A LABORATORY ACTIVITY IN BIOELECTRICAL IMPEDANCE ANALYSIS Elliot Mylott ([email protected]) Sabrina Hoffman Ralf Widenhorn ([email protected]) Physics Department Portland State University, Portland, OR European Journal of Clinical Nutrition 63, 619-626 (May 2009) OMRON Body Fat Analyzer (healthgoods.com)
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A Laboratory activity in Bioelectrical Impedance Analysis
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A LABORATORY ACTIVITY IN BIOELECTRICAL IMPEDANCE ANALYSIS
(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
•Body impedance frequency dependant
•Single Frequency BIA uses 50kHz
•More complex body models approximated with series circuit
Single Frequency Series Equivalent
Bio-Impedance Analysis BIAEvaluation of Nutrition and Hydration Status Using Vectorgram and BiaGram,(rjlsystems.com)
Circuit Analysis
22cXRZ
RcXtan tanRcX
2tan1
2
ZR
• Measured Impedance and Phase Leads to Reactance and Resistance
• Comparison of voltage across a known resistor gives gain and phase
•Current
•Impedance
•Phase
Measurement I – NI ELVIS and LabView
Tto 1360 DAQ must have a high sampling rate.
Measurement II – Apparatus Competition
Main Components:• Function Generator• Differential Amplifier• Gain / Phase Detector
• Outputs DC Voltage proportional to Z and
Mass Calculation
Estimate mass of a resistor
Wikipedia, Electrical resistivity and conductivity
In human testing • Cylinder model• Measure of Fat Free Mass• Length Height• Density approximately equal
to that of water• Coefficients and fitting factors