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Biomedical subjects

C A Johnson

Publications and source records attributed to C A Johnson.

At least 361 records · Page 20Linked to original sources
PubMed1985

Multiple embryo-transplant offspring produced from quartering a bovine embryo at the morula stage.

A non-surgical embryo collection was completed on a day 7 superovulated Chianina donor cow. Because all but two of the ova from the collection were unfertilised and a surplus of potential recipients was available, one embryo (an excellent quality late morula) was dissected into four equal portioned 'quarter' embryos using a simplified micromanipulation procedure. Each quarter embryo was then placed in a 0.25 ml French straw and non-surgically transplanted to four different crossbred beef recipient females. The remaining embryo was similarly transplanted to a herd mate recipient as an intact embryo. One recipient returned to oestrus, one recipient had an extended post transfer cycle and the two remaining recipients produced a live quarter embryo transplant calf each within 24 hours of the other. The intact embryo placed in a herd mate recipient did not produce a transplant calf. To the authors' knowledge, these transplant offspring are the first live births reported from a non-surgically collected later-stage bovine morula (day 7), which had been dissected into quarters and then individually transplanted non-surgically to recipient females. The procedure was relatively simple to perform and was completed in less than one hour.

Animals↗
PubMed1985

Transplantation of human basal cell carcinomas to athymic mice.

Basal cell carcinomas (BCCs) obtained from 22 subjects undergoing microscopically controlled surgery were transplanted to 40 athymic (nude) mice. With no further immunosuppression of the mice, no tumor growth was noted in the first 14 attempts. When mice were further immunosuppressed with anti-lymphocyte serum (ALS) injections and by splenectomy, successful tumor growth was achieved in 15 of 22 mice by a subcutaneous implantation technique and in 1 of 4 by a superficial grafting technique. Transplanted BCC retained the morphology and basement membrane proteins typical of human BCC. As determined by autoradiography, 3H-thymidine was incorporated primarily in the peripheral palisaded cells of the transplanted tumor. Successful use of the athymic mouse model for study of human BCC requires use of mice further immunosuppressed by splenectomy and ALS, and the use of a subcutaneous implantation technique. With the use of this model, studies of the biology of human BCC may be possible.

Animals↗
PubMed1985

Attrition in prevention research.

Selective attrition can detract from the internal and external validity of longitudinal research. Four tests of selective attrition applicable to longitudinal prevention research were conducted on data bases from two recent studies. These tests assessed (1) differences between dropouts and stayers in terms of pretest indices of primary outcome variables (substance use), (2) differences in change scores for dropouts and stayers, (3) differences in rates of attrition among experimental conditions, and (4) differences in pretest indices for dropouts among conditions. Results of these analyses indicate that cigarette smokers, alcohol drinkers, and marijuana users are more likely to drop out than nonusers, limiting the external validity of both studies. For one project, differential rates of attrition among conditions suggested a possible attrition artifact which will interfere with interpretation of outcome results, possibly masking true program effectiveness. Recommendations for standardizing reports of attrition and for avoiding attrition through second efforts are made.

Adolescent↗
PubMed1985

Self-initiated smoking cessation among high school students.

The purpose of this study was to examine psychosocial predictors of self-initiated smoking cessation among high school students. Students from nine high schools were pretested using a questionnaire which assessed smoking behavior, beliefs about positive and negative consequences of smoking, moral attitudes toward smoking, normative expectations about smoking, rebelliousness, peer smoking and parent smoking. Smokers identified at pretest were reexamined three months and fifteen months later. Three variables, moral attitudes, peer smoking and positive beliefs about smoking significantly discriminated continuing smokers from quitters at the three-month posttest. Three different variables, negative beliefs about smoking, parental smoking and rebelliousness significantly discriminated between those who quit and later relapsed and those who quit and maintained their non-smoking status at the 15 month posttest. Smoking characteristics at pretest failed to discriminate either those who would quit or those who would maintain their non-smoking status. Results support the development of public information programs which encourage early cessation of smoking which feature the development of appropriate attitudes and beliefs and which foster social support.

Adolescent↗
PubMed1985

Quantitative office perimetry.

