Lower Limb Exercise and Abdominal Aortic Hemodynamics

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Lower Limb Exercise and Abdominal Aortic
Hemodynamics

• Christopher P. Cheng, Ph.D.
• Glagov Symposium
• February 20th, 2003

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Introduction Disease Localization
Supraceliac
Infrarenal
Spiral CT
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Introduction Hemodynamics
Good
Must quantify hemodynamics to understand disease
processes
High, steady shear
Bad
Low, oscillating shear
(Cybulsky and Gimbrone 1991, Nobutaka et al.
1996, Sessa et al. 1994, Zarins et al. 1983)
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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)
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Methods Exercise MRI

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Methods Data Acquisition

• 2 hours fasting
• Rest acquisition
• Exercise 150 RestHR
• Respiratory comp.
• Cardiac gating
• Surface coil

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Methods Image Data
Rest
Exercise
Supraceliac
Infrarenal
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Methods Flow and Wall Shear Stress
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Methods Flow and Shear Oscillations
(He and Ku 1996)
(Taylor et al. 2002)
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Results Outline

• Healthy subjects aged 20 to 30 (11 subjects)
• Healthy subjects aged 50 to 70 (8 subjects)

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Results Young Normals
Rest
Exercise
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Results Young Normals
Rest
Exercise
Supraceliac
Infrarenal
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Results Young Normals
Mean Blood Flow
Flow Oscillations

Supraceliac




Infrarenal


plt0.05 Supraceliac/Infrarenal plt0.05
Rest/Exercise
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Results Young Normals
Wall Shear Stress
Supraceliac
Infrarenal
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Results Young Normals
Mean Wall Shear Stress
Shear Oscillations


Supraceliac



Infrarenal



plt0.05 Supraceliac/Infrarenal plt0.05
Rest/Exercise
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Results Young Normals
Summary

• 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

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Results Young vs. Older Normals

• With advancing age
• Incidence and severity of atherosclerosis
  increases
• Reduced nitric oxide release
• Elastin degrades
• Collagen/Elastin ratio increases
• Aorta dilates and stiffens

Groups anthropometrically similar Same heart
rate increase
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Results Young vs. Older Normals
Young
Older
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Results Young vs. Older Normals
Mean Blood Flow
Flow Oscillations
Supraceliac
Infrarenal
plt0.05 between Young and Older
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Results Young vs. Older Normals
Mean Wall Shear Stress
Shear Oscillations


Supraceliac






Infrarenal
plt0.05 between Young and Older
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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

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Future Directions

• Vascular Biology
• Exercise Blood Flow Simulations
• Applications to Congenital Heart Disease
• Pre- and Post-operative Studies

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