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Biomedical subjects

D K Myers

Publications and source records attributed to D K Myers.

At least 19 recordsLinked to original sources
PubMed2000

A rural perspective on home care communication about elderly patients after hospital discharge.

Little is known about home health agencies (HHA) and their integration in the continuum of care in rural areas. The aims of this study are to describe the amount and type of patient-related data transferred by discharging hospitals to rural HHAs and to explore the influence of selected organizational factors on that communication process using a previously tested model of interorganizational communication. In this study, 446 closed-case, elderly patient records at three rural HHAs were reviewed using the Referral Data Inventory. Rural HHAs receive about half of the literature-recommended referral data, characterized primarily by background data, some medical data, and almost no psychosocial or nursing-care data. Referrals transmitted by telephone and written data were superior to referrals transferred by a telephone call only. Hospital-affiliated HHAs received significantly greater amounts and richer types of referral data than did free-standing HHAs. Findings suggest that cost-saving measures in the referral process need investigation.

Aged↗
PubMed1998

Aspartame: neuropsychologic and neurophysiologic evaluation of acute and chronic effects.

BACKGROUND: Neurobehavioral symptoms have been reported anecdotally with aspartame. OBJECTIVE: This study sought to determine whether aspartame can disrupt cognitive, neurophysiologic, or behavioral functioning in normal individuals. DESIGN: Forty-eight healthy volunteers completed a randomized, double-blind, placebo-controlled, crossover study. The first month was aspartame free. Subjects then consumed sodas and capsules with placebo, aspartame, or sucrose for 20 d each. Order was randomized and subjects were assigned to either a high- (45 mg x kg body wt(-1) x d(-1)) or low- (15 mg x kg body wt(-1) x d(-1)) dose aspartame group. Neuropsychologic and laboratory testing was done on day 10 of each treatment period to determine possible acute effects and on day 20 for possible chronic effects. RESULTS: Plasma phenylalanine concentrations increased significantly during aspartame treatment. Neuropsychologic results; adverse experiences; amino acid, insulin, and glucose values; and electroencephalograms were compared by sex and by treatment. No significant differences were found for any dependent measure. CONCLUSION: Large daily doses of aspartame had no effect on neuropsychologic, neurophysiologic, or behavioral functioning in healthy young adults.

Adult↗
PubMed1997

Influence of invertase activity and glycerol synthesis and retention on fermentation of media with a high sugar concentration by Saccharomyces cerevisiae.

In the past, the fermentation activity of Saccharomyces cerevisiae in substrates with a high concentration of sucrose (HSuc), such as sweet bread doughs, has been linked inversely to invertase activity of yeast strains. The present work defines the limits of the relationship between invertase activity and fermentation in hyperosmotic HSuc medium. Fourteen polyploid, wild-type strains of S. cerevisiae with different invertase levels gave a similar ranking of fermentation activity in HSuc and in medium in which glucose and fructose replaced sucrose (HGF medium). Thus, invertase is unlikely to be the most important determinant of fermentation in sweet doughs. Yeasts produce the compatible solute-osmoprotective compound glycerol when exposed to hyperosmotic environments. Under low sugar concentrations (and nonstressing osmotic pressure), there was no correlation between glycerol and fermentation activities. However, there was a strong correlation between the ability of yeasts to ferment in HSuc or HGF medium and their capacity to produce and retain glycerol intracellularly. There was also a strong correlation between intracellular glycerol and fermentation activity of yeasts in a medium in which the nonfermentable sugar alcohol sorbitol replaced most of the sugars (HSor), but the ability to produce and retain glycerol was greater when yeasts were incubated in HGF medium under the same osmotic pressure. The difference between the amounts of glycerol produced and retained in HSor and in HGF media varied with strains. This implies that high fermentable sugar concentrations cause physiological conditions that allow for enhanced glycerol production and retention, the degree of which is strain dependent. In conclusion, one important prerequisite for yeast strains to ferment media with high concentrations of sugar is the ability to synthesize glycerol and especially to retain it.

