Biomedical subjects

P Avan

Publications and source records attributed to P Avan.

At least 37 records · Page 2Linked to original sources

PubMed1999

A model of cochlear function assessment during reversible ischemia in the Mongolian gerbil.

An in vivo model in the Mongolian gerbil is used to assess the auditory changes during reversible cochlear ischemia. This model allows the recordings of cochlear potentials (microphonics, summating potential and compound action potential) and otoacoustic emissions (cubic difference tones, CDTs), together with laser Doppler cochlear blood flow (CBF) measurements, over reversible cochlear ischemia. Ischemia is achieved by compression of the eighth nerve complex at the porus of the internal acoustical meatus, whereas the compression release allows the reperfusion to occur. While CBF monitoring permits to objectively determine the degree of ischemia and reperfusion, the combined analysis of cochlear potentials and CDTs makes it possible to point out the preferential site of main functional damage within the cochlea, i.e., outer hair cells (OHCs), inner hair cells, or ganglia cells. At least three ischemia-reperfusion sequences can be used on one side, and sometimes both ears can serve for experiments. This model could be applicable for testing drugs with alleged protective effects against cochlear ischemia and/or reperfusion, in treated vs. non-treated animals.

Animals↗

PubMed1999

Auditory screening in neonates by means of transient evoked otoacoustic emissions: a report of 2,842 recordings.

The principal goal of an early identification program is to identify hearing impairment present at birth, in order to effect appropriate intervention as early as possible. Although recent research provides some evidence for the value of transient evoked otoacoustic emissions (TEOAEs) in neonate hearing screening, data are needed from large-scale clinical evaluations about the value of using TEOAEs for screening not only high-risk but also healthy neonates. A cohort of 1,421 neonates (2,842 ears) from the well-baby nursery was screened with TEOAEs in a 2-stage process. Neonates were referred from the first test prior to being discharged from the hospital. Those who failed were rescreened before the end of the first month. Those who did not pass the second-stage TEOAE screening were referred for diagnostic audiological evaluation for confirmation of hearing loss. Neonates transferred to a neonatal intensive care unit were not included in this study. Two neonates with bilateral sensorineural hearing loss of >40 dB hearing level were identified from this cohort. This study demonstrates the feasibility and the limitations of using TEOAEs as a universal hearing screening tool for all neonates. It confirms that the prevalence of hearing impairment in neonates has to be taken into account, even in a group of children without high-risk criteria. In France, a prevalence of 1.4 per 1,000 would represent 1,000 deaf children born every year, with reference to about 700,000 births per year. This study suggests that such universal screening programs would substantially increase the rate of early-identified infants with significant hearing impairment.

Acoustic Stimulation↗

PubMed1998

Assessment of postoperative pain after laryngeal surgery for cancer.

OBJECTIVES: To assess the intensity of postoperative pain after laryngeal surgery for cancer and the efficacy of analgesic injections at fixed hours. DESIGN: A prospective clinical study performed during the 3 days following laryngeal cancer surgery. SETTING: A university medical center. PATIENTS: Fifteen men (age range, 38-74 years) having just undergone a partial or total laryngectomy for epidermoid carcinoma. INTERVENTIONS: The analgesic treatment consisted of intravenous administrations at fixed hours (propacetamol or nalbuphine hydrochloride), with the possibility of rescue doses on demand. Pain and anxiety were assessed by means of visual analog scales (graduated from 0-10) every 3 hours on postoperative day 1, then every 6 hours on postoperative days 2 and 3. Objective criteria, ie, heart and respiratory rates and mean blood pressure, were measured with the same schedule. MAIN OUTCOME MEASURES: Postoperative pain and anxiety intensities and their variations were analyzed. Correlations between postoperative pain and other criteria were researched. RESULTS: Postoperative pain had a high initial level (maximum median, 7), then decreased and reached a score of 3 at the 30th hour. Unpredictable individual peaks of pain were reported. Anxiety was never high (maximum median, 4). No individual correlation was found between pain and objective parameters. CONCLUSIONS: After laryngeal surgery for cancer, pain can reach high levels, particularly in the first hours following recovery. Analgesic administrations at fixed hours are not effective enough. Postoperative analgesic treatment should aim to prevent the high initial pain and be individually adapted.

