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Biomedical subjects

R C Burns

Publications and source records attributed to R C Burns.

31 records · Page 2Linked to original sources
PubMed1968

The acetylene-ethylene assay for n(2) fixation: laboratory and field evaluation.

The methodology, characteristics and application of the sensitive C(2)H(2)-C(2)H(4) assay for N(2) fixation by nitrogenase preparations and bacterial cultures in the laboratory and by legumes and free-living bacteria in situ is presented in this comprehensive report. This assay is based on the N(2)ase-catalyzed reduction of C(2)H(2) to C(2)H(4), gas chromatographic isolation of C(2)H(2) and C(2)H(4), and quantitative measurement with a H(2)-flame analyzer. As little as 1 mumumole C(2)H(4) can be detected, providing a sensitivity 10(3)-fold greater than is possible with (15)N analysis.A simple, rapid and effective procedure utilizing syringe-type assay chambers is described for the analysis of C(2)H(2)-reducing activity in the field. Applications to field samples included an evaluation of N(2) fixation by commercially grown soybeans based on over 2000 analyses made during the course of the growing season. Assay values reflected the degree of nodulation of soybean plants and indicated a calculated seasonal N(2) fixation rate of 30 to 33 kg N(2) fixed per acre, in good agreement with literature estimates based on Kjeldahl analyses. The assay was successfully applied to measurements of N(2) fixation by other symbionts and by free living soil microorganisms, and was also used to assess the effects of light and temperature on the N(2) fixing activity of soybeans. The validity of measuring N(2) fixation in terms of C(2)H(2) reduction was established through extensive comparisons of these activities using defined systems, including purified N(2)ase preparations and pure cultures of N(2)-fixing bacteria.With this assay it now becomes possible and practicable to conduct comprehensive surveys of N(2) fixation, to make detailed comparisons among different N(2)-fixing symbionts, and to rapidly evaluate the effects of cultural practices and environmental factors on N(2) fixation. The knowledge obtained through extensive application of this assay should provide the basis for efforts leading to the maximum agricultural exploitation of the N(2) fixation reaction.

Journal Article↗
PubMedDate not supplied

Synthetic diamonds as in vivo radiation detectors.

Synthetic diamonds with controlled amounts of impurity atoms can be manufactured so that, as thermoluminescent dosimeters, they can be made to have sensitivities at least as good as presently available commercial thermoluminescent dosimeters. They also exhibit, for radiations normally found in therapy situations, a linearity of response that extends from less than 0.01 Gy (1 rad) to over 10 Gy (1000 rad). Their physical size and form, crystals which can have volumes of less than 1 mm3, make them ideal candidates for in vivo monitoring of radiation fields, particularly electron fields where high-resolution measurements are essential for accurate isodose line determinations. Aspects of dose response from gamma-ray beams in relation to the type and concentrations of the impurity atoms within the diamond are discussed, and some experimental values for gamma, x-ray, and electron beams are presented.

Carbon↗
PubMedDate not supplied

Long-term central venous access vs other home therapies: complications in patients with acquired immunodeficiency syndrome.

One hundred and forty silicone catheters were inserted in 127 patients for long-term intravenous access with a cumulative follow-up time of 21,125 catheter-days (58 patient-years). Fifty-six patients had acquired immunodeficiency syndrome (AIDS); 44 were not AIDS patients and were receiving ambulatory home parenteral nutrition, whereas the remaining 27 did not have AIDS and were receiving home antibiotic therapy. Patients had a mean of 1.1 catheters inserted, and the rate of Hickman catheter-related sepsis was 0.18 per 100 catheter days or 0.6 septic episodes per patient year of treatment. Catheter-related sepsis was higher in AIDS patients (p < .01) and in patients receiving parenteral nutrition (p < .05) compared with those receiving antibiotic therapy. Prior catheter infection and AIDS were the most significant predictors of catheter infection (p < .01). Staphylococcus aureus was the most commonly isolated pathogen (61%) in AIDS patients. Fever (p < .001) and relative leukocytosis (p < .02) were the most common signs of infection. Only 14 infected catheters (37.8%) were salvaged by antibiotic therapy after the initial infection episode, and 6 of these catheters (42.9%) had recurrent multiple infections. In addition, inflammatory bowel disease was found to be a risk factor for venous thrombosis (p = .018). We conclude that because immunocompromised patients have a high risk of infection, catheter-related sepsis in these patients should be treated by catheter removal and antibiotics.

Acquired Immunodeficiency Syndrome↗