Un bien escaso e imprescindible para la vida : el desafío de su preservación

Fil: Reyes Toso, Carlos F. Universidad de Buenos Aires. Facultad de Medicina; ArgentinaEl ser humano posee aproximadamente entre un 75% y un 45% de agua corporal total en su ciclo vital, en un equilibrio dinámico en el que los egresos son compensados con los ingresos. La realización de las diferentes funciones orgánicas lleva a la pérdida diaria de una importante cantidad de agua, cerca de dos litros. Este valor puede ampliarse considerablemente en condiciones climáticas adversas o al practicar actividades laborales o deportivas extenuantes. El organismo sólo es capaz de producir por óxido-reducción una pequeña cantidad de agua diariamente. Por esta razón, la única forma de cubrir este déficit es con el ingreso de agua, ya sea en forma líquida o formando parte de los alimentos

Oracle Complexity Reduction for Model-free LQR: A Stochastic Variance-Reduced Policy Gradient Approach

We investigate the problem of learning an $\epsilon$-approximate solution for the discrete-time Linear Quadratic Regulator (LQR) problem via a Stochastic Variance-Reduced Policy Gradient (SVRPG) approach. Whilst policy gradient methods have proven to converge linearly to the optimal solution of the model-free LQR problem, the substantial requirement for two-point cost queries in gradient estimations may be intractable, particularly in applications where obtaining cost function evaluations at two distinct control input configurations is exceptionally costly. To this end, we propose an oracle-efficient approach. Our method combines both one-point and two-point estimations in a dual-loop variance-reduced algorithm. It achieves an approximate optimal solution with only $O\left(\log\left(1/\epsilon\right)^{\beta}\right)$ two-point cost information for $\beta \in (0,1)$

Learning Personalized Models with Clustered System Identification

We address the problem of learning linear system models from observing multiple trajectories from different system dynamics. This framework encompasses a collaborative scenario where several systems seeking to estimate their dynamics are partitioned into clusters according to their system similarity. Thus, the systems within the same cluster can benefit from the observations made by the others. Considering this framework, we present an algorithm where each system alternately estimates its cluster identity and performs an estimation of its dynamics. This is then aggregated to update the model of each cluster. We show that under mild assumptions, our algorithm correctly estimates the cluster identities and achieves an approximate sample complexity that scales inversely with the number of systems in the cluster, thus facilitating a more efficient and personalized system identification process

Evaluación de la actividad antiulcerogénica de Atriplex undulata sobre estómagos de ratones administrados con Indometacina

La administración de antiinflamatorios no esteroides (AINEs) como la indometacina produce lesiones gástricas al disminuir los factores gastroprotectores. Para prevenir la formación de úlceras durante los tratamientos clínicos prolongados con AINEs, se administran en forma conjunta protectores gástricos como la ranitidina o el omeprazol. Estos compuestos pueden reducir sensiblemente las lesiones gástricas, pero producen efectos secundarios. Entre estos efectos, son de importancia clínica y productiva el aumento significativo de las bacterias gástricas. Este aumento predispone a que los animales sufran infecciones intestinales y diarreas, reduciendo la absorción de nutrientes y retrasando el desarrollo. Teniendo como objetivo buscar compuestos que reemplacen el uso de estos protectores gástricos, en este trabajo se evaluó la actividad antiulcerogénica de extractos hidroalcohólicos de Atriplex undulata. Los ensayos se llevaron a cabo provocando lesiones gástricas por estrés inducido por hipotermia e inmovilización y por administración de indometacina. La dosis de extracto hidroalchólico proveniente de 0,5 g de planta desecada resuspendida en carboximetilcelulosa previnieron en forma significativa (p≤0,05) la formación de úlceras en ratones sometidos a estrés y a estrés e indometacina. Estos resultados permitieron concluir que los extractos hidroalcohólicos de Atriplex undulata previenen las lesiones gástricas inducidas por estrés. Al someter a los ratones a estrés y a los efectos de la indometacina se determinó que también previenen significativamente (p≤0,05) la formación de úlceras en presencia de un AINE inhibidor de la síntesis de prostaglandinas. En estudios próximos, se realizarán ensayos clínicos para evaluar el potencial uso de fármacos elaborados a partir de Atriplex undulata como protectores gástricos durante los tratamientos prolongados con AINEs.&nbsp

Modelo experimental para evaluar compuestos gastroprotectores en ratones sometidos a estrés y tratados con indometacina

Se describe un modelo experimental para evaluar el efecto gastroprotector de extractos vegetales en ratones sometidos a estrés y administrados con antiinflamatorios no esteroides (AINEs). Este modelo experimental reproduce casos clínicos en los cuales los animales que sufren estrés por dolor durante procesos inflamatorios, traumáticos o quirúrgicos desarrollan lesiones gástricas que se agravan cuando son medicados con AINEs con el objetivo de disminuir la inflamación y el dolor. Frecuentemente se administran antisecretores para prevenir las lesiones en la mucosa gástrica. Para investigar nuevos fármacos gastroprotectores, con mayor eficacia y menores efectos colaterales en estos casos clínicos, se requiere de un modelo experimental que lo reproduzca. Para lograr este objetivo, en este trabajo se describe un protocolo que combina dos reconocidos modelos experimentales en ratones. Uno de ellos induce úlceras por estrés provocado por hipotermia e inmovilización y el otro produce daño gástrico por administración de indometacina. La combinación de ambos métodos en un solo ensayo permite observar que los animales sometidos a estrés y tratados con indometacina sufren mayor daño gástrico que los sometidos a estrés o administrados con indometacina respectivamente. Considerando que los mecanismos involucrados en el daño gástrico producido por estrés son distintos a los provocados por AINEs, el protocolo propuesto es adecuado para seleccionar drogas que protejan la mucosa gástrica en animales que sufren estrés por dolor y que están siendo tratados con AINEs

