Hero P. Wit

Attitude and help-seeking for hearing impairment

The aim of the present study was to investigate help-seeking for hearing impairment in the elderly, and to compare groups showing dissimilar help-seeking on their attitude toward hearing loss and hearing aids. Attitude factors were based on a revised version of the Health Belief Model, and included beliefs about: the severity of the hearing problems, the benefits of a hearing aid, barriers to hearing aid use, and the opinions of significant others. Hearing threshold levels were determined for a random sample (N = 624) of subjects aged 57 years or older from 12 general practices. Those with a mean loss of 35 dBHL in both ears (23.1%) were considered hearing impaired. Of every four hearing impaired subjects, approximately one had not discussed the impairment with his doctor and one had discussed it but did not have a hearing aid trial. About 40% of the hearing impaired individuals had a hearing aid, and relatively few had given up using it (6% of those who had an aid). These results showed a higher incidence of help-seeking for hearing impairment than comparable British studies. After the influence of hearing impairment was controlled for, the following relationships between attitude and help-seeking were found: (1) non-consulters perceived their impairment as relatively inconsequential, most frequently demonstrated a passive acceptance of hearing problems with increasing age, saw least benefits of hearing aid use, and experienced little social pressure to seek help; (2) those who did not try an aid after consulting their doctor stood out because they saw most stigma-related barriers to hearing aid use and felt their significant others agreed with them on this negative evaluation of aids; and (3) current users had the most favourable attitude toward hearing aids.

Quantum limits to oscillator stability: theory and experiments on acoustic emissions from the human ear

Abstract Statistical properties of acoustic emissions from a human ear are measured and compared with the theory of quantum-limited oscillations. Theory and experiment are in excellent agreement, both in qualitative and quantitative features, strongly supporting previous theoretical arguments for the importance of quantum noise in the inner ear.

Middle ear influence on otoacoustic emissions. I: Noninvasive investigation of the human transmission apparatus and comparison with model results

Evoked otoacoustic emissions (EOAEs) are generated within the cochlea in response to external sounds, and they can be acoustically detected in the external auditory meatus after backward propagation through the middle ear. In addition to being used to probe the cochlear mechanisms, they are expected to be sensitive to minute changes in middle ear impedance. Systematic measurements of the changes in the vectorial components of EOAEs were carried out after various manipulations of the human middle ear in order to characterize the influence of stiffness and inertia of the stapes and tympanic-membrane systems. For this purpose, stapedius muscle contractions were elicited by high-level contralateral sound, controlled changes in middle ear pressure (range +/-100 daPa) were produced and the tympanic membrane was loaded with water droplets. A computer model of the middle ear network was implemented using a standard lumped-element electric analog of the middle ear (Zwislockis model). Forward and backward transmission changes were simulated and model predictions were compared to experimental data. Apart from the case of positive middle ear pressures, a close qualitative correspondence was found between model and real-ear results. Each of the effects was characterized by a unique pattern of phase and magnitude changes as a function of frequency, in relation to the mechanical characteristics of the involved subsystem (i.e. stapes stiffness, tympanic-membrane stiffness or mass) and its resonance properties. Owing to their high sensitivity, EOAEs could be helpful for an accurate individual multifrequency analysis of middle ear impedance by comparisons under rest and test conditions.

