recognised by the National Institute of Health and Clinical Excellence in the UK. ⋯ The PFO closure procedure appeared to be safe and was associated with the majority of divers being able to successfully return to unrestricted diving.
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Diving medicine is a peculiar specialty. There are physicians and scientists from a wide variety of disciplines with an interest in diving and who all practice 'diving medicine': the study of the complex whole-body physiological changes and interactions upon immersion and emersion. To understand these, the science of physics and molecular gas and fluid movements comes into play. ⋯ A significant relationship between PFO and cerebral damage, in the absence of high-risk diving or DCI, has yet to be confirmed. Studying PFO-related DCI provides us with unique opportunities to learn more about the effect of gas bubbles in various tissues, including the central vascular bed and neurological tissue. It may also serve to educate divers that safe diving is something that needs to be learned, not something that can be implanted.
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Letter Case Reports
Inner-ear decompression sickness: 'hubble-bubble' without brain trouble?
Inner-ear decompression sickness (DCS) is an incompletely understood and increasingly recognized condition in compressed-air divers. Previous reports show a high association of inner-ear DCS with persistent foramen ovale (PFO), suggesting that a moderate-to-severe right-to-left shunt might represent a major predisposing factor, and more properly defining it as an event from arterial gas embolism (AGE). However, other conditions characterized by bubbles entering the arterial circulation, such as open-chamber cardiac surgery, do not produce inner-ear involvement, while sometimes damaging the brain extensively. ⋯ This would support either of two hypotheses: (a) that the brain is indeed relatively protected from arterial bubbles that preferentially harm the inner ear where, however, they only rarely infiltrate, or (b) that direct bubble formation within the inner ear cannot be completely discarded, and that the elevated PFO-inner-ear DCS association might be, in this latter case, merely circumstantial. We favour the hypothesis that inner-ear DCS might be related to AGE in an anatomically vulnerable region. More precise data regarding the exact incidence of inner-ear involvement, isolating those subjects with moderate-to-severe shunt, should be obtained before exploring the risk-to-benefit ratio given by transcatheter occlusion of a PFO for prevention of inner-ear DCS; odds that could end up to be sensibly different with respect to other types of DCS presentation.
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Observational Study
An observation of venous gas emboli in divers and susceptibility to decompression sickness.
Decompression sickness (DCS) results from the formation of bubbles within the tissues and blood in response to a reduction in environmental pressure. Venous gas emboli (VGE) are common after diving and are usually only present in small numbers. Greater VGE numbers are an indication of decompression stress, and can be reliably detected using ultrasound imaging. ⋯ Higher maximum VGE grades and longer durations of VGE following decompression were associated with a history of DCS and, in particular, musculoskeletal DCS. Although the exact mechanism of DCS remains poorly understood, our data suggest some individuals are inherently more prone to develop VGE, increasing the probability of DCS. Modification of diving practices in those with high VGE grades could potentially decrease DCS risk in these individuals.