Examinando por Autor "Contreras, R."

Mostrando 1 - 5 de 5
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    COVID-19: What Iodine Maps From Perfusion CT can reveal—A Prospective Cohort Study.
    (BioMed Central Ltd, 2020-10) Santamarina, M.G.; Boisier Riscal, D.; Beddings, I.; Contreras, R.; Baque, M.; Volpacchio, M.; Martinez Lomakin, F.
    Background: Subtraction CT angiography (sCTA) is a technique used to evaluate pulmonary perfusion based on iodine distribution maps. The aim of this study is to assess lung perfusion changes with sCTA seen in patients with COVID-19 pneumonia and correlate them with clinical outcomes. Material and methods: A prospective cohort study was carried out with 45 RT-PCR-confirmed COVID-19 patients that required hospitalization at three different hospitals, between April and May 2020. In all cases, a basic clinical and demographic profile was obtained. Lung perfusion was assessed using sCTA. Evaluated imaging features included: Pattern predominance of injured lung parenchyma in both lungs (ground-glass opacities, consolidation and mixed pattern) and anatomical extension; predominant type of perfusion abnormality (increased perfusion or hypoperfusion), perfusion abnormality distribution (focal or diffuse), extension of perfusion abnormalities (mild, moderate and severe involvement); presence of vascular dilatation and vascular tortuosity. All participants were followed-up until hospital discharge searching for the development of any of the study endpoints. These endpoints included intensive-care unit (ICU) admission, initiation of invasive mechanical ventilation (IMV) and death. Results: Forty-one patients (55.2 ± 16.5 years, 22 men) with RT-PCR-confirmed SARS-CoV-2 infection and an interpretable iodine map were included. Patients with perfusion anomalies on sCTA in morphologically normal lung parenchyma showed lower Pa/Fi values (294 ± 111.3 vs. 397 ± 37.7, p = 0.035), and higher D-dimer levels (1156 ± 1018 vs. 378 ± 60.2, p < 0.01). The main common patterns seen in lung CT scans were ground-glass opacities, mixed pattern with predominant ground-glass opacities and mixed pattern with predominant consolidation in 56.1%, 24.4% and 19.5% respectively. Perfusion abnormalities were common (36 patients, 87.8%), mainly hypoperfusion in areas of apparently healthy lung. Patients with severe hypoperfusion in areas of apparently healthy lung parenchyma had an increased probability of being admitted to ICU and to initiate IMV (HR of 11.9 (95% CI 1.55–91.9) and HR 7.8 (95% CI 1.05–61.1), respectively). Conclusion: Perfusion abnormalities evidenced in iodine maps obtained by sCTA are associated with increased admission to ICU and initiation of IMV in COVID-19 patients. [Figure not available: see fulltext.] © 2020, The Author(s).
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    Cytotoxic Effect of Puya chilensis Collected in Central Chile
    (SAGE Publications Inc., 2022-04) Echeverria-Echeverria, C.; Valderrama-Villarroel, A.; Ortega, M.; Contreras, R.; Zúñiga, G.; Alvarado-Soto, L.; Ramírez-Tagle, R.
    This study sought to evaluate the pharmacological activity of metabolites isolated from the dried and lyophilized ethanol extracts as well as other solvent fractions of the currently endangered Puya chilensis Molina (Chagual) by analyzing their effects on a human hepatocellular carcinoma (HCC) cell line. We identified several active metabolites from Chagual extracts and two, in particular, carnosol, were found in all the prepared fractions. In addition, Chagual exhibited considerable cytotoxicity against the cancer cell line used in this study, with a half-maximal inhibitory concentration (IC50) of 0.44 ± 0.11 and 0.27 ± 0.04 after a 72-hour treatment and, therefore, has the potential for further investigation as a source of candidate therapeutic agents.
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    Effect of electron-withdrawing substituents on the electrophilicity of carbonyl carbons
    (Elsevier, 2005-01) Contreras, R.; Andres, J.; Domingo, L.; Castillo, R.; Perez, P.
    The substituent effects on the carbonyl carbon atom for a series of twelve substituted phenyl acetates have been rationalized using a global electrophilicity index. This index is linearly correlated with the experimental reaction rate coefficients. We found that, in contrast to the proposed interpretation based on experimental 13C NMR chemical shifts and ground state destabilization calculations, the electrophilicity of carbonyl compounds increases due to the effect promoted by electron-withdrawing groups in these systems.
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    Hardness and softness kernels, and related indices in the spin polarized version of density functional theory
    (Elsevier, 2006-02) Guerra, D.; Contreras, R.; Perez, P.; Fuentealba, P.
    In this Letter, the mathematical expressions corresponding to the kernel, local and global spin softness have been derived, and their relationship with other indices have been explored. Introducing various spin kernels, the mathematical framework of the spin polarized version of the chemical reactivity indices have been completed. Furthermore, new linear response functions have been defined and their relationship with the softness hierarchy are exposed. Finally, the importance of some of these indices has been illustrated for the reactivity pattern of open shell molecules.
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    Local reactivity index as descriptor of benzene adsorption in cluster models of exchanged zeolite-Y
    (Elsevier, 2004-01) Santos, J.; Chamorro, E.; Contreras, R.; Fuentealba, P.
    The adsorption of benzene over sites I, II and III of Cu- and Na-exchanged zeolite-Y, has been studied using the energy profiles for the host-guess interaction, and electronic descriptors of reactivity such as the electronic chemical potential and a local σk index recently defined. Both, the energy and the reactivity index based models consistently complement each other to give a correct interpretation of the reactivity and selectivity patterns experimentally established for these systems.