Biomedical subjects

K Yuen

Publications and source records attributed to K Yuen.

25 records · Page 2Linked to original sources

PubMed1984

Dose-response analysis of cadmium in man: body burden vs kidney dysfunction.

The primary objective of this study was to develop dose-response relationships of cadmium in human beings. In vivo measurements of kidney, liver, urine, and blood cadmium, and urinary levels of beta 2-microglobulin and total protein were obtained in 82 industrially exposed workers and 30 control subjects. The values of 200 micrograms/g creatinine for urinary beta 2-microglobulin and 250 mg/g creatinine for urinary total protein were used to define the upper limit for normal kidney function. Forty-one of the cadmium workers (18 active, 23 retired) were classified as having abnormal kidney function; all control subjects had normal kidney function. Most workers with Cd above 70 ppm in the liver were judged to have some evidence of kidney abnormalities. The dose-response relationship for liver cadmium for the actively employed workers could be described by a linear logistic regression model: (Formula: see text) where p is the individual's probability of having kidney dysfunction. The loss of cadmium from the kidney following dysfunction prohibited a direct logistic analysis of the kidney cadmium data. However, when the linear relationship between kidney and liver cadmium for the subjects with normal kidney function was combined with the logistic equation for the liver, a predicted-response curve was obtained for the kidney. The logistic models predict a 50% probability of having kidney dysfunction at 38.4 mg for the kidney and 42.3 ppm for the liver, respectively.

Body Burden↗

PubMed1984

Improved models for determination of body fat by in vivo neutron activation.

In the present study, two different models of body composition, based on data obtained by nuclear techniques are used. Total body nitrogen, calcium, and chlorine were obtained by total body neutron activation. Total body chlorine was used to estimate extracellular water, and total body calcium to determine bone mineral and extracellular solids. Total body potassium was measured by whole body counting to obtain the body cell mass. In addition, total body water was measured by the tritium dilution technique. It was found that either model can be used equally well to measure total body fat in normal subjects. Estimation of body fat as the difference between body weight and the sum of total body nitrogen (protein), total body water, and bone ash (model 1) appears to have an advantage over model 2, which uses body cell mass, extracellular water, and extracellular solids, particularly for patients with metabolic disorders. This advantage is partly due to the fact that the parameter protein (total body nitrogen) is less affected in metabolic disorders than the more labile total body potassium. The closely correlated results obtained with the two models based on nuclear measurements support the conclusion that these techniques provide reliable measurements of total body fat.

Adipose Tissue↗

PubMed1984

Application of moiré topography to mantle treatment.

We believe moiré topography is a particularly suitable technique for establishing contours on patients receiving mantle treatment. We derive the fundamental moiré equation from a novel, but simple, consideration of moiré phenomena. Our apparatus is designed to give a difference in height of approximately 1.0 cm between successive moiré fringes. Using an inclined plane test object, an accuracy of better than 3 mm is obtained.

Anthropometry↗

PubMed1977

Analysis of the systemic corticosteroid sensitivity of patients with primary open-angle glaucoma.

Patients with primary open-angle glaucoma have an ocular and systemic sensitivity to corticosteroids. We adapted a cellular assay that used peripheral blood lymphocytes to detect this corticosteroid sensitivity in vitro in a microtiter assay. It reduced the time, cost, and amount of blood required to examine a patient. We examined ten subjects on three separate days and demonstrated that the reliability of one 50% inhibitory concentration was about 76%. We then studied 25 patients with primary open-angle glaucoma and 25 control subjects using this in vitro assay. The patients with primary open-angle glaucoma were significantly more sensitive to corticosteroids than the control subjects (P less than .001).

Administration, Topical↗

PubMed1977

Sunlight and cataract: an epidemiologic investigation.

Cataract prevalence data from two large U.S. sources were divided according to small geographic areas for which average annual sunlight hours were determined from a map prepared by the U.S. Weather Bureau. Several non-cataract disease controls were chosen from the same geographic locations (separately for each data set). It was found that the cataract-to-control ratios for persons aged 65 years or older were significantly larger in locations with large amounts of sunlight compared to those in locations with small amounts (P less than .05). Discussion of some possible biases in the data leads to the conclusion that the biases, if they exist, are probably not large. The authors believe, however, that more research should be done before the association between sunshine and cataract is considered established.

Aged↗

PubMedDate not supplied

A differential method for inhomogeneity correction on dose in a photon beam.

For a uniform slab of inhomogeneity in a supervoltage beam, correction factors can be calculated from the Batho equation. In this report, we present a method for calculating the effect of an annular inhomogeneity, concentric about the beam axis, upon the dose at a point on the axis and below the annulus. A derivation of the equation required in the calculation for supervoltage radiation is given. Results from measurements made in 60Co beams for polystyrene foam, cedar, and aluminum annuli, all having 3.0 x 2.0 cm2 in cross section but with different inside diameters, are compared with correction values calculated by the method. For situations where the annulus is just submerged in the phantom, measured and calculated values are in good agreement. For a general situation, two calculation types are proposed and the data show that in general the measured scatter perturbation lies between the calculated values of the two types. Application of our technique predicts a sign reversal in the scatter perturbation due to an inhomogeneity. This reversal has previously been observed and reported and is also demonstrated in our measurements.

Cobalt Radioisotopes↗

PubMedDate not supplied

Practical application of the differential Batho method for inhomogeneity correction on kerma in a photon beam.

The Batho equation gives a satisfactory method to correct the dose for points in the electronic equilibrium region for a uniform slab of inhomogeneity in a photon beam. In spite of the many investigations, we believe no simple and adequate method has been found for routine clinical dose calculations which require dose correction of a small-volume inhomogeneity in an arbitrary location. In the present report, we combine the values of the two calculation types of the differential Batho method, which we have developed previously, to give a new calculated value for the scatter perturbation due to an annulus of inhomogeneity. The coefficients in the combination, which we derived from a detailed analysis of the scatter perturbation, are simple geometrical ratios. The new calculated values are in good agreement with measured values. We believe this application of the differential Batho method can provide a practical and accurate method of correcting for inhomogeneities of any size and shape in clinical dose calculations.

Humans↗