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Biomedical subjects

A Levasseur

Publications and source records attributed to A Levasseur.

At least 19 recordsLinked to original sources
PubMed2006

Effect of substrate temperature on morphology and electrochemical performance of radio frequency magnetron sputtered lithium nickel vanadate films used as negative electrodes for lithium microbatteries.

Lithium nickel vanadate thin films were prepared by radio frequency magnetron sputtering at various substrate temperatures (Ts). These thin films have been investigated as anode electrode material in the use of microbatteries. Films were characterized by Rutherford backscattering spectroscopy, nuclear reaction analysis, Auger electron spectroscopy, glancing-incidence X-ray diffraction analysis, Raman spectroscopy, scanning electron microscopy, atomic force microscopy, and high-resolution transmission electron microscopy techniques. The anodic electrochemical performances of the films have been evaluated by cyclic voltammetry at a scan rate of 1 mV/s and by galvanostatic cycling, with lithium metal as the counter and the reference electrode, and cycled in the range of 0.02-3.0 V at a current density of 75 microA/cm2. Thin films prepared at a Ts of 650 degrees C show a discharge capacity at the 20th cycle of 1100 (+/-10) mAh/g, which exhibited excellent capacity retention with a small capacity fade.

Journal Article↗
PubMed2003

Natural and recombinant fungal laccases for paper pulp bleaching.

Three laccases, a natural form and two recombinant forms obtained from two different expression hosts, were characterized and compared for paper pulp bleaching. Laccase from Pycnoporus cinnabarinus, a well known lignolytic fungus, was selected as a reference for this study. The corresponding recombinant laccases were produced in Aspergillus oryzae and A. niger hosts using the lacI gene from P. cinnabarinus to develop a production process without using the expensive laccase inducers required by the native source. In flasks, production of recombinant enzymes by Aspergilli strains gave yields close to 80 mg l(-1). Each protein was purified to homogeneity and characterized, demonstrating that the three hosts produced proteins with similar physico-chemical properties, including electron paramagnetic resonance spectra and N-terminal sequences. However, the recombinant laccases have higher Michaelian (Km) constants, suggesting a decrease in substrate/enzyme affinity in comparison with the natural enzyme. Moreover, the natural laccase exhibited a higher redox potential (around 810 mV), compared with A. niger (760 mV) and A. oryzae (735 mV). Treatment of wheat straw Kraft pulp using laccases expressed in P. cinnabarinus or A. niger with 1-hydroxybenzotriazole as redox mediator achieved a delignification close to 75%, whereas the recombinant laccase from A. oryzae was not able to delignify pulp. These results were confirmed by thioacidolysis. Kinetic and redox potential data and pulp bleaching results were consistent, suggesting that the three enzymes are different and each fungal strain introduces differences during protein processing (folding and/or glycosylation).

Aspergillus niger↗
PubMed2003

Three related TrIV genes: comparative sequence analysis and expression in host larvae and Cf-124T cells.

We report on the cloning and sequencing of two Tranosema rostrale ichnovirus (TrIV) genes, and assess their relatedness to TrV1, the gene encoding the most abundant TrIV transcript in last-instar Choristoneura fumiferana larvae parasitized by T. rostrale. One of the two newly isolated genes, TrV2, features an organization similar to that of TrV1, with one intron flanked by two exons; it encodes a 102 amino acid protein showing 79% similarity to TrV1. The third gene, TrV4, encodes a larger protein (143 aa) displaying similarity to the other two only over the first approximately 50 amino acid residues of its sequence; the remaining portion contains an imperfect octad repeat. Although the TrV4 gene contains only one exon, it has an intron similar in size and sequence to that of TrV1 and TrV2; in fact, the non-coding regions of all three genes show higher sequence identity than the coding regions, pointing to their common origin. Southern analysis suggests that each gene maps to a different TrIV genome segment, with homologous sequences apparently present on other segments. TrV1 and TrV4 transcription in penultimate (5th) instar hosts, parasitized shortly after the molt, was strong for both genes 1 and 2 days p.p., with transcript abundance decreasing after the final molt; thus, neither of these genes is upregulated during induction of developmental arrest in last-instar hosts. Cf-124T cells inoculated with T. rostrale calyx fluid showed significant levels of apoptosis 24-72 h p.i.; TrV1 was detected in the culture medium, suggesting that this and/or other TrIV-encoded proteins may be responsible for the observed cytopathic effect. Southern and Northern analyses, using DNA and RNA extracted from infected Cf-124T cells, revealed the presence of both TrV1- and TrV4-carrying genome segments and transcripts, but neither DNA, at least in episomal form, nor mRNA persisted for more than a few days p.i. This in vitro system may provide a suitable starting point for the study of TrIV gene functions.

