Temporary Hearing Threshold Shift Research Articles

Temporary Hearing Threshold Shift in California Sea Lions (Zalophus californianus) Due to a Noise Band Centered at 32 kHz

To determine their frequency-dependent susceptibility to noise-induced temporary hearing threshold shift (TTS), two California sea lions (Zalophus californianus) were exposed for 60 min to a continuous one-sixth-octave noise band (NB) centered at 32 kHz as the fatiguing sound, at sound pressure levels of 132 to 156 dB re 1 µPa (sound exposure levels [SELs] of 168 to 192 dB re 1 µPa2s). Using a psychoacoustic technique, TTSs were quantified at the center frequency of the fatiguing sound and at half an octave and one octave above the center frequency (at 32, 44.8, and 63 kHz). When significant TTS occurred, higher SELs resulted in greater TTSs. TTSs and hearing recovery patterns were similar in both sea lions. The mean onset of TTS1-4 min (defined as 6 dB TTS) in sea lion F01 is estimated to occur after exposure to an SEL of 179 dB re 1 µPa2s (at hearing test frequency 44.8 kHz). After exposure to an SEL of 180 dB re 1 µPa2s, a mean TTS1-4 min of 6.7 dB was measured at hearing test frequency 44.8 kHz. In California sea lions, TTS onset levels are not as closely related (especially at the lower and higher frequencies) to the unmasked hearing thresholds (audiograms) as was previously assumed.

Similar susceptibility to temporary hearing threshold shifts despite different audiograms in harbor porpoises and harbor seals.

When they are exposed to loud fatiguing sounds in the oceans, marine mammals are susceptible to hearing damage in the form of temporary hearing threshold shifts (TTSs) or permanent hearing threshold shifts. We compared the level-dependent and frequency-dependent susceptibility to TTSs in harbor seals and harbor porpoises, species with different hearing sensitivities in the low- and high-frequency regions. Both species were exposed to 100% duty cycle one-sixth-octave noise bands at frequencies that covered their entire hearing range. In the case of the 6.5 kHz exposure for the harbor seals, a pure tone (continuous wave) was used. TTS was quantified as a function of sound pressure level (SPL) half an octave above the center frequency of the fatiguing sound. The species have different audiograms, but their frequency-specific susceptibility to TTS was more similar. The hearing frequency range in which both species were most susceptible to TTS was 22.5-50 kHz. Furthermore, the frequency ranges were characterized by having similar critical levels (defined as the SPL of the fatiguing sound above which the magnitude of TTS induced as a function of SPL increases more strongly). This standardized between-species comparison indicates that the audiogram is not a good predictor of frequency-dependent susceptibility to TTS.

Effects of Cross-linked Hyaluronic Acid in a Rat Model of Vestibular and Cochlear Toxicity.

To investigate the effects of cross-linked hyaluronic acid (CLHA) in an experimental model of vestibulotoxicity and cochleotoxicity. Twenty-eight female Wistar albino rats (200-250 g) were divided into four groups. Group A received 0.06 mL of 13.33 mg/mL gentamicin, Group B received 0.06 mL of CLHA, Group C received 0.03 mL of 26.66 mg/mL gentamicin and 0.03 mL CLHA, and Group D received 0.06 mL of 0.09% saline. All groups underwent auditory brainstem response testing at 4-32 kHz, signal-to-noise ratio of distortion product otoacoustic emission measurements at 1.5-8 kHz and vestibular tests on days 0,1,7,10. The rats were sacrificed, and their labyrinths were histologically assessed and scored. The hearing thresholds of Groups A and C were similar and significantly higher than those of the other groups at all frequencies, beginning from day 1. The vestibular and histological scores of Groups A and C were similar and significantly higher than those of the other groups from day 1. The audiological results, vestibular scores, and histological scores of Groups B and D were similar, except for a temporary middle ear effusion and hearing threshold shift in Group B. No significant deterioration was observed in the audiological, vestibular, and histological analyses of Groups B and D. That both Group A and Group C similarly showed worsening audiological, vestibular, and histological tests suggests that CLHA did not alter the pharmacokinetics and histologic results of gentamicin.

Repair of noise-induced damage to stereocilia F-actin cores is facilitated by XIRP2 and its novel mechanosensor domain.

