Asymmetric vestibular evoked myogenic potentials in unilateral Menière patients.

Vestibular evoked myogenic potentials (VEMPs) were measured in 22 unilateral Menière patients with monaural and binaural stimulation with 250 and 500 Hz tone bursts. For all measurement situations significantly lower VEMP amplitudes were on average measured at the affected side compared to the unaffected side. Unilateral Menière patients have, in contrast to normal subjects, asymmetric VEMPs, indicating a permanently affected vestibular (most likely otolith) system at the side of hearing loss. The diagnostic value of VEMP amplitude asymmetry measurement in individual patients is low, because of the large overlap of the VEMP amplitude asymmetry range for unilateral Menière patients with that for normal subjects.

The effect of changes in perilymphatic K+ on the vestibular evoked potential in the guinea pig.

To investigate the effect on the functioning of the vestibular system of a rupture of Reissner's membrane, artificial endolymph was injected in scala media of ten guinea pigs and vestibular evoked potentials (VsEPs), evoked by vertical acceleration pulses, were measured. Directly after injection of a sufficient volume to cause rupture, all ears showed a complete disappearance of VsEP, followed by partial recovery. To investigate the effect of perilymphatic potassium concentration on the vestibular sensory and neural structures, different concentrations of KCl were injected directly into the vestibule. The KCl injections resulted in a dose-dependent decrease of VsEP, followed by a dose-dependent slow recovery. This animal model clearly shows a disturbing effect of a higher than normal K(+) concentration in perilymph on the vestibular and neural structures in the inner ear. Potassium intoxication is the most probable explanation for the observed effects. It is one of the explanations for Menière attacks.

Three-dimensional reconstruction of the pigeon inner ear.

Three-dimensional reconstructions of the inner ear of the pigeon (Columba livia domestica), from two-dimensional images, obtained with (conventional) light microscopy or orthogonal-plane fluorescence optical sectioning (OPFOS), are presented. The results are compared with available information on the dimensions and orientation of the semicircular canals.

Acute endolymphatic hydrops has no direct effect on the vestibular evoked potential in the guinea pig.

To investigate the effect of an acute endolymphatic hydrops on the functioning of the vestibular system a hydrops was created by microinjection of artificial endolymph through the basilar membrane into scala media in 10 guinea pigs. To control for the effect of perforation of the basilar membrane, the same procedure was performed in 9 other guinea pigs, but without injection of endolymph. Contralateral ears served as control ears. Vestibular evoked potentials, evoked by vertical acceleration pulses applied to the guinea pig's head, were measured in all ears before, immediately after, and 2, 4, and 5 hours after perforation/injection. Acute endolymphatic hydrops did not affect the amplitude of the VsEP immediately after injection. After 4 to 5 hours VsEP was significantly reduced in both hydrops and perforated-only ears, compared to control ears. However, no significant difference was found between VsEP of the hydrops ears and perforated-only ears. Reduction of VsEP is not caused by a direct hydromechanical effect on the vestibular system, but possibly by leakage of perilymph through the perforation hole, supporting the membrane rupture theory for Menière-attacks.

A Bast-like valve in the pigeon?

The first description of the presence of a utriculo-endolymphatic valve in human fetuses was given by Bast in 1928. Since then this valve-like structure is called Bast's valve. Its exact function has not yet been established. The general opinion is that it has a protective function by having the possibility to separate the superior endolymphatic compartments of the labyrinth from the inferior compartment. Phylogenetically seen birds are the first vertebrates with a cochlear duct and a distinct inferior and superior part of the labyrinth. A structure in the pigeon inner ear, resembling Bast's valve in mammals, is described.

Three-dimensional reconstruction of the guinea pig inner ear, comparison of OPFOS and light microscopy, applications of 3D reconstruction.

