Biomedical subjects

G M Clark

Publications and source records attributed to G M Clark.

At least 145 records · Page 8Linked to original sources

PubMed1997

Comparison of current waveforms for the electrical stimulation of residual low frequency hearing.

Many cochlear prostheses employ charge-balanced biphasic current pulses. These pulses have little energy at low frequencies resulting in limited stimulation of low frequency hearing by mechanical responses to the electrical stimulus. However, if electro-mechanical transduction within the cochlea is nonlinear, electrical stimulation with asymmetric, charge-balanced current pulses may result in a mechanical response with significantly more low frequency energy. We estimated the mechanical response at low frequencies to pulsatile electrical stimulation of the cochlea. The auditory nerve compound action potential evoked by low frequency tones was forward-masked by a train of symmetric or asymmetric current pulses. Masking by asymmetric current pulses was not significantly different from masking by symmetric pulses matched for pulse duration and charge. In conclusion, there appears to be no advantage to using asymmetric current pulses for the mechanical stimulation of residual low frequency hearing by electrical stimulation of the cochlea.

Animals↗

PubMed1997

Variability of amplitude and area of the auditory nerve compound action potential.

The strength of neural response to sensory stimuli is often estimated by measurement of the amplitude of gross neural potentials. These gross potentials reflect the summed activity of a population of neurons. The amplitude of these potentials is dependent upon the synchrony of the contributing neural responses. We compared the variability of the peak-to-peak amplitude of the auditory nerve compound action potential (CAP) with that of the area under the peaks. The area under the peaks was significantly less variable than the amplitude for responses to low frequency stimuli. Responses to other stimuli showed differences in the same direction, but these were not significant. We conclude that the area under these peaks is a more precise measure of neural response than measurement of waveform amplitude at least for responses to low frequency stimuli.

Acoustic Stimulation↗

PubMed1997

Health and poverty in rural Scotland.

This paper presents findings from a study on rural disadvantage to explore the implications of disadvantage for the health of rural communities and the organisation and delivery of health care services in rural areas. Rural health research has been a neglected topic. Yet previous research has reported the importance local people and practitioners place on the provision and organisation of health services in rural areas.' The research reported in this paper further emphasises this point and, in addition, provides empirical data on local people and practitioners perceptions of health issues and health services in four areas of rural Scotland.

Health Services Accessibility↗

PubMed1997

Speech perception results for children with implants with different levels of preoperative residual hearing.

OBJECTIVE: Many reports have established that hearing-impaired children using the Nucleus 22-channel cochlear implant may show both significant benefits to lipreading and significant scores on open-set words and sentences using electrical stimulation only. These findings have raised questions about whether severely or severely-to-profoundly deaf children should be candidates for cochlear implants. To study this question, postoperative results for implanted children with different levels of preoperative residual hearing were evaluated in terms of speech perception benefits. STUDY DESIGN/SETTING: A retrospective study of the first 117 children, sequentially, to undergo implantation in the Melbourne and Sydney Cochlear Implant Clinics was undertaken. All children had been assessed by and received their implants in a tertiary referral centre. MAIN OUTCOME MEASURES: To assess aided residual hearing, the children were grouped into four categories of hearing on the basis of their aided residual hearing thresholds measured preoperatively. To assess benefits, the scores of children on standard speech perception tests were reviewed. As different tests were used for children with different ages and language skills, children were grouped into categories according to the level of postoperative speech perception benefit. RESULTS: The results showed that children in the higher categories of aided preoperative residual hearing showed significant scores on open-set word and sentence perception tests using the implant alone. For children in lower categories of aided residual hearing, results were variable within the groups. More than 90% of children with implants with aided residual hearing thresholds in the speech range above 1 kHz achieved open-set understanding of words and sentences. CONCLUSION: While the results of this preliminary study confirm previous findings of differential outcomes for children with different levels of preoperative residual hearing, they suggest that children with severe to profound hearing impairments should be considered for cochlear implantation.

Auditory Threshold↗

PubMed1997

The effect of language knowledge on speech perception: what are we really assessing?

