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Biomedical subjects

Y Cazals

Publications and source records attributed to Y Cazals.

At least 55 records · Page 3Linked to original sources
PubMed1987

Glycerol-induced changes in the cochlear responses of the guinea pig hydropic ear.

Pigmented guinea pigs were chronically implanted with bilateral round-window electrodes. Endolymphatic hydrops was induced by obstruction of the endolymphatic duct on one side. At 1-5 months post-surgery, glycerol was orally administered to each animal and the acute effect on cochlear and eighth nerve responses was investigated. Doses from half to four times the clinical dose of glycerol failed to improve the CAP audiogram in operated ears and were often found to raise the thresholds. Glycerol was found to diminish the amplitude of the summating potential as well as that of the compound action potential. Similar effects were observed for the higher doses in the control ears, although no effect was seen when doses used were equal to or less than the clinical dose. Our data suggest that the cochlear conditions in the guinea pig model of hydrops differ notably from those seen in patients with Ménière's disease.

Animals↗
PubMed1987

Rapidly fluctuating thresholds at the onset of experimentally-induced hydrops in the guinea pig.

Pigmented guinea pigs were chronically implanted bilaterally with a platinum electrode on each round window. After recovery the endolymphatic sac was destroyed and the duct blocked on one side only; the other side was employed as a control. The round window response thresholds on both sides were recorded several times per week over a three month period. There were three main results. A sensitivity loss of up to 20 dB was observed for frequencies between 250 Hz and 6.4 kHz within two weeks post-op. At the end of three months the threshold elevation for these frequencies was as much as 50 dB. On the other hand the thresholds for frequencies between 8 and 16 kHz remained within 10 dB of their pre-operative value for at least two months. The thresholds fluctuated with a shift of as much as 25 dB within 24 h. The threshold elevation was associated with a decrease in the latency, at threshold, of the round window AP response which at frequencies between 250 Hz and 6.4 kHz was as short as that for 8 kHz. This observation suggested that it was the base, only, of the cochlea which responded. The present study has indicated that experimentally induced endolymphatic hydrops in the guinea pig mimics well the progressive and fluctuating hearing loss characteristic of Ménière's disease.

Animals↗
PubMed1987

Eighth nerve auditory evoked responses recorded at the base of the vestibular nucleus in the guinea pig.

Anatomical and physiological studies of brainstem acoustic nuclei involving the classical ascending auditory pathway or the cerebellar and reticular pathways imply that all afferents from the cochlea terminate in the cochlear nucleus. In the experimental pathology of complete and selective destruction of the cochlea in the guinea pig acoustic responses still evoked at mid and high intensities, demonstrated to come from the saccule, show a pattern of far field evoked brainstem potentials quite different from that of normal animals. Intracranial electrophysiological investigations of the brainstem were undertaken in such pathological animals and in normal guinea pigs for comparison. In both cases acoustic responses were recorded at the base of the vestibular nucleus, showing a first peak corresponding to an eighth nerve projection and after a synaptic delay a second peak of local activation. In normal animals acoustic responses from the vestibular nucleus showing normal threshold and tuning curves may represent a direct projection from the cochlea.

Animals↗
PubMed1987

Ototoxicity of teicoplanin in the guinea pig.

Experiments were performed on guinea pigs to assess the eventual ototoxic side effects of a new glycopeptide antibiotic called teicoplanin. For a better validation, in the same study other animals were treated with tobramycin, a well known ototoxic antibiotic of the aminoglycoside family, and a group of control animals was also constituted. Antibiotic treated animals were injected with the high dose of 90 mg/kg/day during 21 consecutive days. Electrophysiological measures of equilibrium and acoustic functions were taken and morphological evaluations of the cochleas were performed. The results indicate that in these animal experiments teicomycin appears to be clearly toxic for the vestibule and the cochlea.

Animals↗
PubMed1986

Extracochlear implants.

A unichannel extracochlear implant designed and made in our laboratory was tried on several patients. Results to date are very similar in all cases. Very rudimentary auditory information is provided, which can help totally deaf patients.

Cochlear Implants↗
PubMed1985

Otoconia and neural junctions of type I hair cells in amikacin-treated guinea pigs presenting saccular acoustic responses.

Using the experimental guinea pig model, in which total and selective destruction of the cochlear receptor revealed saccular acoustic responses, ultrastructural observations were made on otolithic organs using electron microscopy. Scanning electron microscope studies of otoconia from the saccule and utricle of experimental animals did not show any differences with control animals. Quantitative and qualitative observations of sensory neural junctions of Type I cells also did not show any abnormality. These results confirm the extremely selective toxicity of amikacin for the cochlea, and thus strongly suggest that an acoustic reception by the saccule is a normal feature of the guinea pig inner ear.

Amikacin↗
PubMed1985

[Personal experience with a unicanal extracochlear implant in reference to rehabilitation in total bilateral deafness. Multicenter study. Preliminary report].

