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Biomedical subjects

A Ramos

Publications and source records attributed to A Ramos.

At least 127 records · Page 7Linked to original sources
PubMed2000

Extraintestinal infection due to Hafnia alvei.

The aim of this study was to establish the clinical features of extraintestinal infections caused by Hafnia alvei. Over a 5-year period (1994-1998), data were collected regarding inpatients (n = 8) with nosocomial (n = 5) or community-acquired (n = 3) infections caused by Hafnia alvei. The mean age of the patients was 47 +/- 21 years. Three patients had hospital-acquired urinary tract infections. Hafnia alvei also caused community-acquired cholangitis, cholecystitis, appendicitis, psoas abscess and prosthetic endocarditis. Hafnia alvei was susceptible to amoxicillin/clavulanic acid and to first-generation cephalosporins in two cases. Susceptibility to aminoglycosides, imipenem, cotrimoxazole, ciprofloxacin, piperacillin and cefotaxime was very good (8/8). Four patients required invasive treatment.

Adult↗
PubMed2000

Dependence of pulser driving responses on electrical and motional characteristics of NDE ultrasonic probes

Acoustic performance in ultrasonic transmitters can be improved by means of a suitable electrical driving response and matching/tuning networks. It is important to predict this electrical response, but doing so is not easy because it departs notably from the nominal pattern with the loading probes. In practice, the analysis of HV pulser spikes in NDE applications requires fairly complex models in the transient regime and, in addition, non-linear problems could arise, especially in the case of tuned transmitters. In this paper, the most relevant influences of loading characteristics of NDT ultrasonic probes on the pulser electrical driving responses are evaluated in time and frequency domains. Conventional pulse generators and typical NDE pulsers are considered. Driving responses are analysed across commercial ultrasonic probes and, alternatively, across similar purely electrical loads. Distinct influences on pulser responses from electrical and motional sections of the probes are identified. All these aspects are studied on the basis of experimental and computer results.

Journal Article↗
PubMed2000

Definition and measurement of the normalized electrical impedance of lossy piezoelectric resonators for ultrasonic transducers

Relevant equivalent circuit parameters and values of material constants of a piezoelectric resonator can be determined from measurements of its electrical input impedance as a function of frequency. The complex electrical impedance curves and the associated critical frequencies are the basis of this characterization by the piezoelectric resonance method. In this paper, the previously introduced concept of normalized electrical impedance of the lossy resonator, extended to include piezoelectric losses, is applied to the analysis of the effects of different types of intrinsic losses on peak values, bandwidths and characteristic frequencies. The resulting impedance patterns depend solely on the electromechanical coupling coefficient and the loss tangents, providing a useful tool for the analysis of low-Q resonators. The normalized impedance is experimentally evaluated from the basic data provided by an HP 4194A impedance analyser by means of specifically developed ASP programs.

Journal Article↗
PubMed2000

Glyphosate adsorption on soils of different characteristics. Influence of copper addition.

Results of glyphosate (GPS) adsorption on three soils of different characteristics show that the interaction of this pesticide with the soils was not related to their CEC and clay minerals content, but to the content of iron and aluminum amorphous oxides and organic matter. The presence of Cu in treatment solutions enhanced GPS adsorption, due to several reasons: GPS coordinates strongly to Cu, and Cu GPS complexes formed seem to have higher ability to be adsorbed on the soil than free GPS; GPS adsorption can take place on sites where Cu was previously adsorbed, acting as a bridge between the soil and GPS; when Cu was present the solution pH decreased, and GPS adsorption increased, since lower pHs lead to the formation of GPS species with lower negative charge, which are adsorbed more easily on the negatively charged soil surfaces.

Adsorption↗
PubMed2000

Removal of xenoreactive antibodies by protein-A immunoadsorption: experience in 22 patients.

The presence of naturally occurring anti-Galalpha1-3Gal (antialphaGal) Ab in human serum is believed to be a major factor in the pathogenesis of hyperacute rejection of discordant organ xenografts such as the pig-to-human combination. Galalpha1-3Gal epitopes are expressed on pig tissues and the binding of anti-Galalpha1-3Gal leads to endothelial cell activation and complement-mediated hyperacute graft rejection. Several strategies have been suggested in donor animals or in the xenograft recipient to overcome the anti-alphaGal barrier. Protein-A immunoadsorption (PAIA) was developed for the in vivo removal of circulating Ab and it has been shown to be effective in cases where pathogenic auto or alloAb are present. The aim of our study was to analyze the effect of PAIA on total and xenoreactive serum anti-alphaGal immunoglobulin levels in a group of patients treated with this technique for different diseases. After three consecutive sessions of PAIA, total and xenoreactive IgG and IgM immunoglobulin levels were decreased by more than 50% of pre-treatment levels. So we conclude that PAIA is an effective method to significantly reduce circulating Ab, including xenogeneic IgM and IgG Ab. This mode of therapy might be considered as a tool to overcome hyperacute xenograft rejection. PAIA combined with other therapeutic approaches may well protect the xenograft.

