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PubMed1988

Effects of intense pure tones on auditory temporal acuity.

Gap detection thresholds (GDTs) were obtained from human listeners before and after exposure to a brief 0.4- or 1.7-kHz tone. The temporary threshold shift (TTS) produced 2 min after an exposure was approximately 10 dB. GDT stimuli were octave-band noises centered at one of three frequencies: the exposure frequency, one-half octave above the exposure frequency or one octave above the exposure frequency. GDTs were obtained at 35, 55, and 75 dB SPL at each center frequency. GDT and TTS recovery were monitored at logarithmically-spaced time intervals after the exposures. Following the 1.7-kHz exposure, shifts in post-exposure GDT were only obtained with the low-level stimulus conditions--the magnitude of GDT shift was correlated with the size of the TTS, and the shifts in GDT and absolute threshold required similar amounts of time to recover. Significant post-exposure shifts in GDT were also observed following the 0.4-kHz exposure. However, shifts were found at frequencies where there was no measurable TTS, and they required longer periods of time to recover than did absolute threshold.

Auditory Fatigue↗
PubMed1988

Protection against noise trauma by pre-exposure to a low level acoustic stimulus.

Guinea pigs were pre-exposed to a low level acoustic stimulus prior to exposure to a stimulus known to yield a permanent threshold shift. This pre-treatment resulted in: 1) approximately a 20 dB reduction in the threshold shift relative to animals not pre-exposed, and 2) complete recovery from the threshold shift after 2 months.

Acoustic Stimulation↗
PubMed1989

Functional role of the olivo-cochlear bundle: a motor unit control system in the mammalian cochlea.

A fiber optic lever is applied to the measurement of the motion of the basilar membrane motion in guinea pigs. In response to intense tones from either ear, the motion includes a substantial summating shift in the mean position in addition to a travelling wave originally described by von Békésy. His stroboscopic technique and most techniques used since have been concentrated upon measuring vibrations of the basilar membrane synchronous with the stimulus and have been insensitive to variations in the baseline position such as a summating component of motion analogous to the extracellular summating potential. In addition to the role of the outer hair cells in providing normal hearing sensitivity, they evidently play a role in regulating the mean position of the basilar membrane. For a fixed frequency, the polarity of the mean position varies systematically with sound level and place and summates with time since onset. Since these cells are the target cells for the olivocochlear bundle, homeostasis in the cochlea would appear to be linked efferent function and involve cochlear mechanics. The negative damping hypothesis asserts that hair cell activity is necessary for low thresholds. The results presented here demonstrate that OHC activity exists independent of neural thresholds. The discussion develops the concept that threshold losses are due to a mismatch of opposing tonic forces which normally maintain the mean position of the basilar membrane. Structure is examined in relation to function and the group of outer hair cells innervated by a single medial efferent neuron is identified as a motor unit. Implications of central control of individual motor units include peripheral involvement in selective attention tasks.

Acetylcholine↗
PubMed1989

The origin of the low-frequency microphonic in the first cochlear turn of guinea-pig.

Low-frequency microphonic potentials (100 Hz to 2000 Hz) have been measured in the first turn of the guinea pig cochlea before and after a variety of manipulations of the cochlea. These included ablation of the apical turns, iontophoresis of streptomycin, dc current injection into the first turn, acoustic trauma and two-tone interference with pure tones. These manipulations indicate that the low-frequency microphonic measured in the first turn and at the round window is generated predominantly by the hair cells of this region. It is a convenient and relatively uncomplicated indicator of the integrity of the mechano-electrical transduction process of these cells.

Acoustic Stimulation↗
PubMed1995

Reduction in excitability of the auditory nerve following electrical stimulation at high stimulus rates.

