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Stanford University - Cardiovascular Biomechanics Research Laboratory
Lower Limb Exercise and Abdominal Aortic Hemodynamics
Christopher P. Cheng, Ph.D.Glagov SymposiumFebruary 20th, 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
Rest
Exercise
Stanford University - Cardiovascular Biomechanics Research Laboratory
Methods: Flow and Wall Shear Stress
-5
0
5
10
15
0.0 0.2 0.4 0.6 0.8
Time (sec)
Flo
w R
ate
(L/m
in)
Stanford University - Cardiovascular Biomechanics Research Laboratory
Methods: Flow and Shear Oscillations
11
2mean
mag
OSI
11
2mean
mag
QOFI
Q
-5
0
5
10
15
0.0 0.2 0.4 0.6 0.8
Time (sec)
Flo
w R
ate
(L/m
in)
-5
0
5
10
15
0.0 0.2 0.4 0.6 0.8
Time (sec)
She
ar S
tres
s (d
ynes
/cm
2)
(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
Rest Exercise
Stanford University - Cardiovascular Biomechanics Research Laboratory
-40
120
0
-40
Vel
ocit
y (c
m/s
)
0
-40
Vel
ocit
y (c
m/s
)
120
120
0
-40
Vel
ocit
y (c
m/s
)
0
-40
Vel
ocit
y (c
m/s
)
120
Results: Young Normals
A B C
A B CA B C
A B C
-5
0
5
10
15
0.0 0.2 0.4 0.6 0.8
Time (sec)
Flo
w R
ate
(L
/min
)
Supraceliac
InfrarenalA
BC
-5
0
5
10
15
0.0 0.2 0.4 0.6 0.8
Time (sec)
Flo
w R
ate
(L
/min
)
Supraceliac
Infrarenal
A
B C
Rest Exercise
Supraceliac
Infrarenal
Stanford University - Cardiovascular Biomechanics Research Laboratory
6.8
2.8
5.1
0.9
0.0
2.0
4.0
6.0
8.0
10.0
Rest Exercise
Flow
Rat
e (L
/min
) Supraceliac
Infrarenal
0.000.01 0.00
0.11
0.0
0.1
0.2
0.3
0.4
0.5
Rest ExerciseO
scill
ator
y F
low
Ind
ex Supraceliac
Infrarenal
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
-5
0
5
10
15
20
0.0 0.2 0.4 0.6 0.8
Time (sec)
She
ar S
tres
s (d
ynes
/cm
2)
Supraceliac
Inf rarenal
-5
0
5
10
15
20
0.0 0.2 0.4 0.6 0.8
Time (sec)
She
ar S
tres
s (d
ynes
/cm
2)
Supraceliac
Inf rarenalSupraceliac
Infrarenal
Stanford University - Cardiovascular Biomechanics Research Laboratory
0.010.01 0.00
0.13
0.0
0.1
0.2
0.3
0.4
0.5
Rest ExerciseO
scill
ator
y S
hear
Ind
ex Supraceliac
Infrarenal6.2
3.5
5.2
1.3
0.0
2.0
4.0
6.0
8.0
Rest Exercise
She
ar S
tres
s (d
ynes
/cm2 )
Supraceliac
Infrarenal
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 similarSame % 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
-5
0
5
10
15
0.0 0.4 0.8 1.2
Time (sec)
Flo
w R
ate
(L
/min
)
Supraceliac
Infrarenal
-5
0
5
10
15
0.0 0.4 0.8 1.2
Time (sec)
Flo
w R
ate
(L
/min
)
Supraceliac
Infrarenal
-5
0
5
10
15
0.0 0.2 0.4 0.6 0.8
Time (sec)
Flo
w R
ate
(L
/min
)
Supraceliac
Infrarenal
-5
0
5
10
15
0.0 0.2 0.4 0.6 0.8
Time (sec)
Flo
w R
ate
(L
/min
)
Supraceliac
Infrarenal
Young Older
Stanford University - Cardiovascular Biomechanics Research Laboratory
2.8
0.9
6.8
5.1
2.3
0.9
6.0
4.9
0.0
2.0
4.0
6.0
8.0
10.0
Supraceliac Infrarenal Supraceliac Infrarenal
Rest Exercise
Flow
Rat
e (L
/min
)
Young
Older
Results: Young vs. Older Normals
Infrarenal
Supraceliac
* p<0.05 between Young and Older
0.01
0.11
0.00 0.000.00
0.14
0.00 0.000.00
0.10
0.20
0.30
0.40
0.50
Supraceliac Infrarenal Supraceliac Infrarenal
Rest ExerciseO
scill
ator
y Fl
ow In
dex
Young
Older
Mean Blood Flow Flow Oscillations
Stanford University - Cardiovascular Biomechanics Research Laboratory
0.01
0.13
0.01 0.00
0.07
0.25
0.00 0.000.00
0.10
0.20
0.30
0.40
0.50
Supraceliac Infrarenal Supraceliac Infrarenal
Rest ExerciseO
scill
ator
y Sh
ear I
ndex
Young
Older
3.5
1.3
6.25.2
2.0 1.4
7.3
16.5
0.0
5.0
10.0
15.0
20.0
25.0
Supraceliac Infrarenal Supraceliac Infrarenal
Rest Exercise
Wal
l She
ar S
tress
(dyn
es/c
m2 )
Young
Older
Results: Young vs. Older Normals
**
*
*
Infrarenal
Supraceliac
* p<0.05 between Young and Older
Mean Wall Shear Stress Shear 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
ExperimentalSubjects & Patients
Charles Taylorand CardiovascularBiomechanicsLaboratory
MR-Cycle TeamDoug SchwandtEric ToppJim AndersonME282
RadiologyClaudia CooperRobert HerfkensNorbert Pelc
Palo Alto VARonald DalmanSheila CooganShawna ThunenPhyllis McgrathSurgery Residents
Whitaker Foundation