Browsing by Author "Valenzuela, Felipe"

Now showing 1 - 7 of 7
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    Comparison of LED- and LASER-based fNIRS technologies to record the human peri-spinal cord neurovascular response
    (2024) Caulier-Cisterna, Raill; Appelgren-Gonzales, Juan -Pablo; Oyarzun, Juan -Esteban; Valenzuela, Felipe; Sitaram, Ranganatha; Eblen-Zajjur, Antonio; Uribe, Sergio
    Recently, functional Near-Infrared Spectroscopy (fNIRS) was applied to obtain, non-invasively, the human peri-spinal Neuro-Vascular Response (NVR) under a non-noxious electrical stimulation of a peripheral nerve. This method allowed the measurements of changes in the concentration of oxyhemoglobin (O2Hb) and deoxyhemoglobin (HHb) from the peri-spinal vascular network. However, there is a lack of clarity about the potential differences in perispinal NVR recorded by the different fNIRS technologies currently available. In this work, the two main noninvasive fNIRS technologies were compared, i.e., LED and LASER-based. The recording of the human peri-spinal NVR induced by non-noxious electrical stimulation of a peripheral nerve was recorded simultaneously at C7 and T10 vertebral levels. The amplitude, rise time, and full width at half maximum duration of the perispinal NVRs were characterized in healthy volunteers and compared between both systems. The main difference was that the LED-based system shows about one order of magnitude higher values of amplitude than the LASER-based system. No statistical differences were found for rise time and for duration parameters (at thoracic level). The comparison of point-to-point wave patterns did not show significant differences between both systems. In conclusion, the peri-spinal NRV response obtained by different fNIRS technologies was reproducible, and only the amplitude showed differences, probably due to the power of the system which should be considered when assessing the human peri-spinal vascular network.
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    Coping with Natural Disasters and Urban Risk: An Approach to Urban Sustainability from Socio-Environmental Fragmentation and Urban Vulnerability Assessment
    (Emerald Group Publishing Limited, 2014) Link, Felipe; Barth, Katrin; Harris, Jordan Michael; Irarrazaval Irarrazaval, Felipe; Valenzuela, Felipe; Welz, Juliane; William G. Holt; CEDEUS (Chile)
    Purpose - Cities have been exposed to a variety of natural disasters such as flooding, extreme temperatures, storms, earthquakes, and other natural shocks, and have had to respond and adapt to such pressures over time. In the context of global climate change, natural disasters have increased across the globe. Apart from climate change, many urban environments in Latin America are experiencing significant transformations in land use patterns, socio-demographic change, changing labor markets, and economic growth, resulting from recent decades of globalization. Such transformations have resulted in the internal fragmentation of cities. In this context, the purpose of the present chapter is to demonstrate the importance in both theoretical and methodological terms, of integrating the concept of socio-environmental fragmentation into urban vulnerability research in order to make progress toward higher degrees of local sustainability in those areas of the city that suffer natural disasters and fragmentation. Methodology/approach - A mixed methods approach is used in order to combine different technical issues from urban and climate change studies. Findings - The findings are related to the importance of an integrated approach, regarding the complexity of urban life, and the relationship between the urban, the social, and the environmental phenomenon. Social implications - This chapter relates to the revisit of the current state of preparedness and to determine whether further adaptations are required. The authors understood that these kinds of mixed approaches are necessary in order to understand the new complexity of urban processes.
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    From Community to Public Familiarity: Neighborhood, Sociability, and Belonging in the Neoliberal City
    (SAGE PUBLICATIONS INC, 2021) Link, Felipe; Senoret, Andres; Valenzuela, Felipe
    Current urban neoliberalism processes have shaped and changed contemporary cities, including the local scale's built environment and social relations. This article aims to study how such transformations affect local sociability by analyzing the effects of neighborhoods' morphology and socio-demographic characteristics on different forms of interactions and how they affect the sense of belonging. Taking the Metropolitan Area of Santiago, Chile, as a case study, we gathered secondary data on urban morphology and surveyed ten neighborhoods to measure sociability patterns. The results obtained from multilevel logistic regression models show that time living in the neighborhood and public pedestrian space is the most critical factor affecting neighborhood sociability. Moreover, instead of local ties, public familiarity is the form of sociability with the most substantial effects on a sense of belonging. We conclude that recent neighborhoods, formed by neoliberal urbanization, tend to discourage neighborhood sociability and a sense of belonging.
