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The remarkable specificity and sensitivity of otoacoustic emissions (OAEs) in identifying cochlear dysfunction, and the speed and objectivity with which the test can be conducted has made the OAE procedure the 'standard-of-care' in pediatric audiology assessment. Together with the auditory brainstem responses (ABRs), the OAE procedure not only separates sensory from neural impairment, but also facilitates early audiologic diagnosis and management. This article describes some unique applications of the OAE procedure in the diagnosis, monitoring and treatment of auditory dysfunction.

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OBJECTIVE: To investigate the effects of chronic tobramycin treatment on distortion product otoacoustic emission (DPOAE) latencies and response growth detection thresholds in human subjects to determine the sensitivity of these DPOAE features to ototoxic damage. DESIGN: Six groups of children in two different age ranges were tested: three groups in the 7 to 14 yr age range, i.e., six children with normal hearing, four cystic fibrosis (CF) patients who received no aminoglycosides, and eight CF patients who received low- to moderate-cumulative doses of tobramycin (< 1250 mg/kg) for respiratory infections; and three groups of five subjects each in the 15 to 23 yr age range, i.e., the healthy group and the CF groups that received low- (< 285 mg/kg) and moderate-(1000 to 2000 mg/kg) cumulative drug dosages. The aggregate drug dosages compiled longitudinally over the past 5 yr were used to group the drug-treated CF patients. All subjects showed normal audiometric profiles (< or = 25 dB HL in the conventional frequency region and age-appropriate thresholds as described by Osterhammel and Osterhammel [1979] in the high-frequency region) and DP-grams (absolute DPOAE and noise amplitudes being consistent with the normative data obtained with the CUBeDIS system at this institution). RESULTS: Even though the audiometric profiles and DP-grams of all drug-treated CF groups were identical to their healthy counterparts, the DPOAE latencies and growth function thresholds showed significant changes. Whereas low and low-to-moderate doses of tobramycin were related to DPOAE latency prolongations, higher cumulative drug doses of 1000 to 2000 mg/kg produced significant reductions in DPOAE latencies. Response growth detection thresholds at high frequencies showed significant elevations in all CF patient groups treated with tobramycin, regardless of drug dosages, as compared with the control subjects. CONCLUSIONS: DPOAE amplitudes may not reflect the earliest changes produced by chronic aminoglycoside treatment, suggesting that cochlear ototoxicity may be more effectively monitored through the assessment of latencies and response growth detection thresholds. These findings pertain at least to the early stages of ototoxicity development, specifically during chronic tobramycin treatment. In light of the small sample size, however, these outcomes must be considered as tentative.

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The role of the medial efferent system in altering and/or regulating outer hair cell function in the mammalian cochlea has been proposed by a number of investigators. This study measured contralateral suppression of distortion product otoacoustic emissions (DPOAEs) in cystic fibrosis (CF) patients, treated for lung infections with low to moderate cumulative doses of tobramycin, to ascertain the contributions of the efferent-based mechanisms in the development of ototoxicity. The results showed significant suppression of DPOAEs in tobramycin-treated children compared to both nondrug-treated CF and normal children of similar ages. Since DPOAE amplitudes were comparable across the drug-treated and control groups of subjects, pronounced DPOAE suppression in the drug-treated group may be attributed to the instability of the cochlear amplifier induced by the tobramycin treatment. These findings also suggest that enhanced contralateral suppression may be the first sign of a developing ototoxicity.

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Oto-spondylo-megaepiphyseal dysplasia (OSMED) is considered to be an autosomal recessive disorder characterized by sensorineural hearing loss, short extremities in spite of normal body length, and abnormally thick joints. We present audiologic results and follow-up of two siblings (normal mother, affected father, 3 of 4 affected children). Given the severity of the hearing loss and, in some cases, severe myopia, early audiologic intervention is highly desirable.