Acetaminophen↗

PubMed1998

CD1 hearing-impaired mice. I: Distortion product otoacoustic emission levels, cochlear function and morphology.

The levels of distortion product otoacoustic emissions (DPOAEs) were measured in a strain of hearing-impaired mutant mice (CD1) at various stages of outer hair cell impairment and compared to those of a control inbred strain (CBA/J). Parallel measurements of cochlear potentials and auditory brainstem evoked responses (ABRs) were performed and surface preparations of organs of Corti were observed using phalloidin staining of filamentous actin. Comparison of DPOAEs (elicited by stimulus levels of 60 and 70 dB SPL) with standard functional tests allowed the categorization of CD1 ears into two groups on the basis of the presence or absence of DPOAE, which corresponded to mean ABR thresholds greater or less than 40 dB nHL respectively. When adopting ABR threshold as the gold standard, this procedure yielded rates of false-positives and -negatives ranging from 5 to 16%. However, individual predictions of electrophysiological function from DPOAE levels were not accurate, owing to their large variance, and attempts to optimize stimulus levels did not reduce this variance. In contrast, the profiles of DPOAE level vs. f2 exhibited large correlations with ABR threshold profiles as a function of f2. It was also noteworthy that the mean levels of DPOAEs in CD1 mice recorded in frequency intervals with normal ABR thresholds were significantly smaller than those of CBA/J mice. Although hearing loss was revealed early both by DPOAEs and by other functional tests, surface preparations often remained normal until about 3-4 months of age.

Acoustic Stimulation↗

PubMed1998

CD1 hearing-impaired mice. II. Group latencies and optimal f2/f1 ratios of distortion product otoacoustic emissions, and scanning electron microscopy.

In our companion paper (Le Calvez et al., 1998), the levels of distortion product otoacoustic emissions (DPOAE) were collected in the ears of CD1 mice with progressive degeneration of cochlear outer hair cells (OHC). Their comparison to standard functional measurements such as auditory-evoked brainstem responses (ABR) showed that CD1 ears could be classified as normal or impaired in a frequency-specific manner using DPOAE levels. The present work reports how DPOAE phases and levels of young CD1 mice were affected by varying the frequency ratio of eliciting stimuli at frequencies f1 and f2. Normally hearing CBA/J mice served as controls. The rate of phase change of DPOAE when f1 was varied and f2 was fixed allowed the group delay of DPOAE to be derived. The changes of DPOAE levels during this procedure disclosed bandpass characteristics that several reports (Fahey and Allen, 1986; Brown and Gaskill, 1990) assumed to be the reflection of important features of cochlear micromechanics, possibly in relation to the coupling of OHCs to the tectorial membrane. Group delays became significantly shorter when ABR thresholds exceeded 40 dB elevation. The bandpass filter characteristics strikingly depended on auditory function so that the optimal ratio f2/f1 progressively shifted from 1.24 to 1.50 or more when hearing loss increased. A difference was also noted between CD1 ears whose ABR thresholds were not yet increased and control CBA/J (optimal ratio 1.20). Scanning electron microscopy disclosed a variety of often minor OHC lesions that were only roughly correlated with cochlear function. However, the presence of abnormalities in the reticular lamina associated with early changes of DPOAE fine structure as a function of f2/f1 supported the hypothesis of some involvement of micromechanical features in the bandpass filter characteristics of DPOAE. The sensitivity of their measurement in pathological situations is potentially interesting.

Animals↗

PubMed1998

Direct evidence of cubic difference tone propagation by intracochlear acoustic pressure measurements in the guinea-pig.

