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Biomedical subjects

W P Gibson

Publications and source records attributed to W P Gibson.

At least 19 recordsLinked to original sources
PubMed1995

A new incision for placement of cochlear implants.

A straight, vertical post-aural incision for the 'Cochlear' multichannel cochlear implant has been evaluated in 52 patients (20 adults and 32 children). Nineteen of the children were under three years of age and five of these were under two years of age. The 7 cm long incision is placed approximately 3 mm behind the post-auricular crease and runs from the tip of the mastoid to a point 3 cm above the superior attachment of the pinna. The incision heals within several days. Because the incision is straight interruption of the blood supply to the flaps raised is the least possible. This also minimizes the possibility of scalp necrosis and implant extrusion. The likelihood of infection is reduced by the small size of the incision, minimal soft tissue dissection and small amount of dead space. Rapid healing has occurred in all cases despite infection in one.

Adult↗
PubMed1992

When the diagnosis of deafness is wrong.

OBJECTIVE: To describe three children in whom there had been major errors in the diagnosis of hearing loss. CLINICAL FEATURES: In three children (two developmentally delayed, one not developmentally delayed) hearing thresholds obtained by behavioural testing were later proven wrong. This resulted in significant family distress and inappropriate educational approaches. INTERVENTION AND OUTCOME: Electrocochleography and brainstem audiometry were performed, demonstrating normal cochlear function. Simultaneous microinspection of the ears gave information about current or old middle ear disease and the likelihood of past conductive hearing loss. In each case hearing aids could be discarded, enabling parents and teachers to concentrate on one rather than multiple problems. CONCLUSION: Electrocochleography and brainstem audiometry should be used more frequently to check the diagnosis of hearing loss in children who are developmentally delayed, hyperactive or autistic and who do not give consistent responses to behavioural testing. It should also be considered if parents are firmly convinced that the diagnosis of deafness is wrong.

Adolescent↗
PubMed1992

Electrocochleography in the diagnosis of perilymphatic fistula: intraoperative observations and assessment of a new diagnostic office procedure.

The intraoperative electrocochleogram (ECochG) was investigated during stapedectomy surgery and during cochleostomy surgery. This provided the justification for obtaining recordings with the oval window (OW) or round window (RW) intact and then when there was a definite fistula. It was noteworthy that no ECochG changes occurred on merely opening the OW or RW, but that marked changes occurred on removing perilymph, even by gentle suction. On raising the intrathoracic pressure and replacing the perilymph, the ECochG potentials usually recovered. Based on these intraoperative observations, an office procedure was designed. The subject was asked to raise the intrathoracic pressure on several occasions and changes in the amplitude of the ECochG potential were noted. An increase of over 15 percent in the action potential (AP), with or without a decrease in the negative summating potential (SP) during the period of raised intrathoracic pressure, was used as the diagnostic criteria for a perilymphatic fistula. A decrease in the AP with or without an increase in the negative SP immediately on relaxing after a period of raised intrathoracic pressure was also treated as a positive diagnostic criterion. Seventy-one normal ears were investigated and a positive result was recorded in two ears (false positive rate: 2.8%). Two hundred and six ears, strongly suspected as having a perilymph leak on the basis of the clinical history and vestibular signs have been investigated over the past 4 years. Ninety positive diagnoses have been reached and 46 of these ears have been surgically explored.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed1991

Intraoperative electrocochleographic monitoring of inner ear surgery for endolymphatic hydrops. A review of cases.

