Biomedical subjects

C Muchnik

Publications and source records attributed to C Muchnik.

35 records · Page 2Linked to original sources

PubMed1990

Iontophoresis with an adrenergic alpha-blocker in acoustic overstimulation.

To study the influence of sympathetic innervation on the amount of threshold shift (TS) induced by sound overstimulation, iontophoresis with phentolamine, a known adrenergic alpha-blocker, was performed on awake guinea pigs. The sound exposure following this induced a significantly lesser degree of TS when compared with the control group. These findings indicate that iontophoresis may be of great help in transporting specific ionized chemical compounds through the intact cochlear walls in a completely non-invasive manner for studying cochlear physiology.

Acoustic Stimulation↗

PubMed1990

The influence of the efferent system on acoustic overstimulation.

Since the first anatomical description by Rasmussen, the efferent innervation of the ear has been extensively investigated in order to establish its role in the hearing process. It is accepted that the olivocochlear bundle (OCB) influences the activity of the afferent fibers and through it, the peripheral ear is controlled by higher centers as well as connected to the other ear. Cody and Johnstone (1982) and Rajan and Johnstone (1983) concluded that the amount of ipsilateral temporary threshold shift (TTS) was reduced by simultaneous contralateral acoustic stimulation or by destroying the contralateral cochlea. They attributed the results to the efferent system. It was our aim to investigate whether, and under which conditions, the amount of TTS would be influenced by the efferent system. The efferent innervation was eliminated by cutting the superior vestibular nerve. Two factors influenced the magnitude of TTS; the integrity of the OCB and the functional condition of the contralateral ear.

Acoustic Stimulation↗

PubMed1990

Perilymphatic fistula in the guinea pig.

Clinical reports on perilymphatic fistulae (PLF) of the round window membrane (RWM) have shown different degrees of hearing loss. However, the hearing can also be entirely unaffected. Experimentally induced PLF of the RWM in animals showed results similar to those of the clinical reports, although some researchers have concluded that perforation of the RWM per se does not necessarily induce significant hearing loss. The purpose of the present study was to clarify if, and how, PLF of RWM in the guinea pig actually affects the auditory action potentials. During 1 h of observation following perforation of the RWM, the immediate and continuous effect of the PLF was evaluated. In more than 50% of the animals, different amounts of threshold shift were obtained. In another group of guinea pigs an attempt was made to clarify the findings by reducing the cerebrospinal fluid pressure before perforating the RWM.

Animals↗

PubMed1989

Validity of tympanometry in cases of confirmed otosclerosis.

The otoadmittence or impedance measurements are common procedures in the diagnosis of middle ear pathologies. The present study was undertaken for the purpose of studying the clinical validity of static admittance values in 42 confirmed otosclerotic ears. For both 220 Hz and 660 Hz probe tones only one third of the otosclrotic ears had low admittance values, as expected. The remainder showed admittance values in the normal or high ranges. No significant correlation was found between air bone gap (ABG) and the admittance values.

Acoustic Impedance Tests↗

PubMed1989

Auditory and vestibular findings in Waardenburg's type II syndrome.

A group of 33 patients with the autosomal dominant form of Waardenburg Type II syndrome underwent hearing and vestibular examination. A bilateral, symmetrical, sensorineural hearing loss was found in 51 per cent of the tested subjects. The severity of hearing loss varied from mild to severe. Strong evidence indicated the possible progressive nature of the hearing loss. Concerning the frequency of vestibular findings, the study highlights the frequent divergence between cochlear and vestibular involvement.

Abnormalities, Multiple↗

PubMed1989

Low frequency air-bone gap in Menière's disease without middle ear pathology. A preliminary report.

The audiograms of some patients suffering from Meniere's disease show an unexplained conductive component, or air-bone gap (ABG), predominantly in the low frequencies. Neither the history nor physical findings support poor eustachian tube function, ossicular chain abnormalities, chronic ear disease, physical trauma, or otosclerosis as a cause of this audiometric finding. In the present study, 40 patients diagnosed as suffering from classical Meniere's disease were evaluated audiometrically. Thirteen (32.5%) of these patients demonstrated a low frequency ABG. An otologic evaluation was performed on each patient who exhibited the abnormal finding, but no middle ear pathology was discovered. An otherwise unexplained low frequency ABG in patients with Meniere's disease suggests the possibility of an "inner ear" conductive hearing loss. This conductive component may result from endolymphatic hydrops or perilymphatic hypertension (i.e., an inner ear hyperpressure exerted against the medial surface of the stapedial footplate) rather than from middle ear pathology. "Inner ear" conductive hearing loss is thought to be caused by an increase in inner ear fluid volume (endolymphatic hydrops) and pressure (endolymphatic or perilymphatic hypertension), which dampens footplate mobility medially and which is directly related to a relative inner ear or labyrinthine hyperpressure. Since the footplate mobility is only dampened and not fixed, a stapedial reflex may still be elicited.

