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Biomedical subjects

M Roberts

Publications and source records attributed to M Roberts.

At least 505 records · Page 28Linked to original sources
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Smoking and diabetes.

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Diabetes Complications↗
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Component selection to optimize blood flow for continuous arteriovenous hemofiltration and dialysis.

Blood flow with an arteriovenous access is limited by the resistance of the catheters and hemofilters or dialyzers in the extracorporeal system. Resistance data from manufacturers are varied as to the test conditions used, however, making it difficult to select optimum components. Furthermore, the same size catheters may have varying inner diameters, resulting in large differences in flow resistance. The pressure at various flow rates was determined using a water manometer. The pressure/flow relationship for catheters gave a curve, whereas the logarithmic function resulted in a straight line with a slope of 1.48. The pressure/flow relationship for hemofilters and dialyzers was a straight line with an intercept close to the origin. The data in the tables for flow resistance at 50 and 100 ml/min can be used to compare the various components, and to estimate flow in a given extracorporeal system.

Blood Flow Velocity↗
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"Machineless" nutritional hemodialysis.

It was previously demonstrated that with nutritional hemodialysis (NH), an adaptation of continuous arteriovenous hemodialysis (CAVHD), glucose and aminoacids are efficiently transferred from the dialysate to the patient. Intravenous monitors were used to control dialysate flow and ultrafiltration, and a water manometer provided fail-safe operation. Pressure measurements with low flux dialyzers indicated that a gravity system was possible. This observation formed the basis for the current study. Nutrient dialysate was prepared by adding glucose and amino acid to a bicarbonate dialysate. Subsequently, the bicarbonate dialysate was eliminated by reducing the dialysate volume and increasing the glucose concentration. Dialysate flow was controlled with a valve postdialyzer, and ultrafiltration adjusted by varying the height of the dialysate container. At a glucose concentration of 14.4 gm/dl and outflow rate of 3.9 ml/min, 97% of the glucose in the dialysate was transferred to the patient. Compared with intravenous nutrition, NH is as easy to perform, less costly, does not provide fluid, and is inherently fail-safe. As no equipment is required, many patients can be treated simultaneously. "Machineless" NH suggests the possibility of machineless CAVHD, which could provide dialysis and parenteral nutrition to many acute renal failure patients after a major disaster.

Amino Acids↗
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Prediction of phototoxic potential using human A431 cells and mouse 3T3 cells.

An assay using established cell lines, human A431 epidermal cells and mouse 3T3 fibroblasts, has been developed to predict the phototoxic potential of compounds. The test determines the viability of the two cell lines in response to UV light in both the presence and absence of the test compound. The end point for cytotoxicity is determined from the mitochondrial dehydrogenase conversion of a tetrazolium salt (MTT) to a colored formazan product. The cytotoxicity of the test compound is established prior to UV exposure, and the highest no-effect concentration observed is then applied to cells that are subsequently exposed to different periods of UVA and UVA plus UVB light. A phototoxic effect is considered to have occurred when a biologically significant enhancement of toxicity is shown for the UV light with the compound present when compared to that of UV light alone. The test system has been validated with 30 compounds classified as strong, idiosyncratic, and negative based on the frequency of reported adverse reactions in humans. The in vitro phototoxicity assay was able to highlight the potential for phototoxicity in the strong category of phototoxic compounds and several of the idiosyncratic compounds. Only one of the negative compounds produced any activity in the assay in terms of enhancing UV toxicity. Some of the compounds were shown to protect the cells from the toxic effects of UV exposure.

Animals↗
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Heart transplantation in the United Kingdom: who waits longest and why.

BACKGROUND: This study aims to identify characteristics that increase the chance of death of potential cardiac transplant recipients before donor organs become available. METHODS: Between June 1, 1988, and May 31, 1993, 332 patients were accepted for heart transplantation; 235 underwent surgery. Ninety-seven patients had not received transplants; of these, 71 died, 13 were transferred to other lists, and 13 were awaiting organs at the close of the study. Median waiting time for those patients who received organs was 109 days, whereas patients who did not receive organs spent a median of 94 days on the list. Recipients are matched to donor organs according to blood group, size (height), and, recently, preoperative transpulmonary pressure gradient. Recently cytomegalovirus antibody mismatches (positive donor to negative recipient) have been avoided where possible. These factors, together with age, gender, underlying diagnosis, previous heart surgery, and Toxoplasma antibody status were studied to assess their influence on waiting time and survival. RESULTS: No characteristics were found significantly to influence survival after acceptance, so that the chance of death while the patient was waiting for heart transplantation is mainly affected by the severity of disease and the length of time a patient waits. In multivariate analyses the following were independently significantly associated with shorter waiting times: small patients (< 1.7 m tall; p = 0.005), patients with blood types B and AB (p = 0.003), and patients with cardiomyopathy (p < 0.001). CONCLUSIONS: These results can be used by cardiologists to help assess the time at which a patient should be referred for transplantation.

Blood Grouping and Crossmatching↗