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Biomedical subjects

R I Davis

Publications and source records attributed to R I Davis.

29 records · Page 2Linked to original sources
PubMed1989

The relation among hearing loss, sensory cell loss and tuning characteristics in the chinchilla.

Evoked-potential tuning curves were obtained on over 150 chinchillas before and after acoustic overstimulation in order to relate the effects of changes in frequency selectivity to sensory cell loss over a wide range of hearing loss. Pre- and post-exposure measures of auditory thresholds and masked thresholds (simultaneous tone-on-tone paradigm) were obtained in each animal at 0.5, 1.0, 2.0, 4.0, 8.0 and 11.2 kHz, using the auditory evoked potential recorded from the inferior colliculus. Three tuning curve variables (Q10dB, low-frequency slope and high-frequency slope) were compared to the amount of noise-induced permanent threshold shift and to the percent sensory cell loss produced by a variety of noise exposures. Based upon large sample averages, frequencies showing permanent threshold shifts in excess of 10 dB also showed statistically significant differences between pre- and post-exposure measures of all three tuning curve variables. Shifts of less than 10 dB were not accompanied by statistically significant changes in the tuning curve variables. The percentage of outer hair cell loss, and percentage change in tuning curve characteristics showed systematic and parallel increases as threshold shifts increased at all probe tone frequencies except 8.0 and 11.2 kHz. In general, the results were consistent in showing that there is a systematic change in the variables which define the quality of tuning as hearing loss progressively increases and that these changes are clearly related to outer hair cell losses.

Acoustic Stimulation↗
PubMed1989

Noise and vibration interactions: effects on hearing.

There is the suggestion in the literature that vibration may potentiate the effects of noise and may thus increase the risk of hearing loss in a variety of exposure situations. However, in human experimental studies, which, by necessity, are limited to low levels of exposure, the effects measured are relatively small. A very limited number of animal studies have also shown an enhanced noise-induced hearing loss in the presence of vibration, but the scope of these studies is limited. The animal studies (chinchilla) that form the basis of this report were performed using a 30-Hz, 3g rms and a 20-Hz, 1.3g rms cage vibration separately and in combination with continuous noise (95-dB, 0.5-kHz octave band) and impact noise (113, 119, or 125 dB peak SPL) exposure paradigms. All exposures lasted for 5 days. The impact noise exposures were designed to have approximately equal total energy. Temporary and permanent threshold shifts were measured using evoked potentials, and sensory cell loss was measured using surface preparation histology. The results obtained from some of the noise/vibration paradigms showed that such exposures can alter some of the dependent measures of hearing. This effect was statistically significant only for the stronger vibration exposure conditions and was evident primarily in the extent of the outer hair cell losses and in the shape of the PTS audiogram.

Animals↗
PubMed1988

Carcinoma of the extrahepatic biliary tract: a clinicopathological and immunohistochemical study.

The clinical and histological findings in 15 cases of carcinoma arising from the extrahepatic biliary tract are reviewed. The clinical findings are in agreement with previously reported series and the dismal prognosis is confirmed. The prognosis does not appear to be related to tumour size, site, mitotic count or laboratory data on presentation. Only histological grading of the tumour is related to prognosis. Perineural tumour infiltration was a prominent feature and dysplasia within adjacent bile duct epithelium was present in five cases. The value of carcinoembryonic antigen (CEA) as a histological tumour marker was investigated. All tumours from the upper and middle biliary tree expressed this antigen. Although immunocytochemistry is seldom needed to assess malignancy in large surgical resection specimens anti-CEA helps delineate the extent of tumour infiltration and discriminates between normal and dysplastic or malignant epithelium; anti-CEA may also be helpful in identifying foci of malignancy in small sclerotic biopsy specimens.

Adult↗
PubMed1987

The effects of alerting tasks on caloric induced vestibular nystagmus.

The present study compared the effects of four different mental altering tasks on the speed of the nystagmic slow component during caloric testing in 40 young adults. Subjects were randomly divided into four groups (10/group) and stimulated twice in each ear in a counterbalanced manner according to test ear, irrigating temperature, and alerting task. Analysis of the data revealed significant differences between treatment effects on the magnitude of the slow phase velocity of nystagmus. Results suggest that passive listening does not sufficiently alert subjects to ensure the adequate release of nystagmus suppression during vestibular testing.

