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 Roldán-Alzate Department of Biomedical Engineering Advisor: Professor Naomi Chesler Department of Biomedical Engineering1 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…………………………………………………………………………....222 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.3 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 modified Bernoulli equation to find the blood pressure of the pulmonary artery. Pulmonary 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 Roldán-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 Figure 1: Pulmonary blood flow to heart (pulmonary artery/branches in blue) (CIC, 2005).4 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