Impact of occupational noise on pure-tone threshold and distortion product otoacoustic emissions after one workday

Narrow-band chirp and tone burst auditory brainstem response as an early indicator of synaptopathy in industrial workers exposed to occupational noise

This study aims at characterizing and comparing the findings of auditory brainstem response (ABR) using narrow-band chirp (NB-chirp) and tone burst (TB) for both latency and amplitude parameters among those exposed to occupational noise and to determine which among the two serves as a better indicator of noise-induced cochlear neuropathy. Forty adult males in the age range of 20-35 years were considered, wherein 20 of them were exposed to noise > 80 dB (A) for 8 hours per day constituting Noise-exposed group; and Control group consisted of 20 individuals without occupational noise exposure. ABR was recorded using NB-chirp and TB for four frequencies at 80 dB nHL through Etymotic Research - 3A (ER-3A) Insert phones using Interacoustics Eclipse EP-25 in individuals with and without noise exposure. MANOVA was performed to compare between TB ABR and NB-chirp ABR between the two groups. Statistical analysis revealed a notable difference for NB-chirp comparisons between the two groups at three frequencies: 500 Hz, F(1, 38) = 10.6; 1000 Hz, F(1, 38) = 7.91; and 2000 Hz, F(1, 38) = 6.64. Whereas, the difference was evident at only 500 Hz: F(1, 38) = 4.98 in case of TB ABR. However, there was no significant difference seen at any of the frequencies for amplitude parameters in both TB and NB-chirp ABR. Latency of wave V using NB-chirp was considered to be a better indicator compared to TB, acting as a better clinical tool in early identification, diagnosis, and monitoring of noise induced hearing loss (NIHL).

Utility of otoacoustic emissions and olivocochlear reflex in predicting vulnerability to noise-induced inner ear damage

Aim:

The aim of the present study was to explore the possible utility of otoacoustic emissions (OAEs) and efferent system strength to determine vulnerability to noise exposure in a clinical setting.

Materials and Methods:

The study group comprised 344 volunteers who had just begun mandatory basic training as Hellenic Corps Officers Military Academy cadets. Pure-tone audiograms were obtained on both ears. Participants were also subjected to diagnostic transient-evoked otoacoustic emissions (TEOAEs). Finally, they were all tested for efferent function through the suppression of TEOAEs with contralateral noise. Following baseline evaluation, all cadets fired 10 rounds using a 7.62 mm Heckler & Koch G3A3 assault rifle while lying down in prone position. Immediately after exposure to gunfire noise and no later than 10 h, all participants completed an identical protocol for a second time, which was then repeated a third time, 30 days later.

Results:

The data showed that after the firing drill, 280 participants suffered a temporary threshold shift (TTS) (468 ears), while in the third evaluation conducted 30 days after exposure, 142 of these ears still presented a threshold shift compared to the baseline evaluation [permanent threshold shift (PTS) ears]. A receiver operating characteristics curve analysis showed that OAEs amplitude is predictive of future TTS and PTS. The results were slightly different for the suppression of OAEs showing only a slight trend toward significance. The curves were used to determine cut points to evaluate the likelihood of TTS/PTS for OAEs amplitude in the baseline evaluation. Decision limits yielding 71.6% sensitivity were 12.45 dB SPL with 63.8% specificity for PTS, and 50% sensitivity were 12.35 dB SPL with 68.2% specificity for TTS.

Conclusions:

Interestingly, the above data yielded tentative evidence to suggest that OAEs amplitude is both sensitive and specific enough to efficiently identify participants who are particularly susceptible to hearing loss caused by impulse noise generated by firearms. Hearing conservation programs may therefore want to consider including such tests in their routine. As far as efferent strength is concerned, we feel that further research is due, before implementing the suppression of OAEs in hearing conservations programs in a similar manner.

Analysing use of the Chinese HHIE-S for hearing screening of elderly in a northeastern industrial area of China

OBJECTIVE

The aim of the present study was to investigate the use of Chinese version of HHIE-S as a hearing screening tool for the elderly in an industrial area in northeast China.

DESIGN

Prevalence, sensitivity and specificity of Chinese version of HHIE-S were calculated. Factors that had impact on HHIE-S were analysed.

STUDY SAMPLE

Five hundred and seventy Mandarin speaking participants, aged from 50 to 85 years were included. They were tested with pure tone audiometry and Chinese version of HHIE-S.

