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Biomedical subjects

C A Nelson

Publications and source records attributed to C A Nelson.

At least 127 records · Page 7Linked to original sources
PubMed1977

Characterization of plasma low density lipoproteins on nonhuman primates fed dietary cholesterol.

LDL from animals of three nonhuman primate species, Macaca mulatta, Macaca fascicularis, and Cercopithecus aethiops, were studied. A standard preparation of 125I-LDL was added to isolated lipoprotein mixtures just prior to separation of plasma lipoproteins by agarose gel chromatography. A relative size index, rI, was determined by dividing the elution volume of the iodinated LDL by the elution volume of the sample LDL, both volumes being determined simultaneously during chromatographic elution. Comparison of rI with molecular weights measured by flotation equilibrium analysis in the analytical ultracentrifuge showed a linear relationship across a molecular weight range of 2.5-8.0 X 10(6), r = 0.985. A regression equation describing this relationship was used to calculate molecular weights of LDL from a group of M. fascicularis that were fed cholesterol-containing diets. In these animals, plasma cholesterol concentration ranged from 100 to over 700 mg/dl and was highly correlated with LDL molecular weight and with the micromolar concentration of the LDL. Using multiple regression analyses, the two variables of plasma LDL could be shown to account for 94% of the variation in plasma cholesterol concentration in the M. fascicularis of this study. Micromolar concentration and molecular weight of LDL were not correlated with each other, suggesting that in M. fascicularis at least two independent types of controls are operative in the response of plasma LDL to dietary cholesterol. The increase in LDL molecular weight was associated with a large increase in cholesteryl ester content and concomitant smaller increases in protein, phospholipid, and free cholesterol. As molecular weight increased, these components appeared to be added to the LDL particles together as discrete increments of fixed composition. The data are consistent with a spherical model of LDL structure with a core of cholesteryl ester and triglyceride and a 21.3 A-thick coat of phospholipid, free cholesterol, and protein.

Animals↗
PubMed1975

Anticoagulant activity of heparin in intravenous fluids.

The anticoagulant activity of heparin dissolved in intravenous solutions was measured by two different methods of heparin assay. Both procedures showed markedly reduced anticoagulant activity within four hours after the addition of heparin to the solutions. When measured according to the procedure of Yin, heparin in the intravenous solutions fully regained its lost anticoagulant activity after 24 hours at room temperature. When measured by the thrombin time, however, the heparin anticoagulant activity reamained reduced. The source of heparin, from either the lung or intestine, does not explain the reduction in anticoagulant activity. Although its cause is unknown, the erratic behaviour of heparin in intravenous solutions stresses the importance of a laboratory monitor of heparin therapy.

Anticoagulants↗
PubMedDate not supplied

The nature of early memory.

Despite tremendous gains in our understanding of the development of memory during the infancy period, relatively little is known about the neural bases of early memory. This is unfortunate, as elucidating the neurobiological mechanisms that mediate changes in memory would likely yield important insight into the concept of infantile amnesia, that is, the inability to recall those events that occur during the first 3-4 years of life. This paper begins by describing the major types of memory adults are capable of and the corresponding neural substrate of each type. A brief exposition of the neural bases of memory development is then provided, including a description of recent work that examines long-term memory in infancy. It is concluded that maturation of cortical areas in the temporal and frontal cortices that transpires between the ages of 1 and 4 years likely accounts for our lack of access to our earliest memories. It is also argued that the examination of the electrophysiological correlates of memory development may shed light on these cortical changes.

Adult↗
PubMedDate not supplied

Family decision-making to withdraw life-sustaining treatments from hospitalized patients.

BACKGROUND: With a national trend toward less aggressive treatment of hospitalized terminally ill patients, families increasingly participate in decisions to withdraw life-sustaining treatment. Although prior research indicates decision making is stressful for families, there have been no psychometric reports of actual stress levels and few discussions of the reasoning used by families compared to clinicians in reaching the decision. OBJECTIVES: The purpose of this study was to assess levels of family stress associated with decisions to withdraw life-sustaining treatments, to assess factors that affected stress, and to compare families and clinicians on their reasoning about the decision. METHODS: Data were collected from hospital decedent charts, family members of decedents, and clinicians who cared for decedents. Data from families were collected in individual interviews, shortly after decedent death and 6 months later, using psychometric measures and semi-structured interview questions. Clinicians were interviewed once shortly following patient death. RESULTS: Family stress associated with the withdraw decision was high immediately following the death of the decedent and, while it decreased over time, remained high a half a year later. Several factors affected stress; most notably, stress was highest in the absence of patient advance directives. In reaching the decision, both families and clinicians prioritized what the patient would want, although families, more strongly than clinicians, endorsed doing everything medically possible to prolong the patient's life. CONCLUSIONS: Findings add compelling evidence for the power of advance directives, whether written or verbal, to reduce the stress associated with family decision-making.