Acoustic Stimulation↗
PubMed1987

Pilomatrixoma mimicking breast carcinoma.

A case of pilomatrixoma occurring in the breast of a middle-aged male is presented. Many of the clinical features of this case were not typical of a pilomatrixoma and it was originally diagnosed clinically as a breast carcinoma.

Breast↗
PubMed1987

Chondrosarcoma developing in synovial chondromatosis. A case report.

Synovial chondromatosis is a rare condition in which osteocartilaginous nodules are formed by synovial metaplasia and become intra-articular loose bodies. It is usually monarticular, most commonly affecting the knee and is regarded as invariably benign. There are reports of malignant change, but only the two case studies of Mullins, Berard and Eisenberg (1965) and of Dunn et al. (1974) fully document the development of chondrosarcoma in this condition. We report a patient with a long history of histologically proven synovial chondromatosis in whom the condition became clinically aggressive and underwent malignant transformation to chondrosarcoma.

Adult↗
PubMed1983

Temporal summation in normally and abnormally hearing chinchillas.

Young adult monauralized chinchillas (N:5) were conditioned to cross a barrier in response to 7 pure tones from .5-4 kc/s. Tone bursts were either 20- or 500-msec long. Individual S's yielded threshold data for the longer duration comparable to published norms. Group mn difference between thresholds at 20- vs 500-msec durations [i.e., temporal summation (TS)] was 7 db, or 4.7 db less than TS reported for normal chinchillas reported by Wall et al (J. Aud. Res., 1981, 21, 29-37) and others. One S yielded no TS. After exposure for 4 hrs to a 2-kc/s tone at 120 db SPL, group mn thresholds for the 20-msec tones were only 1 db poorer than those for 500-msec tones (i.e., negligible TS). TS is clearly altered in noise-induced hearing loss.

Acoustic Stimulation↗
PubMed1979

Renal metastases from well differentiated follicular thyroid carcinoma: a case report with light and electron microscopic findings.

The second case of metastatic follicular carcinoma of the thyroid presenting during life as bilateral renal masses is described. Metastases appeared 18 years after resection of the primary and on clinical evaluation were confined to the kidneys. Although most malignant tumors which present clinically in the kidney are primary there, a review of the literature indicates that the possibility of metastatic tumor must be kept in mind, particularly when the renal tumor is bilateral.

Adenocarcinoma↗
PubMedDate not supplied

Comparison between AER and behavioral thresholds in normally and abnormally hearing chinchillas.

The present study compared the auditory evoked response (AER) and behavioral thresholds from the chinchilla before and after acoustic overstimulation. Bipolar electrodes were chronically implanted in the inferior colliculus of seven monauralized behaviorally conditioned animals (shock-avoidance). AER to 20-msec and behavioral thresholds to 20- and 500-msec tone bursts were determined for a range of frequencies before and after a 4-hour exposure to a 2000 Hz, 120dB SPL pure tone for six of the animals. One animal served as control and received no exposure. Results revealed a relatively close correspondence between AER and behavioral thresholds both before and after noise exposure in the same animal. Postexposure AER and behavioral thresholds displayed mild to moderate losses in sensitivity in the 1 to 4 kHz range. These findings justify further development of this particular AER as an indicator of hearing sensitivity in the chinchilla.

Animals↗
PubMedDate not supplied

The role of tuning curve variables and threshold measures in the estimation of sensory cell loss.

Auditory-evoked potential tuning curves were collected at six frequencies before and 30 days after various noise exposures in 363 chinchillas using a simultaneous masking paradigm. Traditional bivariate and multiple linear regression/correlation analyses were performed in an effort to determine the extent to which sensory cell damage could be estimated from a knowledge of audiometric and tuning curve variables. The results showed strong correlations between percent outer hair cell (%OHC) loss and permanent threshold shift (PTS) and between %OHC loss and the tuning curve variables Q10 dB and high- and low-frequency slopes (SHF, SLF). The correlations were strongest between PTS and %OHC loss. However, the proportion of variability (r2) in %OHC loss attributable to variability in the predictor variable(s) (i.e., PTS) could be increased significantly by adding the Q10 dB of the tuning curve whose probe frequency was centered in the octave band length of the cochlea corresponding to the frequency at which the PTS occurred. The r2 values could be further increased by including audiometric and tuning curve variables from frequencies adjacent to the octave band being evaluated.

Animals↗