915 resultados para Relative risk aversion
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BACKGROUND: Hirschsprung's disease is a congenital gut motility disorder, characterised by the absence of the enteric ganglion cells along the distal gut. The aim of this study was to describe the epidemiology of Hirschsprung's disease, including additional congenital anomalies, total prevalence, trends, and association with maternal age. METHODS: Cases of Hirschsprung's disease delivered during 1980 to 2009 notified to 31 European Surveillance of Congenital Anomaly registers formed the population-based case-series. Prevalence rates and 95% confidence intervals were calculated as the number of cases per 10,000 births. Multilevel Poisson regression was performed to investigate trends in prevalence, geographical variation and the association with maternal age. RESULTS: There were 1,322 cases of Hirschsprung's disease among 12,146,210 births. The total prevalence was 1.09 (95% confidence interval, 1.03-1.15) per 10,000 births and there was a small but significant increase in prevalence over time (relative risk = 1.01; 95% credible interval, 1.00-1.02; p = 0.004). There was evidence of geographical heterogeneity in prevalence (p < 0.001). Excluding 146 (11.0%) cases with chromosomal anomalies or genetic syndromes, there were 1,176 cases (prevalence = 0.97; 95% confidence interval, 0.91-1.03 per 10,000 births), of which 137 (11.6%) had major structural anomalies. There was no evidence of a significant increased risk of Hirschsprung's disease in cases born to women aged ≥35 years compared with those aged 25 to 29 (relative risk = 1.09; 95% credible interval, 0.91-1.31; p = 0.355). CONCLUSION: This large population-based study found evidence of a small increasing trend in Hirschsprung's disease and differences in prevalence by geographic location. There was also no evidence of an association with maternal age. Birth Defects Research (Part A), 100:695-702, 2014. © 2014 Wiley Periodicals, Inc.
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El presente trabajo traslada el debate académico alrededor del mayor riesgo de pobreza que afrontan las mujeres en relación a los hombres al contexto español. Tras una breve revisión bibliográfica de los datos disponibles sobre la pobreza femenina en países industrializados y sus posibles causantes, se ponen a prueba esos mismos factores potencialmente culpables en el caso español. Del EU-SILC de 2010 se ha sacado una muestra formada únicamente por mujeres y hombres que o bien viven solos o con hijos a su cargo y, partiendo de ella, el método de la regresión logística ha concluido que hay factores exclusivamente explicativos de la pobreza femenina. Ser madre soltera, ser joven (entre 16 y 25 años) y no haber nacido en España tienen una importante capacidad explicativa de la pobreza femenina mientras no son significativas como explicación de la pobreza masculina. Si a estos factores añadimos no tener un trabajo, un bajo logro educativo y no recibir ningún subsidio individual, obtenemos un conjunto de factores que explican un 26.8% de los casos de mujeres españolas pobres que viven solas o son madres solteras. Estos datos ponen de relieve la necesidad de más investigaciones al respecto que consigan un mayor poder explicativo.
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BACKGROUND: Cytomegalovirus (CMV), human herpesvirus-6 and -7 (HHV-6 and -7) are beta-herpesviruses that commonly reactivate and have been proposed to trigger acute rejection and chronic allograft injury. We assessed the contribution of these viruses in the development of bronchiolitis obliterans syndrome (BOS) after lung transplantation. METHODS: Quantitative real-time polymerase chain reaction of bronchoalveolar lavage samples were performed for CMV, HHV-6 and -7 in a prospective cohort of lung transplant recipients. A time-dependent Cox regression analysis was used to correlate the risk of BOS and acute rejection in patients with and without beta-herpesviruses infection. RESULTS: Ninety-three patients were included in the study over a period of 3 years. A total of 581 samples from bronchoalveolar lavage were obtained. Sixty-one patients (65.6%) had at least one positive result for one of the beta-herpesviruses: 48 patients (51.6%) for CMV and 19 patients (20.4%) for both HHV-6 and -7. Median peak viral load was 3419 copies/mL for CMV, 258 copies/mL for HHV-6, and 665 copies/mL for HHV-7. Acute rejection (>or=grade 2) occurred in 46.2% and BOS (>or=stage 1) in 19.4% of the patients. In the Cox regression model the relative risk of acute rejection or BOS was not increased in patients with any beta-herpesviruses reactivation. Acute rejection was the only independently associated risk factor for BOS. CONCLUSIONS: In lung transplant recipients receiving prolonged antiviral prophylaxis, reactivation of beta-herpesviruses within the allograft was common. However, despite high viral loads in many patients, virus replication was not associated with the development of rejection or BOS.
