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A Laboratory activity in Bioelectrical Impedance Analysis

A Laboratory activity in Bioelectrical Impedance Analysis. OMRON Body Fat Analyzer (healthgoods.com). Elliot Mylott ( emylott@pdx.edu) Sabrina Hoffman Ralf Widenhorn (ralfw@pdx.edu). European Journal of Clinical Nutrition 63, 619-626 (May 2009). Physics Department

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A Laboratory activity in Bioelectrical Impedance Analysis

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  1. A Laboratory activity in Bioelectrical Impedance Analysis OMRON Body Fat Analyzer (healthgoods.com) Elliot Mylott (emylott@pdx.edu) Sabrina Hoffman Ralf Widenhorn(ralfw@pdx.edu) European Journal of Clinical Nutrition 63, 619-626 (May 2009) Physics Department Portland State University, Portland, OR

  2. Bioelectrical Impedance Analysis OMRON Body Fat Analyzer (healthgoods.com) RJL Bioelectric Impedance Analyzer (rjlsystems.com\products)

  3. The Body as an RC Circuit (Liedtke, Principles of Bioelectrical Impedance Analysis 1997) • Reactive components due to cellular walls • Resistive components due to both intra- and extracellular fluid • Current flows primarily through Fat Free Mass

  4. Series Equivalent Circuit Single Frequency Series Equivalent Bio-Impedance Analysis BIA Evaluation of Nutrition and Hydration Status Using Vectorgram and BiaGram, (rjlsystems.com) • Body impedance frequency dependant • Single Frequency BIA uses 50kHz • More complex body models approximated with series circuit

  5. Circuit Analysis • Comparison of voltage across a known resistor gives gain and phase • Measured Impedance and Phase Leads to Reactance and Resistance

  6. Measurement I – NI ELVIS and LabView • Current • Impedance • Phase DAQ must have a high sampling rate.

  7. Measurement II – Apparatus Competition • Main Components: • Function Generator • Differential Amplifier • Gain / Phase Detector • Outputs DC Voltage proportional to Z and

  8. Mass Calculation • In human testing • Cylinder model • Measure of Fat Free Mass • Length Height • Density approximately equal to that of water • Coefficients and fitting factors empirically derived • Example equation to determine total body water (TBW) Wikipedia, Electrical resistivity and conductivity Estimate mass of a resistor Lukaski and Bolonchuk, Aviation Space and Environmental Medicine59 1163-1169, 1988) http://nutrition.uvm.edu/bodycomp/bia/lesson4.html

  9. Multi-frequency BIA • Students can explore • Series and Parallel impedance combinations • More accurate models for human electrical characteristics • Relationship between frequency and impedance American Journal of Clinical Nutrition 1996; 64: 388S-96S

  10. Summary • Introductory Physics Level Laboratory Exercise Exploring: • Resistance, reactance • Parallel and Series Impedance • Phasor diagrams and phase shifts • Waveform measurement • Resistivity, density and mass • RC Circuits • Electrical Characteristics of the body

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