Search PubMed⌕ Search

Biomedical subjects

A R Thornton

Publications and source records attributed to A R Thornton.

At least 37 records · Page 2Linked to original sources
PubMed1995

Failure to clinically predict NICU hearing loss.

Neonatal intensive care unit (NICU) survivors demonstrate handicapping sensorineural hearing loss up to 50 times more frequently than normal newborns, yet little is known about the etiology of the hearing loss. Theoretically, accurate identification and triage of a particular infant based on a clinical profile would be useful. Forty NICU graduates of The Massachusetts General Hospital were selected for a detailed retrospective chart review evaluating prenatal, perinatal, and NICU medical conditions and treatment. Twenty-three patients identified with hearing loss and 17 infants with normal hearing were compared clinically. Univariate and multivariate analysis was performed on a subpopulation of patients (20 with hearing loss and 16 with normal hearing). A history of ventilation was associated with hearing loss (P = .0023), but this factor was not absolute. No other clinical parameters were convincingly linked to hearing loss. We conclude that reliance on risk factors is an inadequate clinical method to select a patient for a hearing test and that each NICU survivor deserves audiometric evaluation.

Audiometry↗
PubMed1995

The effect of stimulus rate on the contralateral suppression of transient evoked otoacoustic emissions.

A new technique, which uses Maximum Length Sequences (MLSs) to enable the recording of TEOAEs at very fast rates, has been described previously. Such a technique enables rate studies to be carried out and here the effects of stimulus rate on the contralateral suppression of TEOAEs (Collet effect) have been studied. The results show that the Collet effect has virtually disappeared by a click stimulation rate of 2000 clicks/s. The waveform changes caused by the 'adaptation' due to increase in stimulus rate and the 'suppression' due to contralateral stimulation have been evaluated and compared. The comparison indicates that the same mechanism may be involved in both; the increase in stimulus rate leading to an ipsilateral suppression, greater in value but the same in form as the contralateral suppression.

Acoustic Stimulation↗
PubMed1995

Isochronic mapping of the auditory brainstem response: normative results.

Isochronic mapping involves recording multi-channel evoked potentials from scalp electrodes and plotting contours of peak latencies. In this study, auditory brainstem responses were recorded from 20 electrode sites for left, right and binaural stimulation of each ear of 10 male and 10 female, normally hearing, young adults. Analysis of the data showed that the stimulus parameters of intensity, polarity and rate had no significant effect on the maps. On monaural stimulation, wave V was recorded first at the contralateral mastoid and ipsilaterally frontally and last at the ipsilateral mastoid some 350, mu s later. Binaural stimulation gave a symmetrical map, with wave V recorded first frontally and last at the occiput. In contrast, wave III was recorded first ipsilaterally and frontally and last at the contralateral mastoid. Wave II was recorded first at the rear of the contralateral mastoid and last forward of the ipsilateral mastoid. Comparisons between these results and human physiological studies are in agreement for waves V and III but do not support the concept of the VIIth nerve alone as the generator for wave II. These results suggest that this technique is a potentially useful diagnostic tool and it is intended to evaluate it by testing patients with a range of sensory, peripheral-neural and central-neural pathologies.

Audiometry, Pure-Tone↗
PubMed1995

Difficulties experienced in implementing the ABR travelling wave velocity (Delta V) technique with two commercially available systems.

The ABR Delta V technique involves measuring the difference in latency of the wave V click-evoked ABR in the presence of ipsilateral high-pass noise filtered at 1.42 kHz and at 5.68 kHz. It has been reported that a small latency difference between the two conditions is suggestive of Ménière's disease. The aim of this study was to establish normative data for two commercially available systems. The latency differences obtained in the present study are considerably smaller than those previously reported in the literature. Other problems, including difficulty in identifying wave V in the masked conditions, prevent us from currently using this test technique. There are a number of technical problems which may account for some of the problems experienced when implementing the Delta V technique with commercial equipment and there is at least the possibility that the problems may be overcome in the future.

