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Biomedical subjects

N Dillier

Publications and source records attributed to N Dillier.

At least 37 records · Page 2Linked to original sources
PubMed1990

Experimental endolymphatic hydrops: are cochlear and vestibular symptoms caused by increased endolymphatic pressure?

The correlation between inner ear pressure and cochlear function was investigated in guinea pigs with unilaterally obliterated endolymphatic sacs and ducts. In 11 animals that developed endolymphatic hydrops, auditory thresholds as monitored by auditory evoked action potentials had increased with recruitment. Most of these animals also experienced episodes of spontaneous nystagmus. In control ears endolymphatic pressure did not differ more than 0.5 cm H2O from perilymphatic pressure. In six of 11 hydropic ears, endolymphatic pressure was more than 0.5 cm H2O higher than perilympathic pressure; auditory thresholds in all these ears had deteriorated within 2 weeks before pressure recording. No further hearing deterioration within this period was noted in five hydropic ears with endolymphatic pressure equal to or lower than perilymphatic pressure. Endolympathic-perilymphatic pressure gradients may contribute to auditory threshold increase in endolymphatic hydrops, but are not its only cause.

Animals↗
PubMed1990

Comparison of hearing aids and cochlear implants in profoundly and totally deaf persons.

Cochlear implants are increasingly used in the rehabilitation of the profoundly and totally deaf. Usually, insufficient gain of speech discrimination with a powerful conventional hearing aid is considered as a prerequisite for a cochlear prosthesis. With recent improvements of electronic systems, the criterion for this decision may change. To keep pace with the technical progress, a battery of speech sound tests suited for minimal auditory capabilities (MAC-battery) was developed and applied to groups of patients fitted with conventional instruments and with two different types of cochlear implants. Based on the comparison of the MAC-battery results of hearing aid groups, with the average performance of an implanted group, most conventionally fitted regular users of hearing aids should not be considered as candidates for cochlear implantation. The MAC-battery, although not a strictly standardized procedure, is a useful instrument for patient counselling and for the selection of implant candidates.

Adolescent↗
PubMed1990

Endoneurial fluid pressure in the facial nerve of guinea pigs and rabbits.

Endoneurial fluid pressure (EFP) was measured in the facial nerve in rabbits and guinea pigs using a servo-controlled micropipette system. EFP in the tympanic segment was 5.3 +/- 1.2 cm H2O in rabbits and 4.1 +/- 0.9 and 4.2 +/- 0.9 cm H2O in the tympanic and mastoid segment respectively in guinea pigs, while EFP in the sciatic nerve was around 2 cm H2O. The higher pressure in the facial nerve may be related to the proximo-distal flow of the endoneurial fluid in peripheral nerves.

Animals↗
PubMed1990

Wearable digital speech processor for cochlear implants using a TMS320C25.

Based on a single-chip DSP (TMS320C25, Texas Instruments) a programmable battery-operated sound processor with a digital encoder interface for the Nucleus-22 cochlear implant (CI) was built. The number of quasi-simultaneously addressed electrodes is only limited by the selected pulse width and the maximum rate of stimulation and can be as high as 10 electrodes at 300 Hz repetition rate. Implementation of various processing strategies (formant or channel vocoder, filterbank, zero crossings, etc.) is possible as well as sophisticated adaptive noise reduction. Programs and stimulation parameters are stored in electrically erasable memory and may be updated via a host computer. The built-in analog output may be used for single-channel stimulation or acoustic verifications of the sound processing algorithms. The power consumption with current 16K word data memory and at maximum stimulation rate is about 1 Watt, which necessitates recharging of batteries after 11 h.

Cochlear Implants↗
PubMed1989

Comparison of single-channel extracochlear and multichannel intracochlear electrodes in the same patient.

A postlingually deaf patient who had been using a single-channel extracochlear implant for 5 years was reimplanted in the same ear with a 22-channel intracochlear device after electrical failure of the internal receiver. In the subsequent follow-up period, auditory performance was investigated in a series of tests with nonspeech and speech material. Two weeks after processor fitting most test scores were equal or better with the new implant. Three months later, with only minimal training, the patient's performance in sentence, numerals and vowel tests was markedly improved. Analysis of vowel confusion matrices indicated a high percentage of F2 information perceived (53% compared with 5% with the single-channel device) and somewhat less F1 information (35% compared with 4% using the single-channel device). Further improvements of speech discrimination (especially consonant recognition) are conceivable if the fine temporal resolution provided by some single-channel devices can be combined with the spectral resolution of multichannel systems.