The fine tuning mechanisms involved in the normal processing of sound in the cochlea are non-linear, hence combination tones are generated inside the cochlea when a pair of low-level pure tones with neighbouring frequencies f1 and f2 is used as a stimulus. Their detection as sounds in the ear canal proves that they undergo backward propagation in the cochlea and through the middle ear, and the non-invasive measurement of the combination tone at 2f1-f2, called the cubic difference tone (CDT), has become a routine method of monitoring cochlear function. In order to gain information on the hypothetical places where CDTs are generated, on their intracochlear levels and propagation velocities, direct measurements of CDT pressure waves were carried out in scala vestibuli and tympani of the first and second turn of the guinea-pig cochlea. Cubic difference tones at 2f1-f2 varied from 0.75 to 9 kHz and were measured with a miniature piezoresistive transducer. Its high sensitivity allowed the detection of CDTs whenever their levels exceeded 5 dB SPL in the ear canal, i.e. 40 dB SPL (re: 20 microPa) inside the cochlea. The levels of CDTs were similar in scala vestibuli of the first and second turn. Phase comparisons between measurements at 2f1-f2 in the first and second turn allowed determination of the place where the CDT phase was minimum. It provided an estimation of the generation site of the CDT, which appeared to be close to the place tuned to f2 for stimulus levels lower than 70 dB SPL. Forward and backward travel times from one turn to the other were assessed at several frequencies, and both values were shorter than 0.2 ms. In contrast, the overall 'round-trip' delay of CDTs, measured in the ear canal, was about five times larger, suggesting that local filtering processes rather than propagation delays account for the overall CDT delay.

Acoustic Stimulation↗

PubMed1998

Characteristics of the acoustic distortion product 2f2-f1 from the normal human ear.

The aim of this study was to determine the basic properties of the 2f2-f1 distortion product otoacoustic emissions (DPOEs) in 36 normally hearing subjects and to compare their characteristics with those of the 2f1-f2 DPOEs. The influence of stimulation parameters on 2f2-f1 DPOE behaviour was examined: i) stimulation levels varied from 40 to 70 dB sound pressure level in 10 dB steps; and ii) two values of the f2/f1 ratio were used (1.12 and 1.22). The prevalence and the level of the 2f2-f1 DPOEs depended on three parameters: f2 frequency, stimulation level and f2/f1 ratio. The results showed many differences between the characteristics of 2f1-f2 and 2f2-f1 DPOEs, probably due to their being generated by different mechanisms. Thus, the 2f2-f1 DPOEs may provide different information about the cochlear status and could be of clinical interest.

Acoustic Stimulation↗

PubMed1997

[Non-invasive monitoring of intracranial pressure changes through the ear].

Otoacoustic emissions are low energy vibrations generated by the inner ear during the physiologic process of hearing. The authors measured transiently evoked otoacoustic emissions in normal hearing individuals placed in Trendelenburg position and during diagnostic elevation of intracranial pressure in neurosurgical patients. In Trendelenburg position and at elevated intracranial pressure and reproducible phase shift of otoacoustic emissions could be observed. This phase shift was linear to the pressure increase of intracranial liquids. According to the hypothesis of the authors intracranial pressure increase is transmitted to the inner ear (possibly by the cochlear aqueduct) and thereby the mechanical load on the stapes footplate is elevated. This, in turn, causes a stiffening of the annular ligament which changes the angle of the impedance vector and thereby the phase of the whole vibrating system. By measuring the phase of otoacoustic emissions it is possible to monitor intracranial pressure in various clinical states.

Ear, Inner↗

PubMed1997

Ontogenesis of rat cochlea. A quantitative study of the organ of Corti.

