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PubMed1992

Glycocalyx heterogeneity in normal and hydropic cochleas of the guinea pig.

The endo- and perilymphatic glycocalyx of the cochlear epithelia were investigated ultrastructurally in normal and hydropic cochleas using the electron-dense markers cationized ferritin and colloidal thorium. In the normal cochleas all epithelial surfaces showed reactivity with both markers. Using cationized ferritin, no regional differences in reactivity could be demonstrated. With colloidal thorium, however, the apical membranes of the outer hair cells reacted more intensely than either the basolateral membranes or the membranes of the supporting cells of the organ of Corti. Cationized ferritin reactivity was not affected by digestion with either neuraminidase or hyaluronidase. In contrast, colloidal thorium reactivity of the endolymphatic surfaces was greatly reduced after neuraminidase digestion. Reactivity of the cell membranes lining the perilymphatic compartments of the cochlea was less affected by neuraminidase digestion, except for the basolateral membranes of the sensory and supporting cells of the organ of Corti, which demonstrated a greatly reduced reactivity. These findings indicate that the glycocalyx of the epithelial surfaces lining the endolymphatic compartment has a high content of sialic acid. The differences that are observed in normal cochleas in regard to colloidal thorium reactivity between the apical membranes of the outer hair cells and the membranes of the Deiters' cells, could not be demonstrated in hydropic cochleas. This probably contributes to the early functional changes in outer hair cells observed in experimental hydrops.

Animals↗

PubMed1993

Neonatal cochlear hearing loss results in developmental abnormalities of the central auditory pathways.

We have used animal models of long term neonatal cochlear hearing loss to study developmental plasticity of the central auditory pathways. Newborn chinchilla pups and feline kittens were treated with the ototoxic drug amikacin, so as to induce basal lesions in the cochlea. At maturity these animals were used in single unit electrophysiological mapping studies, in which the cochleotopic organization of primary auditory cortex (of the cat) and the inferior colliculus of the midbrain (in the chinchilla) were mapped. We have observed, both in the midbrain and auditory cortex, massive reorganization of frequency representation. Most striking were the presence of large monotonic regions (i.e. large areas in which all neurons have similar tuning properties). Cochlear lesions which involve inner hair cells clearly modify the normal development of cochleotopic representation in the midbrain and cortical regions. We suggest that similar abnormal patterns of frequency representation will exist in human subjects with long term neonatal hearing loss.

Amikacin↗

PubMed1994

Perilymph pressure during hypobaric conditions--cochlear aqueduct obstructed.

Nine cats with the cochlear aqueduct surgically blocked were anaesthetised, put in a pressure chamber, and stepwise exposed to hypobaric pressure, each of the two steps lasting 5 min. The chamber pressure was reduced to -5 and -7 kPa. Concluding the experiment the cats were observed for 5 min after restoration of atmospheric pressure. The perilymph, tympanic cavity, cerebrospinal fluid, central venous, arterial and surrounding chamber pressures were continuously recorded. Reduced chamber pressure caused relative overpressure within the tympanic cavity, thereby inducing pressure gradients between the chamber, the tympanic cavity, the labyrinth and the cerebrospinal fluid and vascular pressures respectively. Our results demonstrate that hypobaric effects on the labyrinth are mediated via pressure changes in the tympanic cavity and not by systemic, vascular or cerebrospinal fluid influence. Substantial perilymph overpressure lasted throughout the hypobaric conditions. The magnitude and the duration of this overpressure were influenced by the patency of the Eustachian tube whereas the rate of the pressure change in the chamber was of little importance. As atmospheric pressure was restored in the chamber the overpressure in the labyrinth was reversed to underpressure--relative to pre-experimental conditions.

Animals↗

PubMed1994

Estimated annual number of patients treated for sensorineural hearing loss in Japan. Results of a nationwide epidemiological survey in 1987.

We mailed questionnaires to 98 university hospitals and 939 hospitals with 200 beds or more throughout Japan asking for information on patients treated for sensorineural hearing loss between January 1 and December 31, 1987. The number of patients treated for sensorineural hearing loss in 1987 in Japan was estimated 13,900-19,600, ii) idiopathic bilateral progressive sensorineural hearing loss 13,900-19,600, ii) idiopathic bilateral progressive sensorineural hearing loss in 800-2,000, iii) perilymphatic fistula in 200-310, iv) mumps deafness in 200-400, and v) unilateral profound deafness in 2,000-3,000. Sex ratio (men over women) was 0.9 in sudden deafness and mumps deafness, 1.1 in idiopathic bilateral progressive sensorineural hearing loss and 1.5 in perilymphatic fistula. Patients were distributed with a definite peak from 50 to 59 years old in sudden deafness, from 30 to 39 years old in perilymphatic fistula, and two apparent peaks in teenagers and those aged 60-69 years in idiopathic bilateral progressive sensorineural hearing loss.

