This document discusses measuring pulse wave velocity (PWV) to evaluate arterial stiffness and cardiovascular risk. [1] PWV is measured using the Aixplorer ultrasound system, which can image vessel walls at 2,000 Hz to calculate wall motion velocity. [2] PWV is measured at the beginning and end of systole by determining the time for the pulse wave to travel between two arterial points. [3] The system displays PWV values and a map of wall velocities over time, allowing evaluation of arterial stiffness as a cardiovascular risk predictor.

1. Clinical Innovation:
Pulse Wave Velocity
Aixplorer®
1

2. The cardiovascular risks
What are the known cardiovascular risks?
The most common causes and risk factors
Reliable predictors
The arterial pressures
The arterial wall stiffness
Measuring the Pulse Wave Velocity with Aixplorer®
Arterial pulse wave
Arterial stiffness E and c velocity of the arterial pulse wave
Ultrafast imaging and the wall motion
The wall motion and the velocity of the arterial pulse wave
User interface: PWV mode through images
Main stiffness evaluation by competition
Conclusion

3. The Cardiovascular risks

4. The cardiovascular risks
Cardiovascular diseases (CVD) are the major cause of deaths worldwide:
• 17.3 million people died from CVDs in 2008 (30% of all deaths)
• Over 80% of CVD deaths in low- and middle-income countries.
• By 2030, 23.6 million people will die from CVDs.
• WHO South-East Asia Region, CVD cause 3.6 million deaths/year (1/4 all deaths).
• Europe: 49% of all deaths; estimated cost €169 billion/year
• They involve the heart and the bloods vessels
• They can affect the brain, the heart, kidneys, the abdomen...
The most common causes and risk factors
Amongst several risk factors: ageing, smoking, cholesterol, blood pressure,
diet
Their consequences: Atheroma, distensibility of the vessels, blood flow
decrease, aneurysm, high arterial pressure

5. Reliable predictors
I. The arterial pressures
1. Definitions
Systolic peak pressure: P1 (comes earlier with ageing) 120 mmHg
Semi-delayed systolic peak: SP
Difference between the 2 pressures: DP
Diastolic pressure: DP
Mean pressure: MP= DP + 1/3 PP= Q. R PP
with Q the blood flow and R the resistivity of the arterial
system
60 mmHg
Pulsed pressure: PP = SP –DP
It seems to be the best preditor of the state of the big arterial vessels and of the left ventricle.
PP depends on the speed of the LVE, on the peripheral resistances, and on the mainly on
the stiffness of the aortic tree.

6. 2. Measurements in different places along the vasculature
• Aorta: central pressure, the most representative of the
cardiovascular risk, but invasive method, very rarely used
• Carotid artery: results are supposed to be the closest to aortic
measurements
• Brachial artery: the most commonly used, because easy, non-
invasive, long history (Chinese practice)
• Femoral artery
Raw measurements performed in different places cannot be
compared.
They need to be transformed if one wants to compare them.

7. 7

8. Reliable predictors
II. The arterial wall stiffness
Arterial
Blood
wall
Pressure
stiffness

9. Reliable predictors
II. The arterial wall stiffness
• Blood pressure (and PP) affects the wall stiffness during the
cardiac cycle: ongoing phenomenon
(non-linearity of vessel wall)
• But the global vessel wall stiffness affects the way the blood
pressure changes (Pulsed Pressure) during the cardiac cycle (the
stiffer the vessel, the higher the PP)
• Knowing the PP (brachial measurement) is not enough.
• Assessing the stiffness of the vessel wall during the cardiac
cycle may bring additional information to the clinician, as
another predictor of cardiovascular impairment.

10. Reliable predictors
II. The arterial wall stiffness
• Vessel wall stiffness seems to increase due to several factors:
• Natural ageing of the wall
• Atheromateous disease
• Hemodynamic changes
• Increased vessel wall stiffness also becomes a cardiovascular risk:
• Hypertrophy of the LV
• Vessel wall structural lesions
• Expected benefits
• Knowing the Pulsed Pressure and the vessel Wall Stiffness may have
a high potential in enabling the clinician to distinguish between causes
and consequences of a given cardiovascular impaired status.
• It may also help in assessing the efficacy of cardiovascular drug
treatments.

11. The arterial pulse wave
• At each contraction of the heart, the left
ventricle sends 40% of the volume of blood
ejected towards periphery.
From the heart
This is called the systole.
• Because of the contracting heart, the blood
flow running in the arteries takes the form
towards periphery
of a pulsed flow.
• It is described as a pulse wave,
propagating from hearth towards periphery
with a velocity depending on physical
properties of the vessels, and
especially on their stiffness.
NB: At every arterial bifurcation, reflected
pulse wave propagates backwards and mixes
with the original, incident pulse wave.

