PubMed Health⌕ Search

Biomedical subjects

B Normand

Publications and source records attributed to B Normand.

At least 19 recordsLinked to original sources
PubMed2005

Quantum statistics of interacting dimer spin systems.

The compound TlCuCl(3) represents a model system of dimerized quantum spins with strong interdimer interactions. We investigate the triplet dispersion as a function of temperature by inelastic neutron scattering experiments on single crystals. By comparison with a number of theoretical approaches we demonstrate that the description of Troyer, Tsunetsugu, and Würtz [Phys. Rev. B 50, 13 515 (1994)10.1103/Phys. Rev. B 50, 13515] provides an appropriate quantum statistical model for dimer spin systems at finite temperatures, where many-body correlations become particularly important.

Journal Article↗
PubMed2005

Microcirculatory and clinical effects of serial percutaneous application of carbon dioxide in primary and secondary Raynaud's phenomenon.

BACKGROUND: A randomized double-blind monocentric trial was conducted at the spa of Royat, France, in patients with mild Raynaud's phenomenon (one or two attacks a day during the autumn and winter months). Hemodynamic changes were quantified by laser Doppler flow (LDF) and computerized chronothermometric test (CT) during local application of CO2 and compared with the usual clinical parameters. PATIENTS AND METHODS: Patients were randomized to 18 days of CO2 (group 1) or 9 days of air + 9 days of CO2 (group 2). The gas was applied at a constant temperature to previously humidified skin on the forearm. Effects of the active treatment were measured by LDF and continuing benefits by computerized chronothermometric test (CT test). Clinical assessment was made on four occasions (before, in the middle and at the end of treatment, and three months afterwards) on the basis of the number of daily attacks and the duration and severity of the attacks. RESULTS: LDF showed a significant increase in digital blood flow (+ 41%) and in vasomotion (+ 42%) during CO2 treatment but no change on placebo treatment. CT test showed a comparable response to cold in the two groups during treatment. Three months later, however, warming time was significantly decreased (by 7 minutes: 25%) and warming rate increased (+ 22.4%) in group 1 (intergroup difference: p = 0.02). There was no difference between groups in the weekly number of attacks during treatment periods. In contrast there was a moderate increase in both groups in the winter months. There was no increase in the severity of the attacks nor in their duration. CONCLUSION: In this clinical trial, LDF evidenced positive effects of percutaneous application of natural CO2 gas on vasomotricity and vasomotion while CT test showed that patients who had received 18 days of CO2 adapted more easily to exposure to cold. Clinical improvement seems to be masked by winter weather conditions.

Administration, Cutaneous↗
PubMed2004

Kosmotropes and chaotropes: modelling preferential exclusion, binding and aggregate stability.

Kosmotropic cosolvents added to an aqueous solution promote the aggregation of hydrophobic solute particles, while chaotropic cosolvents act to destabilise such aggregates. We discuss the mechanism for these phenomena within an adapted version of the two-state Muller-Lee-Graziano model for water, which provides a complete description of the ternary water/cosolvent/solute system for small solute particles. This model contains the dominant effect of a kosmotropic substance, which is to enhance the formation of water structure. The consequent preferential exclusion both of cosolvent molecules from the solvation shell of hydrophobic particles and of these particles from the solution leads to a stabilisation of aggregates. By contrast, chaotropic substances disrupt the formation of water structure, are themselves preferentially excluded from the solution, and thereby contribute to solvation of hydrophobic particles. We use Monte Carlo simulations to demonstrate at the molecular level the preferential exclusion or binding of cosolvent molecules in the solvation shell of hydrophobic particles, and the consequent enhancement or suppression of aggregate formation. We illustrate the influence of structure-changing cosolvents on effective hydrophobic interactions by modelling qualitatively the kosmotropic effect of sodium chloride and the chaotropic effect of urea.

Binding Sites↗
PubMed2004

Detection of topological transitions by transport through molecules and nanodevices.

