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PubMed1987

The impedance bridge and ENG controlled fistula test: results in children with unilateral deafness and comparison with normal controls.

The diagnosis of a perilymph fistula is normally made on clinical grounds. Thus in most cases suspicion is raised by the clinical history and the presence of a fistula confirmed at operation. In children such fistulae may be relatively silent and the diagnosis difficult to establish. This paper reports the results of using an impedance bridge and ENG-controlled fistula test in the routine screening of 24 children with unilateral sensorineural deafness, and compares the results obtained to those found from testing 21 normal and asymptomatic children of comparable age and sex. These tests have shown that fistula testing may mimic a previously recorded gaze or positional nystagmus and hence give false positive results. In the routine testing of patients with deafness only 1 subject had nystagmus invoked by fistula testing alone, and in this case it was obvious from all other criteria that no fistula was present. The conclusions drawn are that the method is prone to error if spontaneous, gaze and positional nystagmus are not recorded and that in routine clinical use the test may produce erroneous results. New criteria for the interpretation of the test in children are suggested, but it seems that the best means of diagnosis still remains an accurate history and a readiness to explore the ear to confirm the diagnosis.

Acoustic Impedance Tests↗
PubMed1983

Effect of sound stimulation at several levels on concentrations of primary amines, including neurotransmitter candidates, in perilymph of the guinea pig inner ear.

Perilymph, which bathes the sensory cells of the cochlea, was collected from guinea pigs exposed to noise and analyzed via two cation-exchange HPLC procedures with fluorescence detection, resolving 51 and 81 primary-amine compounds, respectively, at a sensitivity limit of 0.1 pmol relative to leucine. During a first period, each animal was either exposed to noise at 80, 90, or 115 decibels sound-pressure level or maintained in silence (controls), and during a second period, the same animal was maintained in silence. Perilymph was collected during both periods, and perilymphatic components were compared, within animals and across animals, for several levels of sound stimulation. A gamma-aminobutyric acid-like component was elevated in the first period in proportion to stimulus intensity by the various methods of comparison, suggesting an auditory-neurotransmitter role for this component. Aspartic acid was elevated in the second period, 2-3.5 h after onset of sound stimulation, compatible with the release of aspartic acid from central auditory synapses. In addition, a methionine-enkephalin-like component, distinct from leucine-enkephalin, was detected in perilymph from control animals and was elevated in response to noise at 115 decibels. Regression coefficients, determined for the relation between sound intensity and first-period concentrations or the difference between first and second-period concentrations, indicated zero linear regression at p = 0.05 for glutamic acid, aspartic acid, glycine, taurine, and 39 other perilymphatic components, consistent with the hypothesis that these compounds are unlikely to be peripheral auditory neurotransmitters.

Acoustic Stimulation↗
PubMed1979

The nature of the negative endocochlear potentials produced by anoxia and ethacrynic acid in the rat and guinea-pig.

1. The alterations in the Na+ and K+ concentrations of the cochlear endolymph and in the endocochlear potential were followed simultaneously by means of ion-sensitive and conventional micro-electrodes during simple anoxia, during anoxia after i.v. ethacrynic acid and after i.v. ethacrynic acid alone. The endolymphatic pH changes were measured separately and the effect of perilymphatic ethacrynic acid upon the endocochlear potential was investigated. 2. The over-all Na+:K+ permeability ratio for the endolymph system was determined in individual animals for the first time using an indirect method. The normal mean values of 0.27 (rat) and 0.38 (guinea-pig) were increased after ethacrynic acid. Permeability changes occurred during anoxia but were delayed in onset. 3. The negative endocochlear potentials in each situation behaved quantitatively like modified K+ diffusion potentials largely dependent upon the K+ and Na+ gradients between endolymph and perilymph.

Animals↗
PubMed1982

Correspondence principle in cochlear mechanics.

When only long waves play the most important part in the cochlea, the response can be described by a most simplified model, the one-dimensional model. When short waves are to be included, a more complex model is needed. The response then depends on the dimensionality of the model and is much harder to obtain. This applies especially to the region in the neighborhood of the point where the basilar membrane shows resonance. Both two- and three-dimensional models have been studied to assess the effects of short and long waves. The relative importance of the part played by short waves depends on the damping constant (or loss factor )delta associated with the resonance of the basilar membrane (BM). For very small delta a three-dimensional model is really necessary, it cannot be replaced by a model of lower dimensionality. When delta is small, but not too small, the three-dimensional model can be made equivalent to a two-dimensional one, provided the latter is modified ina specific manner. This paper shows why this is so and which conditions have to be met. The two-dimensional model must undergo two modifications to effect this equivalence. The first modification ensures that the model has the same long-wave behavior. In the second place, a specific additional mass ("added mass") reactance should be added to Z(kappa). An expression for the limiting value of delta, above which this correspondence is valid, is given in the paper. A second, larger, limit is presented as well: when delta is above this limit, the responses of both the three-dimensional and the two-dimensional model are equivalent to that of an appropriately chosen one-dimensional model. In this case too, long-wave behavior must be matched and an "added mass" reactance must be included in Z(kappa). This holds true for the entire cochlea including the region of resonance. For both types of transition the amount of "added mass" is given.