A systematic quantitative set of data concerning the organ of Corti in developing Sprague-Dawley rats at intervals from 18 days of gestation to 10 days after birth (DAB) is provided in this study. Using phalloidin staining, the total number of inner and outer hair cells, the whole length of cochlea, as well as the diameter of inner and outer hair cells and the intercellular space between inner hair cells were determined in order to analyze the quantitative change of inner and outer hair cells during development and to explore some roles of the factors regulating the growth of cochlea. The results show that: (1) The length of cochlea approached its adult size by 7DAB. (2) The growth of the extreme part of the apex was responsible for the delayed elongation of the cochlea. (3) Growth in the cochlear length mainly results from an increase of cell diameter tempered by a decrease of intercellular space. (4) The adult size of inner and outer hair cells was obtained by 7-14DAB. (5) The final number of inner and outer hair cells was reached at 3DAB and remained constant through adulthood. No significant hair cell overproduction and cell death were observed during ontogenesis of the cochlea. The negligible importance of overproduction and missing hair cells during hair cell differentiation suggest that there is a precise regulation phenomenon for producing the right spatial organization of the organ of Corti.

Actins↗

PubMed1997

Monitoring of functional changes after transient ischemia in gerbil cochlea.

Ischemia and reperfusion are involved in numerous sensorineural pathologies. A model of reversible cochlear ischemia has been designed in Mongolian gerbil. Selective labyrinthine ischemia of variable duration (4-10 min) was achieved through a posterior transcranial approach. Ischemia and reperfusion were controlled with the help of laser Doppler velocimetry. Functional changes were monitored every 1-10 s throughout experiments, using cochlear potentials and otoacoustic emissions. After interruption of blood flow, all signals rapidly began to decay. In contrast to cochlear potentials, otoacoustic emissions always exhibited a plateau before reaching noise floor only after approximately 4-5 min. Upon ischemia release, cochlear blood flow recovered instantly and completely and cochlear potentials rapidly improved in most cases, in contrast to otoacoustic emissions that underwent a delayed decay after immediate partial recovery. The phase and group latency of otoacoustic emissions exhibited only small changes throughout ischemia and reperfusion, suggesting adaptive rather than damaging mechanisms. Cochlear function returned to normal after 5 min 30 s ischemia but longer complete ischemia sometimes led to irreversible damage despite the systematic presence of some recovery just after ischemia release. This behavior suggests that reperfusion in itself can be deleterious to a sensorineural organ and this model can be useful for identifying the noxious mechanisms of ischemia and reperfusion.

Animals↗

PubMed1997

Reverse middle-ear transfer function in the guinea pig measured with cubic difference tones.

Otoacoustic emissions are increasingly useful for determining cochlear function noninvasively. It is widely agreed that these acoustic signals reflect micromechanical processes in the cochlea. However, their quantitative interpretation requires knowledge of the ways in which vibrations travelling back to the ear canal from the cochlea are shaped by the middle ear. An intracochlear source is needed to derive the reverse middle-ear transfer function (rMETF) by comparing pressure in the external ear canal to the corresponding pressure in scala vestibuli. In the present study, the rMETF was obtained in vivo in the guinea pig using as intracochlear sound source the cubic difference tones (CDTs) generated by a pair of external pure tones. With a closed ear canal and open bulla, the rMETF was found to be flat (-35 dB) over a broad frequency range (1.5-8 kHz). The differences between forward and reverse METF could be explained by different loads acting on the middle ear network, which depends on the direction of signal transmission. With knowledge of the rMETF, it becomes possible to quantify CDTs within the cochlea by measuring them noninvasively in the ear canal.

Acoustic Stimulation↗

PubMed1997

Click-evoked otoacoustic emissions and the influence of high-frequency hearing losses in humans.

Click-evoked otoacoustic emissions (cEOAEs) are thought to reflect the presence of highly tuned mechanisms involved in sound processing inside the cochlea. When the sensitivity and tuning of the inner ear are impaired in some frequency range, the spectral components of cEOAEs in the same frequency range are expected to be altered if the previous premise is correct. Although clinical experience does not contradict such an interpretation, fundamental aspects of cEOAE generation and propagation in the cochlea are not clear enough to preclude possible additional influences of remote cochlear places on cEOAE. In order to analyze this possibility, ultra-high-frequency hearing thresholds between 8 and 16 kHz were assessed in 43 human subjects that had clinically normal hearing thresholds in the frequency range of cEOAEs. The magnitude of their cEOAEs was found to be correlated to their average ultra-high-frequency hearing threshold, especially when ears presenting spontaneous otoacoustic emissions were not taken into account (p = 0.002, r2 = 0.29). Age and ultra-high-frequency hearing thresholds were correlated (p < 0.01, r2 = 0.40); thus it is not possible to exclude that aging was the primary cause of the observed trend. The contribution of ultra-high-frequency hearing status to cEOAE magnitude, perhaps in relation to age, seems to explain a significant part of the variance of "normative" emission data and may be of interest for early detection of high-frequency hearing impairments.

