Nonlinear complexification of periodic orbits in the generalized Landau scenario.

We have found a way for penetrating the space of the dynamical systems toward systems of arbitrary dimension exhibiting the nonlinear mixing of a large number of oscillation modes through which extraordinarily complex time evolutions may arise. The system design is based on assuring the occurrence of a number of Hopf bifurcations in a set of fixed points of a relatively generic system of ordinary differential equations, in which the main peculiarity is that the nonlinearities appear through functions of a linear combination of the system variables. The paper outlines the design procedure and presents a selection of numerical simulations with a variety of designed systems whose dynamical behaviors are really rich and full of unknown features. For concreteness, the presentation is focused on illustrating the oscillatory mixing effects on the periodic orbits, through which the harmonic oscillation born in a Hopf bifurcation becomes successively enriched with the intermittent incorporation of other oscillation modes of higher frequencies while the orbit remains periodic and without the necessity of bifurcating instabilities. Even in the absence of a proper mathematical theory covering the nonlinear mixing mechanisms, we find enough evidence to expect that the oscillatory scenario be truly scalable concerning the phase-space dimension, the multiplicity of involved fixed points, and the range of time scales so that extremely complex but ordered dynamical behaviors could be sustained through it.

Nonlinear oscillatory mixing in the generalized Landau scenario.

We present a set of phase-space portraits illustrating the extraordinary oscillatory possibilities of the dynamical systems through the so-called generalized Landau scenario. In its simplest form the scenario develops in N dimensions around a saddle-node pair of fixed points experiencing successive Hopf bifurcations up to exhausting their stable manifolds and generating N-1 different limit cycles. The oscillation modes associated with these cycles extend over a wide phase-space region by mixing ones within the others and by affecting both the transient trajectories and the periodic orbits themselves. A mathematical theory covering the mode-mixing mechanisms is lacking, and our aim is to provide an overview of their main qualitative features in order to stimulate research on it.

miRNA let-7e targeting MMP9 is involved in adipose-derived stem cell differentiation toward epithelia.

miRNA let-7e is involved in stem cell differentiation, and metalloproteinases are among its potential target genes. We hypothesized that the inhibitory action of let-7e on regulation of MMP9 expression could represent a crucial mechanism during differentiation of adipose-derived stem cells (ASCs). ASCs were differentiated with all-trans retinoic acid (ATRA) to promote differentiation, and the effect of let-7 silencing during differentiation was tested. Results indicate that ASCs cultured with ATRA differentiated into cells of the epithelial lineage. We found that ASCs cultured with ATRA or transfected with miRNA let-7e expressed epithelial markers such as cytokeratin-18 and early renal organogenesis markers such as Pax2, Wt1, Wnt4 and megalin. Conversely, the specific knockdown of miRNA let-7e in ASCs significantly decreased the expression of these genes, indicating its vital role during the differentiation process. Using luciferase reporter assays, we also showed that MMP9 is a direct target of miRNA let-7e. Thus, our results suggest that miRNA let-7e acts as a matrix metalloproteinase-9 (MMP9) inhibitor and differentiation inducer in ASCs.

Ligasure versus diathermy hemorrhoidectomy under spinal anesthesia or pudendal block with ropivacaine: a randomized prospective clinical study with 1-year follow-up.

PURPOSE: We evaluate the safety and efficacy of a spinal anesthesia with lidocaine versus a local anesthesia of pudendal block with ropivacaine combined with intravenous sedation in the hemorrhoidectomy procedure and also we compared the short- and long-term efficacy of conventional diathermy versus Ligasure diathermy hemorrhoidectomy. METHODS: Seventy-four patients of grade III or IV hemorrhoids were randomized to conventional diathermy hemorrhoidectomy under spinal (n = 19) or local anesthesia (n = 18) and Ligasure diathermy hemorrhoidectomy under spinal (n = 17) or local anesthesia (n = 20). Time of follow-up was 12 months. RESULTS: Patients operated under local anesthesia had less pain (p < 0.01), less analgesic requirements (p < 0.001), shorter hospital stay (p < 0.01), and less postoperative complications (p < 0.05). A shorter operating time (p < 0.001) and less complications at 4 months postoperatively (p < 0.05) was observed in the Ligasure group, but differences at 12 months were not found. CONCLUSIONS: Hemorrhoidectomy under local anesthesia with pudendal block with ropivacaine and sedation reduced postoperative pain, analgesic requirements, and postoperative complications, and can be performed as day-case procedure. Ligasure diathermy hemorrhoidectomy reduced operating time and was equally effective than conventional diathermy in long-term symptom control.