Three-dimensional (3D) reconstruction of anatomical structures can give additional insight into the morphology and function of these structures. We compare 3D reconstructions of the guinea pig inner ear, using light microscopy and orthogonal plane fluorescence optical sectioning microscopy. Applications of 3D reconstruction of the inner ear are further explored. For each method two bullas were prepared for 3D reconstruction. Both methods are explained. In general, the 3D reconstructions using orthogonal plane fluorescence optical sectioning microscopy are superior to light microscopy. The exact spiral shape of the cochlea could be reconstructed using orthogonal plane fluorescence optical sectioning microscopy and the length of the basilar membrane measured. When a resolution of 20 microm is sufficient, orthogonal plane fluorescence optical sectioning microscopy is a superior technique for 3D reconstruction of inner ear structures in animals.

Changes in CMDP and DPOAE during acute increased inner ear pressure in the guinea pig.

During and after an increase of inner ear pressure, induced by injection of artificial perilymph, the 2f1 - f2 and f2 - f1 distortion products (DPs) in cochlear microphonics (CM) and otoacoustic emissions (OAE) were recorded in the guinea pig. An inner pressure increase of approximately 600 Pa gave only small changes in CMDP and DPOAE. Along with a decrease in f1 amplitude, a small decrease in amplitude of the 2f1 - f2 and a small increase in the f2 - f1 were measured in CM. This matches a shift from a symmetrical position of the operating point for hair cell transduction, leading to an increase in even-order distortion and a decrease in odd-order distortion. Similar, a decrease in 2f1 - f2 DPOAE was expected. This might be the case at the generation sites but this effect was then more than compensated for by a better middle ear transfer, accounting for the increase of 0.4 dB of the 2f1 - f2 DPOAE amplitude. In conclusion, changes of overall inner ear fluid pressure have minor effects on cochlear function. This is a relevant finding for further understanding of diseases with changed inner ear fluid volumes, as Ménière's.

Morphology and function of Bast's valve: additional insight in its functioning using 3D-reconstruction.

The utriculo-endolymphatic valve was discovered by Bast in 1928. The function of Bast's valve is still unclear. By means of orthogonal-plane fluorescence optical sectioning (OPFOS) microscopy 3D-reconstructions of the valve and its surrounding region are depicted. The shape of the duct at the utricular side is that of a flattened funnel. In the direction of the endolymphatic duct and sac this funnel runs into a very narrow duct. The valve itself has a rigid 'arch-like' configuration. The opposing thin, one cell-layer thick, utricular membrane is highly compliant. We propose that opening and closure of the valve occurs through movement of the flexible base/utricular membrane away from and toward the relatively rigid valve lip.

Functional imaging of the central auditory system using PET.

In the last few decades functional neuroimaging tools have emerged to study the function of the human brain in vivo. These techniques have increased the knowledge of how the brain processes stimuli of different sensory modalities, including auditory processing. Positron emission tomography (PET) has been used for nearly 20 years to study changes in cerebral blood flow associated with auditory stimulation in normal and hearing impaired subjects. PET studies gave insight into the neural base of processing basic sound features such as frequency and intensity, but complex stimuli such as speech and music have also been investigated extensively. Knowledge of the normal auditory function of the brain helps us to understand the neural base of hearing deficits and provides ideas for possible treatments. Although functional magnetic resonance imaging (fMRI) is replacing PET in many neuroimaging studies nowadays, PET still holds unique advantages and can give us valuable knowledge about the auditory cortex and auditory perception.

Psychological assessment of patients with Menière's disease.

The objective of this study was to evaluate daily stressors, coping, personality, physical and mental health, and quality of life in Menière patients. 110 consecutive patients with definite Menière's disease were assessed using the Dutch Daily Hassles List, Coping Inventory for Stressful Situations (CISS), Symptoms Checklist 90 (SCL-90), NEO Five Factor Inventory (NEO-FFI), General Health Questionnaire (GHQ-12), and the Short Form Health Survey 36 (SF-36). Duration and subjective severity of symptoms were scored using a self-report questionnaire. It was shown that Menière patients had more daily stressors, used certain coping strategies less often, and had more psychopathology (e.g. anxiety and depression), and a worse quality of life compared to healthy reference groups. No abnormalities in personality were found. Patients with more severe symptoms had more psychopathology and a worse quality of life than patients with mild symptoms. The psychological profile of Menière patients seems comparable to patients with other chronic diseases. The outcomes should be used to intensify psychological support in patients with this disabling disease.