Adult↗

PubMed1997

Statistical evaluation of hearing screening by distortion product otoacoustic emissions.

The aim of this study was to provide a statistical evaluation of the screening properties of distortion product otoacoustic emissions (DPOEs) in individuals with clinically normal hearing and in patients with pure sensorineural deafness of various degrees. The main informational parameters used were sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and the analysis of receiver operating characteristic (ROC) curves. For each frequency tested, ears were classified as a function of their audiometric threshold. Two groups were defined relative to an arbitrary reference, the "audiometric criterion." The PPV decreased and NPV increased with increases in the audiometric criterion. Each point of the ROC curve represents the relationship between the false alarm rate and the hit rate for each audiometric criterion ranging between 10 and 75 dB hearing level: the lower the audiometric criterion, the lower the hit rate value, and the lower the false alarm value. The audiometric criterion giving the highest hit rate and the lowest false alarm rate was 55 to 60 dB hearing level for primaries at 60 and 70 dB sound pressure level, or 25 to 30 dB hearing level for primaries at 30, 40, and 50 dB sound pressure level. These two different behaviors of ROC curves are consistent with the hypothesis that DPOEs do not represent activity at a single location along the basilar membrane.

Adolescent↗

PubMed1997

Characteristics of transient-evoked otoacoustic emissions (TEOES) in neonates.

Transient-evoked otoacoustic emissions (TEOEs) were measured in 1164 ears from 582 neonates without any risk of hearing impairment in order to define basic characteristics useful in deciding if TEOEs could be considered as "normal" in a screening test. Five neonates had no recordable TEOE and ABR thresholds greater than 30 dBnHL. Technical conditions have been analysed using the intensity of the click stimulation, the time necessary to record TEOEs, and the noise floor in the external ear canal (i.e. A-B magnitude). The TEOE magnitude varied between 6.6 dB SPL and 38 dB SPL (mean = 21.75 dB SPL). Only 5% of the tested neonates had a TEOE magnitude lower than 7.75 dB SPL. The TEOE magnitude for the right ear of a neonate was statistically different from those recorded in the left ear (22.4 dB SPL versus 21 dB SPL). The mean TEOE magnitude for male ears was statistically different from those recorded in female ears (21.4 dB SPL versus 22.1 dB SPL).

Acoustic Stimulation↗

PubMed1996

The efferent-mediated suppression of otoacoustic emissions in awake guinea pigs and its reversible blockage by gentamicin.

The physiology of the medial efferent olivocochlear system involves suppressive interactions of contralateral sounds on ipsilateral sound-evoked responses, but its role is largely unknown to date. Medial efferents act at the level of cochlear outer hair cells via cholinergic synapses and might affect their mechanical activity, thereby modulating auditory sensitivity. The aim of the present work was to obtain noninvasive measurements of distortion-product otoacoustic emissions (DPOEs), which reflect outer hair cell function, in order to establish the characteristics of medial efferent-induced suppression in awake, restrained guinea pigs. A clear suppression of DPOEs was induced by continuous contralateral white noise presented at 20-70 dB SPL, in the absence of any confounding effect of anesthesia, middle-ear muscles, or acoustic cross talk. Recently, acute injection of a high dose of the aminoglycoside antibiotic gentamicin (150 mg/kg) was reported to alter the suppressive effect of contralateral noise on eighth nerve-compound action potentials, presumably by blocking efferent synapses to outer hair cells. This hypothesis was confirmed with DPOEs for which a single injection of gentamicin at the same dose abolished suppression after about 1-2 h, whereas no change in basal levels was observed. Complete recovery was obtained after 48 h. This experiment may provide an easy, noninvasive tool for studying auditory function with and without functioning efferents.