Upward displacement of the odontoid process into the foramen magnum: a palaeopathological case

An upward displacement of the odontoid process into the foramen magnum was observed in the skeletal remains of a young male unearthed from a 14th to 17th century cemetery in the north-eastern Italy. Examination of skull bone vestiges and computed tomography scan analysis of the axis exhibited a clear-cut contact zone between the odontoid process and the anterior border of the foramen magnum. In addition, the odontoid process appeared backward deviated. Findings suggest a possible diagnosis of basilar impression/invagination. This anomalous contact may cause compression of neural and vascular structures with a multifaceted series of clinical symptoms. We are unable to set our finding into a complete presumptive diagnostic outline because there is no chance to estimate either the magnitude of the whole craniovertebral junction defect but we believe that the present case contributes to the general knowledge of the craniovertebral region and to bone pathology in ancient times

Return and abort trajectory optimisation for reusable launch vehicles

Among the future space access vehicles, the lifting body spaceplane is the most promising approach to prevent damage to both the launcher and the payload in case of loss of thrust. The glide performances of the vehicle allow the recovery in both nominal and abort cases. The approach presented is used in the investigation of the unpowered descent paths of a sample vehicle through trajectory optimisation. The vehicle's downrange and crossrange limits are obtained for aborts in multiple flight conditions

Predictive value of hematological and phenotypical parameters on postchemotherapy leukocyte recovery

Background: Grade IV chemotherapy toxicity is defined as absolute neutrophil count <500/μL. The nadir is considered as the lowest neutrophil number following chemotherapy, and generally is not expected before the 7th day from the start of chemotherapy. The usual prophylactic dose of rHu-G-CSF (Filgrastim) is 300 μg/day, starting 24-48 h after chemotherapy until hematological recovery. However, individual patient response is largely variable, so that rHu-G-CSF doses can be different. The aim of this study was to verify if peripheral blood automated flow cytochemistry and flow cytometry analysis may be helpful in predicting the individual response and saving rHu-G-CSF. Methods: During Grade IV neutropenia, blood counts from 30 cancer patients were analyzed daily by ADVIA 120 automated flow cytochemistry analyzer and by Facscalibur flow cytometer till the nadir. "Large unstained cells" (LUCs), myeloperoxidase index (MPXI), blasts, and various cell subpopulations in the peripheral blood were studied. At nadir rHu-G-CSF was started and 81 chemotherapy cycles were analyzed. Cycles were stratified according to their number and to two dose-levels of rHuG-CSF needed to recovery (300-600 vs. 900-1200 μg) and analyzed in relation to mean values of MPXI and mean absolute number of LUCs in the nadir phase. The linear regressions of LUCs % over time in relation to two dose-levels of rHu-G-CSF and uni-multivariate analysis of lymphocyte subpopulations, CD34+ cells, MPXI, and blasts were also performed. Results: In the nadir phase, the increase of MPXI above the upper limit of normality (>10; median 27.7), characterized a slow hematological recovery. MPXI levels were directly related to the cycle number and inversely related to the absolute number of LUCs and CD34 +/CD45+ cells. A faster hematological recovery was associated with a higher LUC increase per day (0.56% vs. 0.25%), higher blast (median 36.7/μL vs. 19.5/μL) and CD34+/CD45+ cell (median 2.2/μL vs. 0.82/μL) counts. Conclusions: Our study showed that some biological indicators such as MPXI, LUCs, blasts, and CD34 +/CD45+ cells may be of clinical relevance in predicting individual hematological response to rHu-G-CSF. Special attention should be paid when nadir MPXI exceeds the upper limit of normality because the hematological recovery may be delayed. © 2009 Clinical Cytometry Society

Capitate-trapezoid synostosis: analysis of an Early Bronze Age case and review of the literature

Background: Carpal synostoses are congenital defects characterised by complete or incomplete coalition of two or more carpal bones. Although most of these defects are discovered only incidentally, sometimes they become clinically manifest. Among the different types of carpal coalition, the synostosis between capitate and trapezoid bones is quite rare, with only sparse data available in the literature. The aim of this report was to describe a case of capitate-trapezoid synostosis (CTS) observed in an ancient human skeleton, as well as to scrutinise the pertinent literature in order to assess for the characteristics of this type of defect, including its potential relevance to clinical practice. Materials and methods: We studied the skeletal remains of an Early Bronze Age male warrior affected by incomplete CTS. Macroscopic and radiological examination of the defect was carried out. We also performed a comprehensive PubMed search in the Medline and other specialty literature databases to retrieve and analyse data relevant to the subject under consideration. Results and Conclusions: The present case is the most ancient CTS ever found. In those literature-reported cases accompanied by careful anatomical description, such as the present one, incomplete coalition invariably occurs between the dorsal surfaces of the two bones, this characteristic emerging as a distinctive morphological trait. Literature analysis further suggests that the true prevalence of CTS is likely to be higher than estimates based on data gathered from radiology series, and that this defect may be associated with pain and carpal bossing more frequently than generally though