Prolonged exposure to loud noise has been shown to affect inner ear sensory hair cells in a variety of deleterious manners, including damaging the stereocilia core. The damaged sites can be visualized as 'gaps' in phalloidin staining of F-actin, and the enrichment of monomeric actin at these sites, along with an actin nucleator and crosslinker, suggests that localized remodeling occurs to repair the broken filaments. Herein, we show that gaps in mouse auditory hair cells are largely repaired within 1 week of traumatic noise exposure through the incorporation of newly synthesized actin. We provide evidence that Xin actin binding repeat containing 2 (XIRP2) is required for the repair process and facilitates the enrichment of monomeric γ-actin at gaps. Recruitment of XIRP2 to stereocilia gaps and stress fiber strain sites in fibroblasts is force-dependent, mediated by a novel mechanosensor domain located in the C-terminus of XIRP2. Our study describes a novel process by which hair cells can recover from sublethal hair bundle damage and which may contribute to recovery from temporary hearing threshold shifts and the prevention of age-related hearing loss.

Applying technical guidance from the USA for management of impacts of anthropogenic noise on wildlife in other countries: the Canadian context

Technical Guidance from the US National Marine Fisheries Service recommends Federal agencies use estimated thresholds for peak sound pressure levels and weighted cumulative sound exposure levels for the onset of permanent (and temporary) hearing threshold shifts in marine mammals. These dual metrics were developed to inform impact assessments within the US legal landscape. Despite its merits, the Technical Guidance contains uncertainties due to limited data on marine mammal hearing and auditory response to noise. The underlying assumptions about how representative existing data are for all marine mammal species also create limitations in the applicability of the Technical Guidance. These limitations warrant consideration before the Technical Guidance can be applied effectively in other jurisdictions with different legal standards. Using the Canadian legal framework as a working example, we found that many Canadian species are underrepresented in the dataset informing the Technical Guidance. The Technical Guidance also does not address all relevant noise impact types. Thus, the Technical Guidance alone cannot address all Canadian legal standards and, if the Technical Guidance is incorporated, some adjustments to the criteria within may be needed to meet the precautionary requirements of many Canadian legal standards.

Temporary threshold shifts in Boris the bottlenose dolphin (Tursiops truncatus), varying noise duration and intensity

There is much concern regarding increasing noise levels in the ocean and how it may affect marine mammals. Early on, there was little information regarding how sound affects marine mammals and no empirical data on the relationship between noise intensity and exposure duration. Working with Boris the bottlenose dolphin, Tursiops truncatus, we explored the effects of octave-band noise, and sonar signals on odontocete hearing and noise-induced temporary hearing threshold shifts (TTS). Sound pressure levels (SPLs) and exposure durations were varied to measure the effects of exposure duration and amplitude. Hearing thresholds were initially measured behaviorally, and later using auditory evoked potentials before and after sound exposure to track TTS and recovery. These efforts showed that threshold shifts were not linear but rather shorter sounds required greater sound exposure levels to induce TTS; a contrast to some early published literature. Further, sound exposure levels of sonar signals required to induce TTS were high, supporting the notion that relatively short sounds must be of relatively high intensity to induce threshold shifts. From these data and this remarkable animal, a novel algorithm was written that predicts the physiological effects of anthropogenic noise if the intensity and duration of exposure are known.

The adaptation of noise-induced temporary hearing threshold shift predictive models for modelling the public health policy.

It has been shown that monitoring temporary threshold shift (TTS) after exposure to noise may have a predictive value for susceptibility of developing permanent noise-induced hearing loss. The aim of this study is to present the assumptions of the TTS predictive model after its verification in normal hearing subjects along with demonstrating the usage of this model for the purposes of public health policy. The existing computational predictive TTS models were adapted and validated in a group of 18 bartenders exposed to noise at the workplace. The performance of adapted TTS predictive model was assessed by receiver operating characteristic (ROC) analysis. The demonstration example of the usage of this model for estimating the risk of TTS in general unscreened population after exposure to loud music in discotheque bars or music clubs is provided. The adapted TTS predictive model shows a satisfactory agreement in distributions of actual and predicted TTS values and good correlations between these values in examined bartenders measured at 4 kHz, and as a mean at speech frequencies (0.5-4 kHz). An optimal cut-off level for recognizing the TTS events, ca. 75% of young people (aged ca. 35 years) may experience TTS >5 dB, while <10% may exhibit TTS of 15-18 dB. The final TTS predictive model proposed in this study needs to be validated in larger groups of subjects exposed to noise. Actual prediction of TTS episodes in general populations may become a helpful tool in creating the hearing protection public health policy. Int J Occup Med Environ Health. 2023;36(1):125-38.