Rupture of Reissner's membrane during acute endolymphatic hydrops in the guinea pig: a model for Ménière's disease?

CONCLUSION: The changes in cochlear function during a destructive acute endolymphatic hydrops were relatively small. This might be consistent with the hypothesis that an endolymphatic hydrops is a marker of disordered inner ear homeostasis rather than the cause of the clinical symptoms of Ménière's disease. OBJECTIVE: Assessment of cochlear function during induction of a destructive acute endolymphatic hydrops. MATERIALS AND METHODS: During repetitive microinjections of 0.5 microl of artificial endolymph at a rate of 50 nl/s the 2f1-f2 and f2-f1 cochlear microphonics distortion products (CMDP) and 2f1-f2 distortion products otoacoustic emissions (DPOAE) were recorded in the guinea pig. RESULTS: A 'catastrophe' occurred in the inner ear when 2.5-3.5 microl of artificial endolymph was injected. A rupture of Reissner's membrane was then found, most often in the apical turn of the cochlea. This rupture had only minor effects on the endocochlear potential, whereas it caused a marked decrease in 2f1-f2 DPOAE amplitude. The 2f1-f2 and f2-f1 CMDP amplitude increased during each injection prior to the rupture. After the rupture the f2-f1 CMDP amplitude decreased during each injection, possibly due to a shift of the cochlear transducer operating point position.

Changes in distortion of two-tone cochlear microphonic and otoacoustic emission signals during an acute endolymphatic hydrops in the guinea pig.

An acute endolymphatic hydrops was induced by the injection of 1.1 mul of artificial endolymph into the scala media of guinea pig cochleas. This volume corresponds with an acute endolymphatic hydrops of 23%. During and after the injection, cochlear function was assessed by measuring the 2f(1)-f(2 )and f(2)-f(1) distortion products in cochlear microphonics (CMDP) and the 2f(1)-f(2) distortion product otoacoustic emission (DPOAE). A reversible pressure increase of 23 Pa and a relatively stable endocochlear potential (EP) were accompanied by a mean decrease in 2f(1)-f(2) DPOAE of only 3.4 dB. Similarly, the 2f(1)-f(2) CMDP amplitude change was minimal during and after the injection. The only substantial change was measured in the f(2)-f(1) CMDP amplitude. The measured range of distortion amplitudes during an acute endolymphatic hydrops can be related to small changes in the cochlear transducer operating point.

The relationship of the round window membrane to the cochlear aqueduct shown in three-dimensional imaging.

The round window membrane and cochlear aqueduct complex in the guinea pig are reconstructed with 3D-imaging, using orthogonal plane fluorescence optical sectioning (OPFOS). The 3D-images show that the periotic duct and the aqueduct are connected to a pouch-like extension of the round window. The function of this may be regulation of aqueduct flow resistance under the influence of a pressure difference between inner ear fluid and middle ear.

Morphology of the endolymphatic sac in the guinea pig after an acute endolymphatic hydrops.

The role of the endolymphatic sac (ES) in endolymph volume homeostasis is speculative. The present study investigates changes of the ES's epithelia and luminal filling after induction of an acute endolymphatic hydrops. After microinjection of 1.1 mul artificial endolymph into scala media of the cochlea, guinea pigs were terminated immediately (n = 6) or after different time intervals ; 1/2 h (n = 3), 1 h (n = 4) and 2 h (n = 4). Inner ear specimens were processed for light and/or transmission electron microscopy. The non-injected contralateral ear served as a histological control. Correct injection was confirmed by detection of microspheres in the endolymphatic compartment after the same microinjection procedure. In all specimens, ribosome rich cells and intraluminal macrophages appeared to be actively involved in degradation of homogeneous substance (HS) by secreting lytic enzymes and digestion, respectively. Amazingly, in our study no ES differences were found between injected and non-injected ears and no distinct changes were observed in guinea pigs terminated after different time intervals. The ES's luminal HS was always present and often to a large extent. This is in contrast with [Hear. Res. 138, 81] dramatic changes were observed. Endolymph volume homeostasis is a complex mechanism, in which the role of HS remains obscure.