Nucleotides modulate renal ischaemia-reperfusion injury by different effects on nitric oxide and superoxide.

1. The present study investigated the effects of kidney ischaemia duration on nitric oxide (NO) and superoxide (O2-) generation at reperfusion and the role of xanthine and adenosine as mediators of NO/O2- generation. 2. The effect of the duration of ischaemia on renal nucleotide levels was studied in two ischaemic groups (10 and 30 min). The role of adenosine and xanthine was studied in ischaemic-reperfused groups (subjected to 10 and 30 min ischaemia and 60 min reperfusion). 3. Tissue levels of adenosine decreased significantly after 30 min ischaemia, whereas xanthine/hypoxanthine levels increased concomitantly with renal dysfunction and histological damage. 4. Nitric oxide production increased significantly after 10 min ischaemia and 60 min reperfusion, whereas lipoperoxidation increased significantly after 30 min ischaemia and 60 min reperfusion. The administration of theophylline (40 mg/kg, i.p.) reversed the early increase in NO production. 5. Xanthine supplementation decreased renal function and increased lipoperoxidation. 6. In conclusion, NO/O2- production and the subsequent renal injury/dysfunction may be modified by changes in the adenosine and xanthine levels of the injured kidney, although the present data show a significant in vivo role only for xanthine.

Phase synchronization in bidirectionally coupled optothermal devices.

We present the experimental observation of phase synchronization transitions in the bidirectional coupling of chaotic and nonchaotic oscillators. A variety of transitions are characterized and compared to numerical simulations of a time delayed model. The characteristic 2pi phase jumps usually appear during the transitions, specially in those clearly associated with a saddle-node bifurcation. The study is done with pairs of optothermal oscillators linearly coupled by heat transfer.

Gestión clínica de la lista de espera en un servicio de cirugía general / Management of the hospital waiting list in a general surgery department

Introducción. Presentamos nuestra experiencia en la gestión clínica de la lista de espera del Servicio de Cirugía General del Hospital de Viladecans (hospital público del Institut Català de la Salut).Objetivos. Diseño de una base de datos para la gestión clínica de la lista de espera del servicio de cirugía general, y evaluación de los resultados tras su diseño y aplicación.Material y método. Base de datos creada a tal fin, y que recoge todos los pacientes incluidos en lista de espera para intervención quirúrgica electiva durante un período de 5 años (desde el 1 de enero de 1996 al 31 de diciembre de 2000).Resultados. El número de intervenciones quirúrgicas electivas año tras año se ha mantenido por debajo de la demanda, creando un déficit que equivaldría a incrementar nuestra actividad en un 23,8 por ciento para adecuarla a la demanda. La lista de espera para la cirugía electiva ha estado condicionada a la presión de urgencias, que ha ido progresivamente en aumento. El criterio establecido de prioridad se ha demostrado útil, habiendo operado el 60,8 por ciento de los pacientes preferentes antes de 3 meses, y el 65,2 por ciento de los pacientes no preferentes entre 3 y 9 meses.Conclusiones. 1) Existe un progresivo incremento de la demanda de servicios quirúrgicos en nuestra área de influencia. 2) Se ha logrado una mejor gestión clínica, con un progresivo descenso en el número de anulaciones y un incremento en la actividad quirúrgica. 3) Se ha reducido el número de reprogramaciones de un 32 a un 14,3 por ciento. 4). Calculamos un déficit de recursos (horas de quirófano) que equivaldría a un 23,8 por ciento de nuestra actividad quirúrgica actual para poder adecuarnos a la demanda. 5) La base de datos diseñada por nosotros ha demostrado ser un instrumento útil de gestión de nuestra lista de espera (AU)

CO2 in static mesenteric venous blood during intestinal ischemia and ischemic preconditioning in rats.

