Kenneth E. Money

Semicircular Canal Fractures in Squirrel Monkeys Resulting from Rapid Decompression: Interpretation and Significance

A recent histological study of monkeys rapidly decompressed from deep dives has revealed that, in some cases, there are fractures of the bone surrounding the semicircular canals. In some monkeys sacrificed within a few days of their dives, there are full thickness breaks across the bony canal walls. In others, sacrificed several months after a dive, these fractures have become infiltrated by the ectopic growth of new bone which also invades the otic fluid spaces. It now appears that the new bone growth is caused not only by a ripping or irritation of the endosteum, which lines the inside of the bony canals, but also, at least in some cases, by a rupturing of the very hard petrous bone itself. It is difficult to avoid the conclusion that, somehow, large forces are developed within the inner ear or within the petrous bone during decompression.

Deuterium oxide modification of neuronal characteristics in the visual cortex of the cat.

The receptive field area and the spontaneous activity of complex visual cortical cells were investigated in the cat before, and after, the administration of deuterium oxide (D2O). In cats with intact labyrinths, the receptive field area of the cell usually expands, and the spontaneous activity increases. In bilaterally labyrinthectomized animals, these changes are absent. Also, D2O does not alter the spontaneous firing rate in non-visual cortical cells in normal cats.

Induced Vestibular Dysfunction in Squirrel Monkeys During Rapid Decompression

The symptoms of postural instability and dizziness associated with decompression sickness could be ascribed to either damage of the vestibular apparatus or to central nervous system damage. However, a histological study of monkeys exposed to decompression reveals that these symptoms primarily result from damage to the vestibular apparatus (unless there are accompanying central deficits). Furthermore, the damage is of a type that causes new bone growth to occlude the otic fluid spaces of the semicircular canals. In some instances, there is sufficient bone growth to render the cristae ampullares as non-functional end organs. Such diminished vestibular function would present a serious threat to the diver.