OBJECTIVE: The authors examined whether open-set speech perception scores are limited by knowledge of vocabulary and syntax and further considered whether remediation of vocabulary and syntax will increase open-set speech perception scores. STUDY DESIGN: This was a repeated-measures study design in the setting of a primary (elementary) school for the hearing-impaired. PATIENTS: The study population was composed of three hearing-impaired children using Nucleus 22-channel cochlear implant. INTERVENTION: Intervention used was language remediation sessions. MAIN OUTCOME MEASURES: The main outcome measures were assessment of auditory-alone speech perception benefit using open-set words and sentences and assessment of syntactic knowledge using the Test of Syntactic Ability. Outcome measures were applied before and after remediation. RESULTS: Child 1 and child 2 showed a significant postremediation improvement in their overall scores on the Test of Syntactic Ability and in their ability to perceive words learned during remediation. Child 1 and child 2 also showed a significant improvement in their scores on a modified Bamford-Kowal-Bench open-set sentence test, which specifically targeted grammatical constructs trained in remediation sessions. CONCLUSIONS: Remediation of language knowledge deficits significantly improved open-set speech perception for two children, suggesting a need to include language remediation in cochlear implant habilitation programs.

Adolescent↗

PubMed1997

Insulin receptor expression and clinical outcome in node-negative breast cancer.

The insulin receptor (IR), a ligand-activated tyrosine kinase, is present in breast cancers, but its relationship to patient survival is unknown. The IR was measured in 584 tumor specimens from patients with node-negative breast carcinoma by frozen-section immunohistochemistry and light microscopy. The immunostaining signal was quantitated in relation to both the staining intensity and the proportion of positive malignant epithelial cells. Analyses indicated that patients with tumors with undetectable IR content in malignant epithelial cells (260 cases) had a relatively lower predicted 5-year disease-free survival (DFS) (69% +/- 3%) than did patients with tumors with detectable IR content (324 cases; DFS 76% +/- 3%, p = .032). The significance of IR content in these breast malignant epithelial cells was then analyzed along with patient age, tumor size, progesterone and estrogen receptor status, p53 accumulation, and S-phase. Multivariate analysis of these data revealed that after adjustment for these other variables, IR content was the strongest independent predictive factor for DFS (relative risk = 1.73, p = .005). Interestingly, in a small subset of patients with very high IR content (n = 62), DFS was decreased. These data indicate that IR content in node-negative breast cancers is a significant major predictor of reduced DFS. Moreover, they raise the possibility that the measurement of IR content might provide important information concerning breast cancer biology.

Adult↗

PubMed1996

Pitch comparisons of acoustically and electrically evoked auditory sensations.

Cochlear implant users with some residual hearing in the non-implanted ear compared the pitch sensations produced by acoustic pure tones and pulsatile electric stimuli. Pitch comparisons were obtained for pure tones and electrical stimuli presented at different positions (electrodes) in the scala tympani, keeping the electric pulse rate fixed at 100, 250, or 800 pps. Similarly, pitch comparisons were obtained for electrical stimuli with variable pulse rates presented to two fixed electrode positions (apical and basal) in the cochlea. Both electrode position and pulse rate influenced the perceived pitch of the electrical signal and 'matched' electric and acoustic signals were found over a wide range of frequencies. There was a large variation between listeners. For some stimuli, listeners had difficulty in deciding whether the acoustic or electric stimulus was higher in pitch. Despite the variability, consistent trends were obtained from the data: higher frequencies tended to be matched by more basal electrodes for all pulse rates. Higher frequencies tended to be matched by higher pulse rates for both electrode positions. The electrode positions that 'matched' pure tones were more basal than predicted from the characteristic frequency coordinates of the basilar membrane in a normal human cochlea.

Acoustic Stimulation↗

PubMed1996

Practical p-value adjustment for optimally selected cutpoints.

This paper concerns a series of simulations undertaken to examine the effects of two data features--number of cutpoints and true marker prognostic effect size--on three methods of p-value adjustment (asymptotic, P(acor); improved Bonferroni, P(bon); and empirical permutation, P(emp)). H(o) rejection rates for P(emp) and P(bon) are almost indistinguishable from those for an independent validation sample (P(vld)), while those of P(acor) are somewhat conservative, especially when the number of cutpoints is small. Analysis of a new breast cancer prognostic marker, heat shock protein 70, illustrates the methods. These results underscore many of the problems associated with data-derived cutpoints in general, and the need for p-value adjustment.

Bias↗

PubMed1996

Cochlear histopathologic characteristics following long-term implantation. Safety studies in the young monkey.

