Stanford University - Cardiovascular Biomechanics Research Laboratory Lower Limb Exercise and Abdominal Aortic Hemodynamics Christopher P. Cheng, Ph.D. Glagov Symposium February 20 th, 2003

Stanford University - Cardiovascular Biomechanics Research Laboratory Introduction: Disease Localization Spiral CT Supraceliac Infrarenal

Stanford University - Cardiovascular Biomechanics Research Laboratory Introduction: Hemodynamics Must quantify hemodynamics to understand disease processes Low, oscillating shear High, steady shear (Cybulsky and Gimbrone 1991, Nobutaka et al. 1996, Sessa et al. 1994, Zarins et al. 1983) Good Bad

Stanford University - Cardiovascular Biomechanics Research Laboratory Introduction: Exercise Systemic  Exercise capacity, HDL  Body fat, blood pressure, LDL  Heart disease and other Local  Blood flow  Aortic and lower extremity vascular disease Exercise is the most effective treatment for arterial insufficiency in the lower extremities * Hinder, halt, regress atherosclerosis (Weitz et al.1996)

Stanford University - Cardiovascular Biomechanics Research Laboratory Methods: Exercise MRI (Designed and constructed by Doug Schwandt, Eric Topp, James Anderson, ME282 group) 1.5T Conventional Magnet 0.5T Open Magnet

Stanford University - Cardiovascular Biomechanics Research Laboratory Methods: Data Acquisition 2 hours fasting Rest acquisition Exercise = 150% RestHR Respiratory comp. Cardiac gating Surface coil

Stanford University - Cardiovascular Biomechanics Research Laboratory Methods: Image Data Supraceliac Infrarenal RestExercise

Stanford University - Cardiovascular Biomechanics Research Laboratory Methods: Flow and Wall Shear Stress

Stanford University - Cardiovascular Biomechanics Research Laboratory Methods: Flow and Shear Oscillations (He and Ku 1996)(Taylor et al. 2002)

Stanford University - Cardiovascular Biomechanics Research Laboratory Results: Outline Healthy subjects aged 20 to 30 (11 subjects) Healthy subjects aged 50 to 70 (8 subjects)

Stanford University - Cardiovascular Biomechanics Research Laboratory Results: Young Normals Supraceliac Infrarenal RestExercise

Stanford University - Cardiovascular Biomechanics Research Laboratory Velocity (cm/s) Velocity (cm/s) Velocity (cm/s) Velocity (cm/s) 120 Results: Young Normals ABC ABCABC ABC A B C A B C RestExercise Supraceliac Infrarenal

Stanford University - Cardiovascular Biomechanics Research Laboratory Results: Young Normals Mean Blood Flow * ** * p<0.05 Supraceliac/Infrarenal ** p<0.05 Rest/Exercise Flow Oscillations * ** * ** Supraceliac Infrarenal

Stanford University - Cardiovascular Biomechanics Research Laboratory Results: Young Normals Wall Shear Stress Supraceliac Infrarenal

Stanford University - Cardiovascular Biomechanics Research Laboratory Results: Young Normals Mean Wall Shear Stress * ** * * ** Shear Oscillations * p<0.05 Supraceliac/Infrarenal ** p<0.05 Rest/Exercise Supraceliac Infrarenal

Stanford University - Cardiovascular Biomechanics Research Laboratory Results: Young Normals Significant increases in flow and wall shear stress as a result of light exercise More dramatic increases at infrarenal level Oscillations present at the infrarenal level at rest eliminated with exercise Summary

Stanford University - Cardiovascular Biomechanics Research Laboratory Results: Young vs. Older Normals Groups anthropometrically similar Same % heart rate increase With advancing age –Incidence and severity of atherosclerosis increases –Reduced nitric oxide release –Elastin degrades –Collagen/Elastin ratio increases –Aorta dilates and stiffens

Stanford University - Cardiovascular Biomechanics Research Laboratory Results: Young vs. Older Normals YoungOlder

Stanford University - Cardiovascular Biomechanics Research Laboratory Results: Young vs. Older Normals Infrarenal Supraceliac * p<0.05 between Young and Older Mean Blood FlowFlow Oscillations

Stanford University - Cardiovascular Biomechanics Research Laboratory Results: Young vs. Older Normals * * * * Infrarenal Supraceliac * p<0.05 between Young and Older Mean Wall Shear StressShear Oscillations * * * *

Stanford University - Cardiovascular Biomechanics Research Laboratory Results: Young vs. Older Normals Summary Older subjects experience lower wall shear stress at the supraceliac level at rest Older subjects experience greater oscillations in wall shear stress at supraceliac and infrarenal locations at rest Older subjects may achieve greater benefit from exercise

Stanford University - Cardiovascular Biomechanics Research Laboratory Future Directions Vascular Biology Exercise Blood Flow Simulations Applications to Congenital Heart Disease Pre- and Post-operative Studies

Stanford University - Cardiovascular Biomechanics Research Laboratory Acknowledgments Experimental Subjects & Patients Charles Taylor and Cardiovascular Biomechanics Laboratory MR-Cycle Team Doug Schwandt Eric Topp Jim Anderson ME282 Radiology Claudia Cooper Robert Herfkens Norbert Pelc Palo Alto VA Ronald Dalman Sheila Coogan Shawna Thunen Phyllis Mcgrath Surgery Residents Whitaker Foundation