Adult↗
PubMed1994

Clinical use of otoacoustic emissions in children with autism.

Transient-evoked otoacoustic emissions (TEOAEs) may offer an objective way of evaluating the peripheral auditory systems of difficult-to-test patients. Children with autism are often suspected of hearing loss, but frequently will not respond on traditional behavior auditory tests. The clinical feasibility of obtaining TEOAEs on children with autism was evaluated here. The use of TEOAEs for 6 children (12 ears) with autism is described here regarding the acquisition of data, the presence of emissions, and their amplitudes and reproducibility. Emissions were recorded for 9 of the 12 ears; the lack of emissions for the remaining 3 ears was due to lack of patient cooperation. The results suggest that TEOAEs may be a valuable part of the audiologic test battery for children with autistic behavior. The ease of obtaining emissions for these children with autism is discussed.

Adolescent↗
PubMed1994

A model to evaluate and maximize hearing aid performance by integrating the articulation index across listening conditions.

A method for integrating the articulation index (AI) across listening conditions was developed and applied to a preliminary model for evaluating and optimizing prescriptions of hearing aid characteristics. The model takes hearing threshold, masking of noise, self-masking of speech, high level cochlear distortion, and the peak-clipping effects of a hearing aid into account. The integrated AI (IAI) across a range of listening conditions is used as a criterion for evaluating a specific hearing aid response characteristic and calculating an optimal frequency-gain characteristic that maximizes the IAI. For a high-frequency hearing loss, the frequency-gain characteristics and IAI's derived from an optimal IAI (OIAI), POGO, and NAL prescriptions are compared for two of listening situations: a quiet setting and a setting with a signal-to-noise ratio of -3 dB. The results predict that, in quiet, the OIAI prescription is not significantly different from the well-established prescriptive procedures such as the POGO and the NAL. For the noise condition, however, the optimal IAI model is predicted to be better in terms of speech intelligibility.

Acoustic Stimulation↗
PubMed1994

Technical aspects of recording evoked otoacoustic emissions using maximum length sequences.

Our previous work has demonstrated the feasibility of recording evoked otoacoustic emissions (EOAEs) using maximum length sequence (MLS) techniques. New equipment has been constructed, using standard DSP boards and computers, which permits stimulation at much higher rates. The technical aspects of analogue-to-digital converter (ADC) requirements, stimulus problems, artefacts, signal-to-noise ratio (SNR) computations and MLS application are considered here and illustrated with data from the new system.

Ear, Inner↗
PubMed1994

Feasibility of otoacoustic emission detection followed by ABR as a universal neonatal screening test for hearing impairment.

The feasibility of attempting a two-stage universal screening test for auditory impairment was assessed at a large district maternity hospital. The first stage was measurement of otoacoustic emissions using the Programmable Otoacoustic Emission Measurement System. Those failing the first stage proceeded to automated analysis of auditory brainsteam responses. A single tester working for 6 h on 6 days per week attempted to test all babies born between the hours of midday and midnight for 2 weeks and then all babies born between midnight and midday for a further 2 weeks. Of 217 babies born during the study periods, one infant died and three were still receiving intensive care at the end of the study. Of the remaining 213 infants, auditory testing was undertaken in 201 infants (94%). Eight infants (4%) who failed the first stage of the screening test did not undergo the second stage. Of those 193 infants completing the screen, one (0.5%) failed the screen unilaterally. There were no bilateral failures. Three testers, working two and a half whole-time equivalents, should be adequate to achieve a coverage of 90% and a specificity of 99% for this screen in this clinical setting.

Cross-Sectional Studies↗
PubMed1994

A comparison of neonatal evoked otoacoustic emissions obtained using two types of apparatus.

