Biomedical subjects

M Claassen

Publications and source records attributed to M Claassen.

4 recordsLinked to original sources

PubMed2006

Pitfalls with rapid HIV antibody testing in HIV-infected children in the Western Cape, South Africa.

BACKGROUND: Rapid HIV antibody tests are commonly used for HIV diagnosis in the developing world. These tests are generally reported as sensitive, despite paucity of evaluations in paediatric populations. OBJECTIVES: We tested specimens of paediatric patients, known to be HIV-infected, to detect any false negative tests and determine associations with such an outcome. STUDY DESIGN: One hundred and fifty-three specimens, from 109 patients, recorded to be HIV-infected by standard testing, were tested on the Capillustrade mark HIV-1/HIV-2 test (Trinity Biotech, Ireland); 150 specimens also had sufficient volume to be tested on Abbott Determinetrade mark HIV1/2 assay (Abbott GmbH, Wiesbaden, Germany). Treatment information, CD4 counts and HIV-1 viral load measurements were obtained from patient files and laboratory databases. RESULTS: Twenty-one of 153 specimens tested negative on the Capillus (sensitivity 86.3%). False negative results by Capillus were associated with antiretroviral treatment (ART) (p=0.0018) and lower HIV-1 viral load (p=0.013). Serial dilutions of some of the specimens indicated that both rapid tests, and the Capillus in particular, became negative at lower dilutions than an HIV enzyme immunoassay (EIA). CONCLUSIONS: The Capillus test had an unexpectedly low sensitivity in a South African population of HIV-infected children that had access to antiretroviral treatment, posing a risk of false negative HIV testing.

AIDS Serodiagnosis↗

PubMed2000

A handful of questions. Supporting parental decision making.

Advances in healthcare have improved the survival rates of children with serious health problems. Parents, relieved that their child is alive, often face the challenge of caring for a child with a chronic illness and must make healthcare decisions that have life-long consequences. Supporting parents through the decision-making process is a complex challenge for the advanced practice nurse. This article offers an original and dynamic decision-making assessment tool to help the advanced practice nurse provide effective evaluation and appropriate support for the parents. This "Handful of Questions" was created using a patient-oriented decision-making model by Pierce and the work of other decision-making researchers. The literature reviewed includes the topics of surrogate parental decision making and an examination of the relationship between the decision-maker and healthcare providers.

Adult↗

PubMed1998

Histochemical differentiation between nitric oxide synthase-related and -unrelated diaphorase activity in the rat olfactory bulb.

The widely used NADPH-diaphorase reaction for demonstrating neuronal nitric oxide synthase is not as specific as previously thought, as it visualizes both a nitric oxide synthase-related activity and a nitric oxide synthase-unrelated diaphorase. In the present study, we used the rat olfactory bulb as a model to characterize the NADPH-diaphorase activity of neuronal nitric oxide synthase histochemically in comparison with neuronal nitric oxide-unrelated diaphorase activity. The NADPH-diaphorase activity of nitric oxide synthase peaked at pH 8 and at Triton X-100 concentrations of 1-2.5%. It was stable in an acidic environment but was reduced in the presence of Triton X-100 and was inactivated by the flavoprotein inhibitor, diphenyleneiodonium. It preferred beta-NADPH as the co-substrate to alpha-NADPH and alpha-NADH. In contrast, nitric oxide synthase-unrelated diaphorase peaked at pH 10, displayed a Triton X-100 optimum at a concentration of 1%, was unstable in an acidic environment and used beta-NADPH, alpha-NADPH and alpha-NADH to similar extents. Differences in the characteristics between neuronal nitric oxide synthase-related and nitric oxide synthase-unrelated NADPH-diaphorase can be used to increase the specificity of the histochemical nitric oxide synthase marker reaction.

Animals↗

PubMed1989

Red cell distribution at microvascular bifurcations.

The distribution of red cell and blood volume flow was studied at 65 arteriolar bifurcations in the rat mesentery. Hematocrit and flow velocity were measured simultaneously in all three vessel segments constituting a bifurcation. Blood flow distribution was manipulated by irreversibly occluding downstream side branches of one of the daughter vessels. The dependence of fractional red cell volume flow on fractional blood flow was described using a three-parameter (X0, B, A) logit function. The critical volume flow fraction below which only plasma enters a downstream branch (X0), the nonlinearity of the relation between red cell and blood volume flow (B), and the asymmetry of that relation which is described by the parameter A decrease with increasing diameter of the vessel feeding the bifurcation. At diameters above 30 microns, phase separation is very limited. In addition, the nonlinearity parameter B decreases with decreasing hematocrit in the feeding vessel. The asymmetry parameter A strongly depends on the diameter ratio between the two daughter branches: For a given fractional blood flow, the smaller branch receives more red cells than the larger branch. Using a model for plasma skimming based on the assumption of a planar separating surface, the shape of the radial hematocrit profile in the feeding vessel has been calculated. The model predicts a decrease in local hematocrit from the vessel axis toward the wall with a distinct marginal zone free from cell centers. With increasing vessel diameter the hematocrit profile becomes more blunted while the width of the marginal zone increases.

Animals↗