E. Laukli

Development of early auditory-evoked responses in the cat.

The post-natal development of the auditory-evoked responses to 1- and 4-kHz tone bursts has been studied in the cat with subcutaneous electrodes and signal-averaging techniques. A cochlear microphonic response antedates the earliest appearance of brain stem potentials by 1 or 2 days, and can be recorded in some animals on the first post-natal day with the 4-kHz stimulus. The earliest brain stem response consists of three or four low-voltage waves,which increase to six in the 2nd week. Latency shortening and amplitude growth occur for all waves, but are most pronounced in the later part of the response. The characteristics of the summating potential, and the variable influence of rate effects on wave amplitude are described for the different age-groups.

High-Frequency Audiometry Normative Studies and Preliminary Experiences

A new, commercial high-frequency audiometer, Demlar 20K, for measuring hearing thresholds between 8 and 20 kHz has been used routinely in different patient groups and in a control population over the past 3 years. Test-retest studies have shown that this instrument can be used in the clinic with approximately the same degree of reproducibility as in conventional audiometry. While inter-subject variation is comparatively large, repeated evaluations can be performed in individual cases with an acceptable degree of reliability. This techniques can be helpful in differentiating between noise damage and presbycusis. Pre- and post-operative high-frequency audiometry may prove to be of value in the assessment of middle ear surgical techniques.

Presbyacusis—hearing thresholds and the ISO 7029

The purpose of this study was to analyse the changes inpure-tone hearing thresholds with age. We studied a randomsample of 232 elderly subjects with a battery ofaudiological tests, including pure-tone audiometry in theconventional and extended high-frequency range, usingthe normative distributions from the InternationalOrganization for Standardization (ISO) standard 7029for comparison. Sixty otologically normal (ON) subjectswere selected for comparative analysis with theunscreened (US) sample, and for description of genderand age group differences. With the use of a mathematicaltransformation of threshold data, it was found thatthe ISO 7029 normative a coefficient in females may beset too low compared to our sample in the lower frequencies,leading to an underestimation of hearingthresholds in ON females. In our ON sample, hearingthresholds deteriorated with age in the extended highfrequencyaudiometric range. No gender threshold differenceswere found, although the prevalence of unmeasurableresponses was higher in males at some of thesefrequencies. The ON screening criteria in ISO 7029 maybe unreliable in subjects over 60 years of age, as thresholddifferences between ON and US subjects were not consistentat any frequency. Sumario El propósito de este estudio fue analizar los cambios delos umbrales auditivos con tonos puros por efecto de laedad. Estudiamos una muestra de 232 adultos mayorescon una batería de pruebas audiológicas en la que seincluyó la audiometría de tonos puros en los rangos defrecuencias convencional y en el extendido a las frecuenciasagudas, usando como comparación el estandar 7029de las distribuciones normativas de la Organización parala Estandarización Internacional (ISO). Se seleccionaronsesenta sujetos otológicamente normales (ON), parahacer un análisis comparativo con una muestra notamizada (US) y para describir las diferencias por géneroy por grupo de edad. Con el uso de una transformaciónmatemática de los datos de los umbrales, se encontró queel coeficiente normativo a del ISO 7029 en mujeres, puedehaberse fijado demasiado bajo en comparación con nuestramuestra en las frecuencias graves, favoreciendo unasubestimación de los umbrales auditivos en las mujeresON. En nuestra muestra ON, los umbrales auditivos sevieron deteriorados por la edad en el rango audiométricoextendido a las frecuencias agudas. No se encontrarondiferencias en los umbrales por género pero en hombres,la prevalencia de respuestas no medibles en algunas delas frecuencias agudas fue alta. El criterio de identifi-cación en ON con el ISO 7029 puede ser no confiable ensujetos mayores de 60 años mientras que las diferenciasde umbrales entre sujetos ON y US no fueron consistentesen ninguna frecuencia.

Multifrequency tympanometry. Preliminary experiences with a commercially available middle-ear analyzer.

Normal ears and ears affected by various pathologies were studied with a clinical middle-ear analyzer according to the multifrequency tympanometric concept, by which the resonance frequency of the tympanic membrane/middle-ear system can be determined. This frequency varies considerably in normal ears with a mean value close to 1 kHz. Ears with pathologies in the tympanic membrane and otosclerotic ears have resonance frequencies differing significantly from those of normal ears. The effects may be explained by considering mass and stiffness components.

An Audiometric Test Battery for the Evaluation of Occupational Exposure to Industrial Solvents

Subjects exposed to various industrial solvents were evaluated with a test battery comprising both peripheral and central auditory tests. After otoscopy, all subjects underwent the following audiometric procedures: air- and bone-conduction in the conventional frequency range, air-conduction in the extended high-frequency range, speech recognition score, low-pass filtered speech recognition, stapedius reflex threshold, stapedius reflex decay, auditory brainstem response, and cognitive event-related responses. Apart from mild to moderate sensorineural hearing loss found in some of the subjects, the peripheral tests were normal in most subjects. The central tests (filtered speech and cognitive responses) showed varying degrees of abnormality which may reflect different levels of disease in this group of subjects.