Adolescent↗

PubMed1994

Endoscopic diagnosis of idiopathic perilymphatic fistula.

The usefulness of endoscopic examination for the diagnosis of idiopathic perilymphatic fistula (IPLF) was investigated. Eight patients presenting with unilateral sensorineural hearing loss and vertigo underwent endoscopic examination by the transtubal or transtympanic approach. In 5 out of the 8 patients, transtubal endoscopy was carried out using a superfine flexible endoscope. With this approach, no abnormal findings were visualized. A perilymphatic leak from the round window was observed in 2 patients by means of transtympanic examination using a needle scope. These findings were confirmed in both patients by microscopic observation during tympanotomy. In one patient who was finally diagnosed with IPLF, the transtympanic endoscopy failed to detect perilymphatic leakage. Although incision of the tympanic membrane is necessary for the examination, transtympanic endoscopy is useful for the diagnosis of IPLF. Further improvement of the superfine flexible fiberscope is necessary before transtubal observation of the tympanic cavity can be effectively conducted.

Adult↗

PubMed1997

Synaptic repair mechanisms responsible for functional recovery in various cochlear pathologies.

In some cochlear pathologies, temporary hearing loss can be followed by complete or partial functional recovery. Our previous findings suggest the involvement of an excitotoxic (glutamate-related) disruption of inner hair cell (IHC)-auditory nerve synapses, followed by synaptic regeneration. It is essential to understand the molecular mechanisms responsible for this synaptic repair if new therapeutic strategies are to be developed. In guinea pig cochleas, acute synaptic excitotoxic damage (mimicking what occurs with acoustic trauma or local ischemia) is achieved by locally applying AMPA, a glutamate agonist. This results in a total disruption of all IHC-auditory dendrite synapses, together with a disappearance of cochlear potentials. Within the next 5 days, however, a recovery of both the normal pattern of IHC innervation and the physiological responses is observed. The fact that the blockage of the NMDA receptors during functional recovery delayed the regrowth of neurites and the restoration of hearing suggests that glutamate plays a neurotrophic role via activation of NMDA receptors. Experiments are in progress to investigate, among other factors, the role of other glutamate receptor subunits. A reversible in vivo antisense strategy is being developed to overcome the lack of specificity of some antagonists. First results bode well for future pharmacological therapies in cochlear pathologies where glutamatergic synapses are likely to be involved; i.e., noise trauma, ischemia-related sudden deafness, and neural presbycusis.

Animals↗

PubMed1997

Osmotic drugs in the treatment of cochlear disorders: a clinical and experimental study.

On the grounds of positive results obtained with Meniere's patients, agents such as glycerol and mannitol have been included in the therapeutical protocol of other cochlear disorders presenting with hearing loss either of sudden onset, but not observed at an early stage, or accompanied by tinnitus and aural pressure. Intravenous infusions of either 10% glycerol or 18% mannitol were given to selected patients 3 to 6 times with a time interval of 1 to 3 days. Hearing loss, tinnitus and aural pressure were evaluated as improved, unchanged or worsened. In 33% of the glycerol group and 23.8% of the mannitol group we observed hearing threshold improvement, while aural fullness improved in 45% of the glycerol and 56.2% of the mannitol groups, and tinnitus was only relieved in 13.1% of the glycerol and 5.8% of the mannitol group. A parallel experimental study was carried out on guinea-pigs in order to shed light on the effects of mannitol and glycerol on the inner ear. Cochlear blood flow was measured with a laser Doppler flowmeter at the level of the basal turn of the cochlear lateral wall, both in normal and hydropic guinea-pigs, before and after osmotic intraperitoneal infusion. Basal values in the normal cochlea were much higher than in the hydropic one, and both mannitol and glycerol markedly influenced the local blood flow in the normal cochlea, giving few or no changes in the hydropic one.

Animals↗

PubMedDate not supplied

Tonotopic mapping in auditory cortex of the adult chinchilla with amikacin-induced cochlear lesions.

We have found a reorganization of tonotopic maps (based on neuron response thresholds) in primary auditory cortex of the adult chinchilla after amikacin-induced basal cochlear lesions. We find an over-representation of a frequency that corresponds to the border area of the cochlear lesion. The reorganization observed is similar in extent to that previously seen in a developmental model. The properties of neurons within the over-represented area were investigated in order to determine whether their responses originated from a common input (an indication of true plasticity) or represented only the result of truncating the activity of the sensory epithelium ("pseudo-plasticity"). Some aspects of our data fit with a true plasticity model and indicate the potential for the deafferented cortex of the mature cortex to regain connections with the surviving sensory epithelium.