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Dans cette thèse, nous étudions les aspects comportementaux d'agents qui interagissent dans des systèmes de files d'attente à l'aide de modèles de simulation et de méthodologies expérimentales. Chaque période les clients doivent choisir un prestataire de servivce. L'objectif est d'analyser l'impact des décisions des clients et des prestataires sur la formation des files d'attente. Dans un premier cas nous considérons des clients ayant un certain degré d'aversion au risque. Sur la base de leur perception de l'attente moyenne et de la variabilité de cette attente, ils forment une estimation de la limite supérieure de l'attente chez chacun des prestataires. Chaque période, ils choisissent le prestataire pour lequel cette estimation est la plus basse. Nos résultats indiquent qu'il n'y a pas de relation monotone entre le degré d'aversion au risque et la performance globale. En effet, une population de clients ayant un degré d'aversion au risque intermédiaire encoure généralement une attente moyenne plus élevée qu'une population d'agents indifférents au risque ou très averses au risque. Ensuite, nous incorporons les décisions des prestataires en leur permettant d'ajuster leur capacité de service sur la base de leur perception de la fréquence moyenne d'arrivées. Les résultats montrent que le comportement des clients et les décisions des prestataires présentent une forte "dépendance au sentier". En outre, nous montrons que les décisions des prestataires font converger l'attente moyenne pondérée vers l'attente de référence du marché. Finalement, une expérience de laboratoire dans laquelle des sujets jouent le rôle de prestataire de service nous a permis de conclure que les délais d'installation et de démantèlement de capacité affectent de manière significative la performance et les décisions des sujets. En particulier, les décisions du prestataire, sont influencées par ses commandes en carnet, sa capacité de service actuellement disponible et les décisions d'ajustement de capacité qu'il a prises, mais pas encore implémentées. - Queuing is a fact of life that we witness daily. We all have had the experience of waiting in line for some reason and we also know that it is an annoying situation. As the adage says "time is money"; this is perhaps the best way of stating what queuing problems mean for customers. Human beings are not very tolerant, but they are even less so when having to wait in line for service. Banks, roads, post offices and restaurants are just some examples where people must wait for service. Studies of queuing phenomena have typically addressed the optimisation of performance measures (e.g. average waiting time, queue length and server utilisation rates) and the analysis of equilibrium solutions. The individual behaviour of the agents involved in queueing systems and their decision making process have received little attention. Although this work has been useful to improve the efficiency of many queueing systems, or to design new processes in social and physical systems, it has only provided us with a limited ability to explain the behaviour observed in many real queues. In this dissertation we differ from this traditional research by analysing how the agents involved in the system make decisions instead of focusing on optimising performance measures or analysing an equilibrium solution. This dissertation builds on and extends the framework proposed by van Ackere and Larsen (2004) and van Ackere et al. (2010). We focus on studying behavioural aspects in queueing systems and incorporate this still underdeveloped framework into the operations management field. In the first chapter of this thesis we provide a general introduction to the area, as well as an overview of the results. In Chapters 2 and 3, we use Cellular Automata (CA) to model service systems where captive interacting customers must decide each period which facility to join for service. They base this decision on their expectations of sojourn times. Each period, customers use new information (their most recent experience and that of their best performing neighbour) to form expectations of sojourn time at the different facilities. Customers update their expectations using an adaptive expectations process to combine their memory and their new information. We label "conservative" those customers who give more weight to their memory than to the xiv Summary new information. In contrast, when they give more weight to new information, we call them "reactive". In Chapter 2, we consider customers with different degree of risk-aversion who take into account uncertainty. They choose which facility to join based on an estimated upper-bound of the sojourn time which they compute using their perceptions of the average sojourn time and the level of uncertainty. We assume the same exogenous service capacity for all facilities, which remains