Two-phase endolymphatic hydrops: A new dynamic guinea pig model

The classical guinea pig model for Menieres disease, in which endolymphatic hydrops was achieved by destruction of the endolymphatic sac and obliteration of the endolymphatic duct, is a non-physiological profound model with shortcomings in relation to Menieres disease as seen in patients. We developed a more subtle animal model; the two-phase endolymphatic hydrops. This model is based on a combination of chronic endolymphatic sac dysfunction, induced by slight destruction of the most distal part of the endolymphatic sac, and acute stress-induced endolymph production by stimulation of the Na/K-ATPase in the stria vascularis with aldosterone. Light microscopy of the fluid compartments of four groups of cochleas was used to examine them for the presence of endolymphatic hydrops: i) Normal (control) cochleas showed no hydrops; ii) some of the non-operated (no destruction) aldosterone-treated cochleas showed small degrees of hydrops mainly present in the basal turns; iii) mild dissection of the endolymphatic sac without administration of aldosterone produced a hydrops which was mainly present in the cochlear apex; iv) combination of chronic endolymphatic sac dysfunction and acute attacks of endolymph production by aldosterone administration revealed the most severe degrees of hydrops in all cochlear windings, damage to cochlear structures, and cellular disturbances of the epithelial lining of the endolymphatic sac. This new model may represent a more physiologic and dynamic approach to Menieres disease and may explain the etiology of many symptoms in patients such as the fluctuant nature and the types of sensoneuronal hearing losses.

Glottal volume velocity waveform characteristics in subjects with and without vocal training, related to gender, sound intensity, fundamental frequency, and age

Glottal volume velocity waveform characteristics of 224 subjects, categorized in four groups according to gender and vocal training, were determined, and their relations to sound-pressure level, fundamental frequency, intra-oral pressure, and age were analyzed. Subjects phonated at three intensity conditions. The glottal volume velocity waveforms were obtained by inverse filtering the oral flow. Glottal volume velocity waveforms were parameterized with flow-based (minimum flow, ac flow, average flow, maximum flow declination rate) and time-based parameters (closed quotient, closing quotient, speed quotient), as well as with derived parameters (vocal efficiency and glottal resistance). Higher sound-pressure levels, intra-oral pressures, and flow-parameter values (ac flow, maximum flow declination rate) were observed, when compared with previous investigations. These higher values might be the result of the specific phonation tasks (stressed /ae/ vowel in a word and a sentence) or filtering processes. Few statistically significant (p < 0.01) differences in parameters were found between untrained and trained subjects [the maximum flow declination rate and the closing quotient were higher in trained women (p < 0.001), and the speed quotient was higher in trained men (p < 0.005)]. Several statistically significant parameter differences were found between men and women [minimum flow, ac flow, average flow, maximum flow declination rate, closing quotient, glottal resistance (p < 0.001), and closed quotient (p < 0.005)]. Significant effects of intensity condition were observed on ac flow, maximum flow declination rate, closing quotient, and vocal efficiency in women (p < 0.005), and on minimum flow, ac flow, average flow, maximum flow declination rate, closed quotient, and vocal efficiency in men (p < 0.01).

Intratympanic gentamicin therapy for control of vertigo in unilateral Menière's disease: a prospective, double-blind, randomized, placebo-controlled trial

Conclusions. Intratympanic application of gentamicin is a relatively safe and efficient treatment for the reduction of complaints of vertigo attacks associated with Menières disease. The treatment also reduces the severity of the perceived aural fullness. Objective. To investigate the effectiveness of intratympanic gentamicin treatment in patients with unilateral Menières disease. Subjects and methods. In a prospective, double-blind, randomized, placebo-controlled clinical trial subjects scored vertigo complaints, aural fullness and tinnitus, before, during and up to 1 year after treatment. Hearing loss was monitored with pure tone audiometry. Results. Gentamicin treatment resulted in a significant reduction of the score for vertigo complaints and the score for perceived aural fullness. A small increase in hearing loss (average 8 dB) was measured in the gentamicin group.

Measurement of the mechanical compliance of the endolymphatic compartments in the guinea pig

During injection of artificial endolymph into scala media of the guinea pig, fluid pressure was simultaneously measured in endolymph and perilymph with micropipettes. Pressure differences in the order of 10 Pa could reproducibly be measured upon injection of 2-4 microl of artificial endolymph with a rate of 50 nl/s. Injection of larger volumes damaged the endolymphatic system. From the results, values were derived for the compliances of the membranes surrounding scala media and the vestibular part of the endolymphatic system. The shape of the pressure-time curve during and between repetitive injections of fluid could well be described with a two-component model for the endolymphatic system, consisting of two compartments with compliant walls, connected through a flow resistance. With this model, a larger compliance was found for the second compartment (vestibular part of endolymphatic system) than for the first compartment, into which fluid was injected (scala media).