Carbohydrate Metabolism↗
PubMed1995

Relative biological effectiveness of tritium for induction of myeloid leukemia in CBA/H mice.

To help resolve uncertainties as to the most appropriate weighting factor for tritium beta rays, a large experiment was carried out to measure the relative biological effectiveness (RBE) of tritiated water compared to X rays for the induction of myeloid leukemia in male mice of the CBA/H strain. The study was designed to estimate the lifetime incidence of myeloid leukemia in seven groups of about 750 mice each; radiation exposures were approximately 0, 1, 2 and 3 Gy both for tritiated water and for X rays. The lifetime incidence of leukemia in these mice increased from 0.13% in the control group to 6-8% in groups exposed to higher radiation doses. The results were fitted to various equations relating leukemia incidence to radiation dose, using both the raw data and data corrected for cumulative mouse-days at risk. The calculated RBE values for tritium beta rays compared to X rays ranged from 1.0 +/- 0.5 to 1.3 +/- 0.3. A best estimate of the RBE for this experiment was about 1.2 +/- 0.3. A wR value of 1 would thus appear to be more appropriate than a wR of 2 for tritium beta rays.

Animals↗
PubMed1989

Dose-rate effects of mammary tumor development in female Sprague-Dawley rats exposed to X and gamma radiation.

Mammary tumour development was followed in two experiments involving a total of 2229 female Sprague-Dawley rats exposed to various doses of X or gamma rays at different dose rates. The data for another 462 rats exposed to tritiated water in one of these experiments were also analyzed. The incidence of adenocarcinomas and fibroadenomas at a given time after exposure increased linearly in proportion to total radiation dose for most groups. However, no significant increase in adenocarcinomas was observed with chronic gamma exposures up to 1.1 Gy, and the increase in fibroadenomas observed with chronic gamma exposures at a dose rate of 0.0076 Gy h-1 up to an accumulated dose of 3.3 Gy was small compared to that observed after acute exposures. The incidence of all mammary tumors increased almost linearly with the log of dose rate in the range 0.0076 to 26.3 Gy h-1 for 3 Gy total dose of gamma rays. The effects of X rays appeared to be less influenced by dose rate than were the effects of gamma rays.

Adenocarcinoma↗
PubMed1988

Impact on radiogenic cancer risk of persons exhibiting abnormal sensitivity to ionizing radiation.

Human genotypes are known "that confer both increased susceptibility or resistance to DNA damage and increased cancer risk after exposure to carcinogenic agents, including ionizing radiation" (NAS 1980). The existence of sensitive subgroups at elevated risk, if they are of appreciable size, could have significant impact on the actual distribution of risk. The radiosensitive disorder ataxia-telangiectasia (A-T) serves as a good example: the significant "at risk" group, A-T heterozygotes, is estimated to comprise between 0.5% and 5% of the total population, and has a twofold elevated lifetime risk of fatal neoplasia. Other genetic syndromes that manifest abnormal radiosensitivity are also known, but no estimates are available for the population frequency of all such phenotypes, or for their overall degree of increased risk. As the first part of a program addressing these questions, we have developed a rapid and inexpensive assay for screening members of the general population for abnormal radiosensitivity; such persons would be regarded as at presumptive elevated risk of radiogenic cancer. Our method utilizes lymphoblastoid cell lines and chronic as opposed to acute gamma-ray exposure to amplify the difference between normal and somewhat sensitive strains. A simple "grow-back" assay assesses the survival response. Information on the extent of natural variation in inherited susceptibility to radiogenic cancers could be most useful for radiation protection in the future.

Cell Line↗
PubMed1987

Some factors affecting the sensitivity of cultured human cells to high-LET radiation.