Amino Acid Sequence↗
PubMed2002

Evidence for a conserved polydnavirus gene family: ichnovirus homologs of the CsIV repeat element genes.

In Campoletis sonorensis Ichnovirus (CsIV), the repeat element genes constitute a gene family of 28 members. In the present work, we document the presence of members of this gene family in two additional ichnoviruses, Hyposoter didymator Ichnovirus (HdIV) and Tranosema rostrale Ichnovirus (TrIV). Two repeat element genes, representing at least one functional gene, were identified in TrIV, whereas HdIV was found to contain at least three such genes. In both HdIV and TrIV, the known repeat element genes are encoded on single genome segments, with hybridization studies suggesting the presence of other, related but as yet uncharacterized genes. The HdIV and TrIV repeat element genes are all transcribed in infected caterpillars, although differences exist among genes in levels and in tissue specificity of expression. A heuristic tree was generated indicating that the repeat element genes are more similar within a species of wasp than between species, with TrIV genes being more closely related to the CsIV than to the HdIV genes. These results suggest that the most significant duplication, divergence, and expansion of the repeat element genes occurred after speciation. The finding that repeat element genes form an interspecific family within the genus Ichnovirus supports the view that the proteins they encode play an important role in ichnovirus biology.

Amino Acid Sequence↗
PubMed1995

Long-term risk stratification with dipyridamole imaging.

This study was undertaken to assess the reliability of clinical parameters and dipyridamole-thallium 201 images for predicting the occurrence of future cardiac events (nonfatal myocardial infarction or cardiac death). Dipyridamole myocardial perfusion imaging is routinely performed in patients who have possible or known coronary disease and a low exercise tolerance. A total of 753 patients underwent clinical assessment and semiquantitative dipyridamole-201TI imaging and were followed up as outpatients. Patients who underwent coronary revascularization during the follow-up period were excluded from the study because the decision to intervene would have been based at least in part on the test itself. There were 82 cardiac events and 54 noncardiac deaths, and 11 patients were lost to follow-up after a mean follow-up of 15 months. With use of a quantitative index reflecting the amount of jeopardized myocardium, patients could be stratified by dipyridamole imaging into subsets with coronary morbidity and mortality rates ranging from 1% to 89%, (p = 0.0001). When clinical and scintigraphic variables were subjected to backward stepwise logistic regression analysis, the significant predictors of cardiac events were the jeopardized myocardium index by scintigraphy (p < 0.0001), left ventricular hypertrophy on the electrocardiogram (p = 0.0009), and transient dipyridamole-induced left ventricular cavitary dilatation (p = 0.0073). Quantitative dipyridamole-201TI imaging appears to be a powerful predictor of future cardiac events in patients with coronary disease and a low exercise tolerance and is a potentially useful contributor to risk-profile assessment and to the treatment of these patients.

Aged↗
PubMed1994

Artificial intelligence versus logistic regression statistical modelling to predict cardiac complications after noncardiac surgery.

The traditional approach to developing models predictive of cardiac events has been to perform logistic regression (LR) analysis on a variety of potential predictors. An alternative to use an artificial intelligence system called a neural network (NN) which simulates biological intelligence. To evaluate the potential applicability of the latter method, we compared the ability of LR and NN techniques to predict cardiac events after noncardiac surgery. A total of 200 patients (training group) underwent cardiac risk assessment before major noncardiac surgery using 17 clinical parameters and 7 quantitative indices based on dipyridamole-thallium imaging. There were 21 post-operative myocardial infarctions and/or cardiac deaths. Data from the training group were used to develop two predictive models: one based on backward stepwise LR multivariate statistical analysis and the other one using a neural network. Both models were then validated on a second group of 160 consecutive patients also referred for preoperative risk stratification (validation group). The NN consisted of 14 input, 29 hidden, and 1 output neurons and used a back-propagation algorithm (learning rate 0.2, training tolerance 0.5, sigmoid transfer function). The sensitivity, specificity, positive and negative predictive accuracies for the prediction of postoperative events in the validation group of 160 patients were, respectively, 67% (6/9), 82% (124/151), 18% (6/33), and 98% (124/127) for LR, and 67% (6/9), 96% (145/151), 50% (6/12), and 98% (145/148) for the NN, with a difference in specificity which attained statistical significance (p < 0.01). Artificial intelligence may provide a useful alternative to conventional LR statistical analysis for the purpose of preoperative cardiac risk assessment.

