Introduction: The Eustachian tube (ET) is the key to pressure equalization between the middle ear and ambient pressure. To date, little is known about differences of the opening mechanisms under hyper- or hypobaric conditions. Aim of this study was to compare standard ET opening parameters during standardized hypo- and hyperbaric exposures. Methods: Thirty healthy participants were exposed to a standardized profile of decompression and compression (SPDC) in a hypo-/hyperbaric pressure chamber. Impedance, expressed as tympanic membrane compliance, was recorded at intervals during the excursions from 1 atmosphere absolute (atm abs) to 0.8 and 1.2 atm abs respectively. Parameters for tubal opening were obtained during SPDC: ET opening pressure (ETOP), ET opening duration (ETOD) and ET opening frequency (ETOF), hypobaric (Phase 1) and hyperbaric (Phase 2) data were compared. Results: Mean value for Valsalva maneuver ETOP was 40.10 +/- 19.02 mbar in Phase 2 vs. 42.82 +/- 21.75 mbar in Phase 1. For ETOD it was 2.80 +/- 2.09 seconds in Phase 2 vs. 2.51 +/- 1.90 seconds in Phase 1. For swallowing, mean value for ETOP was 33.47 +/- 14.50 mbar in Phase 2 vs. 28.44 +/- 14.04 in Phase 1. ETOD was 0.82 +/- 0.60 seconds in Phase 2 vs. 0.76 +/- 0.55 seconds in Phase 1. There was no statistical significance for ETOP, ETOD and ETOF between the two phases. Conclusion: No statistical significant difference was evident for active pressure equalization (Valsalva and swallowing) between a hyperbaric setting (dive) and a hypobaric setting (flight) in healthy subjects
