Pedro Almeida

Matching LED and Driver Life Spans: A Review of Different Techniques

A review of various proposed schemes to increase the reliability and life span of solid-state lighting (SSL) systems is presented in this article. Since the mainstream devices employed for such lighting systems are inorganic, high-power light-emitting diodes (LEDs), which are devices characterized by their very long life, most of the questions in reliability and endurability arise from the electronic offline circuit driving the LEDs. Issues regarding the limited reliability of specific components, such as electrolytic capacitors, are introduced. Several power-?conversion configurations aimed to capacitance reduction and capacitor technology exchange are put forward as alternative solutions for implementing long-life drivers, with remarks on both their benefits and drawbacks. An extensive literature review on the topic is carried out, and some practical outcomes from recent research on offline LED driving are highlighted.

Factores relacionados con la aparición de complicaciones vasculares periféricas tras procedimientos intervencionistas cardiovasculares percutáneos

Antecedentes La aparicion de complicaciones vasculares en los procedimientos cardiovasculares percutaneos conlleva una mayor morbilidad para el paciente, una prolongacion de la estancia hospitalaria y motiva un aumento de costes. Diversas variables clinicas y del procedimiento se han asociado como predictores de la aparicion de complicaciones vasculares, pero no existe informacion sobre que influencia ejercen variables relacionadas con la experiencia en el desarrollo de complicaciones vasculares. Objetivo El proposito de este estudio fue determinar el tipo e incidencia de complicaciones vasculares en pacientes sometidos a procedimientos cardiovasculares percutaneos, asi como identificar factores predictores y determinar la influencia de la experiencia profesional y la complejidad de la tecnica utilizada en la aparicion de estas complicaciones. Metodos y resultados Se incluyeron en el estudio 1.008 pacientes consecutivos sometidos a procedimientos cardiovasculares percutaneos (750 diagnosticos y 258 terapeuticos). El 70% eran varones con edad media de 63 ± 23 anos. Se produjeron un total de 55 complicaciones vasculares (5,6%): 36 hematomas (3,6%), 14 seudoaneurismas (1,4%), 2 fistulas arteriovenosas (0,2%), 2 episodios isquemicos en los miembros inferiores (0,2%) y un hematoma retroperitoneal (0,1%). Unicamente 28 pacientes presentaron complicaciones graves (2,8%). Por analisis multivariado, las variables asociadas con una mayor incidencia de complicaciones vasculares fueron la experiencia en la realizacion de la hemostasia (odds ratio [OR], 3,36; intervalo de confianza del 95% [IC del 95%], 1,37-8,22), el tratamiento previo con aspirina (OR, 2,69; IC del 95%, 1,31-5,52), la puncion en la arteria femoral izquierda (OR, 2,53; IC del 95%, 1-1,02), la permanencia del introductor mas de 60 min (OR, 1,02; IC del 95%, 1,01-1,04) y la duracion de la hemostasia mas de 30 min (OR, 1,01; IC del 95%, 1-1,02). Conclusiones Las complicaciones vasculares perifericas tras procedimientos cardiovasculares percutaneos son bajas y la mayoria relacionadas con aspectos del procedimiento que son potencialmente evitables con un adecuado plan de formacion y entrenamiento.

