Modélisation de surfaces à l'aide de fonctions splines :

Ce travail se décompose en trois parties distinctes. Dans la première partie, on introduit un algorithme du type Gauss-Seidel pour la minimisation de fonctionnelles symétriques semi-définies positives. La convergence de cet algorithme est démontrée. En application, on donne deux méthodes de lissage de surfaces. Ces méthodes sont basées sur l'idée de ramener un probleme de lissage a deux dimensions a la resolution d'une suite de problèmes a une dimension faciles a résoudre. Pour cela on utilise l'opération d'inf-convolution spline. Dans la deuxième partie, on introduit une nouvelle methode pour la conception d'un verre progressif. Ce verre est représente par une surface suffisamment régulière, a laquelle on impose des conditions sur ses courbures principales dans certaines zones (zone de vision de loin et zone de vision de pres), et des conditions sur ses directions principales de courbure dans d'autres zones (zone nasale et zone temporale). La surface est écrite sous forme de produit tensoriel de b-splines de degré quatre. Pour la calculer, on est amené a minimiser un opérateur non quadratique. Cette minimisation est alors effectuée par un procédé itératif dont on a teste numériquement la convergence rapid

Oral clonidine vs midazolam in the prevention of sevoflurane-induced agitation in children. A prospective, randomized, controlled trial

Background. This randomized, double-blind study tested the hypothesis that, in comparison with midazolam, premedication with oral clonidine reduces the incidence of emergence agitation in preschool children anaesthetized with sevoflurane. Methods. Sixty-eight ASA I-II children undergoing circumcision were randomized into three groups to receive different oral premedication given 30 min before anaesthesia: midazolam 0.5 mg kg-1, clonidine 2 μg kg-1, and clonidine 4 μg kg-1. Sevoflurane anaesthesia was administered via a facemask (O2/ N2O: 40/60). Analgesia was with penile block (bupivacaine 0.5% 0.3 ml kg-1) and rectal paracetamol (30 mg kg-1). During the first postoperative hour, children were evaluated using a modified 'objective pain scale'. Results. Only the 4 μg kg-1 dose of clonidine was associated with a significant reduction in emergence agitation. Fewer children in the clonidine 4 μg kg-1 group displayed agitation (25%) than in the midazolam group (60%) (P = 0.025). Incidence of hypotension and bradycardia, time to first micturition and first drink did not differ among groups. Conclusions. In comparison with midazolam, clonidine 4 μg kg-1 reduced sevoflurane-induced emergence agitation without increasing postoperative side-effects. © The Board of Management and Trustees of the British Journal of Anaesthesia 2007. All rights reserved.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

A comparison of midazolam and clonidine as an oral premedication in pediatric patients

Background: To compare oral midazolam (0.5 mg/kg) versus oral clonidine (4 μg/kg) as a premedication in pediatric patients aged between 2-12 years with regard to sedation and anxiolysis. Methods: Sixty pediatric patients belonging to the American Society of Anesthesiologists class I and II between the age group of 2-12 years scheduled for elective surgery were randomly allocated to receive either oral midazolam (group I) 30 min before induction or oral clonidine (group II) 90 min before induction of anesthesia. The children were evaluated for levels of sedation and anxiety at the time of separation from the parents, venepuncture, and at the time of mask application for induction of anesthesia. Results: After premedication, the percentage of children who were sedated and calm increased in both the groups. The overall level of sedation was better in the children in the clonidine group, but children in the midazolam group had a greater degree of anxiolysis at times of venepuncture and mask application. In addition, midazolam did not cause significant changes in hemodynamics unlike clonidine where a significant fall in blood pressure was noted, after premedication, but preinduction. Conclusion: We conclude that under the conditions of the study, oral midazolam is superior to clonidine as an anxiolytic in pediatric population. Clonidine with its sedative action especially at the time of separation from parents along with its other perioperative benefits cannot be discounted