Relation between change of hearing and (modified) Amsterdam Inventory for Auditory Disability and Handicap Score.

This study investigates the test-retest distributions and the interval for true score change of the (modified) Amsterdam Inventory for Auditory Disability and Handicap [(m)AIAD], when the latter is used to measure the effect of an intervention. In a previous study the reliability and validity of the (m)AIAD in a cohort of hearing impaired patients were found to have satisfactory high values. In this prospective study, 66 patients underwent a tympanoplasty operation. Preoperatively and postoperatively pure tone audiometry was performed, and at the same time the subjective hearing ability was established by means of the (m)AIAD. The correlation between threshold change and score change was 0.35 (Pearson's r). Scores on the (m)AIAD had to change by at least 16 to be qualified as a true change. For only nine of 66 subjects this criterion was fulfilled. No clear relation exists, except for these nine subjects, between threshold change and score change in this patient population. The study also shows that disability questionnaires have their limitations, when using them to measure the result of a medical intervention in an individual patient.

Effect of acute inner ear pressure changes on low-level distortion product otoacoustic emissions in the guinea pig.

OBJECTIVE: To determine a relation between acute inner ear pressure changes and cochlear function as measured by low-level 2f(1)-f(2) distortion product otoacoustic emissions (DPOAEs). MATERIAL AND METHODS: During and after a change in inner ear pressure induced by injection or aspiration of perilymph, the 2f(1)-f(2) DPOAE at 4.5 kHz generated by low-level primaries was recorded in the guinea pig. RESULTS: Large changes in overall inner ear pressure produced only small changes in the 2f(1)-f(2) amplitude and phase. During injection of 0.5 microl of artificial perilymph into the scala tympani over a 10-s period, the mean inner ear pressure increased by approximately 500 Pa, with an accompanying mean increase in the 2f(1)-f(2) amplitude of 0.7 dB. During aspiration of 0.5 microl of perilymph over a 10-s period, the mean inner ear pressure decreased by approximately 700 Pa, with an accompanying mean decrease in the 2f(1)-f(2) amplitude of 0.9 dB. Changes in DPOAE amplitude followed inner ear pressure changes with a delay of 1-2 s. The magnitude and sign of the amplitude changes can (partly) be explained by a change in oval window stiffness. No explanation was found for the measured delay. CONCLUSION: Clinically, these experiments can be of value in gaining insight into the pathophysiological mechanisms of pathological pressure changes as seen in Meniere's disease and perilymphatic fistulae.

Cochlear aqueduct flow resistance depends on round window membrane position in guinea pigs.

The resistance for fluid flow of the cochlear aqueduct was measured in guinea pigs for different positions of the round window membrane. These different positions were obtained by applying different constant pressures to the middle ear cavity. Fluid flow through the aqueduct was induced by small pressure steps superimposed on these constant pressures. It was found that the resistance for fluid flow through the aqueduct depended on the round window position but not on flow direction. The results can be explained by special fibrous structures that connect the round window with the entrance of the aqueduct. It was also found that the equilibrium inner ear pressure depends on middle ear pressure, indicating that the aqueduct does not connect the inner ear with a cavity with constant pressure.

Perilymphatic and endolymphatic pressures during endolymphatic hydrops.

We analysed the fluid pressure in the perilymphatic and endolymphatic spaces of the cochlea in eight guinea pigs after endolymphatic hydrops (EH) was surgically created. The control experiments were done in the opposite ears. EH was histologically confirmed after the conclusion of the pressure measurements. No statistically significant pressure difference between the scala media and the scala tympani was found, either in ears with EH or the control ears. However, the endocochlear potential, which we evaluated for position verification of the measurement pipette in the cochlea, was statistically significantly decreased in ears with EH.