Adolescent↗
PubMed2000

Expression and immunological evaluation of the Escherichia coli-derived hepatitis C virus envelope E1 protein.

Immunological response against envelope protein E1 is very important in natural hepatitis C virus (HCV) infection, although it is insufficient to clear the viraemia. The HCV genomic region encoding the first 149 amino acids of the envelope E1 protein (E1(340), amino acids 192-340) was expressed in Escherichia coli (to a level of 30% of the whole cellular proteins) and purified to 85%. We measured the immune response in rabbits and mice as well as the reactivity against 37 human sera raised against the whole recombinant protein and E1-encoding peptides. From this, 51.1% of human sera were found to react with E1(340). High-level antibodies against E1(340) were obtained in rabbits and mice when immunized. These antibodies had a similar peptide-recognition pattern to that described previously for human sera. The most reactive region was located at the N-terminus of the E1 protein. Cellular immunity in mice was evaluated by delayed-type hypersensitivity assay. It revealed the induction of a CD4+ T-cell-mediated response by this protein. This E1(340) protein and the animal-derived anti-E1 sera are immunological tools that could aid in the monitoring and development of anti-HCV therapies.

Amino Acid Sequence↗
PubMed2000

Metabolic characterization of Lactococcus lactis deficient in lactate dehydrogenase using in vivo 13C-NMR.

The metabolism of glucose by nongrowing cells of Lactococcus lactis strain FI7851, constructed from the wild-type L. lactis strain MG1363 by disruption of the lactate dehydrogenase (ldh) gene [Gasson, M.J., Benson, K., Swindel, S. & Griffin, H. (1996) Lait 76, 33-40] was studied in a noninvasive manner by 13C-NMR. The kinetics of the build-up and consumption of the pools of intracellular intermediates mannitol 1-phosphate, fructose 1,6-bisphosphate, 3-phosphoglycerate, and phosphoenolpyruvate as well as the utilization of [1-13C]glucose and formation of products (lactate, acetate, mannitol, ethanol, acetoin, 2,3-butanediol) were monitored in vivo with a time resolution of 30 s. The metabolism of glucose by the parental wild-type strain was also examined for comparison. A clear shift from typical homolactic fermentation (parental strain) to a mixed acid fermentation (lactate dehdydrogenase deficient; LDHd strain) was observed. Furthermore, high levels of mannitol were transiently produced and metabolized once glucose was depleted. Mannitol 1-phosphate accumulated intracellularly up to 76 mM concentration. Mannitol was formed from fructose 6-phosphate by the combined action of mannitol-1-phosphate dehydrogenase and phosphatase. The results show that the formation of mannitol 1-phosphate by the LDHd strain during glucose catabolism is a consequence of impairment in NADH oxidation caused by a highly reduced LDH activity, the transient production of mannitol 1-phosphate serving as a regeneration pathway for NAD+ regeneration. Oxygen availability caused a drastic change in the pattern of intermediates and end-products, reinforcing the key-role of the fulfilment of the redox balance. The flux control coefficients for the step catalysed by mannitol-1-phosphate dehydrogenase were calculated and the implications in the design of metabolic engineering strategies are discussed.

Anaerobiosis↗
PubMed2000

Presence of human immunodeficiency virus (HIV) type 1, group M, non-B subtypes, Bronx, New York: a sentinel site for monitoring HIV genetic diversity in the United States.

In the United States, human immunodeficiency virus (HIV) type 1, group M, subtype B is the predominant subtype. A cross-sectional study of HIV-infected patients at the Bronx-Lebanon Hospital Center, Bronx, NY, between September 1997 and February 1998 identified 3 (1. 2%) of 252 persons infected with non-B subtypes: subtypes A and F, 1 each, and 1 potential recombinant subtype B(env)/F(prt). All 3 persons were born in the United States and tested positive for HIV antibodies between 1988 and 1997 while living in the Bronx. None reported travel to other countries, receipt of blood products, or drug injection. This study is among the first to indicate probable transmission of non-B HIV-1 subtypes in the United States. The occurrence of non-B HIV-1 subtypes in long-term US residents without a history of foreign travel may have implications for the evaluation and development of antiretroviral drugs, vaccines, and tests intended for use in the United States to diagnose HIV infection and screen blood.

