Effect of practical layered dielectric loads on SAR patterns from dual concentric conductor microstrip antennas.

Radiation patterns of 2 and 4cm square Dual Concentric Conductor (DCC) microstrip antennas were studied theoretically with Finite Difference Time Domain (FDTD) analysis and compared with experimental measurements of power deposition (SAR) in layered lossy dielectric loads. Single and array configurations were investigated with 915 MHz excitation applied across either one, two or four sides, or four corners of the square apertures. FDTD simulations were carried out for realistic models of a muscle tissue load coupled to the DCC antennas with a 5 mm thick bolus of either distilled water or low loss Silicone Oil. This study characterizes the effect on SAR of adding three additional thin dielectric layers which are necessary for clinical use of the applicator. These layers consist of a 0.1 mm thick dielectric coating on the array surface to provide electrical isolation of DCC apertures, and 0.15 mm thick plastic layers above and below the bolus to contain the liquid. Experimental measurements of SAR in a plane 1 cm deep in muscle phantom agree well with theoretical FDTD simulations in the multi-layered tissue models. These studies reveal significant changes in SAR for applicator configurations involving low dielectric constant (Er) layers on either side of a high Er water bolus layer. Prominent changes include a broadening and centring of the SAR under each aperture as well as increased SAR penetration in muscle. No significant differences are noted between the simple and complete load configurations for the low Er Silicone Oil bolus. Both theoretical and measured data demonstrate relatively uniform SAR distributions with > 50% of maximum SAR extending to the perimeter of single and multi-aperture array configurations of DCC applicators when using a thin 5 mm water or Silicone Oil bolus.

A new polymethylmethacrylate membrane for hemodialysis.

High molecular weight (MW) solutes are not removed during conventional hemodialysis (HD), and their accumulation is thought to play a role in some long-term HD complications (anemia, bone and joint pain, neuropathy, itching). The present trial was conducted to evaluate the removal capacity during in vivo HD of a new polymethylmethacrylate (PMMA) membrane (Filtryzer BK-F, 1.3 m2) compared to conventional PMMA (BK-P, 1.6 m2) and to cellulose acetate (CA, 1.3 m2). BK-F dialyzers, with a pore size of 100 A degrees and 62% porosity, are designed to remove high MW substances. Ten stable anuric RDT patients (53 +/- 13 years) were treated for one week with each membrane in a randomized sequence. Plasma concentrations of creatinine, BUN and beta 2-microglobulin (beta 2-M) were measured before (b) and after (a) HD to determine the reduction rate for these substances (%). Beta 2-M concentration after HD was corrected for changes in distribution volume. Samples of spent dialysate were collected after 3 minutes, 120 minutes and at the end of HD sessions, and appropriately treated and concentrated for HPLC analysis. The reduction rate for BUN and creatinine was similar for the 3 membranes. BK-F showed a higher beta 2-M reduction rate than BK-P (p < 0.005) or CA (p < 0.0001). HPLC analysis of dialysate showed prevalent peaks < 4 kilodaltons (kDa) throughout HD for BK-P and CA. Solutes > 10 kDa were infrequently detected. Peak profile during HD with BK-F was quite different, showing a predominant peak > 50 kDa which also included albumin. However, albumin loss significantly decreased after 120 minutes and at the end of dialysis compared with the 3-minute values, and was lower than that reported in CAPD patients. With BK-F a peak of MW > 500 kDa was also detected which previous studies indicated as a range characterized by the presence of erythropoiesis inhibitors. Use of the BK-F membrane in HD could afford satisfactory removal of high MW substances, thereby preventing or controlling some long-term HD complications such as anemia or beta 2-M amyloid formation.

Geographic factors and plasma selenium in uremia and dialysis.

The importance of selenium (Se) as an essential trace element for man has been increasingly recognized. Blood Se levels in chronic uremic patients are frequently reported to be lower than in controls. Definitive determination of the Se status in uremic patients, however, is hampered by the wide range of blood Se content in humans from different parts of the world. The present study was designed to assess and compare the Se status in two European populations from Rostock (Germany) and Chieti (Italy). Plasma Se levels were evaluated in healthy controls, chronic renal failure nondialyzed patients (CRF) and hemodialysis patients (HD). All Se determinations were performed in a single laboratory. The Se concentration was significantly higher (p < 0.005) in Italian healthy controls than in German healthy controls. In contrast, Se levels were similar in both CRF and HD patients from both cities. In both countries, the Se concentration in CRF and HD patients was significantly lower (p < 0.001) than in their corresponding controls, but no difference between CRF and HD was found. CRF and HD patients from the two countries showed quite similar laboratory and anthropometric data. In CRF patients in Chieti, a significant (p < 0.05) negative correlation between plasma Se and serum creatinine was found. In both HD groups, the length of time on HD and type of membrane dialyzer used did not influence the Se status. A significant positive correlation (p < 0.01) between Se levels and the protein catabolic rate was found in both HD groups. Uremia seems to be a strong factor which overrules the difference in Se levels that is present in healthy adults from different European countries. Uremia in itself may influence and level the Se concentration in patients with geographic diversity.

