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Biomedical subjects

J Wyatt

Publications and source records attributed to J Wyatt.

123 records · Page 7Linked to original sources
PubMed1986

Nutrition guidelines for burned patients.

Among all hospitalized patients, burned patients have been shown to have the greatest increase in metabolic demand. However, the temptation to overfeed those patients must be recognized, as that practice may lead to increased morbidity. Care must be taken to provide an appropriate nutritional regimen in order to minimize protein catabolism and to promote wound healing. Several formulas for calculating energy and protein needs for burned patients have been reviewed for this article, along with guidelines for estimating other nutrients for such patients. Methods for providing nutrition therapy depend on many factors, such as extent and degree of injury and gastrointestinal function. The feeding methods most commonly used are parenteral (peripheral and central venous alimentation) and enteral (oral and naso-gastric tube feeding). Guidelines for using both parenteral and enteral feedings are discussed, as well as reliable methods for evaluating the nutrition assessment of the burned patient. It must be noted that standard assessment parameters are often unreliable, and their limitations are also addressed. In addition, several new parameters are introduced, including compliance with caloric goal, corrected weight change, and prediction of total urinary nitrogen to be used to calculate nitrogen balance.

Anthropometry↗
PubMed1986

Accurate and independent measurement of volume and hemoglobin concentration of individual red cells by laser light scattering.

Cell volume (MCV) and hemoglobin concentration (MCHC) are the red cell indices used to characterize the blood of patients with anemia. Since the introduction of flow cytometric methods for the measurement of these indices, it has generally been assumed that the values derived by these instruments are accurate. However, it has recently been shown that a number of cellular factors, including alterations in cellular deformability, can lead to inaccurate measurement of cell volume by these automated instruments. Because cell hemoglobin concentration and hematocrit are computed from the measured values of cell volume, accuracy of these indices is also compromised by inaccurate determination of cell volume. A recently developed experimental flow cytometric method based on laser light scattering, which can independently measure volume and hemoglobin concentration, has been used in the present study to measure MCV and MCHC of density-fractionated normal and sickle red cells, hydrated and dehydrated normal red cells, and various pathologic cells. We found that the new method accurately measures both volume and hemoglobin concentrations over a wide range of MCV (30 to 120 fL) and MCHC (27 to 45 g/dL) values. This is in contrast to currently available methods in which hemoglobin concentration values are accurately measured over a more limited range (27 to 35 g/dL). In addition, as the experimental method independently measures volume and hemoglobin concentration of individual red cells, it allowed us to generate histograms of volume and hemoglobin concentration distribution and derive coefficient of variation for volume distribution and standard deviation of hemoglobin concentration distribution. We have been able to document that volume and hemoglobin concentration distributions can vary independently of each other in pathologic red cell samples.

Anemia, Sickle Cell↗
PubMed1985

The structural organization of skeletal proteins influences lipid translocation across erythrocyte membrane.

In order to define the influence of skeletal protein organization on transmembrane phospholipid movement in erythrocyte membranes, we measured the translocation rate of lysophosphatidylcholine in pathologic red cells. A simple method based on the differential extraction of lysophosphatidylcholine from the red cell membrane by saline and albumin solutions was used to quantitate the translocation rate. Two groups of pathologic red cells were chosen for these studies: red cells with quantitative deficiencies of the skeletal proteins, spectrin and protein 4.1, and sickle erythrocytes in which controlled reorganization of the membrane was induced by hemoglobin polymerization. Marked increase in lipid translocation rate was seen in red cells having quantitative deficiencies of spectrin and protein 4.1. The magnitude of the increase in translocation rate in spectrin-deficient red cells was related to the magnitude of protein deficiency. Translocation rate in sickle erythrocyte membranes increased by 50% upon deoxygenation as a result of sickle hemoglobin polymerization. No increase in translocation rate was seen in normal cells upon deoxygenation. By manipulating the extent of membrane reorganization that occurred following deoxygenation of sickle cells, we have been able to show that skeletal reorganization induced by hemoglobin polymerization and not hemoglobin polymerization per se is responsible for the increase in translocation rate. Together, these findings imply that the structural organization of membrane skeletal proteins plays an important role in regulating the rate of transbilayer movement of lipids across the erythrocyte membrane.

Anemia, Sickle Cell↗
PubMed1985

Retrospective study of histological features of acute rejection in renal allografts and comparison with circulating T cell populations.