This study presents a preliminary comparison of six commercially-available automated threshold static parameters, consisting of three projection perimeters (Humphrey Field Analyzer, Squid, and Octopus 500) and three light-emitting diode (LED) perimeters (Dicon 2000, Fieldmaster 50, and Digilab 350). Eighteen individuals were included in the study: 6 normal observers (31-58 years old), six patients with glaucomatous field loss in both eyes (55-70 years old), and six patients with neuro-ophthalmologic or retinal visual field abnormalities in both eyes (12-61 years old). Three aspects of quantitative testing were evaluated: (1) the patients' and normal observers' acceptance and subjective impressions of the test procedure; (2) the technician's ease of operating the device and related tasks; and (3) practitioner-oriented considerations such as test-retest reliability, comparability of test results and testing time. Our results showed that no device was clearly superior to the others in all respects. Patients were most favorably impressed with the Octopus 500, Squid, and the Fieldmaster 50, while technician impressions were most favorable to the Humphrey Field Analyzer and the Squid. The projection perimeters (Humphrey Field Analyzer, Squid, and Octopus 500) were the easiest to perform cross-comparisons of test results, although there was considerable variation in the clarity of data interpretation from one case to another. Test-retest reliability and the time of testing varied among the six automated perimeters.

Adolescent↗
PubMed1985

How much is an icon worth?

We report a new technique for assessing the amount of information extracted from the icon that follows a briefly presented picture. The problem of how to measure such information was formulated in terms of how much physical exposure of a picture an icon is worth. Consider two types of stimulus presentations, each with a base duration of d ms. The first is a d-ms picture followed by an icon, and the second is a d + a-ms picture not followed by an icon. How large does a have to be so that equivalent amounts of information are extracted in the two cases? To answer this question, we showed people pictures and later tested their memory for the pictures. We found that the physical exposure duration needed to reach a particular level of performance was approximately 100 ms longer when an icon was not permitted versus when the icon was permitted. This value was independent of the base duration and the luminance of the picture. Moreover, the same value was obtained using three different kinds of memory test and four different sets of pictures. We conclude that an icon is worth approximately 100 ms of additional physical exposure duration. A reasonable explanation for this robust equivalence between icon and stimulus is that the same encoding processes are responsible for extracting information from the icon and from the physical stimulus. Therefore, any variable that affects these encoding processes must affect extraction of information from the icon and the physical stimulus in an identical manner. This prediction was confirmed for one such variable, picture luminance.

Figural Aftereffect↗
PubMed1985

Accuracy of knowledge of family history of cardiovascular disorders.

There has been increased interest in the use of familial trends in physical and psychological disorders for identifying individuals at risk; research on individuals who have relatives with certain health problems may contribute to knowledge of etiology. In addition, accurate family health information may allow targeting of prevention and early detection programs to minimize cost and maximize utility. This study compared 292 undergraduates' reports of their parents' and grandparents' histories of six medical disorders with the parents' reports. Results showed moderate agreement concerning the parents' health, but substantial disagreement concerning the grandparents' health. Demographic and personality variables did not predict accuracy of students' reports of parental hypertension. Among the disorders, differences in agreement of reporting arose; the most salient condition, heart attack, had the highest agreement for both parents and grandparents. These results suggested that caution is necessary in evaluating family health information from subjects in research and from target individuals in prevention programs. This problem is especially serious for disorders such as hypertension, which is less salient and which also shows age-related penetrance, with the disorder often not evident until the 5th or 6th decade of life.

Arteriosclerosis↗
PubMed1985

Does performance of tasks affect the resting focus of accommodation?

Measurements of the resting focus of accommodation were obtained with an infrared optometer while subjects engaged in four tasks: (1) passive viewing in darkness; (2) passive viewing of a laser speckle pattern; (3) active judgment of motion in a laser speckle pattern; and (4) mental arithmetic in darkness. The results showed resting focus measures to be comparable under all four conditions for some subjects. However, other subjects exhibited consistent increases or decreases in the resting focus position when asked to judge the direction of speckles within the laser test pattern or perform mental arithmetic. This finding suggests that "effort to see" may influence the resting focus of some subjects. Implications for measurement procedures and population estimates of the resting focus are discussed.

Accommodation, Ocular↗
PubMed1985

Vancomycin disposition during continuous ambulatory peritoneal dialysis: a pharmacokinetic analysis of peritoneal drug transport.