Underwater Noise Level Recordings from a Water Intake Pontoon and Possible Impacts on Yangtze Finless Porpoises in a Natural Reserve.

Simple SummaryRelocation of endangered freshwater cetaceans in natural reserves is an effective conservation strategy to recover their populations. However, due to historical reasons, some natural reserves have facilities that cannot be removed, such as water intake pontoons that are important for residents nearby. These facilities generate underwater noise which may affect cetaceans. To investigate the potential impacts of underwater noise from water intake pontoons on freshwater cetaceans, this study measured such noise within a Yangtze finless porpoise (Neophocaena asiaeorientalis) nature reserve, analyzed its effects on porpoise behavior, vocalization, and hearing, and explored porpoise adaptation to the transient holding pen environment. This study provides a reference for assessing whether human facilities have impacts on freshwater cetaceans.Underwater noise pollution caused by human activities may affect freshwater cetaceans to different degrees. To analyze the impacts of water intake pontoons on Yangtze finless porpoises (Neophocaena asiaeorientalis), this study collected underwater noise data from such a pontoon in a nature reserve, plotted the power spectral density of acoustic signals, and calculated the root mean square sound pressure levels and the magnitude of sound source levels. The 1/3-octave sound pressure level root mean square values at the transient holding pens were <18.0 kHz, 39.5−60.0 kHz, which were slightly higher than the Yangtze finless porpoise hearing threshold curve values and therefore could be perceived. However, the results indicated that the porpoises would not develop a temporary hearing threshold shift. Meanwhile, pontoon noise did not interfere with the porpoises’ high-frequency acoustic signal nor did it affect their echolocation; it significantly interfered with their low-frequency acoustic signal, however, and the mother–child communication of the finless porpoises was affected, but this effect was quickly compensated due to the limited space range of the holding pens. Through this study of Yangtze finless porpoises, this paper provides a reference for assessing whether human facilities have impacts on freshwater cetaceans.

Temporary Hearing Threshold Shift in California Sea Lions (Zalophus californianus) Due to One-Sixth-Octave Noise Bands Centered at 0.6 and 1 kHz

To determine the frequency-dependent susceptibility of California sea lions (Zalophus californianus) to noise-induced temporary hearing threshold shift (TTS), one of two subjects were exposed for 60 minutes to two continuous one-sixth-octave noise bands (NBs) as fatiguing sounds: one centered at 0.6 kHz, at sound pressure levels (SPLs) of 168 to 174 dB re 1 µPa (sound exposure levels [SELs] of 204 to 210 dB re 1 µPa2s), or one centered at 1 kHz, at SPLs of 144 to 159 dB re 1 µPa (SELs of 180 to 195 dB re 1 µPa2s). Using a psychoacoustic technique, TTSs were quantified at 0.6, 0.85, 1, 1.2, 1.4, and 2 kHz (at the center frequency of each NB, half an octave higher, and one octave higher). When significant TTS occurred, higher SELs resulted in greater TTSs. In the sea lion that was tested 1 to 4 minutes after exposure to the fatiguing sounds, the largest TTSs occurred when the hearing test frequency was half an octave higher than the center frequency of the two fatiguing sounds. The highest TTS levels elicited were 8.7 dB at 0.85 kHz and 9.6 dB at 1.4 kHz. When their hearing was tested at the same time after the fatiguing sounds stopped, initial TTSs and hearing recovery patterns were similar in both sea lions. These findings will contribute to the protection of hearing of species in the Otariidae family from anthropogenic noise by facilitating the development of an evidence-based underwater sound weighting function.

