Analysis of probe fitting stimulus properties on transient evoked otoacoustic emissions

The Effect of Parkinson's Disease on Otoacoustic Emissions and Efferent Suppression of Transient Evoked Otoacoustic Emissions

Purpose Several studies have demonstrated increased auditory thresholds in patients with Parkinson's disease (PD) based on subjective tonal audiometry. However, the pathophysiological mechanisms underlying auditory dysfunction in PD remain elusive. The primary aim of this study was to investigate cochlear and olivocochlear function in PD using objective measurements and to assess the effect of dopaminergic medication on auditory function. Method Eighteen patients with PD and 18 gender- and age-matched healthy controls (HCs) were included. Patients with PD participated in medication on and off conditions. Linear mixed models were used to determine the effect of PD on tonal audiometry, transient evoked and distortion product otoacoustic emissions (OAEs), and efferent suppression (ES). Results Tonal audiometry revealed normal auditory thresholds in patients with PD for their age across all frequencies. OAE signal amplitudes demonstrated a significant interaction effect between group (PD vs. HC) and frequency, indicating decreased OAEs at low frequencies and increased OAEs at high frequencies in patients with PD. No significant differences were found between patients with PD and HCs regarding ES. In addition, no significant effect of medication status was found on auditory measurements in patients with PD. Conclusions Altered OAEs support the hypothesis of cochlear alterations in PD. No evidence was found for the involvement of the medial olivocochlear system. Altogether, OAEs may provide an objective early indicator of auditory alterations in PD and should complement subjective tonal audiometry when assessing and monitoring auditory function in PD.

Short-Term Test-Retest Reliability of Contralateral Suppression of Click-Evoked Otoacoustic Emissions in Normal-Hearing Subjects

Purpose The objective of the current study was to investigate the short-term test-retest reliability of contralateral suppression (CS) of click-evoked otoacoustic emissions (CEOAEs) using commercially available otoacoustic emission equipment. Method Twenty-three young normal-hearing subjects were tested. An otoscopic evaluation, admittance measures, pure-tone audiometry, measurements of CEOAEs without and with contralateral acoustic stimulation (CAS) to determine CS were performed at baseline (n = 23), an immediate retest without and with refitting of the probe (only CS of CEOAEs; n = 11), and a retest after 1 week (n = 23) were performed. Test-retest reliability parameters were determined on CEOAE response amplitudes without and with CAS, and on raw and normalized CS indices between baseline and the other test moments. Results Repeated-measures analysis of variance indicated no random or systematic changes in CEOAE response amplitudes without and with CAS, and in raw and normalized CS indices between the test moments. Moderate-to-high intraclass correlation coefficients with mostly high significant between-subjects variability between baseline and each consecutive test moment were found for CEOAE response amplitude without and with CAS, and for the raw and normalized CS indices. Other reliability parameters deteriorated between CEOAE response amplitudes with CAS as compared to without CAS, between baseline and retest with probe refitting, and after 1 week, as well as for frequency-specific raw and normalized CS indices as compared to global CS indices. Conclusions There was considerable variability in raw and normalized CS indices as measured using CEOAEs with CAS using commercially available otoacoustic emission equipment. More research is needed to optimize the measurement of CS of CEOAEs and to reduce influencing factors, as well as to make generalization of test-retest reliability data possible.