Eustachian tubal function during immersion.

The effects of head-out immersion on active and passive middle ear pressure equilibration were studied in three otologically normal scuba divers. Results were compared with the equilibration capacity recorded in the nonimmersed sitting and supine positions. Head-out immersion had only a minor effect on the ability to equilibrate the middle ear pressure actively during descent; passive ear clearing during ascent was slightly more difficult compared with this capacity in the sitting nonimmersed position. In the supine position ear clearing was significantly more difficult during both ascent and descent, which indicates that it is preferable to assume an upright body posture during exposures to pressure changes in dry pressure chambers. Mechanisms that might influence the ability to equilibrate the middle ears are discussed.