Overexposure effects of a 1-kHz tone on the distortion product otoacoustic emission in humans

Evaluation of the Decrease in DPOAE Levels After VEMP Testing in Clinical Patients Referred to the Vertigo Outpatient Clinic

Background/Objectives: The objective of this study is to determine whether the strong acoustic stimuli used in vestibular evoked myogenic potential (VEMP) testing contribute to distortion product otoacoustic emission (DPOAE) level reduction due to noise-induced hearing loss. Methods: The DPOAE levels were measured routinely to evaluate vestibular balance disorders with sensorineural hearing loss and to monitor changes in cochlear function before and after VEMP. The changes in DPOAE levels after VEMP testing in 174 patients (80 males and 94 females; median age, 53 years [interquartile range, 39-67 years; range, 15-85 years]) who were examined in the vertigo outpatient clinic between June 2021 and December 2024 were retrospectively analyzed. Results: The DPOAE levels decreased significantly after VEMP testing at 1.4 kHz, 2 kHz, 2.8 kHz, sum all 1/2 octave, and average 1/2 octave (1-6 kHz). The decrease in DPOAE levels at 6 kHz exhibited a significant negative linear correlation with age (the coefficient of determination: 0.0189, p = 0.01), but not sex or side. Conclusions: The strong sound stimulation used in VEMP testing can decrease DPOAE levels. The frequencies at which DPOAE levels decreased significantly were overtones of the stimulus frequency, suggesting a possible effect of acoustic stimulation. VEMP testing can be an invasive test method and should be performed with detailed consideration of the risks and benefits. The age factor can influence the decrease in DPOAE levels in VEMP testing.

The Effect of Short-Term Noise Exposure on Audiometric Thresholds, Distortion Product Otoacoustic Emissions, and Electrocochleography

Purpose The purpose of the study was to examine the effect of short-term noise exposure on audiometric thresholds, distortion product otoacoustic emissions (DPOAEs), and electrocochleography (ECochG) as a function of ear and sex. Method Preexposure and postexposure measures of audiometric thresholds, DPOAEs, and ECochG indices were examined. Sixteen male and 16 female adults participated. Participants were exposed to a 2000-Hz narrowband noise presented at 105 dBA for 10 min. Results Following noise exposure, significantly ( p < .0001) larger auditory threshold differences were observed for left ears. Larger auditory threshold differences were also observed for 3000 and 4000 Hz versus 2000 and 6000 Hz. DPOAE absolute amplitude differences increased with decreasing L ₁, L ₂ level ( p < .0001). DPOAE absolute amplitude differences also significantly rose with increasing f₂ frequencies ( p < .0001). Females generally had larger DPOAE absolute amplitude differences than males ( p < .05). Summating potential amplitudes were significantly larger for female left ears following noise exposure ( p = .03). Left-ear summating potential/action potential amplitude ratios and summating potential/action potential area ratios were increased following noise exposure ( p < .05). Conclusions Utilizing a test battery to examine the effects of short-term noise exposure can reveal the functional status of different structures in the cochlea. There appears to be a susceptibility of the left ear to short-term loud noise exposure. Findings with respect to a sex susceptibility to short-term loud noise exposure were not strong, as sex differences were only observed for a subset of the conditions.

Modeling signal-to-noise ratio of otoacoustic emissions in workers exposed to different industrial noise levels

Introduction:

Noise is considered as the most common cause of harmful physical effects in the workplace. A sound that is generated from within the inner ear is known as an otoacoustic emission (OAE). Distortion-product otoacoustic emissions (DPOAEs) assess evoked emission and hearing capacity. The aim of this study was to assess the signal-to-noise ratio in different frequencies and at different times of the shift work in workers exposed to various levels of noise. It was also aimed to provide a statistical model for signal-to-noise ratio (SNR) of OAEs in different frequencies based on the two variables of sound pressure level (SPL) and exposure time.