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We evaluated the effect of electrode montage on the spectrum of the infant auditory brainstem response (ABR). Spectral profiles of ipsilateral, contralateral, noncephalic, and horizontal recordings obtained in response to slow and fast repetition rates and at low and high stimulus intensities were also evaluated. Findings indicate that the spectrum of the infant ABR is dominated by low-frequency energy, maximal below 200 Hz. The spectra of ipsilateral and noncephalic recordings are the strongest irrespective of stimulus intensity or repetition rate. Increase in stimulus intensity or repetition rate typically enhances the amount of energy below 200 Hz. These results reinforce the clinical utility of ipsilateral and noncephalic recordings for screening, threshold measurement, and neurodiagnostic purposes.

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This study examined auditory-evoked brainstem responses (ABR) in the deermouse (Peromyscus maniculatus) during torpor and arousal. The ABR of the euthermic deermouse consisted of five waves occurring in a time frame of 10 ms. During torpor, ABR wave I could be elicited at slow, but not fast stimulation rates indicating variability in neural activity along the auditory pathway. Arousal was heralded by the appearance of all the components of the ABR evoked in response to both slow and fast click rates signaling functional restoration of auditory neural activity during this phase.

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The present study compares ipsilateral, contralateral, horizontal and non-cephalic auditory-evoked brainstem responses (ABR) obtained from normal infants (39-42 weeks' post-conceptional age) to assess their utility in auditory neurodiagnosis. Wave latencies, wave amplitudes and waveform morphology were evaluated at slow and fast repetition rates. Ipsilateral and horizontal recordings obtained with a fast stimulation rate provide best waveform characteristics for neurodiagnostic interpretation. Further enhancement of wave V amplitude and separation of IV-V wave complex may be achieved by using the non-cephalic recording montage. Compromised or low amplitude components on contralateral measurements may confound neurological interpretation.

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This study examined the utility of a methacrylate-based embedding medium and microwave staining for light microscopic quantification of hair cells and spiral ganglion cells in the mouse cochlea. The most important phase of the preparation process involved slowing down the polymerization process. The tissue molecules so locked within the plastic matrix produced excellent preservation of the organ of Corti and adjacent structures including the spiral ganglion, as well as tissue ionic charges. Excitable by microwaves, these ionic charges accelerated the movement of the basic dye (hematoxylin) into the tissue, reducing the time for this segment of the staining process from approximately 45 minutes to 1-2 minutes. When embedded in glycol methacrylate (GMA), acidic dyes show less stain-cell affinity so that staining intensity and time cannot be improved significantly. However, addition of color extenders to the counterstain eosin produced distinguished staining of all tissue constituents. Thus, a combination of GMA embedding medium, use of the microwave for staining and addition of color extenders to the counterstain generated excellent structural resolution and contrast. This made both hair cell and spiral ganglion cell counts possible from within the same specimen and provided an opportunity for qualitative evaluation as well.

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This study investigated the effects of increased body temperature on the latencies and amplitudes of the auditory-evoked brainstem response (ABR) in mice. Six eleven-week-old male CBA/CaJ mice were anesthetized with pentobarbital and screened for normal hearing. Hyperthermia was induced by placing the animal in a thermostatically controlled chamber; a thermistor connected to a digital thermometer measured the rectal temperature. ABRs were evoked with broad-band clicks presented at repetition rates of 21.1/s and 61.1/s. The latencies and amplitudes of waves I-V were measured at 1-degree and/or 0.5-degree intervals between 37 and 42 degrees C. Temperature elevation between 37 and 41 degrees C shortened the latencies of all the ABR waves, the effect being linear and cumulative across the time window. Change in this trend occurred between 41 and 42 degrees C, whereby the latencies of all the waves stabilized or showed minimal prolongation. Amplitudes of the most robust waves I and II showed a trend similar to the latencies, whereas the later waves showed erratic and uninterpretable changes. These findings in the mouse may be indicative of the physiological limit of thermal tolerance and as such may be regarded as a premonitory signal of permanent damage.

