stanford university - cardiovascular biomechanics research laboratory lower limb exercise and...

Stanford University - Cardiovascular Biomechanics Research Laboratory

Lower Limb Exercise and Abdominal Aortic Hemodynamics

Christopher P. Cheng, Ph.D.Glagov SymposiumFebruary 20th, 2003


Introduction: Disease Localization

Spiral CT

Supraceliac

Infrarenal


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


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)


Methods: Exercise MRI

(Designed and constructed by Doug Schwandt, Eric Topp, James Anderson, ME282 group)

1.5T Conventional Magnet 0.5T Open Magnet


Methods: Data Acquisition

• 2 hours fasting• Rest acquisition• Exercise = 150%

RestHR

• Respiratory comp.• Cardiac gating• Surface coil


Methods: Image Data

Supraceliac

Infrarenal

Rest

Exercise


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)


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)


Results: Outline

• Healthy subjects aged 20 to 30 (11 subjects)

• Healthy subjects aged 50 to 70 (8 subjects)


Results: Young Normals

Supraceliac

Infrarenal

Rest Exercise


-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


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


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


Mean Blood Flow

* **

* p<0.05 Supraceliac/Infrarenal** p<0.05 Rest/Exercise

Flow Oscillations

* **

* **

* **

*

* **

**

Supraceliac

Infrarenal



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


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


Mean Wall Shear Stress

* **

* **

* **

* **

*

* **

**

**

Shear Oscillations

* p<0.05 Supraceliac/Infrarenal** p<0.05 Rest/Exercise

Supraceliac

Infrarenal



• 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


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



-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


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


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


Rest ExerciseO

scill

ator

y Fl

ow In

dex

Young

Older

Mean Blood Flow Flow Oscillations


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


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


Rest Exercise

Wal

l She

ar S

tress

(dyn

es/c

m2 )

Young

Older


**

*

*

Infrarenal

Supraceliac

* p<0.05 between Young and Older

Mean Wall Shear Stress Shear Oscillations

*

*

*

*



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


Future Directions

• Vascular Biology• Exercise Blood Flow Simulations• Applications to Congenital Heart

Disease• Pre- and Post-operative Studies


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

stanford university - cardiovascular biomechanics research laboratory lower limb exercise and...

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