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Biomedical subjects

G M Clark

Publications and source records attributed to G M Clark.

At least 487 records · Page 27Linked to original sources
PubMed1982

A 12-consonant confusion study on a multiple-channel cochlear implant patient.

A consonant confusion study was undertaken on a multiple-channel cochlear implant patient using a wearable speech processing device. This patient suffered from total bilateral deafness acquired postlingually. The consonants /b/, /p/, /m/, /v/, /f/, /d/, /t/, /n/, /z/, /s/, /g/, /k/ were presented in a VCV context with the vowel /a/ as in father by a male and female speaker under three conditions: lipreading alone; electrical stimulation alone using the wearable speech processor and multiple-channel cochlear implant; lipreading in conjunction with electrical stimulation. No significant difference was detected between the results for the male and female speakers. The percentage correct scores for the pooled results of both speakers were lipreading alone--30%; electrical stimulation alone--48%; lipreading with electrical stimulation--70%. Performance was significantly better for lipreading with electrical stimulation than for lipreading alone and for electrical stimulation alone than for lipreading alone. An information transmission analysis demonstrated the effective integration of visual and auditory information for lipreading with electrical stimulation. There was a significant improvement in performance for the electrical stimulation alone condition over the 2 months of the study in contrast to no such improvement for lipreading alone.

Cochlear Implants↗
PubMed1982

Psychophysical studies for two multiple-channel cochlear implant patients.

Psychophysical studies were conducted on two multiple-channel cochlear implant patients to examine the nature of the hearing sensations produced by electrical stimulation of auditory nerve fibers using electrodes at different sites in the scala tympani (one electrode at a time). Both time-invariant stimuli, whose parameter values did not vary in time, and time-varying stimuli, specified by a linear variation in parameter values, were used. A sharpness ranking study using time-invariant signals suggested that the hearing sensations produced by different electrodes varied from dull to sharp in an apical to basal direction in the scala tympani. A categorization study showed that the hearing sensations produced by two adjacent electrodes (1.5 mm apart) were rarely confused for a restricted range of time-invariant pulse rates. Discriminability studies by a same-different procedure for stimuli with pulse rate below 250 pps showed: (1) relative difference limens of 6% to 12% for time-invariant pulse rates, and 9% and 13% for time-varying pulse rates; (2) stimuli with time-varying electrode position differing in the direction of electrode trajectory were readily discriminated; and (3) the discrimination of time-varying pulse rates deteriorated with decreases in the duration of the variation, while the discriminability of single-electrode trajectories was the same for the three durations: 25, 50, and 100 ms. A speech processing strategy was also proposed on the bases of these results.

Auditory Perception↗
PubMed1982

Steroid hormone receptors and carcinoma of the breast.

The estrogen receptor (ER) assay has become a standard practice in the management of advanced breast cancer. Tumors lacking ER respond infrequently to endocrine therapy, whereas response rates of 50-60% are observed in ER+ tumors. Recent studies indicate that the ER status of the primary tumor is a good predictor of the endocrine dependence of metastatic tumors at the time of subsequent relapse. Furthermore, the absence of ER in the primary tumor is an important independent prognostic indicator of higher rate of recurrence and shorter survival. Quantitative analysis of ER and assay of progesterone receptor (PgR) are useful for increasing the accuracy of selecting patients for hormonal therapy; tumors with a high quantitative ER content or those with a positive PgR display the highest objective response rates. Preliminary analysis suggests that the presence of PgR may be the best available tumor marker of hormone dependence.

Adolescent↗
PubMed1982

Increased haematopoietic stem cell survival in mice injected with tocopherol after X-irradiation.

Tocopherol injection (2.5 mg) immediately after irradiation reduced lethality only during bone-marrow syndrome. Endogenous spleen colony count at 8 days after X-radiation were significantly greater in vitamin-E-injected mice compared to noninjected or vehicle-injected animals; however, 59Fe incorporation into spleen and bone marrow did not suggested enhanced erythropoietic activity in vitamin-E-injected groups at 2,4,8 and 10 days following irradiation. Mitotic index and frequency of micronuclei in marrow at 24 hours post irradiation (3 Gy) were unaffected by tocopherol injection. The uptake of tritium from injected 3H-tocopherol suggests that tocopherol has been accumulated in spleens but not marrows of irradiated animals within a few hours. Also tocopherol has no effect on endogenous spleen colony counts if injected after 5 hours nor is there an effect on the seeding efficiency of exogenous bone-marrow cells injected into recipients receiving tocopherol after irradiation.

Animals↗
PubMed1981

Gram-negative bacteremias. Analysis of factors for clinical assessment of gentamicin resistance.

We reviewed the charts of 163 patients with 183 episodes of Gram-negative bacillary bacteremia to determine a clinical profile that would select patients at high risk for experiencing gentamicin-sulfate-resistant Gram-negative bacillary bacteremia at our hospital. Gentamicin-resistant Gram-negative bacilli were only associated with institution-acquired bacteremia. Among institution-acquired episodes, urinary tract infection, diagnostic or therapeutic procedures of the lower respiratory tract or urinary tract, presence of pneumonic infiltrate on chest roentgenogram, prior therapy with gentamicin, and prior therapy with other antibiotics were significant risk factors. Because only two of the 29 gentamicin-resistant bacteria that were tested against amikacin base were resistant to amikacin, we advocate initial treatment with amikacin for patients with evidence of an institution-acquired Gram-negative bacteremic episode. Gentamicin is still our initial choice for a community-acquired episode.