RESULTS

The prevalence of hearing handicap was 55.3%. The sensitivity and specificity of HHIE-S were 84.5% and 58.3% respectively when the pass/fail criteria were set at PTA^0.5-4kHz >40 dBHL. In general, HHIE-S total and subscale scores were significantly associated with severity of hearing impairment. After stratified by severity of hearing impairment, both the prevalence of reported handicap and the scores of HHIE-S were not significantly associated with age. Male participants had significantly higher HHIE-S scores than female participants did.

CONCLUSIONS

The Chinese version of HHIE-S contributes useful information to identifying hearing handicap and addressing the rehabilitative needs in the elderly in an industrial city in Mainland China.

A Role of Medial Olivocochlear Reflex as a Protection Mechanism from Noise-Induced Hearing Loss Revealed in Short-Practicing Violinists

Previous studies have indicated that extended exposure to a high level of sound might increase the risk of hearing loss among professional symphony orchestra musicians. One of the major problems associated with musicians' hearing loss is difficulty in estimating its risk simply on the basis of the physical amount of exposure, i.e. the exposure level and duration. The aim of this study was to examine whether the measurement of the medial olivocochlear reflex (MOCR), which is assumed to protect the cochlear from acoustic damage, could enable us to assess the risk of hearing loss among musicians. To test this, we compared the MOCR strength and the hearing deterioration caused by one-hour instrument practice. The participants in the study were music university students who are majoring in the violin, whose left ear is exposed to intense violin sounds (broadband sounds containing a significant number of high-frequency components) during their regular instrument practice. Audiogram and click-evoked otoacoustic emissions (CEOAEs) were measured before and after a one-hour violin practice. There was a larger exposure to the left ear than to the right ear, and we observed a left-ear specific temporary threshold shift (TTS) after the violin practice. Left-ear CEOAEs decreased proportionally to the TTS. The exposure level, however, could not entirely explain the inter-individual variation in the TTS and the decrease in CEOAE. On the other hand, the MOCR strength could predict the size of the TTS and CEOAE decrease. Our findings imply that, among other factors, the MOCR is a promising measure for assessing the risk of hearing loss among musicians.

The olivocochlear system and protection from acoustic trauma: a mini literature review

Large intersubject variability in the susceptibility to noise-induced hearing loss (NIHL) is known to occur in both humans and animals. It has been suggested that the olivocochlear system (OCS) plays a significant role in protecting the cochlea from exposure to high levels of noise. A mini literature review about the scientific evidence from animal and human studies about the association between the function of the OCS and susceptibility to NIHL was carried out. Animal data consistently show that de-efferented ears exhibit larger temporary threshold shift (TTS) and permanent threshold shift (PTS) than efferented ears. Data from human studies do not consistently show a correlation between the strength of the OCS function and amount of TTS. Further research on human subjects is required to determine how the OCS function could be used to predict susceptibility to NIHL in individual subjects.

Otoacoustic-emission-based medial-olivocochlear reflex assays for humans

Otoacoustic emission (OAE) tests of the medial-olivocochlear reflex (MOCR) in humans were assessed for viability as clinical assays. Two reflection-source OAEs [TEOAEs: transient-evoked otoacoustic emissions evoked by a 47 dB sound pressure level (SPL) chirp; and discrete-tone SFOAEs: stimulus-frequency otoacoustic emissions evoked by 40 dB SPL tones, and assessed with a 60 dB SPL suppressor] were compared in 27 normal-hearing adults. The MOCR elicitor was a 60 dB SPL contralateral broadband noise. An estimate of MOCR strength, MOCR%, was defined as the vector difference between OAEs measured with and without the elicitor, normalized by OAE magnitude (without elicitor). An MOCR was reliably detected in most ears. Within subjects, MOCR strength was correlated across frequency bands and across OAE type. The ratio of across-subject variability to within-subject variability ranged from 2 to 15, with wideband TEOAEs and averaged SFOAEs giving the highest ratios. MOCR strength in individual ears was reliably classified into low, normal, and high groups. SFOAEs using 1.5 to 2 kHz tones and TEOAEs in the 0.5 to 2.5 kHz band gave the best statistical results. TEOAEs had more clinical advantages. Both assays could be made faster for clinical applications, such as screening for individual susceptibility to acoustic trauma in a hearing-conservation program.

