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Biomedical subjects

D Prasher

Publications and source records attributed to D Prasher.

At least 19 recordsLinked to original sources
PubMed2002

Effect of MRI noise on cochlear function.

A disadvantage of magnetic resonance imaging (MRI) is the high level of noise produced (peaking between 122 dB and 131 dB). We used otoacoustic emissions (OAEs) as a method to quantify the effect of MRI-generated noise on the cochlea. OAEs were measured in 16 patients before and after MRI and in 16 controls. OAEs decreased in patients after MRI, but the controls, who were not exposed to MRI noise, showed no decrease over the same period. The change in OAEs shows a clear effect of MRI noise on cochlear function, despite use of earplugs. The importance of correctly fitted earplugs cannot be underestimated.

Cochlea↗
PubMed1999

Speech pattern audiometry in hearing impaired children.

The aim of this study was to investigate the use of speech pattern audiometry (SPA) in assessing speech perception abilities of a group of 25 children with sensorineural hearing loss, and to compare their aided performance on SPA tests of four different phoneme contrasts with scores achieved on recorded Manchester Junior Word Lists (MJWL) at their most comfortable listening level (MCLL). The listeners were 25 children, 19 with congenital and six with acquired hearing loss aged between eight and 14 years. They were classified into three groups according to the severity of the hearing loss in the better hearing ear (20-60 dB HL, 61-80 dB HL and >81 dB HL). The SPA tests evaluated listeners' ability to identify word-initial plosives differing in the phonetic features of voicing and place of articulation. The main outcome measures were the SPA gradient measures, the SPA labelling function configuration and MJWL scores. The group with the most severe hearing loss (>81 dB HL) showed significantly poorer performance on the SPA tests and MJWL tests than the groups with mild (20-60 dB HL) to moderate (61-80 dB HL) hearing losses. There was significantly better performance on the two plosive voicing contrast tests than the two plosive place contrasts. For the MJWL, the performance of the group with the more severe hearing loss was also significantly different from the mild and moderate hearing loss groups. A MJWL score of up to 75% was associated with the random labelling configuration on all four SPA tests, emphasizing the different aspects of speech perception that were being examined with each type of test. This study suggests that there is a place for SPA as part of the test battery for speech perception testing in hearing-impaired children.

Child↗
PubMed1999

A comparison of noise induced disability assessments in the UK and Poland.

The difference between the legal assessment of the disability associated with noise induced hearing loss and that experienced by the worker has not as yet been successfully resolved. Legal assessment is driven by financial consideration rather than the rehabilitation needs of the subject. The aim of this paper is to present this problem and consider the formulae currently used in the UK and Poland in the assessment of noise induced hearing disability.

Audiometry, Pure-Tone↗
PubMed1999

Tinnitus and impulse noise-induced hearing loss in drop-forge operators.

Tinnitus is frequently accompanied by noise-induced hearing losses, and perhaps as it is assumed--particularly with those arising from exposure to impulsive types of noise. In order to explain it and to estimate a prevalence of tinnitus in the industrial, impulse noise workers the group of 261 drop-forge operators exposed to impulses with peak levels of 135 dB versus 169 age-matched controls was subjected to otological and audiometric examination, and then the complaints for tinnitus in both groups have been analysed. The prevalence of tinnitus, highest in operators with longer exposure duration (> 10 years) was found in 184 individuals (70.4%) versus 6 (3.5%) in controls. The findings closely corresponded with the degree of impulse noise-induced hearing loss. As the maximum audiometric notch was mostly localised at 6 kHz and rarely at 4 kHz, consequently the approximate pitch of the tinnitus was related to the frequencies where hearing was most affected. It is concluded that impulse noise-induced tinnitus may be sometimes more severe in its effects than is hearing loss, thus it creates an additional reason for strict hearing conservation programmes.

Adult↗
PubMed1999

The role of otoacoustic emissions in screening and evaluation of noise damage.

Otoacoustic emissions have been shown to be extremely useful in screening for hearing impairment in babies. This review considers the current evidence available with regard to the role of otoacoustic emissions in the screening for noise induced cochlear damage. A number of studies indicate that otoacoustic emissions provide an indication of cochlear damage prior to any change in the pure tone audiometric threshold. There is also some evidence that the medial efferent system evaluation using contralateral sound activated suppression of emissions indicates dysfunction after noise exposure. Increased variability of spontaneous emissions has also been shown to be associated with the presence of tinnitus in various aetiologies.

