La organización a gran escala de canales turbulentos

En esta tesis se investigan el origen y la organización de las estructuras grandes que se encuentran en las regiones logarítmica y exterior de la turbulencia parietal. Estas estructuras contienen la mayor parte de la energia cinética turbulenta, son responsables de una fracción apreciable de la resistencia de fricción y juegan un papel fundamental en el transporte turbulento. A pesar de su relevancia, existe mucha menos información acerca de las estructuras grandes que acerca de las estructuras pequeñas de la región de la pared. Esto se debe a la dificultad que entraña su análisis. Para nuestro estudio hacemos uso de los resultados de nuevos experimentos numéricos del flujo turbulento en canales planos, realizados a números de Reynolds, ,más altos y en dominios computacionales más grandes que los existentes hasta la fecha. Parte de los resultados de estos experimentos está disponible en el sitio http://torroja.dmt.upm.es/ftp/channels. alojado en España, o en la réplica http://davinci.tam.uiuc.edu/data/channels. alojada en EE. UU. También es posible acceder a la base de datos completa siguiendo el procedimiento indicado en htlp://davinci.tam.uiuc.edu/content/Channeldata.html. Los resultados indican que las fluctuaciones turbulentas de velocidad en las direcciones paralelas a la pared se organizan formando estructuras muy grandes, cuyo tamaño escala con el espesor del flujo. Estas estructuras, que hemos denominado modos globales, penetran desde el centro del canal hasta la zona de la pared, lo cual explica el escalado incompleto del espectro de energía en esta región. Hemos mostrado que la escala de velocidad de los modos globales es la velocidad media en el centro del canal, llegando a un escalado mixto para en la región exterior, que se reduce a - para. Hemos estudiado las propiedades de semejanza del espectro de energía en la regióN intermedia del flujo, encontrando anomalías en la relación entre las longitudes yanchuras de las escalas grandes de . La forma del escalado anómalo, -, sugiere que las estructuras grandes de son estelas dejadas por objetos compactos de v y W, las cuales se difunden bajo el efecto de la viscosidad turbulenta -. Este fallo de semejanza conduce a correcciones logaritmicas en varios rangos del espectro clásico, que han sido comprobadas usando datos de nuestras simulaciones y de experimentos de laboratorio provenientes de distintos flujos de pared a números de Reynolds mayores que los nuestros. Se ha analizado el origen de las estructuras grandes de la capa logaritmica, hallando que este se encuentra en eyecciones intensas que provienen de la región de la pared. Para este análisis hemos desarrollado un método que permite aislar y clasificar las eyecciones, basándonos en la evidencia de que están asociadas a racimos de torbellinos arraigados en la pared que alcanzan la región intermedia. El campo de velocidad medio condicionado a cada una de estas eyecciones revela una estructura muy larga de,cuya geometría es consistente con el escalado anómalo del espectro en la región intermedia. Estos resultados proporcionan una base estructural para nuestro modelo basado en estelas

A clinical method for mapping and quantifying blood stasis in the left ventricle

In patients at risk of intraventrcular thrombosis, the benefits of chronic anticoagulation therapy need to be balanced with the pro-hemorrhagic effects of therapy. Blood stasis in the cardiac chambers is a recognized risk factor for intracardiac thrombosis and potential cardiogenic embolic events. In this work, we present a novel flow image-based method to assess the location and extent of intraventricular stasis regions inside the left ventricle (LV) by digital processing flow-velocity images obtained either by phase-contrast magnetic resonance (PCMR) or 2D color-Doppler velocimetry (echo-CDV). This approach is based on quantifying the distribution of the blood Residence Time (TR) from time-resolved blood velocity fields in the LV. We tested the new method in illustrative examples of normal hearts, patients with dilated cardiomyopathy and one patient before and after the implantation of a left ventricular assist device (LVAD). The method allowed us to assess in-vivo the location and extent of the stasis regions in the LV. Original metrics were developed to integrate flow properties into simple scalars suitable for a robust and personalized assessment of the risk of thrombosis. From a clinical perspective, this work introduces the new paradigm that quantitative flow dynamics can provide the basis to obtain subclinical markers of intraventricular thrombosis risk. The early prediction of LV blood stasis may result in decrease strokes by appropriate use of anticoagulant therapy for the purpose of primary and secondary prevention. It may also have a significant impact on LVAD device design and operation set-up

Determinants of Severity in Acute Pancreatitis : A Nation-wide Multicenter Prospective Cohort Study

OBJECTIVE: The aim of this study was to compare and validate the different classifications of severity in acute pancreatitis (AP) and to investigate which characteristics of the disease are associated with worse outcomes. SUMMARY OF BACKGROUND DATA: AP is a heterogeneous disease, ranging from uneventful cases to patients with considerable morbidity and high mortality rates. Severity classifications based on legitimate determinants of severity are important to correctly describe the course of disease. METHODS: A prospective multicenter cohort study involving patients with AP from 23 hospitals in Spain. The Atlanta Classification (AC), Revised Atlanta Classification (RAC), and Determinant-based Classification (DBC) were compared. Binary logistic multivariate analysis was performed to investigate independent determinants of severity. RESULTS: A total of 1655 patients were included; 70 patients (4.2%) died. RAC and DBC were equally superior to AC for describing the clinical course of AP. Although any kind of organ failure was associated with increased morbidity and mortality, persistent organ failure (POF) was the most significant determinant of severity. All local complications were associated with worse outcomes. Infected pancreatic necrosis correlated with high morbidity, but in the presence of POF, it was not associated to higher mortality when compared with sterile necrotizing pancreatitis. Exacerbation of previous comorbidity was associated with increased morbidity and mortality. CONCLUSION: The RAC and DBC both signify an advance in the description and differentiation of AP patients. Herein, we describe the complications of the disease independently associated to morbidity and mortality. Our findings are valuable not only when designing future studies on AP but also for the improvement of current classifications

Contemporary use of cefazolin for MSSA infective endocarditis: analysis of a national prospective cohort

Objectives: This study aimed to assess the real use of cefazolin for methicillin-susceptible Staphylococcus aureus (MSSA) infective endocarditis (IE) in the Spanish National Endocarditis Database (GAMES) and to compare it with antistaphylococcal penicillin (ASP). Methods: Prospective cohort study with retrospective analysis of a cohort of MSSA IE treated with cloxacillin and/or cefazolin. Outcomes assessed were relapse; intra-hospital, overall, and endocarditis-related mortality; and adverse events. Risk of renal toxicity with each treatment was evaluated separately. Results: We included 631 IE episodes caused by MSSA treated with cloxacillin and/or cefazolin. Antibiotic treatment was cloxacillin, cefazolin, or both in 537 (85%), 57 (9%), and 37 (6%) episodes, respectively. Patients treated with cefazolin had significantly higher rates of comorbidities (median Charlson Index 7, P <0.01) and previous renal failure (57.9%, P <0.01). Patients treated with cloxacillin presented higher rates of septic shock (25%, P = 0.033) and new-onset or worsening renal failure (47.3%, P = 0.024) with significantly higher rates of in-hospital mortality (38.5%, P = 0.017). One-year IE-related mortality and rate of relapses were similar between treatment groups. None of the treatments were identified as risk or protective factors. Conclusion: Our results suggest that cefazolin is a valuable option for the treatment of MSSA IE, without differences in 1-year mortality or relapses compared with cloxacillin, and might be considered equally effective