The transient evoked otoacoustic emission (TEOAE), generated by a click and recorded in the ear canal is influenced by many factors. Of these, the form of the stimulus, the characteristics of the microphone, amplifiers and filter are probably the major ones. In addition, the acoustical loading of the ear canal by the probe may interact with the TEOAE measurement. Data presented here were obtained from 64 babies tested on each of 3 days post partum. The differences in the TEOAEs produced by the ILO88 and POEMS instruments can be quite marked. The ILO88 TEOAEs consistently have larger high frequency components than do the emissions from the POEMS system. The ILO88 system also gives higher correlations between repeat recordings. Such differences point out the need for explicit standards in probe design.

Equipment Design↗
PubMed1994

Experience of using vibrotactile aids with the profoundly deafened.

This is a summary of clinical experience and research findings gathered from using vibrotactile aids over 7 years. This interest grew from a research project to evaluate four wrist-worn vibrotactile aids for the rehabilitation of the profoundly deaf. To facilitate this, a training programme was developed to help patients get the most from the aid. Having found that the RNID/Summit Tam vibrotactile aid was the most appropriate, this has been fitted to over 50 patients. The results of the comparative trial, an evaluation of our methods and a discussion of our clinical experience using vibrotactile aids with profoundly deafened patients are presented.

Deafness↗
PubMed1994

Significance of false-positive auditory brainstem response: a clinical study.

Auditory brainstem response (ABR) is a good screening test for cerebellopontine angle (CPA) tumors and other retrocochlear diseases. The pathologic correlates of many cases with positive ABR remain unknown. A two-staged clinical study was performed to help us understand the significance of a false-positive ABR. In the first stage, data from 66 patients with abnormal ABR were reviewed. Nineteen patients had identifiable causes for the ABR abnormality, whereas 47 patients had no lesions identified. In the second phase of the study 21 of the 47 patients were re-evaluated with a minimum follow-up period of 1 year. A detailed interval history was obtained, and the work-up, including imaging studies, was repeated in an attempt to reach a diagnosis. One patient was found to have a CPA tumor, but for nine patients a definite final diagnosis could not be determined. The implications of abnormal ABR and normal initial imaging study are discussed, and a plan for the work-up of these patients is suggested.

Adult↗
PubMed1993

Evoked otoacoustic emissions in preterm infants.

Since Kemp's discovery of the otoacoustic emissions phenomenon [7], much study has been given to understanding the nature of it and its ontogeny. Development of the evoked otoacoustic emissions (EOAE) has spurred much interest because they may used as a valid and relatively quick test to assess cochlear integrity in the very youngest patients. One thing that has been learned is that EOAE amplitudes are much larger in normal ears of infants than in normal ears of adults. We asked about the form of this development in a longitudinal, rather than cross-sectional, study in an investigation on children born before 40 weeks postconceptional age. We were able to examine reliably five ears of four preterm babies while they remained in the neonatal intensive care unit. The EOAEs of these ears were then studied to determine whether and how they changed over time. To do this, we examined both their amplitudes and their spectral properties. It turned out that there are properties of the EOAE spectrum that may be related to post-conceptional age. These are described herein. These findings are expected to have considerable clinical utility as more and more researchers are able to confirm their validity.

Evoked Potentials, Auditory↗
PubMed1993

High rate otoacoustic emissions.

One of the practical problems of testing young children using evoked otoacoustic emissions (EOAEs) is that there is a need for the child to be quiet for a period of a minute or so. To achieve this can mean test periods of 10 min or longer. A new application of maximum length sequences (MLSs) to EOAEs is described that enables the test to be performed in a few seconds or less. Data from adults and neonates obtained at stimulation rates up to 840 clicks/s are presented and compared with conventionally derived emissions and the implications and applications of this new method are assessed.

Acoustic Stimulation↗
PubMed1993

Auditory brainstem responses recorded at fast stimulation rates using maximum length sequences.