Temporary Hearing Threshold Shift in California Sea Lions (Zalophus californianus) Due to One-Sixth-Octave Noise Bands Centered at 8 and 16 kHz: Effect of Duty Cycle and Testing the Equal-Energy Hypothesis

To determine the frequency-dependent susceptibility of California sea lions (Zalophus californianus) to noise-induced temporary hearing threshold shift (TTS), two subjects were exposed for 60 min to two fatiguing sounds: continuous one-sixth-octave noise bands (NBs) centered at 8 kHz (at sound exposure levels [SELs] of 166 to 190 dB re 1 µPa2s) and at 16 kHz (at SELs of 183 to 207 dB re 1 µPa2s). Using a psychoacoustic technique, TTSs were quantified at 8, 11.3, 16, 22.4, and 32 kHz (at the center frequency of each NB, half an octave higher, and one octave higher). For both NBs, higher SELs resulted in greater TTSs. In the SEL ranges that were tested, the largest TTSs occurred when the hearing test frequency was half an octave higher than the frequency of the fatiguing sound. When their hearing was tested at the same time after the fatiguing sounds stopped, initial TTSs and hearing recovery patterns were similar in both sea lions. The effect of fatiguing sound duty cycle on TTS was investigated with the 8 kHz NB, using 1,600 ms signals at a mean sound pressure level (SPL) of 154 dB re 1 µPa. Duty cycle reduction from 100 to 90% resulted in a large decrease in TTS; no TTS was observed at duty cycles ≤ 30%. The equal-energy hypothesis was tested with the 8 kHz NB and found to hold true: five combinations of SPL and exposure duration all resulting in a 182 dB SEL produced similar initial TTSs in both sea lions. These findings will contribute to the protection of otariid hearing from anthropogenic noise by facilitating the development of evidence-based underwater sound weighting functions. Our results also show that the introduction of short inter-pulse intervals to underwater sounds aids in the protection of otariid hearing by allowing recovery to take place.

Temporary Hearing Threshold Shift in California Sea Lions (Zalophus californianus) Due to One-Sixth-Octave Noise Bands Centered at 2 and 4 kHz: Effect of Duty Cycle and Testing the Equal-Energy Hypothesis

In one of a series of studies of noise-induced hearing loss to determine the frequency-dependent susceptibility of California sea lions (Zalophus califor-nianus) to temporary hearing threshold shift (TTS), two subjects were exposed for 60 min to two different fatiguing sounds. These were continuous one-sixth-octave noise bands (NBs), centered at 2 kHz, at sound pressure levels (SPLs) of 138 to 167 dB re 1 µPa (resulting in sound exposure levels [SELs] of 174 to 203 dB re 1 µPas), and at 4 kHz, at SPLs of 133 to 169 dB re 1 µPa (resulting in SELs of 169 to 205 dB re 1 µPas). Using a psychoacoustic technique, TTSs were quantified at 2,2.8,4.2,5.6, and 8 kHz (at the center frequency of each NB, at half an octave higher, and at one octave higher). After exposure to both NBs, higher SELs resulted in greater TTS at all healing frequencies that were tested. TTSs and healing recovery patterns were similar in both sea lions. The effect of fatiguing sound duty cycle on TTS was investigated with the NB at 4 kHz and with 1.6-s signal duration, at a mean SPL of 169 dB re 1 µPa. Duty cycle reduction from 100 to 90% resulted in the largest decrease in TTS, and no TTS occurred at duty cycles ≤ 60%. The equal-energy hypothesis was investigated with the NB at 4 kHz: five combinations of SPL and exposure duration that resulted in the same SEL (197 dB re 1 µPas) produced similar initial TTSs in both sea lions. Susceptibility of California sea lions to TTS is higher than previously believed; for sounds around 2 and 4 kHz, it is similar to the susceptibility of harbor seals (Phoca vitulina). These data will contribute towards the development of an evidence-based underwater sound weighting function for the protection of Otariidae.

