Does the endolymphatic sinus function as a one-way valve?
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Animals↗
Biomedical subjects
Hero P Wit
Publications and source records attributed to Hero P Wit.
A simple model for the generation of the vestibular evoked myogenic potential (VEMP).
OBJECTIVE: To describe the mechanism by which the vestibular evoked myogenic potential is generated. METHODS: Vestibular evoked myogenic potential generation is modeled by adding a large number of muscle motor unit action potentials. These action potentials occur randomly in time along a 100 ms long time axis. But because between approximately 15 and 20 ms after a loud short sound stimulus (almost) no action potentials are generated during VEMP measurements in human subjects, no action potentials are present in the model during this time. RESULTS: The evoked potential is the result of the lack of amplitude cancellation in the averaged surface electromyogram at the edges of this 5 ms long time interval. CONCLUSIONS: The relatively simple model describes generation and some properties of the vestibular evoked myogenic potential very well. SIGNIFICANCE: It is shown that, in contrast with other evoked potentials (BAEPs, VERs), the vestibular evoked myogenic potential is the result of an interruption of activity and not that of summed synchronized neural action potentials.
Action Potentials↗
The ordering of milestones in language development for children from 1 to 6 years of age.
PURPOSE: To scale language milestones in a group of 527 children to provide an instrument for screening language development. Procedure The questionnaire regarding these milestones was completed by parental report. It was evaluated whether the scaled milestones satisfied the assumptions of the Mokken item response model. RESULTS: The scalability of the final scale of 14 milestones was strong (H = .95), its reliability was high (rho = .96), and it satisfied the assumptions of the Mokken model. CONCLUSIONS: A single, unidimensional scale of diverse milestones was developed. It taps lexical, syntactic, and phonological skills, as well as both receptive and expressive language skills, and is well suited for mapping progress in language ability.
Age Factors↗
Evaluation of the relation between audiometric and psychometric measures of hearing after tympanoplasty.
The objective of this prospective study was to evaluate the relation between audiometric and psychometric measures after tympanoplasty from the perspective of preoperative selection of patients and postoperative assessment of the results of reconstructive middle ear surgery. Hearing (dis)ability was measured by means of pure-tone audiometry and a validated self-assessment questionnaire: the (modified) Amsterdam Inventory of Auditory Disability and Handicap (m)AIAD. Average hearing thresholds and (m)AIAD scores were evaluated for 80 patients, pre- and 12 months postoperatively. The average improvement of the air conduction threshold in the operated ear was 5.4 (+/-14.3) dB; the average improvement in the (m)AIAD score was 2.9 points (+/-12.1). Although not very strong, the audiometric improvement and increase in (m)AIAD score are significantly related. After the calculation of postoperatively measured mean scores on the (m)AIAD for different 10-dB intervals of postoperative hearing loss averaged over both ears, an interesting relation between the (m)AIAD score and hearing losses emerges. The (m)AIAD score is almost independent of hearing loss for postoperative hearing levels between 25 and 40 dB. Residual hearing loss has to become less than 25 dB before a smaller hearing loss corresponds with a higher (better) (m)AIAD score. For losses larger than 40 dB the (m)AIAD score clearly decreases with increasing hearing loss. Finally, even small residual hearing losses lead, on average, to (m)AIAD scores that are substantially lower than the score for normally hearing subjects. In general, the patient benefit seems related to the magnitude of improvement in the air-conduction thresholds, rather than to the achievement of a certain threshold level. In addition, even small residual hearing losses (less than 25 dB HL) still lead, on average, to (m)AIAD scores that are substantially lower than the scores for normally hearing subjects.
Adolescent↗
Analysis of cortisol and other stress-related hormones in patients with Ménière's disease.
