1. 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
Josh White-BSAC
Sarah Offut-BWIG

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

3. 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

4. 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

5. 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

6. 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

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

8. Circuitry Measuring change in blood resistivity Sample and Hold
Filtering
Current amplitude and frequency
Data interpretation

9. Past Semester Results
Occluded artery test
Δ Impedance not visible

10. Current Work- Circuit Testing
Circuit Changes
Constant current source
Reduced ripple
Verified circuit performance
Phantom circuit to mimic expected change
1 part in 1000 signal change

11. Circuit Testing

12. Past Semester Design PVC Shell Rubber Elastomeric Foam Tin electrodes
0.9% NaCl solution
10 kHz input signal, .9 mA

13. Current Work – Finger-holder
Parameters to Vary
Finger-holder volume
Insulator placement
Electrode placement
Verify signal
Cuff Design I V

14. Future Work – Finger-holder
Arm-rest
Generalization
Hinges
Electrode and insulator placement
Insulator material and geometry
Frequency testing versus skin impedance
Phantom for calibration

15. Questions??

16. References
Webster J. G., 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:
World Health Organization: