Long-term evidence of noise-induced permanent threshold shift in a harbor seal (Phoca vitulina).

In psychophysical studies of noise-induced hearing loss with marine mammals, exposure conditions are often titrated from levels of no effect to those that induce significant but recoverable loss of auditory sensitivity [temporary threshold shift (TTS)]. To examine TTS from mid-frequency noise, a harbor seal was exposed to a 4.1-kHz underwater tone that was incrementally increased in sound pressure level (SPL) and duration. The seal's hearing was evaluated at the exposure frequency and one-half octave higher (5.8 kHz) to identify the noise parameters associated with TTS onset. No reliable TTS was measured with increasing sound exposure level until the second exposure to a 60-s fatiguing tone of 181 dB re 1 µPa SPL (sound exposure level 199 dB re 1 µPa2s), after which an unexpectedly large threshold shift (>47 dB) was observed. While hearing at 4.1 kHz recovered within 48 h, there was a permanent threshold shift of at least 8 dB at 5.8 kHz. This hearing loss was evident for more than ten years. Furthermore, a residual threshold shift of 11 dB was detected one octave above the tonal exposure, at 8.2 kHz. This hearing loss persisted for more than two years prior to full recovery.

Effect of impact pile driving noise on marine mammals: A comparison of different noise exposure criteria.

Regulators in Europe and in the United States have developed sound exposure criteria. Criteria range from broadband levels to frequency weighted received sound levels. The associated differences in impact assessment results are, however, not yet understood. This uncertainty makes environmental management of transboundary anthropogenic noise challenging and causes confusion for regulators who need to choose appropriate exposure criteria. In the present study, three established exposure criteria frameworks from Germany, Denmark, and the US were used to analyse the effect of impact pile driving at a location in the Baltic Sea on harbor porpoise and harbor seal hearing. The acoustic modeling using MIKE showed that an unmitigated scenario would lead to auditory injury for all three criteria. Despite readily apparent variances in impact ranges among the applied approaches, it was also evident that noise mitigation measures could reduce underwater sound to levels where auditory injuries would be unlikely in most cases. It was concluded that each of the frameworks has its own advantages and disadvantages. Single noise exposure criteria follow the precautionary principle and can be enforced relatively easily, whereas criteria that consider hearing capabilities and animal response movement can improve the accuracy of the assessment if data are available.

Simultaneous dichotic loudness balance (SDLB): Why loudness "fatigues" with two ears but not with one.

In the laboratory method called simultaneous dichotic loudness balance (SDLB), the contribution-to-loudness that arises from the listener's continually exposed "fatiguing" ear is required to be matched (balanced) by the listener, by adjusting the intensity of a noncontinuous stimulus at the other ("comparison") ear. The latter intensity usually declines, allegedly indicating "fatigue" of the contribution-to-loudness from the "fatiguing" ear. However, no "fatigue" is found when one ear alone (with the other ear in quiet) experiences a continuous well-suprathreshold stimulus. This is a quandary that remains unresolved. The present article offers a resolution, through a novel conceptual model in which any ear experiencing stimuli acts through a well-characterized physiological structure, the olivocochlear bundle, to "turn down the volume" at the opposite ear. The model explains how "fatigue" varies in eight different SDLB conditions, some having several subconditions. Altogether, the model demonstrates that "fatigue" is an artifact of SDLB itself.

Influence of Acoustic Overstimulation on the Central Auditory System: An Functional Magnetic Resonance Imaging (fMRI) Study.

BACKGROUND The goal of the fMRI experiment was to explore the involvement of central auditory structures in pathomechanisms of a behaviorally manifested auditory temporary threshold shift in humans. MATERIAL AND METHODS The material included 18 healthy volunteers with normal hearing. Subjects in the exposure group were presented with 15 min of binaural acoustic overstimulation of narrowband noise (3 kHz central frequency) at 95 dB(A). The control group was not exposed to noise but instead relaxed in silence. Auditory fMRI was performed in 1 session before and 3 sessions after acoustic overstimulation and involved 3.5-4.5 kHz sweeps. RESULTS The outcomes of the study indicate a possible effect of acoustic overstimulation on central processing, with decreased brain responses to auditory stimulation up to 20 min after exposure to noise. The effect can be seen already in the primary auditory cortex. Decreased BOLD signal change can be due to increased excitation thresholds and/or increased spontaneous activity of auditory neurons throughout the auditory system. CONCLUSIONS The trial shows that fMRI can be a valuable tool in acoustic overstimulation studies but has to be used with caution and considered complimentary to audiological measures. Further methodological improvements are needed to distinguish the effects of TTS and neuronal habituation to repetitive stimulation.

Fatigue Modeling via Mammalian Auditory System for Prediction of Noise Induced Hearing Loss.

Noise induced hearing loss (NIHL) remains as a severe health problem worldwide. Existing noise metrics and modeling for evaluation of NIHL are limited on prediction of gradually developing NIHL (GDHL) caused by high-level occupational noise. In this study, we proposed two auditory fatigue based models, including equal velocity level (EVL) and complex velocity level (CVL), which combine the high-cycle fatigue theory with the mammalian auditory model, to predict GDHL. The mammalian auditory model is introduced by combining the transfer function of the external-middle ear and the triple-path nonlinear (TRNL) filter to obtain velocities of basilar membrane (BM) in cochlea. The high-cycle fatigue theory is based on the assumption that GDHL can be considered as a process of long-cycle mechanical fatigue failure of organ of Corti. Furthermore, a series of chinchilla experimental data are used to validate the effectiveness of the proposed fatigue models. The regression analysis results show that both proposed fatigue models have high corrections with four hearing loss indices. It indicates that the proposed models can accurately predict hearing loss in chinchilla. Results suggest that the CVL model is more accurate compared to the EVL model on prediction of the auditory risk of exposure to hazardous occupational noise.

Noise-induced hearing loss in marine mammals: A review of temporary threshold shift studies from 1996 to 2015.

One of the most widely recognized effects of intense noise exposure is a noise-induced threshold shift­an elevation of hearing thresholds following cessation of the noise. Over the past twenty years, as concerns over the potential effects of human-generated noise on marine mammals have increased, a number of studies have been conducted to investigate noise-induced threshold shift phenomena in marine mammals. The experiments have focused on measuring temporary threshold shift (TTS)­a noise-induced threshold shift that fully recovers over time­in marine mammals exposed to intense tones, band-limited noise, and underwater impulses with various sound pressure levels, frequencies, durations, and temporal patterns. In this review, the methods employed by the groups conducting marine mammal TTS experiments are described and the relationships between the experimental conditions, the noise exposure parameters, and the observed TTS are summarized. An attempt has been made to synthesize the major findings across experiments to provide the current state of knowledge for the effects of noise on marine mammal hearing.

Effects of exposure to intermittent and continuous 6-7 kHz sonar sweeps on harbor porpoise (Phocoena phocoena) hearing.

Safety criteria for mid-frequency naval sonar sounds are needed to protect harbor porpoise hearing. A porpoise was exposed to sequences of one-second 6-7 kHz sonar down-sweeps, with 10-200 sweeps in a sequence, at an average received sound pressure level (SPLav.re.) of 166 dB re 1 µPa, with duty cycles of 10% (intermittent sounds) and 100% (continuous). Behavioral hearing thresholds at 9.2 kHz were determined before and after exposure to the fatiguing noise, to quantify temporary hearing threshold shifts (TTS1-4 min) and recovery. Significant TTS1-4 min occurred after 10-25 sweeps when the duty cycle was 10% (cumulative sound exposure level, SELcum: ∼178 dB re 1 µPa(2)s). For the same SELcum, the TTS1-4 min was greater for exposures with 100% duty cycle. The difference in TTS between the two duty cycle exposures increased as the number of sweeps in the exposure sequences increased. Therefore, to predict TTS and permanent threshold shift, not only SELcum needs to be known, but also the duty cycle or equivalent sound pressure level (Leq). It appears that the injury criterion for non-pulses proposed by Southall, Bowles, Ellison, Finneran, Gentry, Greene, Kastak, Ketten, Miller, Nachtigall, Richardson, Thomas, and Tyack [(2007). Aquat. Mamm. 33, 411-521] for cetaceans echolocating at high frequency (SEL 215 dB re 1 µPa(2)s) is too high for the harbor porpoise.

The effect of occupational noise exposure on tinnitus and sound-induced auditory fatigue among obstetrics personnel: a cross-sectional study.

OBJECTIVE: There is a lack of research on effects of occupational noise exposure in traditionally female-dominated workplaces. Therefore, the aim of this study was to assess risk of noise-induced hearing-related symptoms among obstetrics personnel. DESIGN: A cross-sectional study was performed at an obstetric ward in Sweden including a questionnaire among all employees and sound level measurements in 61 work shifts at the same ward. PARTICIPANTS: 115 female employees responded to a questionnaire (72% of all 160 employees invited). MAIN OUTCOME MEASURES: Self-reported hearing-related symptoms in relation to calculated occupational noise exposure dose and measured sound levels. RESULTS: Sound levels exceeded the 80 dB LAeq limit for protection of hearing in 46% of the measured work shifts. One or more hearing-related symptoms were reported by 55% of the personnel. In logistic regression models, a significant association was found between occupational noise exposure dose and tinnitus (OR=1.04, 95% CI 1.00 to 1.09) and sound-induced auditory fatigue (OR=1.04, 95% CI 1.00 to 1.07). Work-related stress and noise annoyance at work were reported by almost half of the personnel. Sound-induced auditory fatigue was associated with work-related stress and noise annoyance at work, although stress slightly missed significance in a multivariable model. No significant interactions were found. CONCLUSIONS: This study presents new results showing that obstetrics personnel are at risk of noise-induced hearing-related symptoms. Current exposure levels at the workplace are high and occupational noise exposure dose has significant effects on tinnitus and sound-induced auditory fatigue among the personnel. These results indicate that preventative action regarding noise exposure is required in obstetrics care and that risk assessments may be needed in previously unstudied non-industrial communication-intense sound environments.

[Auditory fatigue]. / Fatiga auditiva.

INTRODUCTION AND OBJECTIVES: Given the relevance of possible hearing losses due to sound overloads and the short list of references of objective procedures for their study, we provide a technique that gives precise data about the audiometric profile and recruitment factor. Our objectives were to determine peripheral fatigue, through the cochlear microphonic response to sound pressure overload stimuli, as well as to measure recovery time, establishing parameters for differentiation with regard to current psychoacoustic and clinical studies. MATERIAL AND METHOD: We used specific instruments for the study of cochlear microphonic response, plus a function generator that provided us with stimuli of different intensities and harmonic components. In Wistar rats, we first measured the normal microphonic response and then the effect of auditory fatigue on it. RESULTS: Using a 60dB pure tone acoustic stimulation, we obtained a microphonic response at 20dB. We then caused fatigue with 100dB of the same frequency, reaching a loss of approximately 11dB after 15minutes; after that, the deterioration slowed and did not exceed 15dB. By means of complex random tone maskers or white noise, no fatigue was caused to the sensory receptors, not even at levels of 100dB and over an hour of overstimulation. CONCLUSIONS: No fatigue was observed in terms of sensory receptors. Deterioration of peripheral perception through intense overstimulation may be due to biochemical changes of desensitisation due to exhaustion. Auditory fatigue in subjective clinical trials presumably affects supracochlear sections. The auditory fatigue tests found are not in line with those obtained subjectively in clinical and psychoacoustic trials.

Effects of mid-frequency active sonar on hearing in fish.

Caged fish were exposed to sound from mid-frequency active (MFA) transducers in a 5 × 5 planar array which simulated MFA sounds at received sound pressure levels of 210 dB SPL(re 1 µPa). The exposure sound consisted of a 2 s frequency sweep from 2.8 to 3.8 kHz followed by a 1 s tone at 3.3 kHz. The sound sequence was repeated every 25 s for five repetitions resulting in a cumulative sound exposure level (SEL(cum)) of 220 dB re 1 µPa(2) s. The cumulative exposure level did not affect the hearing sensitivity of rainbow trout, a species whose hearing range is lower than the frequencies in the presented MFA sound. In contrast, one cohort of channel catfish showed a statistically significant temporary threshold shift of 4-6 dB at 2300 Hz, but not at lower tested frequencies, whereas a second cohort showed no change. It is likely that this threshold shift resulted from the frequency spectrum of the MFA sound overlapping with the upper end of the hearing frequency range of the channel catfish. The observed threshold shifts in channel catfish recovered within 24 h. There was no mortality associated with the MFA sound exposure used in this test.

Preferred sound levels of portable music players and listening habits among adults: a field study.