We analyze the phase transitions of an interacting electronic system weakly coupled to free-electron leads by considering its zero-bias conductance. This is expressed in terms of two effective impurity models for the cases with and without spin degeneracy. Using the half-filled ionic Hubbard ring, we demonstrate that the weight of the first conductance peak as a function of external flux or of the difference in gate voltages between even and odd sites allows one to identify the topological charge transition between a correlated insulator and a band insulator.

Journal Article↗
PubMed2004

Spin-charge separation in Aharonov-Bohm rings of interacting electrons.

We investigate the properties of strongly correlated electronic models on a flux-threaded ring connected to semi-infinite free-electron leads. The interference pattern of such an Aharonov-Bohm ring shows sharp dips at certain flux values, determined by the filling, which are a consequence of spin-charge separation in a nanoscopic system.

Journal Article↗
PubMed2004

Solvent-induced micelle formation in a hydrophobic interaction model.

We investigate the aggregation of amphiphilic molecules by adapting the two-state Muller-Lee-Graziano model for water, in which a solvent-induced hydrophobic interaction is included implicitly. We study the formation of various types of micelle as a function of the distribution of hydrophobic regions at the molecular surface. Successive substitution of nonpolar surfaces by polar ones demonstrates the influence of hydrophobicity on the upper and lower critical solution temperatures. Aggregates of lipid molecules, described by a refinement of the model in which a hydrophobic tail of variable length interacts with different numbers of water molecules, are stabilized as the length of the tail increases. We demonstrate that the essential features of micelle formation are primarily solvent-induced, and are explained within a model which focuses only on the alteration of water structure in the vicinity of the hydrophobic surface regions of amphiphiles in solution.

Colloids↗
PubMed2002

Magnon dispersion in the field-induced magnetically ordered phase of TlCuCl3.

The magnetic properties of the interacting dimer system TlCuCl3 are investigated within a bond-operator formulation. The observed field-induced staggered magnetic order perpendicular to the field is described as a Bose condensation of magnons which are linear combinations of dimer singlet and triplet modes. This technique accounts for the magnetization curve and for the field dependence of the magnon dispersion curves observed by high-field neutron scattering measurements.

Journal Article↗
PubMed2001

Order by disorder from nonmagnetic impurities in a two-dimensional quantum spin liquid.

We consider doping of nonmagnetic impurities in the spin-1/2, 1/5-depleted square lattice. This structure, whose undoped phase diagram offers both magnetically ordered and spin-liquid ground states, is realized physically in CaV4O9. Doping into the ordered phase results in a progressive loss of order, which becomes complete at the percolation threshold. By contrast, doping into the spin liquids creates a phase of weak but long-ranged antiferromagnetic order, a true order-by-disorder phenomenon. We study the phase diagram of the doped system by computing the static susceptibility and staggered magnetization using a stochastic series-expansion quantum Monte Carlo technique.

Journal Article↗
PubMed2001

Vocal cord dysfunction after left lung resection for cancer.

OBJECTIVES: To evaluate the prevalence, the impact-related postoperative complications and the risk factors of vocal cord dysfunction (VCD) after left lung resection for cancer. METHODS: From February 1996 to April 1999, a review of prospectively gathered data was performed on 99 consecutive patients who underwent a pneumonectomy (n=50) or a lobectomy (n=49) with a mediastinal lymph node dissection. A fiber optic laryngeal examination was performed preoperatively for all patients and within the first week postoperatively in patients with symptom(s) or sign(s) of VCD or respiratory complications. RESULTS: Thirty-one patients (31%) had a postoperative VCD (group VCD) and 68 (68%) did not (group non-VCD). Mortality rate was 19% in group VCD and 9% in group non-VCD (P=0.13). Group VCD patients developed more pulmonary complications (P=0.014) and cardiac complications (P<0.001) compared to group non-VCD patients. A higher rate of reintubation (P=0.005), pneumonia (P=0.06), arrhythmia (P=0.002), cardiac failure (P<0.001) was noticeable in group VCD and may account for the higher rate of complications in this group. Using multivariate analysis, preoperative radiotherapy (P=0.001) and pneumonectomy (P=0.008) were predictive of postoperative VCD. Hospital stay was 22+/-16 days in group VCD and 13+/-9 days in group non-VCD (P<0.002). CONCLUSION: VCD is a frequent event that can lead to dramatic pulmonary complications. We would recommend to track it and to treat it as early as possible.