constant throughout. We first analyse the collective behaviour generated by the customers' decisions. We show that the system achieves low weighted average sojourn times when the collective behaviour results in neighbourhoods of customers loyal to a facility and the customers are approximately equally split among all facilities. The lowest weighted average sojourn time is achieved when exactly the same number of customers patronises each facility, implying that they do not wish to switch facility. In this case, the system has achieved the Nash equilibrium. We show that there is a non-monotonic relationship between the degree of risk-aversion and system performance. Customers with an intermediate degree of riskaversion typically achieve higher sojourn times; in particular they rarely achieve the Nash equilibrium. Risk-neutral customers have the highest probability of achieving the Nash Equilibrium. Chapter 3 considers a service system similar to the previous one but with risk-neutral customers, and relaxes the assumption of exogenous service rates. In this sense, we model a queueing system with endogenous service rates by enabling managers to adjust the service capacity of the facilities. We assume that managers do so based on their perceptions of the arrival rates and use the same principle of adaptive expectations to model these perceptions. We consider service systems in which the managers' decisions take time to be implemented. Managers are characterised by a profile which is determined by the speed at which they update their perceptions, the speed at which they take decisions, and how coherent they are when accounting for their previous decisions still to be implemented when taking their next decision. We find that the managers' decisions exhibit a strong path-dependence: owing to the initial conditions of the model, the facilities of managers with identical profiles can evolve completely differently. In some cases the system becomes "locked-in" into a monopoly or duopoly situation. The competition between managers causes the weighted average sojourn time of the system to converge to the exogenous benchmark value which they use to estimate their desired capacity. Concerning the managers' profile, we found that the more conservative Summary xv a manager is regarding new information, the larger the market share his facility achieves. Additionally, the faster he takes decisions, the higher the probability that he achieves a monopoly position. In Chapter 4 we consider a one-server queueing system with non-captive customers. We carry out an experiment aimed at analysing the way human subjects, taking on the role of the manager, take decisions in a laboratory regarding the capacity of a service facility. We adapt the model proposed by van Ackere et al (2010). This model relaxes the assumption of a captive market and allows current customers to decide whether or not to use the facility. Additionally the facility also has potential customers who currently do not patronise it, but might consider doing so in the future. We identify three groups of subjects whose decisions cause similar behavioural patterns. These groups are labelled: gradual investors, lumpy investors, and random investor. Using an autocorrelation analysis of the subjects' decisions, we illustrate that these decisions are positively correlated to the decisions taken one period early. Subsequently we formulate a heuristic to model the decision rule considered by subjects in the laboratory. We found that this decision rule fits very well for those subjects who gradually adjust capacity, but it does not capture the behaviour of the subjects of the other two groups. In Chapter 5 we summarise the results and provide suggestions for further work. Our main contribution is the use of simulation and experimental methodologies to explain the collective behaviour generated by customers' and managers' decisions in queueing systems as well as the analysis of the individual behaviour of these agents. In this way, we differ from the typical literature related to queueing systems which focuses on optimising performance measures and the analysis of equilibrium solutions. Our work can be seen as a first step towards understanding the interaction between customer behaviour and the capacity adjustment process in queueing systems. This framework is still in its early stages and accordingly there is a large potential for further work that spans several research topics. Interesting extensions to this work include incorporating other characteristics of queueing systems which affect the customers' experience (e.g. balking, reneging and jockeying); providing customers and managers with additional information to take their decisions (e.g. service price, quality, customers' profile); analysing different decision rules and studying other characteristics which determine the profile of customers and managers.