While recent studies have suggested that electrical stimulation of the auditory nerve at high stimulus rates (e.g., 1000 pulses/s) may lead to an improved detection of the fine temporal components in speech among cochlear implant patients, neurophysiological studies have indicated that such stimulation could place metabolic stress on the auditory nerve, which may lead to neural degeneration. To examine this issue we recorded the electrically evoked auditory brainstem response (EABR) of guinea pigs following acute bipolar intracochlear electrical stimulation using charge-balanced biphasic current pulses at stimulus rates varying from 100 to 1000 pulses/s and stimulus intensities ranging from 0.16 to 1.0 microC/phase. Charge density was held constant (approximately 75 microC cm-2 geom/phase) in those experiments. To monitor the recovery in excitability of the auditory nerve following this acute stimulation. EABR thresholds, wave I and III amplitudes and their latencies were determined for periods of up to 12 h following the acute stimulation. Higher stimulus rates and, to a lesser extent, higher intensities led to greater decrements in the post-stimulus EABR amplitude and prolonged the recovery period. While continuous stimulation at 100 pulses/s induced no decrement in the EABR, stimulation at 200 and 400 pulses/s produced an increasingly significant post-stimulus reduction of the EABR amplitude, which showed only partial recovery during the monitoring period. No EABR response could be evoked immediately following stimulation at 1000 pulses/s, using a probe intensity 16-19 dB below the stimulus intensity. However, partial EABR recovery was observed for wave III following stimulation at the lowest stimulus intensity (0.16 microC/phase). These stimulus-induced reductions in the EABR amplitude were also reflected in increased thresholds and latencies. Providing stimulus rate and intensity were held constant, stimulation at different charge densities (37.7, 75.5 and 150.7 microC cm-2 geom/phase) had no influence on the post-stimulus EABR recovery. Significantly, the introduction of a 50% duty cycle into the stimulus pulse train resulted in a more rapid and complete post-stimulus recovery of the EABR compared to continuous stimulation. These data suggest that stimulus rate is a major contributor to the observed reduction in excitability of the electrically stimulated auditory nerve. This reduction may be a result of an activity-induced depletion of neural energy resources required to maintain homeostasis. The present findings have implications for the design of safe speech-processing strategies for use in multichannel cochlear implants.

Animals↗
PubMed1996

Intensity-dependent peak shift in cochlear transfer functions at the cellular level, its elimination by sound exposure, and its possible underlying mechanisms.

Our systematic study of cochlear transfer functions has confirmed earlier results that, in a normal cochlea, the cochlear AC responses at any given cochlear location do not have a fixed best frequency at which the response is maximal. The best frequency depends on sound intensity, shifting to lower frequencies as the intensity is increased. This phenomenon may account for the so called 'half-octave shift' of maximum cochlear damage relative to the frequency of the damaging sound observed in studies of auditory noise exposure. Our experimental results combined with the results of others and with our model studies bring us to the conclusion that, at low to moderate sound intensities, the dependence of the best frequency on sound intensity is due to an effect of the active feedback, which decreases as sound intensity increases. Consequently, the feedback, when present, must shift the best frequency upward.

Acoustic Stimulation↗
PubMed2005

The effect of an age-related hearing loss gene (Ahl) on noise-induced hearing loss and cochlear damage from low-frequency noise.

Inbred C57BL/6J mice carry two copies of an age-related hearing loss gene (Ahl). It has been shown that these mice begin losing high-frequency hearing at two months. Several functional studies have reported that the Ahl gene renders mice more susceptible to noise-induced hearing loss (NIHL) than strains which do not carry this gene [e.g., Hear. Res. 93 (1996) 181; Hear. Res. 155 (2001) 82; J. Assoc. Res. Otolaryngol. 2 (2001) 233]. Johnson et al. [Hear. Res. 114 (1997) 83] developed a congenic B6.CAST-+Ahl mouse which carries the wild-type allele from Mus musculus castaneus at the Ahl locus. Five each of young C57BL/6J males and females, and B6.CAST-+Ahl males were exposed to a 4-kHz octave band of noise at 108 dB SPL for 4 h. Non-noise-exposed mice of the same strains and age served as controls. The noise-exposed mice were functionally tested for ABR thresholds and DPOAE levels pre-exposure and three times post-exposure: 0 days to determine the magnitude of temporary threshold shift (TTS); 6 days to determine rate of recovery; and 20 days to determine the magnitude of permanent threshold shift (PTS). At 20 days post-exposure, the animals underwent cardiac perfusion to fix their cochleae. The isolated cochleae were embedded in plastic and dissected into flat preparations. By phase-contrast microscopy, each cochlea was evaluated from apex to base to quantify the losses of hair cells, nerve fibers and stria vascularis and to localize stereocilia damage. Functional data from each mouse were aligned with the cytocochleogram using the frequency-place map of Ou et al. [Hear. Res. 145 (2000) 111; Hear. Res. 145 (2000) 123]. Sizable variation in the magnitude of TTS, PTS and hair-cell loss was found among mice of the same genetic strain. The congenic B6.CAST-+Ahl male mice had significantly less TTS immediately post-exposure than C57BL/6J males or females but not less PTS or hair-cell losses at 20 days post-exposure. These results indicate that, at one month of age, mice carrying two copies of the Ahl gene have an increased susceptibility to TTS from a low-frequency noise before they have any indication of age-related hearing or hair-cell loss. However, this appeared not to be the case for PTS. The Ahl gene appears to play a role in susceptibility to NIHL but, other genes as well as systemic and local factors must also be involved.

