Analysis of current density and related parameters in spinal cord stimulation

A volume conductor model of the spinal cord and surrounding anatomical structures is used to calculate current (and current density) charge per pulse, and maximum charge density per pulse at the contact surface of the electrode in the dorsal epidural space, in the dorsal columns of the spinal cord and in the dorsal roots. The effects of various contact configurations (mono-, bi-, and tripole), contact area and spacing, pulsewidth and distance between contacts and spinal cord on these electrical parameters were investigated under conditions similar to those in clinical spinal cord stimulation. At the threshold stimulus of a large dorsal column fiber, current density and charge density per pulse at the contact surface were found to be highest (1.9·105 ¿A/cm2 and 39.1 ¿C/cm2 ·p, respectively) when the contact surface was only 0.7 mm 2. When stimulating with a pulse of 500 ¿s, highest charge per pulse (0.92 ¿C/p), and the largest charge density per pulse in the dorsal columns (1.59 ¿C/cm2·p) occurred. It is concluded that of all stimulation parameters that can be selected freely, only pulsewidth affects the charge and charge density per pulse in the nervous tissue, whereas both pulsewidth and contact area strongly affect these parameters in the nonnervous tissue neighboring the electrode contact

Vaccine Myths: Setting the Record Straight

Despite their standing as one of the most remarkable public health achievements, vaccines have been surrounded by dangerous myths since the development of the smallpox vaccine in the 18th century. In recent decades, with the publication of a fraudulent article linking vaccines to autism, the involvement of celebrities in the debate, and the rise of the internet and social media as sources for information for patients, these myths have become more widespread. This paper reviews four common vaccine myths: vaccines cause autism, vaccines are not safe, too many vaccines are given too soon, and the influenza vaccine is not necessary. For each of these myths, we review the origin and spread of misinformation. The authors then present the scientific evidence against each myth. Extensive research has found no link between vaccines, and particularly the MMR vaccine or the preservative thimerosal, and autism. The U.S. and world health agencies have effective mechanisms in place to review and monitor vaccine safety. These systems have worked to detect and evaluate even rare vaccine adverse events. The recommended vaccine schedule is safe for infants’ immune systems. The flu vaccine is an essential tool in the fight against the seasonal influenza deaths. A consequence of these myths is that parents are choosing to delay or refuse recommended vaccines for themselves and their children. This has resulted in outbreaks of measles, pertussis, H. influenza type b, varicella, and pneumococcal disease in the United States. Unvaccinated and undervaccinated children risk contracting the disease themselves, and pose a risk to their community as herd immunity decreases. It is important to explore and refute the myths leading to decreased vaccination rates, so health care providers and parents can make educated decisions to protect children and ensure public health

Simulation of intrafascicular and extraneural nerve stimulation

A model of nerve stimulation for control of muscle contraction and ensuing isometrical muscle force has been developed and implemented in a simulation algorithm. A description of nerve fiber excitation was obtained using probability distributions of a number of excitation parameters. The volume conduction model of the stimulated nerve incorporates both inhomogeneities and anisotropy within the nerve. The nerve geometry was assumed to be cylindrically symmetric. The model of the nerve fiber excitation mechanism was based on that of D.R. McNeal (1976), using the Frankenhaeuser-Huxley equations. Simulations showed that the diameter dependence of nerve fiber recruitment is influenced by the electrode geometr

Creating safety nets through semi-parametric index-based insurance: A simulation for Northern Ghana

In West Africa, farm income is highly exposed to risks from crop failure in the drier, inland areas, and from fluctuations in (world market) prices in the wetter coastal areas. As individuals and even extended families are poorly equipped to deal with these, provision of social safety nets is required Our paper reviews the situation in Ghana and the way in which the new financial instrument of index-based insurance might contribute to better it, focusing on the estimation of a crop indemnification scheme for farmers in Northern Ghana. It recalls that in a poor rural area like Northern Ghana, provision of social safety almost coincides with food security management, and must, therefore, distinguish three basic subtasks: distributing income entitlements (possibly indemnification payments from insurance) to the poor, ensuring collection of taxes (possibly insurance premiums) to fund the arrangement, and assuring delivery of staple goods, such as food to the all households, including the poor. We point out that crop insurance, in any form can at best entitle the poor, and with adequate premiums, become adequately funded, albeit that current experience suggests that farmers tend to be reluctant and to find it difficult to fulfill their obligations. Our main remark is, however, that unless the actual availability of goods is assured, the indemnification from crop insurance will under droughts only cause prices to rise and channel away scarce food from the uninsured to the insured. In short, in poor areas such as Northern Ghana co-ordinated food security management is key, particularly under severe droughts, with crop insurance possibly playing a role in the spheres of entitlement and taxation. Turning to the modalities of crop insurance, we mention the advantages of the index-based approach, which as compared to the individualized contracts of commercial insurance greatly reduces transaction costs by basing the indemnification payments on objectively and easily measurable variables, such as rainfall data collected at weather stations, and world prices of main export goods. Our contribution is an improvement of the indemnification schedules. Rather than specifying a synthetic schedule or estimating is as a parametric form, we estimate it as an optimal indemnification that minimizes farmers' risk of having their income drop below the poverty line, while restricting the indemnification to be an unknown function of index variables on weather and prices. We adapt kernel learning technique to conduct this estimation, so as to ensure that the schedule is self-financing, up to a subsidy. Our application is for Northern Ghana where poverty is highest and farming conditions are most risky. We test the scheme's performance as a social safety net in terms of its capacity to reduce basis risk and alleviate poverty. Although our schedule definitely outperforms the parametric forms, basis risk and associated poverty remain considerable.Risk and Uncertainty,

Feeding Practices and Growth of Children Under 20 Months of Age in Madrid.

The feeding habits of 344 children under 20 months of age were obtained from mothers using the dietary history method supplemented with questions on milk feeding and weaning. Infants were remarkably similarly fed. No relations were found between breast-feeding and socioeconomic group, age of the mother or sex of the baby. Neither did socioeconomic group, sex or birth weight of the baby influence the timing of complementary feeding; however, the latter was significantly correlated to both mother's age and feeding method at the age of three months. In addition, six anthropometric measurements of the children were taken. These anthropometric results showed that the children were, on average, taller and heavier, but leaner than those of relevant national and international growth references. Fifty one samples of home-prepared baby meals together with 46 food diaries of infants of seven and eight months were collected. The meals were analysed chemically and the diaries were calculated for daily intake of energy, macronutrients and six minerals. The meals had high protein but low fat content, with accordingly a low energy density. The children's mean daily nutrient intake showed also high protein and low fat levels due to the meals; nevertheless, intakes of energy and minerals were adequate. About 20% of the baby meals had a high sodium level. Children in this study were apparently well-fed and thriving. Compliance with present guidelines on infant nutrition is high, just minor changes are needed to improve actual practices: breast-feeding should last longer, complementary foods should be introduced later and salt and sugar should be avoided in baby meals. Mothers, particularly those in the low socioeconomic group, need better understanding of gluten and its introduction into the infant's diet