Adolescent↗

PubMed1988

Chronic labyrinthine ischemia.

The purpose of the present study was to describe the audiological and vestibular deficit in patients presumed to suffer from chronic impairment of the blood supply to the labyrinth. Thirty-nine subjects affected by various pathologies often impairing systemic blood circulation, which also presented labyrinthine damage of unclear origin, were evaluated for a possible relationship between these two conditions. At the time of this study 80 per cent of the subjects showed also a certain degree of increased blood viscosity. The most common finding in the group was slow and progressive bilateral sensorineural loss of hearing. In most of the subjects the labyrinthine damage began with high-tone loss which, in time, became a flat curve. Less common, but still found in many patients, was a fluctuation in threshold. Short periods of spontaneous subjective improvement in hearing were accompanied by a better result in the Pure Tone Audiogram and Speech Reception Threshold. The discrimination scores remained generally lower than expected. Vestibular examination revealed pathological results for all the subjects in at least some of the tests. The mild subjective complaints concerning equilibrium could be explained by a central nervous system compensation.

Aged↗

PubMed1988

ECoG results in perilymphatic fistula: clinical and experimental studies.

Patients with perilymphatic fistula have been described as having symptoms similar to Meniere's disease and endolymphatic hydrops. Direct clinical or experimental evidence linking the two inner ear disorders has been lacking. An enhancement of the summating potential observed with electrocochleography suggests a diagnosis of ELH in both of these inner ear disorders. In this study, ECoG results of 27 patients with surgically confirmed PLF are reported. Fourteen patients with surgically confirmed spontaneous PLF had abnormal ECoG. Six of these 14 patients had normal hearing. The ECoG changes in patients with Meniere's disease and those with surgically confirmed PLF are identical, indicating the underlying pathologic change in both is hydrops. But there is no specific diagnostic abnormality on ECoG that differentiates these two inner ear disorders. Also, an experimental model of PLF was developed and studied in guinea pigs. "Inactive" PLF is defined as "an opening was made into the cochlea, but if no perilymph moved out through the fistula, it was defined as inactive" An "active" PLF occurs when perilymph actually moves from the inner ear out to the middle ear. ECoGs were recorded before and after creation of an "active" PLF. ECoG abnormalities were seen in "active" PLF and correlated with histologic data demonstrating ELH. An abnormally enhanced summating potential was demonstrated after active removal of perilymph through the experimentally created fistula. Cochlear duct histology showed hydropic distention of Reissner's membrane in the experimental ears and no changes in the membranous labyrinths of the unoperated, control ears.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗

PubMed1987

Surgical approach to the superior vestibular nerve in guinea pigs.

The superior vestibular nerve carries homo- and contra-lateral efferent fibers to the cochlea. The subarcuate fossa, a tube-like structure in the temporal bone of the guinea pig, can be used to reach the superior vestibular nerve at the level of the internal acoustic meatus. Normally, this structure accommodates the dorsal and ventral floccular extension of the cerebellum. This technique has several advantages. Firstly, a reduced cranial opening is necessary; secondly, less cerebellar tissue is sacrificed. Then there is the relative insulation of the operative field, and finally, it presents a straight guide to the internal auditory meatus and vestibular nerve.

Animals↗

PubMed1987

Cochlear action potentials threshold and systemic arterial pO2.

A progressive decrease in arterial pO2 was induced in Hartley guinea pigs (GP) by having them rebreathe the air entrapped in a closed circuit from which the CO2 was continuously absorbed. Following this slow-developing hypoxemia, a sequence of events concerning the ear could be observed. Firstly, a fluctuation in cochlear action potentials (CAP) was noted. This appeared only at stimulus intensities near the threshold and was not evident at higher intensities. At a mean arterial pO2 level of 30 mm Hg, this phenomenon was observed in 60% of the GP. At a mean pO2 of 24.66 mm Hg, a shift in threshold occurred in all GP. Finally, when the blood pO2 reached an average of 14.92 mm Hg, no CAP response could be elicited, even at click intensity of 120 dB SPL. The 30 mm Hg oxygen concentration in the arterial blood was considered as a "critical level" at which the cochlear function starts to deteriorate in guinea pigs.

Animals↗

PubMed1985

Basic metabolic rate in emotional stress: its potential influence on cochlear function.