Adolescent↗
PubMed2000

Fluid flow induced by nonuniform ac electric fields in electrolytes on microelectrodes. I. Experimental measurements

Under the influence of an ac electric field, electrolytes on planar microelectrodes exhibit fluid flow. The nonuniform electric field generated by the electrodes interacts with the suspending fluid through a number of mechanisms, giving rise to body forces and fluid flow. This paper presents the detailed experimental measurements of the velocity of fluid flow on microelectrodes at frequencies below the charge relaxation frequency of the electrolyte. The velocity of latex tracer particles was measured as a function of applied signal frequency and potential, electrolyte conductivity, and position on the electrode surface. The data are discussed in terms of a linear model of ac electroosmosis: the interaction of the nonuniform ac field and the induced electrical double layer.

Journal Article↗
PubMed2000

Fluid flow induced by nonuniform ac electric fields in electrolytes on microelectrodes. II. A linear double-layer analysis

Frequency-dependent fluid flow in electrolytes on microelectrodes subjected to ac voltages has recently been reported. The fluid flow is predominant at frequencies of the order of the relaxation frequency of the electrode-electrolyte system. The mechanism responsible for this motion has been termed ac electro-osmosis: a continuous flow driven by the interaction of the oscillating electric field and the charge at the diffuse double layer on the electrodes. This paper develops the basis of a theoretical approach to this problem using a linear double layer analysis. The theoretical results are compared with the experiments, and a good correlation is found.

Journal Article↗
PubMed2000

Raman spectroscopy of hypersonic shock waves

Raman spectroscopy is shown to be an efficient diagnostic methodology for the study of hypersonic shock waves. As a test, absolute density and rotational population profiles have been measured across five representative normal shock waves of N2 generated in a free jet, spanning the Mach number range 7.7<M<15.3. The interconversion of three differentiated populations (cold, scattered, and rethermalized molecules) across these shock waves shows a largely bimodal rotational distribution function with additional contribution of scattered molecules, in close analogy with the velocity distribution function known from helium shock waves [G. Pham-Van-Diep et al., Science 245, 624 (1989)]. Quantitative data on invariance trends of density profiles and properties of the wake beyond the shock waves are reported.

Journal Article↗
PubMed2000

Avalanches in fine, cohesive powders

We have investigated the onset of avalanches in fine, cohesive granular materials. In our experiments shear stress is generated by tilting an initialized bed of powder and increasing the angle of tilt until the powder avalanches. We find that the angle alpha of the avalanche decreases with increasing bed width. The avalanche depth increases with the bed width and, in all cases, is of the order of several millimeters, which is much greater than the particle size. We carry out a macroscopic analysis of the avalanche process based on Coulomb's method of wedges. This analysis shows the fundamental role played by powder cohesion and boundary conditions on avalanches in fine cohesive powders. This behavior contrasts with the behavior of noncohesive grains, such as dry sand, where avalanches consist of superficial layers of about ten grains. The reason behind this is that for our experimental powders (particle diameter approximately 10 &mgr;m) the van der Waals interparticle adhesive force exceeds several orders of magnitude particle weight. Adhesive forces oppose gravity, and as a result fine cohesive powders settle in very open structures as compared to noncohesive granular materials. Because of the dominance of adhesive forces over particle weight, our materials behave more like wet sand.

Journal Article↗
PubMed2000

Sodium-dependent nitrate transport at the plasma membrane of leaf cells of the marine higher plant Zostera marina L.

NO(3)(-) is present at micromolar concentrations in seawater and must be absorbed by marine plants against a steep electrochemical potential difference across the plasma membrane. We studied NO(3)(-) transport in the marine angiosperm Zostera marina L. to address the question of how NO(3)(-) uptake is energized. Electrophysiological studies demonstrated that micromolar concentrations of NO(3)(-) induced depolarizations of the plasma membrane of leaf cells. Depolarizations showed saturation kinetics (K(m) = 2.31 +/- 0.78 microM NO(3)(-)) and were enhanced in alkaline conditions. The addition of NO(3)(-) did not affect the membrane potential in the absence of Na(+), but depolarizations were restored when Na(+) was resupplied. NO(3)(-)-induced depolarizations at increasing Na(+) concentrations showed saturation kinetics (K(m) = 0.72 +/- 0.18 mM Na(+)). Monensin, an ionophore that dissipates the Na(+) electrochemical potential, inhibited NO(3)(-)-evoked depolarizations by 85%, and NO(3)(-) uptake (measured by depletion from the external medium) was stimulated by Na(+) ions and by light. Our results strongly suggest that NO(3)(-) uptake in Z. marina is mediated by a high-affinity Na(+)-symport system, which is described here (for the first time to our knowledge) in an angiosperm. Coupling the uptake of NO(3)(-) to that of Na(+) enables the steep inwardly-directed electrochemical potential for Na(+) to drive net accumulation of NO(3)(-) within leaf cells.

