Altérations de la repolarisation ventriculaire induites par l’exercice dans la sténose congénitale modérée de la valve aortique

Introduction: La surcharge de pression ventriculaire augmente à l’exercice chez les patients avec une sténose de valve aortique (SVA). Lorsqu’il n’y a aucun symptôme apparent, il est cependant difficile d’indiquer l’intervention chirurgicale en utilisant seulement les indices de surcharge de pression ventriculaire. D’autres paramètres, tels que la dispersion de la repolarisation ventriculaire (d-QT), qui augmentent avec le gradient de pression transvalvulaire (GPT), n’ont pas été étudiés dans la SVA. L’objectif de l’étude était de déterminer le modèle de réponse du segment QT et de la d-QT à l’épreuve d’effort chez des enfants avec une SVA congénitale modérée afin d’évaluer l’impact de la surcharge de pression ventriculaire selon une perspective électrophysiologique. Matériel et méthodes: 15 patients SVA modérés ont été comparés à 15 sujets contrôles appariés pour l’âge (14.8±2.5 ans vs. 14.2±1.5 ans) et pour le sexe (66,7% de sujets mâles). Tous les sujets ont fait une épreuve d’effort avec enregistrement électrocardiographique à 12 dérivations. Le segment QT a été mesuré à partir du début du complexe QRS jusqu’à l’apex de l’onde T (QTa) au repos, à l’effort maximal ainsi qu’après 1 et 3 minutes de récupération. La longueur du segment QT a été corrigée selon l’équation de Fridericia et la d-QT a été calculée. Résultats: La longueur du segment QT corrigée (QTc) était similaire au repos entre les groupes d’étude, mais était significativement élevée chez les SVA en comparaison avec le groupe contrôle à l’effort maximal (p=0.004) ainsi qu’après 1 (p<0.001) et 3 (p<0.001) minutes de récupération. Une interaction significative a été identifiée entre les groupes pour la d-QT (p=0.034) et les tests post hoc ont révélé une différence significative seulement au repos (p=0.001). Conclusions: Les anomalies de repolarisation ventriculaire peuvent être révélées par l’évaluation de la repolarisation électrique lors de l’épreuve d’effort chez les SVA modérées asymptomatiques. L’utilisation de la réponse du QT à l’effort pourrait être bénéfique pour l’optimisation de la stratification du risque chez ces patients.

Global and Regional Ventricular Repolarization Study by Body Surface Potential Mapping in Patients with Left Bundle-Branch Block and Heart Failure Undergoing Cardiac Resynchronization Therapy

Background: The controversial effects promoted by cardiac resynchronization therapy (CRT) on the ventricular repolarization (VR) have motivated VR evaluation by body surface potential mapping (BSPM) in CRT patients. Methods: Fifty-two CRT patients, mean age 58.8 +/- 12.3 years, 31 male, LVEF 27.5 +/- 9.2, NYHA III-IV heart failure with QRS181.5 +/- 14.2 ms, underwent 87-lead BSPM in sinus rhythm (BASELINE) and biventricular pacing (BIV). Measurements of mean and corrected QT intervals and dispersion, mean and corrected T peak end intervals and their dispersion, and JT intervals characterized global and regional (RV, Intermediate, and LV regions) ventricular repolarization response. Results: Global QTm (P < 0.001) and QTcm (P < 0.05) were decreased in BIV; QTm was similar across regions in both modes (P = ns); QTcm values were lower in RV/LV than in Intermediate region in BASELINE and BIV (P < 0.001); only RV/Septum showed a significant difference (P < 0.01) in the BIV mode. QTD values both of BASELINE (P < 0.01) and BIV (P < 0.001) were greater in the Intermediate than in the LV region. CRT effect significantly reduced global/regional QTm and QTcm values. QTD was globally decreased in RV/LV (Intermediate: P = ns). BIV mode significantly reduced global T peak end mean and corrected intervals and their dispersion. JT values were not significant. Conclusions: Ventricular repolarization parameters QTm, QTcm, and QTD global/regional values, as assessed by BSPM, were reduced in patients under CRT with severe HF and LBBB. Greater recovery impairment in the Intermediate region was detected by the smaller variation of its dispersion.

