Biomedical subjects
Publications and source records attributed to S Vieira.
We present local tunneling microscopy and spectroscopy measurements at low temperatures in single crystalline samples of the magnetic superconductor ErNi2B2C . The electronic local density of states shows a striking departure from s-wave BCS theory with a finite value at the Fermi level, which amounts to half of the normal phase density of states.
Echography is a useful tool to diagnose a thrombosis; however, since it is difficult to learn to perform this procedure, the objective of this work is to create a simulation to allow students to practice in a virtual environment. Firstly, a physical model of the thigh was constructed based on experimental data obtained using a force sensor mounted on a robotic arm. We present a spring damper model consisting of both linear and non-linear elements. The parameters of each of these elements are then fitted to the experimental data using an optimization technique. By employing an implicit integration to solve the dynamics of the system we obtain a stable physical simulation at over 100 Hz. Secondly, a haptic interface was added to interact with the simulation. Using a PHANToM force-feedback device may touch and deform the thigh in real-time. In order to allow a realistic sensation of the contact we employ a local modeling technique allowing to approximate the forces at much higher frequency using a multi-threaded architecture. Finally, we present the basis for a fast echographic image generation depending on the position and orientation of the virtual probe as well as the force applied to it.
Summary. Background. This report describes the case of a patient with focal epithelial hyperplasia (FEH), a rare but distinctive entity of viral aetiology with characteristic clinical and histopathological features. Case report. The condition is usually seen in children and adolescents of American Indian and Eskimo background. Surgical removal of papillomatous lesions is the treatment of choice, either for aesthetic reasons, or when the lesions interfere with function or are readily traumatized. Recurrence and the site of new lesions are unpredictable, and continued review of the patient is often necessary. The patient described here has been followed for 24 months without recurrences or changes in the aspect of the remaining lesions. Conclusion. This case highlights a possible genetic predilection for FEH, since the patient is a descent of a Brazilian Xavante Indian.
The pressure dependence of the critical temperature T(c) and upper critical field H(c2)(T) has been measured up to 19 GPa in the layered superconducting material 2H-NbSe2. T(c)(P) has a maximum at 10.5 GPa, well above the pressure for the suppression of the charge density wave (CDW) order. Using an effective two-band model to fit H(c2)(T), we obtain the pressure dependence of the anisotropy in the electron-phonon coupling and Fermi velocities, which reveals the peculiar interplay between CDW order, Fermi surface complexity, and superconductivity in this system.
Sixty-five children underwent liver transplantation (LTx) from March 1995 to December 2002. Cirrhosis due to biliary atresia was the main indication, and hepatic artery thrombosis (HAT) the most common vascular complication (n = 5). Other vascular problems were portal vein thrombosis and stenosis. Another patient developed hepatomegaly and ascites due to a late stenosis of the left hepatic vein anastomosis. The two cases of venous stenosis were successfully treated by percutaneous angioplasty. One graft with HAT was saved, but four children died awaiting retransplant.
Pressure/volume (P/V) curves can be measured by static methods, constant or sinusoidal flow methods and the dynostatic method that allows a breath-to-breath determination of P/V curves. Recent ventilators are equipped with specific flow generators and software aimed at obtaining P/V curves without disconnecting the patient from the ventilator. The most recent generation of computed tomography scanners allows the quantitative determination of lung aeration, lung volumes (gas and tissue), alveolar recruitment and lung overinflation of the whole lung. In the supine position, the acute respiratory distress syndrome (ARDS) lung is characterised by an increase in lung tissue that predominates in upper lobes and a massive loss of aeration that predominates in lower lobes. In a minority of ARDS patients, the loss of aeration is homogeneously distributed. The overall lung volume of upper lobes is preserved suggesting an alveolar flooding-induced loss of aeration. In contrast, the overall lung volume of lower lobes is reduced because the heart and the abdomen exert an external compression that contributes to the loss of aeration. The P/V curve is a lung recruitment curve and the chord compliance indicates the potential for recruitment. In such patients, alveolar recruitment resulting from positive end-expiratory pressure is not accompanied by lung overinflation. In a majority of acute respiratory distress syndrome patients, upper lobes remain partially or totally aerated despite a marked regional increase in lung tissue. The upper lobes' overall lung volume is either normal or increased, suggesting that the lung does not collapse under its own weight as generally believed. In lower lobes, the overall lung volume is reduced because the heart and the abdomen exert an external compression that contributes to the loss of aeration. The pressure/volume curve is influenced by the recruitment of poorly and nonaerated lung regions and by the mechanical properties of the part of the lung remaining aerated. In such patients, alveolar recruitment resulting from positive end-expiratory pressure >10 cmH2O is preceded and accompanied by lung overinflation.