The purpose of this review of cases was to determine whether or not the SP/AP amplitude ratio changes during unidirectional inner ear valved shunt surgery for the decompression of the hydropic labyrinth in Meniere's disease. A series of 62 patients underwent shunt surgery over a 20 month period. In 43 cases (43 ears), ECoG responses were successfully recorded throughout the duration of surgery. A pair of two-tailed paired t-tests were computed for SP/AP amplitude ratios acquired during intraoperative ECoG monitoring at the baseline and closing stage of surgery. The first t-test compared the mean SP/AP amplitude ratios at baseline and closing for those cases in which the SP/AP amplitude ratio at baseline was abnormal (baseline > 35%). The t was significant, t(19) = 4.63, p < 0.01). The second t-test compared the mean SP/AP amplitude ratios at baseline and closing for those cases in which the SP/AP amplitude ratio at baseline was WNL (baseline < or = 35%). The t was insignificant, t(20) = 0.31, p > 0.05. Variations between baseline and closing measurements were categorized as either a reduction, no change (very stable over time), or an increase in the SP/AP amplitude ratio. A change in the SP/AP amplitude ratio from baseline to closing of > or = 7% (x = 2%, SD = 2%) was considered statistically significant. Overall (43 cases), 49% of the variations fell into the no change category, with 42% and 9% of the cases placed in the reduction and increase categories, respectively. Of the cases (22) in which the baseline measurement was outside the limits of normal, 64% showed a reduction, 32% showed no change, and 4% showed an increase in the SP/AP amplitude ratio at closing. Changes in the SP/AP amplitude were observed at various stages of the surgical procedure. Reductions were found at each of the five surgical steps identified, with the majority of the changes almost evenly divided between the stages of mastoid drilling and opening sac. Increases in the SP/AP amplitude ratio were found in four cases. The increases were observed during drilling of the mastoid bone in two cases and sac decompression and opening the sac in the remaining cases.

Acoustic Stimulation↗
PubMed1991

The use of intraoperative electrocochleography in Meniére's surgery.

Intra-operative electrocochleography was undertaken during surgery for Meniére's disease. It was found that the electrocochleogram (ECoG) provided a stable measure which accurately reflected changes within the inner ear during surgery. During salt osmosis of the round window, a rapid change in the summating potential versus action potential ratio (SP/AP) occurred which showed when the endolymphatic hydrops (ELH) had been altered. During a modified cochleostomy procedure, the ECoG showed when the cochlear duct had been ruptured. Forty ears were monitored during endolymphatic sac surgery. Twenty-five of these ears showed stable ECochG which did not alter at any time during the procedure; however, 8 of these ears showed normal SP/AP ratios during the surgery despite having been abnormal in the week prior to surgery. The SP/AP ratio was reduced in 8 ears, increased in 3 ears and showed other changes which were probably due to unstable electrode positioning in 4 ears. It was concluded that endolymphatic sac or duct surgery altered the inner ear physiology in a significant number of ears affected by endolymphatic hydrops.

Acoustic Stimulation↗
PubMed1991

The use of electrocochleography in the diagnosis of Meniére's disease.

The use of transtympanic electrocochleography (ECochG) is discussed in the diagnosis of endolymphatic hydrops. The electrophysiological concepts which may explain the finding of an increased negative summating potential (SP) in human recordings are discussed. The click SP/AP ratio and the absolute values of the 1 kHz 90 dB NHL tone burst were obtained in 42 normal ears, 48 sensory ears and 80 Meniére's ears and compared. It was found that the use of a 1 kHz tone burst increased the accuracy of diagnosis especially in ears with a hearing loss of less than 40 dB NHL from a false negative level of 54% (click SP/AL) to 23% (1 kHz tone burst SP). It was concluded that the 1 kHz tone bursts improved the accuracy of transtympanic electrocochleography in the diagnosis of Meniére's disease.

Acoustic Stimulation↗
PubMed1991

Epithelial migration in the external auditory canal and the movement of the chondro-osseous junction.

Epithelial migration occurs in a lateral direction from the tympanic membrane to the external auditory canal. The underlying mechanism which determines the direction of this laterally directed movement has not been elucidated. This study attempts to analyze whether migration is stimulated at the chondro-osseous junction, the very place where squamous cells stop migrating and desquamate. Active movement of the junction is postulated as a stimulus for the migratory process. Such movement may be caused by contraction of the peri-auricular muscles which attach to the cartilaginous canal. In this study, eight guinea pigs underwent unilateral facial nerve section in order to paralyze the peri-auricular muscles and thus diminish active movement of the junction. Migration times were determined for both operated and unoperated ears. No significant difference was noted between the two groups. One may conclude that paralysis of the peri-auricular muscles does not alter the time taken for skin migration in the external auditory canal.

Animals↗
PubMed1990

Measurement of auditory brainstem responses evoked by electrical stimulation with a cochlear implant.