Comparative effects of decay of DNA-bound 125I, of gamma-radiation and of tritiated water on survival of the proliferative ability of cultured cells were examined. The results confirm a previous report that cells frozen to -196 degrees C in the presence of 2M glycerol have lost a considerable proportion of their intracellular water. The data also suggest that the fraction of the lethal damage caused by deposition of radiation energy in intracellular water close to the DNA is greater for gamma-radiation than for the decay of DNA-bound 125I. Inherited differences in the sensitivity of untransformed fibroblasts from individual humans to ionizing radiations and other DNA-damaging agents are being explored. The ratios of the sensitivities of various cell lines to particular agents can vary several-fold. Thus the RBE of various radiations is affected not only by the irradiation conditions and the water content of the cells but also by inherited abnormalities in the DNA repair systems in human cells.

Animals↗
PubMed1984

Occurrence of mammary tumors in rats after exposure to tritium beta rays and 200-kVp X rays.

The RBE for tritium was estimated in reference to 200-kVp X rays, using acceleration of breast tumor appearance in the female Sprague-Dawley rat as the end-point. Chronic X-ray doses of 0.3-2.0 Gy were delivered over 10 days. Intraperitoneal injections of tritiated water ranging in concentrations from 45 to 370 MBq/100 g body wt were administered, followed by four additional injections at 2-day intervals and half of the initial concentrations. Seventy-five percent of the total tritium dose was delivered to the mammary gland within the first 10 days and 95% within the first 20 days after the start of the tritium exposure. RBE estimations were based on various criteria including the tumor incidence per Gy at 450 days postirradiation and the time required to induce tumors in 50% of the animals at risk. The results suggest that tritium beta rays are about 1.1-1.3 times more effective than chronic 200-kVp X rays for acceleration of the appearance of rat mammary tumors. However, the uncertainties involved in these calculations are such that the effects of tritium beta rays could not be reliably distinguished from those of chronic 200-kVp X rays. Measured differences in RBE values were slightly larger for the comparison between acute and chronic X rays than for the comparison between chronic tritium beta rays and chronic X rays.

Animals↗
PubMed1978

Repair of the double-strand breaks produced by 125I disintegrations in the DNA of Micrococcus radiodurans.

Wild-type M. radiodurans and two radiosensitive mutants were used to study the lethal effects of 125I disintegrations in their DNA. The relative sensitivities of these three strains to inactivation by gamma-radiation were reflected in their relative sensitivities to inactivation by 125I decay. The number of double-strand (ds) breaks in the DNA appeared to be similar at levels of gamma-radiation and of 125I decay that reduced survival to 10%. All three strains of M. radiodurans rapidly repaired ds breaks produced in their DNA by either gamma-radiation or 125I disintegrations. If one ds break per is a lethal event [Kirsch et al., 1975], cells of the three strains tested would die only when they had left unrepaired one ds break out of an initial 45,600 or 1800 ds breaks per single cell.

Cell Survival↗
PubMed1976

DNA turnover and thymidine re-utilization in mouse tissues.

Mice were injected intravenously with tritiated thymidine (TdR) and 125I-labeled iododeoxyuridine (IUdR) in low doses to provide a simultaneous labeling of tissue DNA with non-toxic amounts of these two precursors. The total activity per organ and the ratio of the two isotopes was measured in the DNA at various times between 1 and 15 days after the injection. Since TdR from dying cells is re-utilized more effeciently than IUdR from the same cells, more labeled TdR than IUdR was retained in the tissue DNA in these experiments. From the slopes of the regression lines, the true rated of turnover of replicating tissue DNA and the per cent re-utilization of TdR were calculated. Re-utilization of TdR varied from 37 to 60% in the six tissues examined.

Animals↗
PubMed1975

Incorporation of thymidine and iodeoxyuridine in mammalian cells in vitro.

The incorporation of labelled thymidine (dT) and iododeoxyuridine (IdU) into DNA was studied with tissue culture cells and with normal mouse cells in vitro. The rates of incorporation and the ratio dT/IdU incorporation both varied from one type of cell to another and from one suspending medium to another. Despite the known complexity of the regulation of DNA synthesis, the data for incorporation of exogenous dT and IdU could be fitted reasonably well by a model for single-step enzymic process. Deviations from the theoretical predictions were minimal in the presence of fluorodeoxyuridine.

Binding, Competitive↗