12. Arterial stiffness and velocity of the arterial pulse wave
During the systole:
increase of the intravascular pressure,
expansion of the wall of the artery,
energy storage.
During the diastole:
basal shape recovered, delivery of the
stored energy, decrease of the
intravascular pressure.
The stiffness of the arterial wall regulates
the blood flow, i.e. the pulse wave.
The stiffer the arterial wall, the faster the
pulse wave.
The Pulse Wave Velocity is a relevant indication of arterial stiffness.

13. Measuring the Pulse Wave Velocity
with Aixplorer®

14. UltraFast™ Imaging and the wall motion (1/2)
• Thanks to the UltraFast™ Imaging
technology, available on Aixplorer®,
the vessel walls can be imaged in B-
mode at 2,000 Hz (i.e. 2,000 flat
acquisitions per second).
• Aixplorer® uses Tissue Doppler
Imaging algorithms on the B Mode
acquisitions to calculate the speed at
which the diameter of the vessel is
enlarging or reducing.
• With TDI, both the mean velocity of
deformation and its direction,
towards or away from the probe, can
be retrieved.
Electrocardiogram of the sane volunteer

15. Ultrafast imaging and the wall motion (2/2)
Direction of blood flow
color code: v in mm/s
x
x(mm) x(mm)
time (s)
A given color shows the group of points with a given velocity
reported to time.

16. The wall motion and the velocity of the arterial pulse wave
V (cm/s) C (m/s)
t
t
A . v c = Dx /Dt
Dx
A’ v
Dt
x x
2 points of the wall have the same velocity with a time shift Dt
This time shift is the time needed by the arterial pulse wave to travel from the first
point to the second one.
The velocity of the pulse wave is C
PWV ~ 5 m/s (ES) and 6 m/s (LS)in the carotid 17

17. Ultrafast imaging and the wall motion (2/2)
We measure the PWV at 2 different times of the cardiac cycle:
• When the vessel diameter is enlarging the fastest: fastest increase
of blood pressure => Beginning of the systole
• When the vessel diameter is decreasing the fastest: fastest
decrease of the blood pressure => End of the systole
Direction of blood flow
color code: v in mm/s
x
ES
x(mm) x(mm)
time (s)

18. PWV through images
19

19. Acquisition
1 Application, preset, probe
Select Vascular / Carotid with SL15-
4 or SL10-2
2 Select the B-Mode
• The walls have to be as parallel as
possible to the probe (the intima-media
must be very clearly seen)
• Scanning plane: make sure to scan
following a diameter of the artery
3 On the Touchscreen, press PWV
(or "S" shortcut if configured)
 ✖ Acquisition time: 2s
• Avoid the bifurcation No movement is required during
the acquisition

20. After the acquisition
New page of the Touchscreen

21. After the acquisition
The B-Mode image on the monitor

22. Segmentation
4 If the segmentation is not adequate,
change the position and/or the size of
the box.
At the bottom of the monitor

23. Values of the velocity
Press Select on the control panel.
5 The map of the wall velocities over time is displayed as well as the values
velocity at the beginning of the systole and at the end of the systole.

24. Other techniques to evaluate PWV
Competition
25

25. Measure of the Pulse Pressure
• The PP is well correlated with the stiffness.
• Method : aplanation tonometry.
• At the wrist, the radial artery is slightly aplaned with a
micromanometer-typed probe (pencil probe).
• The measured and registered pressure is equal to the
transmural pressure.
• The brachial pressure at the left arm is registered for the
calibration of the tonometer and a transfer function gives the
aortic PP
SphygmoCor  Requires calibration with a sphygmometer
 Gives a measurement of the PP, and of the PWV
26

26. Measurement of the PWV
• Measures the transit time of the
pulse wave between to distant
pressure sensors and the distance
between the 2 selected points
• PWV = D/T and PW≈ (E)1/2
• Gives an estimation of the aortic
stiffness
 Simple and robust technique
 Dedicated apparatus and learning
curve needed
 High quality of the transducer is
CompliorSP needed
 Difficult with high BMI
 Issue with estimation of D
 Not a local technique

27. Local measure of the PWV
Technique called "Echotracking", based on the Doppler effect.
Measurements needed:
• The diameter of the vessel: D
• The variations of D
• The thickness of the artery
• The brachial pressure
Calculates the PWV based on a relationship from Moëns et Korteweg (1878):
c= (E h0 /r D0)1/2
Conditions of validity of the relationship are not well satisfied.
 Local measurement
Esaote  Non direct
 Hypotheses

28. Comparison with our new feature
SSI PWV Echotracking Complior
Direct measure   
Local   
Easy to perform   
Aortic PWV   
Clinical value New tool  Publications  Gold standard

- We have a new tool that combines most advantages of other techniques
- One problem: lack of some clinical feedback (new tool)
- Solutions:
On carotid: correlation study with echotracking and ShygmoCor (ongoing)

29. Conclusion

30. New tool for the clinicians to measure PWV
• Quick acquisition that can be performed in less
than 1 min at the end of a conventional
vascular Doppler exam
• Direct measurement (time of flight)
• Easy to perform
(with a good experience in carotid scanning)
• Has the potential to become a new tool to be
used by radiologists