The main purpose of this descriptive field study was to explore music listening habits and preferred listening levels with portable music players (PMPs). We were also interested in seeing whether any exposure differences could be observed between the sexes. Data were collected during 12 hours at Stockholm Central Station, where people passing by were invited to measure their preferred PMP listening level by using a KEMAR manikin. People were also asked to answer a questionnaire about their listening habits. In all, 60 persons (41 men and 19 women) took part in the questionnaire study and 61 preferred PMP levels to be measured. Forty-one of these sound level measurements were valid to be reported after consideration was taken to acceptable measuring conditions. The women (31 years) and the men (33 years) started to use PMPs on a regular basis in their early 20s. Ear canal headphones/ear buds were the preferred headphone types. Fifty-seven percent of the whole study population used their PMP on a daily basis. The measured LAeq60 sec levels corrected for free field ranged between 73 and 102 dB, with a mean value of 83 dB. Sound levels for different types of headphones are also presented. The results of this study indicate that there are two groups of listeners: people who listen less frequently and at lower, safer sound levels, and people with excessive listening habits that may indeed damage their hearing sensory organ in time.

Temporary threshold shifts at 1500 and 2000 Hz induced by loud voice signals communicated through earphones in the pinball industry.

To assess the risk of hearing loss among workers using earphones as communication devices at noisy worksites, we compared temporary threshold shifts (TTS) between ears on which workers wore earphones and ears on which no earphones were worn. We measured ambient noise and personal noise exposure as well as noise generated by and passed through earphones by applying frequency analysis at three pinball facilities during their hours of actual operation. We assessed hearing levels before and after a work shift (prework and postwork) of 54 workers by pure tone audiometry at six frequencies. The time-weighted averages for ambient noise and personal noise exposure exceeded 85 dB(A) and 90 dB(A), respectively. Overall sound pressure levels generated by and passing through earphones reached 109 dB(A). The one-third octave band spectrum of the earphone noise during the shift exceeded 90 dB(SPL) in the range of 315-2000 Hz. The number of ears demonstrating a TTS, defined as a shift of 10 dB or more in postwork over prework hearing thresholds, was significantly greater at 1500 and 2000 Hz among ears with earphones (P < 0.05 and P < 0.01, respectively) compared to those without. The reverse was observed at 4000 Hz for ears without earphones (P < 0.01). Workers wearing earphones or headsets as communication devices in noisy environments are exposed to high risk of hearing loss, particularly at the frequencies of 1500 and 2000 Hz. Ideally, hearing conservation programs for such workers should account for potential hearing losses at frequencies of 2000 Hz or lower frequencies induced by amplified voice signals.

Diabetes impairs recovery from noise-induced temporary hearing loss.

OBJECTIVES/HYPOTHESIS: The purpose of this study is to investigate whether diabetes impairs the recovery from noised-induced temporary hearing loss. METHODS: Twenty-eight male Wistar rats were divided into three groups: control, diabetes with insulin control (DI), and diabetes without insulin control (DM). Diabetes was induced by intraperitoneal injection of streptozotocin. All animals were exposed to white noise at 110 dB SPL for 8 hours. Auditory brainstem response (ABR) thresholds and distortion product otoacoustic emission (DPOAE) amplitudes were measured for all animals 1 day prior to noise exposure to obtain a baseline for hearing function, and then 1 hour, 1 day, 2 days, 4 days, 7 days, and 14 days after noise exposure. RESULTS: One hour post exposure, ABR thresholds shifted markedly, and DPOAE was reduced similarly in all groups. Both ABR thresholds and DPOAE returned to the baseline in the control group at day 1, but they were not back to the baseline in the DM group even by day 14. Compared with the control group, the ABR threshold shifts and DPOAE returned to baseline more slowly in the DI group. CONCLUSIONS: The present study suggests that diabetic patients need proper blood sugar control and probably need more effective preventive measures to preserve their hearing from the effects of noise. Laryngoscope, 2009.

Dorsal cochlear nucleus hyperactivity and tinnitus: are they related?

PURPOSE: Eight lines of evidence implicating the dorsal cochlear nucleus (DCN) as a tinnitus contributing site are reviewed. We now expand the presentation of this model, elaborate on its essential details, and provide answers to commonly asked questions regarding its validity. CONCLUSIONS: Over the past decade, numerous studies have converged to support the hypothesis that the DCN may be an important brain center in the generation and modulation of tinnitus. Although other auditory centers have been similarly implicated, the DCN deserves special emphasis because, as a primary acoustic nucleus, it occupies a potentially pivotal position in the hierarchy of functional processes leading to the emergence of tinnitus percepts. Moreover, because a great deal is known about the underlying cellular categories and the details of synaptic circuitry within the DCN, this brain center offers a potentially powerful model for probing mechanisms underlying tinnitus.

Susceptibility to impulse noise trauma in different species: guinea pig, rat and mouse.