Artificial Intelligence↗
PubMed1994

Prognostic implications of transient left ventricular cavitary dilation during exercise and dipyridamole-thallium imaging.

OBJECTIVE: To determine the prognostic implication of exercise and dipyridamole-induced transient left ventricular cavitary dilation (TLVD). DESIGN: TLVD was observed and a follow-up obtained in 61 patients after exercise and in 62 patients following dipyridamole infusion. PATIENTS: There was no statistical difference between groups in terms of sex, history of hypertension, diabetes, renal failure, previous myocardial infarction, severity of angina syndrome, congestive heart failure, resting electrocardiographic (ECG) abnormalities, clinical or ECG signs of ischemia during stress, number of reversible perfusion defects on thallium images or duration of follow-up (21 months). RESULTS: Dipyridamole patients were slightly older (64 versus 57 years) and displayed more thallium redistribution (P = 0.002). After a mean follow-up of 21 months, both fatal and nonfatal (myocardial infarction or cardiac death) cardiac events were more frequent in the dipyridamole group (50% versus 9%, P = 0.0001). CONCLUSIONS: Patients with dipyridamole-induced TLVD are at greater risk than those with exercise-induced TLVD at the authors' institution.

Aged↗
PubMed1991

In vivo glomerular filtration rate measurement based solely on image processing.

A simple and reliable technique was developed to measure split renal glomerular filtration (GFR) based solely on image processing of the standard 20-minute Tc-99m DTPA renogram. It requires neither syringe counting nor blood or urine sampling. Using three sequential blood samples in 36 patients, GFR values correlated well (r = 0.92) with in vitro GFR measurements.

Adult↗
PubMed1990

Standing views to differentiate gallbladder or bile leak from duodenal activity on cholescintigrams.

Confusing a gallbladder or bile leak with duodenal activity is a common source of error in the interpretation of cholescintigrams. Techniques such as supplementary oblique views, delayed views, the "water test," dynamic display and combined cholescintigraphy and ultrasound have been used with varying degrees of success. As illustrated in two cases, supplementary standing views provide a simple alternative method to differentiate gallbladder from small bowel activity.

Adolescent↗
PubMed1989

Bone imaging after cementless press fit total hip arthroplasty.

In view of the high rate of loosening of conventional cemented hip prostheses, cementless implants are gaining popularity in Europe and North America. Smooth-surfaced "press fit" prostheses are designed for autolocking in the femoral canal at the time of installation. Fifteen patients were prospectively followed by bone imaging with Tc-99m MDP at three-month intervals after cementless "press fit" hip arthroplasty to define the "normal" distribution of mechanical stress to the surrounding bone, as well as the incorporation of bone allografts used for reconstruction of resorption sites in cases of revision surgery.

Adult↗
PubMed1983

Lymphoscintigraphic demonstration of intestinal lymphangiectasia.

The authors report a case of intestinal lymphangiectasia that was clearly demonstrated during abdominal lymphoscintigraphy using Tc-99m Sb colloid. Although lymphoscintigraphy has been used in many different clinical situations, this is, to our knowledge, the first scintigraphic description of this disease. Clinical and pathologic presentations of intestinal lymphangiectasia are briefly reviewed. Some possible approaches to the confirmation of the presence of a protein-losing gastroenteropathy are mentioned.

Adult↗
PubMed1983

131I-iodocholesterol (NP-59) scintigraphy in adrenocortical diseases.

The diagnostic usefulness of adrenal imaging with 131I-iodocholesterol (NP-59) is now well established. In order to correlate histopathology with the adrenal scan the authors examine and report their experience in 37 patients with surgically proven adrenal lesions or pituitary adenomas. This series included 24 patients with Cushing's syndrome: 14 caused by benign adrenal adenoma and 10 due to bilateral pituitary-ACTH-dependent adrenocortical hyperplasia. Ten patients with primary aldosteronism were submitted to surgery which confirmed the presence of aldosterone-producing adrenal adenomas. Two women with hyperandrogenism (due to virilizing ovarian tumors) had normal adrenals but the ovarian stromal luteoma markedly concentrated the iodocholesterol while the arrhenoblastoma did not. A patient with adrenal hematoma is also included in this report. The overall histopathological correlation with the radiocholesterol scintiscan yields an accuracy in our series of 97% (36/37). The false-negative adrenal scan (also missed by other non-invasive techniques) occurred in a patient with an aldosterone-producing adrenal adenoma measuring 1.0 X 1.5 cm.

19-Iodocholesterol↗