Animals↗

PubMed1996

Otoacoustic emissions: a new tool for monitoring intracranial pressure changes through stapes displacements.

Changes in hydrostatic intracranial pressure (ICP) are thought to be transmitted to cochlear liquids, thereby altering the mechanical load on the stapes footplate. Hence the stiffness of stapes' annular ligament is expected to reflect ICP changes. Corresponding middle-ear transmission changes have been assessed using click-evoked otoacoustic emissions (EOAE) in two experiments. The first one was performed in 22 normal human subjects submitted to posture changes. In the second one, controlled ICP increases were applied to 18 patients in neurosurgery operating theater. EOAEs were monitored in these subjects throughout the experiments and their phases and amplitudes were analyzed as a function of frequency. ICP affected EOAEs in a systematic manner in both experiments, i.e., the main effect of ICP increase was phase lead of EOAE components below 2 kHz without any significant amplitude or frequency shift. Their variations were much more evident than the modifications in middle-ear impedance assessed by standard impedance or admittance measurements. The second experiment led to a quantitative linear relationship between ICP and EOAE phases. It demonstrated that the sensitivity of EOAE phase monitoring technique proves to be quite high, i.e., 55 daPa increases in ICP are readily detected in all subjects. The results are consistent with the predictions of classical middle-ear models as to the transmission alterations induced by ICP-related changes in the stiffness of the annular ligament of the stapes. Non-invasive monitoring of ICP in patients with hydrocephalus treated with ventriculo-peritoneal shunts might be attempted with this technique, although it is restricted to patients with detectable EOAEs (i.e., about 50% in this series).

Acoustic Stimulation↗

PubMed1996

[Postoperative pain evaluation in the surgery of head and neck cancers].

UNLABELLED: Postoperative pain has rarely been assessed after ENT surgery for cancer. Its evaluation is difficult because of the frequent lack of speech after this type of surgery. OBJECTIVES: to assess postoperative pain after pharyngeal and laryngeal surgery for cancer. PATIENTS AND METHOD: prospective study in 13 men (38-71 ans) operated on by total laryngectomy with or without partial pharyngectomy. A standardised treatment using propacetamol and nalbuphine was systematically prescribed. Pain, anxiety and relief were assessed with the help of visual analogue scales (VAS). Heart rate, mean blood pressure and respiratory rate were evaluated too. RESULTS: mean postoperative pain was maximal just after recovery (6,64 +/- 2,14 cm) then decreased regularly. Initial mean score of anxiety was 3,14 +/- 3 cm and then was decreasing too. Anxiety and pain did not correlate except in 2 cases. None of the 3 objective parameters correlated with pain. CONCLUSION: postoperative pain can be assessed reliably after pharyngolaryngeal cancer surgery and is probably underrated. Its high initial score indicates that efforts must be focused on pre-emotive analgesia. Its high individual variability let us hypothesise that PCA systems should be effective.

Adult↗

PubMed1996

[Characteristics of 2F2-F1 distorsion products in adults with normal hearing].

Acoustic distorsion products (ADP) are otoemissions which the cochlea emits in response to stimulation by two pure frequencies, f1 and f2. ADP 2f1-f2 has been widely studied, however little work has been reported on ADP 2f2-f1. We performed a study in 34 adults with normal hearing to determine the normal values (incidence and amplitude) of ADP and compared them with the ADP 2f1-f2. Two f2/f1 ratios were used (1.22 and 1.12). Different behaviors were observed between the two types of ADP. These results suggest that the mechanisms generating the two ADP are different and that, consequently, ADP 2f2-f1 should have clinical implications different than ADP 2f1-f2.

Acoustic Stimulation↗