Diving Hyperb Med
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A persistent foramen ovale (PFO) and other types of right-to-left shunts are associated with neurological, cutaneous and cardiovascular decompression illness (DCI). A right-to-left shunt is particularly likely to be implicated in causation when these types of DCI occur after dives that are not provocative. It is believed that venous nitrogen bubbles that form after decompression pass through the shunt to circumvent the lung filter and invade systemic tissues supersaturated with nitrogen (or other inert gas) and as a result there is peripheral amplification of bubble emboli in those tissues. ⋯ The increased risk of DCI in people with migraine with aura is because migraine with aura is also associated with right-to-left shunts and this increased risk of DCI appears to be confi ned to those with a large PFO or other large shunt. Various ultrasound techniques can be used to detect and assess the size of right-to-left shunts by imaging the appearance of bubble contrast in the systemic circulation after intravenous injection. In divers with a history of shunt-mediated DCI, methods to reduce the risk of recurrence include cessation of diving, modification of future dives to prevent venous bubble liberation and transcatheter closure of a PFO.
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Review
Pathophysiology of inner ear decompression sickness: potential role of the persistent foramen ovale.
Inner-ear decompression sickness (inner ear DCS) may occur in isolation ('pure' inner-ear DCS), or as part of a multisystem DCS presentation. Symptoms may develop during decompression from deep, mixed-gas dives or after surfacing from recreational air dives. Modelling of inner-ear inert gas kinetics suggests that onset during decompression results from supersaturation of the inner-ear tissue and in-situ bubble formation. ⋯ A similar difference in gas kinetics may explain the different susceptibilities of cochlear and vestibular tissue within the inner-ear itself. The cochlea has greater perfusion and a smaller tissue volume, implying faster inert gas washout. It may be susceptible to injury by incoming arterial bubbles for a shorter time after surfacing than the vestibular organ.