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BACKGROUND: Secondary prevention programs for patients experiencing an acute coronary syndrome have been shown to be effective in the outpatient setting. The efficacy of in-hospital prevention interventions administered soon after acute cardiac events is unclear. We performed a systematic review and meta-analysis to determine whether in-hospital, patient-level interventions targeting multiple cardiovascular risk factors reduce all-cause mortality after an acute coronary syndrome. METHODS AND RESULTS: Using a prespecified search strategy, we included controlled clinical trials and before-after studies of secondary prevention interventions with at least a patient-level component (ie, education, counseling, or patient-specific order sets) initiated in hospital with outcomes of mortality, readmission, or reinfarction rates in acute coronary syndrome patients. We classified the interventions as patient-level interventions with or without associated healthcare provider-level interventions and/or system-level interventions. Twenty-six studies met our inclusion criteria. The summary estimate of 14 studies revealed a relative risk of all-cause mortality of 0.79 (95% CI, 0.69 to 0.92; n=37,585) at 1 year. However, the apparent benefit depended on study design and level of intervention. The before-after studies suggested reduced mortality (relative risk [RR], 0.77; 95% CI, 0.66 to 0.90; n=3680 deaths), whereas the RR was 0.96 (95% CI, 0.64 to 1.44; n=99 deaths) among the controlled clinical trials. Only interventions including a provider- or system-level intervention suggested reduced mortality compared with patient-level-only interventions. CONCLUSIONS: The evidence for in-hospital, patient-level interventions for secondary prevention is promising but not definitive because only before-after studies suggest a significant reduction in mortality. Future research should formally test which components of interventions provide the greatest benefit.
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BACKGROUND: Efavirenz and abacavir are components of recommended first-line regimens for HIV-1 infection. We used genome-wide genotyping and clinical data to explore genetic associations with virologic failure among patients randomized to efavirenz-containing or abacavir-containing regimens in AIDS Clinical Trials Group (ACTG) protocols. PARTICIPANTS AND METHODS: Virologic response and genome-wide genotype data were available from treatment-naive patients randomized to efavirenz-containing (n=1596) or abacavir-containing (n=786) regimens in ACTG protocols 384, A5142, A5095, and A5202. RESULTS: Meta-analysis of association results across race/ethnic groups showed no genome-wide significant associations (P<5×10) with virologic response for either efavirenz or abacavir. Our sample size provided 80% power to detect a genotype relative risk of 1.8 for efavirenz and 2.4 for abacavir. Analyses focused on CYP2B genotypes that define the lowest plasma efavirenz exposure stratum did not show associations nor did analysis limited to gene sets predicted to be relevant to efavirenz and abacavir disposition. CONCLUSION: No single polymorphism is associated strongly with virologic failure with efavirenz-containing or abacavir-containing regimens. Analyses to better consider context, and that minimize confounding by nongenetic factors, may show associations not apparent here.
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The purpose of this meta-analysis was to examine the efficacy of maintenance treatments for bipolar disorder. Placebo-controlled or active comparator bipolar maintenance clinical trials of ≥6 months' duration with at least 15 patients/treatment group were identified using Medline, EMBASE, clinicaltrials.gov, and Cochrane databases (1993 to July 2010). The main outcome measure was relative risk for relapse for patients in remission. Twenty trials (5,364 patients) were identified. Overall, lithium and quetiapine were the most studied agents (eight and five trials, respectively). The majority of studies included patients who had previously responded to treatment for an acute episode. All interventions, with the exception of perphenazine+mood stabilizer, showed a relative risk for manic/mixed or depressive relapse below 1.0, although there was variation in the statistical significance of the findings vs. placebo. No monotherapy was associated with a significantly reduced risk for both manic/mixed and depressed relapse. Of the combination treatments, only quetiapine+lithium/divalproex, was associated with a significantly reduced risk vs. comparator (placebo+lithium/valproate) for relapse at both the manic/mixed and depressed poles of bipolar illness. Limitations for the analysis include differences in study durations and definitions of relapse. In conclusion, available maintenance therapies show considerable variation in efficacy. The efficacy of lithium and divalproex has been confirmed, but newer therapies, such as a number of atypical antipsychotics were also shown to be effective in bipolar disorder. Efficacy of all maintenance interventions needs to be balanced against the safety and tolerability profiles of individual agents.
