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??