127 research outputs found
Role of a heart valve clinic programme in the management of patients with aortic stenosis.
No full textpeer reviewedAIMS: We sought to assess the efficacy of a heart valve clinic (HVC) follow-up programme for patients with severe aortic stenosis (AS). METHODS AND RESULTS: Three hundred and eighty-eight consecutive patients with AS (age 71 +/- 10 years; aortic-jet velocity 5.1 +/- 0.6 m/s) and an indication for aortic valve replacement (AVR) were included. Of these, 290 patients presented with an indication for surgery at their first visit at the HVC and 98 asymptomatic patients who had been enrolled in an HVC monitoring programme developed indications for surgery during follow-up. Time to symptom detection was significantly longer in patients that presented with symptoms at baseline (352 +/- 471 days) than in patients followed in the HVC (76 +/- 75 days, P /=III) was present in 61% of patients being symptomatic at the initial visit and in 34% of patients in the HVC programme (P < 0.001). CONCLUSION: Delays in referral and symptom reporting as well as symptom denial are common in patients with AS. These findings support the concept of risk stratification to identify patients who may benefit from elective surgery. A structured HVC programme results in the detection of symptoms at an earlier and less severe stage and thus in an optimized timing of surgery
Modeling of a trickling filter reactor for the hydrolysis of corncob leaf
No full textgraficas, ilustraciones, tablasEl desarrollo de nuevos procesos es un tema de gran interés para la ingeniería de reactores, ya que se hace necesario mejorar e implementar nuevas prácticas en la industria que garanticen un futuro sostenible mediante la transformación de diferentes materiales. En general, la aplicabilidad de estos procesos a escala comercial está limitada por la complejidad de las reacciones en serie que se dan y las tecnologías de baja eficiencia, lo que conduce a que sean económicamente inviables. Por lo tanto, es necesario un profundo conocimiento del proceso y su operatividad para proponer tecnologías innovadoras que contribuyan a superar las restricciones mencionadas, mejorando así la incorporación de nuevos procesos para la transformación de materiales lignocelulósicos. En esta disertación, se desarrolló un nuevo concepto de reactor percolador para la producción y extracción de azúcares como: xilosa, glucosa, manosa, arabinosa y galactosa o subproductos como el furfural. Este proceso se desarrolló utilizando desechos biodegradables como la hoja de mazorca debido a que un material económico y de alta disponibilidad en Colombia.
El análisis del reactor se realizó en tres etapas: el modelamiento del reactor percolador mediante el software de Matlab® y la integración de este modelamiento con sección experimental para obtener los parámetros cinéticos que modelan la hidrólisis de la hemicelulosa y finalmente optimización de las concentraciones de los azúcares.
En la etapa del modelamiento del reactor percolador, se obtuvieron las ecuaciones del balance de masa que predecían las concentraciones de los productos y subproductos de la descomposición de la hemicelulosa de la hoja de mazorca. Para la obtención del modelamiento se realizó una caracterización del material lignocelulósico, obteniendo así los porcentajes de hemicelulosa, celulosa y lignina presentes en la materia para ser adaptados al modelo. El modelamiento del reactor percolador se desarrolló mediante el software Matlab®, utilizando una subrutina de optimización global y el comando fmincon para minimizar la función objetivo que consistía en minimizar la sumatoria de los residuales al cuadrado.
Una vez obtenido el modelamiento, éste se ajustó con los resultados de los datos experimentales de la hidrólisis de la hoja de mazorca. El ajuste del modelo del reactor percolador se realizó mediante un diseño secuencial obteniéndose la estimación de parámetros cinéticos, para esto primero se seleccionó las condiciones iniciales experimentales, luego se ajustaron los parámetros, seguidamente se utilizó el modelo secuencial para la predicción de nuevas condiciones de operación. Se hizo necesario la verificación de la calidad de la predicción del modelo (varianza de los parámetros del modelo), donde la varianza se ajustó a un valor máximo del 6%, para termina el proceso de ajuste.
