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PubMed1994

[Functional and morphological changes in the cochlea of cholesterol fed guinea pigs].

Although sensory neural hearing loss stemming from hypercholesterolemia has received attention in recent years, no information is available about inner ear injuries resulting from this condition. In this study, we prepared guinea pig models at hypercholesterolemia and observed the inner ear with a transmission electron microscope, and also investigated the effect of vitamin E (Vit. E) on these injuries. One hundred and thirty-nine white male Hartley guinea pigs weighing a mean of 250 g each were divided into three groups. Group A consisted of the control animals, which were fed by a stock diet. Group B animals were fed by a hyperlipid diet (2.5% cholesterol, 0.25% cholic acid, and 7.5% cattle fat). Group C animals were fed by a Vit. E-added (50 units/100 g) hyperlipid diet. All the animals were sacrificed either one, two or three months after treatment and the cochlea duct vasculature, cochleal nerve fiber under spiral limbus, stria vascularis and inner hair cell and outer hair cell of Corti's organ was observed with a transmission electron microscope. Cholesterol, triglyceride, and TBARS values were concurrently measured in the serum. Auditory threshold was measured by auditory brain stem response (ABR). In groups B and C, cholesterol and triglyceride levels remained high,. The TBARS level elevated in group B but remained unchanged in groups A and C. In groups B and C, the threshold of ABR increased mildly. The cholesterol load led to injuries in the endothelium of the vasculature dominating the cochlea.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1999

Inner ear barotrauma after stapedectomy in the guinea pig.

OBJECTIVE: The safety of scuba diving after stapedectomy is controversial. Stapedectomy is thought to predispose to inner ear barotrauma (e.g., perilymph fistula); however, many individuals continue to scuba dive following stapedectomy without ill effects. The purpose of this study was to evaluate the cochlear effects of barotrauma, similar to that experienced with scuba diving, on inner ears previously treated with stapedectomy. STUDY DESIGN: Prospective, controlled. METHODS: Sixteen Hartley albino guinea pigs underwent unilateral total stapedectomy followed by hyperbaric dives on 5 consecutive days, beginning 3 weeks after stapedectomy. Cochlear effects were determined using click and tone-pip evoked electrocochleographic thresholds and cochlear hair cell counts. RESULTS: Mean auditory thresholds increased by 29 dB after stapedectomy (P < .001), then remained stable thereafter. Mean thresholds in both the operated and control ears did not change with hyperbaric dives. Evidence of middle ear barotrauma (e.g., hemorrhage or tympanic membrane perforation) was observed in eight poststapedectomy ears and five control ears, but none demonstrated significant threshold elevation greater than or equal to 10 dB. Hair cell counts were not different between operated and control ears. CONCLUSIONS: Stapedectomy does not appear to predispose to cochlear sequelae in the guinea pig model of diving-related barotrauma.

Acoustic Stimulation↗
PubMed2005

Hearing in fishes under noise conditions.

Our current knowledge on sound detection in fishes is mainly based on data acquired under quiet laboratory conditions. However, it is important to relate auditory thresholds to background noise in order to determine the signal-detecting abilities of animals in the natural environment. We investigated the influence of two noise levels within the naturally occurring range on the auditory sensitivity of two hearing specialists (otophysines) and a hearing generalist. Audiograms of the goldfish Carassius auratus, the lined Raphael catfish Platydoras costatus and the pumpkinseed sunfish Lepomis gibbosus (hearing generalist) were determined between 200 and 4000 Hz (100-800 Hz for L. gibbosus) under laboratory conditions and under continuous white noise by recording auditory evoked potentials (AEPs). Baseline thresholds showed greatest hearing sensitivity around 500 Hz in goldfish and catfish and at 100 Hz in the sunfish. Continuous white noise of 110 dB RMS elevated the thresholds by 15-20 dB in C. auratus and by 4-22 dB in P. costatus. White noise of 130 dB RMS elevated overall hearing thresholds significantly in the otophysines by 23-44 dB. In the goldfish, threshold did not shift at 4 kHz. In contrast, auditory thresholds in the sunfish declined only at the higher noise level by 7-11 dB. Our data show that the AEP recording technique is suitable for studying masking in fishes, and that the occurrence and degree of the threshold shift (masking) depend on the hearing sensitivity of fishes, the frequency, and noise levels tested. The results indicate that acoustic communication and orientation of fishes, in particular of hearing specialists, are limited by noise regimes in their environment.

Acoustic Stimulation↗
PubMed2003

Occupational toluene exposure and auditory function: results from a follow-up study.

