We studied the mechanical behavior of membranes of calf pericardium, similar to those employed in prosthetic valve leaflets, when subjected to tensile fatigue. The objective was to assess its durability, as a fundamental property of cardiac bioprosthesis, and analyze the energy consumption. For this purpose, the authors built a hydraulic simulator to subject a spherical valve leaflet made of calf pericardium to cyclic stress mimicking cardiac function. A total of 522 assays were performed in 40 samples, subjected to cyclic pressures greater than 6 atm, and 482 subjected to pressures ranging between 2 and 6 atm. The mathematical expression that establishes the relationship between the pressure exerted and the frequency was obtained. If we assume that the function is continuous, this equation provides the range of fatigue tolerated for a given number of cycles. Using the optimal values (the five highest values per series), the expression was found to be y = 9.95x(-0 1214) (R(2) = 0.955), where x represents the frequency in cycles per second and y the pressure in atmospheres. In addition, we established the mathematical relationship between the energy consumed and the frequency, which was a function of the pressure exerted, regardless of the region or zone from which the samples had been obtained. The methods of manual and morphology-based selection employed produced widely dispersed results. When a mechanical criterion was included, the similarity in the energy consumed during fatigue testing markedly improved the correlation, with a coefficient of determination between paired samples of R(2) = 0.7477. A mechanical criterion, such as energy consumption, can help to improve sample selection and produce more consistent results. Finally, we obtained the mathematical expression that relates the energy consumed to the pressure exerted and the number of cycles per second to which the valve leaflet was subjected. This procedure enables us to establish the limit to the energy that a biomaterial can consume over a period of time during which it is subjected to a working pressure and, thus, calculate more precisely its durability.
Aim: To communicate the results of the Spanish Home Parenteral Nutrition (HEN) registry of the NADYA-SENPE group for the year 2015.Material and methods: Data was recorded online by NADYA group collaborators that were responsible of the HPN follow-up from 1 st January to 31 st December 2015.Results: Two hundred and thirty-six patients with 243 episodes of NPD were recorded from 40 hospitals. This represents a rate of 5.08 patients/million habitants for 2015. The most frequent pathology in adults was other (26.3%) followed by palliative oncological (21.6%). The most common complication was catheter-related sepsis which presented a rate of 0.53 infections/1,000 days of HPN. Sixty-four episodes were fi nished; the main cause was death (43.7%) and resuming to oral via (32.8%).Conclusions: we fi nd increasing centers and professional partners, responding to the progressively more patients with parenteral nutrition support at home. The main indications for the establishment of NPD and causes termination of treatment remain stable. ResumenObjetivo: comunicar los datos del registro de Nutrición Parenteral Domiciliaria (NPD) del grupo de trabajo NADYA-SENPE del año 2015.Material y métodos: recopilación de los datos de NPD del registro online del grupo de Nutrición Artifi cial Domiciliaria y Ambulatoria (NADYA) desde el 1 de enero de 2015 al 31 de diciembre de 2015.Resultados: se registraron 236 pacientes, con 243 episodios de NPD procedentes de 40 hospitales, lo que representa una tasa de 5,08 pacientes/millón de habitantes/año 2015. La patología más frecuente en los adultos fue "otros" (26,3%) seguido por "oncológico paliativo" (21,6%). La complicación más frecuente fue la séptica relacionada con el catéter, que presentó una tasa de 0,53 infecciones/1.000 días de NPD. Finalizaron 64 episodios, la principal causa fue el fallecimiento (43,7%) y el "paso a la vía oral" (32,8%).Conclusiones: constatamos el aumento de los centros y profesionales colaboradores, dando respuesta a la cantidad progresivamente mayor de pacientes con soporte nutricional parenteral en domicilio. Se mantienen estables las principales indicaciones para el establecimiento de NPD y las causas de fi nalización del tratamiento.
The mechanical behavior of porcine pericardium was analyzed to compare it with that of calf pericardium employed in valve leaflets for cardiac bioprostheses. Forty samples of pericardium were subjected to uniaxial tensile testing, 20 as controls and 20 exposed to loads increasing stepwise from 0.5 to 1.5 kg and to 3 kg, and thereafter to rupture, with a return to zero load between each new increment. Another 20 samples were used in biaxial tensile tests involving the application of loads increasing stepwise (to 0.5, 1.5, 3 and 5 kg) until rupture with a zero-load interval before each increment. The ultimate stresses were very similar, showing no statistically significant differences when compared in terms of type of assay, controls and study samples or region of pericardial tissue being tested. In the stepwise biaxial assays, the mean stresses at rupture were also very homogeneous. Using morphological and mechanical criteria for sample selection, it was possible to obtain mathematical fits for the stress/strain relationship, with excellent coefficients of determination. The relationship between the area under the stress/strain curve and the load applied or the strain observed was also studied in the biaxial assay as an equivalent to the cycles of hysteresis produced in the test. The increment in the area under the curve (the energy consumed) may be a good parameter for assessing the changes in the collagen fiber architecture of the pericardial tissue, changes that may help to detect early failure.
Que le dijo el movimiento comunista internacional a GramsciNo tengo edad, no tengo edaaaad para amarte . . . -Roque DaltonNumerous studies exist on the dissemination of Antonio Gramsci's work in Latin America. That the subject merited an international conference organized by the Instituto Gramsci (Gramsci Institute) in Italy titled "Political Transformations in Latin America: Gramsci's Presence in Latin America Culture" 1 in itself demonstrates the importance of his ideas in the region. I would like to advance some observations concerning this process.First, chronology: the history of the relationship between Latin America and Gramsci's thought can be divided into two distinct periods, one extending from the 1950s to 1975 and the other from 1975 to the present. During the first period, Argentina and Brazil were the principal centers for the publication of Gramsci's writings. The Argentine editions of the Editorial Lautaro, which was associated with the Partido Comunista de la Argentina (Communist party of Argentina-PCA), achieved the first continental diffusion of Gramsci's work, 2 and after 1963 the editions of the Pasado y Presente group appeared, along with the Brazilian editions of Civilização Brasileira. 3 During the second period, according to José Aricó (1988: 12, using an expression 9
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