During intestinal ischemia, CO2 accumulates in tissue as a result of bicarbonate buffering of anaerobic acid generation. Previous studies have shown that nitric oxide (NO) generated during ischemic preconditioning acts as a glycolytic modulator, thus decreasing tissue lactate production. We studied if ischemic preconditioning induces NO-dependent changes in static mesenteric venous blood Pco2 values and CO2 accumulation during intestinal ischemia. Superior mesenteric venous (smv) acid base variables were studied in 4 groups of rats: a control group (C), an ischemic (90-min period of flow arrest) group (I), an ischemic group subjected to previous ischemic preconditioning (P), and an ischemic group subjected to previous ischemic preconditioning in which nitric oxide synthase (NOS) was inhibited by N-nitro-L-arginine methyl ester (L-NAME) administration (P+N). Preconditioning induced acidosis in smv blood during reperfusion before ischemia, but this effect was counteracted by L-NAME. Group P showed the lowest values of end-ischemic tissue lactate, smv blood CO2 accumulation, and LDH in perfusate, whereas group P+N showed the highest level of LDH in perfusate but the lowest end-ischemic smv blood Pco2 and acidity. We conclude that lower ischemic CO2 accumulation in static smv blood, but not lower end-ischemic Pco2, was related with the protective effect of ischemic preconditioning in our rat model. Thus, the use of stagnant smv blood Pco2 as an indicative of intestinal dysoxia can lead to misinterpretations if a broader acid-base picture is not considered.

Effects of adenosine on ischaemia-reperfusion injury associated with rat pancreas transplantation.

BACKGROUND: During cold preservation, cellular consumption of adenosine triphosphate leads to the accumulation of nucleotides and nucleosides. The precise role of adenosine in modulating the inflammatory response of cold-preserved pancreas after reperfusion remains to be elucidated. The aim of this study was to assess the influence of adenosine on the inflammatory response associated with the process of ischaemia-reperfusion in rat pancreas transplantation. METHODS: The effect of adenosine from preservation solution on the levels of high-energy nucleotides and their breakdown products after cold ischaemic preservation was determined. In addition, the inflammatory response associated with the process of ischaemia-reperfusion in pancreas transplantation was quantified with and without pretreatment with the adenosine antagonist theophylline, and during preservation of the organ in University of Wisconsin solution with and without adenosine. RESULTS: Adenosine from preservation solution is able to modify the nucleotide and nucleoside content of preserved pancreas, indicating that adenosine is incorporated and metabolized in tissue. Administration of the adenosine antagonist to transplanted rats moderated the increases in nitrite and nitrate, myeloperoxidase activity and lipoperoxidation levels in the pancreas. CONCLUSION: Adenosine in the preservation solution may enhance the inflammatory response in rat pancreas transplantation.

Full instability behavior of N-dimensional dynamical systems with a one-directional nonlinear vector field

We show how certain N-dimensional dynamical systems are able to exploit the full instability capabilities of their fixed points to do Hopf bifurcations and how such a behavior produces complex time evolutions based on the nonlinear combination of the oscillation modes that emerged from these bifurcations. For really different oscillation frequencies, the evolutions describe robust wave form structures, usually periodic, in which self-similarity with respect to both the time scale and system dimension is clearly appreciated. For closer frequencies, the evolution signals usually appear irregular but are still based on the repetition of complex wave form structures. The study is developed by considering vector fields with a scalar-valued nonlinear function of a single variable that is a linear combination of the N dynamical variables. In this case, the linear stability analysis can be used to design N-dimensional systems in which the fixed points of a saddle-node pair experience up to N-1 Hopf bifurcations with preselected oscillation frequencies. The secondary processes occurring in the phase region where the variety of limit cycles appear may be rather complex and difficult to characterize, but they produce the nonlinear mixing of oscillation modes with relatively generic features.

Experimental observation of the amplitude death effect in two coupled nonlinear oscillators

The amplitude death phenomenon has been experimentally observed with a pair of thermo-optical oscillators linearly coupled by heat transfer. A parametric analysis has been done and compared with numerical simulations of a time delayed model. The role of the coupling strength is also discussed from experimental and numerical results.

N-dimensional dynamical systems exploiting instabilities in full.