OBJECTIVE: To evaluate the safety of cochlear implantation in children 2 years of age or younger using a non-human primate model. DESIGN: Histopathologic study. SUBJECTS: Five macaque monkeys. INTERVENTION: A commercially produced electrode array was implanted for 3 years. RESULTS: Histologic examination demonstrated the biocompatibility of the scala tympani electrode array. Limited soft-tissue growth and new bone growth were observed in the lower basal turn. There was no evidence of intracochlear infection. Evidence of minimal insertion trauma was seen. Hair cell loss was, in general, confined to the region of the electrode array, with normal hair cell populations toward the apex, although there was evidence of hair cell preservation adjacent to the array. At least 20% of spiral ganglion cells were preserved even in regions with a smaller proportion of hair cells. CONCLUSIONS: Even after extended periods of implantation, the electrode array is well tolerated, and there is substantial preservation of neural elements.

Animals↗

PubMed1996

Does age at cochlear implantation affect the distribution of 2-deoxyglucose label in cat inferior colliculus?

Cochlear implants are one treatment for children who are born deaf or become deaf before acquiring language. The question of optimum age for implantation arises. Using an animal model, we have studied the response of the auditory brainstem to implantation at various ages. Neonatally, pharmacologically deafened cats were implanted with a 4-electrode array in the left cochlea at ages from 100 to over 180 days. Eleven were chronically stimulated (1000 h if possible) with charge-balanced, biphasic current pulses; eight were unstimulated controls. In a terminal experiment, each animal received [14C]2-deoxyglucose i.v. preceding a 45-min stimulation program. The fraction of the right inferior colliculus (IC) with a significant accumulation of label was calculated. If age at implantation were a significant factor in determining the size of the responding region, the fraction would depend on the age; this was not observed. However, there was considerable variation in the IC fraction sizes within both stimulated and unstimulated groups, leading to the conclusion that there are factors other than age which determine the size of the responding region. Thus, for deaf children of corresponding ages, age at implantation may not be of critical importance.

Aging↗

PubMed1996

A comparison of questionnaire versus monofilament assessment of neurosensory deficit.

PURPOSE: Because neurosensory deficit is commonly reported by patients after orthognathic surgery, it is important to know how accurately patients can report their own sensory deficit. This analysis compares the results of objective neurosensory tests with the results of a subjective patient questionnaire. MATERIALS AND METHODS: Before and 6 months after bilateral mandibular sagittal ramus split osteotomy, 101 patients with class II facial deformities were asked to rate sensations of numbness or tingling in the area of the mental nerve. Simultaneously, they were objectively tested using monofilament neurosensory tests (light touch and brush stroke direction). RESULTS: More than 70% of patients subjectively reported neurosensory problems, but objective assessment identified neurosensory deficits in less than 60% of the patients. The sensitivity and specificity of the patients' subjective assessments were 75.3% and 52.8%, respectively, for the light touch test, and 77.9% and 59.8%, respectively, for the brush stroke test. CONCLUSIONS: It was concluded that when monofilament neurosensory testing is used as the gold standard, patients appear to overreport neurosensory problems; ie, the positive predictive value of patient reports is only 63.2%, resulting in frequent false positives.

Adolescent↗

PubMed1996

A case-control study of cryptorchidism and maternal hormone concentrations in early pregnancy.

Serum samples taken between 6 and 20 weeks of gestation were obtained from 28 mothers who gave birth to cryptorchid sons (cases) and from 108 control mothers. In comparison with controls the cases had 10% higher geometric mean oestradiol (95% CI -13% to +39%: P=0.42) and 10% lower geometric mean testosterone (95% CI -27% to +10%: P=0.30). Among the samples collected between 6 and 14 weeks of gestation geometric mean concentrations of oestradiol and testosterone were 5% lower (95% CI -32% to +31%: P=0.74) and 25% lower (95% CI -45% to +1%: P=0.06) respectively in cases than in controls. Among the samples collected between 15 and 20 weeks of gestation geometric mean concentrations of oestradiol and testosterone were 29% higher (95% CI -8% to +79%: P=0.14) and 21% higher (95% CI -8% to +60%: P=0.18) respectively in cases than in controls. The results do not support the hypothesis that cryptorchidism may be caused by high concentrations of oestradiol in the maternal blood during the first phase of testicular descent, but suggest that the possible association of cryptorchidism with low maternal testosterone during early gestation should be further investigated.

