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Biomedical subjects

A R Thornton

Publications and source records attributed to A R Thornton.

At least 55 records · Page 3Linked to original sources
PubMed1991

A non-invasive, objective test of endolymphatic hydrops.

Our previous work has shown that auditory brainstem responses (ABRs) can be used to measure the basilar membrane travelling wave velocity (TWV). Based upon the hypothesis that increased pressure in the scala media will increase the stiffness of the basilar membrane and, hence, increase the speed of the travelling wave. ABRs have been used to provide a means of objectively testing for endolymphatic hydrops. Ten normally hearing subjects and 20 Meniere's patients were tested. The data for the Meniere's group show that the TWV was within normal limits at all frequencies tested, except 5.7 kHz. At this frequency, the TWV greatly exceeded that of the normal group. A short duration (15-30 min) clinical test has been developed which involves the recording of two masked brainstem responses and the measurement of the difference in wave V latencies. Clinical verification that the technique is valid was obtained by monitoring patients undergoing glycerol dehydration. The additional hardware to enable this test to be carried out with a standard evoked response system has been constructed and three, parallel, clinical trials are in hand. Currently, this technique is being applied to longitudinal studies of Meniere's patients and to evaluating the action and efficacy of various drugs. A double-blind trial using a placebo and two different drugs is underway and preliminary results are presented here.

Adolescent↗
PubMed1991

Apparent travelling wave velocity changes in cases of endolymphatic hydrops.

This study attempted to develop a test which would be specific for endolymphatic hydrops. It is based upon the hypothesis that increased pressure in the scala media will alter the stiffness of the basilar membrane and hence increase the speed of the travelling wave. Auditory brainstem-derived responses were used to measure the basilar membrane travelling wave velocity in normals and to take the equivalent measures in Meniere's patients. Ten normally hearing subjects and 20 Meniere's patients were tested. The data for the Meniere's group showed that the travelling wave velocities were within normal limits at all frequencies tested, except 5.7 kHz where the travelling wave velocity greatly exceeded that of the normal group. A theoretical possibility that these findings may be the result of damaged and broadened VIIIth nerve tuning curves is discussed but travelling wave measures and psychophysical tuning curve measurements on the Meniere's group, normals and noise-induced hearing loss (NIHL) cases showed that this was not a significant factor. The data indicate that this technique can detect endolymphatic hydrops and a short duration clinical procedure has been devised.

Adolescent↗
PubMed1991

Isochronic mapping: a preliminary report of a new technique.

A new technique which we have named 'isochronic mapping' is described. The conventional technique of plotting isopotential maps shows little or no contrast for far-field potentials such as the auditory brainstem response (ABR). However, by modifications to the mapping software, the latency values of a peak can be plotted and lines of equal time or isochronic maps can be produced. Data from a normal subject has been obtained for both the compound and derived ABRs and are described in detail. The data are clear but the time delays between earliest and latest projections of a peak are hard to interpret. For monaural click stimulation, wave JV of the ABR projects first to the contralateral side of the head then moves towards the stimulated ear arriving some 0.3 ms later. Possible interpretations of this finding are discussed but further experimentation is needed to develop our understanding of these data.

Acoustic Stimulation↗
PubMed1989

Clinical experience with electroneurography in the pediatric patient.

Electroneurography (ENoG) has demonstrated utility in adults with facial nerve paralysis. We wished to evaluate the possible usefulness of this test in children. Twenty-six patients, aged 3 months through 16 years, were studied. Initial measurements were obtainable in all but two patients; they were successfully tested on a second attempt. All subsequent patient testing efforts were completed, for an overall successful test rate of 95%. Waveform amplitude and morphology were consistent with adult values, except in infants. The most clinically helpful use of this test was to objectively assess facial nerve function, once spontaneous motion was lost in acquired paralysis or if it had never been seen in congenital paralysis. Surprisingly, analysis of the "normal" side of the face proved most informative for three patients. Use of the test as an absolute predictor for return of function is not possible; however, the ENoG results add data that can be incorporated into the clinical information to make such predictions more rational. We conclude that ENoG can be performed on children, and that the measurements, within bounds of interpretation, can offer objective data not usually available in this age population.

