In a community based sample of the population, the prevalence of mitral-valve prolapse was lower than previously reported. The prevalence of adverse sequelae commonly associated with mitral-valve prolapse in studies of patients referred for that diagnosis was also low.

DC-DC converters with voltage boost capability are widely used in a large number of power conversion applications, from fraction-of-volt to tens of thousands of volts at power levels from milliwatts to megawatts. The literature has reported on various voltage-boosting techniques, in which fundamental energy storing elements (inductors and capacitors) and/or transformers in conjunction with switch(es) and diode(s) are utilized in the circuit. These techniques include switched capacitor (charge pump), voltage multiplier, switched inductor/voltage lift, magnetic coupling, and multistage/-level, and each has its own merits and demerits depending on application, in terms of cost, complexity, power density, reliability, and efficiency. To meet the growing demand for such applications, new power converter topologies that use the above voltage-boosting techniques, as well as some active and passive components, are continuously being proposed. The permutations and combinations of the various voltage-boosting techniques with additional components in a circuit allow for numerous new topologies and configurations, which are often confusing and difficult to follow. Therefore, to present a clear picture on the general law and framework of the development of next-generation step-up dc-dc converters, this paper aims to comprehensively review and classify various step-up dc-dc converters based on their characteristics and voltage-boosting techniques. In addition, the advantages and disadvantages of these voltage-boosting techniques and associated converters are discussed in detail. Finally, broad applications of dc-dc converters are presented and summarized with comparative study of different voltage-boosting techniques.

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Background-Studies in selected samples have linked impaired endothelial function with cardiovascular disease and its risk factors. The clinical correlates and heritability of endothelial function in the community have not been described. Methods and Results-We examined a measure of endothelial function, brachial artery flow-mediated dilation (FMD), expressed as both percent (FMD%) and actual dilation by ultrasound with the occlusion cuff below the elbow in 2883 Framingham Study participants (52.9% women; mean age, 61 years). A subset of 1096 participants performed a 6-minute walk test before FMD determination. Mean FMD% was 3.3Ϯ3.0% in women and 2.4Ϯ2.4% in men. In stepwise multivariable linear regression models, FMD% was inversely related to age, systolic blood pressure, body mass index (BMI), lipid-lowering medication, and smoking, whereas it was positively related to female gender, heart rate, and prior walk test. The estimated heritability of FMD% was 0.14. FMD actual dilation findings were similar, except that female sex and BMI were not significantly associated. Conclusions-Increasing age, systolic blood pressure, BMI, and smoking were associated with lower FMD% in our community-based sample, whereas prior exercise and increasing heart rate were associated with higher FMD%. The estimated heritability of FMD was modest. Future research will permit more complete characterization of the genetic and environmental determinants of endothelial function and its prognostic value in the community. Key Words: endothelium Ⅲ epidemiology Ⅲ risk factors Ⅲ genetics B rachial artery flow-mediated dilation (FMD) serves as a measure of endothelial vasodilator function in humans. 1 Experimental and clinical studies suggest that development of endothelial dysfunction, including reduced NO bioavailability, contributes to the atherosclerosis and pathogenesis of cardiovascular disease (CVD) events. 2 Human studies demonstrate that endothelial dysfunction precedes the development of clinically apparent atherosclerosis in individuals with CVD risk factors such as smoking, 3 hypertension, 4 hyperlipidemia, 5 diabetes mellitus, 5 and obesity. 6 Furthermore, effective treatment of risk factors may reverse endothelial dysfunction. 7 Finally, studies in individuals with risk factors or prevalent CVD have demonstrated that endothelial dysfunction identifies patients at risk for future CVD events. 2,8 Previous investigations relating risk factors to endothelial dysfunction largely were limited to small, highly selected samples. Our objective was to assess the independent correlates of endothelial function in a large community-based sample. MethodsThe Framingham Offspring Study design has been described elsewhere. 9 Participants in the seventh examination (1998 to 2001) were eligible for the present investigation (nϭ3539). Exclusion criteria were residence in a nursing home (nϭ205), mastectomy (nϭ34), Raynaud disease (nϭ9), subject refusal (nϭ83), equipment malfunction/miscellaneous (nϭ15), predigital capture (nϭ177), or technically inade...