Hemodialysis with regenerated cellulosic membranes does not reduce plasma selenium levels in chronic uremic patients.

Selenium (Se) is considered an essential and very important trace element for humans. Se blood levels are frequently low in end-stage renal disease (ESRD) patients, but very little has been established concerning the mechanisms that could modify Se status in uremia, including a supposed dialysis-mediated Se depletion. In order to verify whether hemodialysis (HD) can induce a loss of Se, thereby leading or contributing to a low plasma Se concentration, we investigated the effect of HD procedure with the most commonly used regenerated cellulosic membrane (Cuprophan) on plasma Se levels in 20 uremic patients on HD for 62.5 +/- 49.4 months. Plasma Se levels were also determined in 15 chronic renal failure (CRF) nondialyzed patients and in 28 age-matched healthy controls. Se concentration was determined by atomic absorption spectrophotometry. Plasma Se levels of both HD patients (61.3 +/- 8.5 micrograms/L) and CRF nondialyzed patients (56.4 +/- 10.1 micrograms/L) were significantly lower than in normal subjects (78.3 +/- 9.7 micrograms/L, p < 0.001). In CRF nondialyzed patients, a significant (p < 0.05) negative correlation was found between the plasma Se concentration versus serum creatinine values. Within the HD group, plasma Se levels significantly increased after the HD procedure (72.8 +/- 17.2 micrograms/L, p < 0.02) together with hematocrit and total plasma protein values (p < 0.05 and p < 0.001, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of selenium supplementation on immune parameters in chronic uraemic patients on haemodialysis.

BACKGROUND: The involvement of selenium (Se) in immune response has been increasingly recognized, cell-mediated immunity being principally affected by Se deficiency. Blood Se levels in chronic uraemic patients are frequently lower than in controls, and in these patients cellular immunity in generally impaired. METHODS: The present study was designed to assess the effects of Se supplementation over 6 consecutive months on immune parameters in haemodialysis (HD) patients from Rostock (Germany) and Chieti (Italy). In both cities, five patients were supplemented with Se (500 micrograms thrice weekly for 3 months, then 200 micrograms thrice weekly for the next 3 months), whereas another five patients received placebo. All Se determinations were performed in a single laboratory. RESULTS: In both cities, basic plasma Se levels were significantly lower in patients than in their corresponding normal controls. After beginning Se supplementation, plasma Se concentration promptly normalized and levelled off in the normal range throughout the study. Se administration was well tolerated by all patients, and no side-effects attributable to Se toxicity were observed. Although no major change in immunocompetent cells (white blood count, total lymphocyte count, lymphocyte subpopulations) was observed during Se therapy, an improvement in T-cell response to phytohaemoagglutinin (as evaluated in Rostock patients) and a significant progressive increase in delayed-type hypersensitivity (as evaluated in Chieti patients) was observed in supplemented patients. After 6 months of Se therapy, the increase in delayed-type hypersensitivity of supplemented patients proved to be significantly higher when compared to both presupplementation values and to the results found in non-supplemented patients. Three months after suspension of Se supplementation, plasma Se levels and delayed hypersensitivity significantly decreased in Chieti patients, with both parameters returning similar to presupplementation values. CONCLUSIONS: In accordance with previous studies done in non-uraemic subjects, our investigation demonstrates for the first time the immunostimulatory properties of Se in HD patients. Though several problems on Se metabolism in uraemia remain unresolved, in our opinion moderate and safe Se supplementation can be beneficial in chronic uraemic patients.

Zinc-mediated lymphocyte energy charge modification in dialysis patients.

The authors studied the effects of 6 months of zinc therapy on cell-mediated immunity in regular dialysis therapy patients. Serum zinc was significantly enhanced (p less than 0.01) at 2 months. While cells, OKT3, and OKT4 did not show significant variation, but after 6 months of therapy a significant (p less than 0.02) decrease of OKT8 cells, with enhancement of the OKT4/OKT8 ratio, and a significant (p less than 0.01) increase in the Multitest Composite score were found. At the same time, a significant elevation (p less than 0.001) of adenosine triphosphate (ATP), and a reduction (p less than 0.01) of lymphocyte adenosine monophosphate was seen; consequently, energy charge levels increased. Zinc-induced improvement of uremic lymphocyte function is likely mediated by an increase in intracellular ATP.