We report experimental and numerical results showing how certain N-dimensional dynamical systems are able to exhibit complex time evolutions based on the nonlinear combination of N-1 oscillation modes. The experiments have been done with a family of thermo-optical systems of effective dynamical dimension varying from 1 to 6. The corresponding mathematical model is an N-dimensional vector field based on a scalar-valued nonlinear function of a single variable that is a linear combination of all the dynamic variables. We show how the complex evolutions appear associated with the occurrence of successive Hopf bifurcations in a saddle-node pair of fixed points up to exhaust their instability capabilities in N dimensions. For this reason the observed phenomenon is denoted as the full instability behavior of the dynamical system. The process through which the attractor responsible for the observed time evolution is formed may be rather complex and difficult to characterize. Nevertheless, the well-organized structure of the time signals suggests some generic mechanism of nonlinear mode mixing that we associate with the cluster of invariant sets emerging from the pair of fixed points and with the influence of the neighboring saddle sets on the flow nearby the attractor. The generation of invariant tori is likely during the full instability development and the global process may be considered as a generalized Landau scenario for the emergence of irregular and complex behavior through the nonlinear superposition of oscillatory motions. (c) 2000 American Institute of Physics.

Endothelin mediated nitric oxide effects in ischemia--reperfusion associated with pancreas transplantation.

Formation of nitric oxide (NO) in ischemia-reperfusion (I-R) associated with pancreas transplantation could modulate the inflammatory response. In this sense, previous studies have demonstrated the action of NO on vasoactive substances like prostacyclin or endothelin. The present study was designed to evaluate the contribution of endothelin to the inflammatory events induced by NO in the I-R process associated with pancreas transplantation. For this purpose, pancreatic levels of endothelin, neutrophil infiltration, and prostacyclin were evaluated in an experimental model of pancreas transplantation after inhibition of NO synthesis or after NO inhibition plus addition of endothelin. Results show significant posttransplantation increases in endothelin, neutrophil infiltration, and prostacyclin production. These increases were prevented by NO inhibition. Endothelin administration plus nitric oxide inhibition reversed this effect, resulting in an increase in myeloperoxidase and 6-keto-prostaglandin F1alpha. These results suggest that the proinflammatory effects of NO in I-R associated with pancreas transplantation are mediated by the induction of endothelin generation.

Nitric oxide enhances endothelin production in pancreas transplantation.

The role of endothelin and its relationship with nitric oxide (NO) production in ischemia-reperfusion associated with pancreas transplantation has been explored. For this purpose, pancreatic levels of endothelin were evaluated in an experimental model of pancreas transplantation after different periods of cold preservation. The effects of NO synthase inhibition were also evaluated. Results show posttransplantation increases in lipase and endothelin production. The release of lipase and endothelin was only prevented by NG-nitro-L-arginine methyl ester after a short ischemic period. Thus, endothelin synthesis could be a consequence of stimulation with NO in the ischemia-reperfusion associated with pancreas transplantation.

Differential effect of nitric oxide inhibition as a function of preservation period in pancreas transplantation.

The role of nitric oxide, produced during reperfusion as a function of preservation time, in the development of the inflammatory process in pancreas transplantation has been explored. For this purpose, the effect of nitric oxide synthase inhibition, as well as 6-keto-prostaglandin F1alpha, leukotriene B4, and lipoperoxidation levels were evaluated in an experimental model of rat pancreas transplantation after different periods of cold preservation. The results show posttransplantation increases in 6-keto-prostaglandin F1alpha, leukotriene B4, and lipoperoxidation levels in pancreatic tissue and in plasma lipase. When ischemia was induced for 30 min, nitric oxide synthase inhibition prevented these increases, and L-arginine was able to reverse this effect. By contrast, nitric oxide synthase inhibition has no effect when ischemia was prolonged for 12 hr. In summary, this study suggests that, during reperfusion, nitric oxide modulates 6-keto-prostaglandin F1alpha synthesis, lipoperoxidation levels, and the development of pancreatic injury but only when the ischemic period is quite short.

Clinical skills assessment with standardized patients.

Previous projects (Combell I & II) to assess clinical skills were conducted in medical schools in Catalonia, in order to introduce a model of such an assessment using standardized patients (SP). The aim of this study (Combell III) was to measure selected characteristics of our model. Seventy-three medical students in the final year at the Bellvitge teaching unit of the University of Barcelona participated in a clinical skills assessment (CSA) project that used 10 SP cases. The mean group scores for the four components of clinical skills for each day of testing were studied, and ratings for each student in the 10 sequential encounters were checked. The study also compared the clinical skills scores with their academic grades. The total case mean score (mean score of history-taking, physical examination and patient notes scores) was 51.9%, and the mean score for communication skills was 63.6%. The clinical skills scores over the 8 testing days showed no day-to-day differences. The study did not find differences among the sequential encounters for each student (training effect). There was a lack of correlation between clinical skills scores and academic grades. The project demonstrated the feasibility of the method for assessing clinical skills, confirmed its reliability, and showed that there is no correlation between scores with this method and academic examinations that mainly reflect knowledge.