Síndrome de twiddler y fallo de sensado auricular

144 Mujer de 83 anos, hipertensa y obesa, que consulto por disnea. En urgencias presentaba un cuadro de insuficiencia cardiaca, y el electrocardiograma evidencio un bloqueo auriculoventricular completo. Se comenzo tratamiento medico y se implanto marcapasos VDD. Despues del procedimiento solo se hizo una radiografia de torax en proyeccion anteroposterior (fig. 1). El electrocardiograma objetivaba funcionamiento adecuado del marcapasos. Al dia siguiente, se observo un defecto de sensado auricular en los electrocardiogramas, manteniendose una adecuada estimulacion ventricular. Se intento reprogramar el marcapasos sin exito. Se practico una radiografia de torax posteroanterior, que puso de manifiesto una rotacion del generador (fig. 2). En la radiografia lateral se observaba un desplazamiento del cable que se introducia formando un bucle en la cava inferior, dejando alli el dipolo auricular (fig. 3). La punta del cable seguia fijada correctamente al apex del ventriculo derecho. Esto explicaba el defecto de sensado selectivo auricular. La enferma fue reintervenida colocandose correctamente el marcapasos, siendo finalmente dada de alta. El sindrome de twiddler se caracteriza por la disfuncion de un marcapasos1 o de un desfibrilador implantable tanto de localizacion abdominal2 como subpectoral3, secundaria a la rotacion de la bateria en su bolsa subcutanea, con el consecuente desplazamiento de los electrodos. La mayoria de los casos descritos se dan en mujeres mayores y con cierto grado de obesidad que, presumiblemente, tienen un tejido subcutaneo mas laxo4,5. El sindrome de twiddler, facilmente identificable en una radiografia de torax, debe ser considerado cuando se investiguen las causas de disfuncion de un marcapasos o de un desfibrilador implantable. IM A G E N E S E N CA R D I O L O G I A

Efectos renales y sistémicos en la prevención de la nefrotoxicidad por contraste con sueros salino (0,9%) e hiposalino (0,45%)

Introduction and objectives. Physiological and hypotonic saline solutions have been used interchangeably for preventing contrast media nephrotoxicity. No analysis of the possible differential effects of the 2 solutions on the milieu interieur or intercompartmental fluid volumes has been performed. Our aim was to study the systemic and renal effects of 2 types of saline solution regularly used to prevent contrast media nephrotoxicity in patients undergoing coronary angiography. Methods. Changes in electrolyte levels and volume distribution were studied in 71 individuals who were randomized to receive either 0.9% isotonic saline (n=36) or 0.45% hypotonic saline (n=35) during the 12 hours before and after contrast injection (2000 mL in each period). Results. The creatinine level was elevated equally often in the isotonic and hypotonic saline groups. Isotonic saline administration led to reductions in hemoglobin level, hematocrit, and plasma albumin level, and to increases in plasma volume, by 12.3% and 10.4% at 24 and 48 hours, respectively. These changes were significant compared with baseline measurements and compared with the group that received hypotonic saline. Neither of the 2 saline solutions resulted in a change in plasma atrial natriuretic peptide level. Plasma and urine osmolality decreased only with hypotonic saline. The increase in plasma creatinine level was similar with both isotonic and hypotonic saline. Conclusions. During standard therapy for preventing contrast media nephrotoxicity: a) isotonic saline, but not

DCM Integrated Double Buck-Boost led driver with reduced storage capacitance

This work proposes an approach for low frequency current ripple minimization in off-line light-emitting diode (LED) drivers. This strategy is based on the large signal modulation of the duty cycle of a LED converter so that the output ripple can be reduced and, consequently, the required filtering capacitances of the converter can be further decreased. The approach presented in this work is developed by defining a modulation function that allows for a reduction in the storage capacitance, and by analyzing the converter behavior when such function is applied to the driver. The design of the low-frequency filtering element of the converter is performed by using a graphical technique, which allows the designer to evaluate the behavior of the output current ripple and the input current distortion. The analysis is carried out for an Integrated Double Buck-Boost converter and experimental results are shown in order to demonstrate the validity of the proposal.

Analysis of the low-frequency output current ripple in a buck-based LED driver under distinct control techniques

Switched-mode DC-DC converters are used to regulate dc voltages or currents at a certain desired level. Due to inherent switching action, currents and voltages in the circuit tend to oscillate around a given average value, as the output values present some ripple in steady-state condition. The low-frequency output current ripple (OCR) is a key parameter for design considerations when a light-emitting diode (LED) string load is considered. In order to compare their ripple magnitudes under distinct conditions regarding a buck-based LED driver operating in continuous conduction mode (CCM), this paper analyzes the conventional voltage mode control as well as the peak-current mode control in order to compare its OCR responses by the classical control theory. The methods are implemented considering the same control bandwidth so that a proper comparison can be established.