Body Impedance Analysis

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Body Impedance Analysis

• David Fu
• 7-Jan-03

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Content

• Introduction
• Theory of BIA
• Application
• Designation of BIA Equipment
• Problem and Discussion
• Conclusion

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Introduction

• A newer method
• Simplicity
• Safety
• Non-invasive

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Theory of BIA

• A very small current through the body
• 800 mA at 50 kHz
• Measuring its resistance
• Lean tissue offers less resistance
• more water
• electrolytes
• Adipose tissue(Fatty tissue).

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Theory of BIA
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Application
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Application
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Application Testing Procedure

• Do not have exercised or taken a sauna within 8
  hours
• Refrain from alcohol intake for 12 hours prior .
• The height and weight should be accurately
  measured and recorded.
• Quietly during the entire test.

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Application

• The arms 30 degrees from the body and legs not
  touching.
• The electrode sites may need to be cleaned with
  alcohol
• if the skin is dry or covered with lotion.
• Attach the electrodes and patient cables.
• Name, age, gender, height and weight

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Application
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Application
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Designation of BIA Equipment

• Principle
• Measuring the Value of Resistance
• Small current for safety consideration

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Designation of BIA Equipment
Vref
Vout Rf/(RhRf)Vref Rh(Vref-Vout)/VoutRf
????
Rh
Vout
R 1M
Rf
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Designation of BIA Equipment
Vout Zf/(ZhZf)Vref Zh(Vref-Vout)/VoutZf
Vref
AC 50KHz signal gen.
Probe
Zh
Z 1.5K
Vout
Zf
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Problems and Disscussion
Zi Signal Generator inner impedance The Zi will
change by different device component
Vref
AC 50KHz signal gen.
Probe
Zh
Vout
Zf
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Problems and Disscussion

• Solutions
• AC signal generator
• AC constant current source
• AC voltmeter
• Ideal diode circuit
• Peak value detector

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Problems and Disscussion
AC signal gen.
Constant Current
Body Tissue
Ideal Diode
Peak Value Detector
ADC / Algorithm
Body Fat
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Conclusion

• Need more knowledge of both Bio-system and
  Mechatronic system.
• Problems of integration between Bio-system and
  Mechatronic system.
• Safety consideration