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
Nick Harrison- BSAC
Tyler Lark- 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. 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

6. 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

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
Webster J. G., 1998

9. Mechanical Design Restrain Finger Circulation Conductive Voltmeter
Current Source

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

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

12. 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:

13. Questions??