Size and duration of acoustically elicited impedance changes in man

The middle ear muscle reflex in the diagnosis of cochlear neuropathy

Cochlear neuropathy, i.e. the loss of auditory nerve fibers (ANFs) without loss of hair cells, may cause hearing deficits without affecting threshold sensitivity, particularly if the subset of ANFs with high thresholds and low spontaneous rates (SRs) is preferentially lost, as appears to be the case in both aging and noise-damaged cochleas. Because low-SR fibers may also be important drivers of the medial olivocochlear reflex (MOCR) and middle-ear muscle reflex (MEMR), these reflexes might be sensitive metrics of cochlear neuropathy. To test this hypothesis, we measured reflex strength and reflex threshold in mice with noise-induced neuropathy, as documented by confocal analysis of immunostained cochlear whole-mounts. To assay the MOCR, we measured contra-noise modulation of ipsilateral distortion-product otoacoustic emissions (DPOAEs) before and after the administration of curare to block the MEMR or curare + strychnine to also block the MOCR. The modulation of DPOAEs was 1) dominated by the MEMR in anesthetized mice, with a smaller contribution from the MOCR, and 2) significantly attenuated in neuropathic mice, but only when the MEMR was intact. We then measured MEMR growth functions by monitoring contra-noise induced changes in the wideband reflectance of chirps presented to the ipsilateral ear. We found 1) that the changes in wideband reflectance were mediated by the MEMR alone, and 2) that MEMR threshold was elevated and its maximum amplitude was attenuated in neuropathic mice. These data suggest that the MEMR may be valuable in the early detection of cochlear neuropathy.

Acoustic reflex amplitude and noise-induced hearing loss

Acoustic reflex maximum amplitude measurements elicited both contralaterally and ipsilaterally were obtained from subjects with noise-induced hearing loss and compared with those obtained from normal-hearing subjects. The eliciting signal was a pure tone of 1 kHz presented for 1,000 ms. The groups were matched on age, sex, static immittance and ear canal volume. Acoustic reflex amplitudes were clearly reduced in noise-impaired subjects compared with normal-hearing subjects at a frequency where their hearing thresholds were normal.

Relationships between acoustic reflex patterns elicited by unfiltered white noise and narrow band white noise stimuli of different duration but of the same intensity

For the purpose of this study, acoustic signals were generated by an Amplaid MK VI. An Amplaid 702 impedence meter was connected to its averaging section and to its computer. The stimuli were bursts of unfiltered white noise (UWN) and of narrow band white noise (NBWN; 30 db./oct/slope; central frequencies 1,000, 2,000, 4,000 Hz.) lasting 3-1,000 msec., at intensity of 105 db. SPL p.e. The following parameters were evaluated: stapedius contraction latency, amplitude, duration and recruitment time. It was found that latency was independent of the spectrum of the stimulus and its duration. Amplitude and recruitment time, on the other hand, were related to spectrum and duration, while duration of contraction was directly related to the duration of the stimulus only.

Dynamic study of the acoustico-facial reflex by impedance measurement

Dynamic study of the acoustic reflex has brought into evidence that 1. age has a significant influence on various reflex response parameters 2. study of dynamic parameters of the acoustic reflex enables changes in the reflex arc to be objectified. This is therefore an objective measurement of recruitment in impedance measurement. The author proposes to study the following parameters: rise time, recovery time, and the variations of maximum amplitude as function of sound stimulation intensity. Study of these three parameters provides a highly sensitive test of change in the dynamics of the acoustic reflex, for indeed this test reveals pathology well before the Reflex Decay Test does so.

Methodological problems in the determination of homolateral stapedius reflex threshold

Generally, a bilateral symmetry of the acoustic stapedius reflex is assumed. But a homolaterally higher sensitivity has been described. We examined 71 patients with complete unilateral deafness. With a TDH 39 headphone, stimuli of intensities up to 133 dB were conveyed to the deaf ear. A fairly accurate estimate of the normal homolateral threshold is obtained by correcting for the cross-hearing loss and by mathematical consideration of the relative probabilities of the positive and negative cases. Methodology-specific influences are discussed and a correction made for them. The homolateral reflex threshold is 9-14 dB lower than the contralateral reflex threshold.

Comparative study between the normally hearing child and the hard of hearing child, by acoustic impedance measurements of the ear

In the first part, the author makes a comparative study of the tympanometric results obtained from the normally hearing child and the hard of hearing child. The frequency of serous otitis media is statistically higher in the deaf child. The author compares such results of tympanometry as obtained from the child, considers the contribution of this technique to the field of pediatric audiology and suggests a classification of tympanograms in terms of the probe-tone frequency of the impedancemeter. The second part concerns the acoustico-facial reflex. This study compares the recording of the stapedius reflex obtained by pure tone and Narrow-Band noise acoustic stimulation, thanks to Madsen electro-acoustic bridge, in two groups of children, the one consisting of normal hearing children and the other of children suffering from severe perception hearing loss. The study of the stapedius reflex threshold makes it possible to analyse the dynamics of the field of perception in both groups. After an analysis of the results, the author outlines the importance attributable to the study of the stapedius reflex in the child as a means of objectively examining the auditive function and a means of differential diagnosis in cases of sensorineural impairment of the hearing function.

Threshold-duration function of the acoustic reflex in man

The threshold-duration function of the acoustic reflex was investigated in 5 male and 5 female adult, normal-hearing humans and in 3 adult male subjects with hearing loss of cochlear etiology. Reflex threshold was obtained at stimulus durations of 10, 20, 50, 100, 200, and 500 msec and at frequencies of 500, 1 000, 2 000, 3 000, and 4 000 Hz. Three commercially available acoustic bridges were employed, the Madsen ZO-70 and Grason-Stadler 1720 electroacoustic bridges, and the Grason-Stadler-Zwislocki model 3 mechanical-acoustic bridge. A probe-tone frequency of 220 Hz was used in all measures. The reflex threshold-duration function for normal-hearing subjects was found to encompass a much greater range of intensity than the psychophysically assessed auditory threshold temporal integration function. A sex difference was found which may be explained by subclinical noise-induced cochlear pathology in the male subjects with subsequent truncation of the reflex threshold-duration function. The function was also found to be truncated in the 3 subjects with hearing loss diagnosed to be of cochlear etiology. The implications of these findings for control of stimulus duration in clinical reflex measurement was discussed.