A LABORATORY ACTIVITY IN BIOELECTRICAL IMPEDANCE ANALYSIS OMRON

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

Bioelectrical Impedance Analysis OMRON Body Fat Analyzer (healthgoods. com) RJL Bioelectric Impedance Analyzer (rjlsystems. comproducts)

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

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

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

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

Measurement II – Apparatus Competition

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 Wikipedia, Electrical resistivity and conductivity Lukaski and Bolonchuk, Aviation Space and Environmental Medicine 59 1163 -1169, 1988) http: //nutrition. uvm. edu/bodycomp/bia/lesson 4. html

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: 388 S-96 S

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