Auditory Pathways↗
PubMed1995

An unusual case of deafness with speech impairment: lesson in diagnosis and management.

Hearing impairment can be the cause of significant disability and handicap. This medico-legal case demonstrates the need for accurate assessment of both the severity and type of hearing loss if the best clinical management is to be provided. In particular, the case identifies the critical role of additional, objective auditory testing when pure tone audiometry, which depends on the subjective response of the individual, is inconsistent or indicates severe hearing impairment.

Audiometry, Evoked Response↗
PubMed1995

Differential effect of adaptation on the ipsi- and contralateral auditory brainstem pathways.

Auditory brainstem potential components II and V are delayed in the contralateral recording in comparison with that ipsilateral to the stimulus. Wave III is recorded earlier contralaterally. The effect of increasing stimulus repetition rate on the ipsilateral/contralateral latency differences in these components was examined. There is a progressive increase in latency from Wave I to Wave V ipsilaterally with an increase in stimulus rate; however, contralaterally there is no further increase in latency after Wave III. At 40 Hz stimulus rate, therefore, the ipsi/contra difference in the latency of Wave V disappears, suggesting that there is a differential effect of peripheral and central adaptation on the ipsilateral and contralateral auditory pathways.

Adult↗
PubMed1993

Cortical evoked potential criteria in the objective assessment of auditory threshold: a comparison of noise induced hearing loss with Ménière's disease.

Amplitude of the N1 component of the cortical response was used to objectively determine threshold of hearing at 1 kHz and 4 kHz in a series of consecutively referred medicolegal cases with alleged occupational noise induced hearing loss and a control group of patients with Ménière's disease who were not seeking compensation for their hearing loss. The cortical response thresholds were compared with the subjective pure tone audiometric (PTA) thresholds at the same frequencies. The cortical and PTA thresholds were 'within 10 dB' for 84 and 92 per cent of the cases of noise induced hearing loss (NIHL) and Ménière's disease respectively, confirming the validity of CERA as a means of defining accurately the frequency specific thresholds and the audiometric configuration. Of the remaining 16 per cent of NIHL, 13 per cent exaggerated their PTA thresholds at 1 kHz and 10 per cent at 4 kHz whilst the error in cortical threshold estimation was beyond the 10 dB level for three and six per cent of cases at those frequencies respectively. The median exaggeration of threshold was 25 dB. For eight per cent of the Ménière's patients, thresholds exceeded 10 dB at both 1 and 4 kHz, four per cent of whom exaggerated their PTA thresholds and four per cent had a test error greater than 10 dB. A similar percentage (four per cent) of both groups revealed a cortical test error greater than 10 dB whereas three times as many cases of noise induced hearing loss (13 per cent) revealed exaggeration of their subjective audiometric thresholds compared with the Ménière's group (four per cent).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Effectiveness of acoustic reflex threshold criteria in the diagnosis of retrocochlear pathology.

This study examines the acoustic reflex threshold criteria, derived from a large group of patients with cochlear hearing loss proposed by Cohen & Prasher (1992), in order to evaluate their effectiveness in differentiating between cochlear and retro-cochlear lesions. This criterion was tested on 63 patients with surgically confirmed cerebello-pontine angle (CPA) lesions. The false results obtained with this and other criteria were compared. The best balance between the false positive and negative results in the cochlear and retrocochlear group is provided by the criterion of any two adjacent test frequencies (proposed in the companion paper) having an upper limit of 105 dB for hearing below 60 dB and 110 dB for hearing over 60 dB. This study has also singled out the interaural difference criterion as the best diagnostic indicator with the lowest false results with only 1 false negative from 63 CPA cases and 3 false positive cases from 61 cochlear lesions with hearing thresholds over 55 dB.

Acoustic Stimulation↗
PubMed1992

Defining the relationship between cochlear hearing loss and acoustic reflex thresholds.

In this study several methods of defining the relationship between the magnitude of cochlear hearing loss and the acoustic reflex threshold (ART) levels were examined, with a view to defining the appropriate upper limits of ART that would ease clinical applicability and reduce the false positive rate. The 90th percentile, two standard deviations (SD) from the mean, the regression method and an empirical method based on the scatter plots of the ART at each activator frequency were all applied to the results of 99 patients with cochlear and/or peripheral vestibular pathology. The upper limits of ART defined on the basis of the scatter plots provided the most appropriate upper limits for different ranges of hearing loss, with relatively few false positives. A clinical criterion based on the ART levels at adjacent frequencies is proposed, which further reduces the false positive rate and could also prove effective in the differential diagnosis of cochlear from retro-cochlear lesions.