Materials and Methods:

This case–control study was conducted on 45 workers during autumn 2014. The workers were divided into three groups based on the level of noise exposure. The SNR was measured in frequencies of 1000, 2000, 3000, 4000, and 6000 Hz in both ears, and in three different time intervals during the shift work. According to the inclusion criterion, SNR of 6 dB or greater was included in the study. The analysis was performed using repeated measurements of analysis of variance, spearman correlation coefficient, and paired samples t-test.

Results:

The results showed that there was no statistically significant difference between the three exposed groups in terms of the mean values of SNR (P > 0.05). Only in signal pressure levels of 88 dBA with an interval time of 10:30–11:00 AM, there was a statistically significant difference between the right and left ears with the mean SNR values of 3000 frequency (P = 0.038). The SPL had a significant effect on the SNR in both the right and left ears (P = 0.023, P = 0.041). The effect of the duration of measurement on the SNR was statistically significant in both the right and left ears (P = 0.027, P < 0.001).

Conclusion:

The findings of this study demonstrated that after noise exposure during the shift, SNR of OAEs reduced from the beginning to the end of the shift.

Changes in cochlear function related to acoustic stimulation of cervical vestibular evoked myogenic potential stimulation

Evaluation of cervical evoked myogenic potentials (c-VEMP) is commonly applied in clinical investigations of patients with suspected neurotological symptoms. Short intense acoustic stimulation of peak levels close to 130 dB SPL is required to elicit the responses. A recent publication on bilateral significant sensorineural hearing loss related to extensive VEMP stimulation motivates evaluations of immediate effects on hearing acuity related to the intense acoustic stimulation required to elicit c-VEMP responses. The aim of the current study was to investigate changes in DPOAE-levels and hearing thresholds in relation to c-VEMP testing in humans. More specifically, the current focus is on immediate changes in hearing thresholds and changes in DPOAE-levels at frequencies 0.5 octaves above the acoustic stimulation when applying shorter tone bursts than previously used. Hearing acuity before and immediately after exposure to c-VEMP stimulation was examined in 24 patients with normal hearing referred for neurotologic testing. The stimulation consisted of 192 tonebursts of 6 ms and was presented at 500 Hz and 130 dB peSPL. Békésy thresholds at 0.125-8 kHz and DPOAE I/O growth functions with stimulation at 0.75 and 3 kHz were used to assess c-VEMP related changes in hearing status. No significant deterioration in Békésy thresholds was detected. Significant reduction in DPOAE levels at 0.75 (0.5-1.35 dB) and 3 kHz (1.6-2.1 dB) was observed after c-VEMP stimulation without concomitant changes in cochlear compression. The results indicated that there was no immediate audiometric loss related to c-VEMP stimulation in the current group of patients. The significant reduction of DPOAE levels at a wider frequency range than previously described after the c-VEMP test could be related to the stimulation with shorter tone bursts. The results show that c-VEMP stimulation causes reduction in DPOAE-levels at several frequencies that corresponds to half the reductions in DPOAE levels reported after exposure to the maximally allowed occupational noise for an 8 h working day. Consequently, extended stimuli intensity or stimulation repetition with c-VEMP testing should be avoided to reduce the risk for noise-induced cochlear injury.

Evaluation of Distortion Product Otoacoustic Emissions (DPOAEs) among workers at an Industrial Company exposed to different industrial noise levels in 2014

BACKGROUND

Noise-induced hearing loss (NIHL) is usually one of the main problems in industrial settings. The aim of this study was to determine whether changes in the signal-to-noise ratio (SNR) in different DPOAE are caused by exposure to different levels of noise at different time intervals among workers exposed to noise.

METHODS

This case-control study was conducted in the autumn of 2014 on 45 workers at Gol Gohar Mining and Industrial Company, which is located in Sirjan in southeast Iran. The workers were divided into three groups based on their noise exposure, i.e., 1) 15 office workers as a control group with exposure to low levels of noise, 2) 15 workers from manufacturing departments who were exposed to a medium level of noise, and 3) 15 workers from manufacturing departments who were exposed to high levels of noise. The SNRs at the frequencies of 1000, 2000, 3000, 4000, and 6000 Hz were measured in both ears at three different time intervals during the shift work. SNRs of 6 or greater were considered as inclusion criterion. Repeated measures, the Spearman rank-order correlation test, and paired t-test analyses were used with α = 0.05 being the level of significance.