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BACKGROUND: Ischemic stroke is the leading cause of mortality worldwide and a major contributor to neurological disability and dementia. Terutroban is a specific TP receptor antagonist with antithrombotic, antivasoconstrictive, and antiatherosclerotic properties, which may be of interest for the secondary prevention of ischemic stroke. This article describes the rationale and design of the Prevention of cerebrovascular and cardiovascular Events of ischemic origin with teRutroban in patients with a history oF ischemic strOke or tRansient ischeMic Attack (PERFORM) Study, which aims to demonstrate the superiority of the efficacy of terutroban versus aspirin in secondary prevention of cerebrovascular and cardiovascular events. METHODS AND RESULTS: The PERFORM Study is a multicenter, randomized, double-blind, parallel-group study being carried out in 802 centers in 46 countries. The study population includes patients aged > or =55 years, having suffered an ischemic stroke (< or =3 months) or a transient ischemic attack (< or =8 days). Participants are randomly allocated to terutroban (30 mg/day) or aspirin (100 mg/day). The primary efficacy endpoint is a composite of ischemic stroke (fatal or nonfatal), myocardial infarction (fatal or nonfatal), or other vascular death (excluding hemorrhagic death of any origin). Safety is being evaluated by assessing hemorrhagic events. Follow-up is expected to last for 2-4 years. Assuming a relative risk reduction of 13%, the expected number of primary events is 2,340. To obtain statistical power of 90%, this requires inclusion of at least 18,000 patients in this event-driven trial. The first patient was randomized in February 2006. CONCLUSIONS: The PERFORM Study will explore the benefits and safety of terutroban in secondary cardiovascular prevention after a cerebral ischemic event.
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BACKGROUND: At least 2 apparently independent mechanisms, microsatellite instability (MSI) and chromosomal instability, are implicated in colorectal tumorigenesis. Their respective roles in predicting clinical outcomes of patients with T3N0 colorectal cancer remain unknown. METHODS: Eighty-eight patients with a sporadic T3N0 colon or rectal adenocarcinoma were followed up for a median of 67 months. For chromosomal instability analysis, Ki-ras mutations were determined by single-strand polymerase chain reaction, and p53 protein staining was studied by immunohistochemistry. For MSI analysis, DNA was amplified by polymerase chain reaction at 7 microsatellite targets (BAT25, BAT26, D17S250, D2S123, D5S346, transforming growth factor receptor II, and BAX). RESULTS: Overall 5-year survival rate was 72%. p53 protein nuclear staining was detected in 39 patients (44%), and MSI was detected in 21 patients (24%). MSI correlated with proximal location (P <.001) and mucinous content (P <.001). In a multivariate analysis, p53 protein expression carried a significant risk of death (relative risk = 4.0, 95% CI = 1.6 to 10.1, P =.004). By comparison, MSI was not a statistically significant prognostic factor for survival in this group (relative risk = 2.2, 95% CI = 0.6 to 7.3, P =.21). CONCLUSIONS: p53 protein overexpression provides better prognostic discrimination than MSI in predicting survival of patients with T3N0 colorectal cancer. Although MSI is associated with specific clinicopathologic parameters, it did not predict overall survival in this group. Assessment of p53 protein expression by immunocytochemistry provides a simple means to identify a subset of T3N0 patients with a 4-times increased risk for death.
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El presente artículo pretende ampliar el modelo original de SANDMO (Journal of Public Economics, 1981 , Vol. 16), relativo a evasión e imposición óptima, en dos direcciones. De un lado, haciendo extensivo el marco de preferencias redistributivas hacia otros objetivos sociales distintos del utilitarista; asimismo, permitiendo el que los sujetos no defraudadores puedan diferir entre sí, de acuerdo con la bibliografía más corriente sobre el tema, por razón de la capacidad productiva que posean en el mercado de trabajo. Dichas modificaciones, además de deslindar los aspectos de aversión al riesgo de lo que propiamente es el grado de concavidad de la función de bienestar, facilitan una más completa descripción del modo como operan los factores que inciden en la conducta del contribuyente.