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Binaural interaction (BI) waveforms were derived from multichannel recordings of auditory-evoked brainstem responses obtained at moderate and high intensity levels. The component latencies of all the BI responses derived from the contralateral channel were significantly prolonged compared with those derived from ipsilateral and non-cephalic channels. These channel differences were identified only at the moderate intensity level, indicating that BI cannot be isolated from the effects of stimulus interaction at higher intensities. The amplitudes were not significantly different across channels or intensities, indicating that ipsilateral, contralateral or non-cephalic recordings can be used to study BI. However, identification of channel differences on simultaneous multi-channel recordings may provide an index of true neural interaction.

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1. This study measured the changes in the auditory-evoked brainstem responses in the woodchuck (Marmota monax) during hibernation and arousal. 2. The auditory brainstem response of the euthermic woodchuck consisted of four waves occurring in a 10 msec time window after stimulation. 3. In the hibernating woodchuck, waves I and II could be traced down to the lowest body temperatures. 4. As temperatures increased all the components of the ABR emerged. The latencies of all the waves showed systematic decrease with temperature increments, the effect being cumulative across the time window. 5. These findings reflect activity in the VIIIth cranial nerve and the cochlear nuclei during hibernation and restoration of the functional integrity of the brainstem auditory pathway during arousal.

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The use of either cold or warm caloric stimulation alone as a screening tool for unilateral weakness has been suggested as a means of both shortening testing time and reducing patient discomfort. The validity of the monothermal caloric test must be well established before it can be routinely used in clinical situations. The purpose of this investigation was to re-evaluate the monothermal caloric test by examining the correlations between unilateral weakness derived from bithermal caloric stimulation compared to monothermal caloric results using either warm or cool stimulation alone. A retrospective analysis of 200 patients indicated significant correlations between bithermal and monothermal unilateral weakness for patients with unilateral weakness of less than 15% and greater than 30% for both warm and cool water stimulation. For patients with 15% to 30% unilateral weakness, the bithermal and monothermal calorics were significantly correlated for only the cool condition. When predicting normal or greater than 20% unilateral weakness, either of the monothermal calorics have greater than 85% efficiency, with specificity greater than 94% and sensitivity greater than 64%. However, the false-negative rate is 29% for warm and 36% for cool calorics. The high rate of false-negative findings indicates that screening tests have no place in a diagnostic battery, especially in view of the implications for missing significant pathology.

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Thirty-three groups of guinea pigs, consisting of five animals in each group, were exposed to a simulated impact noise with peak levels ranging between 119.5 and 134.5 dB SPL. By varying the repetition rate, different equivalent levels could be set at each peak level. The equivalent levels ranged from 96 to 117 dB SPL, and the exposure duration was 1.5 to 24 hours. The compound action potential thresholds were measured in 1/3-octave steps between 1 and 20 kHz, one month after the exposure. Higher peak levels resulted in a peak-shaped threshold elevation with a maximum around 8 kHz. For constant peak levels, the equal energy theory was supported. For exposures of equal energy but different peak levels, significantly higher threshold elevations resulted after exposure to higher peak levels.

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In order to investigate whether experimental material consisting of noise-exposed animals should be regarded as 'ears' or 'animals', a comparison was made between the permanent threshold shifts in the right and left ears in 53 groups of noise-exposed guinea-pigs, with 5 animals in each group. The action potential (N1) thresholds were measured at fourteen frequencies in both ears. In the noise-exposed animals, the threshold elevations were up to 40 dB. The average right-left correlation coefficient within each group was about 0.79, regardless of noise energy. The degree of correlation was significantly greater after impact noise than after continuous noise. As a consequence of the high right-left correlation, the informative value of measuring a second ear in the same animal was, in our experiments, only 11% of that of the first one. No correlation could be found between the degree of skin pigmentation and the threshold elevation.