[High-resolution distortion-product otoacoustic emissions: method and clinical applications]

Unlike pure tone thresholds that assess both peripheral and central sound processing, distortion-product otoacoustic emissions (DPOAEs) selectively mirror the functioning of the cochlear amplifier. High resolution DPOAEs are missing in the toolbox of routine audiometry due to the fact that high resolution DPOAE measurements are more time-consuming when compared to normal clinical DP grams with rough frequency resolution. Measurements of high resolution DPOAEs allow an early assessment of beginning sensory cell damage due to sound overexposure or administration of ototoxic drugs. When using a rough grid, sensory cell damage would be overlooked as in the early state damage only appears at some distinct cochlear sites. A review is given on the method and application of high resolution DPOAEs.

Distortion Product Otoacoustic Emission (DPOAE) as an Appropriate Tool in Assessment of Otoprotective Effects of Antioxidants in Noise-Induced Hearing Loss (NIHL)

Distortion product otoacoustic emission (DPOAE) appears to be an objective sensitive test of cochlear function. The aim of this study was to investigate whether DPOAE is an appropriate tool for assessment of minute changes in cochlea due to usage of antioxidant material. 48 workers exposed to continuous noise in a textile factory were randomly assigned into three groups: (1) The Control group (n = 16) received no antioxidant drugs, (2) The N-acetyl-cysteine (NAC) group (n = 16) received oral antioxidant NAC (1200 mg/day), (3) The Ginseng group (n = 16) received oral antioxidant Ginseng (200 mg/day). All three groups had a follow-up period of 2 weeks. The cochlear changes were assessed using DPOAE test before starting the daily work shift on first and 15th day. The associations between groups and DPOAE amplitudes after 2 weeks were analyzed using linear regression analysis. Four separate models were fitted by side of ears and frequency. All models were adjusted for baseline amplitude. Reduced (better) amplitude at DPOAE test was found for NAC and Ginseng groups at high frequencies (4 and 6 kHz) in both ears after 2 weeks compared to control group. Moreover, NAC group showed better DPOAE amplitude than Ginseng group. In conclusion, DPOAE seems to be an appropriate tool in assessing minute changes in the cochlea after antioxidant drugs administration.

Assessment of the noise-protective action of the olivocochlear efferents in humans

It has been demonstrated in different mammals that the medial olivocochlear efferents (MOC) exert a noise-protective effect on the cochlea. In humans such an effect has not unambiguously been shown as of yet. The objective of this study was to assess the relationship between MOC activity and susceptibility of the cochlea to noise-induced hearing loss in humans. In 40 normally hearing human subjects, we measured the following: (1) magnitude of temporary threshold shift (TTS) after exposure to 60 min broadband noise of 94 dB SPL and (2) contralateral suppression (CS) of distortion product otoacoustic emissions (which reflects MOC activity) using two different measurement paradigms. CS was measured in duplicate on 2 measurement days. The relationship between TTS and CS was assessed. Individual TTS in the most affected frequencies (4 > 3 > 8 kHz) ranged from 9 to 28 dB HL, with an average maximum TTS of 18.4 dB HL. The amount of CS ranged between 0.3 and 3 dB. The repeatability of CS, evaluated by Cronbach's α value, ranged from 0.76 (acceptable repeatability) to 0.86 (good repeatability). One of the two different measurement paradigms showed a statistically significant inverse correlation between CS magnitude and amount of TTS, which was hypothesized. This is the first study on the relationship between TTS and CS in humans employing TTS induced under controlled laboratory conditions and two different MOC paradigms. The findings are compatible with the hypothesis that MOC activity is noise protective in humans. Future perspectives include modified CS paradigms, longitudinal cohort studies or efforts to also monitor lateral efferent effects in humans.

A prioritization approach for noise risk management in a petrochemical complex

OBJECTIVES

Noise is probably the most common occupational hazard facing workers today. This paper presents a model to evaluate and select a unit as the first priority for implementing noise control measures from the different parts of an industrial complex.

METHODS

For this purpose, a formula was proposed as a priority risk index (NCPI) by considering some criteria, including: the number of exposed workers in each part, their exposure times and the range of sound pressure level. The above criteria were weighed by appending weighting factors, which can be different based upon the environmental noise levels. The environmental noise measurements were also carried out by lattice method according to ISO 9612:2009. At the next stage, the numbers of stations that fell within the desired ranges in the weighting factors table were found. then the priorities were identified using the above criteria and the NCPI.

RESULTS

The results indicate that the compression unit of air plant had the highest score among the different departments of the company under study (NCPI=0.3). Using this model is easy and fast. It is applicable to similar industries and also offers valuable information for prioritizing noise control measures.

