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Finger PlethysmographFinger PlethysmographFor MeasuringFor Measuring
Blood ResistivityBlood ResistivityClient: John G. Webster, Ph.D
Advisor: Thomas Yen, Ph.D.
TeamTeamTim Balgemann- Team LeaderTim Balgemann- Team LeaderLucas Vitzthum- CommunicationsLucas Vitzthum- CommunicationsNick Harrison- BSACNick Harrison- BSACTyler Lark- BWIGTyler Lark- BWIG
OutlineBackgroundProblem StatementTheory
Electrical Biological
ConceptsDesign Components
Circuit DesignMechanical
Future Work
DiabetesBody’s inability to
manage glucose levelsPrevalence 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
Problem StatementDesign 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 TheoryFour electrode impedance plethysmography
2 electrodes pass current through finger2 electrodes measure voltageSignal processingCalculate impedance and resistivity from
voltage output
Biological TheoryHigh blood flow
RBCs align, current meets little resistanceLow blood flow
RBCs misalign, greater resistanceImpedance (ΔZ) results from this
Change in volume of artery Saline solution cancels signal
High Flow Low Flow
Design SpecificationsCircuit
SensitivityAdaptable measurement range (i.e. autoreset)Digital filtering and signal processing
Mechanical DeviceMotion artifactsMinimal electrical signature
CircuitryMeasuring change
in blood resistivitySample and HoldFiltering Current amplitude
and frequencyData interpretation
Webster J. G., 1998
Mechanical Design• Restrain Finger• Circulation• Conductive
Current Source
Voltmeter
Restrain Designs
Air in
Side
Inflatable Cuff Mesh CageBar Cage
Top
Future WorkBuild prototype
Optimize saline solutionCurrent amplitude and frequencyCircuit component values
TestingClinical 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/
Questions??