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Background: Current guidelines for patients with moderate- or high-risk acute coronary syndromes recommend an early invasive approach with concomitant antithrombotic therapy, including aspirin, clopidogrel, unfractionated or low-molecular-weight heparin, and glycoprotein IIb/IIIa inhibitors. We evaluated the role of thrombin-specific anticoagulation with bivalirudin in such patients. Methods: We assigned 13,819 patients with acute coronary syndromes to one of three antithrombotic regimens: unfractionated heparin or enoxaparin plus a glycoprotein IIb/IIIa inhibitor, bivalirudin plus a glycoprotein IIb/IIIa inhibitor, or bivalirudin alone. The primary end points were a composite ischemia end point (death, myocardial infarction, or unplanned revascularization for ischemia), major bleeding, and the net clinical outcome, defined as the combination of composite ischemia or major bleeding. Results: Bivalirudin plus a glycoprotein IIb/IIIa inhibitor, as compared with heparin plus a glycoprotein IIb/IIIa inhibitor, was associated with noninferior 30-day rates of the composite ischemia end point (7.7% and 7.3%, respectively), major bleeding (5.3% and 5.7%), and the net clinical outcome end point (11.8% and 11.7%). Bivalirudin alone, as compared with heparin plus a glycoprotein IIb/IIIa inhibitor, was associated with a noninferior rate of the composite ischemia end point (7.8% and 7.3%, respectively; P = 0.32; relative risk, 1.08; 95% confidence interval [CI], 0.93 to 1.24) and significantly reduced rates of major bleeding (3.0% vs. 5.7%; P<0.001; relative risk, 0.53; 95% CI, 0.43 to 0.65) and the net clinical outcome end point (10.1% vs. 11.7%; P = 0.02; relative risk, 0.86; 95% CI, 0.77 to 0.97). Conclusions: In patients with moderate- or high-risk acute coronary syndromes who were undergoing invasive treatment with glycoprotein IIb/IIIa inhibitors, bivalirudin was associated with rates of ischemia and bleeding that were similar to those with heparin. Bivalirudin alone was associated with similar rates of ischemia and significantly lower rates of bleeding. (ClinicalTrials.gov number, NCT00093158.)
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Biller-Andorno and Jüni (2014), in a widely debated commentary published in the May 22 issue of the New England Journal of Medicine, accept the concept that mammography every 2 years from age 50 can decrease breast cancer mortality by 20%, that is, from five to four deaths per 1000 women over a 10-year period. Both the absolute and the relative risk of breast cancer death may vary depending on the baseline mortality rates in various populations and on the impact of screening mammography in reducing breast cancer mortality, which may well vary around the 20% estimate adopted. We accept, therefore, that there are still uncertainties in the absolute and relative impact of mammography screening on breast cancer mortality, given the different study schemes and mammography intervals, the differences in populations, and the continuous improvements in technology (Warner, 2011; Independent UK Panel on Breast Cancer Screening, 2012). We also agree on the observation that mammography has an appreciable impact on breast cancer mortality (Bosetti et al., 2012), but clearly a much smaller one on total mortality.