Aged↗
PubMed1981

A multiple-channel cochlear implant. Evaluation using speech tracking.

Two totally deaf patients who had received multiple-channel cochlear implants were tested using a speech "tracking" procedure in which they had to repeat verbatim passages of connected discourse. Their performance was assessed by calculating the tracking rate (words per minute) each session. Testing was carried out under two conditions--lipreading alone and lipreading in conjunction with a multiple-channel cochlear implant and laboratory speech processor. Lipreading with the cochlear implant increased the tracking rates by a factor of four for one patient and by a factor of two for the other when compared with lipreading alone.

Cochlear Implants↗
PubMed1981

Adjuvant therapy for stage II, estrogen receptor negative breast cancer.

The estrogen receptor (ER) assay provides information which correlates with the proliferative potential, pathology and prognosis for patients with breast cancer. A review of our natural history data correlating ER and axillary node involvement at the time of mastectomy with prognosis allows the identification of a high risk subset of patients with early recurrence and poor survival. Patients with ER negative, stage II disease had a significantly higher recurrence rate, and poorer overall survival was observed in spite of systemic therapy instituted at relapse. Based on this data we initiated a pilot study of intensive adjuvant therapy for women with ER negative, stage II breast cancer. At a median follow-up of 19 months for 39 treated patients, both a disease free and overall survival advantage is apparent for treated patients. Morbidity was low, with no therapy related hospitalizations. We have demonstrated the feasibility of intensive therapy for this high risk group. For a definitive answer the patient resources of a cooperative group will be needed.

Actuarial Analysis↗
PubMed1981

Potential and problems with growth of breast cancer in a human tumor cloning system.

A human tumor cloning system has been utilized to culture 431 patients' breast cancer specimens. Overall, 288 or 67% of the specimens formed colonies in soft agar. Of the primary lesions 188/260 (72%) formed colonies and 100/171 (58%) of the metastatic lesions formed colonies. The median number of colonies per 500,000 nucleated cells plated was 47 for the primary lesions and 30 for the metastatic lesions. Growth from a variety of metastatic sites ranged from 22% for intradermal lesions to 77% for solid visceral metastases. Methods to increase the number of colonies from a specimen are reported including increasing the number of nucleated cells plated and making a variety of changes in the growth media. None of these methods has had a major impact on colony growth. The antitumor activity of standard anticancer agents such as adriamycin and medroxyprogesterone in the assay is presented. In addition, in vitro results with two new anthracene derivatives demonstrate good antitumor activity for the derivatives. The cloning assay represents a new model for both the basic and clinical studies of human breast cancer.

Anthracenes↗
PubMed1981

Estrogen receptor measurement in low-protein breast cancer cytosols. A modified charcoal technique.

The assay of estrogen receptor (ER) in human breast cancer biopsies is usually excellent using the dextrancoated charcoal method. If the cytosol protein concentration is below 1 mg/ml, however, underestimation of ER content occurs presumably due to adsorption of ER to the charcoal. This problem can be minimized if 1 mg/ml of bovine serum albumin (BSA) is added to the charcoal solution prior to use.

Biopsy↗
PubMed1981

Effects of aging on formalin-fixed brain weight in mice and rats.

In three mouse lineages it was found that during the 18- to 60-day interval after formalin fixation, brain weight was inversely proportional to the age at sacrifice, as was the decline in the weight of the brain during this period. In a second study using rat subjects it was confirmed that the aging difference is due to a reduction, in old age, of the swelling reaction of the brain when first placed in a formalin solution. It was suggested that this easily measured phenomenon might be employed as an operational index of brain aging.

Aging↗
PubMed1981

A multiple-channel cochlear implant: an evaluation using open-set CID sentences.

A multiple-channel cochlear implant and speech processor have been used in two postlingually deaf adult patients with a total hearing loss, to enable them to perceive varying degrees of running speech. The results have veen confirmed with open-set CID everyday sentence tests. Using the implant alone, the patients obtained 8% and 14% scores with prerecorded material, and 34% and 36% scores for "live" presentations. This was equivalent to the perception of 35% of connected discourse. When the implant was used in conjuction with lipreading, improvements of 188% and 386% were obtained over lipreading alone, and the scores were 68% and 98% which were equivalent to the perception of 60% and 95% of connected discourse.

Adult↗
PubMed1980

Differential electrical excitation of the auditory nerve.

The multichannel cochlear prosthesis requires an electrode stimulus configuration which produces a stimulus field spatially localized to each electrode. In this paper, a three-dimensional discrete resistance model of the cochlea was developed which exhibits electrical response properties similar to those observed during electrical stimulation of the cochlea. The model results suggest that the spatial attenuation of current within the cochlea varies greatly in magnitude, depending on the stimulus configuration. In addition, the model suggests that the spatial attenuation of current in both the auditory nerve fiber endings in the organ of Corti and in the myelinated fibers within the cochlear ground paths is different from the voltage attenuation in the scalar fluids. Therefore the efficacy with which a particular stimulus configuration differentially excites local terminal auditory nerve fiber populations cannot be deduced from scalar voltage measurements which have previously been recorded in the literature. Consequently physiological experiments were performed in the cat to measure the current distributions in the terminal nerve fiber region for monopolar and bipolar stimulation of the scala tympani, and also for stimulation between the scala tympani and the scala vestibuli. The mean length constants measured in the basal turn for these stimuli were found to be 12, 3, and 7.5 mm, respectively.

Animals↗