There are now commercially available systems which can provide maximum length sequence averaging techniques. This study examines the effects on auditory brainstem response amplitude and latency of using such a system and stimulating at rates from 9 to 1000 clicks/s. As expected there is considerable adaptation of the response such that at 1000 clicks/s wave V amplitude is only approximately 8% of its low stimulation rate value. As the stimulation rate is increased so the test time taken to obtain a response of the same signal-to-noise ratio as a conventional recording decreases. This process continues up to a maximum click rate of about 200 clicks/s. Thereafter, the response adapts so rapidly that further increases of rate lead to a worsening of performance. Thus, the optimum stimulation rate appears to be of the order of 200 clicks/s and this can give a speed improvement by a factor of approximately 2.8 over conventional recordings taken at 9 or 10 clicks/s.

Adaptation, Physiological↗
PubMed1993

Frequency analysis of the contralateral suppression of evoked otoacoustic emissions by narrow-band noise.

The influence of noise bandwidth on the contralateral masking of click-evoked otoacoustic emissions was investigated by recording emissions from 20 normal subjects with contralateral narrow-band noise, with wide-band noise and without contralateral noise for comparison. Narrow-band noise of five different centre frequencies and three different bandwidths per frequency was used at intensities of 40 and 60 dB SL. Analysis of the emissions showed that the 40-dB SL contralateral noise did not produce a significant amount of suppression. The suppression produced by 60-dB SL noise was spread throughout the frequency range of the emissions, with limited frequency specificity. There was some evidence that the amount of suppression increases with the bandwidth of the noise, particularly for noises centred on 1 and 2 kHz; the wide-band noise produced much greater suppression than any of the narrow bands. There was a large amount of inter-subject variation, which could not be explained by differences in the absolute level of the emissions. One subject with a total unilateral hearing loss in the contralateral ear was also tested, and gave no significant suppression.

Acoustic Stimulation↗
PubMed1993

External- and middle-ear factors affecting evoked otoacoustic emissions in neonates.

Babies without any of the known risk factors for hearing impairment were taken from normal maternity wards and tested daily for 3 days post-partum. Tympanometric and evoked otoacoustic emission data were obtained from 121 babies. Middle-ear pressure and middle-ear compliance values were obtained with a Grason Stadler Middle-Ear Analyser (GSI-33) using a 1000-Hz probe tone. All babies had their evoked emissions measured on the Programmable Otoacoustic Emissions Measurement System (POEMS) equipment. The middle-ear compliance, the proportion of normally shaped tympanograms, the middle-ear pressure and the proportion passing EOAE testing all improved over the 3 days. However, the statistically significant factors affecting the pass rate appeared to be only the middle-ear pressure (for a small number of babies) and the degree of obstruction of the external ear canal. Whilst both these factors play a part in determining emission pass/fail rates they do not fully account for the observed changes in pass rate. There are developmental and other mechanisms which must contribute to the increase in pass rate as the baby matures.

Acoustic Impedance Tests↗
PubMed1993

Click-evoked otoacoustic emissions: new techniques and applications.

There are practical, clinical circumstances in which a decrease in test time for evoked otoacoustic emissions would be of economic or practical value. In addition, there are circumstances in which it is desirable to obtain more diagnostic information from the evoked emission. This preliminary report concerns predominantly one of these aspects but considers both of them. It is not possible to reduce the test time by simply increasing the stimulation rate because responses and stimuli will overlap and give rise to contaminated responses. However, these limitations can be overcome if a maximum length sequence of clicks is used. These sequences of clicks and silences enable responses of a duration greater than the time between stimuli to be recorded and deconvolved to produce an uncontaminated response. Conventional recordings at stimulus rates of 33/s and 50/s have been taken together with maximum length sequence recordings at rates up to 840/s and the waveforms correlate very well. Although the emission shows some adaptation at the highest stimulation rate this does not prevent a significant reduction in test time.

Acoustic Stimulation↗