RESULTS

For all frequencies in the right and left ears, the SNR values were more than 6, thus all SNR values were considered as acceptable responses. The effects of time and sound pressure level (SPL) on SNR were significant for the right and left ears (p = 0.027 and < 0.001, respectively). There was a statistically significant correlation between the SNR values in the right and left ears for the time intervals 7:30-8:00 A.M. and 13:30-14:00 P.M., which implied that an increase in the duration of exposure led to reduced SNR values (p = 0.024, r = 0.948).

CONCLUSIONS

The comparison of the SNR values in the right and left ears (for all frequencies and the three different SPLs) indicated that the values decreased during the shift work.

Is it necessary to penalize impulsive noise +5 dB due to higher risk of hearing damage?

It is studied whether the +5 dB penalty for impulsiveness established by ISO 1999:1990 accounts for a higher risk of noise-induced hearing loss. A total of 16 normal-hearing human subjects were exposed for 10 min to two types of binaural industrial-recordings: (1) a continuous broad-band noise normalized to L(EX,8 h)=80 dBA and (2) the combination of the previous stimulus with an impulsive noise normalized to L(EX,8 h)=75+5(db penalty)=80 dBA (peak level 117 dBC and repetition rate of 0.5 impacts per second). Distortion product otoacoustic emissions (DPOAEs) were measured in a broad frequency range before and in the following 90 min after the exposure. The group results show that the continuous exposure had a bigger impact on DPOAE levels, with a maximum DPOAE shift of approximately 5 dB in the frequency range of 2-3.15 kHz during the first 10 min of the recovery. No evident DPOAE shift is seen for the impulsive + continuous stimulus. The results indicate that the penalty overestimated the effects on DPOAE levels and support the concept that the risk of hearing loss from low-level impulses may be predicted on an equal-energy basis.

Recovery of distortion-product otoacoustic emissions after a 2-kHz monaural sound-exposure in humans: effects on fine structures

A better understanding of the vulnerability of the fine structures of distortion-product otoacoustic emissions (DPOAEs) after acoustic overexposure may improve the knowledge about DPOAE generation, cochlear damage, and lead to more efficient diagnostic tools. It is studied whether the DPOAE fine structures of 16 normal-hearing human subjects are systematically affected after a moderate monaural sound-exposure of 10 min to a 2-kHz tone normalized to an exposure level L(EX,8h) of 80 dBA. DPOAEs were measured before and in the following 70 min after the exposure. The experimental protocol allowed measurements with high time and frequency resolution in a 1/3-octave band centered at 3 kHz. On average, DPOAE levels were reduced approximately 5 dB in the entire measured frequency-range. Statistically significant differences in pre- and post-exposure DPOAE levels were observed up to 70 min after the end of the sound exposure. The results show that the effects on fine structures are highly individual and no systematic change was observed.

Measuring distortion product otoacoustic emissions using continuously sweeping primaries

Distortion product otoacoustic emission (DPOAE) level from normal hearing individuals can vary by as much as 30 dB with small frequency changes (a phenomenon known as DPOAE fine structure). This fine structure is hypothesized to stem from the interaction of components from two different regions of the cochlea (the nonlinear generator region and the reflection component from the DP region). An efficient procedure to separate these two components would improve the clinical and research utility of DPOAE by permitting separate evaluation of different cochlea regions. In this paper, two procedures for evaluating DPOAE fine structure are compared: DPOAE generated by fixed-frequency primaries versus continuously sweeping primaries. The sweep DPOAE data are analyzed with a least squares fit filter. Sweep rates of greater than 8 s per octave permit rapid evaluation of the cochlear fine structure. A higher sweep rate of 2 s per octave provided DPOAE without fine structure. Under these conditions, the longer latency reflection component falls outside the range of the filter. Consequently, DPOAE obtained with sweeping tones can be used either to get more rapid estimates of DPOAE fine structure or to obtain estimates of DPOAE from the generator region uncontaminated by energy from the reflection region.