[Postoperative analgesia following trapeziectomy with continuous intra-articular infusion of ropivacaïne versus continuous perineural infusion. A prospective randomised study]. / Analgésie postopératoire après trapezéctomie par infusion continue de ropivacaïne par cathéter in situ intra-articulaire versus cathéter périnerveux : étude prospective randomisée.

UNLABELLED: A prospective randomised study on 46 patients was performed to evaluate postoperative analgesia after trapezectomy. We compare the efficacy of an in situ catheter 777 (ISC) positioned by the surgeon in the space of the trapezectomy (26 patients) with an axilliary perineural catheter (APC) positioned preoperatively by the anaesthetist (20 patients). The patients were followed-up postoperatively for 48 hours and assessed at 3, 7, 24 and 48 hours, recording pain (VAS), consumption of intravenous rescue analgesia and recovery of sensory and motor function. RESULTS: The mean time to site the ISC was 1 min 30 versus 16 min the APC group. The mean pain scores were: in the ISC group consistently below 2 for the entire postoperative 48 hours. Seven patients (29%) required supplemental analgesia (16 doses). Two patients failed (7.7%) to achieve adequate postoperative analgesia; they were the only patients in whom the surgeon had sited a drain, probably implying a siphoning off of the local anaesthetic solution. In the APC group also less than 2, and rescue analgesia was required by seven patients (35%) (40 doses). In four patients (20%) the pain score remained greater than 4 throughout the study period implying failure of the perineural catheter. There was a more rapid and complete recovery of both sensory and motor function in the group treated with in situ catheters during the study period. There were no haematomata or infections in the tow groups. CONCLUSION: The in situ catheter provided at least as good postoperative analgesia while requiring considerably less time and expertise to site. There was also more rapid recovery of motor and sensory function in patients treated with in situ catheters.

Occurrence and robustness of current reversals in overdamped deterministic ratchets under symmetric forcing.

We analyze the conditions for the existence of current reversals in overdamped deterministic tilting ratchets under symmetric forcing. To this end, we use and extend the formalism recently introduced in R. Salgado-García, M. Aldana, and G. Martínez-Mekler [Phys. Rev. Lett. 96, 134101 (2006)] to transform the equations of motion of the ratchet into discrete circle maps. For a periodic dichotomous forcing we show that the phenomenon of current reversal is not uncommon and exists for a nonzero measure set of the parameter space. Additionally, we show numerically that, for a wide class of ratchet potentials, current reversals also occur when the discontinuous dichotomous forcing is replaced by symmetric continuous driving forces. The likelihood of the occurrence of current reversals is a consequence of the structural stability under small perturbations of the associated circle map with rational rotation number.

Analytical approach to the time-dependent probability density function in tilted periodic potentials.

In this work we introduce a scheme for the calculation of an approximate closed expression for the time-dependent probability density function for overdamped particles in tilted periodic potentials. Our derivation is based on an ansatz for the solution of the corresponding Fokker-Planck equation and on a self-consistent cumulant calculation. The high accuracy of our expression for the time-dependent probability density function is exhibited by comparisons with Langevin dynamics simulations and exact analytic results for the drift and diffusion coefficients. Good agreement is found both, for large and intermediate times.

Synchronization phenomena for a pair of locally coupled chaotic electrochemical oscillators: a survey.

Chaotic synchronization of two locally coupled electrochemical oscillators is studied numerically. Both bidirectional and unidirectional couplings are considered. For both these coupling scenarios, varying the characteristics of the coupling terms (functional form and/or strength) reveals a wide variety of synchronization phenomena. Standard diagnostic tests are performed to verify and classify the different types of synchronizations observed.

Deterministic ratchets, circle maps, and current reversals.

In this work we transform the deterministic dynamics of an overdamped tilting ratchet into a discrete dynamical map by looking stroboscopically at the continuous motion originally ruled by differential equations. We show that, for the simple and widely used case of periodic dichotomous driving forces, the resulting discrete map belongs to the class of circle homeomorphisms. This approach allows us to apply the well-known properties of such maps to derive the necessary and sufficient conditions that the ratchet potential must satisfy in order to have a vanishing current. Furthermore, as a consequence of the above, we show (i) that there is a class of periodic potentials which do not exhibit the rectification phenomenon in spite of their asymmetry and (ii) that current reversals occur in the deterministic case for a large class of ratchet potentials.

Parameter space reduction criteria to search for synchronization domains in coupled discrete systems.

Based on analytical considerations, we introduce criteria that enable us to encapsulate the parameter domains for which chaotic synchronization in linearly coupled map systems may be attained. Our aim is to provide means to readily determine parameter regions which preclude synchronization. This results in a significant reduction of parameter space that one needs to explore. Our findings hold for both identical and quasi-identical (small parameter mismatch) maps subjected to unidirectional and bidirectional coupling. As a testing ground we present numerical calculations for the logistic and cubic maps which validate the predictive capability of our approach. Our main contribution relies on the applicability of one of our criteria to experimental situations. Since in real life it is almost impossible to construct two truly identical systems, the results for quasi-identical maps are of particular relevance.

Translocation properties of primitive molecular machines and their relevance to the structure of the genetic code.

