Pulmonary Flow Resistive Device Taya Furmanski Albert Attia Advisor: Thomas Doyle, M.D. April 9, 2003

Background Hypoplastic Left Heart Syndrome (HLHS) is a condition in which the patient is missing his/her left ventricle 1440 babies are born each year with HLHS Approximately 75% 3-year survival rate No medical treatment for HLHS Only options are operation (reconstruction) or transplantation 300 patients with HLHS are seen at VUMC per year

The Problem Inadequate systemic blood flow Amount of O 2 delivered to the organs decreases significantly “Blue Baby” Flow schematic

How to Solve the Problem Place nozzle in pulmonary arteries (see figure for location) Device will act as resistor Decrease in pulmonary blood flow will cause increase in systemic blood flow Eliminates first two steps of reconstructive surgery Duration of implantation in heart = 6-8 months

Schematic of Flow with and without Device Implanted 3-5 L/min Right Ventricle 1-3 L/min Systemic Artery 1 L/min Pulmonary Artery 1 L/min Pulmonary Artery 3-5 L/min Right Ventricle <1 L/min Systemic Artery 2-3 L/min Pulmonary Artery 2-3 L/min Pulmonary Artery WITHOUT DEVICEWITH DEVICE

Dimensions of the Nozzle Calculations by Craig Russell (ME student) Theories required to solve problem Conservation of mass Conservation of momentum Dimension of end of nozzle still to be determined Pressure drop across nozzle required Will conduct pressure tests to solve for this unknown Pulmonary artery pressure ~20 mmHg 6-10 mm

Alternate Solutions Place nozzle inside stent Use bow-tie shaped stent (see figure) Placing a mesh-like device in the pulmonary arteries

Problems With Alternate Solutions Extremely difficult to place in the artery Placement also a problem Would cause hemolysis (tiny holes would damage red blood cells)

What We Need - Modeling - Prototype can be tested through model to determine effectiveness In vitro model to simulate flow through blood vessels Computer model would allow variables to be altered easily to determine the optimal dimensions of the device

What We Need - Materials & Assistance - Use Vanderbilt shop to mold conical device Use NCIIA to produce working prototype Possibly have a company produce Nitinol prototype Use materials to create physical model that accurately portrays operation of device Assistance of mechanical engineering students (Craig Russell and Chris Owen) and professor (Dr. Mark Stremler) for fluid dynamics calculations Find experienced programmer to develop computer modeling system or use one currently in existence

Why Nitinol? Biocompatible Memory wire—can be molded to desirable shape Can be elongated to fit into catheter, enabling insertion

What We Have Accomplished Thus Far… In-depth research of HLHS Several meetings with Dr. Doyle to discuss the problem and possible solutions Finalizing a design plan Create a plan of attack: start simple and increase complexity Ordered and received Nitinol wire Calculations of fluid dynamics Finalized method of implantation Obtained materials necessary to test physical model

What We Have Yet to Do… Produce prototype of device Test prototype Use Mechanical Engineering Energetics lab to test pressure drop across device Pressure drop calculations will allow proper calculation of dimension of the nozzle Create or find computer model simulation of cardiovascular system

Conclusions Device will decrease blood flow to pulmonary arteries, Increase systemic bloodflow Bypass first two reconstructive (Norwood) surgeries Nitinol is an adequate material for this device Problem more complex than initially anticipated Fluid dynamics calculations Unmeasured pressure difference Device never created before

Recommendations Continue pressure testing In vivo testing i.e. pigs, sheep Human clinical testing IRB approval FDA approval

References 1. Barber, Gerald. Hypoplastic Left Heart Syndrome. Structural Congenital Defects, section date accessed: January 30, web1.tch.harvard.edu/chnews/ /fetalcath.html; date accessed: February 10, Dr. Thomas Doyle; Vanderbilt University Medical Center date accessed: February 25, p.PDF; date accessed: April 8, 2003.