Animals↗
PubMed1983

Elevated bone conduction thresholds associated with middle ear fluid in adults.

Longitudinal observations of adult patients with documented cases of otitis media revealed fluctuations in bone conduction thresholds as well as air conduction thresholds. Previous investigations in this area presented conflicting information regarding temporary and permanent effects of serous otitis media on sensori-neural function. We conducted a detailed study, including complete otologic, audiologic, and tympanometric evaluation, of 30 adult patients exhibiting serous otitis media. Myringotomies were performed on all patients after appropriate medical management failed to clear the middle ear fluid and subsequent hearing loss. Pre- and postmyringotomy audiograms support our conclusion that middle ear fluid can produce artifactual shifts in bone conduction thresholds. Although the data presented was collected from a cohort of adults, the clinical implications are applicable to the pediatric population. We have observed a similar shift in bone conduction thresholds in children exhibiting serous otitis media, and we have observed improvement in the thresholds with removal of the fluid either by appropriate medical management or by myringotomy with fluid aspiration.

Adult↗
PubMed1984

Cochlear damage resulting from exposure to four different octave bands of noise at three ages.

Three age-groups of CBA/J inbred mice were exposed for 5 min to one of four octave bands of 124-dB noise. The ages corresponded to weaning (20 days), early postpuberty (60 days), and adulthood (180 days). Threshold shifts of the electrocochleographically obtained cochlear nerve action potential were determined 4 days following the noise exposure. Pure-tone bursts of 2-64 kHz were used to elicit these responses. Noise-induced threshold shifts (NITS) were progressively greater in those responses that originated from a more basal (high-frequency) portion of the organ of Corti. The 3--6-kHz noise band did not affect thresholds; 6--12- and 12--24-kHz bands produced a NITS of 25--30 dB; and 24--48-kHz noise produced a NITS of at least 18 dB. The 20- and 60-day-old subjects were more severely affected (25 and 23.5 dB average NITS, respectively) than the 180-day-old mice (9.5 dB NITS). Susceptibility to damage at the apex and middle of the organ of Corti declined as a function of age during exposure. But the base of the organ of Corti remained equally susceptible to damage from 6-12-, 12-24-, or 24-48-kHz noise bands, from weaning age to adulthood. When these data were compared with those from another study, it was concluded that an early sensitive period exists for noise-induced damage to the apex and middle of the organ of Corti but that the base maintains its susceptibility for a much longer age span.

Age Factors↗
PubMed1984

Threshold of octave masking as a predictor of temporary threshold shift following repeated noise exposure.

Cumulative auditory effects of repeated exposure to a 3-min 110 dB SPL white noise were examined in 20 subjects (10 male, 10 female). Statistical analysis revealed greater 8-kHz temporary threshold shift in female ears despite equivalent preexposure 8-kHz thresholds across gender. Cumulative effects were seen in thresholds of octave masking scores, especially in female subjects, possibly reflecting increased susceptibility following the second noise exposure.

Acoustics↗
PubMed1991

Prediction of deterioration in hearing due to hearing aid use.

There is a definite risk of overamplification by hearing aids. Guidelines should therefore be established that will minimize the risk of damage to hearing involved in hearing aid use. A mathematical model that can be used for this purpose is derived from equations for predicting noise-induced permanent threshold shift given in International Standard ISO 1999 combined with the Modified Power Law. The model implies that any noise exposure that would cause deterioration of the hearing threshold levels of a person with normal hearing would also be harmful to the hearing of a person with sensorineural hearing impairment. It follows that, in order to ensure that no deterioration occurs in the hearing of a hearing aid user, the output levels from the aid must be such that they would not cause any damage to a person with normal hearing. This constraint can be met for hearing aid users with mild-to-moderate sensorineural hearing loss but cannot be met for users with severe-to-profound loss because it would result in the provision of insufficient gain, particularly at the higher frequencies. If the model is valid, then for this group, some appropriately small amount of hearing damage must be accepted as the cost of the advantages gained from the use of a hearing aid. Verification of the model is essential before the model is used in clinical practice to determine the risk of deterioration in hearing due to hearing aid use.

Auditory Fatigue↗
PubMed1996

[Detection of hearing loss in patrons of a discoteque using TEOAE and DPOAE].