The ototoxicity of occupational exposure to toluene below 50 p.p.m. was investigated in a longitudinal study over 5 yr with four repeated examinations starting with 333 male workers from rotogravure printing plants. Past lifetime weighted average exposures (LWAE) to toluene and noise were determined from individual work histories; recent individual exposures were measured 10 times during the study (toluene, active sampling; noise, stationary measurements). The auditory thresholds were measured with pure tone audiometry. The mean LWAE exposures to toluene and noise were 45 +/- 17 p.p.m. plus 82 +/- 7 dB(A) for printers (high toluene intensity) and 10 +/- 7 p.p.m. plus 82 +/- 4 dB(A) for end-processors (low toluene intensity). The mean current exposures to toluene and noise during the study were 26 +/- 20 p.p.m. plus 81 +/- 4 dB(A) for printers and 3 +/- 3 p.p.m. plus 82 +/- 4 dB(A) for end-processors. Repeated measurement analyses (grouping factors: toluene intensity, exposure duration and noise intensity) and logistic regressions did not reveal significant effects of toluene intensity, of exposure duration and of interactions between toluene intensity and noise intensity. The stratification dependent on noise intensity itself [79 +/- 3 versus 84 +/- 1 dB(A)] was significantly associated with the auditory thresholds. Regarding the missing toluene effects, it was concluded that the threshold level for developing a hearing loss as a result of occupational toluene exposure might be above the actual limit of 50 p.p.m.

Follow-Up Studies↗
PubMed1983

[Brief acoustic stimuli for the recording of brain stem potentials by computer controlled system analysis].

Brief acoustic stimuli are used in the objective assessment of the auditory threshold and in topodiagnosis of pathological processes in the auditory path via registration of brain stem potentials. The type of stimulus, duration, frequency and phase are decisive for the evocation of the brain stem potentials. However, it is still a somewhat unsolved problem as to how to obtain an optimally reproducible kind of stimulation. The pattern of progression of acoustic stimuli is of crucial importance for the recording of early acoustic evoked potentials (EAEP). Using an artificial auditory canal, a measurement device was constructed for recording acoustic stimulus sequences in the auditory meatus. With the help of electronic monitoring it became possible to produce digitally controlled stimulation resulting in utilizing forms of electrical stimuli which cannot be produced in the audiometer, for obtaining suitable electric stimuli. Whereas the curves of the acoustic pressures largely deviate from those of the electrical stimuli, as shown by measurements in the artificial auditory canal (the deviations depending on the headphones used in each case), the transmission properties of the electro-acoustic transducers are processed mathematically on the basis of Fourier's transformation, and such processing makes it possible to electrically produce any desired sequences of acoustic stimuli, taking the transmission properties of the headphones into account. In this manner, synchronous discharging of the sensory cells by brief acoustic stimuli, which is required for EAEP recording, can be optimized.

Acoustic Stimulation↗
PubMed1991

Repeated infant thresholds in operant and nonoperant audiometric procedures.

This study examined test-retest reliability of infant auditory thresholds in a single evaluation session. Eight- to 11-month-olds were assessed in both operant and nonoperant audiometric procedures. Operant testing produced an average of 8.5 thresholds. Mean threshold level did not shift significantly over the course of the operant session, although some individual threshold functions varied from the group trend. Nonoperant assessment yielded two or more measures of threshold for only a portion of the subject group. The pattern of repeated measures for this subgroup showed a significant upward shift in threshold level.

Audiometry↗
PubMed1988

Effect of electrical stimulation of the crossed olivocochlear bundle on temporary threshold shifts in auditory sensitivity. II. Dependence on the level of temporary threshold shifts.

1. This report presents a more detailed examination of crossed olivocochlear bundle (COCB) effects on temporary threshold shifts (TTS). The principal aim was to establish the details of the relationship between the effects of continuous COCB stimulation and the TTS caused by various exposures. Initially, in various groups, different intensities of a 1-min exposure were presented with or without COCB stimulation. Stimulation at any particular rate caused greatest reductions in TTS to occur for the higher intensity exposures than for the lower intensity ones. Thus COCB stimulation at 140 pulses/s reduced maximum threshold losses by the following amounts: 13.33 [106 dB sound pressure level (SPL) exposure], 13.29 (103 dB SPL exposure), 8.9 (101 dB SPL exposure), and 0.77 dB (97 dB SPL exposure). 2. The effect of COCB stimulation was also examined on a shorter duration (30 s) exposure causing TTS intermediate between that due to 1-min exposure at 97 dB SPL and that at 101 dB SPL. Reductions in TTS to the shorter duration exposure were not obtained with COCB stimulation at 140 pulses/s but only when the rate was increased to 260/s. 3. Thus COCB stimulation at any particular rate caused greatest reductions in TTS when the exposure would have caused a large amount of TTS, regardless of the intensity or duration of exposure. These two parameters of the exposure could be traded to provide a level of TTS that would be affected by a standard COCB stimulus. Low-level exposures that caused only small amounts of TTS were not affected by the standard COCB stimulus. As the level of the exposure, and therefore, the ensuing TTS, increased (with increased duration or intensity of exposure), the standard stimulus had greater effects. Increasing the rate of pulses in the COCB stimulus resulted in the low-level exposures now being affected. Even at the higher rate, greatest reductions in TTS were obtained when the exposure would have resulted in high levels of TTS. 4. In an attempt to determine the site of action of the continuous COCB stimulus the endocochlear potential (EP) and the summating potential (SP) were recorded from scala media of the basal turn while applying COCB stimuli similar to those used in the TTS experiments. Although the continuous COCB stimulus caused the traditional changes in the EP and SP associated with COCB stimulation with pulsed short electrical trains, these changes adapted quite rapidly and did not persist for the amount of time shown to be necessary for full reductions in TTS to be obtained.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1996

Tonic, phasic, and transient EEG correlates of auditory awareness in drowsiness.