Free radical enhancement promotes leucocyte recruitment through a PAF and LTB4 dependent mechanism.

In the present investigation we studied the concerted role of superoxide anion, platelet activating factor (PAF) and leukotriene B4 (LTB4) in the mechanism that results in polymorphonuclear leucocyte accumulation induced by oxygen free radicals in rat pancreas. This was done by comparing the effects of a PAF antagonist (BN-52021), a LTB4 inhibitor (MK-886) and superoxide dismutase (SOD) in a experimental rat model of inflammation elicited by the oxygen free radicals induced via infusion of xanthine/xanthine oxidase. Also, the effect of independent LTB4 infusion has been studied. The results show that increases in polymorphonuclear cell infiltration (evaluated by tissue histology), myeloperoxidase and LTB4 levels induced in pancreas by infusion of xanthine/xanthine oxidase were abolished by the administration of either the PAF antagonist, the LTB4 inhibitor, or SOD. The fact that BN-52021 could prevent neutrophil recruitment and LTB4 synthesis suggests that PAF is a necessary step for subsequent LTB4 synthesis and polymorphonuclear leucocyte accumulation.

[Central venous catheter location by endocavitary ECG: an alternative to chest radiography]. / Comprobación de catéter central por electrocardiografía endocavitaria: la alternativa a la radiografía de tórax.

BACKGROUND: The location of a central venous catheter is checked with a chest radiograph. Right endocavitary electrocardiography (ECG), a technique in which the catheter is connected to the ECG recorder wire to record ECG in DII, might be an alternate method to check the position of the catheter. When the catheter enters the right atrium, there is a large increase in the amplitude of P wave. The aim of this study was to compare the efficacy of endocavitary ECG against the chest radiography as a method to check the position of a central catheter, and to determine whether the ECG method can replace the radiological method. MATERIAL AND METHODS: One-hundred central catheters which location was checked by ECG and by chest X-ray entered the study. Efficacy of endocavitary ECG, delay between catheter insertion and radiological check, and the cost of the two methods were studied. RESULTS: Endocavitary ECG determined that de catheter was in a correct position in 80 cases and malpositioned in 20 cases. ECG check agreed with radiological check in 93 catheters. There were 4 false-positive and 3 false-negative cases. The efficacy of endocavitary ECG was 93% (sensitivity: 82%; specificity: 81%; positive predictive rate: 95%; negative predictive rate: 85%). Catheter location was checked immediately on insertion by ECG in all cases, while radiological check was delayed 32 +/- 25 min in the emergency department and 68 +/- 206 min in the admitted patients. The cost of the ECG method was less than that of the radiological method. CONCLUSIONS: The check of the position of a central venous catheter by endocavitary ECG is taster, cheaper, and of similar efficacy to the radiological method. Endocavitary ECG can replace chest X-rays to check the position of the catheter in more than 90% of cases.

[An analysis of the impact of the COMBELL project on clinical medical competence. Competencia clínica Bellvitge]. / Análisis del impacto del proyecto COMBELL sobre la competencia clínica médica.

OBJECTIVE: The most frequent tests for evaluate medical education in our country, do not analyze clinical competence. The aims of this project was to introduce a method for the assessment of clinical skills in two different groups of students using the simulation methodology with standardized patients and to compare with classical methods of assessment. METHODS: Seventy three last year medical students were evaluated using 10 standardized patients encounters in April 1995 (COMBELL III project) and the other group of last year medical students was assessed in March 1996 using the same group of standardized patients (COMBELL IV project). RESULTS: The global score for the COMBELL III, was 50.6% +/- 4.8 lower to COMBELL IV, 55.6% +/- 6 (p = 0.0001), remarking the improving of the item of physical examination (39.6% +/- 7.7 versus 48.1 +/- 9.6 p < 0.0001). Personal intercommunication also improved, 63.1% +/- 11.4 versus 70.4% +/- 12.2 (p = 0.0008). We did not find differences between academic grades and did not find correlations between clinical competence assessment and academic grades in COMBELL III but we found correlations in COMBELL IV. CONCLUSIONS: Our results show that when this new assessment method was introduces in our medical school the clinical competence levels improved.