Expressions are presented to describe the absorption and also clearance of drugs administered into the peritoneal cavity of patients undergoing continuous ambulatory peritoneal dialysis (CAPD). Application of the expressions to vancomycin kinetics in five male CAPD patients showed that therapeutic levels of vancomycin can readily be achieved and maintained in the systemic circulation by administering the appropriate loading and maintenance doses. The intrinsic peritoneal clearance of vancomycin reported here is higher than the apparent clearances reported previously, averaging 300 to 500 ml/min under the conditions used in this study. The low apparent clearances previously reported are useful clinically although they do not represent the true efficiency of vancomycin removal by CAPD. The degree to which apparent clearance underestimates the true intrinsic clearance is exponentially related to the dwell time of dialysate in the peritoneum. Intraperitoneal administration is a practical alternative to other routes for CAPD patients needing antibiotic or other therapy.

Adult↗
PubMed1985

Pharmacokinetics of intravenous ceftizoxime in patients on continuous ambulatory peritoneal dialysis.

The pharmacokinetics of ceftizoxime (CZM) were determined in 16 non-infected CAPD patients. Patients received either 500 mg or 1000 mg CZM by i.v. bolus. The dialysate exchange volume was 2 l. Serum CZM concentrations at 10 min were 69.7 +/- 19.7 micrograms/ml (1000 mg dose) and 39.2 +/- 8.4 micrograms/ml (500 mg dose), and declined to 33.7 +/- 13.9 micrograms/ml and 16.9 +/- 3.2 micrograms/ml respectively at 360 min. Dialysate CZM levels at 10 and 360 min were 1.8 +/- 1.3 and 19.9 +/- 6.6 micrograms/ml respectively (1000 mg dose) and 1.4 +/- 0.9 and 12.6 +/- 3.5 micrograms/ml (500 mg dose). The half-time of CZM was 14.1 +/- 4.6 h. Peritoneal clearance of CZM was low and equilibrium was not achieved in 6 h. However peritoneal CZM concentrations were adequate within 1 h for the treatment of most organisms which cause CAPD-related peritonitis.

Adult↗
PubMed1985

The relationship of breast feeding to third-day bilirubin levels.

The purpose of this study was to determine the relationship of feeding method to serum bilirubin levels on the third day of life. Two hundred eighty-one apparently healthy full-term neonates had third-day bilirubin levels drawn between 58 and 82 hours of age. Mean serum bilirubin levels were 5.6 mg/dL for formula-fed, 6.9 mg/dL for mixed-fed, and 7.5 mg/dL for breast-fed infants. The difference was statistically significant (P less than .01) between the formula-fed and breast-fed groups. Breast-fed infants lost more weight by the third day than formula-fed infants (mean weight loss 180 g for breast-fed infants, 100 g for formula-fed infants). A third-day bilirubin levels among the feeding groups were then compared using an analysis of covariance with weight loss as the covariate. By this method, type of feeding was still a significant predictor of third-day bilirubin levels (P = .04) as was weight loss (P = .03).

Adult↗
PubMed1985

Evaluation and comparison of a radiative energy attenuation method for determining cholesterol in serum.

Determination of cholesterol by a radiative energy attenuation (REA) technique was evaluated and compared with results obtained by the Boehringer Mannheim High Performance Cholesterol Assay and the Du Pont aca. Within-assay and between-assay CVs for the REA method, for two sets of controls, were both less than 5%. We observed no interference with lipemic samples. Analytical recovery averaged 102.8%. We used all three methods for parallel determinations of 217 patients' samples containing a wide range of cholesterol concentrations. Linear regression analysis of the REA results vs those of the comparison methods were as follows: REA = 1.03 Boehringer - 0.072 (r = 0.993) and REA = 1.02 aca - 0.048 (r = 0.995). We also discuss bilirubin interference with the REA method for cholesterol.

Adolescent↗
PubMed1985

The California syndrome. Functional visual complaints with potential economic impact.

The records of 84 patients with functional visual loss (59 adults and 25 children) were reviewed over a six-year period. The patients were between 7 and 69 years of age. In the young patients, psychosocial problems relating to parental divorce, poor school performance and attention-getting behavior were common, while in adult patients, financial gain was present in 51 of 59 (86%) individuals. Over 90% of the claimed abnormalities related to the afferent visual system. Fifty-three percent of the patients had underlying organic problems with functional overlay. Inconsistent test results were the most reliable means of identifying the malingering patients. In California, both ophthalmologists and optometrists are able to declare a patient legally blind as well as visually disabled for the purpose of income tax, workers' compensation, and disability benefits. The potential financial impact of malingering patients is discussed.

Adolescent↗