Influence of middle ear pressure changes on labyrinthine hydrodynamics and hearing physiology

University dissertation from Dept. of Otolaryngology, University Hospital, S22185 Lund, Swedem

Abstract: Results from experimental studies, as well as clinical studies, are used to elucidate the effects of ambient pressure changes on cochlear hydrodynamics and function. The perilymph pressure changes and the pressure release effects of the cochlear aqueduct (CA) and Eustachian tube (ET) in cats exposed to hypobaric pressure are elucidated. The focus is on the emergence of the pressure gradients between the middle and inner ears, as well as their surroundings – the chamber and the cerebrospinal fluid compartment – and the potentially harmful effect on the labyrinth. The equilibration of labyrinthine pressure through the patent CA and alternative pathways is demonstrated, as well as the protective effect of the ET equilibration of middle ear pressure. The design of the clinical studies originates from the experimental studies. The comparison of the electrophysio-logical and psychoacoustic results elucidates the effect of hypobaric pressure on cochlear hydrodynamics in patients with Meniere’s disease. The decisive effect of tympanic pressure on the labyrinthine pressure shown in the experimental studies is clinically verified. The efficiency of the pressure release pathways between the intracranial and cochlear fluids for these patients is analysed further with the TMD technique. A relation was found between the pressure release efficiency and the effect of hypobaric exposure for this group of patients with Meniere’s disease. The results from the experimental and clinical studies demonstrate the importance of tympanic overpressure and the effect on labyrinthine hydrodynamics. The immediate effects of tympanic pressure gradients on the otoacoustic emissions recorded in healthy individuals are elucidated in the last study. The results indicate an effect on cochlear function in addition to changes in tympanic sound-conduction. The otoacoustic emissions may provide a useful method to investigate the effect of ambient pressure changes on the labyrinth.

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