CONCLUSIONS

Therefore, it will be possible to minimize worker exposure to noise in the most polluted places in any industry by identifying the main noise sources and implementing measures suitable for controlling the risk.

A new method to analyze distortion product otoacoustic emissions (DPOAEs) in the high-frequency range up to 18 kHz using windowed periodograms

Distortion product otoacoustic emissions (DPOAEs) are widely used as an objective examination procedure to determine cochlear function. In a clinical routine setting, the amplitude of the DPOAE signal at 2f1 .. f2 is applied as an indicator for a potential hearing loss up to 8 kHz. Due to their poor signal to noise ratio, meatal nodes from standing waves and calibration issues, high-frequency DPOAEs > 8 kHz have hardly been addressed in experimental and clinical audiology so far. Here, we present a new method of measuring DPOAE signal levels based on optimal maximum likelihood estimation with windowed power spectral density estimation of stochastic signals and filtering theory. Analysis of simulated data showed that the proposed method effectively reduces the disturbing noise floor compared to conventional averaging techniques. Robust DPOAE signals were measured in 20 ears from 10 normally hearing young adults (21 to 27 years) from 0:5 to 18 kHz. Repeated DPOAE recordings in one individual yielded a good to very good testretest reliability of the proposed method. These observations are discussed in the context of DPOAE signal processing and possible clinical applications of high-frequency DPOAE measurements.

Impact of three hours of discotheque music on pure-tone thresholds and distortion product otoacoustic emissions

The aim of this study was to investigate whether distortion product otoacoustic emissions (DPOAEs) are a suitable means for detecting changes in outer hair cell (OHC) functionality due to exposure to three hours of discotheque music and whether efferent reflex strength of the medial olivocochlear bundle is able to predict the ear's susceptibility to high-level noise. High-resolution DPOAEs (Δf(2)=47 Hz) were recorded between 3.5 and 4.5 kHz at close-to-threshold primary tone levels. For comparison, high-resolution pure-tone audiometry was conducted in the same frequency range. Efferent reflex strength was measured by means of DPOAEs at a specific frequency with and without contralateral acoustic stimulation. A significant deterioration of more than 10 dB was found for pure-tone thresholds and DPOAE levels indicating that three hours of high-level noise exert a considerable influence on hearing capability and OHC functionality. A significant correlation between shifts in pure-tone threshold and shifts in DPOAE level occurred when removing data with differing calibration across measurements. There was no clear correlation between efferent reflex strength and shifts in pure-tone threshold or shifts in DPOAE level suggesting that the applied measures of efferent reflex strength may not be suitable for quantifying individual vulnerability to noise.

Temporary reduction of distortion product otoacoustic emissions (DPOAEs) immediately following auditory brainstem response (ABR)

The hearing status of an experimental animal is typically assessed in the laboratory setting by the combined use of auditory brainstem response (ABR) and distortion product otoacoustic emissions (DPOAEs), carried out in succession, with the former assay preceding the latter. This study reports a cautionary finding that the use of this accepted regimen yields a reduced DPOAE response. When the DPOAEs were performed after ABR testing, transient reduction of the DPOAE amplitudes was observed at all frequencies in both the inbred, C57/B6 and FVB/N, and the outbred, SW mouse strains. DPOAEs were reduced post-ABR in multiple mouse strains which suggests that this finding is not strain-specific but a general consequence of the preceding ABR analysis. The reduction in DPOAE was temporary: when re-tested at one hour, DPOAE amplitudes recovered to pre-ABR levels. In contrast to the ABR's impact on DPOAE response, ABR thresholds were not altered or reduced when preceded immediately by DPOAE measurements. The molecular alterations underlying the ABR-induced transient reduction of DPOAE remain to be determined. To investigate the potential role of reactive oxygen species in post-ABR DPOAE reduction, transgenic mice over-expressing SOD1, the cytoplasmic enzyme critical for removal of superoxide radicals were subjected to the same auditory testing regimen. Similar to their wild type littermates, the SOD1 transgenic mice also demonstrated post-ABR DPOAE reduction, and thus do not support a role for superoxide radicals in transient reduction of DPOAE. While toxic noise exposure is known to negatively impact OAE, transient decrease in DPOAE levels following standard ABR assay has not been previously described. A practical outcome from this study is a recommendation for reversal of the traditional order for carrying out auditory tests, with the OAE measurements preceding ABR assessment, thus ensuring that the DPOAE response is unaffected.