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OBJECTIVES: Therapeutic coma is advocated in guidelines for management of refractory status epilepticus; this is, however, based on weak evidence. We here address the specific impact of therapeutic coma on status epilepticus outcome. DESIGN: Retrospective assessment of a prospectively collected cohort. SETTING: Academic hospital. PATIENTS: Consecutive adults with incident status epilepticus lasting greater than or equal to 30 minutes, admitted between 2006 and 2013. MEASUREMENTS AND MAIN RESULTS: We recorded prospectively demographics, clinical status epilepticus features, treatment, and outcome at discharge and retrospectively medical comorbidities, hospital stay, and infectious complications. Associations between potential predictors and clinical outcome were analyzed using multinomial logistic regressions. Of 467 patients with incident status epilepticus, 238 returned to baseline (51.1%), 162 had new disability (34.6%), and 67 died (14.3%); 50 subjects (10.7%) were managed with therapeutic coma. Therapeutic coma was associated with poorer outcome in the whole cohort (relative risk ratio for new disability, 6.86; 95% CI, 2.84-16.56; for mortality, 9.10; 95% CI, 3.17-26.16); the effect was more important in patients with complex partial compared with generalized convulsive or nonconvulsive status epilepticus in coma. Prevalence of infections was higher (odds ratio, 3.81; 95% CI, 1.66-8.75), and median hospital stay in patients discharged alive was longer (16 d [range, 2-240 d] vs 9 d [range, 1-57 d]; p < 0.001) in subjects managed with therapeutic coma. CONCLUSIONS: This study provides class III evidence that therapeutic coma is associated with poorer outcome after status epilepticus; furthermore, it portends higher infection rates and longer hospitalizations. These data suggest caution in the straightforward use of this approach, especially in patients with complex partial status epilepticus.
Reasons to use e-cigarettes and associations with other substances among adolescents in Switzerland.
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BACKGROUND: The objectives of this research were to describe the main reason(s) why adolescents use electronic cigarettes, to assess how e-cigarette experimenters and users differ based on personal characteristics, and to determine whether its use is associated with the use of other substances among a representative sample of youths in Switzerland. METHODS: A representative sample of 621 youths (308 females) was divided into never users (n=353), experimenters (Only once, n=120) and users (Several times, n=148) of e-cigarettes. Groups were compared on socio-demographic data and current smoking, alcohol misuse and cannabis use. Reasons for e-cigarette use were compared between experimenters and users. A multinomial regression was performed using never users as the reference category. RESULTS: Forty-three percent had ever tried e-cigarettes, and the main reason was curiosity. Compared to never users, experimenters were more likely to be out of school (Relative Risk Ratio [RRR]: 2.68) and to misuse alcohol (RRR: 2.08), while users were more likely to be male (RRR: 2.75), to be vocational students (RRR: 2.30) or out of school (RRR: 3.48) and to use any of the studied substances (tobacco, RRR: 5.26; alcohol misuse, RRR: 2.71; cannabis use, RRR: 30.2). CONCLUSIONS: Although often still part of adolescent experimentation, e-cigarettes are becoming increasingly popular among adolescents and they should become part of health providers' standard substance use screening. As health providers (and especially paediatricians) do not seem to have high levels of knowledge and, consequently, little comfort in discussing e-cigarettes, training in this domain should be available to them.
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OBJETIVO: Os objetivos deste trabalho são: a) avaliar os procedimentos radiográficos e estimar o valor do kerma no ar na superfície de entrada nos recém-nascidos prematuros submetidos a exames de tórax e abdome, realizados no setor de neonatologia de um hospital público de Belo Horizonte; b) estimar as doses nos órgãos e os respectivos riscos de ocorrência de câncer nesses órgãos em decorrência das exposições à radiação. MATERIAIS E MÉTODOS: Foram analisados os prontuários dos pacientes internados no setor de neonatologia desse hospital durante o período de maio a setembro de 2004, anotando-se os dados antropométricos, data de internação/alta, exames de raios X realizados. O kerma no ar na superfície de entrada foi determinado a partir do rendimento do tubo de raios X e dos parâmetros de irradiação utilizados nos exames. As doses nos órgãos foram estimadas com o software PCXMC e o risco, durante o restante da expectativa de vida, com o software IREP. RESULTADOS: O valor médio do kerma no ar na superfície de entrada por exame foi abaixo do nível de referência da publicação da Comunidade Européia. Para o paciente mais severamente irradiado, os órgãos mais suscetíveis à ocorrência de câncer foram fígado, mama e estômago, com valores máximos de excess relative risk, respectivamente, de 3,4%, 2,3% e 1,7%. CONCLUSÃO: Foi constatada a necessidade de otimização dos procedimentos radiográficos com vista à diminuição do risco para os recém-nascidos, que apesar de ser considerado baixo (comparativamente ao benefício), deve ser sempre diminuído para valores tão baixos quanto razoavelmente exeqüíveis.