Action Potentials↗
PubMed1989

Verification of a new test of endolymphatic hydrops.

A new objective test of endolymphatic hydrops has been described previously. The test uses auditory brain-stem response (ABR) techniques to estimate the basilar membrane travelling wave velocity (TWV). The underlying hypothesis is that raised pressure in the scala media will lead to an increase in the stiffness of the basilar membrane and that this will give rise to a travelling wave velocity that is greater than normal. It was considered that verification of the technique could be obtained by carrying out the new test before and during a glycerol dehydration procedure. Patients who required this procedure for verification of the diagnosis or as a prognostic indicator for sacculotomy, underwent the following tests. Prior to dehydration an audiogram, the ABR TWV test and a blood sample (for plasma osmolality) were taken. The patient was then given the appropriate amount of glycerol mixed with lemon juice and laid on a bed in a test room. The audiogram and a blood sample were repeated every hour and the ABR TWV test was repeatedly carried out every twenty minutes between the other tests. Six of these procedures have been carried out. In five of them the 0.5 and 1 kHz average threshold improved by at least 10dB and in all those cases the ABR TWV test showed an abnormal pre-dehydration result which moved towards the normal value following dehydration. One patient gave ABR TWV results that were within normal limits before and during the procedure and gave an audiometric change of only 5dB.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

The choice of stimuli for ABR measurements.

This tutorial describes some of the stimulus choices available to clinicians performing ABR evaluations. The motivation for choosing particular stimuli is described in relation to the clinical question being asked. Thus, emphasis is directed toward the rationales for choosing different stimuli. Data are reviewed only briefly to illustrate these rationales. Finally, some effort has been made to relate clinical ABR results for certain stimulus conditions to underlying physiological processes in the hope that these discussions will lead to a more complete understanding of the stimulus-response relation.

Acoustic Stimulation↗
PubMed1989

Tonsillectomy haemostasis: diathermy or ligation.

A retrospective and prospective study has been carried out to assess the morbidity associated with the techniques of diathermy and ligation in controlling tonsillectomy haemorrhage. No difference was found in the incidence of haemorrhage between the two techniques. The use of diathermy cuts the operation time by 26%, and has no increase in morbidity.

Adolescent↗
PubMed1989

Clinical methods for the objective estimation of loudness discomfort level (LDL) using auditory brainstem responses in patients.

Our previous work showed that the slope of the JV latency/intensity function can be used to estimate the loudness discomfort level (LDL). In this study, the previous work was repeated using normal subjects and patients whose LDL was unknown at the time of test. The results showed that the original model still applied. Further measures were taken to evaluate clinical methods of applying this technique. Four basic approaches were used, a 'correction factor' model and a 'curve-fitting' model and these were applied to data obtained from measurements taken in both 5 dB and 10 dB increments. The results showed that the 'correction factor' models were better than the 'curve-fit' approach. The prediction of LDL based upon the 5 dB increment data gave the greater accuracy but the 10 dB increment data gave predictions that were sufficiently accurate for clinical use (95% confidence limits of +/- 8 dB). Thus this ABR estimator has wide application and good accuracy in estimating subjective LDL. A clinical protocol for applying this technique is described.

Adolescent↗
PubMed1989

High-frequency monitoring using an electrostimulation audiometer.

