Objective Method of Quantifying Sensorineural Hearing Loss

Abstract

This master’s thesis presents results from a study evaluating several different methods of assessing hearing loss. Twenty-seven participants with sensorineural hearing loss (SNHL) completed a combination of clinical, psychoacoustic, and objective tests. Each test chosen in this study yielded a measure of either inner hair cell loss (IHC) loss or outer hair cell (OHC) loss. The goal of this thesis was to evaluate whether variance in audiometric thresholds in patients with SNHL could be predicted based on different tests of specific hair cell loss. The tests chosen were included because each addresses specific deficits audiograms do not measure, such as holes in hearing and loudness growth. The tasks were the psychophysical tuning curve (PTC) task, psychoacoustic loudness growth, and an auditory brainstem response (ABR) loudness growth task. All tests were completed at 1000 Hz and at 4000 Hz and used an octave-band chirp stimulus. The chirp stimulus simultaneous increases signal to noise ratio, and decreases testing time. It was hypothesized that audiometric thresholds could be predicted through some combination of tests that measure IHC and OHC loss. Since the ABR loudness growth task is an objective test, it was hypothesized that it would be a key predictor at both frequencies. We hypothesized that the subjective tests would only be predictors of audiometric thresholds at 1000 Hz. We were able to significantly predict audiometric thresholds at 1000 Hz from 2 different regressions: 1) tip frequency (from the PTC task) and loudness ranking (from the psychoacoustic loudnesss growth task), as well as from 2) tip frequency and wave V amplitude (from the ABR loudness growth task). None of the predictors were able to explain audiometric threshold shifts significantly at 4000 Hz. In addition, ABR Wave V amplitude correlated with loudness ranking at 1000 Hz but not at 4000 Hz. However, ABR wave V amplitude correlated with stimulus intensity at both frequencies. This thesis provides evidence that ABR loudness growth tasks provide more information about patients compared to more subjective tasks.