Cochlear Implants↗
PubMed1988

[Perception of acoustic speech features with single channel cochlear implants and hearing aids. A comparative analysis].

A newly developed battery of 12 multiple-choice tests for the German language (graded according to difficulty) comprising identification of sentences, words and syllables was applied to 8 patients with single-channel cochlear implants and to 35 deaf hearing-aid users. Phoneme confusion matrices were analysed using sequential information transmission analysis (SINFA) and multi-dimensional scaling (SINDSCAL). Acoustic parameters of the digitally stored test items were compared with the outcome of SINFA and SINDSCAL. It was found that cochlear implant and hearing-aid users relied on the same perceptual dimensions which were correlated to acoustic signal properties of the speech sounds. Best perceived acoustic features were time and amplitude structure of the speech sound (envelope). Fundamental and first formant frequency are evaluated both by implant and hearing-aid users. The use of higher frequency spectral information depends on the amount of residual hearing.

Auditory Threshold↗
PubMed1987

Endolymphatic pressure in experimental hydrops.

Perilymphatic and endolymphatic pressures were consecutively measured by means of a servomechanical nulling pressure system through the round window and basilar membrane one to 2.5 months after obliteration of the left endolymphatic sac and duct in seven guinea pigs. The position of the pipette was monitored by the simultaneous recording of the direct current potential through the micropipette used for the pressure measurement. (1) The perilymphatic and endolymphatic pressures of the control ears were equal. (2) The histological evaluation showed that the ears operated on had a significantly greater endolymphatic space than the control ears. (3) The endolymphatic pressure of the ear operated on was significantly higher (0.78 +/- 0.32 mm Hg) than that of the perilymph. (4) The endolymphatic direct current potential was equal in both ears.

Animals↗
PubMed1987

[Technic and spate results of stapedotomy].

The long-term results of 253 stapedotomies and of 444 stapedectomies were compared. Stapedotomy yielded significantly better and more stable results for the higher frequency range (1-4 kHz) than stapedectomy. Reversal of the classic sequence of the surgical steps of stapedectomy has improved the precision of the technique and reduced the possibility of inner ear trauma. Perforation of the footplate and the introduction of the prosthesis into the stapedotomy opening and its crimping to the long process of the incus are performed before separating the incudostapedial joint and removing the stapes arch. For optimal results the 0.4 mm platinum teflon prosthesis should protrude 0.5 mm into the vestibule. If the incus is too short or the oval window niche too narrow the prosthesis is attached directly to the malleus handle, bypassing the incus.

Follow-Up Studies↗
PubMed1986

Stapedius reflex in multiple sclerosis.

The stapedius reflex (StR) was studied in humans by impedance audiometry. Ipsilateral and contralateral reflexes, obtained from 48 multiple sclerosis (MS) patients and 26 controls, were analysed. MS patients showed smaller reflex amplitudes, longer onset latencies and higher contralateral reflex thresholds. Using onset latencies, 33% of all MS patients had at least two abnormal ipsi- and/or contralateral StRs. If the diagnosis was MS of the definite type, this figure was 39%. The StR is therefore a useful tool for detecting a subclinical lesion in the brainstem and can contribute to the early diagnosis of MS.

Acoustic Impedance Tests↗
PubMed1985

Some aspects of temporal coding for single-channel electrical stimulation of the cochlea.

Estimates of the useful frequency range for single-channel electrical stimulation of the cochlea range from 400 to 4000 Hz. Psychophysical studies in single-channel implant patients are relevant not only to the practical problem of designing stimulation strategies, but also to questions of temporal processing of pitch in the normal auditory nervous system. Patients with single-channel extracochlear devices participated in several experiments involving stimuli differing in fine temporal structure. Stochastic pulse trains, in which the probability of pulse delivery (p) for a given cycle was less than 1.0, were readily discriminated from ordinary pulse trains. Frequency discrimination using stochastic pulse trains differing only in fine temporal structure (but identical average pulse rates) was as good as with ordinary pulse trains or sinusoids for P greater than or equal to 0.5, but deteriorated rapidly for P less than 0.5. Discrimination of triangular and trapezoidal waveforms from square waves was surprisingly good: rise-times (for 0 to maximum current) as low as 0.08 ms could be discriminated. Conversely, detection of jitter in pulse trains was almost an order of magnitude worse. The results show that frequency discrimination for single-channel electrical stimulation of the cochlea is based on discrimination of inter-pulse periods, and that pulse rates which would be unnatural for acoustically-evoked VIIIth nerve activity - up to 750 Hz - are more useful for coding mid-range frequencies than low-rate stochastic stimulations of normal VIIIth nerve firing patterns. The waveform discriminations reported would be obscured by low-pass filtering even at 2000 Hz, and probably depend on changes in relative synchrony among an array of VIIIth nerve units with different thresholds. In general, these results support the use of analog coding schemes with relatively large bandwidth.

