Finger Plethysmograph For Measuring Blood Resistivity Client: John G. Webster, Ph.D Advisor: Thomas Yen, Ph.D. Team Tim Balgemann- Team Leader Lucas Vitzthum- Communications Nick Harrison- BSAC Tyler Lark- BWIG

Outline Background Problem Statement Theory Design Components Electrical Biological Concepts Design Components Circuit Design Mechanical Future Work

Diabetes Body’s inability to manage glucose levels Prevalence is on the rise 26.3 million in U.S. $116 billion excess medical expenditures annually No reliable non-invasive monitoring Hypothesized that blood sugar levels may be correlated with blood resistivity What is diabetes? Marked by irregular blood glucose levels, this is caused by either the pancreas’s inability to produce enough insulin, or the inability to effectively use insulin produced 13.5% increase in last 3 years 26.3 million in US (8% of total US population) Worldwide: 171 million individuals living with diabetes Overall economic burden much higher

Problem Statement Design a finger plethysmograph to measure blood resistivity Goals: Build a mechanical device to secure finger Design a circuit that allows data acquisition of blood impedance

Electrical Theory Four electrode impedance plethysmography 2 electrodes pass current through finger 2 electrodes measure voltage Signal processing Calculate impedance and resistivity from voltage output

Biological Theory High blood flow Low blood flow RBCs align, current meets little resistance Low blood flow RBCs misalign, greater resistance Impedance (ΔZ) results from this Change in volume of artery Saline solution cancels signal High Flow Low Flow

Design Specifications Circuit Sensitivity Adaptable measurement range (i.e. autoreset) Digital filtering and signal processing Mechanical Device Motion artifacts Minimal electrical signature

Circuitry Measuring change in blood resistivity Sample and Hold Filtering Current amplitude and frequency Data interpretation Webster J. G., 1998

Mechanical Design Restrain Finger Circulation Conductive Voltmeter Current Source

Restrain Designs Inflatable Cuff Bar Cage Mesh Cage Top Air in Side

Future Work Build prototype Optimize saline solution Current amplitude and frequency Circuit component values Testing Clinical Trials

References Webster J. G., 1998. Measurement of flow and volume of blood Medical Instrumentation: Application and Design, 3rd Edition ed J G Webster (New York: John Wiley & Sons). Rosenthal, J. H., An inductive plethysmograph for ambulatory ventilation measurement. American Diabetes Association: http://www.diabetes.org/diabetes-statistics.jsp World Health Organization: http://www.who.int/dietphysicalactivity/publications/facts/diabetes/en/

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