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This study was conducted to compare results of SCAN: A Screening Test for Auditory Processing Disorders with other central auditory and language tests. The SCAN, Staggered Spondee Word test (SSW), Competing Sentence test, Peabody Picture Vocabulary Test (PPVT), and the Clinical Evaluation of Language Fundamentals-Revised (CELF-R) were administered to 155 children between the ages of 6 and 15 years. All subjects were referred for possible auditory or language processing disorders. Results showed significant correlations between the SCAN, SSW, and Competing Sentence test results except for Filtered Word and Auditory Figure Ground subtests of SCAN that were not significantly correlated with the Competing Sentence Test. Significant correlations also existed between SCAN and the PPVT, but there were no significant correlations between SCAN and the CELF-R subtests. Patterns of responses according to histories of Attention Deficit Disorders were also found.

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Sixty guinea pigs were exposed to a steady-state broadband noise with a falling frequency spectrum. The sound-pressure level was varied between 96 and 117 dB SPL, and the duration of the exposure was varied from 3 to 12 h. After 4-5 weeks, the auditory thresholds were determined by electrocochleography at 14 frequencies, and the results were compared with a control group. With increasing sound-pressure level, the thresholds became elevated at all frequencies. The maximum threshold elevation also exhibited a slight shift toward higher frequencies. With increasing exposure time, the threshold elevations increased and shifted into the high-frequency region, whereas the low-frequency region was less affected. Linear regression analysis showed that the average threshold elevation between 1 and 20 kHz did not deviate from that predicted by the equal-energy hypothesis. However, the high-frequency loss at 5-20 kHz was very dependent on the exposure time, whereas the 1- to 4-kHz loss was not. There was no sign of any critical intensity with sudden increments in threshold elevation.

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Although the protean manifestations of neurofibromatosis have been studied for many years, much is yet to be learned about this disease in young children. Specifically, little is known about the prevalence and significance of early neurotologic abnormalities in this population. Our review of the recent literature, however, failed to identify any publication on the use of ABR and acoustic reflex testing in the pediatric neurofibromatosis population. This study reports on a standardized differential diagnostic battery conducted on 44 children diagnosed as having neurofibromatosis. Results of the neuroaudiologic battery indicated that 32% of the children had significant abnormalities on ABR and acoustic reflex dynamic tests. This is a substantially higher prevalence of abnormalities than reported by another group at a recent NIH concensus meeting on neurofibromatosis. Discussion of the implications of these findings regarding evaluation protocols, as well as management for this select patient population, will follow.

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Eighteen groups of guinea pigs were exposed to a simulated impact noise for periods of 1.5-24 h. The peak level was kept constant at 131.5 dB and the repetition rate was varied to give seven different equivalent levels (Leq) between 96 and 117 dB. The auditory thresholds were assessed by electrocochleography after 1 month and compared with those of a control group. Significant damage occurred even at the lowest exposure energy used. When the total exposure energy was expressed on a decibel scale, the threshold elevation (1-10 kHz) increased 1.07 dB for each decibel increase in the exposure energy, regardless of the combination of Leq and exposure time. The results of the study thus support the equal-energy hypothesis under these conditions.

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The present study examined the similarities between four auditory adaptation techniques to determine whether the effects were correlated. The four adaptation techniques compared were: Simultaneous Dichotic Loudness Balance technique (SDLB; Hood, 1950), Magnitude Estimated Binaural technique (MEB; Botté, Canévet, & Scharf, 1982), Magnitude Estimated Monaural technique, (MEM; Weiler, Sandman, & Pederson, 1981), and the Monaural Reaction Time technique (RT; Davis & Weiler, 1976). Results did not show significant correlations between the four techniques, except (r = 0.39) between MEB and MEM procedures. This correlation was much less than the reliability of the measures would allow (r = 0.98 and r = 0.99, respectively). Thus, it appears that the different methods either produced different adaptation effects or measured different aspects of auditory adaptation. The normal ear apparently shows several forms of adaptation, which reduces the perceptual strength of a continuing stimulus, in favor of an intermittent, less redundant one.

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