Electronic transport properties of bismuth nanocontacts are analyzed using a low temperature scanning tunneling microscope. The subquantum steps observed in the conductance versus elongation curves give evidence of atomic rearrangements in the contact. The quantum nature of the conductance reveals itself through peaks in the conductance histograms. The shape of the curves at 77 K is described by a simple gliding mechanism for the contact evolution during elongation. The different behavior at 4 K suggests a transition from light to heavy charge carriers as the contact cross section is decreased.
The effects of a minor chemical modification on the microscopic structure of a material in its glass and crystal phases are investigated by the concurrent use of neutron diffraction and computer simulation. Significant changes in short-, intermediate-, and long-range order are found, resulting from the change in molecular structure. These differences are explainable by a shift in the balance between directional and excluded-volume interactions.
We report on tunneling spectroscopy experiments in small grains of the new binary intermetallic superconductor MgB(2). Experiments have been performed at 2.5 K using a low temperature scanning tunneling microscope. Good fit to the BCS model is obtained, with a gap value of 2 meV. In the framework of this model, this value should correspond to a surface critical temperature of 13.2 K. No evidence of gap anisotropy has been found.
BACKGROUND AND OBJECTIVES: Detection of PML-RAR alpha transcripts by RT-PCR is now established as a rapid and sensitive method for diagnosis of acute promyelocytic leukemia (APL). Although the majority of patients in long-term clinical remission are negative by consecutive reverse transcription polymerase chain reaction (RT-PCR) assays, negative tests are still observed in patients who ultimately relapse. Conversion from negative to positive PCR has been observed after consolidation and found to be a much stronger predictor of relapse. This study reports on 47 APL patients to determine the correlation between minimal residual disease (MRD) status and clinical outcome in our cohort of patients. DESIGN AND METHODS: The presence of PML-RAR alpha t transcripts was investigated in 47 APL patients (37 adults and 10 children) using a semi-nested reverse transcriptase-polymerase chain reaction to evaluate the prognostic value of RT-PCR tests. RESULTS: All patients achieved complete clinical remission (CCR) following induction treatment with all-trans retinoic acid (ATRA) and chemotherapy (CHT) or ATRA alone. Patients were followed up between 2 and 117.6 months (median: 37 months). Relapses occurred in 11 patients (9 adults and 2 children) between 11.4 and 19 months after diagnosis (median: 15.1 months) while 36 patients (28 adults and 8 children) remained in CCR. Seventy-five percent of patients carried the PML-RAR alpha long isoform (bcr 1/2) which also predominated among the relapsed cases (9 of 11) but did not associate with any adverse outcome (p= 0.37). For the purpose of this analysis, minimal residual disease tests were clustered into four time-intervals: 0-2 months, 3-5 months, 6-9 months and 10-24 months. INTERPRETATION AND CONCLUSIONS: Children showed persisting disease for longer than adults during the first 2 months of treatment. At 2 months, 10 (50%) of 20 patients who remained in CCR and 4 (80%) of 5 patients who subsequently relapsed were positive. Patients who remained in CCR had repeatedly negative results beyond 5.5 months from diagnosis. A positive MRD test preceded relapse in 3 of 4 tested patients. The ability of a negative test to predict CCR (predictive negative value, PNV) was greater after 6 months (>83%), while the ability of a positive test to predict relapse (predictive positive value, PPV) was most valuable only beyond 10 months (100%). This study (i) highlights the prognostic value of RT-PCR monitoring after treatment of APL patients but only from the end of treatment, (ii) shows an association between conversion to a positive test and relapse and (iii) suggests that PCR assessments should be carried out at 3-month intervals to provide a more accurate prediction of hematologic relapses but only after the end of treatment.