During drowsiness, human performance in responding to above-threshold auditory targets tends to vary irregularly over periods of 4 min and longer. These performance fluctuations are accompanied by distinct changes in the frequency spectrum of the electroencephalogram (EEG) on three time scales: (1) during minute-scale and longer periods of intermittent responding, mean activity levels in the (< 4 Hz) delta and (4-6 Hz) theta bands, and at the sleep spindle frequency (14 Hz) are higher than during alert performance. (2) In most subjects, 4-6 Hz theta EEG activity begins to increase, and gamma band activity above 35 Hz begins to decrease, about 10 s before presentations of undetected targets, while before detected targets, 4-6 Hz amplitude decreases and gamma band amplitude increases. Both these amplitude differences last 15-20 s and occur in parallel with event-related cycles in target detection probability. In the same periods, alpha and sleep-spindle frequency amplitudes also show prominent 15-20 s cycles, but these are not phase locked to performance cycles. (3) A second or longer after undetected targets, amplitude at intermediate (10-25 Hz) frequencies decreases briefly, while detected targets are followed by a transient amplitude increase in the same latency and frequency range.

Acoustic Stimulation↗
PubMed1978

Effects of stimulus duration and stimulus off time on the auditory and acoustic reflex thresholds.

The effects of stimulus duration and stimulus off time on the thresholds of hearing and the acoustic reflex were investigated in 10 normal-hearing subjects and 10 subjects with sensorineural hearing loss. A 1000-Hz stimulus with on-off times of 500-500 msec and 30-30 msec was used to obtain hearing sensitivity and acoustic reflex thresholds via a tracking method. Auditory threshold was poorer for the 30-30 msec tone than the 500-500 msec stimulus in both groups. Using the different stimuli, no significant difference in acoustic reflex threshold was observed in either group. These results suggest that the addition of a short off time modifies the previously observed effects of both duration and off time on the acoustic reflex and auditory threshold.

Adult↗
PubMed1998

Auditory perception following hair cell regeneration in European starling (Sturnus vulgaris): frequency and temporal resolution.

Behavioral detection thresholds, auditory filter widths, and temporal modulation transfer functions were obtained from four starlings before, during and after 11 days of subcutaneous injections of kanamycin, an aminoglycoside antibiotic. Birds were operantly conditioned to respond to pure tones and amplitude modulated noises ranging in frequency from 0.25 to 7 kHz using adaptive staircase procedures and were tested daily for 92 days after the first injection of aminoglycoside. All birds had threshold shifts of at least -60 dB at frequencies above 4 kHz. Lower frequencies were affected in some birds, although none of the birds had hearing loss below 3 kHz. All four birds had wider auditory filters at 5 kHz immediately after the aminoglycoside series. Any changes in frequency resolution at frequencies below 5 kHz were slight, transitory, and rarely observed. Two of the four birds had permanently wider auditory filters at 5 kHz. Temporal modulation transfer functions were briefly affected in two birds during the time of greatest threshold shift. Recovery of detection thresholds began soon after the injections ceased and continued for approximately 60 days. Recovery in frequency resolution lagged behind auditory threshold by about 10 days. Normal temporal resolution was observed in the context of impaired intensity and frequency resolution. Changes in auditory threshold and frequency resolution were closely associated for all birds at 5 kHz, but were correlated with statistical significance in only two birds. Scanning electron microscopy was performed on all four birds after 90 days of recovery and confirmed that the extent of initial damage was consistent with the pattern of observed hearing loss.

Animals↗
PubMed1988

Detection of ABR thresholds with a statistical synchrony measure.

Using the method of Fridman and his colleagues, a statistical test of auditory brainstem responses (ABR) for detecting auditory thresholds is presented. The synchrony measure (SM) which represents the degree of reproducibility for group averages was used to calculate the selected Fourier components of the group averages from phase variance. The sensitivity of the test was demonstrated on 35 normal ABRs with 60 and 45 dB SL stimulus intensity and in the absence of stimulus from the ipsilateral recordings. The SM of all cases of normal ABRs at 60 and 45 dB SL exceeded those in the absence of stimulation. The same procedure was applied to 16 ears with cochlear hearing loss with (4 ears) and without (10 ears) recruitment and 2 ears with relatively normal hearing threshold (less than 30 dB HL). Seven out of 10 ears without recruitment had the SM value at 60 dB SL stimulus intensity significantly lower than those of normal ABRs.

Adolescent↗