We address the question, related with the origin of the genetic code, of why are there three bases per codon in the translation to protein process. As a follow-up to our previous work (Aldana et al., 1998, Martínez-Mekler et al., 1999a,b), we approach this problem by considering the translocation properties of primitive molecular machines, which capture basic features of ribosomal/messenger RNA interactions, while operating under prebiotic conditions. Our model consists of a short one-dimensional chain of charged particles (rRNA antecedent) interacting with a polymer (mRNA antecedent) via electrostatic forces. The chain is subject to external forcing that causes it to move along the polymer which is fixed in a quasi-one-dimensional geometry. Our numerical and analytic studies of statistical properties of random chain/polymer potentials suggest that, under very general conditions, a dynamics is attained in which the chain moves along the polymer in steps of three monomers. By adjusting the model in order to consider present-day genetic sequences, we show that the above property is enhanced for coding regions. Intergenic sequences display a behavior closer to the random situation. We argue that this dynamical property could be one of the underlying causes for the three-base codon structure of the genetic code

Transport properties of the diluted Lorentz slab.

We study the behavior of a point particle incident on a slab of a randomly diluted triangular array of circular scatterers. Various scattering properties, such as the reflection and transmission probabilities and the scattering time are studied as a function of thickness and dilution. We show that a diffusion model satisfactorily describes the mentioned scattering properties. We also show how some of these quantities can be evaluated exactly and their agreement with numerical experiments. Our results exhibit the dependence of these scattering data on the mean free path. This dependence again shows excellent agreement with the predictions of a Brownian motion model.

Statistical characterization of random electrostatic potentials

In this work we study statistical properties of random electrostatic potentials generated by one dimensional lattices with random charges. We show that the resulting random potentials are correlated Gaussian processes, satisfying the Lindeberg version of the central limit theorem, if certain restrictions are imposed on the individual potentials generated by the particles on the lattice. Since most of the point-particle electrostatic potentials occurring in nature satisfy the Lindeberg condition, the correlation properties of the random potentials are not arbitrary and must comply with the central limit theorem. Based on this theorem we can obtain explicit expressions for these correlations. We thus are able to give a characterization of a broad class of potentials yielding feasible physical scenarios. We illustrate some consequences of our findings by considering dynamical properties of a test particle interacting with the lattice. We show how the long range correlations generate statistical features in these properties, which are best exhibited when considering different length scales.

[Postoperative pain and surgical treatment of trapeziometacarpal osteoarthritis of the thumb after ambulatory surgery]. / Douleur postopératoire et cure chirurgicale de rhizarthrose du pouce opérée sur le mode ambulatoire.

OBJECTIVE: The course of pain and the incidence of the side effects from analgesics were evaluated for 15 days in 26 consecutive outpatients who underwent a surgical cure of trapeziometacarpal osteoarthritis of the thumb under regional block. STUDY DESIGN: Prospective study. METHODS: The analgesic regimen prescribed at discharge consisted on a regular administration of a combination of ketoprofen (50 mg.6.h-1) plus the association of acetaminophen and propoxyphene (two tablets.6.h-1). Patients were asked to evaluate their pain using a numerical rating scale graduated from 0 to 10. Data were collected during a telephone interview at day 4, 8 and 15. RESULTS: Overall, patients scrupulously followed the medical prescription. At day four, 80% of patients still needed analgesics. The mean period during which NSAID, acetaminophen and propoxyphene were maintained was 4 and 6 days respectively. Fifty percent of patients reported severe pain during postoperative day 1 and 2. Moderate pain was reported at day 3 and 4 in respectively 54% and 42% of cases. Beyond this period, most patients indicated pain of weak intensity (71% at day 8). Epigastric pain has been noticed for 27% of patients. CONCLUSION: The surgical correction of trapeziometacarpal osteoarthritis of the thumb is frequently performed according to an ambulatory setting. The fact that 50% of patients reported severe pain during the early postoperative period emphasize the inadequacy of our postoperative pain management for this surgical procedure.

Primitive molecular machine scenario for the origin of the three base codon composition.

We set up a scenario for the operation of primordial synthesis machines operating in outer space quasi one dimensional channels, where polymers interact with fixed particles. The scheme allows for polymerization, translocation and translation. We will show that under very general conditions the particle/polymer interaction potential has spatial regularities with an average distance of three between neighboring minima. We present a model that exhibits how primitive molecular machines may convert the structural properties of the potential into locomotion regularities. On average, polymer movement takes place by shifts with long time intervals every three displacements. We argue that this feature is generic and lies at the origin of the three base codon composition.

A case of serotonin syndrome caused by venlafaxine and lithium.

Serotonin syndrome occurred under treatment with average dose of Venlafaxine and lithium in a 50 year-old female patient with a history of sensitiveness to SSRIs. Plasma levels of Venlafaxine and its metabolite were within reference range. Parmacogenetic evaluation indicated normal metabolic pathway.

Coupled trivial maps.

The first nontrivial example of coupled map lattices that admits a rigorous analysis in the whole range of the strength of space interactions is considered. This class is generated by one-dimensional maps with a globally attracting superstable periodic trajectory that are coupled by a diffusive nearest-neighbor interaction.

[Retrobulbar anaesthesia in cataract surgery revisited]. / Réactualisation de l'anesthésie locorégionale pour chirurgie de la cataracte.

Retrobulbar anaesthesia in cataract surgery is advocated so as to decrease anaesthetic risk. The technique of anaesthesia was studied in 100 patients. The study was based on two principles: firstly, it was the anaesthetist who performed the retrobulbar anaesthesia; secondly, retrobulbar anaesthesia was a matter of deliberate choice and not done upon contra-indication of general anaesthesia. After describing the means used in obtaining anaesthesia, akinesia and efficient hypotonia of the eye, the results of the series are reported. The advantages of retrobulbar anaesthesia are discussed. The absence of noxious side-effects is stressed. This anaesthetic technique should be used more often regardless of the patient's condition.