Aged↗
PubMed2000

Aging: a barrier to renutrition? Nutritional and immunologic evidence in rats.

BACKGROUND: Previous reports suggest that correcting the malnourished state is more difficult in elderly people than in younger ones and that protein requirements may be higher in elderly than in younger adults. OBJECTIVE: The aim of this study was to establish whether malnourished old rats respond to protein-supplemented nutritional repletion as do young adult rats. DESIGN: Adult (3 mo old) and old (22 mo old) rats were submitted to dietary restriction programs that induced similar metabolic and nutritional alterations. Malnourished adult and old rats were then killed (R groups) or refed for 1 wk with a high-protein diet (HPD; 23% protein) or a very-high-protein diet (VHPD; 27% protein). Control groups at both ages were fed ad libitum throughout the experiment. Effects of food repletion were evaluated in terms of protein metabolism, intestinal histomorphometry, and nonspecific immune status. RESULTS: In adult rats, HPD sufficed to increase body weight and restore basal values of liver weight and protein content (P: < 0.01 compared with the R adult group), nitrogen balance (P: < 0.01 compared with the R adult group), and hydrogen peroxide production by polymorphonuclear neutrophils and monocytes (P: < 0.01 compared with the R group); VHPD had no supplementary effect except on nitrogen balance. In old rats, HPD was less effective and greater benefit was observed with VHPD in terms of body weight gain (10%; P: < 0.01 compared with the old group fed HPD), albuminemia, muscle weight and protein content, plasma arginine concentration, and hydrogen peroxide production by stimulated polymorphonuclear neutrophils and monocytes compared with the old R group (P: < 0.01). CONCLUSION: Aging is a significant variable affecting the response to nutritional support.

Aging↗
PubMed1999

Prediction of hypoxemia and mechanical ventilation after lung resection for cancer.

BACKGROUND: Hypoxemia usually occurs after thoracotomy, and respiratory failure represents a major complication. METHODS: To define predictive factors of postoperative hypoxemia and mechanical ventilation (MV), we prospectively studied 48 patients who had undergone lung resection. Preoperative data included, age, lung volume, force expiratory volume in one second (FEV1), predictive postoperative FEV1 (FEV1ppo), blood gases, diffusing capacity, and number of resected subsegments. RESULTS: On postoperative day 1 or 2, hypoxemia was assessed by measurement of PaO2 and alveolar-arterial oxygen tension difference (A-aDO2) in 35 nonventilated patients breathing room air. The other patients (5 lobectomies, 9 pneumonectomies) required MV for pulmonary or nonpulmonary complications. Using simple and multiple regression analysis, the best predictors of postoperative hypoxemia were FEV1ppo (r = 0.74, p < 0.001) in lobectomy and tidal volume (r = 0.67, p < 0.01) in pneumonectomy. Using discriminant analysis, FEV1ppo in lobectomy and tidal volume in pneumonectomy were also considered as the best predictive factors of MV for pulmonary complications. CONCLUSIONS: These results suggest that the degree of chronic obstructive pulmonary disease in lobectomy and impairment of preoperative breathing pattern in pneumonectomy are the main factors of respiratory failure after lung resection.

Adult↗
PubMed1999

[The value of procalcitonin in neonatal infections].