The histological severity of acute rejection in renal allografts was determined for 39 rejection episodes in 30 renal transplant recipients. Data were compared with the peripheral blood T cell subset ratios measured before and at the onset of the rejection episode. T cell subset ratios showed no correlation with the histological severity of rejection, nor with the reversibility of the rejection episode. The grade of histological rejection on biopsy was predictive of graft survival. We conclude that renal biopsy remains the best method for determining the severity and outcome of acute allograft rejection episodes.

Adolescent↗
PubMed1982

Lipid translocation across the human erythrocyte membrane. Regulatory factors.

A simple method based on the differential extraction of lysophosphatidylcholine (LPC) by saline and albumin solutions has been developed to study the factors that influence lipid translocation across intact human erythrocyte membrane. With this assay, the rate of LPC translocation across the bilayer at 37 degrees C was found to be 1.87% h (0.0187 h-1). Identical translocation rates were derived for normal cells and cells in which the ATP was totally depleted, implying that the metabolic state of the cell had no influence. In contrast, the translocation rate was strongly influenced by temperature. Above 21 degrees C, the rate doubled for every 51 degrees C increase in temperature, suggesting an important role for diffusion through the lipid phase. Denaturation of a single major skeletal protein, spectrin, by heating cells to 5 degrees C did not alter the translocation rate. However, oxidative cross-linking of a complex of membrane proteins by treatment with diamide significantly increased the rate of translocation at 37 degrees C. Cholesterol enrichment of the cells decreased the apparent rate of translocation but not the total quantity of LPC translocated. Taken together, these data suggest that lipid translocation across the intact human erythrocyte membrane is not energy dependent, and that it is influenced by the organizational state of both the lipid and protein moieties of the membrane.

Biological Transport↗
PubMedDate not supplied

Evaluating medical expert systems: what to test and how?

Many believe that medical expert systems have great potential to improve health care, but few of these systems have been rigorously evaluated, and even fewer are in routine use. We propose the evaluation of medical expert systems in two stages: laboratory and field testing. In the former, the perspectives of both prospective users and experts responsible for implementation are valuable. In the latter, the study must be designed to test, in an unbiased manner, whether the system is used in clinical practice, and if it is used, how it affects the structure, process and outcome of health care encounters. We conclude with proposals for encouraging the objective evaluation of these systems.

Diagnosis, Computer-Assisted↗
PubMedDate not supplied

Evaluating black-boxes as medical decision aids: issues arising from a study of neural networks.

The rigorous evaluation of medical decision aids will be critical to promoting their development, establishing their clinical value and legalizing their use. Many decision aids are transparent in the sense that their internal structure and function can be examined and verified. Some decision aids, however, use complex models of associations in training data to construct 'black-box' systems whose workings are largely impenetrable and inexplicable. The issues surrounding the evaluation of such systems, as exemplified by connectionist (neural network) models, are discussed. For such systems the two major aspects that can be evaluated are the training data from which the system is derived, and its performance on test data. A number of questions about the use of black-box systems as medical decision aids are posed which require consideration by the medical informatics community.

Diagnosis, Computer-Assisted↗
PubMedDate not supplied

Sucrose permeability as a marker for NSAID-induced gastroduodenal injury.

OBJECTIVE: To evaluate sucrose permeability as a non-invasive test for the monitoring of upper gastrointestinal mucosal damage (uGMD) in patients treated with NSAIDs. METHODS: 40 patients with non-inflammatory joint pain were enrolled in a prospective study. Before and after 14 days of ibuprofen treatment (3 x 400 mg/day), the rates of urinary sucrose excretion after an oral sucrose load were assessed. Individuals with increased sucrose permeability underwent endoscopy. RESULTS: 8 patients (20%) showed abnormal sucrose permeability before taking any NSAID. In 5/20 patients (25%) who completed 2 weeks of ibuprofen medication, sucrose excretion increased above the normal level. Endoscopic examination and biopsy revealed mild uGMD, but no ulceration in 8/11 (72%) patients with increased permeability to this marker. CONCLUSION: Sucrose permeability testing is a sensitive procedure for research protocols on NSAID-induced gastropathy. Since this test also seems to detect slight and clinically insignificant mucosal damage, however, its use in clinical decision-making regarding gastroprotective medication is limited.

Adult↗