Infective endocarditis in intravenous drug abusers: an update

Infective endocarditis despite advances in diagnosis remains a common cause of hospitalization, with high morbidity and mortality rates. Through literature review it is possible to conclude that polymicrobial endocarditis occurs mainly in intravenous drug abusers with predominance in the right side of the heart, often with tricuspid valve involvement. This fact can be associated with the type of drug used by the patients; therefore, knowledge of the patient's history is critical for adjustment of the therapy. It is also important to emphasize that the most common combinations of organisms in polymicrobial infective endocarditis are: Staphylococcus aureus, Streptococcus pneumonia and Pseudomonas aeruginosa, as well as mixed cultures of Candida spp. and bacteria. A better understanding of the epidemiology and associated risk factors are required in order to develop an efficient therapy, although PE studies are difficult to perform due to the rarity of cases and lack of prospective cohorts.This work was supported by Portuguese Foundation for Science and Technology (FCT) through the grants SFRH/BPD/47693/2008, SFRH/BPD/20987/2004 and SFRH/BPD/72632/2010 attributed to Claudia Sousa, Claudia Botelho and Diana Rodrigues, respectively

On the optically thick winds of Wolf-Rayet stars

(abridged) The strong winds of Wolf-Rayet (WR) stars are important for the mechanical and chemical feedback of the most massive stars and determine whether they end their lives as neutron stars or black holes. In this work we investigate theoretically the mass-loss properties of H-free WR stars of the nitrogen sequence (WN stars). We connect stellar structure models for He stars with wind models for optically-thick winds and assess how both types of models can simultaneously fulfill their respective sonic-point conditions. Fixing the outer wind law and terminal wind velocity, we obtain unique solutions for the mass-loss rates of optically-thick, radiatively-driven winds of WR stars in the phase of core He-burning. The resulting mass-loss relations as a function of stellar parameters, agree well with previous empirical relations. Furthermore, we encounter stellar mass limits below which no continuous solutions exist. While these mass limits agree with observations of WR stars in the Galaxy, they are in conflict with observations in the LMC. While our results confirm in particular the slope of oft-used empirical mass-loss relations, they imply that only part of the observed WN population can be understood in the framework of the standard assumptions of a smooth transonic flow and compact stellar core. This means that alternative approaches, such as a clumped and inflated wind structure, or deviations from the diffusion limit at the sonic point may have to be invoked. Qualitatively, the existence of mass limits for the formation of WR-type winds may be relevant for the non-detection of low-mass WR stars in binary systems, which are believed to be progenitors of Type Ib/c supernovae. The sonic-point conditions derived in this work may provide a possibility to include optically-thick winds in stellar evolution models in a more physically motivated form than in current models.Comment: accepted by Astronomy & Astrophysic