Amikacin↗

PubMed1990

Frequency specificity of the auditory brainstem response elicited by 1,000-Hz filtered clicks.

In normal-hearing subjects and in subjects with a flat cochlear hearing loss, auditory brainstem responses (ABR) were recorded at various levels of a 1,000-Hz filtered click stimulus with and without high-pass filtered masking noise. The difference in latency of the major peak in the ABR for the masked and unmasked condition was zero at the ABR threshold. We regard this as proof of the frequency specificity of the 1,000-Hz filtered click-stimulated ABR threshold. The difference between ABR threshold and the subjective puretone threshold at 1,000 Hz amounted to 19 dB in normal-hearing subjects and to 10 dB in subjects with a flat cochlear hearing loss. This is probably related to loss of temporal integration and an abnormal loudness growth (recruitment).

Acoustic Stimulation↗

PubMed1990

Changes of stapedius reflex and hearing threshold in patients receiving high-dose cisplatin treatment.

The value of stapedius reflex (SR) measurement in the clinical management of the ototoxic side-effect of cisplatin was examined in 24 patients who had received a dose of 100-120 mg/m2. The main finding was a frequent but inconsistent deterioration of the SR threshold (SRT) at 3 and/or 4 kHz, usually with a moderate rise of the hearing threshold (HT) in the frequency range 3-8 kHz. A hearing loss exceeding 60 dB HL is detected with high probability as an SRT deterioration. None of the patients showed any influence on the SRT before the HT rise could be detected. The SR test cannot replace pure-tone audiometry for the identification of cisplatin ototoxicity. The pathological SR results observed in this study indicated a cochlear lesion. It was not possible to identify those patients most susceptible to ototoxic changes from the pretreatment results of the SR test.

Adult↗

PubMed1993

Frequency selectivity in noise-damaged cochleas.

Measures of auditory threshold and masked threshold were obtained at six audiometric test frequencies along with cochleograms on a total population of 363 noise-exposed chinchillas. Seventy animals were chosen from this sample and were separated into five relatively homogeneous groups based upon the amount of permanent threshold shift and sensory cell losses the animals incurred. Tuning curve (TC) metrics were compared to the mean preexposure TC metrics for each group and to the reference preexposure TC metrics obtained from the sample of 363 animals. These data show that in animals with relatively little hearing loss changes in TC metrics can provide evidence for noise-induced sensory cell losses and that the low frequency slope of the TC is a sensitive index of trauma.

Animals↗

PubMed1996

Clinical interest of brainstem auditory evoked potentials in 72 children with inadequate language development.

The present study is of brainstem auditory evoked potentials (BAEP) in 72 children, of 2 to 13 years of age, showing inadequate language development. The age of the children was mainly below the age of 4 (39 cases = 54%), peaking between 3 and 4 years of age (33 cases = 46%). Even so, 82% of our patients were 3 years old or over: 64% were boys, 36% girls, the proportion of boys falling off with age 26% (19 cases) of BAEPs recorded were normal, 74% (53 cases) pathological. High prevalence of undiagnosed hearing loss was found. Physiopathological BAEP classification showed endocochlear impairment in 68% (36 cases), conductive impairment in 21% (11 cases) and retrocochlear impairment in 11% (6 cases) of subjects. Unilateral impairment (20 cases = 28%) cannot account for inadequate language development; but, in the 8 cases (11%) of total bilateral hearing loss, and the 15 cases (21%) of partial bilateral impairment, hearing loss more or equal to 50 dB HL, impaired hearing would play a role in the retardation.

Aging↗

PubMed1991

Low-frequency masking of brainstem potentials.

The phase and intensity dependence of masking a click by a loud low-frequency tone was examined with brainstem potentials. Wave V latency is practically unaffected; its amplitude, however, is maximally suppressed at a phase of 270 degrees, i.e. rarefaction in the ear canal and basilar membrane displacement towards the scala tympani. Corresponding to subjective threshold, a minor suppression is also observed for the opposite deflection. In the phase of maximal suppression, wave V can be cancelled by a 30 Hz tone of 115 dB SPL up to click intensities of 40 dB HL. With cochlear damage, total suppression can be achieved at even higher click intensities as long as they are close to the subjective threshold. Low-frequency suppression is discussed as a tool applicable for early diagnosis of endolymphatic hydrops.

Acoustic Stimulation↗

PubMed1991

Decompression sickness induced hearing loss. A review.