Cochlea↗
PubMed1984

Results and perspectives with extracochlear round window electrodes.

The results obtained with implanted electrodes at the round window are comparable to results with electrodes in the scala tympani or in the hearing nerve in respect to frequency and amplitude resolution with pulsatile and sinusoidal stimulation (with considerable interpatient variations). Although the subjective quality of the perceived sounds is expected to vary depending on the stimulation site, it seems that timing effects of electrical stimulation may play a major role in pitch perception as required for voice and sound recognition or prosody identification. Our technique is a safe procedure involving only routine middle ear surgery to place the induction coil within the mastoid bone and to put an electrode at the round window margin. By an external stimulator, sounds are transformed to electrical stimuli suited to excite surviving fibers of the cochlear nerve. This helps the patient to communicate and provides some basic cues for speech discrimination.

Adult↗
PubMed1983

Computerized testing of signal-encoding strategies with round-window implants.

After extensive testing of a patient with two bipolar modiolar electrodes connected to a percutaneous plug in 1977, we provided four patients with a single-channel monopolar round-window electrode connected to a tuned radio-frequency receiver coil. Loudness and pitch discrimination and results of psychophysical scaling experiments of extracochlear electrodes are comparable to those with intracochlear stimulation. Extensive testing with a computerized test system and with tape-recorded and live speech material showed that accurate vowel and speaker identification by stimulation alone is possible and that discrimination by lipreading is considerably improved. Interactive training sessions further improve discrimination results. Different signal-encoding algorithms can be used to generate in real time stimulation signals from prestored speech parameters (such as pitch, gain, formants, and zerocrossing intervals).

Adult↗
PubMed1981

Experimental study on the perilymphatic pressure.

The hydrostatic pressure was successfully and accurately measured through the round window membrane of the cat over a wide pressure range and long duration using glass micropipets of 1-5 micrometer tip inner diameter and an active nulling pressure measuring system. The dynamic changes in perilymphatic pressure occurring after inhalation of different gas mixtures (5 percent CO2 and 95 percent O2/carbogen, 5 percent and 10 percent CO2 in room air) were recorded. The maximal oxygenation of the perilymph combined with minimal increase in pressure was achieved following inhalation of carbogen. The correlation between variations of pressure of the perilymph and of the systemic blood circulation shows that a regulatory system is present in the inner ear vessels. The pressure measuring system used has proven to have all the requirements that are needed for its use in humans.

Animals↗
PubMed1980

Encoding and decoding of auditory signals in relation to human speech and its application to human cochlear implants.

A description of the optimal electrode and stimulus configuration, based on mathematical model simulation of (1) the mechanical conduction and (2) the mechanoelectrical transduction of the middle and inner ear, will be presented. It is assumed that a sensorineurally deaf patient, whose auditory nerve is at least partially intact, will be able to hear and understand, when an activation pattern in specific groups of remaining fibers of the hearing nerve can be reproduced in a manner equivalent to normal hearing. The placement of 2 bipolar concentric electrodes in the modiolus of the basal and middle cochlear turn in a deaf patient has provided the opportunity for testing of electrical hearing thresholds, differential thresholds, and electrode impedance changes over a 5-month period, with direct access to the electrodes through a skin window. The stimulator was housed in a pocket case to provide easy use in a daily environment. Bipolar pulses of 0.02-1.0 ms were triggered either by zero crossings or by a speech envelope controlled oscillator. It was found that loudness should be encoded by pulse amplitude or duration rather than by pulse repetition rate, since the charge per pulse was the primary variable of loudness sensation. The periodicity hearing allowed for electrical differential thresholds equivalent to or lower than the acoustical ones in normal persons in the 80- to 150-Hz region. For the optimal coding of speech, a multichannel system of 4-10 electrodes each for different nerve fiber groups will be necessary.

Cochlear Implants↗