Electrostimulation audiometry can provide high-frequency bone-conduction threshold measurements. To evaluate the use of such an audiometer in monitoring hearing, the following areas were investigated. (1) The variability and repeatability of threshold measurements. (2) To see if the instrument could be used on the ward where the patient would have to wear ear plugs to attenuate background noise, the effect of occluding the ears was assessed. (3) The applicability of the instrument to the range of patients in whom monitoring would be appropriate, specifically the relationship between the patient's age and the effective upper frequency limit of the audiometer. The data showed a variability in threshold measurement that is quite comparable with that obtained with conventional audiometry but which became smaller at frequencies of 12 kHz and higher. There was no overall effect on the threshold of occluding the ears, which meant that the instrument can be used to monitor a non-isolated environment such as a ward. The effective cut-off frequency was about 9 kHz for patients aged 55 years, and so the use of an electrostimulation audiometer to monitor high-frequency auditory thresholds is restricted to younger patients.

Adult↗
PubMed1988

Measures for the optimum estimation of audiometric thresholds from the auditory brainstem response potentials.

Auditory brainstem response potentials were recorded from normally hearing subjects using a wide range of stimulus intensities including a below-threshold condition. Various measures, including the traditional Jewett V (JV) amplitude, were taken from the recordings. The probability of incorrectly concluding that a response was present was found by analysing the distribution of the JV amplitude in the no-stimulus recordings and setting an amplitude of 100 nV as the criterion of whether or not a response is deemed to be present. This probability was used to define equivalent criteria for the other measures and evoked potential (EP) thresholds could then be found for each subject and stimulus by finding the lowest stimulus intensity at which the value of the measure being considered was at or above this criterion value. Two measures were found to give significantly lower and less variable EP thresholds than the others; JV amplitude taking into account the JV latency and a self-template measure involving the correlation between the response waveforms at a high stimulus intensity level and the test intensity level. The latter measure indicates that a template-matching method of threshold estimation might be as reliable for this purpose as the measurement of JV amplitude and has the potential diagnostic advantage over JV measurements that it could be readily used with a fully objective automatic threshold evaluation protocol. The probability of making a false-positive error was found to be disconcertingly high at 0.5 for single measures and 0.22 for complex measures. This underlines the need for replicates to be taken as this dramatically reduces the probability of large errors in threshold estimation.

Audiometry, Evoked Response↗
PubMed1988

The acceptability of cochlear implants and vibrotactile aids.

To obtain data on the likely acceptability of cochlear implants (and of vibrotactile aids), a questionnaire was sent to profoundly/totally hearing-impaired patients. The patients were asked how they felt about their current communication problems and possible benefits to be obtained from such devices. Of the 153 replies obtained, the combined 'yes' or 'maybe' responses indicated that 58% would accept an implant. The corresponding figure for vibrotactile aids was 73%. The statistically significant factors correlating with cochlear implant acceptance were the patient's expectation of the benefit it would give, the time needed for rehabilitation and the degree of communication difficulty that they suffer. The only significant factor in acceptance of a vibrotactile aid was whether the patient had attended the IHR clinic. This implies that the underlying factor is the patient's knowledge about these devices.

Adolescent↗
PubMed1987

The objective estimation of loudness discomfort level using auditory brainstem evoked responses.

The loudness discomfort level (LDL) is of importance in the fitting of hearing aids, but very young children are unable to provide a subjective judgement of LDL. Therefore the relationship between Jewett wave V latency and subjective loudness was investigated to ascertain if objective estimation of LDL is possible. ABR recordings were taken from 8 normally hearing subjects at the stimulus intensity corresponding to their LDL and at stimulus levels from 10 to 30 dB below this. The wave V latency/intensity function did not correlate well with the LDL. However, the slope of this function did correlate to a high degree and a predictive model of LDL was derived. Identical measurements were then taken from a sample of 12 cochlear-impaired subjects with a range of audiometric profiles. Their subjective LDLs could be predicted from the wave V latency function to an accuracy of +/- 5 dB, using the model derived from the normally-hearing subjects. This model appeared to be equally valid for all the degrees and profiles of hearing loss included in the sample and showed a closer relationship to LDL than did absolute wave V latency or estimates derived from the acoustic reflex.

Adult↗
PubMed1987

Stimulus, recording and subject factors influencing ABR diagnostic criteria.

