Emerging Technologies for Nutrition Research Potential for Assessing Military Performance Capability (1997) / Chapter Skim
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Emerging Technologies for Nutrition Research, 1997 Pp.
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HISTORY Impedance is the frequency-dependent opposition of a conductor to the flow of an alternating electric current. A measure of impedance (Z)
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present-day areas of impedance cardiography, pulmonary impedance, brain impedance, and impedance imaging. The use of bioelectrical impedance to estimate body composition developed from more recent exploratory works in the areas of single-frequency and multiple-frequency impedance.
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aspects of impedance plots of resistance and reactance (Figure 7-1) relate to physiological characteristics of the body (Boulier et al., 1990; Kanai et al., 1987; Rush et al., 1963)
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Figure 7-2 Intracellular and extracellular electrical circuit diagram. to describe or model the electrical characteristics of the impedance-body intracellular-extracellular water relationships (Nyboer, 1959; Schwan and Kay, 1956)
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these fluid spaces in normal and clinical conditions. Little further work in this area has occurred despite reports that the relative proportions of TBW and ECFV determined from multifrequency impedance are reasonably constant with deviations occurring in disease states (Bolot et al., 1977; Jenin et al., 1975)
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error (RMSE) , and the coefficient of variation (CV)
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QUANTIFICATION OF CHANGES IN BODY COMPOSITION It is important to be able to estimate body composition at any age, but it is equally important that estimates of body composition for the same person at two different ages accurately reflect the change over time. From their analysis of the data from seven studies reporting body composition changes, Forbes and coworkers (1992)
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are more sensitive to changes in body composition than are whole-body impedance measures. This use of a segmental approach to bioelectrical impedance makes use of the work put forth by Settle et al.
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body composition (see Table 7-2)
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(Boulier et al., 1990) , but these investigators used a two-electrode (needle electrode)
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Figure 7-3 Spectrum curve and formula of impedance (expressed in ohms) against frequency (expressed in Hertz)
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of adipose tissue on the trunk than the limbs occurs in the women than the men. Ratios of low-to high-frequency impedance measures of the trunk also were correlated significantly and negatively with levels of TBF and total body %BF (r = -0.7 to -0.9)
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whether there are published studies of bioelectrical impedance with Hispanic-or Asian-American groups. Because of the specificity of these ethnic samples, the results have been anecdotal or of limited application to other corresponding samples in the United States.
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electrodes. The current magnitude is small and not perceived by the subject, but it is large enough that the current produces voltages that are above the interfering electrical ''noise" of the body.
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threshold of perception, and batteries or low-voltage power sources are used. However, there are no formal safety standards for bioelectrical impedance instruments.
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How valid is the bioelectrical impedance technology in the estimation of body composition? The common assumption that the current penetrates cell membranes and freely passes through all fluids is known to be false.
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those with any one of a number of mild disease states or chronic illnesses that do not produce local fluid accumulation. It appears to be of value to assess nutritional status in early HIV infection.
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bioelectrical impedance and its technology are directed to the full report of the NIH Technology Assessment Conference (NIH, 1996)
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Deurenberg, P., and F.J.M. Schouten 1992 Loss of total body water and extracellular water assessed by multifrequency impedance.
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NIH (National Institutes of Health) 1996 Technology Assessment Statement on Bioelectrical Impedance Analysis in Body Composition Measurement, 1994 December 12–14.
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Tedner, B., L.E.
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take, and a whole variety of things, basically because phase angle is probably assessing either a membrane function or a partitioning of intracellular or extracellular water. When you look at performance of the troops, for example, and you start to predict which people should go ahead with a task and which should not, this methodology, if somewhat refined, may really be very appropriate for that.
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WM. CAMERON CHUMLEA: Well, the reactance is supposedly produced by some aspect of the membrane acting as a capacitor.
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