Anthropogenic Sound Exposure-Induced Stress in Captive Dolphins and Implications for Cetacean Health

Many cetaceans are exposed to increasing pressure caused by anthropogenic activities in their marine environment. Anthropogenic sound has been recognized as a possible stressor for cetaceans that may have impacts on health. However, the relationship between stress, hormones, and cytokines secretion in cetaceans is complex and not fully understood. Moreover, the effects of stress are often inconsistent because the character, intensity, and duration of the stressors are variable. For a better understanding of how anthropogenic sounds affect the psychophysiology of cetaceans, the present study compared the changes of cortisol concentration and cytokine gene transcriptions in blood samples and behaviors of captive bottlenose dolphins (Tursiops truncatus) after sound exposures. The sound stimuli were 800 Hz pure-tone multiple impulsive sound for 30 min at three different sound levels (estimated mean received SPL: 0, 120, and 140 dB re 1 μPa) that likely cause no permanent and temporary hearing threshold shift in dolphins. Six cytokine genes (IL-2Rα, IL-4, IL-10, IL-12, TNF-α, and IFN-γ) were selected for analysis. Cortisol levels and IL-10 gene transcription increased and IFNγ/IL-10 ratio was lower after a 30-min high-level sound exposure, indicating the sound stimuli used in this study could be a stressor for cetaceans, although only minor behavior changes were observed. This study may shed light on the potential impact of pile driving-like sounds on the endocrine and immune systems in cetaceans and provide imperative information regarding sound exposure for free-ranging cetaceans.

Temporary Hearing Threshold Shift in a Harbor Porpoise (Phocoena phocoena) Due to Exposure to a Continuous One-Sixth-Octave Noise Band Centered at 0.5 kHz

Temporary Hearing Threshold Shift in a Harbor Porpoise (Phocoena phocoena) Due to Exposure to a Continuous One-Sixth-Octave Noise Band Centered at 0.5 kHz

Temporary hearing threshold shift in harbor seals (Phoca vitulina) due to one-sixth-octave noise bands centered at 0.5, 1, and 2 kHz.

This study concludes a larger project on the frequency-dependent susceptibility to noise-induced temporary hearing threshold shift (TTS) in harbor seals (Phoca vitulina). Here, two seals were exposed to one-sixth-octave noise bands (NBs) centered at 0.5, 1, and 2 kHz at several sound exposure levels (SELs, in dB re 1 μPa2s). TTSs were quantified at the center frequency of each NB, half an octave above, and one octave above, at the earliest within 1-4 min after exposure. Generally, elicited TTSs were low, and the highest TTS1-4 occurred at half an octave above the center frequency of the fatiguing sound: after exposure to the 0.5-kHz NB at 210 dB SEL, the TTS1-4 at 0.71 kHz was 2.3 dB; after exposure to the 1-kHz NB at 207 dB SEL, the TTS1-4 at 1.4 kHz was 6.1 dB; and after exposure to the 2-kHz NB at 215 dB SEL, TTS1-4 at 2.8 kHz was 7.9 dB. Hearing always recovered within 60 min, and susceptibility to TTS was similar in both seals. The results show that, for the studied frequency range, the lower the center frequency of the fatiguing sound, the higher the SEL required to cause the same TTS.

Are fitness instructors at risk of hearing impairment?

The entertainment industry can pose a risk of hearing impairment to employees. The aim of the study is to assess whether occupational exposure to loud sounds (music) is related to temporary hearing threshold shifts in fitness instructors. The study comprised a total of 29 fitness instructors working in fitness clubs. The noise dosimeters were used to determine individual noise exposure during typical 1-2 hours exercises conducting by the instructors. Pure-tone audiometry and Hearing in Noise Test (HINT) were performed before and just after the session to assess temporary changes in hearing. The A-weighted equivalent-continuous sound pressure level (LAeq,T) during typical exercises session ranged from 76.3 to 96 dB. Referring to the 3-dB equal energy rule, such exposures may exceed the upper exposure action value (85 dB) set for the occupational settings by the Directive 2003/10/EC. A significant temporary threshold shift (at least 6 dB) was observed in 33 audiograms (40 %). No impairment of speech understanding was observed in the HINT. Fitness instructors may constitute a population at increased risk of hearing impairment. Further studies are needed to conclude on hearing protection programs in this group of workers.

Temporary Hearing Threshold Shift at Ecologically Relevant Frequencies in a Harbor Porpoise (Phocoena phocoena) Due to Exposure to a Noise Band Centered at 88.4 kHz

Temporary Hearing Threshold Shift at Ecologically Relevant Frequencies in a Harbor Porpoise (Phocoena phocoena) Due to Exposure to a Noise Band Centered at 88.4 kHz

Lack of reproducibility of temporary hearing threshold shifts in a harbor porpoise after exposure to repeated airgun sounds.

