Auditory threshold and inner ear pressure: Measurements in experimental endolymphatic hydrops

Hypothesis: Experimental endolymphatic hydrops leads to an endolymph-perily mph pressure imbalance that is responsible for the loss of auditory sensiti vity in the ear. Background: This study investigates whether intralabyrinthine pressure is a factor in the auditory dysfunction of experimental endolymphatic hydrops. Methods: Auditory function was investigated in 10 guinea pigs 90 to 120 day s after endolymphatic sac ablation by measuring compound action potentials in response to acoustic stimuli including alternating clicks and tone burst s of 0.5, 1, 2, 4, and 8 kHz. After auditory thresholds to the various stim uli were established, endolymphatic and perilymphatic pressures were measur ed with a no-flow micropressure measuring system. Results: Increased auditory thresholds were noted in the hydrops ears at al l tested parameters (p < 0.03). A relative in crease in endolymph over peri lymph pressure was found in hydrops ears as previously reported. The increa se in endolymph-perilymph pressure of hydrops could not be correlated direc tly to the elevated auditory threshold shift. Conclusion: Endolymphatic hydrops is a complex pathologic state with multip le inner ear alterations including abnormal intralabyrinthine pressure. Fac tors other than or in addition to pressure contribute to the auditory thres hold shift of hydrops.