If the diagnostic potential of ABR is to be fully realised, then diagnostic criteria applicable in any clinic and with any equipment are needed. The factors, which may vary between clinics and which can influence the value of a diagnostic criterion, are considered and evaluated. The variables in stimulation and recording parameters and the patient variables which must be taken into consideration in order to achieve internationally applicable standards are detailed. Using the I-V interpeak interval as an example of a parameter for which an international standard may be formulated, the effects of both physical and subject variables and the interactions which they show are given. The interactions between these parameters can account for many of the differences found between different clinics and laboratories. The normative data required by each clinic are outlined and suggestions which could lead to an international standard are made.

Adolescent↗
PubMed1987

The use of flexible probe tubes in insertion gain measurement.

Possible errors in the measurement of insertion gain due to the use of flexible probe tubes are considered and three aspects are investigated. (i) Does the probe tube create an effective vent in the earmould/ear canal system? (ii) Does compressing the probe tube with the earmould affect insertion gain measurement? (iii) Is it possible for a well-fitting earmould to completely compress the probe tube and give entirely spurious results? Comparative measurements were taken using probe tubes passed through the earmould and around the earmould. The results showed that the worst intra-subject standard deviation for the effect of repositioning the probe tube was approximately 5 dB. A statistically significant but small (1.5 dB) effect was produced by the probe tube at 500 Hz. The errors due both to repositioning the probe tube and probe tube compression are significant only at 3 kHz where measurements on one subject showed a 7 dB shift. The effects of probe tube position, probe tube compression and change in placement from the centre of the ear canal to the side produced differences which were significant at 3 and 4 kHz, but again the effect is small (3.2 dB). Complete blockage and marked compression of the probe tube can lead to large measurement errors. However, it is unlikely that an experienced operator would accept data obtained under these conditions as real. The errors involved in using a flexible probe tube placed around the earmould appear to be within limits that will not affect hearing aid prescription to any material degree.

Acoustics↗
PubMed1986

Correlative studies of cochlear neuronal loss with speech discrimination and pure-tone thresholds.

Correlations were made between speech discrimination scores, pure-tone thresholds, and neuronal populations in 28 cochleae which were removed postmortem from elderly patients who had known premortem audiometric records. The predominant pathology present was loss of cochlear neurons. The capability for speech discrimination correlated directly with the innervation density of the 15- to 22-mm region (segment III) of the cochlea. Speech discrimination scores showed an inverse relationship to pure-tone thresholds in the middle frequency range of 1 kHz to 2 kHz.

Aged↗
PubMed1986

Estimation of the number of patients who might be suitable for cochlear implant and similar procedures.

Data have been drawn from four sources to estimate the number of profoundly, bilaterally hearing impaired in Britain who might benefit from a rehabilitational programme which would include cochlear implants and other specialised aids. The sources were: the IHR National Study of Hearing; a total ascertainment survey of General Practitioners, ENT Consultants, Health Visitors etc. in the Wessex Health Region, which requested basic data on their profoundly, bilaterally hearing impaired patients; more detailed questionnaire data obtained directly from a subset of the patients identified in the ascertainment study; and the experience of various cochlear implant centres. Criteria are proposed to select candidates suitable for the initial research and development work on implant devices and to select those who might later be suitable for a routine clinical service with an established technique. Estimates of the corresponding numbers are given. Guidelines for identifying those who might benefit from acoustical aids are offered.

Auditory Threshold↗
PubMed1985

Metabolic facial paralysis in an infant.

A 2-month-old infant developed facial paralysis with a presentation that masqueraded as a possible middle ear tumor. The cause of the paralysis eventually was related to a metabolic consequence of his underlying disorder, cystic fibrosis. To our knowledge, the association of vitamin A imbalance, pseudotumor cerebri, and facial paralysis has not previously been discussed in the otolaryngologic literature.

Cystic Fibrosis↗