Change of guinea pig inner ear pressure by square wave middle ear cavity pressure variation.

The inner ear fluid pressure of guinea pigs was measured during square wave middle ear cavity pressure variation. Time constants were derived for the slopes of the inner ear pressure recovery curves after middle ear pressure change. A "single exponential" function did not fit well and therefore more complicated functions were used for this purpose. For middle ear pressure increasing from zero to a few centimetres of water, returning to zero again, decreasing from zero to minus a few centimetres of water and then returning to zero again, time constants for the inner ear pressure recovery curves were on average 15.0, 8.6, 2.5 and 2.5 s, respectively. The results could not be described using a linear model with constant window membrane compliance and cochlear aqueduct flow resistance. A possible explanation for the large difference in time constants for positive or negative middle ear pressure changes is a dependence on aqueduct flow resistance or round window membrane position.

Three-dimensional Fourier transformation constructive interference in steady state magnetic resonance imaging of the inner ear in patients with unilateral and bilateral Menière's disease.

OBJECTIVE: In this study, three-dimensional Fourier transformation constructive interference in steady state (3DFT-CISS) magnetic resonance imaging was used to quantify the distance between the vertical part of the posterior semicircular canal and the posterior fossa as a measure of the endolymphatic sac and duct in patients with Menière's disease. Differences in this distance between affected and unaffected ears, as well as differences between unilaterally and bilaterally affected patients, were studied and compared with a control group. Also, possible correlations between the measured distance and the duration and severity of symptoms, patient age, and average hearing loss were investigated in the group of patients with Menière's disease. STUDY DESIGN: Retrospective clinical study. SETTING: Tertiary referral center (University Hospital) as part of a large, diagnostic research project on Menière's disease. PATIENTS: Of the 111 patients with Menière's disease initially included, 90 patients underwent 3DFT-CISS MRI. Eighty-six of these patients were analyzed in this MRI study. Fifty-six patients had unilateral Menière's disease, and 30 patients had bilateral Menière's disease (116 affected and 56 unaffected ears). Sixty-two ears in patients without Menière's disease were studied as controls. INTERVENTION: The distance between the vertical part of the posterior semicircular canal and the posterior fossa was determined by 3DFT-CISS MRI. MAIN OUTCOME MEASURES: Contiguous axial 3DFT-CISS MRI slices of 0.7 to 1.0 mm were made by a radiologist according to a strict protocol. Measurements of the distance between the vertical part of the posterior semicircular canal and the posterior fossa were taken by two professionals-a radiologist and an otolaryngologist-using a ruler and the original scan. RESULTS: A significantly smaller distance (2.9 mm) between the vertical part of the posterior semicircular canal and the posterior fossa as visualized on MRI scans was found in the ears of patients with Menière's disease than in the ears of patients in the control group (3.8 mm, p < 0.001). In both uni- and bilaterally affected patients (n = 56 and n = 30, respectively), no significant difference between ears was found (p = 0.44 and p = 0.19, respectively). In bilaterally affected patients, however, this distance (3.2 mm) was significantly greater than the distance in unilaterally affected patients (2.7 mm, p = 0.004). There was no relationship between the MRI-visualized distance between the vertical part of the posterior semicircular canal and the posterior fossa and the duration of disease, average hearing loss, or severity of symptoms in uni- and bilaterally affected patients. CONCLUSION: The difference in MRI-visualized distances between the vertical part of the posterior semicircular canal and the posterior fossa of uni- and bilaterally affected patients strongly suggests that unilateral and bilateral hearing loss are two different entities in patients with Menière's disease. The size of the endolymphatic sac seems not to be the only factor in the pathogenesis of Menière's disease. That the MRI-visualized distance between the vertical part of the posterior semicircular canal and the posterior fossa does not have any relationship to the duration of the disease or to patient age indicates that this distance is a congenital feature.