OBJECTIVE: To evaluate cortisol and catecholamine levels in patients with Ménière's disease. STUDY DESIGN: Prospective, controlled study. SETTING: Tertiary referral center. PATIENTS: Thirty patients with Ménière's disease and 18 healthy controls. MAIN OUTCOME MEASURES: Serum and saliva cortisol, serum cortisol after the dexamethasone suppression test, urine free cortisol, and urine catecholamines. RESULTS: The serum and saliva cortisol levels were higher in Ménière's patients compared with their control group: 440 +/- 127 (n = 28) versus 366 +/- 90 (nmol/L) (n = 18) and 17.2 +/- 6.1 (n = 18) versus 11.6 +/- 4.6 (nmol/L) (n = 9), respectively. Both differences were significant (p < 0.05). There were no dissimilarities in urine cortisol or urine catecholamines for either group. Twenty-eight Ménière's patients were divided into two subgroups, namely, high- and low-cortisol groups, using a serum cortisol level cutoff point of 465 nmol/L (median). The total Ménière's disease time and the duration of tinnitus tended to be longer in the high-cortisol group (p = 0.07, two-tailed). The total Ménière's disease time was 13.5 +/- 9.9 years in the high-cortisol group and 7.1 +/- 7.4 years in the low-cortisol group (n = 14 for both). The subgroups were matched for age, gender, and unilaterally or bilaterally affected ears. CONCLUSION: Patients with Ménière's disease have higher serum cortisol levels. It is suggested that these higher cortisol levels are rather the result than the cause of this chronic disease, because patients affected longer seem to have higher cortisol levels. The exact impact of these higher cortisol levels on the inner ear and endolymph homeostasis is yet unknown.
Adult↗
Evaluation of cochlear function in an acute endolymphatic hydrops model in the guinea pig by measuring low-level DPOAEs.
During and after microinjection of artificial endolymph into scala media of the guinea pig, the 2f1- f2 -DPOAE at 4.5 kHz generated by low-level primaries was recorded. Reproducible changes were measured when 1.1 microl of artificial endolymph was injected at a rate of 1.65 nl/s (1.53-1.83). This volume corresponds with an acute endolymphatic hydrops of 23%. After the onset of injection the inner ear pressure immediately increased to a mean higher level of 22 Pa, whereas the 2f1- f2 -amplitude and -phase did not change for about 1 min. Thereafter, the amplitude decreased 2.6 dB (+/- 0.7) on average and slowly regained almost its initial value, with recovery frequently starting within the period of injection. In an attempt to explain the observed changes in 2f1- f2 -amplitude the basilar membrane displacement towards scala tympani at the 2f1- f2 generation site is estimated to be 19 nm for a 1.1 microl increase of endolymph volume. A small deflection of the outer hair cell stereocilia and as a consequence a change in cell conductance may explain the 2f1- f2 -amplitude changes. However, the precise mechanism of cochlear function change caused by endolymph volume increase (hydrops) remains to be elucidated.
Acute Disease↗
Direct measurement flow resistance of cochlear aqueduct in guinea pigs.
OBJECTIVE: The cochlear aqueduct connects the scala tympani to the subarachnoid space and is the main pressure equalization canal for the inner ear. Increases in inner ear volume and pressure are thought to cause clinical symptoms such as vertigo, tinnitus and fluctuating hearing loss. In this study the flow resistance of the cochlear aqueduct was determined and its relation with inner ear pressure was studied. MATERIAL AND METHODS: Inner ear pressure was measured in the scala tympani through the round window using a micropipette. Through a second micropipette, artificial perilymph was infused into, or withdrawn from, the scala tympani at various constant rates. From the infusion rate and the change in perilymphatic pressure during infusion the flow resistance of the cochlear aqueduct was calculated. RESULTS: The flow resistance was found not to be constant but to depend on the position of the round window membrane and possibly on the magnitude and direction of fluid flow through the aqueduct. Measured flow resistance values were in the range 11-45 Pa s/nl. For very small flow values the flow resistance averaged over 6 animals was 21 Pa s/nl. CONCLUSIONS: The flow resistance of the cochlear aqueduct is not a constant value. The cochlear aqueduct is a canal with dynamic properties and may play a role in the complicated process of inner ear pressure regulation.
