Inner

There are four dominant theories for the clinical and pathological findings associated with DI of the inner ear. They are: (1) explosive / hemorrhagic injuries; (2) counter diffusion; (3) gas induced osmosis; and (4) vascular emboli 92'93.

Explosive / hemorrhagic injuries

In 1980, Landolt et al found hemorrhage in the inner ear of squirrel monkeys subjected to rapid decompression from saturation 94. Three years later Venter was able to show an implosive injury of the semicircular canals as the cause for the hemorrhage 95. The mechanism, they proposed, was one of gas accumulation in temporal bone osteoclast pockets that then explosively ruptured into the inner ear during decompression. Money subsequently found evidence of the same type of injury in a diver who died 56 days after left inner ear DI 96. This mechanism is plausible for deep mixed gas diving, but less convincing for inner ear DI following shallower dives.

Embolism

Blood supply to the inner ear is endarterial and consequently prone to embolic or vascular injury. Embolic disturbance has been shown in cardiac bypass surgery, but how this relates to diving remains uncertain 97.

Counterdiffusion

This theory entertains the possibility that counterdiffusion can occur under conditions where the inert gas in the middle ear differs from that in the breathing mixture. Diffusion through the round or oval window could result in accumulation of inert gas with bubbling, resulting in deafness or vertigo. This theory has developed due to a high prevalence of inner ear DI in helium-oxygen and mixed gas divers 27. Counterdiffusion may also occur within the partitions of the inner ear itself. The vascularity of the inner ear is not uniform: the stria vascularis supplies the endolymph directly and from there inert gas would diffuse to the perilymph. Therefore, with gas switching, it is possible that the endolymph could rapidly take up a new inert gas, e.g. helium, before the perilymph has had time to eliminate the former inert gas. Bubbles could then form within the endolymph with disruption of function and even rupture 27.

Gas-induced Osmosis

Finally, by a similar mechanism, inert gas accumulation in the endolymph could result in gas-induced osmosis: an osmotic fluid shift towards the endolymph resulting in a form of hydrops endolymphaticus analogous to Meniere's disease.

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