1. Pressure-Sensing Catheter Calibration
March 9, 2007
Client:
Nancy Sweitzer, M.D.
Colette Wagner
Team Members:
Danielle Ebben
Anita Zarebi
Anthony Wampole
Erik Yusko
Marty Grasse
Advisor:
William Murphy, Ph.D.

2. Outline Problem Statement Background Design Constraints Status Update
Acrylic Pressure Chamber
Measurement and Control Systems
Future Direction

3. Problem Statement
In order to accurately measure internal blood pressures, a properly calibrated pressure sensitive cardiovascular catheter may be used. The current techniques for calibrating the catheter are unreliable, which causes concern about the validity of the test results. The goal of the project is to devise a testing system which more reliably calibrates and verifies the accuracy of the catheter in both atmospheric tests and tests which simulate internal bodily conditions.

4. Project Background
Catheters used to measure blood pressure inside the heart
Clinical trials in progress
Catheter pressure readings inconsistent
Calibration method of manufacturer unknown
Need an effective way to calibrate the pressure transducers on the catheter

5. Design Constraints Both atmospheric and saline environments
Accuracy to +/- 2 mmHg
Able to achieve 200 mmHg; damage-resistant to 300 mmHg
Temperature control
Cost < $300

6. Design Solution Pressure is transferred to saline
Air/water tight container
Partially filled with saline
Pressure sensor mounted in wall
Air pump compresses air in the top of the container
Pressure is transferred to saline
Operator enters desired pressure
Pressure maintained by feedback from sensor to pump
Compare catheter pressure readings to container pressure

7. Status at End of Semester
Machined container out of acrylic
Attempted to seal with O-ring and cork gasket
Seal around top edge leaky
Donated pump did not generate enough pressure
Feedback loop and temperature control not yet incorporated

8. Box Alterations Reduced height Added stability
2 x 4 x 18 vs. 4 x 4 x 18
Reduces amount of force
Added stability
Screws
Horizontal and Vertical Struts
Completely seal container

9. Additions Due To Sealing
Use of sheath system to thread catheter
Filling port
Over-Pressure valve
Sheath
Catheter
Swagelok

10. Measurement & Control SystemsPC
Visual Basic
High
Current
Source
Voltage
Supply
DAQ
Differential
Amplifier
Two-Stage
Amplifier
SSR
SSR
Air
Pump
Pressure
Transducer
Thermocouple
Nichrome
Element
Pressure Control Block
Temperature Control Block

11. Pressure Control BlockPC
Visual Basic
Pressure sensor
DAQ
Computer
Program
Voltage converted to pressure
Decide appropriate course of action
Voltage
Supply
DAQ
Differential
Amplifier
SSR
Air
Pump
Pressure
Transducer

13. Pressure Control BlockPC
Visual Basic
Pressure sensor
DAQ
Computer
Program
Voltage converted to pressure
Decide appropriate course of action
Voltage
Supply
DAQ
Differential
Amplifier
SSR
Air
Pump
Pressure
Transducer

14. Temperature Control BlockPC
Visual Basic
Heating Element:
nickel chromium wire
Two Stage amplifier:
Differential amp with cold junction compensation
Pure gain amp
PC in turn reads/controls a current flow
High
Current
Source
DAQ
Two-Stage
Amplifier
SSR
Thermocouple
Nichrome
Element

15. Future Direction Acrylic Pressure Chamber
Complete structural stabilization
Machine nichrome wire path
Measuring and Control Systems
Implement amplifier circuits and power supplies
Calibration Protocol
Write a calibration/validation protocol for use

16. Questions?