MRI Compatible Lower Leg Exerciser BME 400 Department of Biomedical Engineering University of Wisconsin Madison December 9 2009 Deborah Yagow Team Leader Colleen Farrell Communicator Val Maharaj BWIG Amy Lenz BSAC Client Alejandro Rold n Alzate Department of Biomedical Engineering Advisor Professor Naomi Chesler Department of Biomedical Engineering Table of Contents Abstract 2 Problem Statement 3 Background and Device Necessity 3 Research and Competition 4 Client Requirements 4 Ergonomics 5 Design Options 6 Design Matrix 6 Final Device 7 Testing 10 Finite Element Analysis Strength Testing 14 Future Work 15 Ethics 17 References 18 Appendices Appendix A Current Patents 19 Appendix B Final Prototype Total and Future Device Total 20 Appendix C Exercise and Testing Protocols 21 Appendix D PDS 22 1 Abstract Magnetic resonance imaging can be used to study pulmonary blood flow in hypertensive patients before and after exercise The goal of this project is to create a device which will be used to exercise subjects to 40 of a predetermined maximal workload in both healthy subjects and patients with hypertension A preliminary cycling device was constructed and tested via Doppler Ultrasound and found to increase the pulmonary systolic pressure an average of 5 54 mmHg This pressure increase was determined using the modified Bernoulli equation with the tricuspid regurgitant velocity 2 Problem Statement The goal of this project is to design and construct a lower leg exerciser that is compatible with MR imaging and Doppler Ultrasound to be used during cardiopulmonary research studies on pulmonary hypertension patients and healthy volunteers The device must have repeatable loads that can be measured and relayed to the patient via biofeedback Background and Device Necessity Pulmonary Hypertension PH is a condition in which the blood vessels of the lungs constrict thickening the walls and leading to increased pressure in the pulmonary arteries The pulmonary pressure cannot be measured with a pressure cuff like systemic pressure and therefore must be estimated using the tricuspid regurgitant jet velocity The tricuspid regurgitant jet is formed from an insufficiency of the tricuspid valve separating the right atrium and right ventricle of the heart As the ventricle contracts a stream of blood leaks back through the valve into the atrium and the velocity of this jet can be used with the Figure 1 Pulmonary blood flow to heart modified Bernoulli equation to find the blood pressure of pulmonary the pulmonary artery Pulmonary artery branches in blue CIC 2005 Hypertension can be of unknown cause primary PH but is more commonly a result of emphysema COPD HIV heart defects or only appears with exercise Primary Pulmonary Hypertension News 2009 Patients are often physically limited by PH and therefore the focus of research here is Does moderate exercise affect the stiffness of the patient s pulmonary artery or their blood pressure The research is being conducted at the Vascular Tissue Biomechanics Laboratory in the Biomedical Engineering Department of the University of Wisconsin Madison by Dr Naomi Chesler and Alejandro Rold n Alzate The study uses MR imaging to scan the activity of the heart in both PH patients and healthy subjects prior to and following exercise Patients will be injected with contrast dye via catheterization in order to produce a better signal in the pulmonary arteries during scanning The subject will then exercise for a predetermined time period to raise the pulmonary blood pressure while non ferrous EKG leads monitor the heart s vital signs After the completion of exercise the subject will be scanned again in order to detect any changes in the pulmonary blood pressure via the tricuspid regurgitant jet Doppler Ultrasound imaging studies of the heart may be carried out as well Although PH severity varies on a patient to patient basis the goal of this research is to find an ideal level of exercise that is of more benefit than harm to a majority of PH patients Similar research studies have been done in the past and have set a precedent protocol for exercise involving subjects with PH One recent case done by Holverda et al 2009 had the 3 workload at which the PH patient exercised increased to 40 of a predicted maximal workload in the first minute while healthy subjects were started at the 40 of the maximum workload for the gender and specific anthropometric measurements Research and Competition A number of other products and projects have been designed to fill the need for an MRI compatible exerciser A Norwegian ergometer company Lode B V provides a number of machines to accomplish exercising while in an MR scanner The machines offered through this company include a pedal system Figure 2 dorsal ankle flexion and both push pull and up down motions The products that are offered through the company may fit the exercise need but are more complicated and expensive than is necessary for this design project The machines include special electronic braking torque measurements and the ability to program up to 24 protocols These features add a significant amount to the cost Figure 2 Lode Ergometer 2009 quoted from Lode representative Dana Burger Dipzinski as 58 000 with shipping and handling and can be alternatively designed for this project Another competitive device was designed by a team out of Northeastern University and is an fMRI compatible mechatronic ankle device This device allows for both isometric and dynamic positioning of the ankle in order to provide imaging of the cortical response This device is constructed from polymers and has a sliding bar which allows for a 40 plantar flexion and 10 dorsiflexion range There is also the option for a pin setting which gives an isometric position While this device allows for movement with the lower extremity via ankle flexion it is not designed to exercise the patient to any specific workload This device is more used in for imaging the brain during ankle movement than as a means to imaging Figure 3 fMRI Compatible Ankle Device Doane 2007 p 102 the heart with exercise Another problem is that since this was a design project of a university it is not commercially available for purchase Client Requirements The client has stipulated certain requirements for the design project in order to fit the needs of the research The target overall cost for the device is 150 The device must be created 4 completely out of MRI compatible materials which excludes any ferrous