Adult↗

PubMed1996

Associations between insulin-like growth factors and their binding proteins and other prognostic indicators in breast cancer.

Recent studies have suggested that insulin-like growth factors (IGFs) and insulin-like growth factor binding proteins (IGFBPs) may be implicated in the development and progression of breast cancer. Prostate-specific antigen (PSA), a serine protease, may play a role in the regulation of IGFs' function through cleavage of IGFBP-3, resulting in release of active IGFs from IGFBP-3. As IGFs, IGFBPs and PSA are all present in breast cancer, possible associations among these proteins were speculated. In this study, we have measured PSA, IGF-I, IGF-II, IGFBP-1 and IGFBP-3 in tumour tissue cytosols from 200 women with primary breast cancer, and have examined relationships between IGFs or IGFBPs and PSA along with other markers, including p53 protein, steroid hormone receptors (oestrogen and progesterone), cathepsin-D, epidermal growth factor receptor, Her-2/neu protein, S-phase fraction and DNA ploidy. Correlations or associations between PSA and IGF-I, IGF-II, IGFBP-1 or IGFBP-3 were not observed. IGF-II was positively correlated with both IGFBP-3 and IGFBP-1. IGF-I was not associated with either of the two binding proteins, nor with IGF-II. Both IGF-II and IGFBP-3 were inversely associated with the oestrogen receptor, and IGFBP-3 was also positively associated with S-phase fraction. Our finding of IGF-II and IGFBP-3 in association with unfavourable prognostic indicators of breast cancer suggests that IGFs may be involved in the progression of breast cancer.

Biomarkers, Tumor↗

PubMed1996

Electrical stimulation of the auditory nerve: the coding of frequency, the perception of pitch and the development of cochlear implant speech processing strategies for profoundly deaf people.

1. The development of speech processing strategies for multiple-channel cochlear implants has depended on encoding sound frequencies and intensities as temporal and spatial patterns of electrical stimulation of the auditory nerve fibres so that speech information of most importance of intelligibility could be transmitted. 2. Initial physiological studies showed that rate encoding of electrical stimulation above 200 pulses/s could not reproduce the normal response patterns in auditory neurons for acoustic stimulation in the speech frequency range above 200 Hz and suggested that place coding was appropriate for the higher frequencies. 3. Rate difference limens in the experimental animal were only similar to those for sound up to 200 Hz. 4. Rate difference limens in implant patients were similar to those obtained in the experimental animal. 5. Satisfactory rate discrimination could be made for durations of 50 and 100 ms, but not 25 ms. This made rate suitable for encoding longer duration suprasegmental speech information, but not segmental information, such as consonants. The rate of stimulation could also be perceived as pitch, discriminated at different electrode sites along the cochlea and discriminated for stimuli across electrodes. 6. Place pitch could be scaled according to the site of stimulation in the cochlea so that a frequency scale was preserved and it also had a different quality from rate pitch and was described as tonality. Place pitch could also be discriminated for the shorter durations (25 ms) required for identifying consonants. 7. The inaugural speech processing strategy encoded the second formant frequencies (concentrations of frequency energy in the mid frequency range of most importance for speech intelligibility) as place of stimulation, the voicing frequency as rate of stimulation and the intensity as current level. Our further speech processing strategies have extracted additional frequency information and coded this as place of stimulation. The most recent development, however, presents temporal frequency information as amplitude variations at a constant rate of stimulation. 8. As additional speech frequencies have been encoded as place of stimulation, the mean speech perception scores have continued to increase and are now better than the average scores that severely-profoundly deaf adults and children with some residual hearing obtain with a hearing aid.

Acoustic Stimulation↗

PubMed1996

The perceptual dimensions of single-electrode and nonsimultaneous dual-electrode stimuli in cochlear implantees.