Noise-induced temporary hearing threshold shift (TTS) was studied in a harbor porpoise exposed to impulsive sounds of scaled-down airguns while both stationary and free-swimming for up to 90 min. In a previous study, ∼4 dB TTS was elicited in this porpoise, but despite 8 dB higher single-shot and cumulative exposure levels (up to 199 dB re 1 μPa2s) in the present study, the porpoise showed no significant TTS at hearing frequencies 2, 4, or 8 kHz. There were no changes in the study animal's audiogram between the studies or significant differences in the fatiguing sound that could explain the difference, but audible and visual cues in the present study may have allowed the porpoise to predict when the fatiguing sounds would be produced. The discrepancy between the studies may have resulted from self-mitigation by the porpoise. Self-mitigation, resulting in reduced hearing sensitivity, can be achieved via changes in the orientation of the head, or via alteration of the hearing threshold by processes in the ear or central nervous system.

Temporary threshold shift following ear canal microsuction

Objectives: To investigate a temporary threshold shift (TTS) of hearing and pain/discomfort caused by the microsuction procedure. Hearing loss induced by impacted cerumen was also investigated.Design: Impacted cerumen was removed from patients using microsuction. Hearing assessments were carried out before the procedure, immediately after and 1-week later. Hearing thresholds measured in different sessions were compared to determine the TTS caused by the microsuction procedure and hearing loss induced by impacted cerumen. A questionnaire was used to evaluate the pain/discomfort experienced by patients.Study Sample: 30 patients (50 ears) were recruited from a cerumen removal clinic.Results: Significant hearing loss caused by impacted earwax was found across individual frequencies (mean 11.4 dB, maximum 38.1 dB). A TTS appeared in 43/50 (86%) ears, ranging from 0 to 16.2 dB averaged across frequencies between 0.25 and 8 kHz, with the highest TTS at 6 kHz. Pain and discomfort levels were both rated low, the mean levels were 1.2 (SD = 0.5) and 1.6 (SD = 0.5) respectively on a scale from 1 to 10.Conclusions: Microsuction appears to be a well-tolerated and preferred procedure for removing impacted cerumen. Because of the significant TTS induced by the microsuction procedure, safety concerns from a hearing perspective should be raised with the patient.

Temporary Hearing Threshold Shift in Harbor Porpoises (Phocoena phocoena) Due to One-Sixth-Octave Noise Bands at 63 kHz

Temporary Hearing Threshold Shift in Harbor Porpoises (Phocoena phocoena) Due to One-Sixth-Octave Noise Bands at 63 kHz

Temporary hearing threshold shift in harbor seals (Phoca vitulina) due to a one-sixth-octave noise band centered at 40 kHz.

As part of a series of studies to determine frequency-dependent susceptibility to temporary hearing threshold shifts (TTS), two female harbor seals (F01 and F02) were exposed for 60 min to a one-sixth-octave noise band centered at 40 kHz at mean sound pressure levels ranging from 126 to 153 dB re 1 μPa [mean received sound exposure level (SEL) range: 162-189 dB re 1 μPa2s]. TTSs were quantified at 40, 50, and 63 kHz within 1-4 min of the exposure for F02 and within 12-16 min of the exposure for F01. In F02, significant TTS1-4 (1-4 min post exposure) occurred at 40 kHz with SELs of ≥183 dB re 1 μPa2s and at 50 kHz with SELs of ≥174 dB re 1 μPa2s. At 63 kHz, TTS1-4 occurred with SELs ≥186 dB re 1 μPa2s. In F01, significant TTS12-16 (12-16 min post exposure) occurred only at 50 kHz with SELs of ≥177 dB re 1 μPa2s. The highest TTSs (27.5 dB in F02, 29.8 dB in F01) occurred at 50 kHz, one-third of an octave above the fatiguing sound's center frequency (SEL = 189 dB re 1 μPa2s); recovery took 2 days in F02 and 4 days in F01. In most other cases, recovery was within 1 h. The seals have a similar susceptibility to TTS from 4 to 40 kHz.