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D Sylwester

Publications and source records attributed to D Sylwester.

14 recordsLinked to original sources
PubMed1985

Confidence intervals and sample size calculations to compare variant frequencies.

Direct mutagenicity tests offer the opportunity of monitoring human populations to detect evidence of genetic damage that occurs in vivo. As such these tests offer the potential of linking earlier exposures to mutagenic agents to subsequent health effects. One such test detects mutant T-lymphocytes that arise in vivo in human peripheral blood. Statistical analysis of the value observed, the variant frequency (Vf), is the subject of this paper. We present and illustrate procedures for finding confidence intervals for a single variant frequency and for the ratio of two independent variant frequencies. We also derive formulae for required sample size to ensure adequate power to detect a specified change in a single variant frequency or a specified difference between two variant frequencies. Our approach is to exploit the approximate normality of the natural logarithm of a Poisson distributed variable. The procedures developed appear to be quite accurate even for the small (5-15) values often observed in the variant frequency assay. Moreover, the procedures are very easy to use and should prove valuable to investigators involved in direct mutagenicity testing.

Drug Resistance↗
PubMed1984

Evidence for an increased risk for hypertension with centrally located body fat and the effect of race and sex on this risk.

Data from the First Health and Nutrition Examination Survey (HANES), 1971-1974, were used to examine the relationship between blood pressure and the distribution of subcutaneous body fat in 5506 survey participants, ages 30-59. Triceps and subscapular skinfolds were used as approximations of peripheral and centrally located body fat. The effects of race, sex and age on the obesity-blood pressure relationship were analyzed. Subscapular skinfold was the better predictor of both systolic and diastolic blood pressure in each race-sex group, sharing all of the association of triceps with blood pressure and having significant predictive power unshared by triceps. The slopes of regression of subscapular skinfolds with systolic blood pressure for each race-sex group were not significantly different. A 1 mm increase in skinfold thickness increased the predicted mean systolic blood pressure by 0.63 +/- 0.03 mmHg (F = 519). Mean diastolic blood pressure rose 0.43 +/- 0.02 mmHg per unit increase of skinfold in whites (F = 549), and 0.14 +/- 0.04 mmHg less in blacks (F = 13), indicating a significant racial difference. Age and subscapular skinfold contributed independently to the variability in blood pressure in each race-sex group. These results demonstrate that the blood pressure of middle-aged Americans is more directly associated with centrally deposited body fat. This finding is true across race and sex groups, and is independent of age.

Adult↗
PubMed1983

Time-lapse cinematographic analysis of beryllium--lung fibroblast interactions.

The proliferative response to beryllium chloride of cells in a population of human lung fibroblasts was quantitatively assessed using time-lapse cinematography. A dose of 0.02 microgram Be/ml, known to decrease the growth rate of fibroblasts, affects an estimated 75% of the cells in the population, increasing their interdivision time (IDT) by approximately 5 hr. The differences in mean 1n(IDT) between treated and control cells were essentially constant for comparable culture sizes ranging from 25 to 250 cells. There was no correlation between mother and daughter cell IDTs in control or treated culture at any culture size. IDTs of sister pairs were highly correlated in control cultures at selected culture sizes while sister pair IDTs of treated cultures were not. The data suggest that while beryllium alters the IDT of fibroblasts, an effect not related to culture size, any given cell affected by beryllium does not impart effects of the mineral to its progeny.

Beryllium↗
PubMed1983

Effectiveness of animal rotation in achieving uniform dust exposures and lung dust deposition in horizontal flow chambers.

An important source of variability of experimental results in inhalation toxicology originates from the nonuniformity of chamber concentrations. Two horizontal flow inhalation chambers were used in evaluating the effect of cage rotation within each chamber on the amount of alpha-quartz deposited in the lungs of male Fischer 344 rats. The alpha-quartz lung burden was determined by quantitative X-ray diffraction. A carefully designed animal rotation schedule significantly reduced the variability in the amount of alpha-quartz deposited in the animals, thereby minimizing effects of chamber nonuniformity due either to design or dust generator characteristics.

Aerosols↗
PubMed1978

Metabolism of concanavalin A-affinity molecular variants of alpha-fetoprotein in rats.

Serum half-lives of unfractionated rat alpha-fetoprotein (AFP), concanavalin A (Con A)-nonreactive AFP, and Con A-reactive AFP in normal 45- to 55-day-old male and female F344 rats were determined to be 19 hours. No significant differences were seen between the half-lives of unfractionated AFP and either of the two Con A-affinity molecular variants of AFP studied. No evidence of interconversion of the Con A-affinity AFP variants during 24 hours in the circulation was found. These results supported the conclusion that the proportions of Con A-affinity molecular variants of AFP in the sera of fetal, newborn, and hematoma-bearing rats result from differences in the relative synthesis rates of the two variants.

Age Factors↗