Middle ear gases.

The ex vacuo theory, claiming that air enters the middle ear through the Eustachian tube and oxygen leaves it into the blood by diffusion, does not provide a complete explanation and description of the mechanism of middle ear aeration. This study shows that both the gas diffusion between the middle ear and the blood and the flow of gas through the Eustachian tube are bidirectional processes for all the gases concerned N2, CO2, O2 as well as H2O.