In vivo quantification of hemodynamic conditions in the human abdominal aorta at rest during lower limb exercise: Research and clinical applications.

摘要

Fluid mechanical forces of blood flow have been shown to affect biologic processes that relate to the development of vascular disease such as atherosclerosis. In addition, it is well known that exercise is correlated with a lower incidence of atherosclerosis. Hence, quantification of blood flow during exercise may help identify some of the mechanisms by which exercise benefits vascular health, and this knowledge can be used to improve prevention and treatment strategies for disease. Furthermore, quantitative analysis of blood flow during exercise can provide important information for vascular disease diagnosis, treatment planning, and intervention assessment.; This Ph.D. dissertation describes novel methods for quantifying hemodynamic conditions in the human abdominal aorta during seated cycling exercise using an interventional open magnet and custom magnetic resonance-compatible stationary cycles. Furthermore, a new method for quantifying vessel wall shear stress using Lagrangian interpolation functions to represent blood velocity profiles is presented. In contrast to previously described approaches, this method can quantify temporally- and circumferentially-resolved wall shear stress on an arbitrarily shaped lumen experiencing complex pulsatile flow.; The techniques developed in this research were applied to quantify hemodynamic conditions in the abdominal aortas of healthy subjects aged 20 to 30, healthy subjects aged 50 to 70, and patients diagnosed with intermittent claudication at rest and during cycling exercise. In the young subjects, a 50% increase in heart rate caused a 6-fold increase in blood flow at the infrarenal level of the aorta, and all flow and wall shear stress oscillations present at rest were eliminated. No statistical differences in hemodynamic conditions were found between males and females among these young subjects. Subjects aged 50 to 70 experienced similar increases in flow rate from rest to exercise as compared to the younger subjects, however, at rest, greater oscillations in wall shear stress were observed in the older subjects. In general, the claudication patients had similar abdominal aortic mean flow and wall shear stress at rest as compared to the healthy older subjects, however, during exercise, most patients could not achieve comparable exercise intensities or increases in flow and wall shear stress as could the healthy subjects.