Our choice of a unicanal extracochlear implant is characterized by a reasonable attitude and simplicity. Simplicity and reason, because the already existing experiments show that in the field of cochlear implants there is no correlation a priori between the satisfaction of the research worker developing a complex electronic system in the laboratory and the satisfaction of the patient benefiting from such a system. Furthermore, the extracochlear implant respects and conserves the anatomical structure of the cochlea. It does not compromise future interventions. A replacement could be carried out in the future should a more perfected system be invented. The latter argument is particularly useful if a child is being considered for an implant. All patients with implants benefit from the following results: the satisfaction of hearing their own voice again, a better control of the voice (loudness and intensity), comprehension is facilitated (lip reading and noise perception), end of the sensation of isolation. The first results obtained are very encouraging. We find it most essential to continue our work in the same manner and with an inter-University working group (GRIC). The standardisation of results of the various teams involved seems to be imperative. We conclude by the following: At the present state of our knowledge, the unicanal extracochlear implant seems to be a reasonable solution and a realistic approach in the rehabilitation of total bilateral deafness.

Aged↗
PubMed1984

First results of chronic electrical stimulation with a round-window electrode in totally deaf patients.

A few patients who had become totally deaf in adulthood were chronically implanted with an electrode on the round window. Elicitable auditory sensations were limited but proved beneficial enough for a small portable stimulator to be suggested for everyday use. Over a period of several months subjects were monitored several times for a few days at the laboratory and trained to make better use of their prosthesis. Such a device appears safe and patients have become attached to its use. One subject suffering from tinnitus was also given another stimulator delivering positive direct current which suppresses the tinnitus.

Adult↗
PubMed1984

Low frequency thresholds assessed with 40 Hz MLR in adults with impaired hearing.

In a group of 30 adults with impaired hearing, objective thresholds defined with 40 Hz middle latency responses (MLR) were compared with subjective audiometric measures. Frequencies of 0.25, 0.5, and 1 kHz were studied. In order to guarantee a good frequency specificity, subjects presenting large high-frequency hearing loss were particularly chosen. The 40-Hz MLR thresholds were generally worse than the audiometric measures. The average difference was around 12 dB, but in about one-third of the cases it was between 20 and 30 dB. Although not perfect, 40-Hz MLR estimates on low frequencies can be very helpful and deserve further consideration, especially in children.

Adult↗
PubMed1983

Artificial activation and degeneration of the cochlear nerve in guinea pigs.

Degeneration of the cochlear nerve was produced in guinea pigs after treatment with high doses of ototoxic antibiotics completely destroying the cochlear receptor. An effective electric stimulation of the inner ear inducing evoked potentials at the auditory cortex was applied over a period of 3.5 months in half of the animals, while the other half was kept for control. The artificial stimulation had no effect on the sensitivity of the inner ear to electric stimulation and did not modify the extent of degeneration of the cochlear nerve.

Amikacin↗
PubMed1983

Hemodilution in sudden deafness: first results.

The technique of hemodilution was assessed in 12 cases of sudden hearing loss as it is known to improve peripheral circulation. Good results were obtained in nine patients. The immediacy of the effects suggests the real efficacy of hemodilution as opposed to spontaneous recovery. Hemodilution is supposed to improve oxygenation in the cochlea. This technique is very simple and quick to perform.

Adult↗
PubMed1983

Intensity difference thresholds assessed with eighth nerve and auditory cortex potentials: compared values from cochlear and vascular responses.

In normal guinea pigs the eighth nerve compound action potential shows a latency of about 1 ms and the evoked early potential at the auditory cortex occurs after about 10 ms. Determination of auditory sensitivity with both responses using tone-bursts of variable rise/fall time and plateau duration showed they are responses to the onset of the stimulus since the existence of a plateau has no effect. Increases in stimulus rise time diminish the synchrony of both responses, the limits were found to be 2 ms for eighth nerve responses and 10 ms for cortical potentials. Amplitude modulation of continuous tones using these time values evokes clear responses at levels which apparently correspond to intensity difference thresholds measured behaviorally by other authors. Similar measures were performed on saccular acoustic responses, using the model of selective cochlear destruction. Evoked responses could also be observed at levels of amplitude modulation similar to those of normal animals. This fine sensitivity reinforces the idea of a functionality of the saccular acoustic reception.

Action Potentials↗
PubMed1983

Acoustically derived auditory nerve action potential evoked by electrical stimulation: an estimation of the waveform of single unit contribution.

An experimental study of the electrical stimulation of the guinea pig cochlea is made using an electrode on the round window for both stimulation and recording. The neural response is separated from the electrical artifact with a masking procedure combined with a low amplification, "statistical" averaging method [Charlet de Sauvage et al., Hear. Res. 2, 343-346 (1980)]. The high electrical impedance required for recording physiological responses implies the use of a current pulse generator. Monitoring of evoked potentials from the auditory cortex provides evidence that the effects of electrical stimulation (and of masking noise) are of auditory origin. The electrically evoked round window response is of very short latency (less than 0.2 ms). There is a response threshold for both electrical stimulus and masking noise. The response amplitude varies monotonically as a function of masking noise or electrical stimulus intensity. Experiments with high-pass noise masking suggest that the electrical stimulus is mainly acting on basal fibers. The response latency and waveform are independent of electrical stimulus intensity, repetition rate, masker level, or spectrum. Little intersubject variation is noted. Our experiments (reciprocal forward masking by electrical and acoustic stimuli) suggest that a direct, instantaneous electrical stimulation of the fibers occurs. We believe that this response to electrical stimulation represents the mean unit response of the auditory nerve fibers. This approach may be useful in the separate study of cochlear and VIIIth nerve functions and in the analysis (deconvolution) of the acoustically evoked compound AP.

Acoustic Stimulation↗