BACKGROUND: The aim of the study was to investigate the potential and difference of pure tone audiogram, TEOAE and DPOAE in the detection of temporary threshold shift. METHODS: 46 disco visitors who were exposed to disco music at an average intensity of 105 dB (A) for 1, 1 1/2 and 2 hours respectively underwent audiological examination before and after noise exposure. Audiological measurements performed were an audiogram and measurements of the TEOAE and DPOAE using the system ILO 92 (Otodynamics). RESULTS: The frequency range where the threshold shift occurred was around 4000 Hz in the 1 hour group and spread over all frequencies when the exposure time increased. The average threshold shift over all frequencies and probands was 6.2 dB for the 1 hour group, 7.1 dB for the 1 1/2 hour group and 10.1 dB after 2 hours of noise exposure. TEOAE amplitudes showed significant reduction only at 2000 and 3000 Hz. Even at threshold shifts exceeding 15 dB, however not in all cases, a reduction of TEOAE amplitudes occurred. Similar results were obtained regarding the DPOAE measurements. CONCLUSIONS: We conclude that TEOAE and DPOAE are not ideal instruments in the detection of temporary threshold shift after noise exposure.

Adolescent↗
PubMed1996

[Amplitude changes in distortion products of otoacoustic emissions after acute noise exposure].

BACKGROUND: The inner ear responds to acute impact of high-intensity noise with a temporary threshold shift (TTS), which represents a reaction of the outer hair cells. That is why TTS should be detectable as changes of distortion-product otoacoustic emissions (DPOAE). METHODS: DPOAE were measured in 102 ears in 59 test subjects with normal hearing before and after definitive noise exposure (20 min of "white noise" at 90 dB HL). We also registrated the TTS (4kHz) immediately after noise and measured DP changes during a 30-min recovery period. RESULTS: Typically we found a reduction of DP amplitude. It averaged between 2.0 and 2.5 dB HL in the frequency range from 2 to 5 kHz. There was no correlation between TTS and DP amplitude reduction at 4kHz. During the recovery period, individual ears showed an erratic pattern of DP amplitudes. However, a tendency toward incremental DP amplitude regeneration appeared after averaging. As many as 10% of the measured ears showed an atypical reaction with an increase of DP amplitudes. Whether the latter is due to errors in the test procedure or is evidence of a particularly stable inner ear remains to be discussed. CONCLUSIONS: The results are further proof for the reaction of the outer hair cells on acute noise impact, which apparently leads to an increase of the stiffness of basilary membrane due to contraction processes. It may be possible to differentiate vulnerable inner ears from stable ones.

Adult↗
PubMed2001

Sensorineural hearing loss after vibration: an animal model for evaluating prevention and treatment of inner ear hearing loss.

Sensorineural hearing loss following a variety of acoustic trauma, including middle ear surgery, is well known. Current literature, which points to the deleterious influence of noise on the inner ear during surgery, has yet to assess the influence of vibration generated by the burr. The purpose of the study reported here was to establish an animal model that mimics drilling and can be used to explore methods of hearing loss prevention and treatment. A specially developed electromagnetic vibrator was calibrated and used in 59 guinea pigs to induce hearing loss. Both young and old guinea pigs were used. The bony external ear canal of guinea pigs were exposed to vibration or sound of varying duration and intensity. The vibration of the temporal bone and noise level in the middle ear were measured. Electrocochleography was recorded to evaluate the hearing loss. Among the young animals, 90% developed a significant threshold shift (TS > 20 dB), when vibrated with 250 Hz at an intensity of 6.2 m/s2 for 15 min. An average of 42 dB TS was observed. With 10 min exposure 63% showed a TS. The older animals vibrated for 5 min developed the same TS (mean TS 34 dB) as the young animals when vibrated for 10 min. The vibration-induced TS showed no recovery within 3 days of observation. In the contralateral ear 4 out of 5 animals showed TS > 20 dB. When exposed to sound levels exceeding the vibration-generated sound in the middle ear (119 dB at 250 Hz) only 2 out of II animals (18%) showed TS. The frequency of TS and level of TS were significantly greater in the vibrated animals than in sound-only exposed animals (p < 0.01). The degree of vibration-induced TS in the present animal model could be controlled by vibration intensity and duration. The older animals were more susceptible to vibration-induced inner-ear damage than younger animals. This model will be used in further studies to find methods for prevention and treatment of hearing loss during ear surgery.

Animals↗
PubMed2003

Effect of ipsilateral and contralateral low-frequency narrow-band noise on temporary threshold shift in humans.

