Testing System for a Pressure Sensitive Cardiovascular Catheter Dec 13 2006 Team Members Danielle Ebben Erik Yusko Anthony Wampole Anita Zarebi Client Colette Wagner Nancy Sweitzer M D Ph D Advisor Professor William Murphy Table of Contents I ABSTRACT 3 II PROBLEM STATEMENT 3 III BACKGROUND 3 IV DESIGN CONSTRAINTS 4 V PRELIMINARY DESIGN ALTERNATIVES 5 I D ESIGN ALTERNATIVE 1 PLUNGER DESIGN 5 II DESIGN ALTERNATIVE 2 BALLOON 6 III DESIGN ALTERNATIVE 3 ROTATING CYLINDER 7 VI ANALYSIS OF DESIGN OPTIONS 9 VII FINAL DESIGN 10 VIII FUTURE WORK 11 IX ETHICAL CONSIDERATIONS 12 X CONCLUSION 12 XI REFERENCES 14 APPENDIX A PRODUCT DESIGN SPECIFICATION PDS 15 APPENDIX B LIST OF MATERIALS 18 APPENDIX C ACKNOWLEDGMENTS 19 2 I Abstract Blood pressures within the heart and surrounding vessels are often measured using catheters that are equipped with pressure transducers The accuracy of blood pressure measurements from these catheters has been called into question as calibration data is not provided by the manufacturer A product is needed to calibrate and verify the pressure transducer measurements while simulating in vivo conditions A product is being developed to encase the catheter in saline solution while achieving pressures up to 200mmHg An air pump increases pressure in the chamber through manual or micro controller control Pressure in the chamber is monitored with an additional pressure transducer imbedded in the tank In a second generation prototype a feedback loop will pressurize the chamber to a value specified by the user via a pressure sensor micro controller and air pump II Problem Statement Internal blood pressures within the heart and surrounding vessels are typically measured with catheters that are equipped with pressure transducers Properly calibrated catheters are required to ensure valid blood pressure measurements during diagnosis and clinical trials Current calibration techniques are thought to be unreliable A product is needed to calibrate and verify catheter pressure transducer measurements while simulating in vivo conditions III Background The traditional process of catheter use in cardiovascular surgery begins with a one hour evaluation of the patient s heart and body After consent for surgery is granted the catheter is guided into the heart via the femoral artery and aorta Figure 1 A drug is then administered to lower the pressure within the heart s walls Finally pressure measurements are obtained with the catheter Clinical trials are being conducted by our client to verify a new blood pressure monitoring technology The pressure readings of the new technology are compared to those given by the catheter and EKG The readings between these devices are expected to be nearly identical within 2 mmHg However Figure 1 The catheter is inserted into the aorta and guided into the heart 1 3 a significant amount of drift and inconsistency in the catheter s pressure readings has been observed particularly at pressures near 200 mmHg 2 First attempts to address this problem began with our client directly contacting Millar Instruments the catheter manufacturer After hearing the problem Millar Instruments sent a new catheter to our client stating that the problem would be fixed with a new catheter During correspondence our client often inquired as to what the validation and verification process for the catheter consisted of and Millar Instruments offered no response Because of this our client felt the need to develop her own method of verifying the catheter s accuracy and presented the problem to our team 2 Our client had previously employed a student to address this problem but the device and process they came up with was not satisfactory A general schematic of this device is shown in Figure 2 Our client is dissatisfied with this design for several reasons The valves that were supposed to close behind the catheter and secure it in place within the tube were leaky This makes the design messy and the pressure readings inconsistent and inaccurate Even when the device was working as it should constant pressure readings were still not observed making the design Figure 2 Previous attempt at a calibration design In this ineffective in meeting the device the catheter is placed in a tube and secured in place needs of our client by valves Saline is then used to pressurize the catheter within the tubing IV Design Constraints Millar Instruments current techniques for calibrating the catheter are unknown Therefore until a testing system is designed that validates the accuracy of the catheter s pressure readings the catheter cannot be considered reliable for clinical use For the catheter s pressure readings to be considered accurate several parameters for the testing system must be taken into account The testing system should be able to validate the catheter s pressure sensor readings at both atmospheric and saline pressure values Additionally the calibration must be done in saline solution where the pressure can be adjusted accordingly A reference pressure sensor is thus needed to help validate and control these pressure values so that they are stable and accurate 4 Because this design is meant to validate the catheter s readings the testing system must be incredibly accurate itself accurately measuring pressures within 2 mmHg Our client has requested that the range of pressures covered extends from atmospheric to 200 mmHg and that the tests be conducted at increments of 50 mmHg The catheter itself can read pressures of up to 300 mmHg As such all design components must be damage resistant at pressures up to 300 mmHg Operating characteristics comprise further concerns for this device The testing system needs to be easily manipulated with one hand so that the other hand is free to adjust the computer program or the catheter itself Also the device cannot be over 50 pounds as it may need to be transported from one hospital room to another Because the device may be used a few times a week until the client s research is complete it must also be reliable for several years Safety is a paramount concern for this testing system particularly because electrical components will be exposed to a conductive solution saline Additionally the catheter will no longer be sterile after it is tested therefore it will require clear labeling and sterilization before being used in the operating room To help with this concern the testing system should be very easy to clean The final concern for our client is cost The lab has
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