Biomedical subjects

P Avan

Publications and source records attributed to P Avan.

76 records · Page 5Linked to original sources

PubMedDate not supplied

Intracochlear acoustic pressure measurements: transfer functions of the middle ear and cochlear mechanics.

Direct intracochlear acoustic pressure recordings (from 20 to 20,000 Hz) are used to measure the middle-ear transfer functions (forward and reverse) and to better understand the cochlear mechanics in the guinea pig. In the forward direction, the middle-ear transfer function is strongly dependent on the frequency and presents a maximum of +30 dB at 1,000 Hz (bulla open). In the reverse direction, the middle-ear transfer function looks like an ideal reverse middle-ear pressure transformer with -35 dB gain and 0 degrees phase lag from 20 to 8,000 Hz (bulla open, closed ear canal). Passive cochlear mechanics is studied with the help of intracochlear pressure measurements and differential cochlear microphonic potential recordings in the different turns.

Acoustic Stimulation↗

PubMedDate not supplied

Frequency-specific information from click evoked otoacoustic emissions in noise-induced hearing loss.

Click evoked otoacoustic emissions (CEOAEs), pure-tone audiograms (PTAs), and Bekesy sweep frequency audiograms were recorded from 15 ears of 11 subjects with noise-induced hearing loss. For all ears, hearing threshold levels > or = 30 dB HL were found at the high frequencies. The aims of the study were to examine whether the decomposition of CEOAEs into narrow band components could identify hearing loss in a frequency-specific manner and to what extent audiometric thresholds could be predicted. CEOAEs were parcelled into 0.5-kHz-wide components by means of the wavelet transform. Reproducibility of CEOAE components was compared with audiometric threshold at corresponding frequencies. A general trend of low reproducibility for increasing audiometric thresholds was found. A reproducibility value of 60 per cent was found to best separate normal and elevated thresholds. The presence of a CEOAE component at a given frequency was always associated with audiometric thresholds < or = 20-25 dB HL. On the other hand, the absence of a component was equally associated either with normal or abnormal hearing levels. Large inter-subject variability was observed. A weak linear relationship was found between reproducibility and audiometric thresholds at corresponding frequencies, indicating that analysis of narrow band CEOAE components is valuable for separating normal from hearing-impaired ears but cannot replace the audiogram.

Acoustic Stimulation↗

PubMedDate not supplied

Contralateral suppression of transient evoked otoacoustic emissions in guinea-pigs: effects of gentamicin.

A single injection of gentamicin in the awake guinea-pig induces a transient blockade of the suppression by contralateral white noise of tone-pip evoked compound action potential (Smith et al., 1994). We report here the reversible blockade, in exactly the same experimental conditions, of the suppression of click-evoked otoacoustic emissions. These observations confirm the transient action of gentamicin at the medial efferent/outer hair cell synapse, likely via the reversible blockade of calcium channels observed in vitro (Dulon et al., 1989).

Acoustic Stimulation↗

PubMedDate not supplied

Fine alterations of distortion-product otoacoustic emissions after moderate acoustic overexposure in guinea pigs.

Guinea pigs were exposed to a pure tone at 6 kHz and 80 dB SPL for 30 minutes in order to induce mild reversible auditory fatigue over the 4 hours following exposure. Cochlear monitoring aimed to compare the shifts in round-window compound action potentials (CAP) thresholds to those of 2f1-f2 distortion-product otoacoustic emissions (DPOAE, frequency of stimuli f1 and f2). Both responses were evaluated every 1/10th octave between 6 and 12 kHz for CAP thresholds, and from 4 to about 14 kHz for DPOAEs in response to 50- and 70-dB SPL stimuli. The auditory fatigue turned out to be sufficiently mild that DPOAEs remained present, so that their microstructure could be followed up while the stimulus frequency ratio f2/f1 was swept from 1.06 to 1.30 (fixed f2) so as to derive DPOAE level profiles against f2/f1 and group latencies. CAP thresholds decreased by about 10 dB above 7.2 kHz, whereas DPOAE amplitudes decreased at most f2 frequencies from 6.6 kHz to 15.2 kHz, with the range of decrease being slightly narrower at higher stimulus intensities. While the mean DPOAE shift after 1 hour was around 5 dB irrespective of stimulus intensity, it tended to increase slightly after 2 hours despite stable CAP thresholds. DPOAE profiles against f2/f1 were slightly modified by the auditory fatigue, so that the maximum tended to be reached at lower ratio. No significant variation of DPOAE latencies was found after acoustic overstimulation. These experiments show that complex DPOAE changes were induced by auditory fatigue and their relationship to CAP threshold changes does not seem to be straight-forward. Nonetheless, fine DPOAE recordings might be useful to detect early changes in cochlear mechanics.

Acoustic Stimulation↗