CONCLUSION: The results indicate that susceptibility to impulse noise differs in the three species. OBJECTIVE: To test the hypothesis that there is different susceptibility to impulse noise trauma in three species: the guinea pig, rat and mouse. MATERIALS AND METHODS: Three groups of animals were exposed to the same impulse noise and the effect on cochlear pathology was examined using auditory brainstem response thresholds. RESULTS: It was found that the rat and mouse are more sensitive to impulse noise than the guinea pig.

Hearing loss from interrupted, intermittent, and time varying non-Gaussian noise exposure: The applicability of the equal energy hypothesis.

Sixteen groups of chinchillas (N=140) were exposed to various equivalent energy noise paradigms at 100 dB(A) or 103 dB(A) SPL. Eleven groups received an interrupted, intermittent, and time varying (IITV) non-Gaussian exposure quantified by the kurtosis statistic. The IITV exposures, which lasted for 8 hday, 5 daysweek for 3 weeks, were designed to model some of the essential features of an industrial workweek. Five equivalent energy reference groups were exposed to either a Gaussian or non-Gaussian 5 days, 24 hday continuous noise. Evoked potentials were used to estimate hearing thresholds and surface preparations of the organ of Corti quantified the sensory cell population. For IITV exposures at an equivalent energy and kurtosis, the temporal variations in level did not alter trauma and in some cases the IITV exposures produced results similar to those found for the 5 day continuous exposures. Any increase in kurtosis at a fixed energy was accompanied by an increase in noise-induced trauma. These results suggest that the equal energy hypothesis is an acceptable approach to evaluating noise exposures for hearing conservation purposes provided that the kurtosis of the amplitude distribution is taken into consideration. Temporal variations in noise levels seem to have little effect on trauma.

An assessment of threshold shifts in nonprofessional pop/rock musicians using conventional and extended high-frequency audiometry.

The clinical value of extended high-frequency audiometry for the detection of noise-induced hearing loss has not been established conclusively. The purpose of this study was to assess the relative temporary threshold shift (TTS) in two frequency regions (conventional versus extended high frequency). In this exploratory study, pure-tone thresholds from 0.5 to 14 kHz were measured in both ears of 16 nonprofessional pop/rock musicians (mean age, 35 yr; range, 27 to 49 yr), before and after a 90-minute rehearsal session. All had experienced repeated exposures to intense sound levels during at least 5 yr of their musical careers. After the rehearsal, median threshold levels were found to be significantly poorer for frequencies from 0.5 to 8 kHz (Wilcoxon signed rank test, p

Evaluation of auditory fatigue in combined noise, heat and workload exposure.

This study was performed in a climatic chamber to evaluate the combined effects of noise intensity, heat stress, workload, and exposure duration on both noise-induced temporary threshold shift (TTS) and the recovery time by adopting Taguch's method. Fourteen subjects without previous significant noise exposure and smoking history were recruited to participate in this study. All hearing threshold levels at eight different frequencies (250 to 8,000 Hz) of better ear were measured in an audiometric booth by using the ascending method in 2 dB steps before each exposure condition. The test was also carried out after exposure to evaluate TTS at various times. The TTS recovery time was assessed using an audiometric test on all subjects at post-exposure times of 2, 20, 40, 60, 80 and 120 min, respectively. It was found that TTS depended mainly on the exposed noise dose and was enhanced by workload and heat stress. The TTS recovery time is dependent upon the magnitude of the initial hearing loss. In conclusion, TTS driven by noise exposure is enhanced by heat and workload. Further studies are required to evaluate the effects of workload with extreme temperature in a workplace environment.

Low-dose, long-term caroverine administration attenuates impulse noise-induced hearing loss in the rat.

CONCLUSION: Physiological and morphological assessments indicated that low-dose and long-term caroverine delivery might be a new approach to protect against impulse noise-induced hearing loss. BACKGROUND: Although the exact mechanisms by which impulse noise causes hearing loss are still unclear, there is accumulating evidence that increased reactive oxygen species (ROS) production and excessive glutamate released from the inner hair cells lead to hair cell loss and consequently hearing loss. Caroverine is an antagonist of two glutamate receptors, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptors in the inner ear, as well as an antioxidant. MATERIALS AND METHODS: In this study, caroverine was delivered subcutaneously using an osmotic pump. This kind of delivery has the advantage, via continuous, long-term and low dose drug administration, of avoiding systemic side effects. RESULTS: It was shown that caroverine could significantly protect the cochlea against impulse noise trauma.