Using a model previously described, prolonged emotional stress was induced in guinea pigs. Under this condition, arterial blood gases, blood glucose level, PO2 and PCO2 in the expired air, and the heat irradiated by the animals were measured and compared to those of the anesthetized guinea pigs. From the present study, two important findings should be mentioned. First, the metabolic rate of the animals under stress was 30% higher than in the anesthetized group. Second, the arterial PO2 level of the animals under stress was significantly lower than that in the anesthetized ones. Evaluating the noxious effect of severe and/or prolonged emotional stress, one should not neglect the increased oxygen demand resulting from the high metabolic rate of the subject. This factor, together with the decreased arterial blood PO2 level, reinforce the hypoxic effects on the cochlear function, caused by the vasoconstriction of the labyrinthine vessels.

Action Potentials↗

PubMed1985

Problems in interpretation of brainstem-evoked response audiometry results.

This report describes 6 cases - 3 adults and 3 children - in which no response could be obtained during the brainstem-evoked response audiometry (ABR) examination. This, in spite of the fact that maximal click intensity was used during the test, and despite the patients' nearly normal hearing sensitivity. All of the cases presented a slight degree of neurological deficiency, which could explain the faulty synchronization of the biological response to clicks. Attention is drawn to the fact that lack of response in ABR in cases with central nervous system involvement is not necessarily proof of severe hearing loss, and could supply important diagnostic cues.

Adult↗

PubMed1985

Minimal time interval in auditory temporal resolution.

Human auditory temporal resolution was measured. Normal-hearing adults in 3 age groups (I: mn age: 24 yrs, N:55; II: mn age: 44.5 yrs, N: 25; III: mn age: 66.4 yrs, N:18) were required to indicate in which of 2 successive noise bursts of relatively low frequency (concentrated from .1-.5 kc/s) a brief temporal gap was inserted. The noise was created by passing a 100-c/s square wave through an electronic switch with virtually instantaneous rise-fall time and through a clinical audiometer to the associated earphone. The level was set at about the loudness of each S's HTL at .25 kc/s. The minimum detectable time interval (delta t) varied lawfully and significantly (p less than .001) with burst duration and with age. For all ages delta t was approximately equal to 3 msec when the burst duration was longest (85 msec), but at the shortest duration (10 msec) it rose to 17.6, 22.2, and 29.9 msec for Grps I-III, respectively. The interaction between age and duration was also significant (p less than .001). It was suggested that establishment of delta t by this or a similar procedure could offer an important parameter for evaluation of auditory function.

Adult↗

PubMed1984

Influence of catecholamines on perilymph Po2.

In a previous study, a special rheological model of intra-arterial perfusion was used to examine the existence and effectiveness of vasomotor control of the cochlear vessels in guinea pigs. Catecholamines were injected intra-arterially into this animal model and the changes induced in the cochlear action potentials were examined. In this investigation, we used the same animal model and technique to measure the perilymph Po2 after perfusion of the cochlea with catecholamines. In addition, the effect of drainage of the CSF before infusion was examined. The results indicated that opening the labyrinth allows the escape of CSF through the patent cochlear duct. This may modify the concentration of the substance under study in the perilymph and cause inaccuracies in the data obtained.

Animals↗

PubMed1983

Influence of catecholamines on cochlear action potentials.

Catecholamines were injected intra-arterially in guinea pigs using a rheological model described elsewhere. With this method, apart from the ear, only a relatively restricted area was perfused with catecholamines, and the amount eventually entering the general circulation was insufficient to change the normal BP. The induced vasoconstriction of the labyrinthine vessels affected the cochlear blood flow and caused an increase of 11.34 dB in the mean action potential threshold. When the rate of catecholamine infusion was increased, associating vasoconstriction of the cochlear vessels with increased BP, deterioration of the action potential threshold was limited to only 2 dB. However, decrease in the normal BP under the same experimental conditions raised the threshold by 21.67 dB.

Animals↗

PubMed1983

A model for research on cochlear hypoxia.

The vessels emerging from one side of the basilar artery are supplied exclusively by the homolateral vertebral artery. Since blood flow is laminar through the vertebrobasilar system, mixing between two sides does not normally occur. Based on this fact, an experimental model for research on cochlear hypoxia is proposed and described. The animal's own blood flow in the vertebral artery is completely replaced by a stream of poorly oxygenated blood injected retrogradely through the ipsilateral axillary artery. In this way, the territory supplied by the vessels emerging from this side of the basilar artery, including the ear, is rendered hypoxic. The changes in the cochlear action potentials induced by the reduced oxygen supply are recorded by a chronically implanted electrode and analyzed.

Animals↗

PubMed1980

Effect of emotional stress on hearing.

An experimental model for emotional stress is described. Emotional stress can affect hearing if severe enough or if it lasts long enough. The noxious effect on the ear can be explained by the high level of blood catecholamines and exaggerated activity of the cochlear sympathetic innervation.

Animals↗