Auditory brainstem responses evoked by electrical stimulation with a Nucleus/Cochlear implant can be measured if care is taken to prevent stimulus artefacts. A simple procedure is described which relies upon a passive LCR filter to prevent the radiofrequency carrier from entering the input of the recording amplifier. The filter simply prevents saturation of the amplifier by the carrier.

Brain Stem↗
PubMed1989

Polarity order of biphasic square pulse electric current stimulation of human cochlear nerve: observations with transtympanic electrodes.

Eighteen totally deaf human cochleae were stimulated with biphasic square pulses of current through transtympanic needle electrodes. The thresholds of the 2 polarity orders, + - and - +, were compared for various pulse durations. For a pulse duration of 500 microseconds the polarity order - + had the lower threshold. For pulse durations of 2 ms and longer, the polarity order + - had the lower threshold. A discussion is given of the significance of the results for finding out the site of cochlear nerve excitation by the stimuli.

Cochlear Nerve↗
PubMed1983

Electrocochleography and the glycerol dehydration test: a case study.

The electrocochleographic changes which occurred during glycerol dehydration in an ear affected by endolymphatic hydrops due to Menière's disease are discussed. This single case study is reported because the recordings were large and stable, and because they clearly showed the electrocochleographic abnormality associated with endolymphatic hydrops; namely, a large summating potential (SP) in relation to the action potential (AP). After dehydration a dramatic improvement occurred in both the pure tone and speech audiogram. The electrocochleogram showed a decrease in the SP amplitude and little change in the AP amplitude so that the SP/AP waveform became almost normal. The significance of these findings is discussed.

Adult↗
PubMed1983

Brainstem auditory-evoked potentials and electrocochleography: comparison of different criteria for the detection of acoustic neuroma and other cerebello-pontine angle tumours.

Different means of identifying the presence of cerebello-pontine angle (CPA) tumours using brainstem auditory-evoked potentials (BAEP) were evaluated. The results from 33 ears affected by tumours were compared with BAEP from 50 normal ears and 23 ears affected by Menière's disease. Measurement of inter-aural latency differences correctly identified 97% of tumours from the normal group, but only 81% of tumours from the Menière group. Comparison of different interwave interval measures showed that the NI to NV interval was the best criterion and correctly identified 90% of the tumours from both the normal and the Menière groups. The use of transtympanic electrocochleography (ECochG) is discussed. Used alone, ECochG was of limited value in detecting CPA tumours except in five out of nine deaf ears where no BAEP were recorded but 'disconnection' action potentials were encountered. By combining BAEP and ECochG, the NI to NV interval could be identified with certainty. Combined BAEP and ECochG recordings were only undertaken when NI was unclear on BAEP recordings or when the ECochG was indicated clinically for the identification of endolymphatic hydrops. In this series, the combined use of BAEP and ECochG resulted in a tumour detection rate of 100% with a false positive rate of zero. The BAEP from the unaffected ear recorded from the ipsilateral and contralateral sides were compared. Significant NI to NV delay was noted, especially on recording from the contralateral side, when there was distortion of the brainstem due to a large tumour. The article concludes with an appendix of six illustrative case reports.

Adult↗
PubMed1982

Binaural voltage summation of brainstem auditory evoked potentials: an adjunct to the diagnostic criteria for multiple sclerosis.

Brainstem auditory evoked potential (BAEP) amplitude is modified according to whether or not the stimulus is applied monaurally or binaurally. In normal subjects, wave V amplitude increases by an average of 68.7% upon changing stimulation from monaural to binaural. From earlier studies there is evidence that brainstem potential amplitude is reduced in patients with multiple sclerosis (MS) but none to suggest that binaural stimulation results in increased amplitude. This study evaluated the extent of binaural summation of BAEPs in patients with MS. In a large majority of patients with MS who have no hearing deficit, BAEPs showed no increase in wave V amplitude on binaural stimulation. This finding is in contrast to the normal group and thus has diagnostic importance. Measurements of binaural summation therefore might usefully be applied to the clinical assessment of disease progression, or lack of it, in individual patients.

Acoustic Stimulation↗