UNLABELLED: The value of procalcitonin (PCT) measurement is not presently completely assessed for the diagnosis of neonatal infections. PATIENTS AND METHODS: This parameter was assessed in a prospective study in the neonatal intensive care unit of Clermont-Ferrand Hospital (France) in comparison to C-reactive protein. All newborn infants admitted before 24 h of life (day 0) in the neonatal intensive care unit were included in the study. Newborns (102) were assigned to one of four groups: group 1: non-infected newborns (n = 41); group 2: possibly infected newborns (n = 33); group 3: probably infected newborns (n = 10); group 4: confirmed infections (n = 18 bacterial or fungal infections). C-reactive protein and PCT were determined in the sera at D0, D1, D3 and D8. We determined the optimal cutoff value of PCT using the Receiver Operating Characteristic curves (R.O.C.). RESULTS: The cutoff value is 1.5 ng/mL at D0 and 10 ng/mL at D1. PCT cutoff value is significantly higher at D1 because of a significant PCT peak on the first day of life independent of any infectious stimulus. Our study shows that at D0 and D1 infected newborn infants had significantly higher mean PCT and C-reactive protein values than non infected newborn infants. C-reactive protein has a better specificity but PCT has better sensitivity and negative predictive value. CONCLUSION: PCT seems to be an interesting marker of neonatal infections especially during the first 24 h of life even though the mechanism of PCT synthesis remains unclear.

Bacterial Infections↗
PubMed1998

Compatibility of tropisetron with glass and plastics. Stability under different storage conditions.

The compatibility of tropisetron (pure undiluted 1 mg mL(-1) and diluted with 5% glucose or 0.9% NaCl (saline)) with glass, poly(vinyl chloride), polypropylene or polyethylene containers has been studied over a period of two weeks. The drug solutions were exposed to different light and temperature conditions. Tropisetron was assayed by high-performance liquid chromatography. The results show that undiluted tropisetron is stable in polypropylene syringes for two weeks under all the storage conditions tested (daylight at room temperature, dark at room temperature, refrigerator at 4 degrees C). Some variations in concentration were observed after dilution of tropisetron but these remained within 10% of the initial concentration. Tropisetron can be stored undiluted at 1 mg mL(-1) in polypropylene syringes, although it is preferable to perform dilutions extemporaneously. Tropisetron diluted with 5% glucose or saline can be kept equally well in glass, poly(vinyl chloride) (Travenol bags) or polyethylene (ecoflac) containers.

Antiemetics↗
PubMed1991

An evaluation of four methods of root canal preparation using 14C urea.

One-hundred twenty single-rooted teeth were used in vitro in order to compare the four following methods of endodontic preparation: manual, Giromatic, MM 3000 Sonic Air with, and sonic air without the contact shaping technique. Each endodontic preparation was filled according to the McSpadden technique. Teeth were immersed in 14C urea. Radioactivity was evaluated qualitatively by autoradiography and quantitatively by scintigraphy. Data were statistically analyzed with a nonparametric test. The results show that the highest degree of leakage occurs with the manual method and that for the three other methods, maximum leakage takes place near the apices.

Dental Leakage↗
PubMed1991

Comparison of the myocardial distributions of 201Tl and 99Tcm-MIBI on SPECT images.

The distributions of 201Tl and 99Tcm-MIBI on stress images were quantitatively measured in a series of 15 patients presenting with documented coronary artery disease. Following two sequential, one-week apart, peak-exercise injections of either 74 MBq of 201Tl or 370 MBq of 99Tcm-MIBI, tomographic views of the myocardium were reconstructed and two thick, central short-axis sections were divided into nine sectors. A sector was considered as showing a defect if its relative activity was lower than 30, 40, 50 or 60% of the highest level of activity in the 18 sectors. Results demonstrate that there were more defects with 201Tl than with 99Tcm-MIBI. However, the difference disappeared if the inferior wall was not included. These results suggest that depth attenuation could be, at least partly, responsible for the higher rate of positive results observed in single photon emission computed tomography with 201Tl than with 99Tcm-MIBI.

Adult↗