Regulation of negative middle ear pressure without tubal opening.

We studied the capacity of the middle ear to regulate a negative pressure despite a closed eustachian tube. The test was performed in a pressure chamber designed for subatmospheric pressures, which enabled us to apply a negative middle ear pressure. In recumbent subjects, the hydrostatic effects of the body position and the negative pressure locked the tube. The subsequent pressure change was monitored by serial tympanometry. Despite a closed eustachian tube, a substantial capacity of reducing negative pressure was present. This capacity is not explained only by hydrostatic effects. The classical "hydrops ex vacuo" theory, which postulates a continuous gas absorption under the present conditions, is not consistent with our findings. Instead, they are in agreement with the view that the turnover of middle ear gas by diffusion is a bidirectional process that may even show a positive balance.