Animals↗
Cochlear aqueduct flow resistance is not constant during evoked inner ear pressure change in the guinea pig.
Inner ear fluid pressure was measured during 6.25 mHz square wave middle ear pressure manipulation, with a perforated tympanic membrane. After a negative-going middle ear pressure change the calculated flow resistance of the inner ear pressure release routes (mainly the cochlear aqueduct) was approximately constant, with a value of 12 Pa s/nl (averaged over two ears), when values for the inner ear window compliance are taken from the literature. After a positive-going middle ear pressure change the calculated flow resistance changed with round window position and with the pressure difference across the cochlear aqueduct. It reached an average maximum value of 114 Pa s/nl. The change of flow resistance during inner ear pressure variation can be explained by a permeability change of the cochlear aqueduct, caused by a change of structures filling the aqueduct and its entrance in scala tympani.
Animals↗
Quantification of audiogram fine-structure as a function of hearing threshold.
We investigated the amount of fine-structure in the audiograms of patients with Menière's disease. Both ears (often an affected and an unaffected ear) were investigated. Data are presented from 39 ears of 21 patients with hearing thresholds varying from about 0 to 70 dB HL. The fine-structure was measured in the frequency range from 500 to 3500 Hz; this agrees with a part of the basilar membrane from 10 to 22.5 mm from the apex. The fine-structure was characterized by means of the number of peaks N(p) and the sum S(p) of the heights of all the peaks in an audiogram. From these quantities, we also determined average peak height H(p). We found a negative correlation between hearing loss and strength of fine-structure, i.e. the higher the thresholds the smaller N(p) and S(p) as well as H(p). Also N(p) and H(p) were correlated, i.e. the more peaks the higher the average peak height. The summated peak height S(p)=N(p)H(p) showed a strong dependence on the hearing loss. In cases of strong fine-structure, S(p) reached values around 200 dB.
Adult↗
Reliability and validity of the (modified) Amsterdam Inventory for Auditory Disability and Handicap.
This study investigated the psychometric adequacy of the (modified) Amsterdam Inventory for Auditory Disability and Handicap ((m)AIAD). The original version of the AIAD was developed by Kramer et al in 1995. Special emphasis was placed on the statistical aspects of the scores, because these properties place limits on the clinical utility of the instrument. The AIAD is a self-assessment questionnaire that consists of 30 questions covering all the relevant factors of disability in individual hearing functioning in daily life. This paper reports data from 94 subjects, aged 17-65 years, with different hearing abilities, who completed a modified version of the AIAD and the Hearing Disability Questionnaire (HDQ), on two occasions 1 month apart. The psychometric adequacy of the AIAD was determined by measuring its reliability and validity. Factor analysis was performed, and the reliability was tested by measuring internal consistency, split-half correlation, and test-retest reproducibility. The validity was tested by measuring construct and criterion validity. The results showed that the reliability of the (m)AIAD was highly satisfactory, with good internal consistency, high split-half correlations, and high test-retest correlations. Construct validity showed a high correlation between scores on the (m)AIAD and scores on the HDQ. Criterion validity showed a moderate but significant correlation between scores on the (m)AIAD and hearing thresholds in dB HL.
Adolescent↗
Cochlear ultrastructure in two-phase endolymphatic hydrops in the guinea-pig.
