Pressure-Sensing Catheter Calibration

Team Members:Danielle Ebben

Anita ZarebiAnthony Wampole

Erik YuskoMarty Grasse

Client:Nancy Sweitzer, M.D.Colette Wagner

Advisor:William Murphy, Ph.D.

March 9, 2007

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

Problem StatementIn 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; damage-

resistant 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 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

Box Alterations Reduced height

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

Use of sheath system to thread catheter

Filling port

Over-Pressure valve

Additions Due To Sealing

Swagelok

SheathCatheter

Measurement & Control Systems

PCVisual Basic

Air Pump

NichromeElement

Pressure Transducer

DAQ

SSRSSR

Thermocouple

DifferentialAmplifier

Two-StageAmplifier

VoltageSupply

HighCurrentSource

Pressure Control Block Temperature Control Block

PCVisual Basic

Air Pump

NichromeElement

Pressure Transducer

DAQ

SSRSSR

Thermocouple

DifferentialAmplifier

Two-StageAmplifier

VoltageSupply

HighCurrentSource

Pressure Control Block Pressure sensor DAQ Computer Program

Voltage converted to pressure

Decide appropriate course of action

PC Visual Basic

Air Pump

Pressure Transducer

DAQ

SSRDifferentialAmplifier

VoltageSupply

PCVisual Basic

Air Pump

NichromeElement

Pressure Transducer

DAQ

SSRSSR

Thermocouple

DifferentialAmplifier

Two-StageAmplifier

VoltageSupply

HighCurrentSource

Pressure Control Block Pressure sensor DAQ Computer Program

Voltage converted to pressure

Decide appropriate course of action

PC Visual Basic

Air Pump

Pressure Transducer

DAQ

SSRDifferentialAmplifier

VoltageSupply

PCVisual Basic

Air Pump

NichromeElement

Pressure Transducer

DAQ

SSRSSR

Thermocouple

DifferentialAmplifier

Two-StageAmplifier

VoltageSupply

HighCurrentSource

Temperature Control BlockPC

Visual Basic

DAQ

SSR

Thermocouple

Two-StageAmplifier

HighCurrentSource

NichromeElement

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

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

Questions?