Adult↗
PubMedDate not supplied

Associations between phenylalanine-to-tyrosine ratios and performance on tests of neuropsychological function in adolescents treated early and continuously for phenylketonuria.

Phenylketonuria (PKU) is a genetic disorder characterized by hyperphenylalaninemia. Treatment involves dietary phenylalanine restriction to prevent mental retardation. Because phenylalanine is involved in tyrosine synthesis and tyrosine is a catecholamine precursor, low tyrosine may lead to brain dopamine deficiencies. Because dopamine is involved in the modulation of prefrontally orchestrated executive functions, deficiencies may lead to executive impairments. Despite treatment, impairments in executive cognitive functions have been reported in young children with PKU. Outcome beyond middle childhood has not been extensively investigated. In this study, PKU-affected adolescents (N = 18) with normal-range IQ scores completed neuropsychological tests, and their performance was compared with unaffected peers (N = 16) and chronically ill controls (N = 17). Results demonstrated that the overall performance of the PKU group did not differ from that of the other two groups, but that performance of the PKU proband was associated with phenylalanine and tyrosine levels, and most strongly with phenylalanine-to-tyrosine ratios at several points in development. These findings provide a preliminary test of the dopamine hypothesis of PKU as it applies to adolescents and young adults.

Adolescent↗
PubMedDate not supplied

Atherogenic diet-induced modification of the subfraction distribution of high density lipoproteins in monkeys.

High density lipoproteins (HDL) were isolated from the plasma of adult male African green monkeys fed control or atherogenic diets and were then subfractionated in a density gradient by centrifugation at 50,000 rpm, 20 degrees C for 18 hours in the Beckman VTi50 vertical rotor. Material from the gradient was pooled into six subfractions for further analysis. With increasing density across the gradient, the subfractions had progressively decreasing flotation rates, molecular weights, apo A-I/apo A-II mass ratios, lipid percentages of mass, and average sizes. Apoprotein content per particle was reasonably constant compared to lipid content. The physical and chemical properties of the HDL subfractions suggested that the gradient separated three subclasses of HDL equivalent to HDL 2b, HDL 2a, and HDL3 of human beings. When values among animals were compared, the atherogenic diet shifted the relationship between total plasma cholesterol concentration and total HDL concentration from a positive to a negative correlation. The subfractions most affected were those of d less than 1.10 g/ml (HDL2b), while the 1.10 less than d less than 1.13 g/ml (HDL2a) subfractions were affected to a lesser degree; the more responsive the animal to dietary cholesterol, the lower was the mass concentrations of these subfractions. This pattern suggested that diet-induced changes in HDL2 subfraction particle concentrations may be related to the development of atherosclerosis in African green monkeys; parallel changes in particle composition were not identified.

Animals↗
PubMedDate not supplied

The IPR inventory: development and psychometric characteristics.

The purpose of this study was to develop, validate, and norm a measure of dimensions of interpersonal relationships that are salient to nursing: social support, reciprocity, and conflict. The selection of these concepts was guided by social exchange and equity theories. In the first phase of the study, 44 respondents were interviewed to provide narrative data from which to develop items so that items would be grounded in lived experience. Content validity of items was judged by a panel of 11 experts. The revised 39-item instrument was tested in successive steps with a total of 340 students, patients, and community residents for reliability and validity, including internal consistency reliability, test-retest reliability, factor analysis, and three forms of validity assessment (theory testing, contrasted groups, and multitrait-multimethod comparison). The three subscales of social support, reciprocity, and conflict demonstrated repeated internal consistency and test-retest reliability. Strong evidence of construct validity was demonstrated for the social support and the conflict subscales; validity of the reciprocity subscale was equivocal.

Adult↗