Otologic manifestations of decompression sickness (DCS) occur only rarely. However, with more frequent exposures to deeper depths in recent years, several reports of hearing loss due to DCS have appeared. Nevertheless, the scant literature directly discussing the subject establishes otologic DCS as an important cause of diving-induced hearing loss. When hearing impairment with or without vestibular symptoms is a solitary manifestation of DCS type II, it may be difficult to distinguish from middle and inner ear barotrauma resulting in labyrinthine window fistula. Once a diagnosis is established, immediate recompression treatment with hyperbaric oxygen may result in complete recovery. The pathologic mechanism is discussed and the pertinent literature reviewed.

Atmospheric Pressure↗

PubMed1991

The choice of ABR click polarity and amplitude variables in multiple sclerosis patients.

Evoked brainstem responses (ABR) to 75 dB nHL condensation (C), rarefaction (R), and alternating (A = C+R) clicks were investigated in healthy subjects and in patients with multiple sclerosis. A new wave IV-V 'shape ratio' (SR IV-V) was most sensitive. SR IV-V correlated most strongly with clinical MS classification, and seemed to be rather specific for retrocochlear dysfunction. Wave IV-V amplitude was also more sensitive than the common IV-V amplitude ratio. The variability of latencies and interpeak latencies was lower in ABR to A clicks than in ABR to either R or to C clicks. In patients, fewer subcomponents were found in ABR to A than in ABR to R and C clicks. ABR to A clicks were on the average slightly more sensitive than either C or R click ABR. Our results suggest that both A-mode ABR and the 'dispersion' variable SR IV-V can be used without significant problems in the diagnosis of brainstem demyelination. A test protocol which requires ABR to both C and R clicks to be abnormal, will, however, be less sensitive, though probably more specific.

Acoustic Stimulation↗

PubMed1992

Cochlear and neural dysfunction in acoustic neuroma: can they be separately revealed by auditory brain-stem wave V latency?

Cochlear and retrocochlear lesions may be differentiated by a diagnostic index (D5), which is derived from the patient's auditory brain-stem wave V latency and pure-tone hearing threshold at 2 to 4 kHz. The D5 values obtained from 49 cases of acoustic neuroma (AN) have been shown to share some properties with D5 values of patients with cochlear hearing loss (280 cases), indicating a lesser prolongation of wave V latency in cases with pronounced hearing loss. Assuming this finding is indicative of some degree of cochlear impairment concomitant to the neural dysfunction, AN data were corrected in an attempt to remove the effects of cochlear impairment. The resulting D5 values could reflect the delay in wave V solely due to the neural dysfunction. A significant relationship between these D5 values and tumour size seems to support this hypothesis.

Adult↗

PubMed1993

Acoustic neuroma and non-tumour retrocochlear patients: audiological features.

Seventeen surgically confirmed acoustic neuroma subjects and seventeen radiologically confirmed non-tumour subjects with retrocochlear pathology of unknown aetiology were selected to investigate retrospectively the diagnostic yield of basic audiological test procedures. Puretone audiometry, tympanometry, reflexometry and auditory brainstem response audiometry were used in the identification of acoustic neuromas versus non-tumour retrocochlear disorders. All subjects had been referred originally for neuroaudiological assessment because of suspected acoustic neuroma and had been found to have a range of abnormal ABR findings consistent with retrocochlear pathology. Detailed retrospective analysis of audiological results following surgical and radiological classification showed subject similarities for most parameters of the individual audiological tests for both acoustic neuroma and non-tumour groups. A significant difference was noted, however, between the two clinical populations for the ABR Wave V absolute interaural latency difference parameter.

Acoustic Impedance Tests↗

PubMed1993

The prevalence of perilymphatic hypertension in subjects with tinnitus: a pilot study.

This study investigated the prevalence of perilymphatic hypertension (raised perilymphatic pressure) in a population of subjects with tinnitus. A review of the literature showed how changes in perilymphatic pressure could affect tympanic membrane displacement measurements. This review also revealed that perilymphatic hypertension was more likely to occur in young females (less than 45 years) than in other subjects. An experiment was designed to test 32 subjects, who were divided into four groups according to their age and sex. These subjects underwent several routine audiological tests and were then tested with the tympanic membrane measurement system to determine the perilymphatic pressure of both ears. Statistical analysis of the experimental results showed that the young females had raised perilymphatic pressure. This was significantly higher than the perilymphatic pressure of the other test groups and of that of a normal population. The young females also exhibited other symptoms indicative of raised perilymphatic pressure. The raised pressure was thought to be due to an increase in fluid pressure which is more likely to occur in females due to variations in the levels of circulating hormones with menstrual irregularities, pregnancy and the menopause.

Adult↗