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Biomedical subjects

M Portmann

Publications and source records attributed to M Portmann.

At least 145 records · Page 8Linked to original sources
PubMedDate not supplied

Electrical stimulation of the ear: experimental studies.

The possibility of stimulating the ear by way of an electrode on the round window in order to relieve tinnitus or to produce auditory sensations has been investigated experimentally in guinea pigs. The deleterious effects of DC currents applied to a normal cochlea clearly demonstrate that this means is unsuitable for use in relieving tinnitus in hearing patients. Although AC currents do not cause further damage in ears with the organ of Corti already destroyed by aminoglycosides, the effects of DC currents in such cases have still to be investigated before they can be recommended for the relief of tinnitus in totally deaf patients. Electrical stimulation of the round window combined with masking has made it possible to record responses of auditory neural elements from the eighth nerve to the auditory cortex. This technique could be promising for the basic study of the central auditory nervous system, both experimentally and clinically, and could lead to a more accurate evaluation of candidates for cochlear prostheses.

Animals↗
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Electrical stimulation of the ear: clinical applications.

Electrical stimulation of the ear in humans was performed with an extracochlear electrode on the round window. With positive currents, suppression of tinnitus could be induced. With negative currents, auditory sensations were evoked. Since electrical stimulation with DC currents may be hazardous in the long term, it cannot yet be proposed for the suppression of tinnitus. However, electrically evoked hearing sensations with AC currents seem to be of definite interest for some totally deaf patients.

Deafness↗
PubMedDate not supplied

Summating potential and water balance in Meniere's disease.

The summating potentials (SP) to free-field 1-, 2-, 4-, and 8-kHz, 90-dB HL tone bursts were recorded by means of transtympanic electrocochleography in 45 patients divided into three groups: those with Meniere's disease, those whose diagnosis was uncertain, and control subjects. The similarities across frequencies between the human SP (promontory) and the experimental SP (DIF component from basal turn) suggest that the SP recorded in electrocochleography originates mostly from the base of the cochlea; negative values were observed at low frequencies (1 to 2 kHz), positive values at high frequencies (8 kHz). Patients with Meniere's disease showed significantly larger SP values than control subjects. The effect of orally administered glycerol on the SP and action potential amplitudes was evaluated by means of automated recordings repeated every 5 minutes. Summating potential values were remarkably constant in the control group. A decrease in SP absolute amplitude was observed in most patients with Meniere's disease and some subjects with uncertain diagnoses, specifically at low frequencies. These changes were frequently associated with action potential amplitude and auditory threshold improvements at low frequencies. It is assumed that the glycerol-induced SP changes at low frequencies are related to modifications in the low frequency mechanical response of the basilar membrane at the basal turn.

Adult↗
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Temporary tinnitus suppression in man through electrical stimulation of the cochlea.

While investigating the possibilities of electrically induced hearing in cases of profound deafness, we observed that very often an appropriate stimulation of the cochlea could result in tinnitus cancellation. We present here a progress report on that phenomenon, including 15 subjects. Such a cancellation was restricted to tinnitus subjectively localized in the ear under test, we observed no effect on noises localized in the other ear, or centrally. This suppression occurred so long as the cochlea was stimulated and stopped when the stimulation ceased. This phenomenon was very reproducible and did not seem to affect simultaneous normal acoustic hearing. It is hypothesized that this phenomenon acts through an inhibition of abnormal activity of sensorineural elements of the electrically stimulated cochlea.

Cochlea↗
PubMedDate not supplied

Transtympanic and surface recordings in the diagnosis of retrocochlear disorders.

A series of patients presenting with subsequently surgically confirmed central tumour involving the auditory pathways were investigated using both transtympanic electrocochleography (TT ECochG) and surface recordings of brainstem evoked responses (BER). While ECochG allows a detailed study of peripheral function, BER allow the investigation of neural conduction up to the level of the inferior colliculus. Valuable information can be obtained from: (1) comparison of the amplitudes of the sensory and neural components of the ECochG; (2) comparison of ECochG, BER and auditory thresholds; (3) time interval measurements between the auditory nerve response (N1 on the ECochG) and the inferior colliculus (wave P4-5 on BER); (4) contralateral comparisons. Similar measurements performed in pure cochlear pathologies, mainly in Meniere's disease, yielded very significant differences.

Audiometry↗
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Electrocochleographic measures of cochlear frequency selectivity in hearing loss of cochlear origin.

One of the basic functions of the cochlea is to separate out the frequency components which are present in complex sounds. This frequency selectivity can be measured objectively in the clinic from the compound action potential (AP) during transtympanic electrocochleography, using a two-tone masking paradigm. An AP is evoked by a test tone near to threshold, and a measure is made of the frequency bandwidth over which this AP can be suppressed by a continuous pure tone masker. In normal-hearing subjects, this frequency range is 0.17-0.39 octaves (test tone pip at 4 or 8 kHz). In patients with cochlear deafness, this bandwidth is greatly enlarged, ranging from 0.42-2.2 octaves. Some observations suggest that a deterioration in frequency selectivity can occur before any important threshold elevation. The early detection of this could be a warning sign of potential cochlear susceptibility. In the clinic the measure is already of use: a deterioration is a positive indication of cochlear involvement in a hearing loss.

Audiometry↗
PubMedDate not supplied

Audiometric and electrophysiological correlations in sudden deafness.

Electrophysiological measures were collected over 3 years in 61 cases of sudden deafness. Electrocochleography (ECochG) and Auditory Brainstem Responses (ABR) using click stimuli were recorded down to threshold and compared with pure-tone and speech audiometry data. This study was intended to precise 1) localization of the disorder, 2) prognosis, 3) analysis of the contribution of different frequencies in click-evoked responses. The following results are: 1) In most cases the observations indicated that the inner ear was affected. 2) However, in 19 cases electrophysiological measures revealed a retrocochlear involvement. Four acoustic neuromas were evidenced by CT scan. In 3 of these, audiometric and electrophysiological thresholds returned merely to normal levels after medical treatment, while brainstem responses remained delayed. Thus in these cases recovery would seem to be related to release of vascular compression in the auditory internal meatus. 3) When the latencies of the VII nerve potential (N1) and wave V (PV) were short, and the therapy undertaken early, a good recovery was often obtained. 4) When recovery occurred on low frequencies only, the electrophysiological responses to the click showed slight latency increases.

Adolescent↗