Cell Membrane↗
PubMed2000

A comparative study of magnetic resonance cholangiography and direct cholangiography.

OBJECTIVE: Magnetic resonance cholangiopancreatography (MRCP) is a rapidly developing method for the noninvasive assessment of the biliary tree and pancreatic duct that obviates the need for contrast medium. We describe our experience with this new diagnostic imaging method in patients with obstruction of the biliary tree. We assessed both the location and cause of obstruction, and compared the results with direct cholangiography. METHODS: Between 1997 and 1998, 81 patients underwent MRCP at our facility. Two different image acquisition protocols (half-Fourier acquisition single-shot turbo spin-echo -HASTE- and rapid acquisition with relaxation enhancement -RARE-) for T2-weighted turbo spin echo sequences as well as cross-sectional fast multiplanar gradient-echo pulse (T1-weighted FL2D) and T2-weighted fast spin echo (T2 TSE) sequences were used. All patients underwent direct (either percutaneous or endoscopic retrograde) cholangiography or surgery for confirmation and/or treatment. The images obtained with MRCP were evaluated by two radiologists with expertise in biliary tree imaging who were unaware of the patient's clinical characteristics, and their diagnostic interpretations were compared with the findings obtained upon surgery or direct cholangiography. RESULTS: The sensitivity and specificity of MRCP in ruling out pathologies and detecting the presence of dilatation of the biliary tree were 100%. In assessing the level of the obstruction, sensitivity and specificity varied with location (intrahepatic/hilar, suprapancreatic, intrapancreatic or ampullary). Sensitivity in these locations was 100, 92, 69 and 86%, respectively, whereas specificity was 100, 94, 92 and 91%, respectively. In determining the cause of the obstruction, the results were variable depending on the cause: choledocholithiasis (sensitivity, 89%; specificity, 90%) malignant obstruction (sensitivity, 92%; specificity, 88%), benign stricture (sensitivity, 63%; specificity, 90%), and chronic pancreatitis (sensitivity, 50%; specificity, 99%). CONCLUSIONS: MRCP offered high diagnostic accuracy in the assessment of the occurrence and location of biliary obstruction. Sensitivity and specificity in establishing the cause varied, and were highest for choledocholithiasis and malignant obstruction. MRCP may be used instead of ERCP, which may then be reserved for patients who are likely to require surgery.

Adult↗
PubMed2000

An echocardiographic description of the Sulzer Carbomedics Synergy ST (Labcor) porcine valve in the aortic position.

BACKGROUND AND AIM OF THE STUDY: The Synergy ST (previously Labcor) valve is constructed from three separate porcine aortic cusps mounted on a scalloped, flexible, acetal copolymer stent. To date, no hemodynamic data describing this valve have been published. The aim of this study was to describe the echocardiographic findings in a population of unselected patients. METHODS: One investigator, who was blinded to valve size, studied 84 patients (31 females, 53 males; mean age 58 years; range: 19-83 years) at four centers in Brazil. The valves were studied at a mean of 31 months after implantation (range: 1-116 months). Mean gradient was calculated using the long modified Bernoulli equation, effective orifice area (EOA) using the classical from of the continuity equation, and resistance as mean gradient/flow. RESULTS: There were no significant differences in peak transaortic velocity and mean gradient between valves of different annulus size. However, EOA was directly related (p = 0.0075) and resistance indirectly related to valve size (p = 0.021, ANOVA). Trivial or mild regurgitation was seen in 31 patients (37%), moderate in three (4%) and severe in two (2%). The regurgitation was solely paraprosthetic in five patients, solely through the valve in 23, and both in seven. Regurgitation through the valve usually occurred adjacent to the commissures. CONCLUSION: The Synergy ST porcine valve has hemodynamics of forward flow similar to that of other stented porcine valves.

Adult↗