OBJECTIVE: To evaluate the effect of ipsilateral and contralateral low-frequency (250 Hz) narrow-band noise (NBN) on the temporary threshold shift (TTS) induced by a 2 kHz tone in young normally hearing subjects with a functioning auditory efferent system. MATERIAL AND METHODS: Sixteen young volunteers served as subjects. All the subjects were young (20-30 years), disease-free and had a medical history negative for otological disease, noise exposure and use of ototoxic drugs. They had normal hearing [thresholds of 125-8,000 Hz below 20 dB hearing level (HL)], transient-evoked otoacoustic emissions and contralateral suppression. The subjects were randomly assigned to one of three different groups. Subjects in Group A (n = 5) were exposed to a 90 dB HL 2 kHz pure tone for 10 min. Subjects in Group B (n = 6) were exposed to a 90 dB HL 2 kHz pure tone and an ipsilateral 45 dB HL 250 Hz NBN for 10 min. Subjects in Group C (n = 5) were exposed to a 90 dB HL 2 kHz pure tone and a contralateral 45 dB HL 250 Hz NBN for 10 min. The right ear served as the test ear. The TTS 2 min after the end of the exposure (TTS2) was measured in all subjects at 2, 3 and 4 kHz. RESULTS: TTS, in Group A was significantly higher at 3 kHz (p = 0.011) and at 4 kHz (p = 0.003) than TTS2 in Group B. At 4 kHz, TTS2 in Group C was significantly higher (p = 0.013) than TTS2 in Group B. Although TTS2 in Group C was lower than TTS2 in Group A, this difference was not significant. The presence of an ipsilateral low-frequency NBN significantly reduced TTS2 induced by a 90 dB HL 2 kHz tone. A contralateral low-frequency NBN reduced TTS2 in this group of subjects; however, the reduction was not significant. CONCLUSION: The results of this study show that an ipsilateral low-intensity, low-frequency (250 Hz) NBN can give protection from a TTS induced by a 2 kHz tone. Contralateral low-frequency NBN did not induce any protective effect.

Acoustic Stimulation↗
PubMed1992

The effect of crossed olivo-cochlear bundle stimulation on acoustic trauma.

To investigate whether the crossed olivo-cochlear bundle (COCB) functions in a protective manner, albino guinea pigs were exposed to sounds of varying intensity (110-130 dB SPL, 3-30 min) with or without electric stimulation of COCB, and the threshold shifts of the compound action potential (CAP) were examined. A statistically significant protective effect was observed in animals exposed to stimuli of intermediate intensity which induce threshold shifts of 50 to 55 dB on average. No protective effect was observed in the groups exposed to greater or milder stimuli. These results are discussed in the light of the available literature.

Acoustic Stimulation↗
PubMed2005

Recreational noise exposure and its effects on the hearing of adolescents. Part II: development of hearing disorders.

Part II, continuation of a previous paper, describes the significant hearing threshold shift found during the third year of the long-term study, which continued to be present in the fourth year, in a number of adolescents classified as Subgroup 2, who showed a higher mean HTL in the middle and especially in the high frequency ranges than the rest of the studied adolescents, classified as Subgroup 1. In both subgroups, the subjects showed high participation in recreational activities; nevertheless, the adolescents in Subgroup 2 showed higher participation in some of them in the last year of the study. From the beginning of the study, the mean HTL of the adolescents in Subgroup 2 was higher than the mean HTL of the adolescents in Subgroup 1. The exposure to high sound levels during leisure activities can be a cause of permanent hearing damage among young people with 'tender ears'.

Adolescent↗
PubMedDate not supplied

Comparison between AER and behavioral thresholds in normally and abnormally hearing chinchillas.

The present study compared the auditory evoked response (AER) and behavioral thresholds from the chinchilla before and after acoustic overstimulation. Bipolar electrodes were chronically implanted in the inferior colliculus of seven monauralized behaviorally conditioned animals (shock-avoidance). AER to 20-msec and behavioral thresholds to 20- and 500-msec tone bursts were determined for a range of frequencies before and after a 4-hour exposure to a 2000 Hz, 120dB SPL pure tone for six of the animals. One animal served as control and received no exposure. Results revealed a relatively close correspondence between AER and behavioral thresholds both before and after noise exposure in the same animal. Postexposure AER and behavioral thresholds displayed mild to moderate losses in sensitivity in the 1 to 4 kHz range. These findings justify further development of this particular AER as an indicator of hearing sensitivity in the chinchilla.

Animals↗