title: Abdominal aortic hemodynamic conditions in healthy subjects aged 50-70 at rest and during lower limb exercise: in vivo quantification using MRI.
abstract: The prevalence of atherosclerosis in the abdominal aorta increases with age and is hypothesized to be related to adverse hemodynamic conditions including flow recirculation and low wall shear stress. Exercise has been shown to modulate these adverse conditions observed in the infrarenal aorta of healthy young subjects at rest. A custom magnetic resonance (MR)-compatible stationary cycle, an open MRI, and custom image processing software were used to quantify hemodynamic conditions in the abdominal aorta at rest and during cycling exercise in healthy subjects aged 50-70 years. The subjects increased their heart rate from 63+/-8 bpm at rest to 95+/-12 bpm during cycling exercise. Supraceliac blood flow increased from 2.3+/-0.4 to 6.0+/-1.4 l/min (P<0.001) and infrarenal flow increased from 0.9+/-0.3 to 4.9+/-1.7 l/min (P<0.001) from rest to exercise. Wall shear stress increased from 2.0+/-0.7 to 7.3+/-2.4 dynes/cm(2) at the supraceliac level (P<0.001) and 1.4+/-0.8 to 16.5+/-5.1 dynes/cm(2) at the infrarenal level (P<0.001) from rest to exercise. Flow and shear oscillations present at rest were eliminated during exercise. At rest, these older subjects experienced lower mean wall shear stress at the supraceliac level of the aorta and greater oscillations in wall shear stress as compared to a group of younger subjects (23.6+/-2.2 years). Compared to the younger subjects, the older subjects also experienced greater increases in mean wall shear stress and greater decreases in wall shear stress oscillations from rest to exercise.
authors.affiliation: Department of Mechanical Engineering, Standford University, Stanford, CA, USA.
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Cheng
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Herfkens
authors.forename: Charles A
authors.initials: CA
authors.lastname: Taylor
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D001012:Aorta, Abdominal / Q000502:physiology*; D001642:Bicycling; D015444:Exercise / Q000502:physiology*; D005260:Female; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D007866:Leg / Q000502:physiology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009991:Oscillometry; D012016:Reference Values; D012039:Regional Blood Flow / Q000502:physiology; D013314:Stress, Mechanical