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Biomedical subjects

R Walker

Publications and source records attributed to R Walker.

At least 253 records · Page 14Linked to original sources
PubMed1992

Linked migration systems: immigration and internal labor flows in the United States.

The relationship between immigration to and labor movements within the United States is examined using a model that links migration, occupations, production and institutional relations in the economy, and economic restructuring. The authors conclude that "native blue-collar workers have been spatially displaced by recent immigration and that the process of capital accumulation, as manifested in economic restructuring, is the driving force behind the mobility system, affecting both immigration patterns and the destination choices of white-collar workers. As a result, we suggest that previous estimates of immigrant impacts on local labor markets may be underestimated."

Americas↗
PubMed1992

[Periodic health examination].

A literature search has been made on the examinations to be performed during the "periodic health exam" on the healthy adult. These examinations shall be performed bearing in mind the prevalence and morbility data of the specific diseases, individual risk factors and the quality (sensibility and specificity) of the diagnostic procedure. The value of regular blood pressure determination, breast exam and cervical cytology with Papanicolaou stain, is well established. However, there is no consensus regarding other determinations, due to the fact that different authors use different approaches. The skin, mouth and thyroid examination for cancer screening is limited only to individuals having risk factors. Heart auscultation for the diagnosis of valvulopathies that could required antibiotic prophylaxis for bacterial endocarditis is important. In individuals over sixty years old, vision acuity and hearing capabilities should be explored, also abdomen should be explored to detect aortic aneurysms. Hypercholesterolemia should be determined in individuals over 20 years old, and PPD should be performed before 35 years old. Concerning the rest of explorations (rectal taction, testicular exploration, etc.) its efficacy has not been clearly established in the screening.

Physical Examination↗
PubMed1991

PRN psychotropic drug use on a psychiatric unit.

PRN psychotropic drug use is a frequent practice on psychiatric units. This study examined medical records for patient demographics and prescribing patterns of drugs. The omission of the indication and frequency of dosing for the drug were common prescribing errors. There was no significant association between diagnosis and whether a patient received PRN drugs. Anxious patients were significantly more likely to receive PRN anxiolytics whereas psychotic patients were as likely to receive PRN anxiolytics as antipsychotics. Anxiolytics also were significantly more likely to be judged effective by the nursing staff than antipsychotics. A perplexing finding was that manic and schizophrenic patients were significantly less likely to receive PRN hypnotics than were patients with Major Depression. The clinical implications of the findings are discussed and recommendations are made to improve standards of practice for this commonplace treatment.

Adult↗
PubMed1991

Disentangling neglect and hemianopia.

In this paper we report findings which question the diagnosis of a hemianopia in B.Q., a 66-year-old lady who shows unilateral spatial neglect following a lesion to the right parietal lobe. The presence of a hemianopia has been indicated following two independent assessments of B.Q.'s visual fields. We examined B.Q.'s performance on a visuo-spatial task in which single or double stimuli were displayed left and right of a central fixation point. B.Q. failed to report left stimuli when the fixation point was continuously displayed (OVERLAP CONDITION). This performance is consistent with the suggestion of a left hemianopia as indicated by perimetric field testing. In a further condition the fixation point was extinguished prior to stimuli onset (GAP CONDITION). B.Q. consistently responded to left stimuli in the gap condition and also showed improved performance to right stimuli. Eye movements were recorded on a separate testing session, in which B.Q. showed a normal saccadic response to left targets in the gap condition, but not during the overlap condition. These results suggest that B.Q.'s failure to report left stimuli during field plotting is due to her neglecting left stimuli and not because she has a visual field defect. By using a testing procedure which reduces the severity of neglect B.Q. is able to respond to left stimuli. Reducing the severity of B.Q.'s neglect also abolishes the apparent hemianopia. Standard field plotting techniques which use a consistently displayed fixation point may not be appropriate for the testing of neglect patients' visual fields.

Aged↗
PubMed1991

Influence of dietary protein and gut microflora on endogenous synthesis of nitrate induced by bacterial endotoxin in the rat.