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    Non-Invasive Functional Evaluation of the Human Spinal Cord by Assessing the Peri-Spinal Neurovascular Network With Near Infrared Spectroscopy
    (2021) Valenzuela, Felipe; Rana, Mohit; Sitaram, Ranganatha; Uribe, Sergio; Eblen-Zajjur, Antonio
    Current medical care lacks an effective functional evaluation for the spinal cord. Magnetic resonance imaging and computed tomography mainly provide structural information of the spinal cord, while spinal somatosensory evoked potentials are limited by a low signal to noise ratio. We developed a non-invasive approach based on near-infrared spectroscopy in dual-wavelength (760 and 850 nm for deoxy- or oxyhemoglobin respectively) to record the neurovascular response (NVR) of the peri-spinal vascular network at the 7th cervical and 10th thoracic vertebral levels of the spinal cord, triggered by unilateral median nerve electrical stimulation (square pulse, 5-10 mA, 5 ms, 1 pulse every 4 minutes) at the wrist. Amplitude, rise-time, and duration of NVR were characterized in 20 healthy participants. A single, painless stimulus was able to elicit a high signal-to-noise ratio and multi-segmental NVR (mainly from Oxyhemoglobin) with a fast rise time of 6.18 [4.4-10.4] seconds (median [Percentile 25-75]) followed by a slow decay phase for about 30 seconds toward the baseline. Cervical NVR was earlier and larger than thoracic and no left/right asymmetry was detected. Stimulus intensity/NVR amplitude fitted to a 2nd order function. The characterization and feasibility of the peri-spinal NVR strongly support the potential clinical applications for a functional assessment of spinal cord lesions.
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    Optimal length of triple therapy for H pylori eradication in a population with high prevalence of infection in Chile
    (BAISHIDENG PUBLISHING GROUP INC, 2007) Riquelme, Arnoldo; Soza, Alejandro; Pedreros, Cesar; Bustamante, Andrea; Valenzuela, Felipe; Otarola, Francisco; Abbott, Eduardo; Arellano, Marco; Medina, Brenda; Pattillo, Alejandro; Greig, Douglas; Arrese, Marco; Rollan, Antonio
    AIM: To compare the efficacy of 7-d versus 14-d triple therapy for the treatment of H pylori infection in Chile, with a prevalence of 73% in general population. METHODS: H pylori-infected patients diagnosed by rapid urease test, with non-ulcer dyspepsia or peptic ulcer disease were randomized to receive omeprazole 20 mg bid, amoxicillin 1 g bid, and clarithromycin 500 mg bid for 7 (OAC7) or 14 (OAC14) d. Primary outcome was eradication rate 6 wk after the treatment. Subgroup analysis was carried out considering the eradication rate among patients with or without peptic ulcer disease and eradication rate among smokers or non-smokers.
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    Segregation, structure and social composition of the metropolitan area of Santiago, Chile. Methodological complexity in the study of social differentiation in space
    (PONTIFICA UNIV CATOLICA CHILE, INST GEOGRAFIA, 2015) Link, Felipe; Valenzuela, Felipe; Fuentes, Luis
    The study of social differentiation in space requires significant theoretical and methodological definitions in order to address the complex relationship between space and society. In that regard, it is possible to identify different lines of research that claim to account for this relationship. The aim of this paper is to present an analysis of social differentiation in space in the metropolitan area of Santiago using socio- spatial typologies. The results indicate that, although it is possible to identify some general patterns that are similar when using different approaches, typology analysis can better address the social complexity of metropolitan space. Finally, this paper aims to account for the centrality of the variable occupation as a factor of social differentiation in the urban context.