Basilar Membrane↗
PubMed1983

Dependence of noise-induced hearing loss upon perilymph magnesium concentration.

Noise-induced hearing loss (NIHL) is significantly greater in rats fed a magnesium-deficient diet than in rats on a magnesium-rich diet. The hearing loss was found to be negatively correlated with the magnesium concentration of the perilymph. It is suggested that also in man, the magnesium concentration in the perilymph may be of importance in determining susceptibility to NIHL.

Animals↗
PubMed1983

Effects of perilymph viscosity on low-frequency intracochlear pressures and the cochlear input impedance of the cat.

Cochlear model calculations are shown to be in reasonable agreement with recent low-frequency measurements of intracochlear pressures and the cochlear input impedance of the cat [V. Nedzelnitsky, J. Acoust. Soc. Am. 68, 1676-1689 (1980); T. J. Lynch, III, V. Nedzelnitsky, and W. T. Peake, J. Acoust. Soc. Am. 72, 108-130 (1982)]. Included in the cochlear model are perilymph viscosity, the measured variation of the area of the scala vestibuli with distance from the stapes [P. Dallos, J. Acoust. Soc. Am. 48, 489-499 (1970)], and finite impedance of the round window membrane. The WKB approximation and its extension to the low-frequency region is used in order to exhibit explicitly the dependence of the model results on the cochlear parameters.

Acoustic Impedance Tests↗
PubMed1985

The anatomical consequences of acoustic injury: A review and tutorial.

The anatomic consequences of acoustic overstimulation are explored in this presentation, and attention is directed toward issues where improvements in technology and empirical observation are needed before further advances in our understanding can be achieved. Gains have been made in the last decade in appreciating sound-induced cochlear injury, but there is now a need to evaluate not only cochlear pathology but also the functional state of the surviving structures. There is a wealth of information about the susceptibility of inner or outer hair cells to acoustic injury; however, the etiology of this injury is not yet fully understood. In addition, current ideas concerning the effects of noise on hair-cell stereocilia, hair-cell synapses, the cochlear vascular supply, and the central auditory pathways are in a state of flux and are either undergoing revision or emerging. Other issues, such as the basis of temporary or permanent threshold shift at the cellular level, and the individual differences in susceptibility to injury are in need of a fresh approach. It would seem that the time is now ripe to review our knowledge, recognize its gaps, and develop testable hypotheses concerning the mechanisms of acoustic injury to the ear.

Animals↗
PubMed1989

Nonlinear and active two-dimensional cochlear models: time-domain solution.

A numerical solution method for two-dimensional (2-D) cochlear models in the time domain is presented. The method has particularly been designed for models with a cochlear partition having nonlinear and active mechanical properties. The 2-D cochlear model equations are reformulated as an integral equation for the acceleration of the basilar membrane (BM). This integral equation is discretized with respect to the spatial variable to yield a system of ordinary differential equations in the time variable. To solve this system, the variable step-size, fourth-order Runge-Kutta method described in Diependaal et al. [J. Acoust. Soc. Am. 82, 1655-1666 (1987)] is used. This method is robust and computationally efficient. The incorporation of a simple middle-ear model can be handled by this method. The method can also be extended to models in which the cochlear partition at each point along its length is represented by more than one degree of freedom.

Basilar Membrane↗
PubMed1990

Flow of endolymph in the inner spiral sulcus and the subtectorial space.

Flows of endolymph within the inner spiral sulcus and the subtectorial space are studied analytically. These flows are driven by boundary displacements and scala media pressure, all prescribed in the form of traveling sine waves with uniform amplitude, wave speed, and wavelength. Prescribed boundary displacements have no axial components and are assumed "small." In the subtectorial space, waves are further assumed "long," and inner and outer hair cells' stereocilia are represented by permeable barriers. Boundary motions of the subtectorial space are assumed to be associated with basilar membrane motion. The localized boundary motions that would presumably accompany independent outer hair cell motions are not admitted. The pressure drop across the barrier representing the inner hair cells' stereocilia is evaluated for four specific input conditions. The results are used to assess its relative sensitivity to three types of boundary displacement and to examine the contribution of endolymph flow to the "second filter." The model predicts the introduction of appreciable tuning (102.3 dB/octave) into the auditory signal between the stages of relative normal displacement of the boundaries of the subtectorial space and the generation of a pressure drop across the inner hair cells' stereocilia. The outer barrier is removed from the model, and the pressure drop across the inner barrier is reevaluated for the same four cases to study its sensitivity to destruction of the outer hair cells' stereocilia. These results are examined in light of data by Robertson and Johnstone [D. Robertson and B. M. Johnstone, J. Acoust. Soc. Am. 66, 466-469 (1979)].

Acoustic Stimulation↗
PubMed1978

Detection of an auditory nerve--activating substance.

A substance or substances capable of increasing the firing rate of primary auditory fibers is detectable in the perilymph of frogs and guinea pigs subjected to sound stimulation. The increase in firing rate occurs in single units of the frog auditory nerve after perilymph obtained from frogs or guinea pigs during sound stimulation is infused into the frog perilymphatic sac. Perilymph collected from animals maintained in silence failed to cause an increase in firing rate of primary auditory fibers of the frog.

Animals↗