Germ-free (GF) rats were maintained on a diet marginally adequate in protein, with and without a supplement of NH4Cl. Their urinary excretion of total nitrogen, nitrate, urea and creatinine was measured before and for 4 days after injection of Escherichia coli endotoxin (lipopolysaccharide; LPS). Although more nitrogen was excreted by rats on the diet supplemented with NH4Cl, nitrate excretion was increased to a similar extent in rats on both diets. This suggests that oxidation of ammonia released by deamination of amino acids is an unlikely pathway of nitrate synthesis. In a second experiment, nitrate excretion before and after injection of LPS was measured in GF and conventional (CV) rats given high- or low-protein diets. Urinary 3-methylhistidine (3MH) was measured as an index of breakdown of tissue protein. In both environments, nitrate excretion was significantly greater, before and after LPS administration, by rats on the high-protein diet than by their counterparts on the low-protein diet, and was generally greater by GF than by CV rats. Since only small, non-significant rises in urinary 3MH were observed after LPS treatment, it was concluded that the bulk of the nitrogen required for nitrate synthesis in response to endotoxin is derived from dietary protein rather than from nitrogenous products of tissue breakdown.

Administration, Oral↗
PubMed1991

Applications of chemical-shift-selective NMR microscopy to the non-invasive histochemistry of plant materials.

Chemical-shift-selective imaging at microscopic resolution has been applied to the study of various plant materials including orange peel, grape berries and both dried and undried fruits of fennel. It is shown that selective imaging of aromatics and carbohydrates as well as water and oil can be performed with in-plane resolution down to 13 microns and slice thicknesses of 1 mm or less, at a field strength of 4.7 Tesla. The noninvasive nature of the method gives it advantages over established methods of plant histochemistry which involve sectioning and staining to reveal different chemical constituents.

Fruit↗
PubMed1991

Agaritine does not mediate the mutagenicity of the edible mushroom Agaricus bisporus.

Ethanolic extracts of the edible mushroom Agaricus bisporus displayed a direct-acting mutagenic response in various Salmonella typhimurium strains, TA104 being clearly the most sensitive. Incorporation of an activation system derived from the liver of mice, hamsters or Aroclor 1254-induced rats failed to increase the mutagenic response. The mutagenic response of ethanolic extracts from various types of mushroom, containing different levels of agaritine (range 0.3-6.5 g/kg fresh weight), was very similar and did not correlate with the agaritine levels. Moreover, use of gamma-glutamyl transpeptidase, the enzyme catalysing the activation of agaritine, as an activation system did not enhance the mutagenicity of the mushroom ethanolic extracts. It is concluded that agaritine is not responsible for the mutagenicity of mushroom extracts.

Animals↗
PubMed1991

Extradural vein puncture--an avoidable complication.

Accidental cannulation of an extradural vein is a troublesome and potentially serious complication of extradural catheter insertion. This study was conducted to assess the influence of posture, catheter size and the injection of saline before catheter insertion, on its occurrence. Eight different techniques were studied based on combinations of these three factors. There was no difference in incidence with respect to posture. The use of 18-gauge catheters, after injection of 10 ml of 0.9% saline, resulted in a significant (p less than 0.01) reduction in the incidence of extradural vein cannulation. This technique is recommended in obstetric patients as a means of avoiding accidental intravenous injection of local analgesic.

Adolescent↗
PubMed1991

The psychosocial effects of acne on adolescents.

