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Biomedical subjects

J M Aran

Publications and source records attributed to J M Aran.

At least 109 records · Page 6Linked to original sources
PubMed1982

[Evaluation of the ototoxicity of aminoglycosides. Comparative study of dibekacin, gentamicin and tobramycin].

Various techniques useful for the precise functional and morphological evaluation of the auditory and vestibular systems in the guinea pig are described. Their application in the comparative study of the ototoxicity of three aminoglycosidic antibiotics (gentamicin, tobramycin and dibekacin) administered at doses of 90 mg/kg/day for 20 consecutive days is presented. In these conditions a severe cochlear impairment was observed with gentamicin and tobramycin while it was minimal with dibekacin. Vestibular impairment was also severe with gentamicin and definite, although less important, with dibekacin and tobramycin.

Aminoglycosides↗
PubMed1982

Loudness recruitment: contributing mechanisms as revealed by cochlear AP measures in man.

A measure of the (average) rate of discharge versus intensity function of cochlear fibers can be obtained from cochlear-evoked compound action potentials using a tone-on-tone forward masking technique. The rationale for the method is presented. This technique was used to investigate, indirectly, cochlear fiber responses in human subjects, both with normal hearing and with deafness of cochlear origin and showing signs of loudness recruitment. In animals with pathologic cochleas, and change in rate of fiber discharge with intensity is more rapid than in normal animals. The present study confirms that this also is the case in human cochlear pathology and suggests that this abnormal steepening of rate versus intensity functions contributes to the phenomenon of loudness recruitment.

Audiometry↗
PubMed1981

Electrical suppression of tinnitus.

The occasional suppression of tinnitus during electrical stimulation of the ear with positive currents has been investigated in 106 patients presenting with any degree of hearing impairment (whether of known or unknown aetiology) from profound deafness to near-normal pure-tone thresholds. Seventy-four percent of these patients presented with tinnitus localized in the ipsilateral ear at the time of examination. The suppression was totally effective in 60% of patients during stimulation through a round-window electrode. The suppression, partial or complete, was obtained in only 43% of patients when stimulation was from the promontory electrode, which served first as a recording electrode for electrocochleography. The sensations (hearing induction and/or tinnitus suppression, and dizziness) during and after the stimulation were evaluated with respect to polarity, intensity and frequency of the electrical impulses. This procedure had several objectives: (1) to confirm the eventual suppression of tinnitus by positive currents; (2) to serve as a tool to differentiate between various types of tinnitus; (3) to assess the possible clinical application for the long-term relief to some patients suffering from tinnitus; (4) to evaluate the possibility of artificial auditory stimulation in profoundly deaf subjects; and (5) to bring some hope to highly disturbed patients.

Deafness↗
PubMed1981

The frequency selectivity of the normal and pathological human cochlea.

Human AP tuning curves (tone on tone simultaneous and forward masking curves) were measured during transtympanic electrocochleography. For subjects with near normal thresholds, average Q10 dB values (simultaneous masking) were 2.3 at 2 kHz, 3.6 at 4 kHz, and 4.7 at 8 kHz. Patients with threshold elevations of more than 40 dB, resulting from sensorineural hearing loss of cochlear origin, had tuning curves less sharply tuned by a factor of 2-3, with Q10 dB values of 1-2 at 2 kHz and at 4 kHz, and 1-2.3 at 8 kHz. AP tuning curves and single fibre tuning curves (frequency threshold curves) were measured in normal guinea pigs; cochlear fibre tuning is sharper than AP tuning (simultaneous masking) by a factor of 1.8 (2-20 kHz). Assuming that this factor can be applied to the human cochlea, estimates of normal human cochlear fibre Q10 dB values are 4.2 at 2 kHz, 6.5 at 4 kHz, and 8.5 at 8 kHz.

Animals↗
PubMed1981

AP tuning curves from normal and pathological human and guinea pig cochleas.

