5 research outputs found
Is loading a significantly influential factor in the development of lithic microwear? An experimental test using LSCM on basalt from Olduvai Gorge
Lithic microwear develops as a result of abrasive friction between a stone tool’s working edge and the surface of a worked material. Variation in the loading (i.e. force) applied to a stone tool during its use alters the amount of friction created between these two materials and should subsequently affect the level of any wear accrued. To date, however, no comprehensive account of the interaction between variable working loads and wear development has been undertaken. If such a relationship does exist, it may be possible to calculate the loading levels applied to stone tool artefacts during their use. Here, we use 30 basalt flakes knapped from raw materials collected in Olduvai Gorge, Tanzania, in a controlled experimental cutting task of standardized duration. Loading levels are recorded throughout with each flake being used with a predetermined load, ranging between 150 g and 4.5 kg. Laser scanning confocal microscopy (LSCM), coupled with the relative area (Srel) algorithm, is used to mathematically document the surface texture of the flakes to determine whether variation in loading does in fact significantly affect the amount of wear on the flake surfaces. Results indicate that working load does play a role in the development of lithic microwear; however, its interaction with other variables, including the naturally rough surface of basalt, may reduce the likelihood of its accurate determination on tools recovered from archaeological deposits
Fatores que afetam a ventilação com o reanimador manual autoinflável: uma revisão sistemática Factors affecting manual resuscitator use: a systematic review
OBJETIVO: O reanimador manual autoinflável é um dispositivo que fornece ventilação com pressão positiva. Pesquisas mostram que, apesar da padronização dos reanimadores manuais autoinfláveis pela American Society for Testing and Materials, diversos fatores afetam o desempenho da ventilação, porém, os resultados são conflitantes. O objetivo desse estudo foi verificar as evidências dos fatores que influenciam a ventilação pulmonar com reanimadores manuais infantil/adulto por meio de uma revisão sistemática da literatura. FONTES DE DADOS: Foram incluídos artigos indexados nas bases Medline, Lilacs e SciELO publicados entre janeiro de 1986 e março de 2011. Utilizaram-se as palavras-chaves: "reanimador manual", "ressuscitador manual", "ventilação manual", "ventilação com pressão positiva", em inglês e português, além de "bag-valve". SÍNTESE DOS DADOS: Foram selecionados 45 artigos, sendo a maioria experimental. Os trabalhos compararam os reanimadores manuais por marcas, modelos e analisaram as características dos profissionais que os utilizam. Estudos verificaram que a eficácia da ventilação com os reanimadores manuais depende da marca, modelo e características funcionais do aparelho utilizado, assim como formação, treinamento e experiência do profissional que os manipula. Outros fatores que podem influenciar são a forma de compressão dos reanimadores manuais, o uso da válvula limitadora de pressão e o fluxo de oxigênio fornecido aos aparelhos. CONCLUSÕES: A variabilidade nos parâmetros ventilatórios fornecidos durante a ventilação com reanimadores manuais não permite uniformizar a técnica, o que prejudica a reanimação cardiopulmonar. Apesar da maioria dos reanimadores manuais parecer estar de acordo com padrões internacionais, os equipamentos devem ser avaliados antes de utilizados no ambiente clínico. Pouco se sabe sobre os modelos pediátricos e neonatais.<br>OBJECTIVE: The manual resuscitator (RM) is a device that provides positive pressure ventilation. Surveys conducted to assess the adequacy of manual resuscitators to American Society for Testing and Materials standards show that several factors affect manual ventilation. However, results are conflicting. The aim of this study was to verify evidence of factors that influence pediatric/adult pulmonary ventilation with manual resuscitator by a systematic review. DATA SOURCE: Original articles indexed in Medline, Lilacs and SciELO published from January 1986 to March 2011. The key-words used were: "manual resuscitator", "manual ventilation", "positive pressure ventilation" in Portuguese and English, as well as "bag-valve". DATA SYNTHESIS: 45 articles were selected, most of them experimental. The studies compared manual resuscitator brands and models, and analyzed the physical characteristics of professionals. The effectiveness of ventilation with manual resuscitator depends on the brand, model and functional characteristics of the equipment. Ventilation also varies with the education, training and experience of the professional who handles the equipment. Other factors that can influence effectiveness are the manual resuscitator compression form, the use of a pressure relief valve and the flow of oxygen provided to the manual resuscitator. CONCLUSIONS: The variability of ventilatory parameters during manual resuscitation does not allow a standardization of the technique, being harmful to cardiopulmonary resuscitation. Although most manual resuscitator seem to follow international standards, the equipment must be evaluated in the clinical settings. There are few studies about pediatric and neonatal manual resuscitator models