The perceptual dimensions evoked by dual-electrode stimulation were investigated in four cochlear implantees. The dual-electrode stimulation consisted of biphasic current pulse trains, such that two intracochlear electrodes each received one pulse in a 250-Hz cycle. The experiments tested the hypothesis that perceptual qualities would be altered when there was an increased likelihood of interactions occurring between the two electrode places. The parameters of the stimulation which were manipulated to test this hypothesis were the time delay between the pulses on the two electrodes (2 ms and a value between 0.62 and 0.92 ms), the distance between the component electrode rings of each bipolar pair (3.75 mm and either 2.25 or 1.5 mm), and the distance between the two bipolar pairs in the dual-electrode stimuli (from 0.75 to 12.0 mm). Five set of 15 loudness balanced stimuli were created, each set having different stimulation parameters. These stimuli consisted of five single-electrode stimuli (a 250-Hz pulse train on each of five electrodes) and the ten dual-electrode stimuli formed by the combinations of those five electrodes. Two perceptual dissimilarity matrices were obtained for each subject and each set, and were analyzed using repeated nonmetric multidimensional scaling techniques. The resultant "stimulus spaces" were then examined to see how many perceptual dimensions the stimuli were best described by, and to what perceptual or stimulus qualities the dimensions might correspond. The results showed that the percept evoked by dual-electrode stimulation contained two main dimensions. Increasing the width of the current path to create substantially overlapping stimulation areas, or altering the temporal delay between the two electrodes, had very little effect on this percept. The position of the stimuli in the two-dimensional space was related to the distances of the two component electrodes along the electrode array. These results are relevant to speech processing strategies and electrode design for cochlear implants, as they imply that the creation of discrete, nonoverlapping areas of stimulation may not cause the percepts to be more distinct, and therefore may not necessarily lead to better speech perception.

Aged↗

PubMed1996

Computer-aided three-dimensional reconstruction in human cochlear maps: measurement of the lengths of organ of Corti, outer wall, inner wall, and Rosenthal's canal.

This paper describes the application of computer-aided three-dimensional reconstruction to measurements of the length of the organ of Corti (mean +/- SD, 35.58 +/- 1.41 mm), scala tympani outer wall (40.81 +/- 1.97 mm), scala tympani inner wall (18.29 +/- 1.47 mm), and Rosenthal's canal center (15.98 +/- 1.33 mm) in eight adult male cochleas. The Rosenthal's canal center ranged between 1 3/4 and 2 turns, did not appear to be linearly related to the organ of Corti, and lay near the basal end of the latter. The length of the organ of Corti measured with three-dimensional reconstruction differed by 7.6% +/- 3.2% ("cutting angle difference") from that derived from traditional two-dimensional reconstruction on the plane perpendicular to the plane of section, and by 2.6% +/- 1.7% ("geometric difference") from that derived from two-dimensional reconstruction on the axial plane at right angles to the modiolar axis.

Aged↗

PubMed1996

Transition planning assessment for secondary-level students with learning disabilities.

This article presents a survey of and recommendations for transition planning assessment for secondary teachers of students with learning disabilities. The author makes a case for redirecting assessment practices in secondary instructional programs to obtain present-level-of-functioning information for IEP planning that extends beyond high school graduation as a single outcome. Critical outcomes in adult adjustment requiring transition planning are presented. Current standardized and nonstandardized assessment procedures that focus on adult outcomes, as well as preferences and interests in planning for the future, are described. The author gives recommendations for planning and conducting transition-needs assessment for secondary schools.

Adolescent↗

PubMed1996

Improved and simplified methods for specifying positions of the electrode bands of a cochlear implant array.

OBJECTIVE: To develop techniques for measuring the positions of the individual electrodes of a multiple channel cochlear implant and for estimating associated characteristic frequencies. BACKGROUND: Information concerning the positions of the individual electrodes of a cochlear implant array is important for analyzing speech perception or psychophysical data and for optimizing speech-processing strategies. This study presents two techniques for obtaining such information from postoperative plain film radiographs. METHODS: A template spiral shape, derived from analysis of the radiographs of 30 cochlear implant patients, is used to obtain measurements of the angular positions of the electrode bands within scala tympani. A research technique measures angular positions and estimates characteristic frequencies for all electrode bands but requires that the positions of two cochlear landmarks and all electrode bands be digitized. A clinical technique provides similar angle and frequency estimates but requires a minimum of information to be extracted visually from the radiograph. The lateral positions of the bands are estimated, in the research technique, using mean outer and inner wall functions obtained from 11 Silastic molds of scala tympani. RESULTS: The mean position of the implanted array relative to the mean scala tympani outer wall function was consistent with published histologic observations of implanted temporal bones. Measured angles did not vary greatly with experimenter or with rotation of the cochlea relative to the radiographic beam by up to 20 degrees. CONCLUSIONS: The techniques described allow, principally, measurement of the longitudinal positions of the bands of a cochlear implant in scala tympani and estimation of corresponding characteristic frequencies.

Cochlea↗