Measures of cochlear selectivity can be obtained from compound responses using tone-on-tone masking procedures [Dallos and Cheatham, J. Acoust. Soc. Am. 59, 591--597 (1976)]. For the normal guinea pig, cochlear fiber tuning is sharper by a factor of 1.8 than AP tuning curves using simultaneous masking (threshold criterion = 25% N1 amplitude reduction). Anesthesia does not appear to affect AP tuning. In pathological cochleas, AP tuning is broadened by a factor of 2--3, and differences between forward and simultaneous masking curves are reduced. Tuning changes can sometimes occur without threshold elevation. AP tuning curves were obtained from humans during transtympanic electrocochleography. For subjects with near normal thresholds, Q10dB values (simultaneous masking) are approximately 2.3 at 2 kHz, 3.6 at 4 kHz, and 4.7 at 8 kHz. Using the relationship between cochlear fiber tuning and AP tuning in the guinea pig, estimates of human cochlear fiber tuning are 4.2 at 2 kHz, 6.5 at 4 kHz, and 8.5 at 8 kHz. Patients with threshold elevations of more than 30 dB resulting from cochlear deafness have AP tuning curves less sharply tuned by a factor of 2--3.

Action Potentials↗
PubMed1980

Acoustic responses after total destruction of the cochlear receptor: brainstem and auditory cortex.

Acoustically evoked neural activity has been recorded from the brainstem and auditory cortex of guinea pigs after complete destruction of the organ of Corti by the aminoglycosidic antibiotic amikacin. These responses to sound differ in important respects from the evoked potentials normally recorded from the auditory pathways. At the brainstem level they resemble the potentials reported by others after stimulation of the vestibular nerve.

Acoustic Stimulation↗
PubMed1980

Threshold elevation at high frequencies of the auditory nerve action potentials in acute versus chronic recordings in guinea pigs.

Thresholds of the auditory nerve compound action potential (CAP) responses to filtered clicks from 0.5 to 40 kHz, defining a CAP frequency threshold curve, have been determined in the same guinea pigs: (1) in acute conditions, the animal still anesthetized at the end of the operation for permanent implantation of a round-window electrode, and (2) several days later in the implanted awake and unrestrained animal. The results show higher CAP thresholds for high frequencies in acute conditions as compared to chronic recordings. This difference appears above about 12.5 kHz and increases progressively to around 40 dB at 40 kHz. Similar effects, although somewhat less pronounced, were observed during anesthesia alone in already implanted guinea pigs. Thes observations could explain the discrepancies which appear between electrophysiological thresholds, acutely recorded either from single fibers or whole-nerve responses, and behavioral audiograms. Moreover, in the accurate evaluation of the cochlea, slight impairments may be masked by this phenomenon as illustrated in guinea pigs treated with low doses of ototoxic antibiotic.

Acoustic Stimulation↗
PubMed1979

"Neural" responses to acoustic stimulation after destruction of cochlear hair cells.

Electrophysiological and histological observations in guinea pig's cochleas after amikacin treatment (14 X 450 mg/kg) confirm the results obtained in a former experiment: clear, short-latency, click-evoked responses were recorded in cochleas with only very few hair cells remaining at the extreme apex. Detailed analysis of these responses strongly indicates a neural origin and confirms their low-frequency sensitivity. Careful histological observations confirm the extensive hair cell loss and the preservation of nerve fibers in the remnants of the organ of Corti and of the vestibular sense organs. These results suggest that the acoustical vibrations either stimulate the vestibular receptors or act directly or through some kind of mechano-electrical transduction on the remaining cochlear nerve fibers.

Amikacin↗
PubMed1977

Neural correlates of electrically-induced cochlear dysfunction.

Prolonged low intensity galvanic currents produce scattered but sharply cicumscribed areas of destruction in the guinea pig cochlea. As well as providing opportunities for studying possible electrically-induced injuries during artificial auditory stimulation of the deaf, such preparations present an unusual opportunity to study the relations between patterns of compound auditory nerve action potentials and morphological changes, which could be useful in evaluating the various computer models of cochlear function at present being developed.

Action Potentials↗