Acoustic Impedance Tests↗
PubMed1991

Dopaminergic induced changes in cognitive and motor processing in Parkinson's disease: an electrophysiological investigation.

Event-related potentials and reaction time measures to auditory discrimination tasks of graded difficulty were used to separate cognitive from motor processing time in 27 patients with newly diagnosed, previously untreated Parkinson's disease and later on optimal levodopa treatment. Before treatment event-related potential P3 and task performance were normal but the reaction time was prolonged compared with age matched controls. After treatment P3 latency was significantly prolonged and the reaction time reduced suggesting a dopamine induced dissociation between cognitive and motor processing. In early Parkinson's disease cognitive processing time remains normal but the motor processing time is prolonged. Dopamine replacement is followed by significantly reduced motor processing time despite increased cognitive processing time. Motor processing may reflect the dopamine status of the putamen whereas dopaminergic over-stimulation of other regions may adversely affect cognitive processing in patients treated with levodopa.

Adult↗
PubMed1990

Sensory and cognitive event-related potentials in myalgic encephalomyelitis.

Myalgic Encephalomyelitis (ME) is a form of post viral fatigue syndrome resulting in myalgia and fluctuating fatiguability. Symptoms reflecting central nervous system dysfunction are common and include muscle weakness, headache, sensory disturbances, poor short term memory and impairment of concentration. In view of the fact that sensory and cognitive disturbances are experienced by many patients objective evidence was sought with multi-modality sensory evoked potentials and auditory event-related cognitive potentials in a group of ME patients both with and without the enteroviral antigen, VP1 test positive. The auditory brainstem, median nerve somatosensory and pattern reversal checkerboard visual potentials were normal for all 37 patients tested. In contrast to the sensory potentials significant differences in the mean latencies of the cognitive potential N2 and P3 were found. Reaction times were also significantly prolonged but the performance in terms of error was not significantly affected. No significant difference emerged in any of the parameters for the VP1 test. P3 was abnormal in latency or amplitude in 36% of the VP1 positive patients for the frequency discrimination task and 48% for the more difficult duration discrimination task. The abnormalities indicate attentional deficits in some patients and slower speed of information processing in others. The prolonged latencies observed in these patients have not been observed in patients with depression in many other studies.

Adolescent↗
PubMed1990

Brainstem potentials in the diagnosis of an acoustic neuroma. An unusual case of normal ipsilateral and abnormal contralateral responses.

An unusual case is presented of a patient with an acoustic neuroma, in whom the responses recorded with the usual derivation of ipsilateral recording and stimulation resulted in a normal response, whereas that derived contralaterally was abnormal. The patient was also reported to have a normal magnetic resonance scan although the tomograms revealed a widening of the internal auditory meatus and subsequent histology confirmed a schwannoma. Postoperatively the hearing was preserved and the brainstem responses showed a typical 'acoustic picture' with a delay of Waves III and V both ipsi and contralaterally. Subsequent testing showed an improvement in the latency of Wave V. Certain hypotheses are advanced regarding the mechanism involved in the latency differences observed between ipsi- and contralateral recordings, but the significance of abnormal prolongation of the latencies of certain components occurring independently in the contralateral response remains obscure. However, this patient's example clearly shows its value in clinical testing.

Audiometry, Pure-Tone↗
PubMed1988

Intraoperative monitoring of the electrocochleogram and the preservation of hearing during acoustic neuroma excision.

We have monitored the electrocochleogram (ECochG) of 24 patients, using a transtympanic electrode, during acoustic neuroma excision. All patients had unilateral tumours with good preoperative hearing and complete excision was achieved in each case. Of the 24 patients, seven retained some hearing, however, a further two patients had normal ECochG waveforms at the end of operation but were nevertheless deaf. Thus, there is not an invariable correlation between immediate preservation of the ECochG and hearing. As expected, tumour size was important in hearing preservation. Five of seven patients with tumours less than 1.5 cm in diameter retained some hearing after operation, whereas 15 of 17 patients with tumours greater than 1.5 cm in diameter were deaf.

Audiometry, Evoked Response↗