Finalmente, con los parámetros cinéticos ajustados, se optimizaron las ecuaciones de los balances que mostraban el comportamiento de la producción de azúcares para obtener concentraciones máximas de xilosa y furfural, por medio de nuevas rutinas de software Matlab®, con el comando fmincon. La productividad del sistema fue más alta que la obtenida en otros reactores para hidrólisis de este tipo de materiales. El desempeño obtenido con estos reactores muestra el potencial de la tecnología desarrollada y es la fuerza impulsora para continuar investigando la optimización de los procesos. (Texto tomado de la fuente)The development of new processes is a topic of great interest for reactor engineering, since it is necessary to improve and implement new practices in the industry that guarantee a sustainable future through the transformation of different materials. The applicability of these processes on a commercial scale is limited by the complexity of the series reactions involved and the low efficiency technologies, which leads to their economic unfeasibility. Therefore, a deep knowledge of the process and its operability is necessary to propose innovative technologies that contribute to overcome the mentioned restrictions, thus improving the incorporation of new processes for the transformation of lignocellulosic materials. In this dissertation, a new concept of percolator reactor was developed for the production and extraction of sugars such as xylose, glucose, mannose, arabinose and galactose or by-products such as furfural. This process was developed using biodegradable wastes such as corncob leaves because it is an inexpensive and highly available material in Colombia.
The reactor analysis was carried out in three stages: modeling of the percolator reactor using Matlab® software and integration of this modeling with experiments to get the kinetic parameters that model the hydrolysis of hemicellulose and finally optimization of the product concentrations.
In the modeling stage of the percolator reactor, mass balance equations were derived to predict the concentrations of the products and by-products from the decomposition of the hemicellulose of the corncob leaf. For the simulation model, a characterization of the lignocellulosic material was performed to measure the percentages of hemicellulose, cellulose, and lignin present in the material to be included in the model. The modeling of the percolator reactor was developed using Matlab® software, using a global optimization subroutine and the fmincon command to minimize the objective function that consisted of minimizing the sum of the squared residuals.
The simulation model was adjusted with the results of the experimental data of the hydrolysis of the cob leaf. The parameters were fitted by a sequential design of experiments, first the initial experimental conditions were selected, then the parameters were adjusted, then the sequential model was used for the prediction of new operating conditions for the next experimental. It was necessary to verify the quality of the model prediction (variance in the model parameters). The variance was adjusted to a value of 5%.
Finally, with the model of the percolator reactor, the operating conditions were optimized to attain maximum concentrations of xylose and furfural. The productivity of the percolator reactor is higher than the one reached by other reactors for hydrolysis of this type of materials. The performance of a percolator reactor is superior to the conventional batch and plug flow reactors.MaestríaMagíster en Ingeniería - Ingeniería QuímicaQuímica Y Procesos.Sede Manizale
Imaging of Mitral Valve Prolapse: What Can We Learn from Imaging about the Mechanism of the Disease?
No full textMitral valve prolapse (MVP) is the most common mitral valve disorder affecting 2%–3% of the general population. Two histological forms for the disease exist: Myxomatous degeneration and fibroelastic disease. Pathological evidence suggests the disease is not confined solely to the valve tissue, and accumulation of proteoglycans and fibrotic tissue can be seen in the adjacent myocardium of MVP patients. MVP is diagnosed by demonstrating valve tissue passing the annular line into the left atrium during systole. In this review we will discuss the advantages and limitations of various imaging modalities in their MVP diagnosis ability as well as the potential for demonstrating extra associated valvular pathologies
LONG-TERM FOLLOW-UP IN MARFAN PATIENTS AFTER SUCCESSFUL SURGERY FOR ACUTE TYPE A AORTIC DISSECTION. THE IRAD EXPERIENCE
No full textTransgenic system for conditional induction and rescue of chronic myocardial hibernation provides insights into genomic programs of hibernation
