Determination of Inactive Powers in a Single-Phase AC Network

Based on the development of the theory of reactive power and distortion power, starting with the works of Fryze and Budeanu, it has been found that the contradictions in the definition of the components of inactive powers are caused by errors in the introduced intermediate concepts and corresponding calculations when switching to nonlinear and non-sinusoidal AC circuits. The materials of the works of modern researchers and the numerical calculations carried out made it possible to trace the differences between reactive power and distortion power, to confirm the orthogonality properties of the active, reactive power, and distortion power components. The paper defines the conditions for achieving a power balance in an AC network with nonlinear loads, compiled and tested criteria leading to the absence of distortion power in a single-phase AC network. Using the time base of the projection of the generalized vectors in vector diagrams, it is shown that compliance with the criteria for the absence of distortion power does not determine the mutual similarity of the voltage curve with the current curve for a nonlinear load. It has been found that the well-known term “distortion power” has an unfortunate wording, since this power, although it characterizes the interaction of harmonics of currents and voltages with different ordinal numbers, is not determined by the visual similarity or the degree of distortion of the load current waveforms relative to the supply voltage curve

Body composition in the elderly: Reference values and bioelectrical impedance spectroscopy to predict total body skeletal muscle mass

BACKGROUND & AIMS: To validate the bioelectrical impedance spectroscopy (BIS) model against dual-energy X-ray absorptiometry (DXA), to develop and compare BIS estimates of skeletal muscle mass (SMM) to other prediction equations, and to report BIS reference values of body composition in a population-based sample of 75-year-old Swedes. METHODS: Body composition was measured by BIS in 574 subjects, and by DXA and BIS in a subset of 98 subjects. Data from the latter group was used to develop BIS prediction equations for total body skeletal muscle mass (TBSMM). RESULTS: Average fat free mass (FFM) measured by DXA and BIS was comparable. FFM(BIS) for women and men was 40.6kg and 55.8kg, respectively. Average fat free mass index (FFMI) and body fat index (BFI) for women were 15.6 and 11.0. Average FFMI and BFI for men were 18.3 and 8.6. Existing bioelectrical impedance analysis equations to predict SMM were not valid in this cohort. A TBSMM prediction equation developed from this sample had an R(pred)(2) of 0.91, indicating that the equation would explain 91% of the variability in future observations. CONCLUSIONS: BIS correctly estimated average FFM in healthy elderly Swedes. For prediction of TBSMM, a population specific equation was required

Bioelectrical impedance spectroscopy in growth hormone-deficient adults.

This study evaluated water compartment assessment by bioelectrical impedance spectroscopy (BIS) by Xitron 4000B in 164 growth hormone-deficient adults on growth hormone replacement therapy, examined the assumed constant body density and gender-specific resistivities in BIS methodology and evaluated a published BMI-adjusted BIS equation. Body composition was measured by BIS, total body potassium (TBK), tritium dilution and dual-energy x-ray absorptiometry (DXA). Tritium dilution and TBK were combined to a reference method for water compartments. Average difference for total body water (TBW) by tritium dilution and by BIS was 0.6 l in women (p > 0.05) and -0.2 l in men (p > 0.05). Average extracellular water (ECW) by the reference method and by BIS differed 1.5 l in women (

Nutrition and physical activity for the prevention and treatment of age-related sarcopenia

Sarcopenia, defined as loss of skeletal muscle mass and function, is associated with adverse outcomes such as physical disability, impaired quality of life and increased mortality. Several mechanisms are involved in the development of sarcopenia. Potentially modifiable factors include nutrition and physical activity. Protein metabolism is central to the nutritional issues, along with other potentially modifying nutritional factors as energy balance and vitamin D status. An increasing but still incomplete knowledge base has generated recent recommendations on an increased protein intake in the elderly. Several factors beyond the total amount of protein consumed emerge as potentially important in this context. A recent summit examined three hypotheses: (1) A meal threshold; habitually consuming 25-30 g protein at breakfast, lunch and dinner provides sufficient protein to effectively stimulate muscle protein anabolism; (2) Protein quality; including high-quality protein at each meal improves postprandial muscle protein synthesis; and (3) performing physical activity in close temporal proximity to a high-quality protein meal enhances muscle anabolism. Optimising the potential for muscle protein anabolism by consuming an adequate amount of high-quality protein at each meal, in combination with physical activity, appears as a promising strategy to prevent or delay the onset of sarcopenia. However, results of interventions are inconsistent, and well-designed, standardised studies evaluating exercise or nutrition interventions are needed before guidelines can be developed for the prevention and treatment of age-related sarcopenia

Body composition and hand grip strength in healthy community-dwelling older adults in sweden

Background: Longevity increases worldwide but there are few studies on body composition and hand grip strength inpopulations over 80 years. Given high prevalence of chronic disease and functional disability in octogenarians, it may be difficult todistinguish effects of ageing from those imposed by disease. The European Consensus definition of sarcopenia recommends usingboth low muscle mass and function for diagnosis. Objectives: Examine body composition and hand grip strength in a selected groupof community-dwelling older adults with high level of functional independence. In addition, longitudinal changes in handgripstrength were examined using previously collected data. Design: Cross-sectional body composition and hand grip strength witha four year retrospective analysis on previously assessed hand grip strength. Setting: Measurements were conducted by homevisits. Participants: 102 community-dwelling 83-96 year-olds, 50 % women. Measurements: Hand grip strength was registered bya dynamometer and body composition analysis using bioimpedance spectroscopy. Results: According to European Consensusdefinition, only 6/102 had normal muscle mass - no men, although 78 % of men and 40 % of women had normal muscle strength.Since previously collected data four years earlier, men had lost strength (p<0.001), while women had not (p=0.202). Conclusions: Subject characteristics and health status support well-preserved body energy, protein stores and muscle strength. Low musclemass was much more prevalent than low muscle strength. Results may give an indication of what constitutes a healthy bodycomposition in oldest old and could serve as a starting point for reference values on healthy body composition in octogenarians