Electrocochleographic and audiometric evaluation of hypobaric effect in Meniere's disease

Objectives: To elucidate the effects of hypobaric pressure on cochlear hydr odynamics in patents with web-defined Meniere's disease. Design: Sixteen pa tients were consecutively selected, Elevated hearing threshold levels and p athological transtympanal electrocochleography (tt-ECOG) were confirmed at the day of trial. The patients were exposed to repeated episodes of hypobar ic pressure in a pressure chamber. The rate (20 daPa/s) and magnitude (-285 daPa) of chamber pressure change were low. The induced tympanic overpressu re (+185 daPa) was continuously monitored and any tympanic equilibration wa s avoided. Methods: The results of Bekesy and speech audiometry as well as tt-ECOG performed immediately before and after exposure were compared. The importance of chamber pressure change, number of hypobaric episodes, durati on of exposure, and the induced relative tympanic overpressure was tested. Results: It is shown that the relative tympanic overpressure is the most im portant factor to affect the cochlear hydrodynamics. Higher relative overpr essure was associated with improvement of hearing threshold levels, while t he ECOG results tended to improve with lower induced tympanic overpressure. Conclusion: The importance of tympanic overpressure shown in this study is in agreement with previous findings from hypobaric animal experiments. The inverse relation of psychoacoustic and ECOG tests suggests that the two me thods evaluate different parameters, perhaps contributing differently to th e physiology of hearing.