Transcript Pressure Control Block

Pressure-Sensing
Catheter Calibration
March 9, 2007
Client:
Nancy Sweitzer, M.D.
Colette Wagner
Advisor:
William Murphy, Ph.D.
Team Members:
Danielle Ebben
Anita Zarebi
Anthony Wampole
Erik Yusko
Marty Grasse
Outline







Problem Statement
Background
Design Constraints
Status Update
Acrylic Pressure Chamber
Measurement and Control Systems
Future Direction
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.
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
www.healthsystem.virginia.edu
Design Constraints





Both atmospheric and saline environments
Accuracy to +/- 2 mmHg
Able to achieve 200 mmHg; damageresistant to 300 mmHg
Temperature control
Cost < $300
Design Solution






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
Status at End of Semester





Machined container out of
acrylic
Attempted to seal with Oring and cork gasket
Seal around top edge
leaky
Donated pump did not
generate enough pressure
Feedback loop and
temperature control not
yet incorporated
Box Alterations

Reduced height

2 x 4 x 18 vs. 4 x 4 x 18


Added stability



Reduces amount of force
Screws
Horizontal and Vertical Struts
Completely seal container
Additions Due To Sealing

Use of sheath system to thread catheter
Sheath
Catheter
Swagelok

Filling port

Over-Pressure valve
Measurement & Control
Systems
PC
Visual Basic
High
Current
Source
Voltage
Supply
DAQ
SSR
Differential
Amplifier
Two-Stage
Amplifier
Air
Pump
Pressure
Transducer
Thermocouple
Pressure Control Block
SSR
Nichrome
Element
Temperature Control Block
Pressure Control Block
PC
Visual Basic
Voltage
Supply


DAQ


Pressure sensor
DAQ
Computer
Program

SSR
Differential
Amplifier

Air
Pump
Pressure
Transducer
Voltage converted to
pressure
Decide appropriate
course of action
Pressure Control Block
PC
Visual Basic
Voltage
Supply


DAQ


Pressure sensor
DAQ
Computer
Program

SSR
Differential
Amplifier

Air
Pump
Pressure
Transducer
Voltage converted to
pressure
Decide appropriate
course of action
Temperature Control Block


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
PC
Visual Basic
High
Current
Source
DAQ
Two-Stage
Amplifier
Thermocouple
SSR
Nichrome
Element
Future Direction

Acrylic Pressure Chamber



Measuring and Control Systems


Complete structural stabilization
Machine nichrome wire path
Implement amplifier circuits and power supplies
Calibration Protocol

Write a calibration/validation protocol for use
Questions?