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Title: Clinical applications of otoacoustic emissions in assessment of olivocochlear dysfunction
Author: Williams, Eve A.
Awarding Body: University of London
Current Institution: University College London (University of London)
Date of Award: 2000
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The efferent olivocochlear system provides feedback to the sensory receptors and afferent nerves of the cochlea. This study examined efferent auditory effects in humans by measurement of otoacoustic emissions during contralateral acoustic stimulation. Results were analyzed with a view to optimizing protocols for non-invasive clinical assessment of olivocochlear dysfunction. An experimental paradigm for assessing the loss of olivocochlear innervation was applied to vestibular nerve section patients whose olivocochlear bundle had been severed for treatment of peripheral labyrinthine disorders. Control patients were studied, who had undergone a similar surgical procedure for vascular decompression of the vestibular nerve, but without section of the olivocochlear fibres. The role of middle ear reflexes was investigated in patients with unilateral section of the middle ear muscle tendons for treatment of myoclonus. Patients with pathological lesions along the olivocochlear pathway from cochlea to cortex were also investigated. Normal subjects demonstrated significant and repeatable inhibition of otoacoustic emission amplitude during contralateral white noise at least 25dB above sensation level in normal subjects. The test was sensitive to olivocochlear disruption via vestibular nerve section, lesions of the olivary nuclei, or cerebello-pontine angle. Cases with a history of noise exposure also showed a loss of inhibitory effects. Control cases with lesions not affecting the olivocochlear pathway maintained normal levels of inhibition. The findings support the conclusion that otoacoustic emissions provide a means of evaluating efferent function, and that surgical or pathological disruption of the olivocochlear system results in a significant loss of efferent auditory effects.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available