To describe the psychosocial impact of acne on adolescents, and, in particular, to assess whether self-concept is affected by medical treatment, we evaluated 39 teenagers presenting for care to a community-based dermatologist. Prior to and following treatment, subjects completed a self-assessment questionnaire, the Piers-Harris self-concept scale, and underwent an objective assessment of acne severity. Fifty-eight percent of subjects were dissatisfied with their facial appearance and this in turn was correlated with feelings of embarrassment and social inhibition (for each, r = 0.48, P less than or equal to 0.005). Subjects' rating of acne severity, but not the dermatologist's, was correlated with dissatisfaction with facial appearance (r = 0.45, P less than or equal to 0.005). Despite these findings, the mean Piers-Harris total t-score (55.4 +/- 7.4) was within the normal range. Fourteen subjects (36%) returned for follow-up and 71% of these were judged by both the dermatologist and themselves to have improved. Following therapy, significant reductions in the adverse consequences of acne were observed with 42% of subjects reporting that their facial appearance was more acceptable to peers, 50% being less embarrassed, and 58% feeling less socially inhibited. Minimal improvement in mean Piers-Harris total t-score was observed (54.6 to 57.4, P = 0.004, paired t-test). Our data demonstrate that acne is perceived by adolescents to have important negative personal and social consequences, and that improvement in these areas may accompany medical treatment.

Acne Vulgaris↗
PubMed1991

Ion exchange chromatography of purified colonic mucus glycoproteins in inflammatory bowel disease: absence of a selective subclass defect.

Previous reports of a selective mucin subclass defect in ulcerative colitis have been reassessed using high performance chromatography (Superose 6 and Mono Q) for mucin purification and fractionation coupled with analysis of the fractions obtained using a combination of enzyme linked lectin and mucin antibody assays. Mucin samples purified from snap frozen rectal biopsy specimens obtained from patients with ulcerative colitis (n = 12), Crohn's disease (n = 5), and non-inflammatory bowel disease control subjects (n = 9) were subject to ion exchange chromatography using a continuous 0-0.35 mol/l NaCl salt gradient with a final 2.5 mol/l NaCl step. In all samples the major proportion (mean (SD) 86.7 (8.9)%) of the mucin detectable by wheat germ agglutinin binding eluted between 0.15 and 0.35 mol/l NaCl with no significant difference in elution profile between ulcerative colitis and control subjects. Significant elution of glycoprotein at less than 0.15 mol/l NaCl did occur, however, when a lower molecular weight mucin containing fraction which contained concanavalin A positive (glucose or mannose containing) material was analysed similarly. Similar ion exchange profiles were obtained when (3H)N-acetylglucosamine labelled mucins were studied after tissue culture of rectal biopsy specimens. No significant alteration in the ion exchange profile of purified mucins in ulcerative colitis has been shown in these studies. It is possible that the previously reported relative depletion of mucin subclass IV (eluting with 0.20 mol/l NaCl) may simply have reflected mucin depletion.

Chromatography, Ion Exchange↗
PubMed1991

Determination of local myocardial electrical activation for activation sequence mapping. A statistical approach.

Electrical activation sequence mapping requires accurate identification of local activation, but because extracellular recordings do not exclusively reflect local events, complex electrograms may be difficult to interpret. In such cases, the assignment of local activation is subject to error that could affect interpretation of the resulting activation maps. The purpose of this investigation was to develop an approach that would provide quantitative indexes of error in the determination of local activation. An electrode array with 64 closely spaced unipolar electrodes was used to record from the left ventricular surface during open heart surgery. Electrograms with multiple deflections were recorded from four patients with scarred myocardium; two other patients with normal myocardial function served as controls. Each of 784 deflections was scored on the basis of three features: evidence for propagation, the configuration of the bipolar signal, and the effect of changing from the chest to an average reference. Local activation was considered probable if evidence for all three features was present and improbable if none of the three features was present. Deflections that were ambiguous with respect to this standard were excluded. Of over 30 test variables analyzed, the three with the greatest power to discriminate signals due to local activation from those due to distant activity were 1) a linear combination of the extracellular potential plus the ratio of the second derivative and the extracellular potential, 2) the second derivative, and 3) the minimum (greatest negative) first derivative. For each of these variables, the threshold value providing the greatest performance was identified by the maximum quality of efficiency, an index of agreement. This statistical approach provides an objective basis for determining local activation and provides a quantitative assessment of error that could enhance interpretation of electrical activation sequence maps.

Differential Threshold↗