Cardiovascular autonomic dysfunction in sickle cell anemia

Sickle cell anemia (SCA) is associated to increased cardiac output, normal heart rate (HR), abnormal QT dispersion and lower diastolic blood pressure (DBP). The mechanisms are still unknown. The objective of this study was to test the hypothesis that there is cardiovascular autonomic dysfunction (CAD) in SCA. The secondary objectives were to distinguish the roles of chronic anemia and hemoglobinopathy and to evaluate the predominance of the sympathetic or parasympathetic systems in the pathogenesis of CAD. Sixteen subjects with SCA, 13 with sickle cell trait (SCT), 13 with iron deficiency anemia (IDA), and 13 healthy volunteers (HV) were evaluated. All subjects were submitted to 24 h-electrocardiogram (24 h-ECG), plasma norepinephrine (NE) measurement before and after isometric exercise (IE), and also Valsalva maneuver (VM), diving maneuver (DV), and tilt test (TT). Baroreflex sensitivity (BRS) was also evaluated. The minimum, average and maximum HR as well as the percentage of bradycardia and tachycardia at 24-h ECG were similar in all groups. NE at baseline and after IE did not differ between groups. The SCA group showed less bradycardia at phase IV of VM, less bradycardia during DV, and also less tachycardia and lower DBP during TT. BRS for bradycardia and tachycardia reflex was decreased in the SCA and SCT groups. In conclusion, 1) there is CAD in SCA, and it is characterized by the reduction of BRS and the limitation of HR modulation mediated by the parasympathetic system; 2) cardiovascular sympathetic activity is preserved in SCA; and 3) hemoglobinopathy is the preponderant ethiopathogenic factor. (C) 2011 Elsevier B.V. All rights reserved.

Refractive index dispersion measurement on nonlinear optical polymer using V-prism refractometer

By using V-prism refractometer, the refractive indices of a polyetherketone (PEK-c) guest-host polymer system were measured with the polymer in solutions. The Lorenz-Lorentz local field formalism was used in the calculation of the refractive indices of the polymers from the measured indices of the polymer solutions and the pure solvent by using V-prism refractometer. The refractive index dispersions of the polymers were obtained by fitting the measured indices of the polymers to Sellmeyer equation. The method allows for an accuracy in index of 0.7% in the determination of the polymer indices. In addition, a large difference between the indices of the polymer and the solvent, and a higher polymer volume fraction in the measured polymer solution are favorable for a high accuracy. (C) 2000 Elsevier Science Ltd. All rights reserved.

Simulations of pollutant dispersion at toll plazas using three-dimensional CFD models

Toll plazas are particularly susceptible to build-ups of vehicle-emitted pollutants because vehicles pass through in low gear. To look at this, three-dimensional computational fluid dynamics simulations of pollutant dispersion are used on the standard k e turbulence model. The effects of wind speed, wind direction and topography on pollutant dispersion were discussed. The Wuzhuang toll plaza on the Hefei-Nanjing expressway is considered, and the effects of the retaining walls along both sides of the plaza on pollutant dispersion is analysed. There are greater pollutant concentrations near the tollbooths as the angle between the direction of the wind and traffic increases implying that retaining walls impede dispersion. The slope of the walls has little influence on the variations in pollutant concentration.

Difference and dispersion : educational research in a postmodern context

Difference and Dispersion is the fourth in a series of annual research papers produced by doctoral students from The Graduate School of Education, The University of Queensland, following their presentation at the School’s annual Postgraduate Research Conference in Education. The work featured herein celebrates the diversity of cultural and disciplinary backgrounds of education researchers who come from as far afield as Germany, Hong Kong, China, Nigeria, Russia, Singapore, Thailand and of course different parts of Australia. In keeping with a postmodern epistemology, ‘difference’ and ‘dispersion’ are key themes in apprehending the multiplicity of their research topics, methodologies, methods and speaking/writing positions. From widely differing contexts and situations, these writers address the consequences, implications and possibilities for education at the beginning of the third millennium. Their interest ranges from location-specific issues in schools and classrooms, change in learning contexts and processes, educational discourses and relations of power in diverse geographical settings, and the differing articulations of the local and the global in situated policy contexts. Conceived and developed in a spirit of ongoing dialogue with and insight to alternative views and visions of education and society, this edited collection exemplifies the quality in diversity and the high levels of scholarship and supervision at one of Australia’s finest Graduate Schools of Education.