No full textA key energy-saving adaptation to chronic hypoxia that enables cardiomyocytes to withstand severe ischemic insults is hibernation, i.e., a reversible arrest of contractile function. Whereas hibernating cardiomyocytes represent the critical reserve of dysfunctional cells that can be potentially rescued, a lack of a suitable animal model has hampered insights on this medically important condition. We developed a transgenic mouse system for conditional induction of long-term hibernation and a system to rescue hibernating cardiomyocytes at will. Via myocardium-specific induction (and, in turn, deinduction) of a VEGF-sequestering soluble receptor, we show that VEGF is indispensable for adjusting the coronary vasculature to match increased oxygen consumption and exploit this finding to generate a hypoperfused heart. Importantly, ensuing ischemia is tunable to a level at which large cohorts of cardiomyocytes are driven to enter a hibernation mode, without cardiac cell death. Relieving the VEGF blockade even months later resulted in rapid revascularization and full recovery of contractile function. Furthermore, we show that left ventricular remodeling associated with hibernation is also fully reversible. The unique opportunity to uncouple hibernation from other ischemic heart phenotypes (e.g., infarction) was used to determine the genetic program of hibernation; uncovering hypoxia-inducible factor target genes associated with metabolic adjustments and induced expression of several cardioprotective genes. Autophagy, specifically self-digestion of mitochondria, was identified as a key prosurvival mechanism in hibernating cardiomyocytes. This system may lend itself for examining the potential utility of treatments to rescue dysfunctional cardiomyocytes and reverse maladaptive remodeling
CHRONOBIOLOGICAL PATTERNS OF ACUTE AORTIC DISSECTION IN MARFAN SYNDROME PATIENTS: DATA FROM THE INTERNATIONAL REGISTRY OF ACUTE AORTIC DISSECTION (IRAD)
No full textHedonic integration with pain and pleasure
No full textThesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, February 2004.Includes bibliographical references (leaves 111-112).This experiment system provides a mechanism to study hedonic sensory integration in human subjects with specific focus on interaction between pain and pleasure. The system allows creation of stimuli segments with varying degrees of intensity and change based on subject's own discomfort thresholds and provides analysis mechanisms which illustrate the impact of mixing concurrent pain and pleasure.by David I. Gilon.M.Eng
Cardiac Tamponade Complicating Type A Acute Aortic Dissection: Insights From 25 Years of Registry Research
No full textMalaltia aòrtica; Tamponament cardíac; Dissecció aòrtica aguda tipus aEnfermedad aórtica; Taponamiento cardíaco; Disección aórtica aguda tipo aAortic disease; Cardiac tamponade; Type a acute aortic dissectionBackground
Cardiac tamponade (TMP) is a catastrophic complication of type A acute aortic dissection (TAAAD), increasing the risk of morbidity and mortality.
Objectives
The present study aimed to assess the characteristics, management, and outcomes of TAAAD patients with preoperative TMP enrolled in the International Registry of Acute Aortic Dissection database from 1996 to 2022.
Methods
Data from 63 aortic centers were analyzed and TAAAD patients with and without preoperative TMP were compared. Multivariable modeling to assess factors associated with the presence of preoperative cardiac TMP and survival curves were performed. Overall median follow-up was 35.8 months (Q1-Q3: 11.6-59.4 months).
Results
Of the 6,014 patients with TAAAD in the International Registry of Acute Aortic Dissection during the 25-year study period, 865 individuals (14.4%) developed TMP. Patients with TMP were older (age 64.9 vs 60.8 years; P < 0.0001) and less often male (61.8% vs 66.8%; P = 0.005). No differences were seen in time to presentation or diagnosis. Prior cardiac surgery was less common in patients with TMP (7.6% vs 12.8%; P < 0.0001). Syncope (37.4% vs 13.4%; P < 0.0001) and coma or altered consciousness (28% vs 8%; P < 0.0001) on presentation were more frequent in the TMP group. The majority of the cohort were managed surgically, rates of which were similar between groups (87.5% vs 87.7%; P = 0.911). In-hospital mortality was higher in patients with TMP (38.4% vs 15.4%; P < 0.001) but 4-year survival was similar (log-rank P = 0.767).
Conclusions
TMP is an important prognosticator of in-hospital mortality. It is associated with increased mortality of TAAAD and prompt surgery is required. Those who survive the hospital course, go on to share the same postdischarge course as those who did not have TMP
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