The BCR-ABL chimeric protein is thought to play a central role in the pathogenesis of Philadelphia (Ph) chromosome-positive leukemias, notably chronic myeloid leukemia (CML). There is compelling evidence that malignant transformation by BCR-ABL is critically dependent on its protein tyrosine kinase (PTK) activity. As a result, multiple signaling pathways are activated in a kinase-dependent manner, and thus the activation of such pathways may affect the expression of genes that confer the malignant phenotype. In this study, we used differential display to investigate the alterations of gene expression in BV173, a CML cell line derived from lymphoid blast crisis, after exposure to ST1571, which selectively inhibits ABL PTK activity. We show that the expression of a set of 12 genes is correlated with the kinase activity and that the profile of these genes reflects mechanisms implicated in the pathogenesis of CML. Several of the genes show a consistent pattern of altered regulation in all Ph-positive lymphoid cell lines, whereas others appear to be unique to BV173 cells. We conclude that BCR-ABL PTK activity drives the expression of specific target genes that contribute to the malignant transformation of Ph-positive cells. The identification of downstream molecules with a consistent regulation pattern may provide suitable targets for therapeutic intervention in the future.
BACKGROUND: Visual evoked potentials (VEPs) and brain stem auditory evoked potentials (BAEPs) have been proposed as tools in the diagnosis of subclinical hepatic encephalopathy (HE). However, little information exists to determine their usefulness in pediatric patients. This study was undertaken to evaluate both methods in the detection of subclinical HE in pediatric liver transplant candidates. METHODS: VEPs and BAEPs were recorded in 15 pediatric liver transplant candidates with no clinical signs of HE. The wave latencies found in these examinations were then compared with those in 16 healthy controls of similar age. Laboratory data on liver function and electroencephalographic data from the patients were also recorded to examine their correlation with the evoked potentials results. RESULTS: No differences were found in the BAEP results between patients and controls. However, in the VEPs, the liver transplant candidates had significantly prolonged N1 (N75) latencies when compared with controls; no significant delay was found in the other waves. In contrast, among the children with liver disease, higher BAEP peak latencies correlated positively with electroencephalographic abnormalities, but this correlation was not observed in VEPs. CONCLUSIONS: Evoked potentials might be of use in detecting alterations related to HE in children. However, further studies are necessary to determine their sensitivity and specificity in this situation.
This study investigated the efficacy of a system for continuous nebulization of terbutaline sulphate in the treatment of acute asthmatic crises in children. The equipment consisted of a condensation nebulizer attached to a 40 liter acrylic tent placed around the patient's head. A prospective, randomized and open clinical trial was conducted. Twenty eight children, 2 to 5 year-old, in acute asthmatic crises were selected. Fourteen were nebulized with terbutaline sulphate while in the control group the aerosolization was proceeded only with half diluted physiologic serum. All patients were administered aminophyline intravenously. The parameter used to evaluate the efficacy of the terbutaline sulphate nebulizing system was clinical improvement measured by the Wood-Downes Score. Two additional parameters indicating terbutaline sulphate absorption were used: reduction of potassium seric levels and positive chronotropic effect. The group treated with terbutaline sulphate showed greater clinical improvement than control group at the 12 hour protocol evaluation as well as lower seric potassium level. A positive chronotropic effect was also observed at the final protocol evaluation. The data showed, preliminarily, that (a) the system for continuous nebulization of terbutaline sulphate was effective in treatment of children's acute asthmatic crises, and (b) there was evidence attesting to the absorption of terbutaline sulphate by the children treatment with it.
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