Endolymphatic hydrops continues to be considered as a pathological factor in the etiology of Meniere's disease. We have developed the two-phase endolymphatic hydrops model, which seems to represent a functional model combining multiple etiologies, and which may resemble the fluctuating characteristics of Meniere's disease. A transmission electron microscopic study was performed on the endolymphatic sacs of four groups of guinea-pig cochleas: (1) controls, (2) non-operated, aldosterone-treated cochleas, (3) operated (dissection of the endolymphatic sac) cochleas, (4) operated and aldosterone-treated cochleas. Light and electron microscopy showed a normal morphology in the controls. Aldosterone as a single treatment resulted in an increased activity of the marginal cells in the stria vascularis. Dissection induced a gradient of degenerative effects and cell loss in the intracellular and extracellular structures of the sensory cells, the stria vascularis and Reissner's membrane, which may be reversible. Subsequent administration of aldosterone induced severe damage and increased cell loss, which may be irreversible. Our findings demonstrate changes that may be reversible due to the compromising effect of a single treatment, and irreversible changes due to interaction of both compromising factors. These findings support our two-phase concept.
Animals↗
Detection of intracochlear and intracranial pressure changes with otoacoustic emissions: a gerbil model.
Increased intracranial pressure (ICP) is known to affect the phases and levels of lower-frequency distortion-product otoacoustic emissions (DPOAE) in a characteristic manner suggestive of an increase in the stiffness of the stapes system, likely in relation to an attendant increased intracochlear pressure (ICoP). DPOAEs may thus provide an easy non-invasive means of gaining access to the otherwise elusive ICoP. However, the mechanisms by which DPOAEs actually relate to ICoP are unclear and may involve changes in the stiffness of the annular ligament, stapedius muscle and even some indirect contributions of other parts of the middle ear such as the tensor tympani. A systematic study of the role of each middle-ear element on ICoP-to-DPOAE relationships as a function of frequency was undertaken in gerbils under direct control of ICP via an intracranial catheter (from 0 to 500 daPa). After the bulla was widely opened, the tendons of the stapedius and tensor tympani muscles were severed in turn. A standard electroacoustic analog model of the middle ear was used for predicting the forward and reverse middle-ear transfer-functions changes under different experimental manipulations and their consequences on DPOAEs. The observed DPOAE changes chiefly consisted in a phase-lead peaking around 2.15 kHz in closed-bulla, and 1.2 kHz in open-bulla conditions. It was proportional to ICP increase provided ICP exceeded a threshold of about 50 daPa. The profiles of DPOAE shifts matched those derived from the premise that ICoP mainly induced a change in the stiffness of the stapes system. The possible involvement of the stapedius muscle was ruled out by the absence of any effect of cutting its tendon so that the intrinsically non-linear stiffness of the annular ligament must have been the main factor. A relatively minor contribution from the tensor tympani was observed, possibly in relation to the detection of ICoP-induced displacement of the ossicular chain by neuromuscular spindles.
Animals↗
Evoked otoacoustic emissions in patients with Ménière's disease.
HYPOTHESIS: This study investigated whether otoacoustic emissions (OAEs) in patients with Ménière's disease show abnormal properties. BACKGROUND: Patients with Ménière's disease experience vertigo, tinnitus, and hearing loss. OAEs are sounds generated in the inner ear, and their presence is associated with normal hearing. METHODS: Click-evoked OAEs and distortion product OAEs were measured in 100 patients with Ménière's disease. RESULTS: The incidence of the emissions in affected ears (56%) was lower than in unaffected (i.e., contralateral) ears (85%). The mean emission amplitude in affected ears was also significantly lower (2.6 dB), and the mean amplitude in unaffected ears was lower than in normal-hearing ears (5.3 dB). These differences were likely caused by the hearing loss involved. Further, ears with OAEs clearly showed smaller hearing losses than ears without OAEs (24-dB difference). The average hearing loss showed correlations with the emission amplitudes, although this correlation was not very strong; when plotted against the smallest hearing loss, a certain upper boundary for the emission amplitude was present. Also, the amplitude of click-evoked OAEs showed a considerable correlation with the largest of the three distortion product OAEs. CONCLUSION: OAEs in patients with Ménière's disease differed from those in normal-hearing ears but did not differ from those in non-Ménière's ears with equivalent hearing loss. This was best observed by comparing emission amplitude with smallest hearing loss instead of mean hearing loss.
Acoustic Stimulation↗