Early Auditory-Evoked Responses: Filter Effects

The early auditory-evoked responses have been recorded in 4 human subjects and 3 cats using a filter band-pass of 2-5 000 Hz. The responses have been subsequently analogue-filtered at different low-pass and high-pass settings. Reduction of low-pass cut-off produces latency increases of similar magnitudes for all waves. Raising the high-pass cut-off results in dramatic changes in the responses, the peaks of the waves being apparently deflected onto the succeeding wave flanks, thus resulting in false latency reductions. The individual waves are affected at different filter settings dependent on their frequency content.

Early Auditory-Evoked Responses in the Cat: Rate Effects

The brain-stem electric responses (BSER) of the cat have been evoked with a 4-kHz tone burst at three stimulus intensity levels, and at interstimulus intervals (ISI) varying fromm 500 to 20 ms. Response amplitude and latency have also been compared in different post-natal age groups, and in bilaterally hearing and unilaterally deaf animals. Increasing reptition rates produce greater latency changes in the youngest animals, whilst all age groups show amplitude decrement at shorter ISI, apart from wave III which increases in amplitude, particularly in bilaterally hearing cats at higher stimulus intensity levels. Wave I shows greater amplitude reduction than do the succeeding waves, which may indicate that the primary cochlear nuclei contribute to later waves of the BSER.

The aging ear: An otomicroscopic and tympanometric study

Objective To analyze changes in tympanometric measures with age and to study some otitis-related issues in the elderly (≥ 60 years) population. Material and Methods The study was designed as a combination of a cross-sectional survey and a controlled study. We studied a random sample of 232 elderly subjects using an extended battery of audiological tests, including pure-tone audiometry. tympanometry with a probe frequency of 226 Hz, otomicroscopy and a standardized questionnaire. A sample of 60 otologically normal subjects were selected for comparative analysis with young healthy controls, and for description of age-related changes and gender differences. Results Using linear regression analyses of ear canal volume, middle ear pressure and tympanic membrane compliance on age, no consistently significant change in these parameters with age was found. When these measures were compared between the elderly and the controls, using parametric and non-parametric statistical tests, no significant differences were found for either gender. The only significant gender difference was found for ear canal volume, which was greater for elderly males than for elderly females In the unscreened elderly sample, the adjusted prevalence for reported previous or current otitis media was 15–27% of the population (95% CI). The adjusted prevalence for reported previous or current chronic otitis media (COM) or sequelae thereof was 1–7% (95% CI). With the exception of cerumen obstruction, the prevalence of outer ear canal-related complaints was 1–7% (95% CI). There were some discrepancies between these reported complaints and the findings at otomicroscopy. Although elderly subjects with COM were found to have poorer hearing at speech frequencies than normal elderly subjects. no such effect was found in subjects with scarring or atrophy of the tympanic membrane. The effect of pathological findings at otomicroscopy on tympanometric measures in the elderly sample was highly variable and no consistent association was found. Conclusions No change in middle ear sound transmission, as assessed by tympanometry, occurs with normal aging. Ear canal volume is smaller in elderly females than elderly males, which is potentially relevant to the study of otoacoustic emissions in the elderly. The estimated prevalence of ear canal-related problems, excluding cerumen obstruction, is of such a magnitude that the introduction of partially implanted hearing aids may be warranted in our elderly population.

High-Frequency Audiometry: Comparison of Electric Bone-Conduction and Air-Conduction Thresholds

Thresholds have been measured with two commercially available high-frequency (HF) audiometers providing respectively air-conduction (AC) and electric bone-conduction (EBC) stimulation. Normative values for the latter have been obtained, and the reduction of HF sensitivity with both stimulus modes documented in two groups aged 50-59 and 70-79 years. EBC reproducibility is of the same order of magnitude as the AC signal through 14 kHz, while the dynamic range is limited to 50 dB. Lateralization of the EBC signal occurs up to at least 17 kHz. The logarithmic conversion factor of Tonndorf and Kurman [Ann. Otol. Rhinol. Lar. 93: 576-582, 1984] does not result in equivalent AC and EBC thresholds at all frequencies, but does provide similar loudness sensation increases. The 40 log (i) re 1 mA conversion factor must be adjusted with a frequency-dependent additive correction.

Identification of Early Auditory-Evoked Responses

Identification of tone-burst-evoked, short-latency auditory responses can be influenced by a variety of factors. Peak definition of the early waves is improved with high-frequency stimuli and at lower filter settings, while contralateral recording facilitates identification of waves IV and V.