AMPLITUDE AND FREQUENCY FLUCTUATIONS OF SPONTANEOUS OTOACOUSTIC EMISSIONS

Amplitude and frequency fluctuations of spontaneous otoacoustic emissions have been studied. Spontaneous otoacoustic emissions were recorded from eight human ears and two frog ears (Rana esculenta). Record length typically was 80 s. For a recorded emission signal, the amplitude signal A(t) (average A0) and time intervals T(ti) between successive positive-going zero crossings (i counts zero crossings) were determined. Emission amplitude and period both showed small fluctuations: delta Arms/A0 ranged from 0.7 X 10(-2) to 6.3 X 10(-2) for human emissions and was 24 X 10(-2) for both frog emissions; delta Trms ranged from 1.4 to 6.9 X 10(-7) s for human emission and was 50.0 and 55.0 X 10(-7) s for the two frog emissions. There was a positive correlation between delta Arms/A0 and delta Trms as determined for different emissions (R = 0.9). Spectra of A(t) and T(ti) revealed that amplitude and period were slowly fluctuating functions: cutoff frequency delta f delta A of the amplitude spectrum ranged from 3 to 18 Hz; delta f delta T ranged from 7 to 32 Hz. Results have been compared to amplitude and frequency fluctuations of a second-order oscillator, that interacts with a noise source. It has been concluded that an oscillator with linear stiffness (for example a Van der Pol oscillator) driven by white Gaussian noise, cannot account for all experimental results. Other possible oscillators (e.g., nonlinear stiffness) and noise sources (e.g., narrow-band noise), that may account for the observed phenomena, are discussed.

WIENER KERNEL ANALYSIS OF INNER-EAR FUNCTION IN THE AMERICAN BULLFROG

The response of 17 primary auditory nerve fibers in the American bullfrog (Rana catesbeiana) to acoustic noise stimulation of the tympanic membrane was recorded. For each fiber, the first- and second-order Wiener kernels, k1 (tau 1) and k2 (tau 1, tau 2), were computed by cross correlation of the stimulus and the response. The kernels revealed amplitude and phase characteristics of auditory filters of both phase-locking and non-phase-locking fibers. Wiener kernels of high- and midfrequency fibers (best frequency, BF > 500 Hz), implied a simple sandwich model, consisting of a cascade of a linear bandpass filter, a static nonlinearity, a linear low-pass filter, and a spike generator. The bandpass filter was at least of order 7, and had a linear phase response, for both the high- and the midfrequency fibers. Averaged across fibers, filter order 2, and cutoff frequency 451 Hz for the second filter in the model was observed. The responses of low-frequency fibers (BF < 500 Hz) could not be fit with the sandwich model, because the Fourier transform K2 (f1,f2) of the second-order Wiener kernel showed significant components at off-diagonal frequencies f1 not equal to +/- f2. The presence of these off-diagonal components shows that, in addition to the phase and gain characteristics of auditory filters, the Wiener kernel analysis reveals nonlinear two-tone interactions.

Are spontaneous otoacoustic emissions generated by self-sustained cochlear oscillators?

Theoretical analyses supporting the assumption that spontaneous otoacoustic emissions (SOAEs) can be described as self-sustained oscillations (requiring a power source) are reviewed and extended. Spectral and statistical properties of spontaneous otoacoustic emissions are examined and shown to be consistent with this assumption. Several alternative models of spontaneous emissions (noise-driven saturating memoryless nonlinearity, noise-driven nonlinear-stiffness oscillator) are examined. Although some of these models are able to produce the types of statistical distributions of amplitude and displacement similar to those observed in the experimental data, this similarity is destroyed upon narrow-band filtering.